General Thoracic Surgery

Pulmonary Function Tests

Spirometry measures the volumes that an individual can breathe in and out, whereas diffusion capacity measures the functional ability, specifically measuring gas diffusion within the lungs (ability of exchange of CO ₂ for O ₂ ). According to guidelines from the European Respiratory Society (ERS) and European Society of Thoracic Surgeons (ESTS), both spirometry (specifically FEV1 [forced expiratory volume in 1 second]) and the assessment of the diffusion capacity of the lungs (DL _CO ) are the most important for assessing preoperative pulmonary function status.

Although prior guidelines from the American College of Chest Physicians (ACCP) in 2007 and the British Thoracic Society (BTS) were selective about use of DL _CO assessment, numerous recent studies have demonstrated that reduced DL _CO levels constitute an independent risk factor for increased mortality and perioperative complications, even in patients with normal FEV1.

Exercise Capacity

The most precise test amongst the exercise assessments is the cardiopulmonary exercise test (CPET). CPET may be performed on a treadmill or on a cycloergometer. The measurement of exercise capacity is peak oxygen uptake expressed by the VO ₂ max parameter. Reduced VO ₂ max results in an increased risk of postresection complications. Specific values of importance:

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  Greater than 75% predicted value or > 20 mL/kg/min: safe to proceed to resection;

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  Less than 65% predicted value or < 16 mL/kg/min: resection not recommended.

Criticism of CPET has been directed at both the difficulty of doing the test and the exorbitant cost. Other low-cost methods for assessment of exercise capacity include the 6-minute walk test (6MWT), shuttle walk test, and stair climbing test.

The distance covered during 6MWT has best been correlated with VO ₂ values in lung transplantation patients but has less correlation with complications after lung resection. During the shuttle walk test, patients walk between two points 10 meters apart and increase their pace (speed) by a signal during the test. The distance covered during this test correlates well with VO ₂ max for the majority of patients. Those patients who walk less than 250 meters are at significantly increased risk of complications after lung resection.

During the stair climbing test, patients climb flights of stairs, with assessment of both distance and number of floors. Patients who climb less than three floors are twice as likely to suffer from complications, have 13-fold increased mortality, and 2.5-fold increased costs of treatment, compared with those who are able to climb five floors of stairs. All patients who are able to climb more than five floors of stairs are able to undergo even a pneumonectomy safely.

Predicted Postoperative Values

After assessment of PFTs and exercise capacity, the final step is the calculation of the predicted postoperative values of FEV1 and DL _CO . The formula used incorporates the number of bronchopulmonary segments removed at the time of resection. The number of bronchopulmonary segments per lobe:

• Right lung: upper lobe (3), middle lobe (2), lower lobe (5)

• Left lung: upper lobe (5–3 apical + 2 lingula), lower lobe (4)

Formula:

Historically, PPO values greater than 50% were ideal. With improvement in surgical and critical care practices, PPO values of 40% are acceptable and can be considered even as low as 30% if the care is at centers of excellence who have robust experience taking care of high-risk patients.