General Medical Information

General Management Pulmonary Disorders

David M. Barrs

Pulmonary problems are the most common complication after surgery. Anesthesia and surgery have profound effects on pulmonary function. All lung volumes, especially vital capacity and functional residual capacity, are decreased, reducing lung compliance and increasing the work of breathing. The result is alveolar hypoventilation with ventilation-perfusion abnormalities and hypoxemia. Extravascular lung water also may be increased from increased hydrostatic pressure secondary to fluid overload and low plasma oncotic pressure. If the pulmonary capillary endothelium also is damaged from exposure to toxic products from injury, infection, or the surgical procedure, increased capillary permeability may increase lung extravascular water. In otolaryngologic procedures, impaired laryngeal protective mechanisms, airway edema, and foreign bodies such as blood clots may promote aspiration.

Treatment is initiated in the preoperative period with preventive measures and identification of the patients who may be at a higher risk for pulmonary problems. Historic symptoms, such as dyspnea on exertion, cough, sputum production, and cigarette smoking, indicate the need for further evaluation. The physical examination should include auscultation during maximal inspiration and forced expiration. Observation of the patient climbing stairs remains a valuable adjunct to clinical estimation of pulmonary reserve. The preoperative chest radiograph can demonstrate pathology, but it is more important when used for postoperative comparison. A preoperative chest radiograph in asymptomatic patients is recommended by the American College of Surgeons for known pulmonary or cardiac disease, age greater than 40 years, high risk for postoperative pulmonary complications, and a positive tuberculin test or high risk for unsuspected tuberculosis. Pulmonary function tests can give the clinician an idea of the degree of alveolar ventilation and the ability to clear secretions in the postoperative period. The best overall predictor of postoperative pulmonary difficulties may be the maximal voluntary ventilation test, which is the largest volume that can be breathed by voluntary effort per minute, extrapolated from rapid breathing into a spirometer during a 15-second interval. This test measures lung function, compliance of the chest wall, strength of the respiratory muscles, and patient motivation and ability to cooperate. Preoperative arte-rial blood gases provide mainly a comparison for postoperative measurements.

Any patient with arterial oxygen tension less than 60 to 70 mm Hg usually has a significant ventilation-perfusion mismatch. An arterial carbon dioxide tension greater than 45 mm Hg indicates significant alveolar hypoventilation and is associated with an increased incidence of postoperative complication. Reversible causes, such as bronchospasm or bronchitis, should be corrected preoperatively.
Preventive measures are begun as soon as a decision to operate is made and are carried through the entire postoperative course. Predisposing factors for lung complications, such as smoking or obesity, and underlying pulmonary conditions, such as chronic bronchitis, chronic obstructive pulmonary disease, and reactive airway disease, are corrected insofar as possible before surgery. Ideally, pulmonary exercises that will be performed postoperatively should be practiced before surgery. These include deep breathing and the use of incentive spirometry. The main thrust of postoperative care is deep-breathing exercises to enhance alveolar aeration and ventilation. Unless secretions are a major problem, coughing may not need to be encouraged and may be detrimental in skull-base procedures with an increased chance of a spinal fluid leak.

The choice of anesthesia is important. Although local anesthesia may seem preferable, general endotracheal anesthesia gives the best control over the airway. Frequent sustained inflation to 20 mL/kg or to an airway pressure of 30 cm H2O should be performed to prevent alveolar collapse. Intravenous crystalloid solutions should be given conservatively, and blood or plasma replacement products should be given with large fluid losses to help maintain normal intravascular colloid pressure and prevent pulmonary edema.

Preventive measures should be continued in the postoperative period. The endotracheal tube should be kept in place as long as necessary to maximize alveolar ventilation. Immediately after endotracheal tube removal, deep-breathing exercises, clearance of respiratory secretions, and frequent turning of the patient are begun. If the patient is unable to perform maximal inhalation exercises or incentive spirometry, continuous positive airway pressure or intermittent positive pressure breathing may be of help in preventing atelectasis.