Preoperative Pulmonary Function Assessment
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:
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:
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.
If the patient has CO2 retention and if it is due to an obstructive defect, the patient is not a candidate for any surgical resection. On the other hand, if the CO2 retention is due to causes other than obstruction, eg: central hypoventilation, it is not a contraindication for surgery. If the FEV1 volume is more than 1 liter, it is unlikely that the CO2 retention is due to obstructive defect.
Hypoxemia is not a consideration. It is quite possible pO2 levels can improve following resection of lung with tumor.
If only an lobectomy is planned, why should I evaluate him for pneumonectomy?
You should always estimate postoperative FEV1 with the assumption that the patient is going to have pneumonectomy. On the operating table, the surgeon may encounter an unexpected node over the pulmonary artery requiring pneumonectomy for surgical cure. If by preoperative PFT evaluation, the patient is not considered a candidate for pneumonectomy, the surgeon should be appraised of that fact. He may be forced to close the chest without attempting a curative surgical resection.
Each segment approximately contributes to 5% of pulmonary function and one can calculate the amount of FEV1 loss based on the anticipated number of segments that are going to be removed. Knowing this information, you can calculate post-op FEV1 volume for cases requiring limited resection.
FEV1 of 800 Ml
When the FEV1 is plotted against CO2 levels in patients with obstructive lung disease, CO2 retention is not seen until FEV1 levels drop below 800 ml. The expected 5 year survival of patients with CO2 retention is less than 50%. Exceptions to this rule should be considered if the patient is not obstructed. Some old women will not even have a predicted FEV1 of 1.6 liters and can have perfectly normal lungs. These patients will be able to tolerate predicted post-op FEV1 values of less than 800 ml. Thus, the criteria of post-op FEV1 volume of 800 ml as the cut off point applies only to patients with obstructive lung disease.
A good performance of MVV indicates an optimal well integrated airway, cardiac, neuromuscular, and CNS status. Surgeons like to use MVV as the most important indicator for good recovery in the post-operative period.
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