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Ann Thorac Surg 1995;59:1433-1434
© 1995 The Society of Thoracic Surgeons
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Introduction |
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 Top Introduction |
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DR DUKE E. CAMERON (Baltimore, MD): I enjoyed your paper very much. I have a question that concerns how well matched these two groups were. You cite in the abstract a number of variables, saying that both groups were well matched, but you did not cite one of the most important in terms of predicting stroke, that is whether or not there is a history of stroke. Are these two groups the same in terms of previous stroke or was previous stroke an exclusion criteron?
DR CRAVER: No, we looked at that. There was no significant difference in their incidence of prior cerebral events or risk factors for cerebral events.
DR CAMERON: Similarly, carotid bruits were not mentioned as to whether or not they played a role.
DR CRAVER: We have really not paid a whole lot of attention to asymptomatic carotid bruits in terms of documenting them. We have taken the clinical tack that if patients are not symptomatic at the time, we do not work up asymptomatic carotid bruits. If they have had a previous event or if they have ongoing cerebral symptoms, then we do work those up. With findings of significant lesions, we electively have the vascular surgeons perform a carotid endarterectomy under local anesthesia, usually 2 days before the coronary bypass operation. With that we have had no increase in perioperative strokes.
DR CAMERON: Finally, did you evaluate neurocognitive function, and how did you define stroke?
DR CRAVER: We evaluated the neurocognitive function very carefully. Christine Morrow, who is an anesthesiologist with a special interest in this area, in the first group had 150 randomized patients picked with detailed neurologic examination involving psychometric testing by trained people preoperatively, immediately postoperatively in the hospital, and at 4 weeks postoperatively in the follow-up visit, and there was no significant difference. In the latter group, that degree of neuropsychometric testing was not done.
The strokes we identified as focal neurologic deficits or psychological aberrations, confusional states, et cetera. In the warm group the incidence of focal deficits was 3.3%, which was significant. The others were 1.2%. In the cold group the incidence of focal deficits was 1.1% with virtually no confusional states.
DR CHRISTOPHER J. KNOTT-CRAIG (Oklahoma City, OK): I enjoyed your paper very much. Do you have any suggestions or recommendations to make with regard to the temperature to which you rewarm your patients? In other words, do you think it is beneficial to rewarm them to a lower core temperature based on the findings that you presented today?
DR CRAVER: We rewarm them slowly. We do not let the perfusate exceed 38°C, and we try to get them to 36°C systemically before coming off bypass, but it was a matter of warming patients slowly internally. And we are willing to take the time to do it, which was demonstrated by extended bypass interval.
DR CHARLES C. CANVER (Madison, WI): Your results are somewhat surprising. In the warm and cold group of patients your cross-clamp time was essentially similar (40 minutes versus 46 minutes). If one agrees with your conclusion, 46 minutes on cardiopulmonary bypass would make a significant difference in cerebral protection between warm and cold groups. In our practice, we do not see any significant neurologic dysfunction in cold or warm cardioplegia patients when the bypass time is 60 minutes or less. However, we see increasing numbers of neurologic complications in patients undergoing combined coronary bypass and valve operations, redo procedures, and operations where prolonged cardiopulmonary bypass was required.
My question is, do you have any data that show the incidence of neurologic events in isolated coronary artery bypass grafting, aortic valve replacement, mitral valve replacement, or combined operations in reference with the cold and warm temperatures? I think if you can show that there is significant difference among those subsets of patients, that would be more convincing evidence for your conclusion.
DR CRAVER: Initially we tried to apply the warm cardioplegia program to everybody. In using warm techniques in the patients who have combined aortic valve disease and coronary disease (who I think are at increased risk for stroke) I had 2 patients of the first 20 who had no reason in the world to have a stroke but had a devastating stroke. So, I stopped, and it is just not something I think is good. I agree with the point you made: as patients have ischemic intervals that extend longer, to an hour, hour and a half, 2 hours, it is certainly more important during that time to lower the temperature. I think the incidence of strokes occurs related to bypass. It is increased by the lengthening of bypass. The longer bypass is the more risk you have; the emboli from the perfusion tubing, the atheroemboli from whatever source, air, et cetera. You have some degree of exposure no matter how long or short patients are on the pump, and the longer it is, the more the exposure. I think what we are demonstrating and what we feel is the case is that a brain that is warm is more subject to injury from these incidental events, whereas a brain that is cooler can tolerate them better. This was also brought out in that 7 of the 23 patients who had strokes in the warm group died of their stroke or died of complications of stroke, whereas of the 6 patients in the cold group who had strokes, none of them died. They all had focal deficits that got better; they went to rehabilitation and are improving. The devastating nature of the ischemic injury that occurs to a warm brain is truly magnified. Laboratory data suggest that too.
DR RICHARD E. MICHALIK (Kingsport, TN): I know that there have been a lot of different approaches to neurologic evaluation of patients at Emory before operation. Did you go back and look at the people who had stroke and do some duplex scans or anything like that? The fact that there seems to be an older group here makes me sort of wonder. And the other thing was, was I right, the patient who spends a few days way, way out in left field, is that defined as a neurologic event?
DR CRAVER: When we looked at the cold group versus the warm group in Dr Martin's paper, there was no difference in the neurologic risk or work-ups in either groups. In the latter group that we did, we would screen them ahead of time. If they had a symptomatic carotid bruit, they had those worked up and dealt with, and then they were entered in the trial just as though they were the elective bypass patients, and those were all included. Patients were not removed if they had a neurologic risk.
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