Airway management

7 Airway management S. V. M A L L E T T D. R. G. BROWNE

Airway management is a broad topic encompassing the fields of emergency medicine, anaesthesia and critical care. This chapter concentrates on those aspects that relate to the provision of artificial airways in the intensive care setting with particular reference to: the indications for and complications of intubation, tracheostomy and cricothyroidotomy; the management and care of these patients, including humidification, extubation and decannulation; and also alternative techniques such as minitracheostomy and assisted ventilation by mask. ENDOTRACHEAL INTUBATION Indications

The major indications for intubation of the trachea include: 1. 2. 3. 4.

maintenance of a clear airway in unconscious patients, or where patency is threatened by upper airway problems such as burns or epiglottitis; to enable ventilation to be controlled mechanically in patients with respiratory failure; protection of the bronchial tree from aspiration when laryngeal reflexes are inadequate; facilitation of the control of bronchial secretions by providing a route for tracheal suctioning.

The difficult intubation

Problems with intubation can be predicted in patients with: 1. 2. 3.

difficulties with neck posturing due to unstable cervical fractures or cervical arthritis; certain anatomical variations such as a small mouth, bull neck, receding lower jaw, prominent central maxillary dentition and high arched palate; limited mouth opening due to trismus or ankylosis of the temporomandibular joint,

Baillidre's ClinicalAnaesthesiology-Vol. 4, No. 2, September 1990 ISBN 0-7020-1465-6

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A small minority of patients will, however, prove quite unexpectedly to be difficult to intubate. The use of assessment and grading techniques such as that described by Mallampati et al (1985), will increase the frequency of prediction of difficult cases and allow proper planning for the maintenance of the airway.

Management of the difficult intubation: techniques The intensive care clinician must be skilled at a variety of methods of airway management, and should have the proper equipment and devices to cover all eventualities readily available on the intensive care unit (ICU) (Figure 1).

Blind nasal intubation. This is a useful technique in circumstances where direct visualization of the glottis is difficult or inadvisable. Transillumination techniques with lighted stylets can facilitate 'blind' techniques, and involve the endotracheal tube being railroaded over the lighted stylet when a bright midline glow in the laryngeal area of the neck has identified intratracheal placement (Ellis et al, 1986). The ambient lighting may affect visualization of the bulb glow, and shielding of the neck may help in conditions of bright lighting.

Figure 1. Difficult intubation aids: (a) Brain's laryngeal mask airway; (b) endotracheal jet catheter with 5 mm Copeland microlaryngoscopy tube (after Bedger and Chang, 1987); (c) extra-long Portex stylet (medium); (d) rigid gum elastic bougie.

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Retrograde intubation. This technique describes intubation of the trachea over a wire or cannula that has been percutaneously placed through the cricothyroid membrane, and then threaded up into the oropharynx (Powell and Ozdil, 1967). This technique may have a place in situations in which it is essential to minimize movement of the neck, such as unstable cervical fractures. The method of retrograde intubation can be combined with the use of a fibreoptic scope to allow direct visualization and therefore prevent the need for any manipulation of the neck (Liechman et al, 1986). Complications associated with translaryngeal procedures, include haemorrhage, vocal cord damage and subcutaneous emphysema (Lyons et al, 1977).

Dual-lumen airway devices. Devices such as the oesophageal tracheal combitube, have recently been introduced into clinical practice (Frass et al, 1987). Such tubes, which are a modification of the oesophageal obturator, were developed to improve airway management in the prehospital setting as the oesophageal obturator airway had a number of problems associated with its use, not least of which was iatrogenic airway obstruction if unrecognized tracheal placement occurred. The oesophageal tracheal combitube, by virtue of its dual lumens, enables a choice of either oesophageal obturation or tracheal ventilation (Frass et al, 1988). One lumen functions as an obturator, with side holes above a lower cuff allowing gas to be exchanged with the trachea, as the tube sits high in the oesophagus, whilst the second lumen functions as a direct conduit for gases should the tube be placed in the trachea. The oropharynx is occluded by a large pharyngeal balloon, thus sealing the upper airway. The combitube can be inserted blindly, without manipulation of the neck, and therefore may be very ..useful in the emergency situation where the potential for cervical spine injury exists. Laryngeal airway. The laryngeal mask airway, introduced by Brain in 1985, has also found a place in the management of patients who present with difficult intubation problems (Brain et al, 1985). The mask can be inserted in a blind fashion and sits over the aperture of the larynx thus maintaining the airway and providing an alternative means to ventilate the patient. It is also possible to pass an intubating bougie or fibreoptic scope through its lumen into the larynx and railroad an endotracheal tube of small diameter over these.

Fibreoptic bronchoscopy. There is no doubt that this represents the best and most controlled method for intubating patients who are known to be difficult problems (Messeter and Peterson, 1980). However, it must be emphasized that this is the case only if the procedure is performed by personnel who are familiar with, and skilled at, the use of fibreoptic intubation techniques.

Endotracheal catheters. The jet-stylet endotracheal catheter, described by Bedger and Chang (1987) for assisting in difficult intubations, is also extremely useful if it becomes necessary to change an endotracheal tube in a patient who is known to be a difficult intubation. Inserting the endotracheal catheter down the inside of the endotracheal tube before its removal, will

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facilitate tube exchange, assure a patent airway and provide a mechanism for continued oxygenation and/or ventilation in these patients.

Percutaneous, translaryngeal ventilation; minitracheostomy and surgical cricothyroidotomy: These techniques remain as alternatives for those patients in whom the above methods fail or are contraindicated (McGill et al, 1982; Yealy and Paris, 1989). Complications of intubation

Early complications Malposition Oesophageal intubation. Accidental intubation of the oesophagus can sometimes be extremely difficult to recognize. Detection of 'normal' breath sounds in the axillae is notoriously misleading, as these may be mistaken for the sounds of air passing along the oesophagus (Scott, 1986). Auscultation of the epigastrium, however, is very reliable (Anderson and Hald, 1989). Detection of physiological quantities of carbon dioxide using capnography, however, is the best indicator of correct tube placement (Birmingham et al, 1986).

Figure 2. Endobronchial intubation, Accidental right main stem intubation, leading to complete collapse of the left lung with shift of the mediastinum to the left hemithorax.

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Endotracheal tubes can migrate out of the trachea and come to lie in the pharynx. This is especially likely to occur if the tube moves so that the cuff is lying at or above the cords, with the danger that the inexperienced may overinflate the cuff in an attempt to abolish the inevitable leak that occurs.

Endobronchial intubation. Stauffer et al (1981) reported a 9% incidence of accidental endobronchial intubations. Not surprisingly, these mostly involved the right main bronchus, which is more directly in line with the trachea. If unrecognized (unilateral chest inflation and increased airway pressures), endobronchial intubation will result in collapse of the opposite lung and hypoxia (Figure 2). It is well-recognized that head flexion and extension can result in substantial tube movement (Conrardy et al, 1976), and tubes must be firmly secured and their position checked regularly on a chest X-ray. In addition, tubes that are too long, as well as being more likely to enter a main bronchus, can induce reflex bronchospasm if the tip impinges on the carina.

Obstruction Obstruction of the endotracheal tube can occur at any time and can be due to a variety of causes including: inspissated secretions or blood, kinking, biting on the tube, cuff herniation, or the bevel of the tube lying against the tracheal wall. Complete obstruction is usually all too obvious, resulting in patient distress, cyanosis, absent chest expansion and excessive airway pressures: and must be dealt with immediately. Partial obstruction, however, maybe misinterpreted as severe bronchospasm (Stoen and SmithErichsen, 1987), and it is essential to exclude mechanical causes of excessive airway pressures (check tube patency with suction catheter, deflate cuff and withdraw slightly) before assuming that the new 'bronchospasm' requires treatment with bronchodilator therapy.

Late complications The incidence and severity of tracheal and laryngeal lesions following intubation are related not only to the duration of intubation, but also to factors such as cuff shape, cuff pressure, tissue compatibility of the tube and cuff material. In general these injuries occur where the airway is under the greatest pressure from the endotracheal tube and/or cuff. With the advent of improved tube and cuff design, the problem of late complications related to intubation has become very much less. Stauffer et al (1981) in their review of complications related to intubation, found a 19% incidence ofpostextubation stenosis (defined as a 10% reduction or greater in the diameter of the laryngeal or tracheal lumen on tomographic analysis) in patientsintubated for up to three weeks. However, none of these patients had prolonged or significant respiratory symptoms.

Mechanisms of tube related injuries The insertion of an endotracheal tube deforms the glottis from its normal

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resting position, the tube tending to lie posteriorly in contact with the mucosa overlying the arytenoid cartilages and vocal cords laterally and the cricoid p0steriorally. The pressures generated by this contact can be quite high, resulting in mucosal oedema, which can progress to ulceration (Weymuller et al, 1983). Healing, with the development of fibrotic scar tissue, will result in stenotic lesions. Other areas vulnerable to injury include the mucosa overlying the third to seventh tracheal rings, the area at risk depending on cuff length and site. Occasionally the anterior tracheal wall distal to the cuff site is ulcerated by prolonged impingement on the tip of the tube. There is certainly a clinical impression that excessive movement and torque on a tube (e.g. the agitated and restless patient) will result in an increased incidence of minor laryngotracheal trauma.

Endotracheal tube design Improved design of endotracheal tubes has done much to reduce the hazards of prolonged intubation, such that it is now acceptable to leave patients intubated for many weeks.

Tube material. The ideal tube should resist kinking and collapse, yet be soft, thermolabile and non-irritant and non-toxic to tissues. Portex, Rusch and Shiley PVC tubes conform to these standards. Each type of tube material has its own inherent elastic recoil, such that the force exerted against the tracheal structures varies with tube shape and material: this is referred to as the tube's tracheal loading force (Steen et al, 1982). Tracheal loading forces, which are due mainly to deformation of the endotracheal tube by the anatomical configuration of the upper airway, are very much less with thermolabile tubes that alter shape to conform to the curves of the patient's airway. Tube size. A tube with an outside diameter considerably less than the diameter of the cricoid ring should be used to avoid the risk of circular subglottic stenosis; also it should be remembered thai the larger the tube the greater the tracheal loading forces. The maximum recommended sizes are a size 9 (external diameter 13 mm; internal diameter 9 mm) in an adult male, and a size 8 (11mm; 8mm) in an adult female. Tube cuff. Tracheal damage, such as tracheal stenosis, resulting from endotracheal tube cuffs is a well-recognized problem: cuff pressures in excess of the mucosal capillary perfusion pressure, i.e. greater than 30 mmHg, being the mechanism of cuff-induced injury (Knowlson and Bassett, 1970). Various cuff designs have been introduced in an attempt to reduce cuff to tracheal wall pressure (CTP); including foam cuffs and double cuffs (McGuinness et al, 1971). However, the only design that has stood the test of time and emerged as the one recommended for intensive care use is the thin-walled, low-pressure, high-volume ('floppy') cuff (Grillo et al, 1971). It is important to appreciate that although CTP is below 30mmHg at seal point with these high-volume cuffs, further inflation with as little as 1-3 ml of

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(a)

(b) Figure 3. Tracheal dilatation. Example of gross tracheal dilatation resulting from progressive over-inflation of a tracheostomy tube's high-volume, 'low-pressure' cuff. CT scans of the upper thorax: (a) normal trachea; (b) dilated trachea with tracheostomy tube in situ.

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air can result in steep increases in intracuff pressure (Wu et al, 1973). If increasing amounts of air are used to inflate the cuff progressively over a period of time in an attempt to overcome a leak, tracheal dilatation may result with the inherent risks of tracheal rupture (Figure 3). No leak ventilation should therefore be achieved with meticulous attention to cuff inflation (Stauffer et al, 1981). Various devices are available to measure intracuff pressure, which should be maintained at 25 mmHg. Intermittent deflation of cuffs is no longer practised, since it is of no use in reducing cuff lesions and may allow aspiration of pooled infected material from the oropharynx. Occasionally patients on intensive care require surgery and it must be remembered that nitrous oxide will diffuse into air-filled cuffs and increase intracuff pressure and volume (Stanley, 1975). Oral versus nasal intubation

Many intensive care units prefer to use nasal rather than oral endotracheal tubes in patients who require prolonged intubation. There is a definite impression that patient comfort is improved, that they tolerate the tube better, and damage to, or occlusion of the tube by biting is prevented. Dubik and Wright (1978) found that long-term nasal intubations were associated with only half as many tracheal injuries as orotracheal intubations, possibly because of lower tracheal loading force (due to less tube distortion), more secure tube immobilization and/or smaller tube size. Stauffer et al also found laryngeal injuries to be less common following nasal, as opposed to oral, intubations. Nasal intubation does, however, have a number of disadvantages and complications: these include epistaxis, trauma to the posterior pharyngeal wall and creation of false passages, necrosis of the external nares and increased resistance to airflow and sometimes difficulty with suctioning in the presence of the smaller tubes required for nasal intubation. Bacteraemia is more common following nasal intubation (Berry et al, 1973) and patients with valvular heart disease or those that are immunocompromised should have antibiotic cover before nasal intubation. Maxillary sinusitis can occur due to impaired drainage as a result of obstruction by the nasotracheal tube (Areus et al, 1974), and should always be excluded in cases of unexplained pyrexia in patients who are nasally intubated. Overall, we feel that in the majority of cases the advantages of nasal intubation outweigh any potential disadvantages. In particular, the improved tolerance and comfort provided by nasal tubes will often lead to significant reductions in sedative requirements, thus helping the weaning process. Extubation

Extubation is only considered when the patient can cough, swallow and protect his/her own airway and has proved capable of sustaining spontaneous ventilation through the tube for an adequate period of time. It is the last criterion that is often difficult to determine in patients who have required prolonged respiratory support and prolonged weaning periods. Recent

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developments in ventilator design have done much to eliminate the increased work of breathing that results from ventilator circuits, demand valves etc. (Bernstein et al, 1989). Consequently many patients are weaned on to full spontaneous respiration whilst still attached to the ventilator. Ventilators such as the Bennett 7200 A and the Servo 900 C have inspiratory work/flow patterns that are similar to those of the normal adult and therefore add only negligible increases in the obligatory work of breathing (Cox et al, 1988). The endotracheal tube itself, however, also creates some increased resistance and Brochard et al (1988) recommend that pressure support (5-8 cm H20) is used to compensate for this in patients breathing spontaneously. An increase in the work of breathing may lead to respiratory muscle fatigue, the physiological response to which is tachypnoea (Road et al, 1987). It is recommended that patients are not allowed to breathe spontaneously through an endotracheal tube at ambient pressure, but rather with CPAP, as this compensates for the loss of physiological retard caused by bypassing the glottis with a tube (Quan et al, 1981). In addition CPAP will also improve lung mechanics and volumes and result in better oxygenation and decreased work of breathing (Katz and Marks, 1985).

Immediate complications following extubation Stridor. Following extubation, stridor will occur in approximately 5% of patients (Stauffer et al, 1981). This is often due to oedema and will usually respond to a nebulized solution of adrenaline (1 ml in 1000 diluted in 5 ml normal saline). Although steroids are frequently used in this situation, their efficacy has not been carefully studied.

Laryngeal incompetence. Long-term intubation may affect the ability to close the larynx. In a group of patients who had been intubated for up to 18 hours and then extubated, 33% aspirated dye administered immediately after extubation, but only 5% did so after 8 hours (Burgess et al, 1979). To avoid the risk of aspiration it is safest not to administer oral fluids for 12 to 24 hours after extubation. (Feeding by means of a nasogastric tube can be continued throughout this period.) In patients intubated for longer periods, structural abnormalities may interfere with glottic closure for much longer.

Late complications following extubation Laryngealstenosis. This extremely rare, but serious complication may occur weeks or even months following extubation. It appears to result from healing of mucosal lesions that result in the formation of scar tissue (Hawkins, 1977). Chronic hoarseness. Following prolonged intubation this may be due to fibrosis of the cords, neurological damage, cricoarytenoid arthritis, dislocation of the arytenoids or formation of granulomas or polyps. Hoarseness is a common problem in the immediate extubation period, but its persistence for more than a week requires careful evaluation by an ENT surgeon.

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TRACHEOSTOMY

Indications 1.

2. 3. 4.

Relief of upper airway obstruction. Chronic: e.g. carcinoma of the glottis. Acute: if upper airway obstruction is complete, many authorities (Heffner et al, 1986), would recommend a cricothyroidotomy because of the markedly increased complication rate of emergency tracheostomies (Stauffer et al, 1981). However, acute upper airways obstruction can almost always be managed initially by endotracheal intubation, followed by an elective tracheostomy at a later date. In these circumstances, it should be remembered that use of a tube of small diameter (e.g. Copeland tube, 5 mm), railroaded over an extra-long intubating bougie, may succeed, where attempts with larger tubes have failed. Laryngeal incompetence: especially if associated with pharyngeal disorders, e.g. neuromuscular diseases, bulbar palsy, cerebrovascular accidents and prolonged coma. Tracheobronchial toilet: access for suctioning (see also Minitracheostomy). Long-term ventilation: provision of an artificial airway where the need for ventilatory assistance is envisaged for more than 14 days: airway management is simplified, patient comfort is improved, vocalization and oral nutrition become possible, and by promoting maximum respiratory efficiency in a handicapped pulmonary system it may facilitate the weaning process (Yung and Snowdon, 1984).

Complications of tracheostomy

Early complications Bleeding. This occurs in approximately 5% of patients, generally from the anterior jugular venous system or thyroid gland isthmus.

Pneumothorax. This can result from injury at the time of surgery. Subcutaneous emphysema. Patients on positive pressure ventilation may develop a tension pneumomediastinum that may rupture into the pleural space. It may become necessary to decompress the subcutaneous emphysema through the tracheostomy wound. Tube displacement. Tube displacement within the first few days after insertion is a serious complication. Because no secure tract will have developed, efforts to reinsert a tracheostomy tube can result in the creation of a false passage in the pretracheal subcutaneous tissue. It must not be forgotten in the heat of the situation, that it is usually perfectly possible to reintubate the patient with an endotracheal tube! Tube extrusion is most likely in situations where there is badly attached ventilator tubing or if the tapes fixing the tube around the neck are too loose (tapes should be tied with the neck of the patient in the flexed position to prevent them becoming loose

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Figure 4. Displaced tracheostomy tube. Tracheostomy tube visible in pretracheal tissue: displacement occurred when the patient was sat up for a routine chest X-ray.

later). Especial care is required when the patient is repositioned, e.g. for chest X-rays (Figure 4). Constant supervision by nursing staff that are experienced in the care and management of patients with tracheostomies cannot be overemphasized. Techniques used to minimize tube displacement include use of stay sutures tied to the trachea and brought to the skin, and also Bjork flaps. There is some evidence that Bjork flaps may be associated with an increased incidence of tracheal stenosis following decannulation (Price, 1983) and their use is becoming less common as a result. Tube occlusion. This complication is minimized by adequate humidification and good suction technique.

When a displaced or blocked tube needs to be changed urgently within the first 48 hours postoperatively, the patient should be intubated immediately with an endotracheal tube to guarantee an airway, and the tracheostomy tube itself should be changed by a surgeon with full resuscitative equipment available. With less urgent situations, where the tube is correctly positioned but suctioning is becoming difficult due to partial blockage, the tracheostomy tube can be changed over a catheter or small cuffless endotracheal tube, the

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latter having the benefit of an outer adaptor to enable assisted ventilation if required.

Late complications Pulmonary infection. A tracheostomy is a major risk factor for respiratory infection. Stauffer et al (1984) estimated the incidence of secondary bacterial invasion of the lungs to be eight times higher following tracheostomy than with prolonged intubation. Pneumonia is the consequence of the changes in airway bacterial colonization that occur following tracheostomy: 60-100% of patients with long-term tracheostomies colonize their tracheobronchial trees with pseudomonas or gram-negative bacilli (Niederman et al, 1984). The severity of the underlying disease state and nutritional status appear to be important factors influencing the likelihood of tracheostomized patients developing pneumonia (Heffner et al, 1986). Tracheal wound infections are also an important source of airway bacterial contamination. Avoidance of nosocomial pneumonia requires strict adherence to sterile technique in tracheostomy care. Tube changing at regular intervals is no longer practised: there is no evidence that this reduces the incidence of infection, and crusting of secretions in the inner lumen should not be a problem provided that humidification is adequate and suctioning is properly and regularly performed.

Tracheal stenosis. The principle long-term risk of tracheostomy is stenosis at the stoma site, but in clinical practice significant stenoses are very rare (Stauffer et al, 1981), as symptoms do not occur until there is at least a 50% reduction in the tracheal lumen (Weber and Grillo, 1978). The formation of stomal strictures is reduced by preventing traction on the tube: flexible

(a)

(b)

Figure 5. Tracheal stenosis. Example of tracheal stenosis resulting from prolonged intubation with a low-volume, high-pressure cuff. (a) Valsalva manoeuvre; (b) quiet breathing.

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catheter mounts with swivels should always be used and the tube secured properly. Tracheal stenosis at the cuff site has become much less of a problem with the use of low-pressure, high-volume cuffs (Figure 5). However, it bears emphasizing again, that this is only the case when the seal pressure is below mucosal capillary perfusion pressure, and overinflation with only a few millilitres of air can result in exponential increases in intracuff pressure (Lewis et al, 1978). The results of Stauffer's study suggest that the severity of airway lesions is greater following tracheostomy than those associated with an endotracheal tube in place for up to three weeks: the overall complication rate was similar (60%), however, those following tracheostomy were judged to be more serious.

Timing of tracheostomy The optimal time to perform a tracheostomy remains controversial (Berlank, 1986). Longer intubation times are the trend, and it would appear that lower morbidity and mortality are achieved through intubation, rather than early tracheostomy. Both endotracheal intubation and tracheostomy present inherent hazards for long-term airway management. Since the advent of 'floppy' cuffs, most of the damage from endotracheal tubes occurs in the posterior larynx, and this progresses in severity with increasing duration of intubation (Whited, 1984). El-Nagger et al (1976) also found a linear correlation between duration of endotracheal intubation and severity of lesions. When comparing endotracheal intubation and tracheostomy, they found a higher incidence of infection in the tracheostomy group and more frequent and severe tracheolaryngeal injury. Whited's study, however, showed that many patients converted to tracheostomy already have damaged airways and suggest that long-term intubation increases the risk of tracheal injury from a subsequent tracheostomy. There is no doubt, however, that many patients become increasingly uncomfortable with the endotracheal tube as they recover. A tracheostomy tube improves patient comfort, allows improved endotracheal suctioning and provides greater latitude in graded decannulation techniques and may well facilitate the weaning process. In 1986, Stock et al, prospectively reviewed perioperative complications in ICU patients receiving elective tracheostomies and found no major complications and only a 6% incidence of minor complications. It is important to note, however, that all their tracheostomies were performed in the intensive care unit by experienced surgeons. They also found that tracheostomies, by simplifying airway management, often allowed earlier discharge from the ICU. There is much to recommend performing tracheostomies in the ICU if the facilities are available: moving critically ill patients dependent on multiple life-support systems is technically difficult, labour intensive and potentially dangerous for the patient. An exact time criteria is not appropriate when determining when to do a tracheostomy, and the decision must be individualized in each case. Every

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patient should be reviewed after 5 to 7 days of intubation and a decision made on the basis of the likely duration of ventilation, mental status, neuromuscular function and presence of any complicating factors, such as sinusitis. At this point, if extubation cannot be foreseen in the near future, then tracheostomy should be strongly considered. Where the situation is uncertain, patients should be reassessed regularly. This is the basis of the approach used by Heffner et al (1985) and avoids unnecessarily premature conversion to tracheostomy.

Special considerations

Speech For patients with a tracheostomy, who may be dependent for weeks or even months on assisted ventilation, the inability to speak and thus communicate effectively, is a considerable frustration to them, their family and those caring for them. Various devices and tubes have been developed to enable speech in these patients (Figures 6 and 7).

Simple methods. Spontaneously breathing patients, if able to generate sufficient airflow, can talk during expiration by simply deflating the cuff and occluding the tracheostomy tube with a finger.

Fenestrated tracheostomy tubes. These tubes allow speech in spontaneously breathing patients, while still providing access for airway suctioning and

, j/-;

;~r ,5

",5"

iii 7]

Figure 6. Speaking tubes: left to right--silver tube, Shileyfenestrated tube (with inner plain tube), Portex vocalaid.

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positive pressure ventilation if needed. Speech is possible by removing the inner tube, deflating the cuff on the outer tube and 'corking' the tube, thereby diverting the expired air through the vocal cords. It must be remembered that when capped, these tubes can produce a significant increase in airways resistance, that may compromise patients with limited respiratory muscle function (Criner et al, 1987). Use of a one-way flap valve (inspiration through the flap, expiration through the upper airway), e.g. de Santi valve, inserted into a suitably modified Shiley cork, will reduce much of this resistance, and may be helpful in some patients as a 'half-way house' measure (Munroe, personal communication).

Speaking tubes. Cuffed, polyvinyl, tracheostomy tubes allowing speech were first introduced in the 1960s. All work on the same principle: that is an extra channel is provided above the cuff and is connected to a source of warm, humidified air/oxygen, which acts as a substitute for the pulmonary bellows. An airflow of 2-10 litres is required, a balance being struck between speech clarity and patient comfort which becomes less with high flows (Hansen, 1975). These tubes also require a significant amount of patient cooperation to enable them to be used properly, and thus have found only a limited place in the ICU setting. Silver tubes. Silver cuffless tubes have an inner removable tube and a one-way flap valve to allow speech. These tubes and de Santi valves may also provide a useful interim measure between 'corking' and decannulation, provided the laryngeal reflexes are competent.

Figure 7. Speaking valves: centre, Shiley fenestrated tube with modified cork and de Santi valve (Munroe modification); left, Solid Shiley Cork; right, 'Passy-Muir' one-way flap valve.

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Decannulation

Decannulation requires that the patient fulfils certain criteria: obviously they must be fully weaned from the ventilator and capable of maintaining their own ventilation. In addition, the presence of a cuffed tube to prevent aspiration or a tube to provide access to the trachea for the control of secretions should no longer be required. If bronchial toilet remains a problem tracheal 'buttons' will maintain patency of the tract and provide a route for endotracheal suctioning. There are several types of these buttons, e.g. Olympic trach-button (Olympic Medical, Seattle), the idea being to maintain the tract open, but leave the tracheal lumen free (Long and West, 1980). Some are also available with one-way flap valves. The danger of these devices is that they may move posteriorly, resulting in tracheal obstruction. A minitracheostomy may be a safer alternative means to provide access for tracheal suctioning. Once decannulated, the tracheostomy stoma is covered with a dry dressing. Unless something solid is placed in the dressing (e.g. a 10 pence coin), the patient may experience problems with entrainment of air and sometimes bits of dressing, delaying closure of the stoma. The tract will usually close spontaneously in days to weeks, but in some cases the stoma may close rapidly and reinsertion of the same-sized tracheostomy tube may be difficult in as little as 24 hours. Occasionally, surgical closure is necessary if the tract fails to close, usually as a result of steroid therapy or stomat infections (Weber and Grillo, 1978). CRICOTHYROIDOTOMY

The role of cricothyroidotomy (insertion of a tracheostomy tube through the cricothyroid membrane) for long-term airway management is somewhat controversial. Following the landmark paper by Jackson (1921), the technique fell into disrepute, because of the excessively high incidence of subglottic stenosis associated with its use. In 1976, Brantigan and Grow, reconsidering the merits of cricothyroidotomy, reviewed the records of nearly 700 patients with long-term cricothyroidotomies and found a low complication rate (6.1%), with no subglottic stenosis and a 2.6% incidence of tracheal stenosis: thus challenging accepted professional dogma. Cricothyroidotomies in their series were performed mainly for patients with respiratory failure requiring ventilation, as opposed to Jackson's patients, who mainly had inflammatory and infective conditions of the upper airway. Brantigan and Grow (1982) point out that acute laryngeal inflammation and mucosal ulceration are the major predisposing factors for the development of stenotic lesions. They recommend endoscopic evaluation of the airway in intubated patients before surgery: if laryngeal pathology is present, cricothyroidotomy should be avoided and a standard tracheostomy performed. Other authors, however, are less than enthusiastic about the merits and place of cricothyroidotomies. In Stauffer's prospective review, there were only two patients who had cricothyroidotomies: both had stenosis, one of which was subglottic. Esses and Jafek (1987), in a retrospective survey of

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1026 patients who had undergone emergency or temporary procedures for airway management, found a 28% complication rate for cricothyroidotomy (76 patients), with a 2.6% incidence of subglottic stenosis. Kennedy (1980), also points out that cricothyroidotomy is far from a benign procedure; and that it is difficult to recommend a technique that can damage the larynx and risk such a devastating complication as subglottic stenosis. In view of the potential for serious complications, there are relatively few indications for cricothyroidotomy and alternative techniques should always be considered. Indications 1. 2.

3.

Sternotomy patients. There is a risk of infection in the sternotomy wound and mediastinitis following conventional tracheostomy. Emergency airway access. It is well known that the complication rate following emergency tracheostomy is at least four times as high as that associated with elective tracheostomy (Stauffer et al, 1981). Cricothyroidotomy is an alternative in this situation because of the superficial location of the surgical site and the absence of important adjacent neural or vascular structures. Esses and Jafek (1987), however, recommend elective conversion to tracheostomy if there is prolonged need for airway control. Palliative control: respiratory hygiene in terminally ill patients; however, minitracheostomy may well be more appropriate.

Contraindications 1. 2. 3.

Paediatric patients have an exceptionally high risk of subglottic stenosis. Endotracheal intubation for more than one week (laryngeal pathology will increase the risk of subsequent stenotic lesions). Presence of laryngeal inflammation or infection.

MINITRACHEOSTOMY Minitracheostomy is an important addition to the range of measures available for the treatment of patients with respiratory problems. First developed in 1984 by Matthews and Hopkinson, minitracheostomy allows access to the airway for suctioning and oxygen entrainment. The trachea is percutaneously cannulated with a small (4 ram) tube passed through a vertical incision made in the cricothyroid membrane, following infiltration with local anaesthetic. (For details of the technique refer to Matthews and Hopkinson (1984) and Choudry and Jackson (1988)). A kit is available from Portex: the Portex Mini-Trach II (Figure 8). Sputum retention The principle indication for minitracheostomy is to allow tracheobronchial

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S . V . MALLEI'T AND D. R. G. BROWNE

Figure 8. Portex Mini-Trach II Kit. The kit consists of (left to right) introducer, 4 mm tube with flange, standard adaptor and scalpel blade with a protective guard.

toilet in patients with sputum retention. If used early, it can often prevent the inevitable downward spiral of hypoxia, confusion and respiratory failure (Lewis et al, 1986). There is no doubt that it fills an important therapeutic gap between simpler methods of dealing with sputum retention (physiotherapy, nasopharyngeal suction) and the more invasive (bronchoscopy and intubation). By leaving the glottis competent, minitracheostomy enables more efficient clearance of secretions than is possible with methods that bypass the glottis and abolish the ability to generate an explosive cough. In addition, the retention of voice and thus the ability to communicate is a significant advantage. Minitracheostomy in the intensive care unit

Recognition of high-risk patients and early use of the technique may avert the need for intubation and ventilation. It has proved useful in the difficult period of weaning when the patient has been extubated (Hart et al, 1987). After a prolonged period of intubation, impaired glottic function and expectoration are not uncommon, and the use of a minitracheostomy at this stage may enable efficient tracheobronchial toilet and prevent the need for reintubation. Minitracheostomy has also been helpful in some patients, who as a result of injury or debility, are unable to cooperate fully with physiotherapy. In addition, it may also enable

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earlier discharge from ICU, as effective suctioning can continue on the ward. The cannula can also be used for the administration of humidified air or oxygen, nebulized drugs, bronchial lavage and retrieval of bacteriology samples for culture. It must be stressed, however, that if respiratory failure is already established, minitracheostomy is not appropriate, and this must be managed with intubation and ventilation. Other uses of minitracheostomy 1. 2. 3. 4. 5.

Emergency access to the airway, e.g. failed intubation or upper airway obstruction. Obstructive sleep apnoea (Hasan et al, 1989). High-frequency jet ventilation (Matthews et al, 1986). Alternative to tracheostomy, before laryngectomy (Harrison and Fielder, 1988). Cardiac surgical patients, to avoid a formal tracheostomy and thus reduce the risk of infection in the sternotomy wound (Kirk, 1986).

Complications of minitracheostomy The true incidence of complications associated with minitracheostomy is difficult to ascertain as most of the reported complications are in the form of isolated case reports. The majority represent technical difficulties at the time of insertion, and undoubtedly these problems will decrease with increased experience and clinical usage.

Bleeding. This is usually external, and minimized by the use of vasoconstrictors (adrenaline) in the local anaesthetic solution. A suction catheter should be passed immediately following insertion to remove any blood or secretions. Daborn and Harris (1989), reported a case of life-threatening bleeding in a patient on anticoagulants who had a subglottic polyp, which was traumatized on insertion of the minitracheostomy tube.

Misplacement. As the tube is inserted 'blind', misplacement is not surprisingly a commonly reported difficulty; various reported misplacements include intra-oesophageal placement (Ryan et al, 1989), intrapleural (Silk and Marsh, 1989) and upward migration through the larynx (West and Coad, 1988). Confirmation of correct placement is essential and a check chest X-ray and lateral X-ray of the neck are mandatory. Aspiration of air on entering the trachea is another confirmatory measure. As a result of these problems, a Seldinger technique has been suggested to enhance the safety of insertion of minitracheostomy tubes (Choudry and Jackson, 1988).

Inhalation. A potentially lethal problem with the original tubes which lacked a flange (Lewis et al, 1986). The introduction of the Portex Mini-Trach II in 1985, with its improved design, allows much more secure fixation and has virtually eliminated this particular problem.

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MALLETT A N D D. R. G. B R O W N E

Contraindications

1. 2. 3. 4.

Established respiratory failure. Inability to protect the airway from soiling and aspiration. Bleeding diathesis/anticoagulant therapy (relative contraindication? ). Caution is advised if using a minitracheostomy for high-frequency jet ventilation because of the risk of displacement and surgical emphysema (Ravialia and Stockwell, 1987).

NON-INVASIVE VENTILATION Nasal CPAP-IPPV

CPAP (continuous positive airway pressure) is known to improve or reverse hypoxaemia in some patients with ventilation/perfusion mismatch and to increase lung volume and compliance, thus decreasing the work of breathing (Katz and Marks, 1985). The use of a tight-fitting mask allows application of CPAP without the need for intubation, and in conjunction with a suitable ventilator this technique can be used to provide assisted ventilation. CPAP delivered by mask for the treatment of obstructive sleep apnoea was introduced by Sullivan et al (1981), who then further developed the idea by adding IPPV. The efficacy and ease of use of nasal IPPV is such that it has become widely regarded as the technique of choice in patients when noninvasive ventilation is indicated (Branthwaite, 1989). Indications

1.

2.

3.

To avoid intubation during an acute exacerbation of chronic respiratory failure. It is particularly useful in patients with a mechanical element to their respiratory problems, such as neuromuscular disorders, fixed rib cage and old healed tuberculosis with extrapulmonary restriction from previous surgery (Carroll and Branthwaite, 1988). Apparently trivial events such as minor respiratory tract infection, sedatives and general anaesthesia, can precipitate respiratory failure in patients with mechanical problems or with chronic obstructive airways disease. It is well known that once ventilated, it is often extremely difficult to wean these patients from their respiratory support, and use of this technique may avert the need for and commitment to conventional ventilation. Nasal IPPV can also be used to assist the sometimes difficult transition period from controlled ventilation to spontaneous respiration and full independence in patients who have required prolonged ventilatory support (Branthwaite, 1989). The method has also proved useful in the management of patients with central sleep apnoea, who characteristically hypoventilate during sleep, and in whom matters are made worse by the administration of sedatives or an anaesthetic (Midgren et al, 1988).

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Requirements for non-invasive ventilation The patient must: 1. 2. 3. 4.

be capable of some period of spontaneous ventilation; have sufficient gas-exchanging surface within the lungs to secure adequate oxygenation and carbon dioxide clearance; be alert, able to clear their secretions and protect their own airway; have a perfect airway all the time.

Disadvantages of non-invasive ventilation 1. 2.

This method requires a tight-fitting mask, secured to the head with a light harness; some patients find this uncomfortable for prolonged periods. Gastric distension can be troublesome, particularly in patients with poor lung compliance, or with neuromuscular disorders resulting in a weak cricopharyngeal sphincter.

Ventilator requirements for mask IPPV It is necessary to use large tidal volumes (approximately twice that required for a comparable patient who is intubated), because of the inevitable leaks around the mask and through the mouth, and the marked increase in dead space, as the nose, mouth, sinuses and pharynx are included in the circuit. It is important to use a ventilator that has a sensitive trigger, with fast response times; this is particularly so in patients with severe airflow limitation, e.g. chronic obstructive airways disease, who have difficulties with some ventilators in generating the threshold in the ventilator circuit needed to initiate a triggered response. An adjustable trigger is very helpful, as if the response time is too short, it is possible to get 'stacking' of breaths.

Airway pressure release ventilation by mask (APRV) This is an alternative method to administer CPAP and ventilatory support. By discontinuing CPAP for a short period, lung volume is reduced and elastic recoil of the lungs causes outflow of gases with carbon dioxide removal. Mechanical inspiration is achieved when airway pressure again increases to CPAP level. Jonsela et al (1988), described the successful use of APRV to wean a patient who had developed mediastinitis after thymectomy, and had proved resistant to all attempts to withdraw or even reduce IPPV, because of impaired respiratory mechanics due to a flail sternum and myasthenia. After a 5 week period of conventional ventilation the patient was weaned within 48 hours of starting APRV. HUMIDIFICATION Inspired gas is warmed and humidified in the nasopharynx and reaches the

434

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upper trachea with a relative humidity of about 90% and a temperature of 32-36~ Humidification and warming continue down the airways so that alveolar gas is fully saturated at 37~ The need for humidification in intubated and recently tracheostomized patients is unquestioned: when the upper airway is bypassed, a continuous loss of moisture and heat occurs, which predisposes the patient to airway damage (depressed ciliary function), inspissated secretions, atelectasis and hypothermia (Chalon et al, 1979). There are essentially two types of humidification in use in most ICUs, the hot water bath type and heat and moisture exchange (HME) condenser humidifiers. (Simple methods, such as regular instillation of a few millilitres of saline down the endotracheal tube or the intermittent use of saline nebulizers, are a useful adjunct and helpful in mobilizing thick inspissated secretions, but are not a replacement for proper humidification.) The ultrasonic humidifiers have many problems, the main one being overhydration, which is a major problem in children and therefore their use cannot be recommended. Hot water humidifiers

These are very efficient humidifiers (e.g. Puritan-Bennett cascade humidifier) used on many ICUs. The hot water bath is heated to approximately 60~ (below this temperature there is a risk of pseudomonas colonization of the water bath), and at the patient end of the tubing gas is delivered with a relative humidity of 100% at a temperature of 37~ They all include thermostatic fail-safe alarms for both bath and delivery tube temperature. They do, however, have a number of problems, including condensation in the tubing, so that water traps have to be emptied regularly, and their efficiency is not always constant, varying with gas flow rate and water temperature. A large vapourizing surface will improve efficiency, but at the same time will increase the internal compliance of the humidifier. Heat and moisture exchangers

HMEs work by trapping endogenous moisture and heat from exhaled gas and returning them to the inhaled gas delivery system, the net effect being conservation of airway humidity and body heat. Much has been written in recent years about the relative efficiency and safety of HMEs for use in ventilated patients in intensive care (Shelly et al, 1986; Turner and Wright, 1987). There is no doubt that HMEs are not as effective in maintaining high relative humidity as are heated humidifiers. However, Bethune (1989), in a review article on their use in over 30 000 patients in 20 years, found they produce satisfactory humidification for virtually all ventilated patients. The uptake of heat and moisture during inspiration which occurs in an endotracheal tube, means that a humidity level of 20 mg/1 delivered at the outer end of the endotracheal tube, will result in a tracheal level of 30 rag/l, and it is known that an inspired humidity of 25-35 rag/1 will preserve mucociliary function (Challon et al, 1979). The successful use of HMEs may also be

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dependent to some extent on the ability of the trachea to compensate for lower levels of humidity, seen in its most extreme form in patients with a permanent tracheostomy, who are able to manage with a level of humidity of approximately 10 mg/1 at the upper end of the trachea during inspiration. The introduction of HMEs which also function as bacterial filters, preventing airborne transmission of infection either to or from the patient has resulted in increased use and popularity of these devices. As well as being less complex and costly than heated humidifiers, HMEs significantly reduce the volume of water in the ventilator circuit, and thus minimize the risk of such potentially fatal situations as blockage of filters or expiratory valves (Buckley, 1984). Cohen et al (1988), in their review of methods of humidification for ICU patients, found a significantly higher rate of endotracheal occlusions (defined as the inability to pass a suction catheter), in patients in whom HMEs were used (15 out of 170 patients), as compared with those receiving cascade humidification (1 out of 81 patients). There was a detectable increase in the incidence of pneumonia, atelectasis and duration of mechanical ventilation associated with H M E use. It is of note that the majority of patients developing occlusions required high (> 10 l/min) minute ventilation. Indeed, Bethune (1989), also made the point that patients with tenacious pulmonary secretions, may well require additional humidification, such as the intermittent use of saline nebulizers connected to a Y piece. The increase in dead space (up to 15%) and resistance created by HMEs (Polysongsang et al, 1986), may also be a problem in patients who are breathing spontaneously through the endotracheal tube. In summary, we feel that whilst HMEs are undoubtedly very effective in providing humidification in the operating room during long surgical procedures, their routine use for ICU patients cannot be recommended without reservation. ICU patients are a heterogeneous group: a large proportion of ventilated patients require high minute volumes at some stage of their illness, and may represent a group predisposed to endotracheal occlusions with HMEs. Cascade humidification is to be preferred in patients ventilated with high minute volumes, in those with tenacious sputum (as in cystic fibrosis and asthma), and in any patients in whom suctioning becomes difficult. The importance of adequate humidification in the intubated patient in the ICU cannot be overemphasized--it is the key to the proper management of the airway. SUMMARY

Personnel working in the intensive care environment will frequently be called upon to deal with a variety of airway problems, ranging from the emergency situation requiring prompt intervention to those situations in which careful, informed decisions have to be made about the appropriateness of various methods of long-term airway management. All ICU staff must be able to cope with the 'difficult' intubation: familiarity

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with the various techniques available for dealing with this problem is essential, together with the necessary skills required for fibreopticintubation. Awareness of the long-term complications resulting from intubation and tracheostomy has led to the development of thermolabile, non-irritant tubes with low-pressure cuffs, which have significantly reduced the incidence of laryngotracheal injury and the formation of stenotic lesions. However, other factors are involved and much can still be done to reduce problems associated with long-term intubation. In patients requiring long-term ventilation, the decision of when, and indeed if, to do a tracheostomy is a difficult one and must be individualized for each patient. There is no doubt that there are more severe complications associated with tracheostomy than with intubation; but at the same time, tracheostomy improves patient comfort, simplifies airway management, and can allow the patient to speak and take oral nutrition. In addition, there is some evidence that a tracheostomy tube may facilitate the weaning process and allow earlier discharge from the intensive care unit. Adequate humidification is fundamental to the proper management of patients with any form of tracheal tube that bypasses the normal humidification processes of the upper airways. Heat and moisture exchangers are efficient and reliable, but due to the heterogeneous nature of the ICU population, they may be unable to provide sufficient humidification in certain groups of patients and heated water humidification must then be used. The recent introduction of minitracheostomies for the treatment of sputum retention, and of non-invasive ventilation techniques in certain groups of patients, has extended the range of treatment options available in patients requiring some interventional support and respiratory care. No doubt further applications for these techniques will be developed in coming years.

Acknowledgement The authors wish to thank the staff of the Medical Library, Medical Illustration, ENT and Radiology Departments of the Royal Free Hospital and Miss Adu Amponsah, ITU Secretary, for their help with the manuscript.

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Berry FA, Blankenbaker WL & Ball CG (1973) A comparison of bacteraemia occurring with naso tracheal and oro tracheal intubation. Anesthesia and Analgesia 52: 873-876. Bethune DW (1989) Humidification in ventilated patients. Intensive and Critical Care Digest 8: 37-38. Birmingham PK, Cheney FW & Ward RJ (1986) Oesophageal intubation--a review of detection techniques. Anesthesia and Analgesia 65" 886-891. Brain AIJ, McGhee TD, McAteer EJ et al (1985) The laryngeal mask airway. Anaesthesia 40." 356--361. Brantigan W & Grow JB (1976) Cricothyroidotomy---elective use in respiratory problems requiring tracheotomy. Journal of Thoracic and Cardiovascular Surgery 71: 72-81. Brantigan W & Grow JB (1982) Subglottic stenosis after cricothyroidotomy. Surgery 91: 217-221. Branthwaite M (1989) Nasal intermittent pressure ventilation. Care of the Critically Ill 4" 139-141. Brochard L, Rua F, Lorino J e t al (1988) Suppression of extra work of breathing due to endotracheal tube. Intensive Care Medicine 14:A1 261. Buckley PM (1984) Increase in resistance of in-line breathing filters in humidified air. British Journal of Anaesthesia 56: 637-643. Burgess GE III, Cooper JR Jr, Marino JR et al (1979) Laryngeal competence after tracheal extubation. Anesthesiology 51: 73-77. Carroll N & Branthwaite MA (1988) Control of nocturnal hypoventilation by nasal intermittent positive pressure ventilation. Thorax 43: 349-353. Challon J, Ali M, Ramanathan S e t al (1979) The humidification of anaesthetic gases--its importance and control. Canadian Anaesthetists Society Journal 26: 361-366. Choudry AK & Jackson IJB (1988) Minitracheotomy--a report of a proposed development. Annals of the Royal College of Surgeons of England 70: 239-240. Cohen CA, Zagelbaum G & Gross D (1982) Clinical manifestations of inspiratory muscle fatigue. American Journal of Medicine 73:308-312. Cohen IL, Weinberg PF, Fein A et al (1988) Endotracheal tube occlusion associated with the use of heat and moisture exchangers in the Intensive Care Unit. Critical Care Medicine 16: 277-279. Conrardy PA, Goodman LR & Lainge F (1976) Alteration of endotracheal tube position. Critical Care Medicine 4: 8-12. Cox D, Tinloi S & Farrimond J (1988) Investigation of spontaneous modes of breathing of different ventilators. Intensive Care Medicine 14: 532-537. Criner G, Make B & Celli B (1987) Respiratory muscle dysfunction secondary to chronic tracheostomy tube placement. Chest 91(1): 139-141. Daborn KA & Harris MNE (1989) Minitracheotomy--a life threatening complication. Anaesthesia 44: 839-840. Dubik MN & Wright BD (1978) Comparison of laryngeal pathology following long term oral and nasal endotracheal intubation. Anesthesia and Analgesia 57: 663-666. Ellis DO, Stewart RD, Kaplan RM et al (1986) Success rates of blind orotracheal intubation using a transillumination technique with a lighted stylet. Annals of Emergency Medicine 15" 138-142. El-Nagger M, Sadagopan S, Levine H et al (1976) Factors influencing choice between tracheostomy and prolonged translaryngeal intubation in acute respiratory failure--a prospective study. Anesthesia and Analgesia 55: 195-201. Esses BA & Jafek BW (1987) Cricothyroidotomy--a decade of experience in Denver. Annals of Otology, Rhinology, and Laryngology 96: 519-524. Frass M, Frezner R, Zdrahal F et al (1987) The oesophageal tracheal combitube: preliminary results with a new airway for CPR. Annals of Emergency Medicine 16: 768--772. Frass M, Frenzer R, Rauscha F et al (1988) Ventilation with the oesophageal tracheal combitube in cardiopulmonary resuscitation. Chest 90: 781-784. Grillo HL, Cooper JD & Geffin B (1971) A low pressure cuff for tracheostomy tubes to minimise tracheal injury. Journal of Thoracic and Cardiovascular Surgery 62: 898907, Hansen A (1975) Vocalisation via a cuffed tracheostomy tube. Anaesthesia 30: 78-79. Harrison CA & Fielder C (1988) Minitracheostomy and laryngectomy. Anaesthesia 43: 900-901.

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Hart AM, Cashman JN & Baldock GJ (1987) Minitracheostomy in the treatment of sputum retention. Intensive Care Medicine 13: 81-82. Hasan A, McGuigan J, Morgan MD et al (1989) Minitracheotomy--a simple alternative to tracheotomy in obstructive sleep apnoea. Thorax 44" 224-225. Hawkins DB (1977) Glottic and subglottic stenosis from endotracheal intubation. Laryngoscope 87: 339-346. Heffner JE, Scott Miller K & Sahn SA (1985) Tracheostomy in the intensive care unit. Part I. Indications, technique and management. Chest 90: 269-274. Heffner JE, Scott Miller K & Sahn SA (1986) Tracheostomy in the intensive care unit. Part II. Complications. Chest 90" 430-435. Jackson C (1921) High tracheotomy and other errors--the chief causes of laryngeal stenosis. Surgery, Gynaecology and Obstetrics 32" 392-398. Jonsela IT, Pertti N & Tahvanainen J (1988) Airway pressure release ventilation by mask. Critical Care Medicine 16: 1250-1251. Katz JA & Marks JD (1985) Inspiratory work with and without continuous positive airway pressure in patients with acute respiratory failure. Anesthesiology 65: 598. Kennedy TL (1980) Epiglottic reconstruction of laryngeal stenosis secondary to cricothyroidotomy. Laryngoscope 90: 1130-1136. Kirk AJB (1986) Minitracheotomy in cardiothoracic practice. Care of the Critically Ill 2: 104-107. Knowlson GTG & Bassett HFM (1970) The pressures exerted on the trachea by endotracheal inflatable cuffs. British Journal of Anaesthesia 42: 834-837. Lewis FR, Schlobohm RM & Thomas AN (1978) Prevention of complications from prolonged tracheal intubation. American Journal of Surgery 135" 452-457. Lewis GA, Hopkinson RB & Mathews HR (1986) Minitracheotomy. Anaesthesia 41: 931935. Liechman M J, Donahoo JS & Macvaugh H (1986) Endotracheal intubation using percutaneous retrograde guide wire insertion followed by antigrade fibre optic bronchoscopy. Critical Care Medicine 14: 589-590. Long J & West G (1980) The evaluation of the Olympic Trache Button as a precursor to tracheostomy tube. American Review of Respiratory Diseases 25: 1242-1243. Lyons GD, Garrett ME & Fourier DG (1977) Complications of percutaneous transtracheal procedures. American Journal of OtolaryngoIogy 86: 633-640. McGill J, Clinton JE & Riuz E (1982) Cricothyroidotomy in the Emergency Department. Annals of Emergency Medicine 11" 361-364. McGuinnis GE, Shively JG, Patterson RL et al (1971) An engineering analysis of endotracheal cuffs. Anesthesia and Analgesia 50: 557-561. Mallampati SR, Gatt SP, Gugino WD et al (1985) A clinical sign to predict difficult intubation--a prospective study. Canadian Anaesthetists Society Journal 32" 429-434. Matthews HR & Hopkinson RB (1984) Treatment of sputum retention by a minitracheotomy. British Journal of Surgery 71" 147-150. Matthews HR, Fisher B J, Smith BE et al (1986) Minitracheostomy a new delivery system for jet ventilation. Journal of Thoracic and Cardiovascular Surgery 92" 673-675. Messeter KH & Petterson KI (1980) Endotracheal intubation with the fibre optic bronchoscope. Anaesthesia 35" 288-294. Midgren B, Petterson K, Hansson L e t al (1988) Nocturnal hypoxaemia in severe scoliosis. British Journal of Diseases of the Chest 82" 226-236. Niederman MS, Ferranti RD, Zeigier A e t al (1984) Respiratory infection complicating long term tracheostomy. The implication of persistent gram negative tracheo bronchial colonization. Chest 85." 39-44. Polysongsang Y, Branson R, Rashskin MC et al (1986) Pressure flow characteristics of commonly used heat and moisture exchangers. American Review of Respiratory Disease 133(part 2): A124. Powell WF & Ozdil T (1967) A translaryngeal guide for tracheal intubation. Anesthesia and Analgesia 46:231-234. Price DG (1983) Techniques of tracheostomy for Intensive Care Unit patients. Anaesthesia 38: 902-904. Quan SF, Falltrick RJ, Schlobohm RM et al (1981) Extubation from ambient or expiratory positive airway pressure in adults. Anesthesiology 55: 53-56.

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Ravialia A & Stockwell MA (1987) Displacement of a minitracheotomy tube during high frequency jet ventilation. Anaesthesia 42: 1306-1307. Road J, Vahi R, Del Rio Pet al (1987) In vivo contractile properties of fatigued diaphragm. Journal of Applied Physiology 63: 471-478. Ryan DW, Dark JH, Musra U et al (1989) Intraoesophageal placement of minitracheostomy tube. Intensive Care Medicine 15: 538-539. Scott DB (1986) Endotracheal intubation--friend or foe? British MedicalJournal292: 15%158. Shelly M, Bethune DW & Latimer RD (1986) A comparison of five heat and moisture exchangers. Anaesthesia 41: 52%532. Silk JM & Marsh AM (1989) Pneumothorax caused by minitracheotomy. Anaesthesia 44: 663-664. Stauffer JL, Olson DE & Petty TL (1981) Complications and consequences of endotracheal intubation and tracheotomy. American Journal of Medicine 70: 65-76. Stanley TH (1975) Nitrous oxide and pressure and volume of high and low pressure endotracheal tube cuffs in intubated patients. Anesthesiology 42: 637-640. Steen JA, Lindholm CE, Bredlik GC et al (1982) Tracheal tube forces on the posterior larynx--index of laryngeal loading. Critical Care Medicine 10: 186-189. Stock MC, Woodward CG & Shapiro BA (1986) Perioperative complications of elective tracheostomy in critically ill patients. Critical Care Medicine 14: 861-863. Stoen R & Smith-Erichsen N (1987) Airway obstruction associated with an endotracheal tube. Intensive Care Medicine 13: 295-296. Sullivan CE, Berthon-Jones M, Issa FG et al (1981) Reversal of obstructive sleep apnoea by continuous positive airway pressure applied through the nares. Lancet i: 862-865. Turner DAB & Wright EM (1987) Efficiency of heat and moisture exchangers. Anaesthesia 42: 1117-1118. Weber AL & Grillo HC (1978) Tracheal stenosis--an analysis of 151 cases. Radiologic Clinics of North America 16: 291-308. West KJ & Coad MR (1988) An unusual complication of mini tracheostomy. Today's Anaesthetist 3: 241. Weymuller EA, Bishop MJ, Fink BR et al (1983) Quantification of intralaryngeal pressure exerted by endotracheal tubes. Annals of Otology, Rhinology, and Laryngology 92: 444-447. Whited RE (1984) A prospective study of laryngo tracheal sequelae in long term intubation. Laryngoscope 94: 367-377. Wu W, Lim I, Simpson FA et al (1973) Pressure dynamics of endotracheal and tracheostomy cuffs. Critical Care Medicine 1: 197-201. Yealy DM & Paris PM (1989) Recent advances in airway management. Emergency Medicine Clinics of North America 7: 83-93. Yung MW & Snowdon SL (1984) Respiratory resistance of tracheostomy tubes. Archives of Otolaryngology 110: 591-595.

ADDENDUM: PERCUTANEOUS

TRACHEOSTOMY

Since t h e p l a n n i n g of this c h a p t e r t h e r e has b e e n a r e c u r r e n c e of i n t e r e s t in p e r c u t a n e o u s t r a c h e o s t o m y t e c h n i q u e s . Ciaglia a n d o t h e r s (1985) d e s c r i b e d a d i l a t a t i o n a l t e c h n i q u e in which i n c r e a s i n g sizes of d i l a t o r a r e p u s h e d o v e r a g u i d e w i r e i n s e r t e d p e r c u t a n e o u s l y into t h e t r a c h e a . T h e t r a c h e o s t o m y t u b e is p u s h e d o v e r t h e last size of d i l a t o r used. M o r e r e c e n t l y , t h e e q u i p m e n t n e e d e d h a s b e c o m e c o m m e r c i a l l y a v a i l a b l e . U s i n g this kit n u m e r o u s t r a c h e o s t o m i e s h a v e b e e n p e r f o r m e d with m i n i m a l c o m p l i c a t i o n s : in a p r e l i m i n a r y series o f 25, two p a t i e n t s with s y s t e m i c c o a g u l o p a t h y h a d significant b l e e d i n g in t h e first 24 h o u r s , t h e r e w e r e no o t h e r c o m p l i c a t i o n s o f i n s e r t i o n , no w o u n d infections a n d no late u p p e r a i r w a y p r o b l e m s in surviving p a t i e n t s ( G . S k o w r o n s k i , p e r s o n a l c o m m u n i c a t i o n ) .