Original article: cardiovascular
The association of lowest hematocrit during cardiopulmonary bypass with acute renal injury after coronary artery bypass surgery

https://doi.org/10.1016/S0003-4975(03)00558-7Get rights and content

Abstract

Background

Acute renal injury is a common serious complication of cardiac surgery. Moderate hemodilution is thought to reduce the risk of kidney injury but the current practice of extreme hemodilution (target hematocrit 22% to 24%) during cardiopulmonary bypass (CPB) has been linked to adverse outcomes after cardiac surgery. Therefore we tested the hypothesis that lowest hematocrit during CPB is independently associated with acute renal injury after cardiac surgery.

Methods

Demographic, perioperative, and laboratory data were gathered for 1,404 primary elective coronary bypass surgery patients. Preoperative and daily postoperative creatinine values were measured until hospital discharge per institutional protocol. Stepwise multivariable linear regression analysis was performed to determine whether lowest hematocrit during CPB was independently associated with peak fractional change in creatinine (defined as the difference between the preoperative and peak postoperative creatinine represented as a percentage of the preoperative value). A p value of less than 0.05 was considered significant.

Results

Multivariable analyses including preoperative hematocrit and other perioperative variables revealed that lowest hematocrit during CPB demonstrated a significant interaction with body weight and was highly associated with peak fractional change in serum creatinine (parameter estimate [PE] = 4.5; p = 0.008) and also with highest postoperative creatinine value (PE = 0.06; p = 0.004). Although other renal risk factors were significant covariates in both models, TM50 (an index of hypotension during CPB) was notably absent.

Conclusions

These results add to concerns that current CPB management guidelines accepting extreme hemodilution may contribute to postoperative acute renal and other organ injury after cardiac surgery.

Section snippets

Population selection

After Institutional Review Board approval (Duke University Medical Center IRB registry #3048-01-8R0ER, approved on August 3, 2001), demographic and outcome data were obtained from the Duke Cardiothoracic Surgery Database for all primary elective coronary artery bypass graft surgeries performed at Duke University Medical Center between February 1995 and February 1997. Patients with concomitant open chamber procedures and preoperative renal failure requiring dialysis were excluded from selection.

Results

A total of 1,404 patients undergoing primary elective CABG surgery met the criteria for analysis. Their demographic profile (Table 1) was similar to that of other previously reported populations [4]. Hematocrit, hemodynamic, and creatinine data are shown in Table 2. Among the excluded patients, 6 died within 48 hours of surgery, 7 were receiving preoperative dialysis, and 5 patients had acute renal failure requiring renal replacement therapy within 10 days of surgery.

In the primary

Comment

We found a significant association between lowest hematocrit during bypass and creatinine rise after coronary bypass surgery that is influenced by body weight. The degree to which lowest hematocrit during bypass is adversely related to postoperative creatinine rise is proportional to increasing body weight (Fig 1). The following example illustrates this finding. In a 75-kg patient there is no association between lowest hematocrit during bypass and postoperative creatinine rise. However in a

Acknowledgements

This work was supported by the Cardiothoracic Division of the Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina. The authors would like to gratefully acknowledge the contribution of Christopher Keith, and Cheryl Stetson, Department of Anesthesiology, Duke University Medical Center, in the preparation of this manuscript.

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