Ann Thorac Surg 2000;69:1075-1076
© 2000 The Society of Thoracic Surgeons
ORIGINAL ARTICLES: CARDIOVASCULAR
Invited commentary
Jeffrey P. Gold, MDa,
Mary E. Charlson, MDa,
Gregg S. Hartman, MDa
a Department of Cardiothoracic Surgery, Albert Einstein College of Medicine, Montefiore Medical Center, 3400 Bainbridge Ave, Fifth Floor, Bronx, NY 10467, USA
e-mail: jgold{at}montefiore.org
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Introduction
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The work presented by Hill and colleagues finds no evidence of a relationship between the mean arterial pressure (MAP) during cardiopulmonary bypass (CPB) and mortality. This study cannot be directly compared to the work of Gold and colleagues [1] as the two studies differ substantially with regard to basic design and other important methodologic issues. The first key methodologic difference involves the basic study design. In the current study, patient blood pressure [BP] was managed "at the discretion of anesthesia personnel" during CPB. Whether the anesthesiologist chose specific BP targets—high or low—for different patients was not recorded and is therefore unknown. It is not possible to know if anesthesiologists actively tried to achieve higher pressures in hypertensive patients, leading to confounding between the two variables. In the Gold study, patients were prospectively randomized preoperatively to MAP ranges (MAP 50–60 [low] or MAP 80–100 [high]) during CPB. Thus, the fundamental difference between Hill’s and Gold’s work stems from a retrospective data analysis (the current work) versus a prospective randomized, controlled blind trial (Gold’s work).
A second important difference deals with the terms "high" and "low" pressure which are used in both studies, but differ importantly in their definition. In the Hill work, MAP less than 50 (integrated area below 50 mm Hg at each minute during CPB) and MAP greater than 50 (integrated area above 50 mm Hg at each minute during CPB) are presented as "low" and "high" MAP, respectively. Further, since patients are classified according to the total minutes over 50 and under 50 it seems entirely possible that a single patient might meet the definitions for both the high and low MAP groups and thus, be counted in both groups. In the Gold study, "low" was a mean pressure during CPB of 50–60 mm and "high" was 80–100. Hill’s study does not report MAP during bypass, but instead reports the number of minutes above and below 50 mm Hg. It is conceivable that all of the patients in the Gold randomized study would be classified as "high" in Hill’s study as the two treatment groups in the Gold study were MAP 50–60 (low) and MAP 80–100 (high), making a comparison impossible.
Third, in the current study, the duration of MAP minutes above or below 50 mm Hg is directly related to the duration of CPB, which is in itself an important predictor of mortality. This is demonstrated in the Hill study and many other studies. The only other multivariate significant predictors of mortality were the Hannan score and the presence of pre-operative hypertension. These findings therefore do not support the conclusion that this study disproves an association between low MAP and mortality, as stated by the authors.
In addition, it is accepted that patients with advanced aortic atheroma grade (IV–V) by transesophageal echocardiography (TEE) have the greatest risk of major neurologic morbidity. These patients are typically hypertensive and have significant peripheral vascular disease [2]. Hill and colleagues do not provide these data for the transesophageal echocardiography (TEE) aortic atherosclerosis grade of their patients. Finally, in examining intraoperative variables relating to mortality, the authors provide no data on the cause of death–an important part of the analysis. This manuscript will help to further stimulate discussion on the interrelationship of the process related variables and their relationship to mortality associated with cardiac surgery.
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References
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Gold J.P., Charlson M.E., Williams-Russo P., et al. Improvement of outcomes after coronary artery bypass. J Thorac Cardiovasc Surg 1995;110:1302-1314.[Abstract/Free Full Text]
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Hartman G.S., Yao F.S.F., Bruefach M., et al. Severity of aortic atheromatous disease diagnosed by transesophageal echocardiography predicts stroke and other outcomes associated with coronary artery bypass grafting surgery. Anesth Analg 1996;83:701-708.[Abstract]
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Introduction
References