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Ann Thorac Surg 2000;70:181
© 2000 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157-1096, USA
e-mail: jhammon{at}wfubmc.edu
After reading this manuscript, I continue to be impressed at the ability to show significant statistical correlation between small differences in intraoperative and postoperative variables in retrospective studies with very large patient numbers. Nevertheless, these investigators are to be congratulated in putting together a polished manuscript using data from more than 5,000 patients undergoing coronary artery bypass grafting in a 2-year period at the Cleveland Clinic. Using these data, they come to the conclusion that patients who arrive in the intensive care unit with a body core temperature of less than 36°C are more likely to have a poor postoperative outcome than those patients who are normothermic. It was reasonably clear, however, that those patients with a higher preoperative risk score, combined with other unfavorable preoperative characteristics (female, smokers, anemic, small body size) were at a much higher risk for mortality, in particular, if their body temperature was lower than 36°C when admitted to the intensive care unit. Thus, is this association between low body temperature and poor outcome simply a measure of overall sickness as a risk factor for operation, or is it an intraoperative variable that can be manipulated to achieve a better outcome?
To make this distinction, they need to tell us two additional pieces of data about their patients. First, what was the coldest temperature on bypass, and were cardiopulmonary bypass core temperatures uniform in all patient groups or different between different types of patients. Second, what was the postoperative cardiac output in patients after removal from cardiopulmonary bypass, and how did this correlate with their body temperature? Colder intraoperative temperatures require more significant active rewarming, which may contribute to poor postoperative outcomes, particularly in the central nervous system. Likewise, it has been observed that those patients with lower cardiac outputs postoperatively do not hold their body temperatures as well, and therefore, are often colder when they get back to the intensive care unit.
There was an interesting association between patients with hypothermic core temperatures and their time on bypass and operating times between end of bypass and intensive care unit admission. Patients with colder temperatures had shorter bypass times, but took longer to stabilize in the operating room before returning them to the intensive care unit. Does this mean that these patients had incomplete revascularization (insufficient conduit, poor distal targets) or did they have more preoperative risk factors, which swayed surgeons into a quicker operation and possibly a less complete revascularization predisposing them to lower cardiac outputs or longer operating room times for hemostasis and metabolic stabilization.
Rather than heed the call for a prospective randomized study, my notion would be for them to go back and more carefully examine those patients who had the most unfavorable outcome in the series, to determine whether cardiopulmonary bypass variables, completeness of revascularization, and certain preoperative risk factors, such as renal failure, unfavorable hematologic profiles, and other severe comorbid factors influenced the postoperative course. This could lay the groundwork for more specific studies to carefully examine intraoperative temperature management.
Related Article
Ann. Thorac. Surg. 2000 70: 175-181.
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