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Ann Thorac Surg 1995;60:609
© 1995 The Society of Thoracic Surgeons
DR HANI SHENNIB (Montreal, PQ, Canada): I enjoyed your presentation, and I have several questions. First, I am concerned about your last statement that you would eliminate the need for doing pulmonary function tests and that perhaps you can determine the immediate outcome of operation without them. You still need pulmonary function tests to look at the long-term effects of operation, eg, functional ability of patients after resection.
My question is, In patients who have had desaturation of less than 90%, have you been able to discriminate outcome based on whether desaturation occurred at any level of function? For example, did the patients with desaturation at rest do worse than the ones with desaturation when they climbed three flights of stairs?
DR RAO: Although we recorded the phase at which a patient had desaturation during exercise oximetry, we did not analyze the results subdivided to the phase of desaturation. Subdividing the analysis, given that only 65 patients showed desaturation with an even smaller number sustaining complications, would not have yielded significantly useful information. Certainly in designing a prospective trial, stratification based on the phase of desaturation may yield additional important information. In an effort to examine levels of sensitivity and specificity, we did evaluate different cutoffs for both tests. Changing the cutoffs only slightly altered the sensitivity, the specificity, and the positive and negative predictive values for each screening test. There were no changes with respect to the relative abilities of oximetry and spirometry (forced expiratory volume in the first second [FEV1]) in predicting outcomes irrespective of the cutoffs chosen.
In terms of long-term functional outcome after lung resection, we believe that exercise oximetry may provide more information than spirometry in regard to activities of daily living. However, we did not examine this outcome in this study.
DR DANIEL L. MILLER (Louisville, KY): Doctor Rao, did you look at the recovery of desaturation in your patients, as this can be a very important determinant of the functional reserve of the patient? If so, did that make a difference in your complication rate? Also, in the patients who required longer periods of desaturation recovery, did they undergo preoperative pulmonary rehabilitation to minimize postoperative complications?
DR RAO: For the purposes of this study, we did not look at the rate of recovery from desaturation. Our physical therapist does comment on this factor for each individual patient, and further investigation may reveal this to be an important marker of underlying pulmonary function. At our institution, patients who are identified as high risk by oximetry, spirometry, or both do undergo a period of respiratory rehabilitation for approximately 4 weeks.
DR MALCOLM M. DeCAMP, JR (Boston, MA): I very much enjoyed your presentation. I think you have highlighted one of the problems in that the simple-to-perform assessments of pulmonary function have not been terribly predictive of which patients will have bad outcomes. Everyone is achieving pretty good outcomes with modern techniques, such as anesthesia management, epidurals, and early ambulation. I wonder if you would comment on what you would do differently now that you have identified perhaps oximetry as a screening tool. What are you going to do for that subgroup of patients you have designated as high risk? Are you going to recommend formal exercise testing in the catheterization laboratory to measure oxygen uptake, other tests that might help us decide whether they have truly inoperable disease, or ways we might be able to get them through their operation more safely?
DR RAO: Thank you. I agree with you. The data presented here support the use of exercise oximetry as a screening test for all patients. Once the high-risk patient is identified, further investigation is warranted to determine the extent and reversibility of the pulmonary disease and to look for comorbid conditions such as cardiac disease. Other more sophisticated measures of pulmonary function such as calculating the predicted postoperative FEV1 using nuclear perfusion scans or maximal oxygen consumption testing can then be used to further characterize these high-risk patients. Exercise oximetry may not be the perfect screening test, but it is a simple and inexpensive tool to evaluate all patients prior to operation. The routine use of pulmonary function tests may not be warranted for all patients referred for pulmonary resection once a standard exercise test procedure has been instituted.
DR HOWARD S. BROWN (Atlanta, GA): Would it not be better to use a predicted percentage rather than stating a specific liter value such as 1.5 L? I think that a percentage of normal would be a better predictor because 1.5 L in a person 190 cm tall is very different from the same value in a person 155 cm tall. Also, I believe that calculating predicted postoperative values using quantitative lung scans to predict values depending on the amount removed would be better than stating a specific preoperative liter figure.
DR RAO: We did not look at the percent predicted FEV1 as a variable. As I previously indicated, there were 23 patients with an FEV1 of less than 1.3 L. I think this group of patients is very similar to patients with a percent predicted FEV1 of less than 75%. Clearly, this represents a group of high-risk patients, yet FEV1 failed to predict any postoperative outcome. In terms of the predicted postoperative FEV1, I believe that the study by Sugarbaker and associates in Boston examined that variable. Doctor Sugarbaker provided their raw data in the report, and our analysis of these data revealed that the sensitivity of that test was in the neighborhood of 55%, which is very comparable with the results we obtained with oximetry.
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