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J Thorac Cardiovasc Surg 2004;127:1226-1227
© 2004 The American Association for Thoracic Surgery
Letter to the editor |
Department of Surgery, University of Illinois at Chicago, Chicago, Ill, USA
To the Editor:
I read with interest the article by Habib and associates1 in the June issue of the Journal concerning the role of the lowest hematocrit as the predictor variable on early and late postoperative outcomes. It is important to maintain the hematocrit within the normal range and avoid extremes. The mere effect of such a strong association begs for a prospective randomized study, as stated by the authors. However, their discussion and conclusion based on the large number of retrospective patients are incomplete. In the field of cardiovascular epidemiology, anemia occurs in 15% to 55% of patients with chronic heart failure.2 However, it is unknown whether a strong association of anemia and heart failure has any temporal and causal relation, that is, whether anemia precedes and leads to heart failure.
Nonetheless, the authors do not mention the characteristics and prevalence of heart failure in the baseline data. An argument for expanded plasma volume occurring in acute heart failure, seen in decompensated heart failure, might contribute to low hemoglobin concentrations. Such a feature is not uncommon in patients undergoing nonpercutaneous transluminal coronary angioplasty in our era.
It would seem intuitive to deduct that patients who undergo off-pump cardiac bypass surgery with minimal blood loss have less activation of the inflammatory cascade from the bypass circuit and do better. However, given the already available data from randomized trials, no difference exists between the 2.3 This suggests a minimal role for the intraoperative spectrum of hematocrit in off-pump surgery. Another important question that was not answered was whether aprotinin was given consistently, because this drug can also modify patients' outcomes.4
Habib and colleagues1 gave no information about the mean number of grafts per patient, perioperative blood loss, blood-saving techniques, and "transfusion trigger." These issues are important because there is a dose-dependent association between blood transfusion and the development of severe postoperative infection and death in patients undergoing cardiac surgery.5
Despite this omission, the overall in-hospital mortality rate is slightly higher than that reported for a similar series of 2,569 patients undergoing coronary artery bypass grafting in whom the "transfusion trigger" during cardiopulmonary bypass (CPB) was a packed-cell volume of less than 20% and mortality was defined as death during the hospital stay or within 30 days of surgery (3.6% vs 2.79%).5
Was the pump primed with blood? Administration of blood during CPB may begin a cascade of events that contributes to postoperative. Thus, whenever possible, preoperative pharmacologic therapy, but not transfusional, treatment of anemia should be used.
Also, the authors probe the data to determine any association of anemia and late mortality. It is interesting that the authors do not report the reason for patient death. Because the case mix of death is important, if cardiovascular death was the cause, did any of the patients who received more blood or had the lowest hematocrit have a lower graft patency in the short and long term?
Finally, according to the range of absolute differences in the perioperative hematocrit shown in Table 1 of the article (difference between preoperative and postoperative CPB hematocrits; range 12%-15.2%), it would seem more reasonable to use this parameter than individual values if the conclusion of increased hemodilution severity is CPB based. If the data are reanalyzed on the basis of the difference between preoperative and postoperative CPB hematocrits, it may be more important that a decrease in hematocrit of more than approximately 10% during bypass is associated with a worse prognosis than discrete values.
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  R. A. Jonas Hematocrit trial J. Thorac. Cardiovasc. Surg., May 1, 2005; 129(5): 1200 - 1200. [Full Text] [PDF]
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