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Ann Thorac Surg 1996;62:974-975
© 1996 The Society of Thoracic Surgeons
DR MARK K. FERGUSON (Chicago, IL): I congratulate Drs Bousamra and Haasler on a very interesting paper. This represents one of the first prospective studies and is a necessary follow-up to the original reports that DLCO is an independent factor associated with the risk of morbidity and mortality in patients undergoing major lung resection.
Their most important finding in this contemporary series of patients was that DLCO correlates with morbidity, particularly pulmonary morbidity. These data reinforce the utility of assessing DLCO in estimating the risk of major lung resection.
They did not confirm that DLCO is correlated with mortality. Their mortality rate in both the low- and high-DLCO groups was quite acceptable, and it is likely that the equivalent rates were due in large part to improved postoperative care, including pain control and aggressive pulmonary toilet. However, I wonder whether the good outcomes in this study were due perhaps to spuriously low DLCO measurements in some of their patients. You mentioned that your DLCO values were corrected for anemia, and I presume that you mean corrected for hemoglobin, on all of the patients. I wonder whether they were also volume adjusted, which generally increases the DLCO value and might have put many of your patients into a low-risk category. I also note that the values of forced expiratory volume in 1 second were relatively high in both of your groups, and I would like you to reflect on whether you think this might have affected the outcome in your patients.
I think the most important original finding in your report is that with long-term follow-up, there was relative pulmonary insufficiency in a large number of patients in the low-DLCO group. These types of analyses are growing more and more important in the managed care climate in which we find ourselves. Perhaps you could speculate whether these relatively poor long-term outcomes will affect the types of operations and the patients for whom you select major lung resection in the future.
DR BOUSAMRA: Thank you, Dr Ferguson. I appreciate your remarks.
First of all, I think this study does not contradict your previous study; we looked at these patients prospectively and believed that if we anticipated complications, we might be able to normalize the mortality rate. We may have been able to reduce the mortality rate by prolonging intensive care and by treating more aggressively postoperative complications related to pain.
With regard to the measurement of diffusion capacity, this measurement is highly variable among laboratories. We did demonstrate reproducibility between the two laboratories in the study, one at the Veterans Hospital and one at the County Hospital. We did not normalize the diffusion capacity to volume. I believe that the DLCO corrected for lung volume is simply a separate value. You can choose either to measure the diffusion capacity or to normalize it to the total lung volume, and each value has merit. If the total lung volume is increased, as it probably is in most emphysema patients or in people with chronic obstructive pulmonary disease whom we are operating on, it will cause the diffusion capacity to be artificially increased, but that would not contradict our results of having a more normal operative mortality rate in patients with low DLCO.
Finally, with regard to the question of chronic dyspnea, one quarter to one third of our patients experienced substantial chronic dyspnea. I think that fact should be considered in physicians' decision-making processes when deciding both whether to offer operation to a patient and whether they should undergo limited or extended pulmonary resection. We know that patients who had simple lobectomy were less likely to have chronic dyspnea than patients who underwent pneumonectomy. It might be that people who undergo a segmentectomy or a wedge resection would be less likely to have chronic dyspnea than patients who undergo a lobectomy. I do not think that the data are so convincing that we should steer people away from resection for fear of having certain degrees of dyspnea, because the majority of these people were offered a curative resection at the price of a 25% risk of chronic dyspnea.
DR THOMAS R. J. TODD (Toronto, Ont, Canada): I think as surgeons we have come to recognize what our medical colleagues have known for a long time, and that is that respiratory rehabilitation not only produces a subjective change in dyspnea, but also can improve objective measures in some of the spirometric studies that we undertake. Given that you were looking at chronic changes in the dyspnea scales, did any of these patients at any point engage in respiratory rehabilitation programs, and did that influence the results?
DR BOUSAMRA: I did not specifically question the patients in that regard, but in my chart reviews, I did not notice that they had undergone any specific pulmonary rehabilitation process. Only a few patients returned to have postoperative spirometric functions remeasured.
DR THOMAS R. CALHOUN (Houston, TX): What was the lower limit of DLCO that you accepted, and what is the lower limit that can be accepted for resection?
DR BOUSAMRA: That is a recurring question for which I do not have a definite answer. We operated on patients whose diffusion capacity preoperatively was as low as 27% predicted for lobectomy and as low as the 40% range for pneumonectomy. We do not have a specific cutoff point. We do believe that the risk increases as the diffusion capacity decreases. But to put forward a cutoff point for DLCO would be premature because our mortality rate in this series was only 5% in patients with low DLCO.
DR THOMAS W. RICE (Cleveland, OH): Do you have any data concerning the lengths of intensive care unit and hospital stays and cost? Do you think that the equal early results are a result of two standards of care for your patients?
DR BOUSAMRA: I do think that the normalization of mortality and the near normalization of morbidity are related to increased intensive care; that is, we recognized that patients with low DLCO would be high risk.
The average lengths of stay were in the range of 12 to 14 days, 12 for the high-DLCO and 14 for the low-DLCO groups, but those data are somewhat skewed in that a large proportion of the patients were at the Veterans Hospital, where the impetus to send people home early is not the same as it is in the community.
DR RICE: What about intensive care unit stay? That is very costly.
DR BOUSAMRA: We did not measure intensive care unit stay.
DR LEWIS WETSTEIN (Freehold, NJ): I also congratulate Dr Bousamra on some extremely insightful work. We have also been very interested in minimizing postoperative morbidity and mortality after lung resections, and therefore have evaluated another index: exercise oxygen consumption. We found that as an independent variable, ie, regardless of the static spirometry (forced expiratory volume in 1 second), exercise oxygen consumption accurately predicts postoperative morbidity and mortality.
Here, however, echoing what Dr Calhoun has asked you, I see no underlying limit of DLCO. As I quickly perused your data, the postoperative morbidity reflected your preoperative forced expiratory volume in 1 second regardless of whether the DLCO was high or low. If I am correct, then, there is no lower limit of DLCO; instead, it still depends on the other physiologic indices. My question is whether postoperative morbidity still really depends on the other physiologic indices.
I commend you once again, because work such as this—dissecting out every physiologic factor and attempting to evaluate it independently—continues to dramatically affect postoperative morbidity and mortality.
DR BOUSAMRA: The DLCO tended to correlate with the spirometric values. We performed a multivariate analysis on patients with complete data and found that age and low DLCO were predictors of increased postoperative morbidity with respect to respiratory complications, but, again, we remained without a specific cutoff point for low DLCO. However, there have been multiple other studies done analyzing exercise desaturation, oxygen consumption, and the like, and it is difficult to define a single value below which patients should not be offered a potentially curative resection. The basic problem is that we do not have any single test that one can measure such that operative resection is uniformly prohibited below a certain value. I think this paper plays a role in adding to the general fund of knowledge by giving us an overall assessment of who should be operated on and who should not.
Related Article
Ann. Thorac. Surg. 1996 62: 968-974.
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