Difference between pre-operative and cardiopulmonary bypass mean arterial pressure is independently associated with early cardiac surgery-associated acute kidney injury

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[greater than or equal to]26 mmHg (odds ratio [OR], 2.8; 95%CI, 1.3-6.1, p=0.009) and CPB flow rate [greater than or equal to]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 [greater than or equal to]25 (OR, 4.2; 1.6-11.2, p=0.004).

Conclusion: 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.

Author: Hussein KanjiCostas SchulzeMarilou Hervas-MaloPeter WangDavid RossMohamad ZibdawiSean Bagshaw
Credits/Source: Journal of Cardiothoracic Surgery 2010, 5:71