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Anaesthesia for diagnostic thoracic surgical procedures
2 Anaesthesia for diagnostic thoracic surgical procedures R. F E N E C K
The concept of using a cylindrical metal tube and source of illumination to examine body cavities was first invented by Bozzini in 1807, but modern bronchoscopy was developed much later in the 19th century by Chevalier Jackson in the USA and by Victor Negus in the UK. In general, the development of anaesthetic techniques and practices for diagnostic thoracic procedures has simply mirrored the development of anaesthesia as a speciality. However, other notable events include the description of apnoeic oxygenation in man by Draper in 1947 and the development of the ventilating bronchoscope slightly later. The development of the venturi jet injector by Sanders in 1967 had a profound effect on the safety of rigid bronchoscopy and its use became widespread, no doubt facilitated by the availability of shortacting muscle relaxants and intravenous anaesthetics. The development of fibreoptics has had a great effect on the investigation of thoracic disease. The fibreoptic bronchoscope was first described in 1968, and since then its use has become commonplace. It is especially useful since its small diameter allows it to penetrate to the 2nd or 3rd generation of subsegmental bronchi which are inaccessible to the rigid instrument. The development of computerized tomography and magnetic resonance imaging have added to the established radiological facilities available, for diagnosis and, finally, the development of medical laser technology has led to the use of lasers in surgical resection of turnouts of the upper airways via the laryngoscope and the bronchoscope.
BRONCHOSCOPY Br0nchoscopy is the most common invasive investigation required for the diagnosis of chest disease. The anaesthetic considerations for fibreoptic and rigid bronchoscopy differ in a number of respects. Fibreoptic bronchoscopy is dealt with first although a more detailed account of aspects of fibreoptic bronchoscopy is available in chapter 3.
Fibreoptic bronchoscopy The advent of fibreoptic bronchoscopy has greatly reduced the incidence of rigid bronchoscopy in many centres, and with it the need for general Baillibre's Clinical Anaesthesiology--Vol.
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anaesthesia since fibreoptic bronchoscopy can easily be carried out under local anaesthesia in adults. Sedative and vagolytic premedication may be given but little or no further intravenous sedation is required and the procedure is usually well tolerated. The instrument is usually passed through the nose and the larynx; the trachea and bronchi are anaesthetized by injecting lignocaine through the instrument under direct vision as it is advanced. Care should be taken not to exceed the safe maximum dose of lignocaine calculated on a weight basis. Fibreoptic bronchoscopy has been shown to be associated with mild hypoxaemia during and following the investigation which is easily treated by increasing the inspired oxygen concentration (Fio2) by controlled oxygen therapy (Sanderson and McDougall, 1978). Airways resistance has also been shown to increase, particularly in patients with obstructive airways disease. Activation of cough and irritant airway reflexes and the generation of mucosal oedema have been implicated as causative factors. The adverse effect on airways resistance has been shown to be minimized by prior treatment with atropine (Neuhaus et al, 1978). Glycopyrrolate may be a suitable alternative. Other bronchodilators may be used if necessary, following the procedure, but care should always be used with/%adrenergic stimulants if cardiovascular side-effects are to be avoided. Fibreoptic bronchoscopy is sometimes undertaken under general anaesthesia, either alone or as part of a combined fibreoptic/rigid bronchoscope procedure. The anaesthetic considerations are for the large part similar to those of rigid bronchoscopy and are best dealt with accordingly.
Rigid bronchoscopy A number of rigid bronchoscopes have been developed to facilitate diagnostic and therapeutic bronchoscopic examination of the airways or to facilitate passage of an endobronchial tube (Figure 1). Rigid bronchoscopy may be carried out in a number of settings: 1. On its own or as part of a combined fibreoptic/rigid procedure for biopsy, removal of foreign bodies, bronchial brushings or suction clearance of blood and secretions. 2. As part of the overall assessment of surgical operability, either alone or combined with another procedure, i.e. mediastinoscopy. 3. By the anaesthetist to facilitate the placement of endobronchial tubes. 4. Increasingly, in selected centres to enable therapeutic manoeuvres such as laser resection of occluding bronchial tumours. These differing indications for bronchoscopy may affect the conduct and particularly the duration of anaesthesia and therefore it is essential for surgeon and anaesthetist to establish their requirements prior to the procedure.
Preoperative assessment The condition of the patient may be widely variable since the procedure is undertaken under a number of differing conditions, e.g. emergency broncho-
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Figure 1. Four rigid (Negus) bronchoscopes and an intubating bronchoscope.
scopy for removal of secretions or control of haemorrhage is often carried out on the seriously ill. In general, attention should be directed to the following areas. The upper airway. Careful evaluation is necessary; in particular, the state of the teeth (dentures, loose teeth, awkward gaps) and movement of the temporomandibular and atlanto-occipital joints should be noted. Similarly, any soft tissue or other abnormalities of the mouth or neck should be checked. Respiratory status. Respiratory function is likely to worsen during bronchoscopy, particularly since instrumentation of the upper respiratory tract is a potent cause of laryngospasm and bronchospasm. Severity of respiratory symptoms is noted and where necessary respiratory function is formally assessed. Sputum production and the presence of copious secretions should be noted, particularly if there is a danger of overspillage, i.e. in bronchiectasis or postpneumonectomy bronchopleural fistula (see chapter 7). It may be necessary to anaesthetize the patient sitting and tilted to the affected side in order to minimize this problem. Similarly, if biopsies are to be taken, haemorrhage may ensue causing profound respiratory and cardiovascular impairment. Cardiovascular status. The haemodynamic consequences of rigid bronchoscopy are qualitatively similar to laryngoscopy but usually greater. Thus,
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hypertension, tachycardia and dysrythmias are frequently seen and may have adverse effects in patients with ischaemic heart disease, valvular heart disease or hypertension.
Other problems complicating general anaesthesia, in particular endocrine, metabolic and neurological disease. In planning the conduct of anaesthesia, communication between surgeon and anaesthetist is vital and in particular the following should be established before anaesthesia: 1. 2. 3. 4.
What is the presumed diagnosis? Are secretions a problem? Will biopsies or brushings be taken? Is it planned to combine rigid and fibreoptic investigations and/or proceed to another procedure such as thoracotomy?
Answers to these questions would enable the anaesthetist to prevent problems developing during the course of the examination.
Management of anaesthesia
Premedication Vagolytic premedication may be required in order to prevent copious salivary secretions during bronchoscopy, and to prevent the bradycardia seen either due to vagal reflexes or repeated suxamethonium. For control of secretions, atropine is most effective by the intramuscular route, although the bradycardia is most effectively prevented and treated by intravenous atropine, although this in turn may cause an unwanted tachycardia. The useful bronchodilator effects of atropine have already been referred to. Hyoscine is more effective as an antiemetic than atropine; glycopyrrolate may be an alternative. If topical analgesia of the upper respiratory tract is required, vagolytic premedication should be withheld until after the patient has been given a suitable lozenge of local anaesthetic to suck. Salivary function is thus preserved and the local anaesthetic more easily dispersed. Since bronchoscopy is often regarded as a short procedure, other premedication has been frequently withheld on the basis that a rapid recovery of consciousness is required together with an active cough reflex and good respiratory drive. This is particularly true if there is bleeding or copious secretions present, and in the frail and elderly patient who may show an unpredictable response to opiate or benzodiazepine premedicants. However, in the younger and fitter patient these arguments are less valid, and sedative premedication may help to provide a more stable course of anaesthesia and a lower incidence of awareness and cardiovascular instability.
Topical anaesthesia Topical anaesthesia is rarely used as the sole anaesthetic for rigid bronchoscopy since it is at best uncomfortable for the patient, and difficult for all but
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the most skilled bronchoscopist. Nevertheless, it is possible to anaesthetize the upper respiratory tract adequately for the procedure. The patient is given an amethocaine lozenge to suck and the resultant anaesthetic solution should be washed throughout the mouth and then swallowed. The superior laryngeal nerves may be anaesthetized by applying swabs soaked in 4% lignocaine to each pyriform fossa. The trachea may then be anaesthetized by injecting 4% lignocaine over the back of the tongue or by using the fibreoptic bronchoscope, injecting under direct vision as described earlier. An alternative is to provide anaesthesia of the trachea following cricothyroid puncture, although this may occasionally be anatomically more difficult than one imagines. A skin bleb of local anaesthetic is raised and the cricothyroid membrane is punctured with a 22 gauge intravenous cannula. The position is confirmed by aspiration of air and the needle withdrawn leaving the cannula in place. Anaesthetic is injected as the patient breathes in deeply. Haemorrhage, infection and subcutaneous emphysema are the most common complications of this procedure. Anaesthesia of the whole of the upper respiratory tract can be provided by ultrasonic nebulization of lignocaine with the patients breathing spontaneously. Nebulizers have been able to provide a mist in which 80% of the particles have a diameter below 10 #m, which will allow deposition of local anaesthetic down to the level of the segmental bronchi (Christoforidis et al, 1971). Other than the problems of patient discomfort and poor endoscopic conditions described earlier, the greatest hazard of this technique lies in the potential for an overdose with local anaesthetic, and care must be taken not to exceed the calculated maximum dose.
General anaesthesia The provision of general anaesthesia and adequate ventilation are so closely associated during rigid bronchoscopy that it is easiest to consider them together.
Spontaneous ventilation. Anaesthesia may be induced intravenously or with an inhalational agent, and deepened using increasing inspired concentrations of inhalational anaesthetic. In theory, any volatile agent that can provide sufficient depth of anaesthesia is satisfactory. In practice, volatile agents with a slower onset and longer duration of action provide better anaesthetic conditions for all but the shortest procedures. It is necessary to produce a deep plane of anaesthesia to ensure good conditions for the bronchoscopy, and, in adults, this may necessitate high inspired concentrations of volatile agent which in turn may have adverse circulatory effects. Recently the concept of minimum alveolar concentration (MAC) has been enlarged to include the alveolar concentration of volatile agents required to prevent responses to certain stimuli (Curling, 1983; see Table 1). It can clearly be seen that the MAC required for uneventful endotracheal intubation or to prevent untoward haemodynamic responses to surgical stimuli are sufficiently large such that they may be associated with unacceptable respiratory and circulatory depression. Conversely, anaesthesia may lighten quickly during the procedure unless anaesthetic gases can be delivered to the patient continuously. This may
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MAC s~ MAC EI 5~ MAC BAR 5~ MAC 95 MAC E195 MAC BAR 95
Halothane
Enflurane
1.0 1.3 1.5 1.2 1.7 2.1
1.0 1.4 1.6 1.1 1.9 2.6
necessitate the anaesthetist and bronchoscopist alternating their tasks every few minutes. The maintenance of spontaneous ventilation during bronchoscopy has certain theoretical advantages, particularly if difficulty in securing the airway is anticipated. Also, preservation of the cough reflex is useful in patients who are at risk from aspiration of secretions or blood, although in practice this reflex often returns sufficiently quickly when an intravenous technique with controlled ventilation is used. Controlled ventilation. Anaesthesia may be induced either intravenously or inhalationally and deepened or maintained by either method. In practice, intravenous induction is the norm, and the choice of agent is determined by conventional anaesthetic considerations. Neuromuscular blockade is usually obtained using a depolarizing relaxant (e.g. suxamethonium) by intermittent bolus doses or by infusion depending on the length of the procedure. The vagal effect of repeated bolus doses of suxamethoxonium may cause a bradycardia, and atropine should be available even in those patients who have received vagolytic premedication. For prolonged procedures, nondepolarizing relaxants appear a logical choice although their onset of action is slower and duration of action is often excessively long. Also, the bronchoscopic conditions achieved may not be as good as those seen with suxamethonium. However, the newer generation of relaxants (atracurium or vecuronium) may prove suitable alternatives for patients in whom anaesthesia and paralysis is required for more than 15 minutes. Passage of the bronchoscope is usually preceded by inflation of the lungs with 100% oxygen and, more controversially, by topical anaesthesia with 4% lignocaine to the larynx and vocal cords. There are disadvantages to topical laryngeal anaesthesia; not least that an early return of the cough reflex may be prevented. However, the incidence of laryngospasm is reduced and possibly that of bronchospasm also, particularly in the shorter procedures. Lignocaine is readily absorbed from the mucosa of the respiratory tract and although this may shorten its analgesic effect it may be useful in suppressing the incidence of ventricular dysrhythmias during bronchoscopy. Finally, the cough reflex is often very active in patients with chronic lung disease, and persistent irritant coughing following bron-
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choscopy may do little to aid removal of blood or secretions and simply worsen gas exchange by preventing normal breathing. The maintenance of anaesthesia during rigid bronchoscopy with controlled ventilation of the lungs is largely determined by the method of ventilation used. The following alternatives are available: Ventilating bronchoscope with a side arm attached to the anaesthetic circuit.
Anaesthetic gases can be delivered to the patient, provided the proximal end of the bronchoscope is occluded during ventilation, either with a transparent window or with the bronchoscopist's thumb. The latter necessitates an intermittent technique. Alternatively, a shortened endotracheal tube can be inserted into the proximal end of the bronchoscope and the patient's lungs ventilated with anaesthetic gases. Similarly, an intermittent anaesthetic/bronchoscopic technique is necessary. . Apnoeic oxygenation. Following 3 minutes preoxygenation, maintenance of arterial Po2 can be achieved utilizing the technique of apnoeic oxygenation. A suitable catheter (8FG) is passed so that the tip lies just above the carina, and oxygen is insufflated down it, at approximately 6 1/ min. Uptake of oxygen continues by mass diffusion, possibly assisted by a minimal ventilating effect produced by the beating heart. However, carbon dioxide elimination is minimal and arterial carbon dioxide tension will rise to an extent dependent on metabolic carbon dioxide production, usually at a rate of 1-6 mmHg/min. Thus this technique is unsuitable for prolonged bronchoscopy. 3. 'Jet' or venturi ventilation. In 1967 Sanders described the jet injector and this has become the most popular method for ventilation during bronchoscopy. A jet of gas is delivered at high pressure through a small needle at the proximal end of the bronchoscope. A negative pressure is generated around the tip of the needle and gas is entrained through the proximal end of the bronchoscope, so that the volume of gas delivered to the patient is the sum of the jet volume and the entrained volume. Any gas may be delivered at high pressure, although in clinical practice this is usually 100% oxygen. The delivery pressure for 100% oxygen from a medical pipeline system is approximately 60 PSI (410 kPa) in the UK, and thus it is important that the injector needle should correspond to the size of the bronchoscope, thus allowing adequate entrainment if extremely high airway pressures are to be avoided. In adults, a 14 or 16 SWG injector needle may be safely used, but in children it is necessary to reduce the size of the injector needle to 19 SWG (or smaller) in order to prevent excessively high airway pressures being generated with consequent barotrauma. Diagnostic rigid bronchoscopy is frequently a quick procedure, and a manually operated switch controlling the injector gas flow is usually adequate. However, combined fibreoptic and rigid bronchoscopic procedures and the development of medical lasers for resection of bronchial tumours have encouraged anaesthetists to develop automatic ventilators capable of delivering driving gases for prolonged procedures, thus freeing the anaesthetist for other tasks. Figure 2 shows one such system for fibreoptic bronchoscopy. The endotracheal tube shown is a Mallinckrodt
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Figure 2. VS 600 ventilator (Accutronic Ltd) capable of respiratory rates from 8 600 breaths/ minute. The driving gas outlet is connected to a Mallinckrodt 'Hi-Lo' Jet endotracheal tube through which a paediatric fibreoptic bronchoscope is passed. ~ cuffed endotracheal tube. In addition to the main lumen through which the fibreoptic bronchoscope is passed it has three others: a) the pilot tube connected to the endotracheal cuff, b) the lumen used to deliver high pressure driving gases, and c) a pressure monitoring lumen with a port opening into the main lumen of the endotracheal tube 2 cm distal to that of port (b). This is particularly useful since PEEP (positive end expiratory pressure) may be generated using this system, due in part to the reduction in effective ventilating area of the endotracheal tube (see Table 2) and also since increasing the respiratory rate may cause gas trapping and alveolar distension if the deflation time constant of the lungs and chest wall is exceeded. The ventilator shown is capable of respiratory rates up to 600/min, although it is more usual to use rates of up to 150/min. Such a system may also be used for rigid bronchoscopy, connecting the high pressure driving gas source from the ventilator to an injector port on the bronchoscope (Figure 3). In this instance a fibreoptic bronchoscope is shown with a simple Negus bronchoscope. However, this method of ventilation may also be used with a modern rigid instrument such as the Storz bronchoscope. One disadvantage of using an automatic ventilator as a driving gas source is that it may be difficult to alternately synchronize ventilation with the bronchoscopist's activities thus minimizing the disconcerting effect of blow-
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Table 2. Measured PEEP generated by insertion of
5.7 mm fibreoptic bronchoscope through different sized endotracheal tubes (Lindholm et al, 1978). Internal diameter of ET tube (mm) 7 8 9
Maximum PEEP measured (cmH20) 35 2O
Figure 3. VS 600 ventilator (Accutronic Ltd) with driving gas outlet connected to a Negus
bronchoscope, through which a paediatric fibreoptic bronchoscope is passed. back o f exhaled gases. This problem is certainly reduced if protective spectacles are w o r n by the bronchoscopist, but it should be remembered that the upper respiratory tract is a source o f potentially infective organisms and adequate measures must be taken to protect staff from unnecessary risks. The recent development o f medical laser technology has been applied to b r o n c h o s c o p y and in particular to the use o f lasers to resect otherwise inoperable bronchial neoplasms occluding the lumen o f a major bronchus. This procedure m a y be undertaken as an emergency, usually in very sick elderly patients, and, although m a n y centres have utilized local anaesthesia
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successfully, the use of general anaesthesia and a rigid bronchoscope may be preferred both from the point of view of patient acceptability and to permit the removal of large pieces of tumour debris using biopsy forceps. The smoke and waste gases generated by the laser may be a problem. This has led to the further development of ventilators working on the principle of alternate gas delivery and gas suction (Paes et al, 1986).
Monitoring during bronchoscopy Previously the short duration and variability of the procedure has meant that monitoring equipment has been used sparingly, if at all, during bronchoscopy. The anaesthetist has instead relied on clinical judgement, i.e. assessment of the patient's colour and a finger on the pulse. However, the development of sophisticated non-invasive techniques of patient monitoring has rendered this obsolete. Alterations in cardiac rate and rhythm are seen frequently during bronchoscopy both as a consequence of the procedure itself and of the anaesthetic agents and neuromuscular relaxants used. ECG monitoring should therefore be considered mandatory. Measurement of blood pressure during bronchoscopy has not been widely undertaken previously. Intermittent sphygmomanometry has been considered too cumbersome to use, given the other demands made on the anaesthetist during the procedure, and indwelling intra-arterial blood pressure monitoring has been considered too invasive. However, the development of automatic non-invasive oscillotonometric blood pressure monitors has altered this situation and the anaesthetist may now obtain an automatic minute-to-minute assessment of blood pressure during the investigation. This may be considered unnecessary by some, but recent studies have shown that the anaesthetic technique used may have a significant effect on the magnitude ofpressor responses during bronchoscopy, and that hyperdynamic circulatory effects may be difficult to obtund. Furthermore, close monitoring of the ECG using an electrode position designed primarily to detect myocardial ischacmia has shown that ischaemic episodes may occur in a significant proportion of patients given a conventional anaesthetic (Wark et al, 1986). It should be remembered that adult patients undergoing bronchoscopy, particularly for presumed carcinoma of the bronchus, have many risk factors in common with patients suffering from ischaemic heart disease, and it is not therefore surprising that such patients are at risk from, and do develop, ischaemic episodes during what is frequently a stressful procedure. The relevance of these ischaemic episodes has been questioned in the past, but again recent evidence would appear to substantiate the view that the development of ischaemic episodes during anaesthesia may correlate with an adverse outcome (Slogoff and Keats, 1985). Thus an anaesthetic technique designed to prevent increases in myocardial work and the development of myocardial oxygen imbalance, and the relevant monitoring which enables the anaesthetist to detect such changes, would be appropriate in patients with a known history of ischaemic heart disease undergoing bronchoscopy. Ever more sophisticated non-invasive monitors are becoming available, including those which allow repeated analysis of the ECG for the early detection of indicators ofischaemia. All of this may seem a
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DIAGNOSTIC THORACIC SURGICAL PROCEDURES Table 3. Arterial blood gas analysis during bronchoscopy; results of series using the Sanders injector technique (100% oxygen). Number of patients Morales et al (1969) Giesecke et al (1978) Wark et al (1986)
14 21 36
Paco2
Pao2
42 200 mmHg 38 116 mmHg 5.08 21.2 kPa
far cry from 'a quick list of a few bronchoscopies' but careful cardiovascular monitoring is not inappropriate in higher risk patients and yet it need not be invasive. Nevertheless, in patients undergoing planned extensive procedures such as multiple biopsy or laser resection, it may be appropriate to use intraarterial monitoring for blood pressure measurement and blood gas analysis. Table 3 shows the results of arterial blood gas analysis carried out on a series of patients undergoing bronchoscopy in whom ventilation was controlled using the Sanders injector. It can be seen that blood gases are well maintained in all these patients. However, in clinical practice, intermittent arterial blood gas analysis is usually considered to be unneccessary and impractical, and the open nature of the venturi circuit makes expired gas analysis difficult. Transcutaneous blood gas monitoring has suffered from a number of technical drawbacks, but the development of pulse oximetry has given the anaesthetist a useful tool for the detection of changes in oxygenation during bronchoscopy. The incidence of awareness ~s dlsturbmgly lllgh for patients unctergolng bronchoscopy and values up to 4% have been reported. There is as yet no commercially available machine that is accepted as a predictable 'depth of anaesthesia' monitor and until such time awareness during anaesthesia will continue to be a problem. Clearly it can be minimized by the use of sedative premedication, and by giving repeat bolus doses of intravenous anaesthetic on a timed basis, rather than being directed by the signs of lightening anaesthesia. For prolonged procedures, continuous intravenous infusions of anaesthetics and the use of nitrous oxide/oxygen mixtures as the venturi driving gas may help. From the foregoing it can be seen that monitoring during bronchoscopy should be directed to providing frequent non-invasive and preferably automated assessment of the patient's cardiovascular status and degree of oxygenation throughout the procedure. It may be that these goals are applicable to all patients undergoing short surgical procedures of any nature. Certainly anaesthesia for any diagnostic thoracic procedure should be monitored to this extent as a minimum, although it may also be considered useful to utilize other devices where appropriate (e.g. nerve stimulators for assessing the degree of neuromuscular blockade, etc.). OESOPHAGOSCOPY Visualization of the oesophagus may be carried out using either a fibreoptic or rigid instrument. The former is frequently undertaken under sedation and
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topical anaesthesia only, whereas rigid oesophagoscopy is usually carried out under general anaesthesia. Once again, combined procedures may be undertaken, particularly if it is desirable to examine the upper gastrointestinal tract. The oesophagoscopy may be undertaken for a number of indications but in a non-specialized acute hospital the most common indication is for the removal of a food bolus or other foreign body causing partial or complete dysphagia. Such patients are not often in a poor risk category but they do have a full stomach which poses a threat to the airway during and after the procedure. In comparison, patients with dysphagia due to malignant or benign strictures are frequently poorly nourished and may be dehydrated, anaemic and suffering from electrolyte imbalance. These latter three problems should be corrected preoperatively. Patients with oesophageal varices may have a significant degree of hepatic impairment with all its implications for the anaesthetist. Patients with achalasia of the cardia, hiatus hernia or oesophageal diverticulum are at increased risk from aspiration of food matter or gastric acid and indeed may already have evidence of aspiration pneumonitis or bronchopneumonia.
Management of anaesthesia Sedative premedication may be given in small dosage by the intramuscular route. In those patients at increased risk of regurgitation and aspiration of gastric acid, it may be worth giving a histamine H2-receptor antagonist (cimetidine or ranitidine) to raise gastric pH for elective procedures. A rapid induction sequence may be necessary, with preoxygenation and cricoid pressure. Cricoid pressure should be carried out to control reflux of oesophageal contents. It is usual to place the patient in a neutral supine position, although a steep head-up tilt may minimize the risk of regurgitation, or a left lateral position may reduce the risk of aspiration should regurgitation occur. The trachea should be intubated with a robust cuffed endotracheal tube; either an armoured latex or flexometallic tube is ideal, and the diameter of the tube should preferably be one size smaller than usual. This will more readily permit the passage of the oesophagoscope and indeed it may be necessary to deflate the endotracheal cuff momentarily as the oesophagoscope passes through the cricopharyngeal sphincter. Full muscular relaxation is best maintained up until this time and may be continued throughout the procedure if the endotracheal tube diameter is too small such that the work of breathing through the increased resistance is excessive. Otherwise, spontaneous ventilation may be permitted. In either event anaesthesia can be maintained with a small increment of volatile agent. Following the procedure anaesthesia is discontinued and the patient recovered on his side with a slight head-down tilt. Suction should be immediately available.
Complications of oesophagoscopy Regurgitation and aspiration is a frequent hazard but thankfully not a common complication. Its prevention can be achieved by close adherence to the principles discussed. Bleeding may be a problem, particularly if biopsies
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have been taken, a stricture has been dilated or palliative oesophageal intubation has been carried out, or in those patients with oesophageal varices. The most serious complication of oesophagoscopy is oesophageal perforation. This may even occur following an uneventful examination and indeed may cause no distress to the patient until some hours later. However, severe localized chest pain usually develops and is associated with surgical emphysema and the signs of pleural effusion, pneumothorax or pneumomediastinum. A chest x-ray provides confirmatory evidence of this. Iatrogenic perforation of the oesophagus carries a high mortality ranging from 34 to 84%. Emergency thoracotomy and repair of the oesophagus should be carried out immediately. Postoperatively, the patient may require intensive or high dependency care facilities for some time and parenteral nutrition. MEDIASTINOSCOPY AND ANTERIOR MEDIASTINOTOMY
Mediastinoscopy Mediastinoscopy is primarily used to provide a histological diagnosis in patients with mediastinal lymphadenopathy and for assessing operability in patients with carcinoma of the bronchus. A small incision is made above the suprasternal notch. The pretracheal muscles are separated by blunt dissection and the pretracheal fascia is incised after which it is possible to insert the mediastinoscope. Needle aspiration and biopsies may be taken during the procedure and mediastinal structures visualized. Mediastinoscopy is a potentially hazardous procedure and careful preoperative evaluation is necessary. This should be directed particularly toward examination for evidence of superior vena caval obstruction or of mechanical obstruction to the upper respiratory tract. Whilst the presence of either of these problems does not contraindicate mediastinoscopy, they certainly make it more hazardous. Superior vena caval obstruction is particularly problematic if it occurs acutely since collateral channels will not have had time to open up. There is a real risk of major haemorrhage during the procedure and crossmatched blood should always be available.
Management of anaesthesia There are no special considerations regarding premedication unless significant respiratory obstruction is present, when drug induced respiratory depression must be avoided. High risk patients may be preoxygenated and anaesthesia induced intravenously, followed by muscular relaxation and endotracheal intubation. Inhalational induction of anaesthesia is an alternative, particularly if there are difficulties anticipated in securing a safe airway. A cuffed, armoured endotracheal tube should be used and a range of sizes should be available, particularly if there is any evidence of tracheal compression. Following intubation, anaesthesia may be maintained using increments of volatile agent in an oxygen/nitrous oxide mixture. Although spontaneous ventilation is acceptable, it is wise to avoid coughing or bucking during the
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procedure and this is usually best achieved if the patient is paralysed and the ventilation controlled. In view of the short duration of the procedure one of the new generation of short-acting non-depolarizing muscle relaxants (vecuronium or atracurium) would be ideal. Haemorrhage can be a serious complication in all patients undergoing mediastinoscopy and for this reason a large bore indwelling intravenous cannula should be inserted. This is usually placed in an upper limb, although theoretically it may be safer in a lower limb, particularly in patients with superior vena caval obstruction, since transfusion would then be carried out via the inferior vena cava and not the superior vena cava. The principles of monitoring outlined earlier in this chapter are applicable to mediastinoscopy with one or two differences. The blood pressure is best monitored non-invasively on the left arm, and the right radial pulse monitored in order to detect compression of the right innominate artery. This may be done either by digital plethysmography or more simply by palpation. Expired gas analysis is easy to carry out and end tidal carbon dioxide monitoring may be useful to enable normocapnic ventilation to be achieved. This may also be used to detect air embolism, which is a potential risk if a tear is made in a venous structure with the patient in a steep head-up tilt. Those patients with any degree of respiratory obstruction preoperatively may be at increased risk from postoperative respiratory failure and great care must be taken in the early postoperative period to ensure adequate gas exchange. A period of postoperative intermittent positive pressure ventilation (IPPV) may be necessary in this situation.
Anterior mediastinotomy This procedure is usually carried out through the bed of the second costal cartilage and is carried out to permit examination of anterior mediastinal structures which are not visible during mediastinoscopy. The anaesthetic management of such patients is usually straightforward. Appropriate premedication is given and anaesthesia induced in the normal manner. Although it is theoretically possible to perform the procedure without opening the pleural cavity, in practice this occurs quite commonly, and therefore endotracheal intubation and controlled ventilation of the lungs is performed. Anterior mediastinotomy is also a useful route for performing open lung biopsy. If this is undertaken, the patient should be closely monitored in the early postoperative period for signs of pulmonary haemorrhage and haemoptysis.
Thoracoseopy Thoracoscopy was first developed in Germany in the early 20th century for use in the surgical management of tuberculosis. It is commonly used as a diagnostic tool for the evaluation of pleural disease, lung parenchymal disease including pulmonary infection and infiltration, and for staging procedures for suspected neoplasms. It is also used for chemical pleurodesis in recurrent pneumothorax.
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Management of anaesthesia Careful preoperative assessment is made taking into account the indication for the procedure and the presence of any complicating factors (e.g. pneumothorax), and appropriate premedication is given. Endobronchial intubation is by no means mandatory but does permit selective one-lung ventilation and collapse of the lung on the operated side. This will lessen the risk of trauma to the lung with the thoracoscope, which may cause severe bleeding. Thus intravenous induction and muscular relaxation with a shortacting depolarizing or non-depolarizing agent is the norm. Ventilation is controlled and with a double-lumen endobronchial tube in place the lung can be collapsed and re-expanded at will. However, some may feel that this makes the anaesthetic unnecessarily complicated with all the inherent problems of one-lung anaesthesia (OLA) (see chapter 4). The principles discussed earlier concerning patient monitoring are applicable here also, and indeed pulse oximetry may be particularly useful in this group of patients in the early detection and treatment of hypoxaemia.
ANAESTHESIA FOR RADIOLOGICAL PROCEDURES
There are a wide variety of radiological techniques available for the investigation of patients with chest disease. These include plain radiography, tomography, fluoroscopy, bronchography, ultrasound, computerized tomography and magnetic resonance imaging. In the investigation of vascular lesions, angiography may be undertaken, and embolization of bleeding points is a new technique which in certain circumstances may be carried out instead of surgery. In all of these techniques general anaesthesia is not required unless patient cooperation is lacking. In the very sick or elderly and in virtually all small children, general anaesthesia will be required. Thus when considering general anaesthesia for thoracic radio-diagnostic procedures we are largely considering a paediatric practice. General considerations
In general terms, anaesthesia in an x-ray department is more difficult than in the routine setting of the operating theatre. Great care should therefore be directed toward checking the anaesthetic machine and ancillary equipment, and making sure that spare laryngoscopes etc. are available and in working order. The anaesthetist should be familiar with the layout of the room and the location of wall points for suction and medical gases, if indeed pipeline gases are provided. It is wise to have everything to hand and emergency drugs should be drawn up prior to the procedure. Investigations may be undertaken for a variety of indications and any assessment of the patient will need to take this into account. In particular, the production of copious quantities of sputum (e.g. bronchiectasis) or compression of the trachea or major bronchi (e.g. by a mediastinal mass) may seriously complicate the management of anaesthesia. In most procedures the anaesthetist will be remote from the
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patient and in this situation endotracheal anaesthesia is mandatory. Extra care should be taken to fix the endotracheal tube, and the use of lightweight materials in the anaesthetic circuit may minimize the risk of inadvertent disconnection or extubation during the investigation. Intravenous access should always be obtained and this should have an injection site remote from the patient. An intravenous infusion with extension tubing is a simple solution. Most x-ray departments are cramped and it may be physically difficult to fit in all the monitoring equipment the anaesthetist requires. Nevertheless, the principles of monitoring discussed earlier apply in this situation also and it should be simple to manage ECG, automated oscillotonometry and pulse oximetry for adult and paediatric patients. Both visual and audible displays may be useful, particularly if the ambient lighting is reduced or the view of the monitoring equipment is obscured from time to time. It is also a good idea to have a torch available. There are no special considerations regarding premedication or induction of anaesthesia and routine regimens will suffice. Although spontaneous ventilation is theoretically acceptable, muscular relaxation and IPPV are more commonly used. This allows the patient's ventilation to be more easily controlled during the procedure, and thus it is easier to synchronize with the radiologist with regard to image or biopsy taking, and, furthermore, scavenging of anaesthetic gases is simplified. Explosive anaesthetic agents are not permissible in x-ray departments but an oxygen/nitrous oxide mixture supplemented as required with either a small dose of fentanyl or small increments of a modern volatile agent are acceptable. However, it should be remembered that short bursts of patient stimulation may occur, e.g. during turning etc., and therefore it is wise to have a syringe of intravenous induction agent available should anaesthesia become inappropriately light. The termination of a radiological procedure may be more difficult to judge than that of operative surgery, and a prolonged recovery period may ensue. If no recovery facilities are available these patients should be recovered by the anaesthetist in the x-ray room where the necessary facilities (i.e. oxygen and suction) are to hand.
Bronchography General anaesthesia is required for bronchography more frequently than for the other radiological procedures mentioned since patient cooperation is essential, and the procedure itself may be unpleasant. Bronchography was first carried out in 1922 by Sicard and Forestier using lipiodol, a substance first introduced as an antisyphilitic by LaFey in 1901. However lipiodol has now been replaced by Dionosil (propyliodide) as a contrast medium. Dionosil is available in either an oil or water-based form. The oil is particularly useful since it is thick and shows up larger airways clearly, whereas aqueous Dionosil will disperse more quickly to the periphery of the lung and, as it is more irritant, may cause troublesome coughing. Bronchography was used primarily for the evaluation of bronchiectasis, and, since this condition is declining, the necessity for the examination has also reduced. However, the anaesthetic management of this group of patients may be difficult and requires careful
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preoperative evaluation. Preoperative assessment should be directed toward the volume o f sputum produced and the posture required for drainage. Physiotherapy should be carried out whenever possible prior to the procedure. This will not only make the procedure safer but also results in a clearer b r o n c h o g r a m . Premedication is subject to the usual considerations and the m e t h o d o f anaesthesia is best determined by whether spontaneous or controlled ventilation will be used during the procedure, and whether endotracheal anaesthesia is anticipated or whether the contrast is to be instilled using a rigid bronchoscope. This latter technique is useful since it is possible to place the catheter delivering the contrast under direct vision, and also to effect rapid and effective suction clearance o f the contrast material at the end o f the procedure. Otherwise, an endotracheal tube with a suction orifice is used, with a catheter passed t h r o u g h the suction orifice d o w n the inner lumen o f the endotracheal tube. It is useful to m a r k the catheter so that it is k n o w n when the tip of the catheter has reached the tip o f the endotracheal tube. In either event, induction and muscle relaxation will permit passage o f the bronchoscope or endotracheal tube, and anaesthesia m a y then be maintained by methods described earlier under the section on bronchoscopy. F o r bilateral investigations it is c o m m o n to examine the right lung first and, if the procedure is carried out with endotracheal anaesthesia, frequent turning m a y be necessary. If controlled ventilation is used, the patient should be apnoeic during injection o f the contrast, and then gentle manual ventilation is used to disperse the contrast media. Following the investigation, care should be taken to clear as much o f the contrast as possible prior to the termination o f anaesthesia, and during the recovery period humidified oxygen, suction and physiotherapy m a y be necessary to further aid this process. REFERENCES Christoforidis AJ, Tomashefsk JF & Mitchell MS (1971) Use of an ultrasonic nebulizer for the application of oropharyngeal, laryngeal and tracheobronchial anesthesia. Chest 59: 629-
633. Curling PE (1983) Anaesthetic for thoracic diagnostic procedures. In Kaplan JA (ed.) Thoracic Anaesthesia, pp 321. London: Churchill Livingstone. Giesecke AH, Gerbershagen HU, Dortman C et al (1978) Comparison of the ventilating and injection bronchoscopes. Anesthesiology 38: 298-303. Lindholm CE, Ollman B, Snyder JV et al (1978) Cardiorespiratory effects of flexible fiberoptic bronchoscopy in critically ill patients. Chest 74:362 368. Morales GA, Epstein BS, Cinco Bet al (1969) Ventilation during general anaesthesia for bronchoscopy. Journal of Thoracic and Cardiovascular Surgery 57:873 878. Neuhaus A, Markowitz D, Rottman HH et al (1978) The effects of fibreoptic bronchoscopy with and without atropine premedication on pulmonary function in humans. Annals of Thoracic Surgery 25: 393-398. Paes ML, Conacher ID & Snellgrove TR (1986) A ventilator for carbon dioxide laser bronchoscopy. British Journal of Anaesthesia 58: 663-669. Sanderson DR & McDougall JC (1978) Transoral bronchofibroscopy. Chest 73:(supplement) 701-703. Slogoff S & Keats AY (1985) Does perioperative myocardial ischaemia lead to post operative myocardial infarction? Anesthesiology 62:107-115. Wark K, Lyons J & Feneck RO (1986) Haemodynamic effects of bronchoscopy. Effect of pretreatment with fentanyl and alfentanil. Anaesthesia 41: 162-167.
The concept of using a cylindrical metal tube and source of illumination to examine body cavities was first invented by Bozzini in 1807, but modern bronchoscopy was developed much later in the 19th century by Chevalier Jackson in the USA and by Victor Negus in the UK. In general, the development of anaesthetic techniques and practices for diagnostic thoracic procedures has simply mirrored the development of anaesthesia as a speciality. However, other notable events include the description of apnoeic oxygenation in man by Draper in 1947 and the development of the ventilating bronchoscope slightly later. The development of the venturi jet injector by Sanders in 1967 had a profound effect on the safety of rigid bronchoscopy and its use became widespread, no doubt facilitated by the availability of shortacting muscle relaxants and intravenous anaesthetics. The development of fibreoptics has had a great effect on the investigation of thoracic disease. The fibreoptic bronchoscope was first described in 1968, and since then its use has become commonplace. It is especially useful since its small diameter allows it to penetrate to the 2nd or 3rd generation of subsegmental bronchi which are inaccessible to the rigid instrument. The development of computerized tomography and magnetic resonance imaging have added to the established radiological facilities available, for diagnosis and, finally, the development of medical laser technology has led to the use of lasers in surgical resection of turnouts of the upper airways via the laryngoscope and the bronchoscope.
BRONCHOSCOPY Br0nchoscopy is the most common invasive investigation required for the diagnosis of chest disease. The anaesthetic considerations for fibreoptic and rigid bronchoscopy differ in a number of respects. Fibreoptic bronchoscopy is dealt with first although a more detailed account of aspects of fibreoptic bronchoscopy is available in chapter 3.
Fibreoptic bronchoscopy The advent of fibreoptic bronchoscopy has greatly reduced the incidence of rigid bronchoscopy in many centres, and with it the need for general Baillibre's Clinical Anaesthesiology--Vol.
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anaesthesia since fibreoptic bronchoscopy can easily be carried out under local anaesthesia in adults. Sedative and vagolytic premedication may be given but little or no further intravenous sedation is required and the procedure is usually well tolerated. The instrument is usually passed through the nose and the larynx; the trachea and bronchi are anaesthetized by injecting lignocaine through the instrument under direct vision as it is advanced. Care should be taken not to exceed the safe maximum dose of lignocaine calculated on a weight basis. Fibreoptic bronchoscopy has been shown to be associated with mild hypoxaemia during and following the investigation which is easily treated by increasing the inspired oxygen concentration (Fio2) by controlled oxygen therapy (Sanderson and McDougall, 1978). Airways resistance has also been shown to increase, particularly in patients with obstructive airways disease. Activation of cough and irritant airway reflexes and the generation of mucosal oedema have been implicated as causative factors. The adverse effect on airways resistance has been shown to be minimized by prior treatment with atropine (Neuhaus et al, 1978). Glycopyrrolate may be a suitable alternative. Other bronchodilators may be used if necessary, following the procedure, but care should always be used with/%adrenergic stimulants if cardiovascular side-effects are to be avoided. Fibreoptic bronchoscopy is sometimes undertaken under general anaesthesia, either alone or as part of a combined fibreoptic/rigid bronchoscope procedure. The anaesthetic considerations are for the large part similar to those of rigid bronchoscopy and are best dealt with accordingly.
Rigid bronchoscopy A number of rigid bronchoscopes have been developed to facilitate diagnostic and therapeutic bronchoscopic examination of the airways or to facilitate passage of an endobronchial tube (Figure 1). Rigid bronchoscopy may be carried out in a number of settings: 1. On its own or as part of a combined fibreoptic/rigid procedure for biopsy, removal of foreign bodies, bronchial brushings or suction clearance of blood and secretions. 2. As part of the overall assessment of surgical operability, either alone or combined with another procedure, i.e. mediastinoscopy. 3. By the anaesthetist to facilitate the placement of endobronchial tubes. 4. Increasingly, in selected centres to enable therapeutic manoeuvres such as laser resection of occluding bronchial tumours. These differing indications for bronchoscopy may affect the conduct and particularly the duration of anaesthesia and therefore it is essential for surgeon and anaesthetist to establish their requirements prior to the procedure.
Preoperative assessment The condition of the patient may be widely variable since the procedure is undertaken under a number of differing conditions, e.g. emergency broncho-
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Figure 1. Four rigid (Negus) bronchoscopes and an intubating bronchoscope.
scopy for removal of secretions or control of haemorrhage is often carried out on the seriously ill. In general, attention should be directed to the following areas. The upper airway. Careful evaluation is necessary; in particular, the state of the teeth (dentures, loose teeth, awkward gaps) and movement of the temporomandibular and atlanto-occipital joints should be noted. Similarly, any soft tissue or other abnormalities of the mouth or neck should be checked. Respiratory status. Respiratory function is likely to worsen during bronchoscopy, particularly since instrumentation of the upper respiratory tract is a potent cause of laryngospasm and bronchospasm. Severity of respiratory symptoms is noted and where necessary respiratory function is formally assessed. Sputum production and the presence of copious secretions should be noted, particularly if there is a danger of overspillage, i.e. in bronchiectasis or postpneumonectomy bronchopleural fistula (see chapter 7). It may be necessary to anaesthetize the patient sitting and tilted to the affected side in order to minimize this problem. Similarly, if biopsies are to be taken, haemorrhage may ensue causing profound respiratory and cardiovascular impairment. Cardiovascular status. The haemodynamic consequences of rigid bronchoscopy are qualitatively similar to laryngoscopy but usually greater. Thus,
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hypertension, tachycardia and dysrythmias are frequently seen and may have adverse effects in patients with ischaemic heart disease, valvular heart disease or hypertension.
Other problems complicating general anaesthesia, in particular endocrine, metabolic and neurological disease. In planning the conduct of anaesthesia, communication between surgeon and anaesthetist is vital and in particular the following should be established before anaesthesia: 1. 2. 3. 4.
What is the presumed diagnosis? Are secretions a problem? Will biopsies or brushings be taken? Is it planned to combine rigid and fibreoptic investigations and/or proceed to another procedure such as thoracotomy?
Answers to these questions would enable the anaesthetist to prevent problems developing during the course of the examination.
Management of anaesthesia
Premedication Vagolytic premedication may be required in order to prevent copious salivary secretions during bronchoscopy, and to prevent the bradycardia seen either due to vagal reflexes or repeated suxamethonium. For control of secretions, atropine is most effective by the intramuscular route, although the bradycardia is most effectively prevented and treated by intravenous atropine, although this in turn may cause an unwanted tachycardia. The useful bronchodilator effects of atropine have already been referred to. Hyoscine is more effective as an antiemetic than atropine; glycopyrrolate may be an alternative. If topical analgesia of the upper respiratory tract is required, vagolytic premedication should be withheld until after the patient has been given a suitable lozenge of local anaesthetic to suck. Salivary function is thus preserved and the local anaesthetic more easily dispersed. Since bronchoscopy is often regarded as a short procedure, other premedication has been frequently withheld on the basis that a rapid recovery of consciousness is required together with an active cough reflex and good respiratory drive. This is particularly true if there is bleeding or copious secretions present, and in the frail and elderly patient who may show an unpredictable response to opiate or benzodiazepine premedicants. However, in the younger and fitter patient these arguments are less valid, and sedative premedication may help to provide a more stable course of anaesthesia and a lower incidence of awareness and cardiovascular instability.
Topical anaesthesia Topical anaesthesia is rarely used as the sole anaesthetic for rigid bronchoscopy since it is at best uncomfortable for the patient, and difficult for all but
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the most skilled bronchoscopist. Nevertheless, it is possible to anaesthetize the upper respiratory tract adequately for the procedure. The patient is given an amethocaine lozenge to suck and the resultant anaesthetic solution should be washed throughout the mouth and then swallowed. The superior laryngeal nerves may be anaesthetized by applying swabs soaked in 4% lignocaine to each pyriform fossa. The trachea may then be anaesthetized by injecting 4% lignocaine over the back of the tongue or by using the fibreoptic bronchoscope, injecting under direct vision as described earlier. An alternative is to provide anaesthesia of the trachea following cricothyroid puncture, although this may occasionally be anatomically more difficult than one imagines. A skin bleb of local anaesthetic is raised and the cricothyroid membrane is punctured with a 22 gauge intravenous cannula. The position is confirmed by aspiration of air and the needle withdrawn leaving the cannula in place. Anaesthetic is injected as the patient breathes in deeply. Haemorrhage, infection and subcutaneous emphysema are the most common complications of this procedure. Anaesthesia of the whole of the upper respiratory tract can be provided by ultrasonic nebulization of lignocaine with the patients breathing spontaneously. Nebulizers have been able to provide a mist in which 80% of the particles have a diameter below 10 #m, which will allow deposition of local anaesthetic down to the level of the segmental bronchi (Christoforidis et al, 1971). Other than the problems of patient discomfort and poor endoscopic conditions described earlier, the greatest hazard of this technique lies in the potential for an overdose with local anaesthetic, and care must be taken not to exceed the calculated maximum dose.
General anaesthesia The provision of general anaesthesia and adequate ventilation are so closely associated during rigid bronchoscopy that it is easiest to consider them together.
Spontaneous ventilation. Anaesthesia may be induced intravenously or with an inhalational agent, and deepened using increasing inspired concentrations of inhalational anaesthetic. In theory, any volatile agent that can provide sufficient depth of anaesthesia is satisfactory. In practice, volatile agents with a slower onset and longer duration of action provide better anaesthetic conditions for all but the shortest procedures. It is necessary to produce a deep plane of anaesthesia to ensure good conditions for the bronchoscopy, and, in adults, this may necessitate high inspired concentrations of volatile agent which in turn may have adverse circulatory effects. Recently the concept of minimum alveolar concentration (MAC) has been enlarged to include the alveolar concentration of volatile agents required to prevent responses to certain stimuli (Curling, 1983; see Table 1). It can clearly be seen that the MAC required for uneventful endotracheal intubation or to prevent untoward haemodynamic responses to surgical stimuli are sufficiently large such that they may be associated with unacceptable respiratory and circulatory depression. Conversely, anaesthesia may lighten quickly during the procedure unless anaesthetic gases can be delivered to the patient continuously. This may
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MAC s~ MAC EI 5~ MAC BAR 5~ MAC 95 MAC E195 MAC BAR 95
Halothane
Enflurane
1.0 1.3 1.5 1.2 1.7 2.1
1.0 1.4 1.6 1.1 1.9 2.6
necessitate the anaesthetist and bronchoscopist alternating their tasks every few minutes. The maintenance of spontaneous ventilation during bronchoscopy has certain theoretical advantages, particularly if difficulty in securing the airway is anticipated. Also, preservation of the cough reflex is useful in patients who are at risk from aspiration of secretions or blood, although in practice this reflex often returns sufficiently quickly when an intravenous technique with controlled ventilation is used. Controlled ventilation. Anaesthesia may be induced either intravenously or inhalationally and deepened or maintained by either method. In practice, intravenous induction is the norm, and the choice of agent is determined by conventional anaesthetic considerations. Neuromuscular blockade is usually obtained using a depolarizing relaxant (e.g. suxamethonium) by intermittent bolus doses or by infusion depending on the length of the procedure. The vagal effect of repeated bolus doses of suxamethoxonium may cause a bradycardia, and atropine should be available even in those patients who have received vagolytic premedication. For prolonged procedures, nondepolarizing relaxants appear a logical choice although their onset of action is slower and duration of action is often excessively long. Also, the bronchoscopic conditions achieved may not be as good as those seen with suxamethonium. However, the newer generation of relaxants (atracurium or vecuronium) may prove suitable alternatives for patients in whom anaesthesia and paralysis is required for more than 15 minutes. Passage of the bronchoscope is usually preceded by inflation of the lungs with 100% oxygen and, more controversially, by topical anaesthesia with 4% lignocaine to the larynx and vocal cords. There are disadvantages to topical laryngeal anaesthesia; not least that an early return of the cough reflex may be prevented. However, the incidence of laryngospasm is reduced and possibly that of bronchospasm also, particularly in the shorter procedures. Lignocaine is readily absorbed from the mucosa of the respiratory tract and although this may shorten its analgesic effect it may be useful in suppressing the incidence of ventricular dysrhythmias during bronchoscopy. Finally, the cough reflex is often very active in patients with chronic lung disease, and persistent irritant coughing following bron-
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choscopy may do little to aid removal of blood or secretions and simply worsen gas exchange by preventing normal breathing. The maintenance of anaesthesia during rigid bronchoscopy with controlled ventilation of the lungs is largely determined by the method of ventilation used. The following alternatives are available: Ventilating bronchoscope with a side arm attached to the anaesthetic circuit.
Anaesthetic gases can be delivered to the patient, provided the proximal end of the bronchoscope is occluded during ventilation, either with a transparent window or with the bronchoscopist's thumb. The latter necessitates an intermittent technique. Alternatively, a shortened endotracheal tube can be inserted into the proximal end of the bronchoscope and the patient's lungs ventilated with anaesthetic gases. Similarly, an intermittent anaesthetic/bronchoscopic technique is necessary. . Apnoeic oxygenation. Following 3 minutes preoxygenation, maintenance of arterial Po2 can be achieved utilizing the technique of apnoeic oxygenation. A suitable catheter (8FG) is passed so that the tip lies just above the carina, and oxygen is insufflated down it, at approximately 6 1/ min. Uptake of oxygen continues by mass diffusion, possibly assisted by a minimal ventilating effect produced by the beating heart. However, carbon dioxide elimination is minimal and arterial carbon dioxide tension will rise to an extent dependent on metabolic carbon dioxide production, usually at a rate of 1-6 mmHg/min. Thus this technique is unsuitable for prolonged bronchoscopy. 3. 'Jet' or venturi ventilation. In 1967 Sanders described the jet injector and this has become the most popular method for ventilation during bronchoscopy. A jet of gas is delivered at high pressure through a small needle at the proximal end of the bronchoscope. A negative pressure is generated around the tip of the needle and gas is entrained through the proximal end of the bronchoscope, so that the volume of gas delivered to the patient is the sum of the jet volume and the entrained volume. Any gas may be delivered at high pressure, although in clinical practice this is usually 100% oxygen. The delivery pressure for 100% oxygen from a medical pipeline system is approximately 60 PSI (410 kPa) in the UK, and thus it is important that the injector needle should correspond to the size of the bronchoscope, thus allowing adequate entrainment if extremely high airway pressures are to be avoided. In adults, a 14 or 16 SWG injector needle may be safely used, but in children it is necessary to reduce the size of the injector needle to 19 SWG (or smaller) in order to prevent excessively high airway pressures being generated with consequent barotrauma. Diagnostic rigid bronchoscopy is frequently a quick procedure, and a manually operated switch controlling the injector gas flow is usually adequate. However, combined fibreoptic and rigid bronchoscopic procedures and the development of medical lasers for resection of bronchial tumours have encouraged anaesthetists to develop automatic ventilators capable of delivering driving gases for prolonged procedures, thus freeing the anaesthetist for other tasks. Figure 2 shows one such system for fibreoptic bronchoscopy. The endotracheal tube shown is a Mallinckrodt
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Figure 2. VS 600 ventilator (Accutronic Ltd) capable of respiratory rates from 8 600 breaths/ minute. The driving gas outlet is connected to a Mallinckrodt 'Hi-Lo' Jet endotracheal tube through which a paediatric fibreoptic bronchoscope is passed. ~ cuffed endotracheal tube. In addition to the main lumen through which the fibreoptic bronchoscope is passed it has three others: a) the pilot tube connected to the endotracheal cuff, b) the lumen used to deliver high pressure driving gases, and c) a pressure monitoring lumen with a port opening into the main lumen of the endotracheal tube 2 cm distal to that of port (b). This is particularly useful since PEEP (positive end expiratory pressure) may be generated using this system, due in part to the reduction in effective ventilating area of the endotracheal tube (see Table 2) and also since increasing the respiratory rate may cause gas trapping and alveolar distension if the deflation time constant of the lungs and chest wall is exceeded. The ventilator shown is capable of respiratory rates up to 600/min, although it is more usual to use rates of up to 150/min. Such a system may also be used for rigid bronchoscopy, connecting the high pressure driving gas source from the ventilator to an injector port on the bronchoscope (Figure 3). In this instance a fibreoptic bronchoscope is shown with a simple Negus bronchoscope. However, this method of ventilation may also be used with a modern rigid instrument such as the Storz bronchoscope. One disadvantage of using an automatic ventilator as a driving gas source is that it may be difficult to alternately synchronize ventilation with the bronchoscopist's activities thus minimizing the disconcerting effect of blow-
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Table 2. Measured PEEP generated by insertion of
5.7 mm fibreoptic bronchoscope through different sized endotracheal tubes (Lindholm et al, 1978). Internal diameter of ET tube (mm) 7 8 9
Maximum PEEP measured (cmH20) 35 2O
Figure 3. VS 600 ventilator (Accutronic Ltd) with driving gas outlet connected to a Negus
bronchoscope, through which a paediatric fibreoptic bronchoscope is passed. back o f exhaled gases. This problem is certainly reduced if protective spectacles are w o r n by the bronchoscopist, but it should be remembered that the upper respiratory tract is a source o f potentially infective organisms and adequate measures must be taken to protect staff from unnecessary risks. The recent development o f medical laser technology has been applied to b r o n c h o s c o p y and in particular to the use o f lasers to resect otherwise inoperable bronchial neoplasms occluding the lumen o f a major bronchus. This procedure m a y be undertaken as an emergency, usually in very sick elderly patients, and, although m a n y centres have utilized local anaesthesia
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successfully, the use of general anaesthesia and a rigid bronchoscope may be preferred both from the point of view of patient acceptability and to permit the removal of large pieces of tumour debris using biopsy forceps. The smoke and waste gases generated by the laser may be a problem. This has led to the further development of ventilators working on the principle of alternate gas delivery and gas suction (Paes et al, 1986).
Monitoring during bronchoscopy Previously the short duration and variability of the procedure has meant that monitoring equipment has been used sparingly, if at all, during bronchoscopy. The anaesthetist has instead relied on clinical judgement, i.e. assessment of the patient's colour and a finger on the pulse. However, the development of sophisticated non-invasive techniques of patient monitoring has rendered this obsolete. Alterations in cardiac rate and rhythm are seen frequently during bronchoscopy both as a consequence of the procedure itself and of the anaesthetic agents and neuromuscular relaxants used. ECG monitoring should therefore be considered mandatory. Measurement of blood pressure during bronchoscopy has not been widely undertaken previously. Intermittent sphygmomanometry has been considered too cumbersome to use, given the other demands made on the anaesthetist during the procedure, and indwelling intra-arterial blood pressure monitoring has been considered too invasive. However, the development of automatic non-invasive oscillotonometric blood pressure monitors has altered this situation and the anaesthetist may now obtain an automatic minute-to-minute assessment of blood pressure during the investigation. This may be considered unnecessary by some, but recent studies have shown that the anaesthetic technique used may have a significant effect on the magnitude ofpressor responses during bronchoscopy, and that hyperdynamic circulatory effects may be difficult to obtund. Furthermore, close monitoring of the ECG using an electrode position designed primarily to detect myocardial ischacmia has shown that ischaemic episodes may occur in a significant proportion of patients given a conventional anaesthetic (Wark et al, 1986). It should be remembered that adult patients undergoing bronchoscopy, particularly for presumed carcinoma of the bronchus, have many risk factors in common with patients suffering from ischaemic heart disease, and it is not therefore surprising that such patients are at risk from, and do develop, ischaemic episodes during what is frequently a stressful procedure. The relevance of these ischaemic episodes has been questioned in the past, but again recent evidence would appear to substantiate the view that the development of ischaemic episodes during anaesthesia may correlate with an adverse outcome (Slogoff and Keats, 1985). Thus an anaesthetic technique designed to prevent increases in myocardial work and the development of myocardial oxygen imbalance, and the relevant monitoring which enables the anaesthetist to detect such changes, would be appropriate in patients with a known history of ischaemic heart disease undergoing bronchoscopy. Ever more sophisticated non-invasive monitors are becoming available, including those which allow repeated analysis of the ECG for the early detection of indicators ofischaemia. All of this may seem a
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DIAGNOSTIC THORACIC SURGICAL PROCEDURES Table 3. Arterial blood gas analysis during bronchoscopy; results of series using the Sanders injector technique (100% oxygen). Number of patients Morales et al (1969) Giesecke et al (1978) Wark et al (1986)
14 21 36
Paco2
Pao2
42 200 mmHg 38 116 mmHg 5.08 21.2 kPa
far cry from 'a quick list of a few bronchoscopies' but careful cardiovascular monitoring is not inappropriate in higher risk patients and yet it need not be invasive. Nevertheless, in patients undergoing planned extensive procedures such as multiple biopsy or laser resection, it may be appropriate to use intraarterial monitoring for blood pressure measurement and blood gas analysis. Table 3 shows the results of arterial blood gas analysis carried out on a series of patients undergoing bronchoscopy in whom ventilation was controlled using the Sanders injector. It can be seen that blood gases are well maintained in all these patients. However, in clinical practice, intermittent arterial blood gas analysis is usually considered to be unneccessary and impractical, and the open nature of the venturi circuit makes expired gas analysis difficult. Transcutaneous blood gas monitoring has suffered from a number of technical drawbacks, but the development of pulse oximetry has given the anaesthetist a useful tool for the detection of changes in oxygenation during bronchoscopy. The incidence of awareness ~s dlsturbmgly lllgh for patients unctergolng bronchoscopy and values up to 4% have been reported. There is as yet no commercially available machine that is accepted as a predictable 'depth of anaesthesia' monitor and until such time awareness during anaesthesia will continue to be a problem. Clearly it can be minimized by the use of sedative premedication, and by giving repeat bolus doses of intravenous anaesthetic on a timed basis, rather than being directed by the signs of lightening anaesthesia. For prolonged procedures, continuous intravenous infusions of anaesthetics and the use of nitrous oxide/oxygen mixtures as the venturi driving gas may help. From the foregoing it can be seen that monitoring during bronchoscopy should be directed to providing frequent non-invasive and preferably automated assessment of the patient's cardiovascular status and degree of oxygenation throughout the procedure. It may be that these goals are applicable to all patients undergoing short surgical procedures of any nature. Certainly anaesthesia for any diagnostic thoracic procedure should be monitored to this extent as a minimum, although it may also be considered useful to utilize other devices where appropriate (e.g. nerve stimulators for assessing the degree of neuromuscular blockade, etc.). OESOPHAGOSCOPY Visualization of the oesophagus may be carried out using either a fibreoptic or rigid instrument. The former is frequently undertaken under sedation and
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topical anaesthesia only, whereas rigid oesophagoscopy is usually carried out under general anaesthesia. Once again, combined procedures may be undertaken, particularly if it is desirable to examine the upper gastrointestinal tract. The oesophagoscopy may be undertaken for a number of indications but in a non-specialized acute hospital the most common indication is for the removal of a food bolus or other foreign body causing partial or complete dysphagia. Such patients are not often in a poor risk category but they do have a full stomach which poses a threat to the airway during and after the procedure. In comparison, patients with dysphagia due to malignant or benign strictures are frequently poorly nourished and may be dehydrated, anaemic and suffering from electrolyte imbalance. These latter three problems should be corrected preoperatively. Patients with oesophageal varices may have a significant degree of hepatic impairment with all its implications for the anaesthetist. Patients with achalasia of the cardia, hiatus hernia or oesophageal diverticulum are at increased risk from aspiration of food matter or gastric acid and indeed may already have evidence of aspiration pneumonitis or bronchopneumonia.
Management of anaesthesia Sedative premedication may be given in small dosage by the intramuscular route. In those patients at increased risk of regurgitation and aspiration of gastric acid, it may be worth giving a histamine H2-receptor antagonist (cimetidine or ranitidine) to raise gastric pH for elective procedures. A rapid induction sequence may be necessary, with preoxygenation and cricoid pressure. Cricoid pressure should be carried out to control reflux of oesophageal contents. It is usual to place the patient in a neutral supine position, although a steep head-up tilt may minimize the risk of regurgitation, or a left lateral position may reduce the risk of aspiration should regurgitation occur. The trachea should be intubated with a robust cuffed endotracheal tube; either an armoured latex or flexometallic tube is ideal, and the diameter of the tube should preferably be one size smaller than usual. This will more readily permit the passage of the oesophagoscope and indeed it may be necessary to deflate the endotracheal cuff momentarily as the oesophagoscope passes through the cricopharyngeal sphincter. Full muscular relaxation is best maintained up until this time and may be continued throughout the procedure if the endotracheal tube diameter is too small such that the work of breathing through the increased resistance is excessive. Otherwise, spontaneous ventilation may be permitted. In either event anaesthesia can be maintained with a small increment of volatile agent. Following the procedure anaesthesia is discontinued and the patient recovered on his side with a slight head-down tilt. Suction should be immediately available.
Complications of oesophagoscopy Regurgitation and aspiration is a frequent hazard but thankfully not a common complication. Its prevention can be achieved by close adherence to the principles discussed. Bleeding may be a problem, particularly if biopsies
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have been taken, a stricture has been dilated or palliative oesophageal intubation has been carried out, or in those patients with oesophageal varices. The most serious complication of oesophagoscopy is oesophageal perforation. This may even occur following an uneventful examination and indeed may cause no distress to the patient until some hours later. However, severe localized chest pain usually develops and is associated with surgical emphysema and the signs of pleural effusion, pneumothorax or pneumomediastinum. A chest x-ray provides confirmatory evidence of this. Iatrogenic perforation of the oesophagus carries a high mortality ranging from 34 to 84%. Emergency thoracotomy and repair of the oesophagus should be carried out immediately. Postoperatively, the patient may require intensive or high dependency care facilities for some time and parenteral nutrition. MEDIASTINOSCOPY AND ANTERIOR MEDIASTINOTOMY
Mediastinoscopy Mediastinoscopy is primarily used to provide a histological diagnosis in patients with mediastinal lymphadenopathy and for assessing operability in patients with carcinoma of the bronchus. A small incision is made above the suprasternal notch. The pretracheal muscles are separated by blunt dissection and the pretracheal fascia is incised after which it is possible to insert the mediastinoscope. Needle aspiration and biopsies may be taken during the procedure and mediastinal structures visualized. Mediastinoscopy is a potentially hazardous procedure and careful preoperative evaluation is necessary. This should be directed particularly toward examination for evidence of superior vena caval obstruction or of mechanical obstruction to the upper respiratory tract. Whilst the presence of either of these problems does not contraindicate mediastinoscopy, they certainly make it more hazardous. Superior vena caval obstruction is particularly problematic if it occurs acutely since collateral channels will not have had time to open up. There is a real risk of major haemorrhage during the procedure and crossmatched blood should always be available.
Management of anaesthesia There are no special considerations regarding premedication unless significant respiratory obstruction is present, when drug induced respiratory depression must be avoided. High risk patients may be preoxygenated and anaesthesia induced intravenously, followed by muscular relaxation and endotracheal intubation. Inhalational induction of anaesthesia is an alternative, particularly if there are difficulties anticipated in securing a safe airway. A cuffed, armoured endotracheal tube should be used and a range of sizes should be available, particularly if there is any evidence of tracheal compression. Following intubation, anaesthesia may be maintained using increments of volatile agent in an oxygen/nitrous oxide mixture. Although spontaneous ventilation is acceptable, it is wise to avoid coughing or bucking during the
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procedure and this is usually best achieved if the patient is paralysed and the ventilation controlled. In view of the short duration of the procedure one of the new generation of short-acting non-depolarizing muscle relaxants (vecuronium or atracurium) would be ideal. Haemorrhage can be a serious complication in all patients undergoing mediastinoscopy and for this reason a large bore indwelling intravenous cannula should be inserted. This is usually placed in an upper limb, although theoretically it may be safer in a lower limb, particularly in patients with superior vena caval obstruction, since transfusion would then be carried out via the inferior vena cava and not the superior vena cava. The principles of monitoring outlined earlier in this chapter are applicable to mediastinoscopy with one or two differences. The blood pressure is best monitored non-invasively on the left arm, and the right radial pulse monitored in order to detect compression of the right innominate artery. This may be done either by digital plethysmography or more simply by palpation. Expired gas analysis is easy to carry out and end tidal carbon dioxide monitoring may be useful to enable normocapnic ventilation to be achieved. This may also be used to detect air embolism, which is a potential risk if a tear is made in a venous structure with the patient in a steep head-up tilt. Those patients with any degree of respiratory obstruction preoperatively may be at increased risk from postoperative respiratory failure and great care must be taken in the early postoperative period to ensure adequate gas exchange. A period of postoperative intermittent positive pressure ventilation (IPPV) may be necessary in this situation.
Anterior mediastinotomy This procedure is usually carried out through the bed of the second costal cartilage and is carried out to permit examination of anterior mediastinal structures which are not visible during mediastinoscopy. The anaesthetic management of such patients is usually straightforward. Appropriate premedication is given and anaesthesia induced in the normal manner. Although it is theoretically possible to perform the procedure without opening the pleural cavity, in practice this occurs quite commonly, and therefore endotracheal intubation and controlled ventilation of the lungs is performed. Anterior mediastinotomy is also a useful route for performing open lung biopsy. If this is undertaken, the patient should be closely monitored in the early postoperative period for signs of pulmonary haemorrhage and haemoptysis.
Thoracoseopy Thoracoscopy was first developed in Germany in the early 20th century for use in the surgical management of tuberculosis. It is commonly used as a diagnostic tool for the evaluation of pleural disease, lung parenchymal disease including pulmonary infection and infiltration, and for staging procedures for suspected neoplasms. It is also used for chemical pleurodesis in recurrent pneumothorax.
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Management of anaesthesia Careful preoperative assessment is made taking into account the indication for the procedure and the presence of any complicating factors (e.g. pneumothorax), and appropriate premedication is given. Endobronchial intubation is by no means mandatory but does permit selective one-lung ventilation and collapse of the lung on the operated side. This will lessen the risk of trauma to the lung with the thoracoscope, which may cause severe bleeding. Thus intravenous induction and muscular relaxation with a shortacting depolarizing or non-depolarizing agent is the norm. Ventilation is controlled and with a double-lumen endobronchial tube in place the lung can be collapsed and re-expanded at will. However, some may feel that this makes the anaesthetic unnecessarily complicated with all the inherent problems of one-lung anaesthesia (OLA) (see chapter 4). The principles discussed earlier concerning patient monitoring are applicable here also, and indeed pulse oximetry may be particularly useful in this group of patients in the early detection and treatment of hypoxaemia.
ANAESTHESIA FOR RADIOLOGICAL PROCEDURES
There are a wide variety of radiological techniques available for the investigation of patients with chest disease. These include plain radiography, tomography, fluoroscopy, bronchography, ultrasound, computerized tomography and magnetic resonance imaging. In the investigation of vascular lesions, angiography may be undertaken, and embolization of bleeding points is a new technique which in certain circumstances may be carried out instead of surgery. In all of these techniques general anaesthesia is not required unless patient cooperation is lacking. In the very sick or elderly and in virtually all small children, general anaesthesia will be required. Thus when considering general anaesthesia for thoracic radio-diagnostic procedures we are largely considering a paediatric practice. General considerations
In general terms, anaesthesia in an x-ray department is more difficult than in the routine setting of the operating theatre. Great care should therefore be directed toward checking the anaesthetic machine and ancillary equipment, and making sure that spare laryngoscopes etc. are available and in working order. The anaesthetist should be familiar with the layout of the room and the location of wall points for suction and medical gases, if indeed pipeline gases are provided. It is wise to have everything to hand and emergency drugs should be drawn up prior to the procedure. Investigations may be undertaken for a variety of indications and any assessment of the patient will need to take this into account. In particular, the production of copious quantities of sputum (e.g. bronchiectasis) or compression of the trachea or major bronchi (e.g. by a mediastinal mass) may seriously complicate the management of anaesthesia. In most procedures the anaesthetist will be remote from the
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patient and in this situation endotracheal anaesthesia is mandatory. Extra care should be taken to fix the endotracheal tube, and the use of lightweight materials in the anaesthetic circuit may minimize the risk of inadvertent disconnection or extubation during the investigation. Intravenous access should always be obtained and this should have an injection site remote from the patient. An intravenous infusion with extension tubing is a simple solution. Most x-ray departments are cramped and it may be physically difficult to fit in all the monitoring equipment the anaesthetist requires. Nevertheless, the principles of monitoring discussed earlier apply in this situation also and it should be simple to manage ECG, automated oscillotonometry and pulse oximetry for adult and paediatric patients. Both visual and audible displays may be useful, particularly if the ambient lighting is reduced or the view of the monitoring equipment is obscured from time to time. It is also a good idea to have a torch available. There are no special considerations regarding premedication or induction of anaesthesia and routine regimens will suffice. Although spontaneous ventilation is theoretically acceptable, muscular relaxation and IPPV are more commonly used. This allows the patient's ventilation to be more easily controlled during the procedure, and thus it is easier to synchronize with the radiologist with regard to image or biopsy taking, and, furthermore, scavenging of anaesthetic gases is simplified. Explosive anaesthetic agents are not permissible in x-ray departments but an oxygen/nitrous oxide mixture supplemented as required with either a small dose of fentanyl or small increments of a modern volatile agent are acceptable. However, it should be remembered that short bursts of patient stimulation may occur, e.g. during turning etc., and therefore it is wise to have a syringe of intravenous induction agent available should anaesthesia become inappropriately light. The termination of a radiological procedure may be more difficult to judge than that of operative surgery, and a prolonged recovery period may ensue. If no recovery facilities are available these patients should be recovered by the anaesthetist in the x-ray room where the necessary facilities (i.e. oxygen and suction) are to hand.
Bronchography General anaesthesia is required for bronchography more frequently than for the other radiological procedures mentioned since patient cooperation is essential, and the procedure itself may be unpleasant. Bronchography was first carried out in 1922 by Sicard and Forestier using lipiodol, a substance first introduced as an antisyphilitic by LaFey in 1901. However lipiodol has now been replaced by Dionosil (propyliodide) as a contrast medium. Dionosil is available in either an oil or water-based form. The oil is particularly useful since it is thick and shows up larger airways clearly, whereas aqueous Dionosil will disperse more quickly to the periphery of the lung and, as it is more irritant, may cause troublesome coughing. Bronchography was used primarily for the evaluation of bronchiectasis, and, since this condition is declining, the necessity for the examination has also reduced. However, the anaesthetic management of this group of patients may be difficult and requires careful
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preoperative evaluation. Preoperative assessment should be directed toward the volume o f sputum produced and the posture required for drainage. Physiotherapy should be carried out whenever possible prior to the procedure. This will not only make the procedure safer but also results in a clearer b r o n c h o g r a m . Premedication is subject to the usual considerations and the m e t h o d o f anaesthesia is best determined by whether spontaneous or controlled ventilation will be used during the procedure, and whether endotracheal anaesthesia is anticipated or whether the contrast is to be instilled using a rigid bronchoscope. This latter technique is useful since it is possible to place the catheter delivering the contrast under direct vision, and also to effect rapid and effective suction clearance o f the contrast material at the end o f the procedure. Otherwise, an endotracheal tube with a suction orifice is used, with a catheter passed t h r o u g h the suction orifice d o w n the inner lumen o f the endotracheal tube. It is useful to m a r k the catheter so that it is k n o w n when the tip of the catheter has reached the tip o f the endotracheal tube. In either event, induction and muscle relaxation will permit passage o f the bronchoscope or endotracheal tube, and anaesthesia m a y then be maintained by methods described earlier under the section on bronchoscopy. F o r bilateral investigations it is c o m m o n to examine the right lung first and, if the procedure is carried out with endotracheal anaesthesia, frequent turning m a y be necessary. If controlled ventilation is used, the patient should be apnoeic during injection o f the contrast, and then gentle manual ventilation is used to disperse the contrast media. Following the investigation, care should be taken to clear as much o f the contrast as possible prior to the termination o f anaesthesia, and during the recovery period humidified oxygen, suction and physiotherapy m a y be necessary to further aid this process. REFERENCES Christoforidis AJ, Tomashefsk JF & Mitchell MS (1971) Use of an ultrasonic nebulizer for the application of oropharyngeal, laryngeal and tracheobronchial anesthesia. Chest 59: 629-
633. Curling PE (1983) Anaesthetic for thoracic diagnostic procedures. In Kaplan JA (ed.) Thoracic Anaesthesia, pp 321. London: Churchill Livingstone. Giesecke AH, Gerbershagen HU, Dortman C et al (1978) Comparison of the ventilating and injection bronchoscopes. Anesthesiology 38: 298-303. Lindholm CE, Ollman B, Snyder JV et al (1978) Cardiorespiratory effects of flexible fiberoptic bronchoscopy in critically ill patients. Chest 74:362 368. Morales GA, Epstein BS, Cinco Bet al (1969) Ventilation during general anaesthesia for bronchoscopy. Journal of Thoracic and Cardiovascular Surgery 57:873 878. Neuhaus A, Markowitz D, Rottman HH et al (1978) The effects of fibreoptic bronchoscopy with and without atropine premedication on pulmonary function in humans. Annals of Thoracic Surgery 25: 393-398. Paes ML, Conacher ID & Snellgrove TR (1986) A ventilator for carbon dioxide laser bronchoscopy. British Journal of Anaesthesia 58: 663-669. Sanderson DR & McDougall JC (1978) Transoral bronchofibroscopy. Chest 73:(supplement) 701-703. Slogoff S & Keats AY (1985) Does perioperative myocardial ischaemia lead to post operative myocardial infarction? Anesthesiology 62:107-115. Wark K, Lyons J & Feneck RO (1986) Haemodynamic effects of bronchoscopy. Effect of pretreatment with fentanyl and alfentanil. Anaesthesia 41: 162-167.