PREOPERATIVE MEASURES TO IMPROVE LUNG FUNCTION

Aside from assessing operability in candidates for lung resection, the major goal of identifying preoperative pulmonary dysfunction is to alter outcome by reducing the morbidity and mortality associated with postoperative pulmonary complications (see Chapter 25 and Chapter 27 ). The assumption is that patients identified as having abnormal function may benefit from therapeutic measures to improve lung function, thereby reducing the likelihood of postoperative complications. Numerous applications of such therapy to poor-risk patients have decreased postoperative complications to levels approaching those found in patients with normal function.

Ideally, a comprehensive rehabilitation regimen of exercise, nutrition, education, and, most importantly, physiotherapy can improve the functional capacity of patients with significant lung disease.^[32] However, such extensive therapy is not practical preoperatively, and limited therapy usually is carried out for 48 to 72 hours before surgery. It is equally important that some of the measures be continued after surgery. The treatment regimen is aimed largely at four modalities: (1) smoking cessation, (2) mobilization of secretions, (3) therapy for bronchospasm, and (4) improved motivation and stamina. Although it is generally assumed that smoking cessation is followed by a decrease in the volume of airway secretions and in airway reactivity and by improved mucociliary transport, these beneficial effects take 2 to 4 weeks to manifest. The shorter-term effects (48 to 72 hours) may instead be increased secretions and hyperactive airways. The major benefit from discontinuing smoking in the immediate preoperative period appears to be the decrease in carboxyhemoglobin content and better oxygen availability to the tissues.^[33] There is additional evidence that the sensitive upper airway reflexes of smokers are reduced by abstinence. It is therefore reasonable to expect the adverse events so common during the induction of anesthesia (i.e., cough, breath-holding, and laryngospasm) to be reduced.^[34]

The removal of secretions is an important component of preoperative preparation, because their persistence increases the likelihood of infection and increased airway reactivity. Antibiotic therapy for patients with chronic bronchitis may be helpful, but the secretions are best loosened by adequate hydration systematically and by heating of aerosol therapy agents. The use of mucolytic agents and oral expectorants is at best of questionable benefit and is fraught with the hazards of increased airway irritability and other side effects, such as gastrointestinal irritation. Mucociliary clearance is impaired in such patients, and cough is ineffective because of an inability to generate sufficient airflow rates. Mechanical measures must be used to dislodge secretions and move them into the more proximal airways, where cough can more readily remove secretions. Such therapy is limited to percussion and vibration combined with postural drainage.

Reactive airways and reversible airflow obstruction are common features, especially in patients presenting for thoracic surgery. The use of medications to establish and sustain normal airway function is important in the perioperative period. β₂ -Sympathomimetic aerosols are the mainstays for treatment and prevention of bronchospasm. The use of the quaternary anticholinergic compound ipratropium may also be helpful, particularly if tachycardia is a concern with β₂ -sympathetic drugs. Theophylline is often added to this regimen; however, there is considerable concern regarding the toxicity and limited efficacy of intravenous theophylline when it is administered in the setting of acute disease.

Patients should be prepared for thoracotomy by improving motivation and stamina. Education and practice with incentive spirometry devices are important in the maintenance of postoperative lung volume and coughing efficacy. Such preparation and continued postoperative use appears to be far more effective than intermittent positive-pressure breathing therapy.

Use of the preparatory respiratory care maneuvers ultimately benefits the patient and contributes to reducing the incidence and severity of postoperative respiratory complications. The question remains, however, whether such an improved outcome is reflected in pulmonary function on spirometric testing. It may be unreasonable to expect a dramatic reversal in airflow obstruction and improved blood gas values with such a brief (48 to 72 hours) regimen. Gracey and colleagues^[35] evaluated pulmonary function before surgery in patients with chronic obstructive pulmonary disease on such a standardized regimen. Although this therapy produced statistically significant changes in several test results of pulmonary function, the functional significance of the changes was doubtful. Nevertheless, the incidence of complications in these patients was dramatically reduced, as has been shown in numerous other studies. There are no definitive data that can identify whether this reduced complication rate results specifically from the preparation regimen, the use of specific agents or techniques, or the increased attention paid to patients in whom airway obstruction or other pulmonary dysfunction is identified.

It appears reasonably well established that patients whose clinical history and physical examination suggest the presence of pulmonary disease are at increased risk if spirometric results are abnormal. It is unclear exactly what should be done for such patients other than an abbreviated regimen of preoperative preparation and concern intraoperatively for control of airway reactivity. Equally uncertain is which test best predicts risk and what further testing is appropriate for patients with abnormal spirometric results. Nevertheless, in patients who are about to undergo pulmonary resection, exercise testing seems to provide the best predictive insight.