In the evaluation of a patient being considered for resectional lung surgery, determination of the patient's pulmonary function is of great importance. Several studies - including routine pulmonary function tests, arterial blood gas analysis, quantitative ventilation-perfusion scanning and exercise testing - should be considered in ascertaining the patient's fitness for the proposed resection from a pulmonary functional standpoint.

Initially, a forced vital capacity (FVC) and forced expiratory volume in one second (FEV-1) need to be performed. When both are 80 percent or greater than the predicted values, a pneumonectomy usually can be tolerated by the patient. When the FEV1 is less than 30 percent of predicted, most resections are contraindicated. When the values fall between these two levels, other tests must be performed to more fully assess the patient's candidacy for the proposed resection.

Arterial blood gases are an indicator of risk associated with resection. Generally a PaO2 greater than 60 torr and a PaCO2 less than 45 torr indicates low risk in most patients. A PaO2 less than 50 torr indicates a greater risk, while a PaCO2 greater than 45 torr indicates a much higher risk for the development of postoperative complications following thoracic surgery. These latter values indicate loss of significant alveolar ventilation and/or a significant loss of pulmonary capillary reserve, which in most instances is a contraindication for any pulmonary resection.

Quantitative ventilation-perfusion scanning can be used to assess the contribution of either lung or a specific lung zone to the overall pulmonary function. Using the data obtained from this test, an estimate of postoperative FEV-1 can be determined. This value can be calculated simply by multiplying the patient's FEV-1 (preoperative) by the percentage of lung perfusion (as determined by the scan) remaining after the proposed lung resection. Usually measured by subtracting the perfusion to the proposed area of the lung to be resected from the total perfusion, this assessment is a valid estimate of remaining lung function following either pneumonectomy or pulmonary lobectomy.

If the postoperative predicted FEV-1 is greater than 800 ml, the patient is deemed able to undergo the proposed resection in most cases. This number is not absolute and, in some instances, the patient's weight, size, physical activity and underlying co-morbid disease presence must be considered in the decision making process. Recently it has been proposed that a predicted postoperative FEV-1 equal to 40 percent of predicted is a satisfactory cutoff point for tolerance to pneumonectomy. In addition to these spirometric assessments of pulmonary function, a postoperative predicted DLCO (diffusing capacity for carbon monoxide) of less than 35 percent also indicates an increased risk associated with major pulmonary resection.

If patients have borderline pulmonary functional studies, evaluation of their tolerance to "moderated exercise" can help the clinician to determine whether to proceed with lung resection. Simple stair climbing has been used as an exercise maneuver with reasonable predictive value for surgical risk. It has been noted that patients who are able to walk up two to three flights of steps without oxygen desaturation or physiologic decompensation usually will tolerate pulmonary lobectomy.

More objective data is obtained, however, by the performance of an "exercise test" in which maximal oxygen consumption, ventilation, arterial blood gases and continuous oxyhemoglobin saturation by pulse oximetry are measured. Such extensive physiologic testing helps to accurately assess ventilation perfusion relationships of the lung in the high-risk surgical patient. A low mortality has been noted in patients who have a maximum oxygen consumption measurement of greater than 20 ml/kg/min undergoing resectional surgery; in these patients, any form of pulmonary resection usually will be tolerated well. Intermediate risk for postoperative complications is present when oxygen consumption values are in the 15 ml/kg/min range.

Although the patient will usually tolerate pulmonary lobectomy or wedge resection, the risk of pneumonectomy may be prohibitive. A maximum oxygen consumption measurement of less than 10 ml/kg/min indicates significant impairment in oxygen delivery and should preclude considerations for any surgical resection.

As is true in most of medicine, each test result needs to be placed into the proper context with regard to the individual patient. In general, no single test can stand alone in determining the absolute risk for surgical resection. The extent of the primary disease process, the overall health and nutritional status, the underlying cardiovascular status and the magnitude of the proposed resection all are important parameters for consideration in assessing the risk for pulmonary resection in the individual patient. The tests of pulmonary function mentioned above can help the primary medical caregiver, pulmonologist and thoracic surgeons in the determination of a patient's candidacy for surgery and thus reduce the potential for postoperative morbidity and mortality following thoracic surgery.

References

1. DeMeester chapter in Roth and Ruchsdeschel. Thoracic Oncology. WB Saunders. 1989.
2. Thomas Shields. Surgical therapy for carcinoma of the lung. Clin Chest Med. 1993; 14:121-147.

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