The objective is to establish that after surgical resection of the lung for a tumor, there will be sufficient pulmonary reserve to keep the patient comfortable, and will not become a respiratory cripple.
You should always evaluate the patient to determine whether he could withstand pneumonectomy even if radiologically only a lobectomy or limited resection is contemplated. On thoracotomy, a surgeon may be forced to do pneumonectomy because of an unexpected node over the pulmonary artery. If you have decided the patient cannot withstand pneumonectomy, this should be addressed with the surgeon ahead of thoracotomy.
Step 1: Routine PFTs. If the patient meets the following criteria, no further workup is necessary:
|FEV1||> 2 liters|
|MVV||> 50% of predicted|
If these criteria were met and the patient were to have pneumonectomy, he would be left with at least 1 liter of FEV1 in the residual lung.
Step 2: If the patient does not meet the above criteria on routine PFT, and if the FEV1 volume is less than 2 liter, we need to perform split lung function testing. Lungs with tumor may not be contributing to total FEV1 volume and thus removal of it may not significantly affect pulmonary function. On the other hand, in some patients the diseased lung is the best lung. The best and most current method of estimating split lung function is to perform quantitative V/Q scan. Perfusion scans correlate better with pulmonary function. One can calculate the FEV1 volume of left over lung by knowing percentage of perfusion to left and right lung. For example:
|Preoperative FEV1||1.5 liters|
|Right Lung Perfusion||30%|
|Left Lung Perfusion||70%|
The tumor is in the right lung. Following resection of the right lung, we can estimate 1.5 x .7 = 1.05 liters of the left lung to remain. The minimum acceptable predicted postoperative FEV1 is 800 ml. If the predicted postoperative FEV1 volume is less than 800 milliliters the patient is not a candidate for pneumonectomy.
Step 3: If the patient has predicted post-operative FEV1 value is less than 800 ml, and if the surgeon still feels that he has a resectable lesion with a good prognosis, the next evaluation would be to occlude the pulmonary artery and measure the pulmonary artery pressure at rest and with exercise. If the pulmonary artery pressure is elevated at rest or with exercise, the patient is not a candidate for pneumonectomy. The patient obviously has no capillary bed reserve and is not able to tolerate the loss of vascular bed. He will develop cor pulmonale and the expected 5 year survival will be less than 50%. This can also be done on the operating table by clamping the pulmonary artery and measuring PA pressures.
I rarely have to go to Step 3 in my clinical practice. We need to address a few of the common questions.