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Principles and practice of thoracic anaesthesia
Thoracic
Principles and practice of thoracic anaesthesia
Thoracic surgical results from 40 UK centres (2005–2006)
John WW Gothard
Lung resection for primary malignant tumours Pneumonectomy Lobectomy/bilobectomy Video-assisted thoracoscopic surgery (VATS) for pulmonary/pleural disease Wedge resection – lung (primary tumour) Wedge resection – lung (other conditions) Pleural procedures – closure air leaks, etc. Pleural procedures – other conditions/ procedures
Abstract Thoracic anaesthesia covers a wide field. This review concentrates on anaesthetic techniques for lung resection in patients with primary carcin oma. This represents a small number of patients in the UK (about 3000) but with a relatively high operative mortality, which ranges from 2.5% for lobectomy to 5%, or higher, for pneumonectomy. Lung resection is normally carried out with the patient in a lateral position. One-lung ven tilation is usually required to facilitate surgery. These two factors have a number of physiological consequences including ventilation–perfusion mismatch with a true shunt through the upper non-ventilated lung. These factors are discussed. The management of one-lung ventilation can be crucial in minimizing periods of hypoxaemia. There is increasing evidence that lung protective ventilation strategies can minimize, but not eliminate, lung trauma during thoracotomy. Guidelines for one lung ventilation including the use of small tidal volumes, permissive hyper capnia and pressure-limited ventilation are discussed in some detail. Specific areas of thoracic anaesthesia are covered that may be useful for examination candidates. These include chest drainage, bronchopleural fistula and the management of video-assisted thoracic surgery (VATS).
Deaths(%)
444 2381
29(6.5) 62(2.6)
104
1(1.0)
691
4(0.6%)
1377
4(0.3%)
1949
30(1.5%)
Adapted from the database of the Society of Cardiothoracic Surgeons of Great Britain and Ireland.
Table 1
Thoracotomy and pulmonary surgery Positioning the patient Most pulmonary resections are undertaken with the patient in a lateral position. Following induction of anaesthesia, intubation, insertion of intravascular lines and confirmation of the side of surgery, the patient is turned into the lateral position. Several devices can be used to stabilize the patient on the operating table (Figure 1). The lower shoulder is pulled through anteriorly, allowing the flexed lower arm to be tucked under the pillow supporting the head. The upper arm is extended and placed over the head, taking care not to stretch the brachial plexus. Some surgeons who use a more anterior muscle-sparing incision prefer to place the upper arm in a padded arm support attached to the head of the operating table. Stability of the pelvis is achieved by flexing the lower leg at the hip and knee while the upper leg, padded with a pillow, is kept relatively straight. Further stability may be achieved with chest and pelvic supports. Once the patient is positioned and all vulnerable areas padded, a warm-air convective heating blanket is applied to minimize heat loss during surgery.
Keywords bronchopleural; chest; drainage; fistula; lobectomy; one-lung ventilation; pneumonectomy; thoracic; true shunt; ventilation–perfusion mismatch
Most lung resections are carried out for the surgical treatment of primary malignant tumours (Table 1). Eighty per cent of primary lung tumours are inoperable at presentation; therefore, only about 3000 of these operations are performed annually in the UK. Mortality for pulmonary resection remains relatively high at 6% for pneumonectomy and 2.6% for lobectomy; therefore, preoperative assessment of these patients is important. The appropriate management of anaesthesia and one-lung ventilation facilitates surgery and is likely to improve outcome. Recently, there has been an increase in the number of thoracic procedures carried out using video-assisted thoracic surgery (VATS). These procedures almost all require one-lung ventilation at times and the observed physiological changes and principles of management are similar to those during pulmonary resection.
Physiological consequences: in the awake patient there is little or no additional ventilation–perfusion mismatch in the lateral position. An increase in perfusion to the lower lung, caused by the effect of gravity on the low-pressure pulmonary circulation, is matched by increased ventilation because this lung is on the steep part of the compliance curve (Figure 2). During anaesthesia the situation changes. In the spontaneously breathing patient there is a reduction in inspiratory muscle tone (particularly the diaphragm) and a decrease in the volume of both lungs with a reduction in functional residual capacity (FRC). The non-dependent upper lung, therefore, moves to the steeper part of the compliance curve and receives more ventilation. Paralysis and
John WW Gothard, MBBS, FRCA, is Consultant Cardiothoracic Anaesthetist at the Royal Brompton Hospital, London, UK. He qualified from St Mary’s Hospital Medical School, London. He has written several textbooks on cardiac and thoracic anaesthesia and has a major interest in thoracic anaesthesia and anaesthesia for congenital heart disease.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:12
Numbers
545
© 2008 Elsevier Ltd. All rights reserved.
Thoracic
in the presence of volatile agents during thoracotomy and OLV. Handling the lung also reduces HPV. Potent inhaled anaesthetic agents (e.g. isoflurane) are not contraindicated during OLV and may be desirable because of their bronchodilator properties and ease of use. Significant inhibition of HPV is more likely with halothane, which should be avoided. Intravenous agents (e.g. propofol) do not inhibit HPV and should improve arterial oxygenation during OLV. Evidence in the literature supports this contention, but it is inconclusive. Therefore, in patients with poor arterial oxygenation during OLV, it might be worth changing to a total intravenous technique.
The lateral thoracotomy position The patient is stabilized by a comfortable mattress. Note the ‘bridge’ raised in the operating table, directly below the chest, to aid surgical access
Analgesia If opioid drugs are to be used postoperatively, it is logical to use the same drugs intraoperatively. If epidural analgesia is to be used postoperatively, it should be established before surgery.
From: J W W Gothard. Anaesthesia for thoracic surgery. Oxford: Blackwell Scientific Publications, 1992
Monitoring Monitoring and vascular access for major pulmonary surgery should be comprehensive (Table 2). Pulmonary artery catheters can be placed in the lung contralateral to surgery only if radiological screening facilities are available. This is unnecessary in routine clinical practice. Transoesophageal echocardiography is not used during routine thoracic surgery but it may be used in the management of high-risk patients in the future.
Figure 1
intermittent positive-pressure ventilation (IPPV) are used during thoracotomy to overcome the problems of the open pneumo thorax created by surgery. The compliance of the non-dependent lung is further increased in this situation. In practice, it is usual selectively to ventilate the lower lung (one-lung ventilation; OLV) at this point and allow the upper lung to collapse. This eliminates the preferential ventilation and facilitates surgical access but causes ventilation–perfusion mismatch.
Compliance curves for upper and lower lungs in the lateral position
Anaesthesia The principles of anaesthesia for thoracic surgery are the same as those for any major surgery. Anaesthesia is usually induced intravenously. The choice of agent is seldom important. Patients presenting for lung resection are unlikely to have a co-existing airway problem and, therefore, a non-depolarizing neuromuscular blocking agent can be used to facilitate intubation and IPPV. Although a long-acting agent is suitable for most operations, shorter-acting agents with incremental doses as required are now more commonly used. Special consideration must be given to patients with muscle weakness caused by myasthenia gravis or the myasthenic syndrome. Occasionally, patients presenting for palliative VATS have an airway problem relating to tracheal or bronchial compression or an endobronchial tumour, but patients undergoing lung resection are more likely to present as a ‘difficult intubation’ on the basis of conventional criteria. Anaesthesia can be maintained with volatile agents delivered in an air/oxygen gas mixture or an oxygen/nitrous oxide mix. Alternatively, anaesthesia can be maintained intravenously with propofol, possibly in combination with remifentanil.
Patient awake
Volume
Lower lung
Pressure
Volume
Patient anaesthetized
Hypoxic pulmonary vasoconstriction Hypoxic pulmonary vasoconstriction (HPV) is a homeostatic mechanism whereby pulmonary blood flow is diverted away from hypoxic or collapsed areas of lung. It might be expected to improve oxygenation during OLV, but in vitro experiments have shown that volatile agents inhibit HPV though in vivo studies have failed to demonstrate gross inhibition. Although volatile agents depress HPV directly, they also enhance it by reducing cardiac output. Therefore, HPV response is apparently unchanged
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:12
Upper lung
Upper lung
Lower lung Pressure From: Yentis S M, Hirsch N P, Smith G B, eds. Anaesthesia and intensive care A–Z. 2nd ed. Oxford: Butterworth-Heinemann, 2000
Figure 2
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© 2008 Elsevier Ltd. All rights reserved.
Thoracic
ventilation is also likely to be beneficial. Limiting ventilation (Table 3) can lead to carbon dioxide retention, but some permissive hypercapnia is preferable to lung trauma.
Monitoring requirements for major pulmonary surgery
Hypoxia during OLV: it is difficult to predict which patients are likely to become hypoxic (arterial oxygen saturation less than 90%) during OLV. Patients with poor lung function are sometimes accepted for lung resection on the basis that their diseased lung is contributing little to gas exchange and this can be confirmed by ventilation–perfusion scanning. Conversely, patients with normal lung function are more likely to be hypoxic during OLV, presumably because an essentially normal lung is being collapsed to provide surgical access. A recent study found that the most significant predictors of a low arterial oxygen saturation during OLV were a right-sided operation, a low oxygen saturation during two-lung ventilation before OLV and a high (or more normal) forced expiratory volume in 1 second (FEV1) preoperatively. Once hypoxia occurs it is important to check the position of the endobronchial tube and readjust it if necessary. A high inflation pressure (more than 30–35 cm H2O) indicates that the tube is displaced. It may be helpful to analyse a flow–volume loop or at least manually reinflate the lung to get a feel for the compliance. If a tube is obstructing a lobar orifice only one or two lobes are being ventilated at most and hypoxia is likely. Suction and manual reinflation of the dependent lung may also be helpful at this stage. Other measures to improve oxygenation include increasing the inspired oxygen concentration, introducing positive endexpiratory pressure (PEEP) to the dependent lung or supplying oxygen to the upper lung via a continuous positive airway pressure (CPAP) system (thereby reducing the shunt). The introduction of PEEP to the lower lung with CPAP (100% oxygen) to the upper lung has also been described but this lowers cardiac output and thus oxygen delivery.
ECG Pulse oximetry End-tidal gas analysis • Carbon dioxide trace particularly useful during OLV Flow–volume loop • Useful during OLV Invasive arterial pressure measurement • Arterial blood gas analysis invaluable during OLV Invasive central venous pressure measurement • Consider for patients undergoing pneumonectomy or if cardiac history Nasopharyngeal temperature • Heat loss significant during thoracotomy Urinary catheter • Appropriate for long procedures • Consider if epidural analgesia is used or if renal function poor ECG, electrocardiogram; OLV, one-lung ventilation.
Table 2
Ventilation Endobronchial tubes or bronchial blockers are inserted immediately after induction of anaesthesia or after preliminary bronchoscopy. Use of these devices to achieve lung separation and collapse of the lung on the operative side is described elsewhere (see pages 538–41, in this issue). Management of OLV: pulmonary blood flow continues to the upper lung during OLV, creating a true shunt where there is blood flow to the alveoli but no ventilation. This shunt is the main cause of hypoxaemia during OLV, though the alveoli with low ventilation–perfusion ratios also contribute. Venous admixture or shunt increases from a baseline of about 10% during two-lung ventilation to 20–30% during OLV. OLV should be established so that it inflates the lung adequately but also minimizes intra-alveolar pressure and prevents diversion of pulmonary blood flow to the upper lung. This is not easy to achieve. High-frequency jet ventilation for thoracic surgery provides ventilation at low airway pressures. Despite its potential advantages it is not in widespread use and this article discusses conventional IPPV. It is reasonable to use an inspired oxygen concentration (FIo2) of 50% initially. When OLV is established this can be increased to 100%, if required. This cannot affect the true shunt in the upper lung but can improve oxygenation via the alveoli with low ventilation–perfusion ratios in the lower lung. There is increasing evidence that overinflating the single lung (volutrauma) can be detrimental and lead to acute lung injury. Deflation and inflation of the lung on the operative side with the potential for ischaemia or reperfusion injury has also been implicated in lung damage. The use of low tidal volumes improves outcome in ventilated patients with acute respiratory distress syndrome and this may also apply to OLV. Pressure-limiting
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:12
Chest drainage Pleural or chest drainage is an essential part of the management of the thoracotomy patient. Chest drains allow the escape of air, blood or fluid from the pleural space to facilitate the re-expansion of remaining lung and elimination of mediastinal shift. Drainage tubes inserted at operation are connected to an underwater seal drain, which acts as a one-way valve. Two chest drains are
Guidelines for one-lung ventilation (OLV) • Inspired oxygen concentration of 50–100% (increase if oxygen saturation <90%) • Normal inspired:expired ratio (1:2) (increase expiratory phase if gas trapping likely) • Consider pressure-limiting ventilation • Use small tidal volumes (e.g. 6 ml/kg) • Allow permissive hypercapnia • Use positive end-expiratory pressure • Avoid overinflation (volutrauma) Table 3
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c ommonly inserted following lung resection (other than pneumonectomy). Low-pressure, high-volume suction is usually applied to the outlet of the drainage bottle to facilitate egress of air. Air leak does not occur after pneumonectomy and, therefore, chest drainage is not mandatory. The chest can be closed without a drain if the surgeon is confident that there is no significant bleeding. If this approach is taken, air is aspirated from the pneumonectomy space to centralize the mediastinum once the patient has been turned into a supine position. Some surgeons leave a basal chest drain in for the first 24 hours following pneumonectomy. This drain is clamped but connected to an underwater seal drainage bottle. The clamp is released for about 2 minutes every hour to allow any accumulated blood to drain. Suction is never applied to a pneumonectomy drain because it pulls the mediastinum across and severely impedes or totally obstructs venous return.
Figure 3 CT scan showing a right-sided bronchopleural fistula, just below the carina, after pneumonectomy.
Termination of anaesthesia and the early postoperative period Once chest drains are in place any remaining lung is suctioned and carefully reinflated, keeping the pressure low. As chest wall closure is completed residual neuromuscular blockade is reversed and anaesthesia lightened. After a straightforward pulmonary resection, it is usual to re-establish spontaneous respiration and extubate the patient in the operating theatre, or soon afterwards in a recovery area. This is best achieved with the patient in a sitting position. After complex or difficult surgery (e.g. lung resection combined with excision of chest wall) it may be prudent to ventilate the patient for a few hours postoperatively.
drain inserted on the pneumonectomized side to remove remaining fluid (suction should not be applied). When surgical repair is to be undertaken, the patient is transported to theatre in the sitting position, with the drain unclamped but with the drainage bottle below the patient. Anaesthetic management: classically a post-pneumonectomy bronchopleural fistula should be isolated with an endobronchial tube placed in the remaining lung before IPPV is commenced. To secure the airway before the administration of a muscle relaxant two methods were advocated: (1) awake endobronchial intubation using local analgesia of the upper respiratory tract and (2) an inhalational induction and intubation under deep inhalational anaesthesia. These techniques should be mentioned by an examination candidate but, in practice, both techniques are fraught with problems, particularly in these debilitated patients. Most thoracic anaesthetists use a conventional intravenous induction, following preoxygenation, with the patient in a sitting position and the drain open. An endobronchial tube can then be inserted safely in the main bronchus under fibre-optic bronchoscopic control after administration of suxamethonium (succinyl choline). IPPV to the isolated lung can then be commenced and the patient positioned for surgery.
Specific procedures Bronchopleural fistula A bronchopleural fistula is a direct communication between the tracheobronchial tree and the pleural cavity (Figure 3). Causes include dehiscence of a bronchial stump following lung resection, trauma, inflammatory lesions (e.g. tuberculosis) and neoplasms. In developed countries, bronchopleural fistula has classically been described in relation to pneumonectomy. Its incidence following pneumonectomy is now low in specialized centres but its anaesthetic management remains an examination topic. Bronchopleural fistula can occur at any time following pneumonectomy, but usually occurs 3–15 days postoperatively. Hospitals accepting major trauma patients may admit patients with traumatic rupture of the major airways after high-speed traffic accidents. These injuries are a form of bronchopleural fistula and usually require surgical repair.
Video-assisted thoracic surgery Video-assisted thoracic surgery (VATS) has been widely adopted for many procedures (Table 1). A small, but important, group of patients also undergo lung volume reduction surgery for emphysema with the use of this technique. VATS is less invasive than open thoracotomy and is carried out through a series of ports inserted through the chest wall. It is vital to collapse the lung on the side of surgery for these procedures and therefore the use of endobronchial tubes and OLV is increasing to facilitate this surgery. There is usually less postoperative pain than after open thoracotomy and length of hospital stay may be reduced. Anaesthetic techniques are similar to those used for lung resection. The operation is usually carried out with the patient in a lateral position, occasionally with the upper arm elevated in an arm rest. It is essential to let the lung down before access ports and telescopes are introduced. Patients presenting for VATS may have abnormal lungs, particularly those scheduled for lung volume reduction surgery.
Bronchopleural fistula after pneumonectomy: the patient usually presents with symptoms related to infected space fluid flowing into the remaining lung. Acute onset with a large fistula presents with severe dyspnoea, with the patient coughing up brownish infected space fluid. Signs of cardiorespiratory failure are also apparent as a result of hypoxia and septicaemia. A chest radiograph confirms the diagnosis, showing loss of pneumonectomy space fluid and consolidation or increased shadowing in the remaining lung (see pages 478–82, November issue). Initial management includes general resuscitation. Oxygen is administered and an intravenous infusion commenced. The patient should be sat up to prevent any further spill-over of space fluid and a chest
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Lung collapse or deflation on the operative side can usually be achieved with a left-sided endobronchial tube because this type of surgery does not breach the airway. Lung collapse during OLV is slow in the presence of marked emphysema, and several techniques have been used to promote this. Some centres insufflate carbon dioxide into the pleural cavity. The gas is delivered at a low pressure and low flow (2 litres/minute) but presents a small risk of gas embolism. Others promote the idea that continued use of 50% nitrous oxide in oxygen as the inspired gas will promote lung collapse. The author does not usually take any specific measures to promote lung collapse apart from ensuring that the lung is not partially ventilating via a leak around the cuff of the endobronchial tube. Occasionally, it is necessary to apply gentle suction to the lung, though with marked emphysema this is relatively ineffective. Once the surgeons have visualized the space and divided adhesions, lung collapse is usually well enough established to allow definitive surgery to proceed. For most VATS, OLV can be managed as described above for lung resection. Lung volume reduction surgery may be carried out bilaterally; therefore, the second stage of the operation is carried out while the patient survives on the previously operated (and transiently damaged) lung. The principles of OLV (Table 3) also apply to general VATS. It is more important with lung volume reduction surgery to limit inflation pressure and to increase the expiratory phase of ventilation (I:E ratios of 1:3 or even up to 1:5) to prevent hyperinflation.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:12
PEEP is generally contraindicated for similar reasons. These limitations of ventilation almost certainly lead to hypercapnia but this is well tolerated in these patients. Gross overinflation of the lung can lead to reduced venous return and cardiovascular collapse. If this is suspected, the patient should be disconnected from the ventilator to allow the ventilated lung to collapse and reduce intrathoracic pressure. After most VATS, the patients can be extubated in the normal way. Following lung volume reduction surgery it is desirable to establish spontaneous respiration as soon as possible to prevent exacerbation of air leaks and further trauma to the stapled or sutured lungs. The authors usually replace the endobronchial tube with a tracheal tube at the end of surgery and wean the patient from ventilation in the intensive care unit over the ensuing few hours. It is mandatory to establish epidural analgesia to facilitate this. ◆
Further reading Gothard JWW, Kelleher A. Essentials of cardiac and thoracic anaesthesia. Oxford: Butterworth-Heinemann, 1999. Levin AI, Coetzee JF, Coetzee A. Arterial oxygenation and one-lung anesthesia. Curr Opin Anaesthesiol 2008; 21: 28–36. Slinger PD. Progress in thoracic anesthesia. Baltimore, MD: Lippincott Williams & Wilkins, 2004.
549
© 2008 Elsevier Ltd. All rights reserved.
Principles and practice of thoracic anaesthesia
Thoracic surgical results from 40 UK centres (2005–2006)
John WW Gothard
Lung resection for primary malignant tumours Pneumonectomy Lobectomy/bilobectomy Video-assisted thoracoscopic surgery (VATS) for pulmonary/pleural disease Wedge resection – lung (primary tumour) Wedge resection – lung (other conditions) Pleural procedures – closure air leaks, etc. Pleural procedures – other conditions/ procedures
Abstract Thoracic anaesthesia covers a wide field. This review concentrates on anaesthetic techniques for lung resection in patients with primary carcin oma. This represents a small number of patients in the UK (about 3000) but with a relatively high operative mortality, which ranges from 2.5% for lobectomy to 5%, or higher, for pneumonectomy. Lung resection is normally carried out with the patient in a lateral position. One-lung ven tilation is usually required to facilitate surgery. These two factors have a number of physiological consequences including ventilation–perfusion mismatch with a true shunt through the upper non-ventilated lung. These factors are discussed. The management of one-lung ventilation can be crucial in minimizing periods of hypoxaemia. There is increasing evidence that lung protective ventilation strategies can minimize, but not eliminate, lung trauma during thoracotomy. Guidelines for one lung ventilation including the use of small tidal volumes, permissive hyper capnia and pressure-limited ventilation are discussed in some detail. Specific areas of thoracic anaesthesia are covered that may be useful for examination candidates. These include chest drainage, bronchopleural fistula and the management of video-assisted thoracic surgery (VATS).
Deaths(%)
444 2381
29(6.5) 62(2.6)
104
1(1.0)
691
4(0.6%)
1377
4(0.3%)
1949
30(1.5%)
Adapted from the database of the Society of Cardiothoracic Surgeons of Great Britain and Ireland.
Table 1
Thoracotomy and pulmonary surgery Positioning the patient Most pulmonary resections are undertaken with the patient in a lateral position. Following induction of anaesthesia, intubation, insertion of intravascular lines and confirmation of the side of surgery, the patient is turned into the lateral position. Several devices can be used to stabilize the patient on the operating table (Figure 1). The lower shoulder is pulled through anteriorly, allowing the flexed lower arm to be tucked under the pillow supporting the head. The upper arm is extended and placed over the head, taking care not to stretch the brachial plexus. Some surgeons who use a more anterior muscle-sparing incision prefer to place the upper arm in a padded arm support attached to the head of the operating table. Stability of the pelvis is achieved by flexing the lower leg at the hip and knee while the upper leg, padded with a pillow, is kept relatively straight. Further stability may be achieved with chest and pelvic supports. Once the patient is positioned and all vulnerable areas padded, a warm-air convective heating blanket is applied to minimize heat loss during surgery.
Keywords bronchopleural; chest; drainage; fistula; lobectomy; one-lung ventilation; pneumonectomy; thoracic; true shunt; ventilation–perfusion mismatch
Most lung resections are carried out for the surgical treatment of primary malignant tumours (Table 1). Eighty per cent of primary lung tumours are inoperable at presentation; therefore, only about 3000 of these operations are performed annually in the UK. Mortality for pulmonary resection remains relatively high at 6% for pneumonectomy and 2.6% for lobectomy; therefore, preoperative assessment of these patients is important. The appropriate management of anaesthesia and one-lung ventilation facilitates surgery and is likely to improve outcome. Recently, there has been an increase in the number of thoracic procedures carried out using video-assisted thoracic surgery (VATS). These procedures almost all require one-lung ventilation at times and the observed physiological changes and principles of management are similar to those during pulmonary resection.
Physiological consequences: in the awake patient there is little or no additional ventilation–perfusion mismatch in the lateral position. An increase in perfusion to the lower lung, caused by the effect of gravity on the low-pressure pulmonary circulation, is matched by increased ventilation because this lung is on the steep part of the compliance curve (Figure 2). During anaesthesia the situation changes. In the spontaneously breathing patient there is a reduction in inspiratory muscle tone (particularly the diaphragm) and a decrease in the volume of both lungs with a reduction in functional residual capacity (FRC). The non-dependent upper lung, therefore, moves to the steeper part of the compliance curve and receives more ventilation. Paralysis and
John WW Gothard, MBBS, FRCA, is Consultant Cardiothoracic Anaesthetist at the Royal Brompton Hospital, London, UK. He qualified from St Mary’s Hospital Medical School, London. He has written several textbooks on cardiac and thoracic anaesthesia and has a major interest in thoracic anaesthesia and anaesthesia for congenital heart disease.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:12
Numbers
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© 2008 Elsevier Ltd. All rights reserved.
Thoracic
in the presence of volatile agents during thoracotomy and OLV. Handling the lung also reduces HPV. Potent inhaled anaesthetic agents (e.g. isoflurane) are not contraindicated during OLV and may be desirable because of their bronchodilator properties and ease of use. Significant inhibition of HPV is more likely with halothane, which should be avoided. Intravenous agents (e.g. propofol) do not inhibit HPV and should improve arterial oxygenation during OLV. Evidence in the literature supports this contention, but it is inconclusive. Therefore, in patients with poor arterial oxygenation during OLV, it might be worth changing to a total intravenous technique.
The lateral thoracotomy position The patient is stabilized by a comfortable mattress. Note the ‘bridge’ raised in the operating table, directly below the chest, to aid surgical access
Analgesia If opioid drugs are to be used postoperatively, it is logical to use the same drugs intraoperatively. If epidural analgesia is to be used postoperatively, it should be established before surgery.
From: J W W Gothard. Anaesthesia for thoracic surgery. Oxford: Blackwell Scientific Publications, 1992
Monitoring Monitoring and vascular access for major pulmonary surgery should be comprehensive (Table 2). Pulmonary artery catheters can be placed in the lung contralateral to surgery only if radiological screening facilities are available. This is unnecessary in routine clinical practice. Transoesophageal echocardiography is not used during routine thoracic surgery but it may be used in the management of high-risk patients in the future.
Figure 1
intermittent positive-pressure ventilation (IPPV) are used during thoracotomy to overcome the problems of the open pneumo thorax created by surgery. The compliance of the non-dependent lung is further increased in this situation. In practice, it is usual selectively to ventilate the lower lung (one-lung ventilation; OLV) at this point and allow the upper lung to collapse. This eliminates the preferential ventilation and facilitates surgical access but causes ventilation–perfusion mismatch.
Compliance curves for upper and lower lungs in the lateral position
Anaesthesia The principles of anaesthesia for thoracic surgery are the same as those for any major surgery. Anaesthesia is usually induced intravenously. The choice of agent is seldom important. Patients presenting for lung resection are unlikely to have a co-existing airway problem and, therefore, a non-depolarizing neuromuscular blocking agent can be used to facilitate intubation and IPPV. Although a long-acting agent is suitable for most operations, shorter-acting agents with incremental doses as required are now more commonly used. Special consideration must be given to patients with muscle weakness caused by myasthenia gravis or the myasthenic syndrome. Occasionally, patients presenting for palliative VATS have an airway problem relating to tracheal or bronchial compression or an endobronchial tumour, but patients undergoing lung resection are more likely to present as a ‘difficult intubation’ on the basis of conventional criteria. Anaesthesia can be maintained with volatile agents delivered in an air/oxygen gas mixture or an oxygen/nitrous oxide mix. Alternatively, anaesthesia can be maintained intravenously with propofol, possibly in combination with remifentanil.
Patient awake
Volume
Lower lung
Pressure
Volume
Patient anaesthetized
Hypoxic pulmonary vasoconstriction Hypoxic pulmonary vasoconstriction (HPV) is a homeostatic mechanism whereby pulmonary blood flow is diverted away from hypoxic or collapsed areas of lung. It might be expected to improve oxygenation during OLV, but in vitro experiments have shown that volatile agents inhibit HPV though in vivo studies have failed to demonstrate gross inhibition. Although volatile agents depress HPV directly, they also enhance it by reducing cardiac output. Therefore, HPV response is apparently unchanged
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:12
Upper lung
Upper lung
Lower lung Pressure From: Yentis S M, Hirsch N P, Smith G B, eds. Anaesthesia and intensive care A–Z. 2nd ed. Oxford: Butterworth-Heinemann, 2000
Figure 2
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© 2008 Elsevier Ltd. All rights reserved.
Thoracic
ventilation is also likely to be beneficial. Limiting ventilation (Table 3) can lead to carbon dioxide retention, but some permissive hypercapnia is preferable to lung trauma.
Monitoring requirements for major pulmonary surgery
Hypoxia during OLV: it is difficult to predict which patients are likely to become hypoxic (arterial oxygen saturation less than 90%) during OLV. Patients with poor lung function are sometimes accepted for lung resection on the basis that their diseased lung is contributing little to gas exchange and this can be confirmed by ventilation–perfusion scanning. Conversely, patients with normal lung function are more likely to be hypoxic during OLV, presumably because an essentially normal lung is being collapsed to provide surgical access. A recent study found that the most significant predictors of a low arterial oxygen saturation during OLV were a right-sided operation, a low oxygen saturation during two-lung ventilation before OLV and a high (or more normal) forced expiratory volume in 1 second (FEV1) preoperatively. Once hypoxia occurs it is important to check the position of the endobronchial tube and readjust it if necessary. A high inflation pressure (more than 30–35 cm H2O) indicates that the tube is displaced. It may be helpful to analyse a flow–volume loop or at least manually reinflate the lung to get a feel for the compliance. If a tube is obstructing a lobar orifice only one or two lobes are being ventilated at most and hypoxia is likely. Suction and manual reinflation of the dependent lung may also be helpful at this stage. Other measures to improve oxygenation include increasing the inspired oxygen concentration, introducing positive endexpiratory pressure (PEEP) to the dependent lung or supplying oxygen to the upper lung via a continuous positive airway pressure (CPAP) system (thereby reducing the shunt). The introduction of PEEP to the lower lung with CPAP (100% oxygen) to the upper lung has also been described but this lowers cardiac output and thus oxygen delivery.
ECG Pulse oximetry End-tidal gas analysis • Carbon dioxide trace particularly useful during OLV Flow–volume loop • Useful during OLV Invasive arterial pressure measurement • Arterial blood gas analysis invaluable during OLV Invasive central venous pressure measurement • Consider for patients undergoing pneumonectomy or if cardiac history Nasopharyngeal temperature • Heat loss significant during thoracotomy Urinary catheter • Appropriate for long procedures • Consider if epidural analgesia is used or if renal function poor ECG, electrocardiogram; OLV, one-lung ventilation.
Table 2
Ventilation Endobronchial tubes or bronchial blockers are inserted immediately after induction of anaesthesia or after preliminary bronchoscopy. Use of these devices to achieve lung separation and collapse of the lung on the operative side is described elsewhere (see pages 538–41, in this issue). Management of OLV: pulmonary blood flow continues to the upper lung during OLV, creating a true shunt where there is blood flow to the alveoli but no ventilation. This shunt is the main cause of hypoxaemia during OLV, though the alveoli with low ventilation–perfusion ratios also contribute. Venous admixture or shunt increases from a baseline of about 10% during two-lung ventilation to 20–30% during OLV. OLV should be established so that it inflates the lung adequately but also minimizes intra-alveolar pressure and prevents diversion of pulmonary blood flow to the upper lung. This is not easy to achieve. High-frequency jet ventilation for thoracic surgery provides ventilation at low airway pressures. Despite its potential advantages it is not in widespread use and this article discusses conventional IPPV. It is reasonable to use an inspired oxygen concentration (FIo2) of 50% initially. When OLV is established this can be increased to 100%, if required. This cannot affect the true shunt in the upper lung but can improve oxygenation via the alveoli with low ventilation–perfusion ratios in the lower lung. There is increasing evidence that overinflating the single lung (volutrauma) can be detrimental and lead to acute lung injury. Deflation and inflation of the lung on the operative side with the potential for ischaemia or reperfusion injury has also been implicated in lung damage. The use of low tidal volumes improves outcome in ventilated patients with acute respiratory distress syndrome and this may also apply to OLV. Pressure-limiting
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Chest drainage Pleural or chest drainage is an essential part of the management of the thoracotomy patient. Chest drains allow the escape of air, blood or fluid from the pleural space to facilitate the re-expansion of remaining lung and elimination of mediastinal shift. Drainage tubes inserted at operation are connected to an underwater seal drain, which acts as a one-way valve. Two chest drains are
Guidelines for one-lung ventilation (OLV) • Inspired oxygen concentration of 50–100% (increase if oxygen saturation <90%) • Normal inspired:expired ratio (1:2) (increase expiratory phase if gas trapping likely) • Consider pressure-limiting ventilation • Use small tidal volumes (e.g. 6 ml/kg) • Allow permissive hypercapnia • Use positive end-expiratory pressure • Avoid overinflation (volutrauma) Table 3
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c ommonly inserted following lung resection (other than pneumonectomy). Low-pressure, high-volume suction is usually applied to the outlet of the drainage bottle to facilitate egress of air. Air leak does not occur after pneumonectomy and, therefore, chest drainage is not mandatory. The chest can be closed without a drain if the surgeon is confident that there is no significant bleeding. If this approach is taken, air is aspirated from the pneumonectomy space to centralize the mediastinum once the patient has been turned into a supine position. Some surgeons leave a basal chest drain in for the first 24 hours following pneumonectomy. This drain is clamped but connected to an underwater seal drainage bottle. The clamp is released for about 2 minutes every hour to allow any accumulated blood to drain. Suction is never applied to a pneumonectomy drain because it pulls the mediastinum across and severely impedes or totally obstructs venous return.
Figure 3 CT scan showing a right-sided bronchopleural fistula, just below the carina, after pneumonectomy.
Termination of anaesthesia and the early postoperative period Once chest drains are in place any remaining lung is suctioned and carefully reinflated, keeping the pressure low. As chest wall closure is completed residual neuromuscular blockade is reversed and anaesthesia lightened. After a straightforward pulmonary resection, it is usual to re-establish spontaneous respiration and extubate the patient in the operating theatre, or soon afterwards in a recovery area. This is best achieved with the patient in a sitting position. After complex or difficult surgery (e.g. lung resection combined with excision of chest wall) it may be prudent to ventilate the patient for a few hours postoperatively.
drain inserted on the pneumonectomized side to remove remaining fluid (suction should not be applied). When surgical repair is to be undertaken, the patient is transported to theatre in the sitting position, with the drain unclamped but with the drainage bottle below the patient. Anaesthetic management: classically a post-pneumonectomy bronchopleural fistula should be isolated with an endobronchial tube placed in the remaining lung before IPPV is commenced. To secure the airway before the administration of a muscle relaxant two methods were advocated: (1) awake endobronchial intubation using local analgesia of the upper respiratory tract and (2) an inhalational induction and intubation under deep inhalational anaesthesia. These techniques should be mentioned by an examination candidate but, in practice, both techniques are fraught with problems, particularly in these debilitated patients. Most thoracic anaesthetists use a conventional intravenous induction, following preoxygenation, with the patient in a sitting position and the drain open. An endobronchial tube can then be inserted safely in the main bronchus under fibre-optic bronchoscopic control after administration of suxamethonium (succinyl choline). IPPV to the isolated lung can then be commenced and the patient positioned for surgery.
Specific procedures Bronchopleural fistula A bronchopleural fistula is a direct communication between the tracheobronchial tree and the pleural cavity (Figure 3). Causes include dehiscence of a bronchial stump following lung resection, trauma, inflammatory lesions (e.g. tuberculosis) and neoplasms. In developed countries, bronchopleural fistula has classically been described in relation to pneumonectomy. Its incidence following pneumonectomy is now low in specialized centres but its anaesthetic management remains an examination topic. Bronchopleural fistula can occur at any time following pneumonectomy, but usually occurs 3–15 days postoperatively. Hospitals accepting major trauma patients may admit patients with traumatic rupture of the major airways after high-speed traffic accidents. These injuries are a form of bronchopleural fistula and usually require surgical repair.
Video-assisted thoracic surgery Video-assisted thoracic surgery (VATS) has been widely adopted for many procedures (Table 1). A small, but important, group of patients also undergo lung volume reduction surgery for emphysema with the use of this technique. VATS is less invasive than open thoracotomy and is carried out through a series of ports inserted through the chest wall. It is vital to collapse the lung on the side of surgery for these procedures and therefore the use of endobronchial tubes and OLV is increasing to facilitate this surgery. There is usually less postoperative pain than after open thoracotomy and length of hospital stay may be reduced. Anaesthetic techniques are similar to those used for lung resection. The operation is usually carried out with the patient in a lateral position, occasionally with the upper arm elevated in an arm rest. It is essential to let the lung down before access ports and telescopes are introduced. Patients presenting for VATS may have abnormal lungs, particularly those scheduled for lung volume reduction surgery.
Bronchopleural fistula after pneumonectomy: the patient usually presents with symptoms related to infected space fluid flowing into the remaining lung. Acute onset with a large fistula presents with severe dyspnoea, with the patient coughing up brownish infected space fluid. Signs of cardiorespiratory failure are also apparent as a result of hypoxia and septicaemia. A chest radiograph confirms the diagnosis, showing loss of pneumonectomy space fluid and consolidation or increased shadowing in the remaining lung (see pages 478–82, November issue). Initial management includes general resuscitation. Oxygen is administered and an intravenous infusion commenced. The patient should be sat up to prevent any further spill-over of space fluid and a chest
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Lung collapse or deflation on the operative side can usually be achieved with a left-sided endobronchial tube because this type of surgery does not breach the airway. Lung collapse during OLV is slow in the presence of marked emphysema, and several techniques have been used to promote this. Some centres insufflate carbon dioxide into the pleural cavity. The gas is delivered at a low pressure and low flow (2 litres/minute) but presents a small risk of gas embolism. Others promote the idea that continued use of 50% nitrous oxide in oxygen as the inspired gas will promote lung collapse. The author does not usually take any specific measures to promote lung collapse apart from ensuring that the lung is not partially ventilating via a leak around the cuff of the endobronchial tube. Occasionally, it is necessary to apply gentle suction to the lung, though with marked emphysema this is relatively ineffective. Once the surgeons have visualized the space and divided adhesions, lung collapse is usually well enough established to allow definitive surgery to proceed. For most VATS, OLV can be managed as described above for lung resection. Lung volume reduction surgery may be carried out bilaterally; therefore, the second stage of the operation is carried out while the patient survives on the previously operated (and transiently damaged) lung. The principles of OLV (Table 3) also apply to general VATS. It is more important with lung volume reduction surgery to limit inflation pressure and to increase the expiratory phase of ventilation (I:E ratios of 1:3 or even up to 1:5) to prevent hyperinflation.
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PEEP is generally contraindicated for similar reasons. These limitations of ventilation almost certainly lead to hypercapnia but this is well tolerated in these patients. Gross overinflation of the lung can lead to reduced venous return and cardiovascular collapse. If this is suspected, the patient should be disconnected from the ventilator to allow the ventilated lung to collapse and reduce intrathoracic pressure. After most VATS, the patients can be extubated in the normal way. Following lung volume reduction surgery it is desirable to establish spontaneous respiration as soon as possible to prevent exacerbation of air leaks and further trauma to the stapled or sutured lungs. The authors usually replace the endobronchial tube with a tracheal tube at the end of surgery and wean the patient from ventilation in the intensive care unit over the ensuing few hours. It is mandatory to establish epidural analgesia to facilitate this. ◆
Further reading Gothard JWW, Kelleher A. Essentials of cardiac and thoracic anaesthesia. Oxford: Butterworth-Heinemann, 1999. Levin AI, Coetzee JF, Coetzee A. Arterial oxygenation and one-lung anesthesia. Curr Opin Anaesthesiol 2008; 21: 28–36. Slinger PD. Progress in thoracic anesthesia. Baltimore, MD: Lippincott Williams & Wilkins, 2004.
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