Introduction: Acute kidney injury (AKI) is a common and serious complication of cardiac surgery. AKI severe enough to necessitate renal replacement therapy (RRT) with hemodialysis or continuous venovenous hemodiafiltration is independently associated with mortality. None of the existing RRT risk models addresses the combined effect of hypotension pre-, during and post-cardiopulmonary bypass (CPB).
Hypothesis: Intraoperative hypotension is associated with postoperative RRT.
Methods: After institutional REB approval, we conducted a retrospective cohort study of consecutive patients who underwent cardiac surgery requiring CPB from November 1, 2009 - March 31, 2015. Excluded were those who were dialysis dependent or underwent off-pump procedures. The primary outcome was postoperative RRT. Primary exposures were the durations of MAP < 65 pre-, during and post-CPB, in minutes. All intraoperative invasive MAP measurements were recorded every 15 secs in an electronic patient record. The relationship between hypotension and RRT was modeled using multivariable logistic regression with adjustment for a priori selected risk factors.
Results: A total of 7537 patients were included in the study, of whom 558 (7.4%) required postoperative RRT. Every 10 additional minutes of MAP < 65 post-CPB was associated with an 8% increased odds of RRT (adjusted OR 1.08, 95% CI 1.05-1.12). MAP < 65 pre- and during CPB were not associated with RRT. Other independent RRT risk factors were heart failure, peripheral vascular disease, preoperative creatinine clearance < 60 ml/min, obesity, anemia, emergent surgery, preoperative cardiogenic shock, redo operations, combined CABG and valve procedures, transfusion of ≥ 4 units of packed red cells, new onset atrial fibrillation and need to reopen postoperatively.
Conclusions: Post-CPB MAP < 65 mmHg was an independent and potentially modifiable RRT risk factor. Other potentially modifiable RRT risk factors were anemia and new onset postoperative atrial fibrillation. Strategies to mitigate RRT may confer important benefits. This study provides an impetus for clinical trials to determine if specific interventions that facilitate prevention and prompt treatment of these modifiable risk factors could also mitigate the risk of RRT.