Anaesthesia for Thoracic Surgery

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Anaesthesia for Thoracic Surgery

Thoracic anaesthesia offers a number of anaesthetic challenges:

In common with major surgery at other sites, thoracic patients frequently:

Diagnosis, staging and resection of intrathoracic malignant disease occupy a large part of thoracic surgical practice. There is also a need for drainage and obliteration of an expanded pleural space to remove infection, or to prevent lung collapse and re-accumulation of air or liquid in the pleural space. Resection of bullous lung disease may improve the respiratory mechanics of the chest if there is parenchymal lung disease elsewhere.

PREOPERATIVE ASSESSMENT

History and Examination

Thoracic patients often exhibit respiratory symptoms of cough, sputum, haemoptysis, breathlessness, wheeze and chest pain, or oesophageal symptoms of dysphagia, pain and weight loss. Other common chest features include hoarseness, obstruction of the superior vena cava, pain in the chest wall or arm, Horner’s syndrome, cyanosis and pleural effusion. Lung tumours may cause extrathoracic features by metastatic spread, principally to brain, bone, liver, adrenals and kidneys, or by endocrine effects such as finger clubbing, hypertrophic pulmonary osteoarthropathy, Cushing’s syndrome, hypercalcaemia, myopathies (e.g. Eaton–Lambert syndrome), scleroderma, acanthosis and thrombophlebitis. Anaemia, cardiac disease and lung disease may cause breathlessness.

To distinguish between loss of lung tissue and reversible airways disease, the patient’s own history of daily activity may reveal diurnal variation in breathlessness and associated symptoms of sputum, stridor and wheeze. Symptoms may conflict with the results of pulmonary function tests, which require voluntary effort, if the tests have been performed ineffectively. Wheeze during expiration and stridor during inspiration are likely to result from airway obstruction below and above the thoracic inlet, respectively.

Production of sputum is the most common stimulus to cough, which is therefore almost universal in cigarette smokers. A dry cough may result from tumour or external compression of the upper airways. Oesophageal tumours are associated with dysphagia. The restriction on ingestion of food exacerbates the cachexia of malignant disease. At induction of anaesthesia, patients are at risk of regurgitation of food and secretions from above the oesophageal obstruction.

Preoperative features of weight loss, protein-calorie malnutrition and hypoalbuminaemia make postoperative pulmonary infection, multi-organ failure and delayed wound healing more likely. Patients with pre-existing chronic lung disease are more likely to suffer postoperative pulmonary complications. Cyanosis may result centrally from intrapulmonary shunting caused directly by diseased tissue or because of lung collapse consequent to proximal airway obstruction. Peripheral cyanosis is possible in the face and arms if the superior vena cava becomes obstructed by mediastinal spread.

Many major thoracic surgical procedures are preceded by rigid bronchoscopy which requires clinical assessment of upper airway patency at the preoperative visit. Forced ventilatory effort by the patient may elicit stridor or wheeze, and palpation of the neck and inspection of the airway demonstrated on chest radiograph may reveal tracheal abnormality.

Investigations

A variety of preoperative investigations are performed to determine resectability. The chest radiograph may reveal changes months before symptoms are manifest. Of symptomatic patients, 98% have chest radiograph abnormalities. Lung tumours are central in 70% of patients and may show collapse or cavitation more peripherally in the lung. Tumours are commonly 3–4 cm in size by the time of presentation. Other features include tracheal deviation, obstruction of the superior vena cava, pleural effusions and air-filled cavities.

Tumour diagnosis and staging involve sputum cytology, bronchoscopy, needle biopsy, mediastinoscopy and mediastinotomy. Computed tomography (CT) and magnetic resonance imaging (MRI) of the chest may reveal the spread of disease. Biochemistry, bone scans and ultrasound scans of the abdomen may detect metastatic disease. Barium studies and oesophageal ultrasound are similarly able to diagnose and stage carcinoma of the oesophagus.

Investigations are used to quantify physiological reserve by measuring mechanical and parenchymal function, and cardiopulmonary interaction. Assessment should be on physiological reserve rather than chronological age. Rather than to deny surgery to patients, this is done to allocate resources to borderline patients to minimize their postoperative complications. Investigations to diagnose lung collapse, oedema, infection and bronchospasm allow patients to be presented in the best possible state on the day of surgery.

Whole-Lung Testing

Spirometry using voluntary effort, pulse oximetry and arterial blood gas tensions breathing air are influenced by the function of the whole lung.

Mechanical testing. Spirometry tests only the mechanical bellows function of the lung. Testing relies on voluntary effort and effective technique by the patient. From total lung capacity, the patient exhales to residual volume to measure the forced vital capacity (FVC). This is reduced in restrictive lung disease, such as cryptogenic alveolar fibrosis. The volume of gas exhaled forcibly in the first second gives the forced expiratory volume in 1 s (FEV1). By definition, FEV1 measures function when the lung is expanded well. In health, patients can exhale 70–80% of their vital capacity in 1 s, the FEV1%. The remainder of the vital capacity may take another 2 s to exhale. With obstructive lung disease, the FEV1% is reduced below 70% and the time taken to exhale the vital capacity is prolonged. The FEV1% of patients with restrictive lung disease is preserved, although the absolute value of FVC, and therefore the volume exhaled in 1 s, is reduced. Values of 2 L for FVC and 1.5 L for FEV1 offer a lower limit when screening for pneumonectomy. An FEV1 of 1.0 L is cautionary for single lobectomy because a whole-lung FEV1 > 800 mL after surgery is required to avoid dependence on mechanical ventilation.

Predicted postoperative (PPO) lung function may be calculated using lung segments. From a total of 19 segments (three in the upper lobes, two in both the middle lobe and lingual and four in the left and five in the right lower lobes; Fig. 33.1), the fraction of lung remaining is multiplied by the preoperative spirometry measurement to give the predicted postoperative measurement of spirometry (PPO FEV1 = preoperative FEV1 × (1 – (resected segments/19))). Using whole-lung spirometry to predict postoperative lung function may be invalidated if the regional function of the lung is not known. For example, a patient with an FEV1 of 1.5 L may have the same or better FEV1 after lobectomy if the main bronchus of the affected lobe was occluded completely at the time of testing before surgery. The oxygenation of blood of such a patient may be improved by the removal of a non-functioning lung or lobe through which considerable right-to-left shunt existed.

Parenchymal lung function. Arterial oxygen tension < 8 kPa or carbon dioxide tension > 6 kPa indicate increased risk for lung resection. The diffusing capacity of carbon monoxide (DLCO) correlates with the total functioning area of the alveolar capillary membrane. Predictive postoperative values may be calculated in the same way as for mechanical function. PPO DLCO values < 40% of predicted in health – normal range 100–150 mL min–1 mmHg–1 – correlate with increased postoperative respiratory complications.

Cardiopulmonary interaction. Cardiopulmonary exercise testing requires a patient to be able to pedal a bicycle ergometer and breathe through a mouthpiece. Increasing exercise to a peak allows calculation of maximum oxygen uptake expressed in mL kg–1 min–1. Patients with VO2max > 10 mL kg–1 min–1 have been able to withstand lobectomy, whereas a PPO VO2max > 15 mL kg–1 min–1 is required to contemplate pneumonectomy.

Invasive Assessment

In patients with borderline lung function for whom surgical resection offers great prognostic advantage, the risks and discomfort of invasive assessment of regional lung function may be worth the information obtained about likely residual function after surgery. Balloon occlusion of a main pulmonary artery before surgery or clamping a pulmonary artery during surgery allows some assessment of pulmonary artery pressures and oxygenation after resection. Inadequate blood oxygenation, arterial carbon dioxide tension greater than 6.0 kPa and mean pulmonary artery pressure greater than 25 mmHg at rest, or greater than 35 mmHg with exercise, indicate inadequate function and increased operative risk.

Any intrathoracic operative procedure places an immediate burden on the right ventricle. Using echocardiography, magnetic resonance scanning or direct pressure measurement, diagnosis of a failing right ventricle or coexisting pulmonary artery hypertension may render a patient’s chest pathology inoperable.

Treatment

Before surgery, patients should be motivated to stop smoking and lose excess weight. Reversible airway narrowing should be treated with bronchodilators such as salbutamol, terbutaline, theophylline, inhaled steroids or sodium cromoglycate. By giving antibiotics to treat chest infection, and loosening and removing bronchial secretions with inhaled nebulized water aerosols, chest physiotherapy and postural drainage, the incidence of pulmonary complications is reduced. Collapse in lung segments not intended for resection should be expanded, and pulmonary oedema treated by improving heart failure. Pulmonary hypertension should be treated where feasible. Overnight, stopping smoking improves bronchial reactivity and reduces carboxyhaemoglobin concentration. Eight weeks after cessation of smoking, the excessive production of mucus is reduced. This makes tracheobronchial clearance easier and improves small airway function.

ANATOMY

The bronchial tree and the views obtained when facing the patient are illustrated in Figure 33.2 and the bronchopulmonary segments are shown in Figure 33.1. The trachea leads from the cricoid cartilage below the larynx at the level of the sixth cervical vertebra (C6) and passes 10–12 cm in the superior mediastinum to its bifurcation at the carina into left and right main bronchi at the sternal angle, T4/5. During inspiration, the lower border of the trachea moves inferiorly and anteriorly. The trachea lies principally in the midline, but is deviated to the right inferiorly by the arch of the aorta. The oesophagus is immediately posterior to the trachea and behind it is the vertebral column. The wall of the trachea is held patent by 15–20 cartilaginous rings deficient posteriorly where the trachealis membrane, a collection of fibroelastic fibres and smooth muscle, lies. It is wider in transverse diameter (20 mm) than anteroposteriorly (15 mm). The trachea passes from neck to thorax via the thoracic inlet at T2.

The right main bronchus is larger and less deviated from the midline than the left. The origin of the right upper lobe bronchus arises laterally 2.5 cm from the carina, whereas the origin of the left upper lobe arises laterally after 5 cm. These dimensions determine the relative ease of isolating and ventilating each lung independently using double-lumen bronchial tubes.

The oesophagus is a continuation of the pharynx at the level of the lower border of the cricoid cartilage (C6) 15 cm from the incisor teeth. It passes immediately anterior to the thoracic spine and aorta and descends through the oesophageal hiatus of the diaphragm at T10, to the left of the midline at the level of the seventh rib. There are four slight constrictions, at its origin, as it is crossed by the aorta and left main bronchus, and at the diaphragm, at 15, 25, 27 and 38 cm from the incisors.

Radiographic Surface Markings

The apices of the lungs extend 2.5 cm above the point at which the middle and inner thirds of the clavicle meet. Lung borders descend behind the medial end of the clavicle to the middle of the manubrium. The lung border is behind the body of the sternum and xiphisternum before sweeping inferiorly and laterally down to the level of the eleventh thoracic vertebra. On the left, at the level of the horizontal fissure at the fourth costal cartilage (T7), the medial border of the lung is displaced to the left of the sternal edge in the cardiac notch. The oblique fissure descends from 3 cm lateral to the midline at T4, inferiorly and anteriorly to the sixth costal cartilage 7 cm from the midline. The diaphragmatic reflection of the pleura extrudes below the lung to the lower border of T12.

INDUCTION AND MAINTENANCE OF ANAESTHESIA

All currently available anaesthetic agents have been used for thoracic surgery. They are used to maintain anaesthesia and haemodynamic stability during the procedure, while allowing the patient to breathe spontaneously in reasonable comfort immediately after surgery is complete. Large doses of i.v. opioid drugs are unlikely to achieve all these aims. Thoracic surgery patients may demonstrate sensitivity to drugs used in anaesthesia because of debility from the extent of their disease or from systemic effects, such as prolonged effects of neuromuscular blocking drugs in patients with Eaton–Lambert syndrome associated with carcinoma of the bronchus.

Lateral Thoracotomy

Many thoracic procedures are performed through a posterolateral thoracotomy incision between fifth and eighth ribs. Patients have to be positioned on their side with the neck flexed, dependent shoulder brought forward and the arm raised under the pillow to protect the shoulder and brachial plexus. The upper shoulder is flexed to 90° and the arm supported. Hips and knees are flexed together with a pillow between the legs. Padding, strapping, lower leg compression devices and diathermy pad complete the preparation for surgery (Fig. 33.3). Positioning with the chest flexed laterally away from the operative side on a beanbag which is then aspirated of air, or breaking the operating table, may improve surgical access. The upper wrist has a tendency to flex, so radial artery cannulae cause less trouble when on the dependent side. Peripheral and jugular veins are more accessible on the operative side.

The Lateral Position

In health, with the chest erect, the right lung takes 55% of the pulmonary blood flow and the left lung 45%. In the right lateral position, the right lung takes 65% and the left lung 35% because of the influence of gravity. In the left lateral position, differences are reversed; the right lung takes 45% and left lung 55%. These changes persist under anaesthesia. However, anaesthesia does affect the changes to ventilation of the two lungs in the lateral position. Awake, there is more ventilation to the dependent lung; similarly, the bases receive proportionately more ventilation than the apices when the chest is erect. The dependent lung has a less negative intrapleural pressure than the upper lung and is on a more favourable part of the pressure–volume curve. A change in pressure produces a greater change in volume in the dependent lung than in the upper lung. Under anaesthesia, conditions for ventilation between the two lungs are reversed. Functional residual capacity is reduced. With paralysis of the diaphragm, the mechanical advantage of the greater curve of the lower diaphragm is lost and the lower lung is compressed by the mediastinum and abdominal contents. Awkward positioning on the operating table may further impede the lower lung. The lower lung is now in a less favourable position on the pressure–volume curve and any change in pressure produces greater change in the volume of the upper lung than the dependent lung. Anaesthesia therefore produces much worse ventilation/perfusion mismatch in the lateral position, with more blood going to the dependent lung and more ventilation going to the upper lung. Application of positive end-expiratory pressure up to 10 cmH2O improves the changes in ventilation and tends to restore ventilation to the dependent lung.

One-Lung Anaesthesia

The principal indications for one-lung anaesthesia are:

Isolation of a diseased lung with sepsis or haemorrhage may be necessary to protect the healthy lung. When there is inadequate ventilation of both lungs because of a large bronchopleural or bronchocutaneous fistula, a large unilateral bulla or because the compliance of two lungs is so different that they require independent ventilation, satisfactory oxygenation may be obtained by ventilation of one lung alone. Pulmonary alveolar proteinosis may be treated by bronchoalveolar lavage. This requires that only one lung be lavaged with liquid at a time, whilst the other is protected. Video-assisted pulmonary and pleural surgery, and intrathoracic, non-pulmonary surgery such as oesophageal, aortic and spinal surgery, may require the lung to be collapsed to allow access to the operative structures.

Ventilation of one lung alone may require a double-lumen tracheal tube (Fig. 33.4), a bronchial blocker (Fig. 33.5) or a bronchial tube. The double-lumen tube has greatest flexibility to allow changes from ventilation of two lungs to one lung then back to two lungs during or at the end of surgery. It allows aspiration of the main bronchi independently, and insufflation of oxygen to the non-ventilated lung. It has a larger external diameter than the bronchial blocker or bronchial tube and may be difficult to position correctly if tracheal and bronchial anatomy is distorted. The two separate lumens are narrow and present a high resistance to spontaneous ventilation. This is overcome by positive pressure ventilation, but a single-lumen tube may have to be substituted at the end of surgery if resumption of spontaneous ventilation is not immediate. A bronchial blocker with a hollow lumen allows insufflation of oxygen, some suctioning and may be used with a jet ventilator, which overcomes some of the disadvantages of the technique. The Rüsch bronchial blocker illustrated in Figure 33.5 has a 170 cm long, 2 mm stem (outside diameter) with a central lumen to a 2.75 mm diameter balloon, which accepts 5 ml of air. It may be passed down a bronchoscope with a lumen greater than 2.8 mm diameter or through the 15 mm tapered connector with a 1.8 mm seal shown.

Positioning Double-Lumen Bronchial Tubes

Double-lumen bronchial tubes provide an effective means of isolating each lung to protect the other from blood and secretions. They allow ventilation of one lung only, or both lungs independently. Being longer and with lumens more narrow than single-lumen tracheal tubes, they have a greater resistance to air flow. They are therefore not usually suitable for spontaneous ventilation. Disposable polyvinyl chloride tubes (Fig. 33.6) have substantially replaced the re-usable red rubber Robertshaw double-lumen tubes. Sizes of tube in common use in adult practice range from 35 to 41 French gauge (FG). Sizes 37–39 are usually suitable for men and 37 for women, but sizes 41 and 35 are available for individuals at extremes of the range of adult build. Left- and right-sided versions of double-lumen bronchial tubes are necessary (Fig. 33.6) because the tracheal portions are curved antero-posteriorly, and the balloon of the right bronchial tube is fenestrated to conduct gases to the right upper lobe bronchus, which would otherwise be occluded by the cuff of the tube (Fig. 33.7). The left upper lobe bronchus arises 2.5 cm further down the main bronchus than the right, so it is less likely to be occluded by the balloon of the bronchial tube.

Positioning a double-lumen bronchial tube correctly is a skill learned quickly with practice. The task is usually straightforward, but however experienced the anaesthetist, great difficulties may be encountered in some patients. An incorrectly positioned double-lumen bronchial tube may rapidly compromise the supply of oxygen to the lungs during thoracic surgery, with disastrous results. The correct position of double-lumen bronchial tubes may be assessed by clinical technique or confirmed using an intubating fibreoptic laryngoscope.

Clinical Assessment

The patient lies supine on a level operating table with the head supported on a single pillow pulled clear of the shoulders to flex the neck and extend the head. After induction of anaesthesia and muscle relaxation, the larynx is identified by laryngoscopy. The double-lumen bronchial tube is held at 90° to its eventual anatomical position on the non-operative side, to align the curve of the bronchial lumen anteroposteriorly. The bronchial lumen is passed between the cords until it rests within the trachea. The double-lumen bronchial tube is then rotated 90° back to point the bronchial lumen towards its intended bronchus. The head is turned away from the side of the bronchial lumen and the double-lumen bronchial tube advanced gently until resistance is encountered and the bronchial tube is thought to be in the correct position. The tracheal cuff is then inflated and the lungs ventilated manually through both lumens of the tube. Visible movement of both sides of the chest, detection of a recognizable trace of exhaled carbon dioxide, breath sounds auscultated in both axillae and an unchanging pulse oximeter reading reassure the anaesthetist that oxygen is being supplied to the lungs. Difficulties encountered whilst isolating individual lungs may be addressed after returning to this position of control.

The tracheal lumen of the breathing circuit is then clamped and the breathing system distal to the clamp opened to air. Breath sounds are confirmed on the bronchial side. Two or more millilitres of air are then injected into the bronchial cuff until the leak of air from the tracheal tube is no longer audible or palpable, and breath sounds auscultated over the side opposite to the bronchial lumen cease. The tracheal lumen is then closed, and the clamp is released and applied to the bronchial system; the circuit is opened and the procedure is repeated to confirm that chest movement and air entry occur to the tracheal side and not the bronchial side and that there are no air leaks from the anaesthetic system. The double-lumen bronchial tube is then secured with a tracheostomy tape at the teeth by a clove hitch, and the tube tie is knotted round the neck by a bow to enable its release quickly when required.

During volume controlled ventilation, when each lumen of the double-lumen tube (DLT) is clamped, there should be a detectable increase in airway pressure during the breathing cycle when the tidal volume is directed down one lung. The peak airway pressure may then be controlled below 30 cmH2O by reducing the tidal volume and increasing the ventilatory rate while maintaining the minute volume of ventilation. If there is no change on the ventilator or airway pressure gauges when one lumen of the tube is clamped, the bronchial lumen is likely to end in the trachea or else there is a substantial leak past the bronchial cuff. The position of the DLT should always be re-checked after the patient has been subjected to any changes in position, e.g. from supine to lateral.

Using the Fibreoptic Intubating Laryngoscope

Confirming the correct position of a double-lumen bronchial tube using a fibreoptic intubating laryngoscope should avoid problems encountered by malposition of the DLT. However, if parenchymal lung disease is so extensive that one lung is insufficient to keep tissues oxygenated, if pneumothorax develops on the side of the ventilated lung or if the double-lumen tube is subsequently dislodged, problems with ventilation and oxygenation may still be encountered.

Positioning the double-lumen tube often leaves the orifice of the right upper lobe bronchus covered by the tip of the bronchial tube (Fig. 33.8).

image The tracheal cuff is then deflated, the laryngoscope is held fixed relative to the patient and the double-lumen tube advanced. The blue bronchial cuff then occludes sight of the orifice of the right upper lobe bronchus until the side hole in the bronchial cuff lies over it. Sight of bronchial rings of the right upper lobe bronchus confirms the correct position of the double-lumen bronchial tube (Fig. 33.9).

image The double-lumen tube is then held firm and the bronchial cuff inflated with 2 mL of air. Uninterrupted sight of the right upper lobe bronchus confirms that this manoeuvre has not moved the side hole of the bronchial tube relative to the bronchus. The bronchi to the right middle and lower lobes may be seen through the distal lumen of the bronchial tube (Fig. 33.10). Withdrawing the intubating laryngoscope may give a view of the origins of all three lobar bronchi (Fig. 33.11).

image The double-lumen tube is then held against the teeth or gums of the maxilla, the mark on the tube there is noted and the laryngoscope is removed from the bronchial lumen. Without moving it, the tube is tied with a clove hitch over this mark and the tube tie tied round the neck with a bow.

image The tracheal cuff is then inflated with 5 mL of air and the fibreoptic laryngoscope is passed down the tracheal lumen until the carina is identified again. The bronchial lumen is seen to pass down the correct main bronchus and the bronchial cuff in its main bronchus is seen to be inflated, but not herniating to impinge over the lumen of the other main bronchus (Fig. 33.12).

image The laryngoscope is removed from the tracheal lumen and both lungs are ventilated.

image Bronchial and tracheal lumens are clamped in turn, observing airway pressures, leaks and the extent of ventilation of each lung.

The fibreoptic bronchoscope is necessary to position bronchial blockers through an endotracheal tube. Once inflated in position, gas can be aspirated through the central channel of the blocker to hasten collapse of the operative lung. When deflated, blockers have a propensity to move and may need to be rechecked using bronchoscopy when re-inflated. Blockers can achieve segmental collapse, leaving other parts of the lung still performing gas exchange.

Passing a suction catheter down the bronchial lumen before starting removes secretions faster than is possible through the suction port of the fibreoptic intubating laryngoscope. Lubrication of the laryngoscope with water-soluble jelly aids its passage down both lumens and prevents the tube being dislodged when the laryngoscope is withdrawn. A bottle of irrigation fluid aspirated through the suction port helps to prevent it being blocked by encrusted aspirate before there is an opportunity to clean the laryngoscope.

Clinical testing is specific – a problem detected with the position of the bronchial double-lumen tube is likely to predict a real problem if left uncorrected before surgery begins. However, it is not sensitive. Inadequate isolation of one lung and excessive airway pressures may be encountered after apparently successful positioning of the tube. Correct alignment of the fenestration in the bronchial cuff over the origin of the right upper lobe bronchus is particularly difficult to predict by clinical means alone, but demonstrable using fibreoptic bronchoscopy.

Mode of Ventilation

Breathing spontaneously through a surgical thoracotomy wound causes the same problem as trauma patients experience with a large open chest wound. The pleural space with the chest open is at atmospheric pressure. During inspiration, gas flows from trachea and lung in the open chest into the dependent lung. During expiration, the flow is reversed, causing the lung in the open chest to inflate. Gas is transferred from lung to lung during the paradoxical ventilation of the lung in the open chest, preventing excretion of carbon dioxide and rendering gas inspired into the dependent lung hypoxic. An occlusive dressing over the chest, or isolation of the lung in the open chest with a blocker or bronchial double-lumen tube, may stop paradoxical ventilation of the lungs. Both devices increase the resistance to gas flow to the dependent lung, and so mechanical one-lung ventilation is usual during thoracic surgery.

Physiological Changes

With one lung perfused but not ventilated, a substantial right-to-left shunt should produce significant hypoxaemia. Because of the greater solubility of carbon dioxide and its more linear dissociation curve, the gradient from arterial to alveolar partial pressure of carbon dioxide is smaller than that for oxygen. Increasing alveolar ventilation of the ventilated lung reduces arterial carbon dioxide tension without substantially increasing arterial oxygen tension. Because of the flat portion of the oxygen dissociation curve when haemoglobin is fully saturated, a further increase in alveolar oxygen tension results in only a small increase in oxygen content in solution, and has no effect on the oxygenation of the blood in the non-ventilated lung. Consequently, a high inspired oxygen fraction does not improve hypoxaemia caused by right-to-left shunt.

The severity of hypoxaemia observed is much less than that expected if regional perfusion remained unchanged. The lateral position directs more blood to the dependent lung due to gravity. In the non-ventilated lung, alveolar hypoxia results in increased vascular resistance, which directs more blood to the dependent ventilated lung, further reducing shunt and hypoxaemia – hypoxic pulmonary vasoconstriction (HPV). HPV is impaired by anaesthetic agents. However, in clinical practice, there are other compensatory mechanisms in the intact human lung to reduce shunt.

HPV has no effect if the alveolar oxygen tension is either 100% or 0%, or if the alveolar oxygen tension is the same throughout all lung units. It is more likely to have an effect with the 20–30% of cardiac output which shunts through the non-ventilated lung during one-lung anaesthesia. HPV effects are also maximal when pulmonary artery pressures and mixed venous oxygen saturation tensions are normal. The results of excessively high or low pulmonary artery pressures exceed the marginal changes in pulmonary artery pressures obtained by HPV. Similarly, an abnormally low mixed venous oxygen tension caused by low cardiac output or high oxygen consumption, for example by hyperthermia or shivering, has a greater influence than any changes possible with HPV. High peak and end-expiratory ventilation pressures in the dependent lung increase its pulmonary vascular resistance and overcome any benefits of HPV in the non-ventilated lung. Excessive alveolar pressures may increase dead space by producing a region of lung which is ventilated but not perfused.

Volatile anaesthetic agents and pulmonary vasodilators such as glyceryl trinitrate, sodium nitroprusside, isoprenaline, dobutamine and nitric oxide have been shown to inhibit HPV. However, there are far more variables clinically than in the controlled conditions of the experimental laboratory bench. Poor positioning of the patient which compromises blood flow to the dependent lung, malposition of a double-lumen bronchial tube, low cardiac output caused by inadequate blood volume replacement or impediment to blood flow by surgical manipulation may have a greater influence on hypoxaemia than the effects of changes in HPV.

Hypoxaemia during one-lung anaesthesia may be minimized by:

Insufflation of oxygen to the non-ventilated lung either at atmospheric pressure or with continuous positive alveolar pressure of 5 cmH2O should avoid the need for pharmacological intervention such as inhaled nitric oxide to the ventilated lung. When the pulmonary artery is clamped during lung resection, the adequacy of gas exchange should be reassessed. The loss of shunt through diseased lung tissue may improve oxygenation and result in better function than expected after removal of lung tissue.

ANAESTHESIA FOR THORACIC SURGERY PROCEDURES

Rigid Bronchoscopy

Rigid bronchoscopy in thoracic surgery is performed most often to obtain tissue diagnosis and determine if a lesion may be resected. Other indications include removal of foreign bodies and secretions, and control of haemorrhage. Therapeutic procedures such as laser therapy, tracheal or bronchial stenting and alveolar lavage may be performed through a rigid bronchoscope.

Anaesthesia should permit the passage of a straight rigid bronchoscope of up to 9 mm external diameter, allow oxygenation and removal of carbon dioxide, avoid awareness, and control movement, coughing and reflex haemodynamic responses to mechanical stimulation of the tracheobronchial tree. This may be achieved by spontaneous ventilation, apnoeic oxygenation or, more usually, positive pressure jet ventilation. Spontaneous ventilation avoids inhaled foreign bodies being propelled more distally into the bronchial tree. However, it offers much less control than when neuromuscular blockade is used, and anaesthesia sufficient to cause respiratory depression is required to control reflex responses to bronchoscopy. Apnoeic oxygenation may be achieved by delivering oxygen into the conducting airways by a catheter and relying on diffusion down a concentration gradient from oxygenated airways to the alveoli, where oxygen is absorbed continuously. Although effective in maintaining oxygenation measured by pulse oximetry, arterial carbon dioxide tension increases by about 0.5 kPa min–1. Using apnoeic oxygenation, enough time may be available to complete the surgical procedure, but eventually, assisted or spontaneous ventilation has to resume to ventilate the alveoli.

Positive pressure ventilation may be performed by intermittent occlusion of the bronchoscope or, more conveniently, by high-pressure jet ventilation using a Sanders Venturi technique. Oxygen at 400 kPa is released by a trigger held by the anaesthetist through a narrow orifice of 18–14 gauge. The gas is directed through the jet at the operator end of the bronchoscope towards the patient end. The high-pressure jet entrains atmospheric air and inflates the chest. Care must be taken to avoid pulmonary barotrauma by limiting delivery of oxygen under pressure to short intermittent bursts according to the chest movement observed and ensuring that there is a large unobstructed opening at the observer end of the bronchoscope to allow gas under pressure to escape from the conducting airways. Oxygenation may be monitored by pulse oximetry. Intermittent ventilation can usually be restricted to times when the operator is not looking down the bronchoscope.

With the patient supine, removal of the pillow or extension of the neck by lowering the head of the operating table may be necessary to allow the bronchoscope to pass down the trachea. Antisialagogue premedication dries oropharyngeal secretions and aids visibility. Induction of anaesthesia by inhalation of a volatile anaesthetic agent may be necessary occasionally to confirm that adequate ventilation can be achieved under anaesthesia where there is some obstruction to the upper airways. Depolarizing or competitive neuromuscular blocking agents may be used according to the needs of the patient or intended procedure. Topical local anaesthetic and a systemic opioid with a rapid onset of action help to obtund the haemodynamic response to bronchoscopy. Intermittent positive pressure ventilation with a Venturi device requires a total intravenous anaesthetic technique.

Local trauma and bleeding are the most common complications. Ventilation after bronchoscopy may be impaired by persisting effects of anaesthetic drugs, or compromise to the upper airway. A chest radiograph in the recovery room may provide early detection of pneumothorax or air in the mediastinum.

Rigid Oesophagoscopy

Fibreoptic oesophago-gastroduodenoscopy is performed usually as an outpatient procedure under sedation, without demands for anaesthetic assistance. Rigid oesophagoscopy under general anaesthesia presents the anaesthetist with patients who are at risk of aspirating gastric contents. Patients with achalasia may have a large volume of fetid fluid accumulated in their oesophagus. All oesophagoscopy patients should undergo rapid sequence induction with the suction catheter to hand and suction switched on. In patients with achalasia, there should be an attempt to drain the oesophagus before anaesthesia, which should be induced in a steep head-up tilt or in the left lateral position.

When anaesthesia has been induced and the cuff of the tracheal tube inflated to protect the airway, the tracheal tube should be passed to the left-hand side of the tongue to allow the oesophagoscope to be inserted behind where the tracheal tube usually lies. The tracheal tube is taped or tied securely, and then held at all times by the anaesthetist. This prevents the tracheal tube being dislodged by the operator on withdrawal of the oesophagoscope on most occasions, and makes the anaesthetist aware immediately of dislodgement of the tracheal tube, regurgitation of fluid into the oropharynx or requests for the tracheal cuff to be deflated as the oesophagoscope is passed through the cricopharyngeal sphincter.

Manipulations to the head or neck may be required to pass the oesophagoscope. Damage to the teeth or mucosal surfaces may occur. When the oesophagoscope has passed down the oesophagus, anaesthesia may be maintained with the patient breathing spontaneously. At the end of the procedure, patients should be awake and able to cough and protect the airway before tracheal extubation, which takes place with the patient lying on the left side with suction apparatus and trained assistance ready to hand as at induction of anaesthesia.

Perforation of the oesophagus is an unusual but serious complication. Patients should have been awake for 1 h after oesophagoscopy without complaint of chest discomfort and have an unchanged chest radiograph before ingestion of oral fluids resumes.

Video-Assisted Thoracoscopic Surgery

Improvements in imaging and thoracoscopic instruments have allowed more elaborate procedures than biopsy, such as lung resection, lung reduction surgery, pleurectomy and sympathectomy to be undertaken by video-assisted thoracoscopic surgery (VATS). The video image is magnified on monitors, but so too is movement and there is little space within the chest for instruments and camera lenses. A collapsed motionless lung may be essential, requiring one-lung anaesthesia. As more extensive procedures are now performed using VATS, so some more minor VATS procedures are being performed by chest physicians using pleuroscopy under local analgesia.

Pain after VATS procedures is less intense and prolonged than after posterolateral thoracotomy. Patients are much more comfortable after the chest drain is removed than thoracotomy patients at the same stage after surgery. A single paravertebral block at the level of the chest drain and intercostal incisions with 20 mL of bupivacaine 0.5% followed by oral analgesia may be sufficient to allow patients to take deep breaths and cough after thoracoscopic surgery.

Pulmonary Lobectomy

One-lung anaesthesia allows dissection in a field disturbed only by the movement of the mediastinum. Inflation of the lung temporarily may help to identify the lung fissures. Passive insufflation of the collapsed lung either through a suction catheter or with 5 cmH2O continuous positive airways pressure may augment oxygenation achieved by one-lung anaesthesia. Surgical traction on mediastinal structures and disturbance to the mediastinum by surgeons’ hands, instruments or retractors may cause bradycardia, interruption of the venous return to the heart or compression of the chambers of the heart.

When the bronchial stump is closed and haemostasis has been secured, the chest may be filled with warm saline and the airway pressure held at 40 cmH2O to test the integrity of the stump.

When chest drains are in position, re-inflation of the remaining lobe(s) is achieved by applying gentle positive pressure to the anaesthetic breathing system. Observing the pleural surface confirms if all superficial lung tissue is re-inflated. As the chest is closed, a subatmospheric pressure of 5 kPa is applied to the chest drains via an underwater seal. A significant air leak through damaged lung becomes apparent immediately if the ventilator reservoir collapses or if a reduction in the expired minute volume is detected by the ventilator alarm. The suction is then disconnected from the chest drains and reapplied when the patient resumes spontaneous breathing. Chest drains are then left without being clamped until the remaining lung has re-expanded fully, drainage has ceased and there is no air leak, when the chest drains are removed.

Pneumonectomy

The operative lung should be collapsed as soon as skin disinfection and draping begin. Problems with oxygenation may then be apparent early in the procedure. Borderline oxygenation may improve when the pulmonary artery is clamped and shunt through the lung to be resected is interrupted. Intrapericardial dissections for tumours that have extensive local spread pose a risk of sudden, substantial haemorrhage. After such dissection, cardiac herniation is a rare but serious cause of complications. The integrity of the stump of the main bronchus may be tested when the lung has been removed, as in lobectomy.

When the chest is closed at the end of surgery, the remaining lung is fully inflated and the chest drain to the pneumonectomy space is clamped. Clamps are released for 5 min every hour to ensure that no air, blood or excess fluid accumulates in the pneumonectomy space. Leaving the chest drains open continuously may lead to a reduction in the pneumonectomy space and the mediastinum being shifted to the operative side as the remaining lung becomes hyperinflated, with consequent respiratory embarrassment. The pleural space fills with serosanguinous fluid after pneumonectomy and fibroses subsequently, reducing the size of the space.

Bronchopleural Fistula

Although most common after lung resection surgery, bronchopleural fistulae may occur after acute respiratory distress syndrome (ARDS), or any intrathoracic sepsis. The chest should be drained before induction of anaesthesia to reduce the amount of purulent fluid in the chest cavity and avoid the prospect of tension pneumothorax. Anaesthesia should be induced with the affected side dependent, followed by prompt bronchial intubation of the main bronchus on the unaffected side, in order to isolate the healthy lung from contamination by purulent secretions from the affected side. After turning, one-lung ventilation allows surgery on the affected side. Should there still be lung tissue on the affected side, high-frequency jet ventilation can keep lung tissue inflated and ventilated in the presence of a large air leak, with mean intrathoracic pressures lower than with conventional intermittent positive pressure ventilation.

Tracheal Surgery

Unless cardiopulmonary bypass is used, there must be a changing sequence of means of ventilating the lungs during surgery, and measures to keep the neck flexed after surgery to avoid tension on the tracheal repair before it heals. Carinal surgery is one of the few remaining indications for a single lumen endobronchial tube.

Until the tracheal lesion is resected, airway obstruction must be overcome during the early stages of anaesthesia. Maintaining spontaneous ventilation initially allows assessment of the adequacy of assisted ventilation under anaesthesia. With the lesion exposed, ventilation of one or both lungs through an incision in the trachea distal to the lesion allows resection of the lesion and repair of the posterior wall of the trachea. A narrow tracheal or bronchial tube is passed through the larynx beyond the anastomotic site, and must allow space for repair of the anterior wall of the trachea. Suturing the chin to the skin over the sternum keeps the neck in flexion until the tracheal anastomosis heals.

Tracheostomy

The neck is extended by placing a sandbag under the shoulders and securing the head on a head ring. The pharynx should be aspirated when surgical dissection of the trachea is complete, because incision of the second and third tracheal rings frequently bursts the cuff on the tracheal tube. The tracheal tube is then withdrawn sufficiently far to allow insertion of the tracheostomy tube, but is not withdrawn from the trachea. This retains a means of ventilating the lung and a conduit into the trachea to replace the tracheal tube over a bougie if initial attempts to introduce the tracheostomy tube are unsuccessful. When the tracheostomy tube is positioned correctly, it is connected to a sterile catheter mount within the draped area and then to the anaesthetic breathing system. The sandbag is removed before the neck wound is sutured.

Pneumomediastinum and pneumothorax may occur intraoperatively because of damage to the posterior tracheal wall. Haemorrhage and damage to other structures may occur immediately, or later as a result of the effects of pressure from a malpositioned tracheostomy tube.

Oesophageal Surgery

Oesophagectomy is often preceded by oesophagoscopy with all the attendant risks of pulmonary aspiration. Thoracic approaches to the oesophagus may require one-lung ventilation to provide access for surgery. Oesophagectomy may take some hours and be associated with considerable fluid loss into the wound and surrounding tissues. After surgery, effective analgesia is necessary to enable the patient to expand the chest and cough effectively. Patients should be nursed sitting or supported on pillows to avoid regurgitation of gastrointestinal fluid and subsequent aspiration. Total parenteral nutrition is not required as a routine, but may be necessary in the presence of postoperative complications such as mediastinitis from an anastomotic leak. Judicious use of i.v. fluids after surgery is required.

POSTOPERATIVE CARE

Pulmonary function is impaired after thoracic surgery beyond any changes expected after lung resection. There is a 35% reduction in functional residual capacity after lung resection, which takes 6–8 weeks to recover to preoperative values. However, thoracic surgery patients should be able to breathe spontaneously immediately after anaesthesia and surgery. A need for mechanical ventilation after surgery is likely to result from problems in patient selection or during surgery and anaesthesia intraoperatively. A mini-tracheostomy tube may be inserted through the cricothyroid membrane at the end of surgery, with the trachea extubated and the lungs ventilated through a laryngeal mask, to help aspiration of the trachea of patients unable to cough effectively. Prolonged mechanical ventilation exposes thoracic patients to regional lung collapse and nosocomial pulmonary infection.

A high inspired oxygen concentration to overcome hypoxaemia is usually required for the first 24 h after surgery and during sleep at night until chest drains are removed. Patients breathing air with a PaCO2 greater than 6.0 kPa before surgery are at increased risk of ventilatory failure after surgery and require oxygen therapy tailored to response. Most other patients benefit from oxygen 40–60% by plastic face mask or nasal prongs.

The posterolateral thoracotomy wound is exceedingly painful. Untreated, each breath provokes pain. To minimize pain, ventilation is rapid and shallow. Analgesia sufficient to permit deep inspiration and productive coughing without respiratory depression is necessary to restore adequate spontaneous ventilation after thoracic surgery. Continuous epidural analgesia or, if that is contraindicated, paravertebral nerve blockade is more likely to achieve these aims than systemic opioid analgesia. Epidural local anaesthetic or opioids, or mixtures of the two, may be infused through a catheter introduced between the fifth and eighth thoracic vertebrae, depending on the sites of wound and chest drains, and the size and alignment of the intervertebral spaces. Bupivacaine 0–15 mg h–1, or fentanyl 0–50 μg h–1, alone or in combination, may be given as continuous infusions or background infusions with additional patient-controlled demands. Paravertebral block delivering local anaesthetics through a catheter inserted at the end of surgery has been demonstrated to be at least as effective as epidural analgesia, with fewer side-effects such as hypotension, urinary retention, itch and respiratory depression.

After oesophageal surgery, oral fluids are withheld for some days while a nasogastric tube drains the stomach. After lung resection in the morning, patients may be able to manage some food in the evening. Intravenous fluids are required for the first 24 h, although less is given than after other forms of major surgery. Maintenance fluids are restricted to avoid pulmonary oedema in remaining lung tissue that has been handled or through which there is a relatively increased pulmonary artery flow after lung resection. Ringer lactate solution 10 mL kg–1 h–1 in theatre and 1 mL kg–1 h–1 thereafter provides maintenance fluids. Blood and colloid may be added to replace further losses and support the circulation.

Patients are likely to be cold after thoracic surgery as a result of lying in theatre covered only by sterile drapes and with the chest open during surgery. Simple means to conserve heat during surgery by warming i.v. fluids and humidification of inspired gases, followed by convective warming blankets in the recovery room, may restore body temperature to normal soon after surgery is finished.

Arrhythmias are common after thoracotomy, especially atrial tachyarrhythmias, which may affect 9–33% of patients over 60 years of age. They occur often 2–3 days after surgery and increase the risk of hypotension and stroke. Prophylaxis has proved ineffective and 85% resolve during hospital stay. Of the remainder, almost all resolve within 2 months.

FURTHER READING

Ambrosino, N., Gabbrielli, L. Physiotherapy in the perioperative period. Best Pract. Res. Clin. Anaesthesiol. 2010;24:283–289.

Banki, F. Pulmonary assessment for general thoracic surgery. Surg. Clin. North Am. 2010;90:969–984.

Bastin, R., Moraine, J.J., Bardocsky, G., et al. Incentive spirometry performance – a reliable indicator of pulmonary function in the early postoperative period after lobectomy? Chest. 1997;111:559–563.

Bernstein, W.K., Deshpande, S. Preoperative evaluation for thoracic surgery. Sem. Cardiothorac. Vasc. Anesth. 2008;12:109–121.

Brister, N.W., Barnette, R.E., Kim, V., Keresztury, M. Anesthetic considerations in candidates for lung volume reduction surgery. Proc. Am. Thorac. Soc. 2008;5:432–437.

Brodsky, J.B., Lemmens, H.J.M. The history of anesthesia for thoracic surgery. Minerva Anestesiol. 2007;73:513–524.

Campos, J.H. Update on selective lobar blockade during pulmonary resections. Curr. Opin. Anaesthesiol. 2009;22:18–22.

Campos, J.H. Update on tracheobronchial anatomy and flexible fiberoptic bronchoscopy in thoracic anesthesia. Curr. Opin. Anaesthesiol. 2009;22:4–10.

Campos, J.H. An update on robotic thoracic surgery and anesthesia. Curr. Opin. Anaesthesiol. 2010;23:1–6.

Castillo, M.D., Heerdt, P.M. Pulmonary resection in the elderly. Curr. Opin. Anaesthesiol. 2007;20:4–9.

Daly, D.J., Myles, P.S. Update on the role of paravertebral blocks for thoracic surgery: are they worth it? Curr. Opin. Anaesthesiol. 2009;22:38–43.

Duggan, M., Kavanagh, B.P. Perioperative modifications of respiratory function. Best Pract. Res. Clin. Anaesthesiol. 2010;24:145–155.

Fischer, G.W., Cohen, E. An update on anesthesia for thoracoscopic surgery. Curr. Opin. Anaesthesiol. 2010;23:7–11.

Hernandez, G., Fernandez, R., Lopez-Reina, P., et al. Noninvasive ventilation reduces intubation in chest trauma-related hypoxemia: a randomized clinical trial. Chest. 2010;137:74–80.

Jaklitsch, M., Billmeier, S. Preoperative evaluation and risk assessment for elderly thoracic surgery patients. Thorac. Surg. Clin. 2009;19:301–312.

McKevith, J.M., Pennefather, S.H. Respiratory complications after oesophageal surgery. Curr. Opin. Anaesthesiol. 2010;23:34–40.

Mineo, T.C. Epidural anesthesia in awake thoracic surgery. Eur. J. Cardio-Thorac. Surg. 2007;32:13–19.

Nagendran, J., Stewart, K., Hoskinson, M., Archer, S.L. An anesthesiologist’s guide to hypoxic pulmonary vasoconstriction: implications for managing single-lung anesthesia and atelectasis. Curr. Opin. Anaesthesiol. 2006;19:34–43.

Ng, J.M. Perioperative anesthetic management for esophagectomy. Anesthesiol. Clin. 2008;26:293–304.

Pompeo, E., Tacconi, F., Mineo, T.C. Awake video-assisted thoracoscopic biopsy in complex anterior mediastinal masses. Thorac. Surg. Clin. 2010;20:225–233.

Rodrigo, J.L., Edguez-Panadero, F. Medical thoracoscopy. Respiration. 2008;76:363–372.

Ross, A.F., Ueda, K. Pulmonary hypertension in thoracic surgical patients. Curr. Opin. Anaesthesiol. 2010;23:25–33.

Round, J.A., Mellor, A.J. Anaesthetic and critical care management of thoracic injuries. J. R. Army Med. Corps. 2010;156:145–149.

Scarci, M., Joshi, A., Attia, R. In patients undergoing thoracic surgery is paravertebral block as effective as epidural analgesia for pain management? Interact. Cardiovasc. Thorac. Surg. 2010;10:92–96.

Schroeder, D. The preoperative period summary. Chest. 1999;115:44S–46S.

Shaw, A. Exploring the perioptome: the role of genomics in thoracic surgery and anaesthesia. Curr. Opin. Anaesthesiol. 2007;20:32–36.

Sherry, K.M. (Ed.), 1996. Management of patients undergoing oesophagectomy. The report of the National Confidential Enquiry into Perioperative Deaths 1996/1997. Nuffield Provincial Hospitals Trust, London, pp. 57–61.

Shimizu, T., Abe, K., Kinouchi, K., Yoshiya, I. Arterial oxygenation during one lung ventilation. Can. J. Anaesth. 1997;44:1162–1166.

Slinger, P. Update on anesthetic management for pneumonectomy. Curr. Opin. Anaesthesiol. 2009;22:31–37.

Slinger, P.D., Johnston, M.R. Preoperative assessment for pulmonary resection. Anesthesiol. Clin. North America. 2001;19:411–433.

Zibrak, J.D. Preoperative pulmonary-function testing. Ann. Intern. Med. 1990;112:763–771.

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