Pulmonary surgery

Flexible bronchoscopy

The flexibility of fibreoptic bronchoscopes allows a view of all the major branches of the tracheobronchial tree with minimal risk of trauma and discomfort for the patient. The procedure can therefore be performed without general anaesthesia, although extensive topical anaesthesia to the airway is required, and most clinicians also provide sedation to relieve the anxiety associated with having a bronchoscopy. Hypoxia during a flexible bronchoscopy is common, occurring in 17% of patients from one study, and supplemental oxygen is therefore normally used. Lung function during bronchoscopy is significantly impaired. While the bronchoscope is in place the functional residual capacity (FRC) is increased by about one-fifth, and forced vital capacity (FVC), forced expiratory volume in one second (FEV ₁ ) and peak expiratory flow are all decreased, indicating expiratory air flow obstruction. These observations are not explained simply by the presence of the bronchoscope in the airway, as the observed airway flow limitation begins after the airway local anaesthetic is applied (before insertion of the bronchoscope) and continues for several minutes after the bronchoscope has been removed, suggesting that a bronchoconstrictor action of the topical anaesthesia is responsible. Respiratory depression may also occur during or soon after bronchoscopy, and the causes of this are uncertain but likely to relate either to the sedative drugs or the topical anaesthesia in the airway. The major limitation of flexible bronchoscopy is the size of the instruments that may be passed down the bronchoscope. They are suitable for visualization and biopsies of the airway, and the development of endobronchial ultrasound has allowed flexible bronchoscopes to also be used for biopsies of mediastinal lymph nodes and tumours, revolutionizing the diagnosis and staging of lung cancer. However, for removal of foreign bodies or airway surgery a larger portal for access to the tracheobronchial tree is required.

Rigid bronchoscopy

Straight, rigid bronchoscopes are available with internal diameters up to 8 mm that may be passed into the trachea, and a variety of instruments can then be used through the bronchoscope. To see around corners in the bronchial tree 30- and 90-degree angled telescopes are used. With rigid bronchoscopy foreign bodies that are wedged in the airway can be removed, tracheal tumours resected, airway haemorrhage treated and stents deployed in the trachea or main bronchi to overcome stenosing tumours or airway leaks. The major disadvantage of the technique is the requirement for general anaesthesia, often in a patient with significant respiratory disease.

Ventilation during a rigid bronchoscopy is challenging, and four main techniques may be used:

• 1.

  Spontaneous ventilation . A ventilating bronchoscope allows the normal anaesthetic breathing system to be attached to a side port of the bronchoscope, which also must have a glass window to occlude its proximal lumen to prevent escape of the anaesthetic gases. Spontaneous breathing may be continued during the procedure, with anaesthesia maintained by inhalational or intravenous agents. Leaks around the bronchoscope are a problem, particularly if the surgeon wishes to pass instruments through the bronchoscope, so this technique is now used only rarely and usually in children in whom the small size of the cricoid cartilage minimizes leakage of inhaled gases from around the bronchoscope.

• 2.

  Positive pressure ventilation . This form of ventilation may be achieved via a ventilating bronchoscope, as described earlier, but once again the lack of a seal between the airway and bronchoscope makes the technique problematic. The most common technique used for ventilation is the Sanders injector, which is a high-pressure oxygen supply (4 atm) intermittently applied to the proximal end of the rigid bronchoscope through a small diameter ‘injector’. As a result of the Venturi effect, the high-velocity jet of oxygen entrains room air and increases the pressure along the bronchoscope, causing lung inflation. Anaesthesia must be maintained by intravenous agents, and adequacy of ventilation can only be assessed by observation of the chest rather than the usual capnography (page 134), but this technique does allow the surgeon to operate down the bronchoscope whilst the patient is being ventilated. The Sanders injector system for ventilation is problematic in patients with lung disease, as the inspired oxygen concentration and pulmonary inflation pressure are variable, influenced not only by the bronchoscope dimensions and side ports but also by the mechanics of the patient’s lungs.

• 3.

  High-frequency jet ventilation (page 384). This may be used during bronchoscopy, and the ability of the technique to ventilate the lungs with minimal increase in airway pressure makes it particularly useful in patients with airway leaks such as bronchopleural fistulae.

• 4.

  Apnoeic oxygenation . This may be used during rigid bronchoscopy, but normally only as a last resort and for a short period of time—that is, until hypercapnia develops (page 133).

Assessing patient fitness for lung resection

Lung function is assessed using either the FEV ₁ or, if the patient has parenchymal lung disease, the diffusing capacity for carbon monoxide ( D l _CO ; page 117). If these are less than 80% of normal predicted values for that patient, an attempt is made to calculate predicted postoperative values based on which anatomical sections of lung need to be removed. Radionucleotide ventilation or perfusion scans or quantitative computed tomography scans may all be used to measure functional lung units; these are useful techniques as they also show which pathological lung units are already not contributing to overall function. Less invasive is the anatomical method in which the lungs are divided into 19 anatomical segments of equal value, and knowing which segments are to be removed enables estimation of postoperative predicted lung function. For many years a general rule of lung resection was that a predicted postoperative FEV ₁ of less than 0.8 to 1.0 L precluded resection, although evidence for this rule is poor. Using an absolute value for FEV ₁ or D l _CO is fraught with difficulties because sex, age and height all affect the normal values, and decisions should now always be based on the values as a percentage of the predicted normal for that patient (page 24).

Different studies have produced varied results on the association between percentage predicted postoperative FEV ₁ or D l _CO and outcome, but a value of less than 40% of predicted normal is now accepted as being associated with an increased mortality and complication rate. For patients in this situation, measurement of preoperative exercise tolerance has the advantage of also including a cardiovascular component to the assessment and may help to further define risks and outcomes. The most objective way of quantifying exercise activity is by measuring $\stackrel{.}{V}$ o _2peak (page 184). Values of less than 15 mL.min ⁻¹ .kg ⁻¹ are again associated with poor outcome. Clinical measures of exercise tolerance have some value, but these must be performed under supervision, as patients’ own reported exercise tolerance is normally greatly exaggerated. Tests which have some limited use in predicting outcome after lung resection include the shuttle test and 6-minute walk test (page 189) and stair climbing (the number of stairs or height of stairs the patient is able to climb ).

Partial lung resection

The magnitude of lung resection operations varies from removal of a small tumour in the lung periphery to a complete pneumonectomy, with the more minor procedures performed via VATS and the more major via a thoracotomy. Wherever possible, dissection is made between lobes or in intersegmental planes. Care is required when operating on pulmonary vessels, particularly pulmonary arteries because they have thin walls and are easy to damage, which can result in significant haemorrhage that may be difficult to control.

Following lung resection, the remaining lung in the hemithorax quickly expands to fill the available space. One or two chest drains are usually placed in the chest cavity and connected to underwater seal systems to allow any air or blood to drain. If the remaining lung does not fully expand, a negative pressure of up to 20 cmH ₂ O may be applied to the drains to encourage expansion.

Pneumonectomy

Resection of an entire lung is usually performed for removal of large, central lung tumours ( Fig. 33.1 , A ). Following pneumonectomy correct management of the empty hemithorax is crucial. If air is drained from the cavity too quickly mediastinal shift will occur, which impairs venous drainage to the heart and can cause cardiovascular collapse. One option is to not leave a drain in the chest cavity and to monitor the position of the mediastinum daily with a chest radiograph. Alternatively, a chest drain can be placed ( Fig. 33.1 , B ), but be clamped for most of the time and only released briefly and intermittently to ensure the pressure in the cavity is approximately atmospheric. A more interventional approach is to measure the pressure in the chest cavity and instil or remove air to maintain a pressure of −2 to −4 cmH ₂ O on inspiration and +2 to +4 cmH ₂ O on expiration. Within a few weeks of pneumonectomy the volume of the hemithorax decreases because of a combination of mediastinal shift, elevation of the diaphragm and contraction of the chest wall, and pleural fluid replaces the air in the chest cavity ( Fig. 33.1 , C ). Over the ensuing months or years, the fluid volume decreases as the mediastinal shift continues, and the other lung herniates anteriorly or posteriorly across the midline to partially fill the vacated hemithorax.

Studies in animals have demonstrated the intriguing phenomenon of ‘neoalveolarization’ following lung resection. Within 20 days of lung resection in mice the number of alveoli in the remaining lung increased by 50%, completely restoring the gas-exchanging surface area. Neoalveolarization probably occurs by new alveoli forming in the walls of existing alveolar ducts and respiratory bronchioles, and is thus far only described in young animals, as would be expected from the observation that in mammals formation of alveoli is a postnatal process (page 176).