title: The association of lowest hematocrit during cardiopulmonary bypass with acute renal injury after coronary artery bypass surgery.
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.
authors.affiliation: Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina 27710, USA. staff002@mc.duke.edu
authors.forename: Madhav
authors.initials: M
authors.lastname: Swaminathan
authors.forename: Barbara G
authors.initials: BG
authors.lastname: Phillips-Bute
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Conlon
authors.forename: Peter K
authors.initials: PK
authors.lastname: Smith
authors.forename: Mark F
authors.initials: MF
authors.lastname: Newman
authors.forename: Mark
authors.initials: M
authors.lastname: Stafford-Smith
mesh_terms: D000208:Acute Disease; D002315:Cardiopulmonary Bypass; D001026:Coronary Artery Bypass / Q000009:adverse effects*; D005260:Female; D006400:Hematocrit / Q000706:statistics & numerical data*; D006801:Humans; D007430:Intraoperative Care; D007674:Kidney Diseases / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012044:Regression Analysis