Interpretation of Pulmonary Function Tests A Practical Guide, 3. ed

10. Preoperative Pulmonary Function Testing

The goals of preoperative pulmonary function testing are (1) to detect unrecognized lung disease, (2) to estimate the risk of operation compared with the potential benefit, (3) to plan perioperative care, and (4) to estimate postoperative lung function. Several studies have shown a high prevalence of unsuspected impairment of lung function in surgical patients and suggest that preoperative pulmonary function testing is underutilized. There is EV1dence that appropriate perioperative management improves surgical outcome in patients with impaired lung function.

10A. WHO SHOULD BE TESTED?

The indications for testing depend on the characteristics of the patient and on the planned surgical procedure. Table 10-1 lists the characteristics of the patient and the surgical procedures for which testing is recommended. We believe that preoperative testing should be done on all patients scheduled for any lung resection. We also recommend testing before upper abdominal and thoracic operation in patients with known lung disease and for smokers older than 40 (up to one-fourth of such smokers have abnormal lung function) because these procedures present the greatest risk for patients with impaired lung function. When a significant abnormality is detected, appropriate perioperative intervention may reduce the morbidity and mortality related to operation. Such intervention includes use of bronchodilators and postoperative use of incentive spirometry. Although the benefit of smoking cessation before operation has not been proved, it is common practice to recommend that smokers, especially those with impaired lung function, stop smoking preoperatively.

TABLE 10-1. Indications for preoperative pulmonary function testing

10B. WHAT TESTS SHOULD BE DONE?

For patients with obstructive disorders, spirometry before and after bronchodilator therapy may be sufficient preoperative testing. However, for those with moderate to severe airway obstruction, arterial carbon dioxide tension (blood gases) should also be measured. Table 10-2 lists general guidelines for interpreting the test results in terms of risk to the patient.

The risk of surgical procedures for patients with restrictive disorders is less well studied than that for patients with obstructive disorders. We recommend following similar guidelines, but keeping in mind the cause of restriction (lung parenchymal disease, chest wall disorders, muscle weakness, obesity).

TABLE 10-2. Guidelines for estimating risk for postoperative respiratory complications

FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; MVV, maximal voluntary ventilation; Paco₂, arterial tension of carbon dioxide.

Indications for measurement of the diffusing capacity of the lungs (Dlco) are not clearly established. We recommend that the Dlco be measured in patients with restrictive disorders to evaluate the severity of gas exchange abnormality. In pulmonary parenchymal disorders, such as pulmonary fibrosis, this abnormality is often more severe than expected from the degree of ventilatory impairment alone.

Oximetry is an inexpensive measure of gas exchange but is relatively nonspecific and insensitive, even when performed during exercise. We do not recommend its use for determining operative risk. It is useful, however, for monitoring oxygen therapy postoperatively.

Maximal voluntary ventilation is also used as a predictor of postoperative respiratory complications. It is less reproducible than the forced expiratory volume in 1 second (FEV1) and is more dependent on muscle strength and effort. For these reasons it is no longer used to determine a subject's eligibility for Social Security disability payments. However, it does have a role in preoperative assessment and is comparable to the FEV1 for predicting postoperative respiratory complications.

10C. ADDITIONAL STUDIES

Quantitative radionuclide scintigraphy has been used to determine regional ventilation and perfusion of the lungs. The results have been used to improve estimates of postoperative pulmonary function, especially for patients with marginal lung function.

Maximal cardiopulmonary exercise studies have been used for preoperative assessment. Several authors have reported low rates of postoperative complications in patients with a maximal oxygen uptake of more than 20 mL/kg per minute and high rates of complications with a maximal oxygen uptake of less than 15 mL/kg per minute. This form of testing requires sophisticated equipment and considerable technical expertise. It is therefore more expensive than other tests. Yet the cost of testing is small compared with that of most surgical procedures.

10D. WHAT IS PROHIBITIVE RISK?

Several algorithms have been developed for calculation of lung function after resection of lung tissue. One approach requires an estimation of the number of lung segments, out of a total of 18, that are likely to be removed. Then the following calculation is performed:

Thus, if five segments are to be removed and the preoperative FEV1 is 2.0 L, the predicted postoperative FEV1 is 1.4 L

The postoperative FEV1 predicted from this calculation is the estimated level of lung function after full recovery, not immediately after operation. In the past, a common recommendation was that surgical resection should not be performed if the predicted postoperative FEV₁ was less than 0.8 L. However, several studies show that with modern postoperative care this is no longer an absolute contraindication. Specialized centers with excellent perioperative care have reported low morbidity and mortality in such severely impaired patients [1].

REFERENCE

1. Cerfolio RJ, Allen MS, Trastek VF, Deschamps C, Scanlon PD, Pairolero PC. Lung resection in patients with compromised pulmonary function. Ann Thorac Surg 62:348-351, 1996.