title: Difference between pre-operative and cardiopulmonary bypass mean arterial pressure is independently associated with early cardiac surgery-associated acute kidney injury.
abstract: BACKGROUND
  Cardiac surgery-associated acute kidney injury (CSA-AKI) contributes to increased morbidity and mortality. However, its pathophysiology remains incompletely understood. We hypothesized that intra-operative mean arterial pressure (MAP) relative to pre-operative MAP would be an important predisposing factor for CSA-AKI.
  
  
  METHODS
  We performed a prospective observational study of 157 consecutive high-risk patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). The primary exposure was delta MAP, defined as the pre-operative MAP minus average MAP during CPB. Secondary exposure was CPB flow. The primary outcome was early CSA-AKI, defined by a minimum RIFLE class - RISK. Univariate and multivariate logistic regression were performed to explore for association between delta MAP and CSA-AKI.
  
  
  RESULTS
  Mean (± SD) age was 65.9 ± 14.7 years, 70.1% were male, 47.8% had isolated coronary bypass graft (CABG) surgery, 24.2% had isolated valve surgery and 16.6% had combined procedures. Mean (± SD) pre-operative, intra-operative and delta MAP were 86.6 ± 13.2, 57.4 ± 5.0 and 29.4 ± 13.5 mmHg, respectively. Sixty-five patients (41%) developed CSA-AKI within in the first 24 hours post surgery. By multivariate logistic regression, a delta MAP≥26 mmHg (odds ratio [OR], 2.8; 95%CI, 1.3-6.1, p = 0.009) and CPB flow rate ≥54 mL/kg/min (OR, 0.2, 0.1-0.5, p < 0.001) were independently associated with CSA-AKI. Additional variables associated with CSA-AKI included use of a side-biting aortic clamp (OR, 3.0; 1.3-7.1, p = 0.012), and body mass index ≥25 (OR, 4.2; 1.6-11.2, p = 0.004).
  
  
  CONCLUSIONS
  A large delta MAP and lower CPB flow during cardiac surgery are independently associated with early post-operative CSA-AKI in high-risk patients. Delta MAP represents a potentially modifiable intra-operative factor for development of CSA-AKI that necessitates further inquiry.
authors.affiliation: Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Canada.
authors.forename: Hussein D
authors.initials: HD
authors.lastname: Kanji
authors.forename: Costas J
authors.initials: CJ
authors.lastname: Schulze
authors.forename: Marilou
authors.initials: M
authors.lastname: Hervas-Malo
authors.forename: Peter
authors.initials: P
authors.lastname: Wang
authors.forename: David B
authors.initials: DB
authors.lastname: Ross
authors.forename: Mohamad
authors.initials: M
authors.lastname: Zibdawi
authors.forename: Sean M
authors.initials: SM
authors.lastname: Bagshaw
mesh_terms: D058186:Acute Kidney Injury / Q000209:etiology / Q000503:physiopathology*; D000368:Aged; D000369:Aged, 80 and over; D001794:Blood Pressure; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D002315:Cardiopulmonary Bypass / Q000009:adverse effects; D015984:Causality; D005260:Female; D006801:Humans; D008297:Male; D057234:Preoperative Period; D011446:Prospective Studies
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