Impact of Per-Operative Hematocrit on Postoperative Acute Kidney Injury following Cardiopulmonary Bypass

Abstract

Background: Acute kidney injury (AKI) is a common serious complication of cardiac surgery. A low hematocrit during cardiopulmonary bypass is associated with an increased risk of acute kidney injury, mainly due to a low oxygen delivery. Hemodilution is required for effective function of cardiopulmonary bypass during cardiac operations and moderate hemodilution is found to be beneficial for renal protection. But extreme per-operative low hematocrit is linked to adverse renal outcome. The main objective of this study was to determine the utility of per-operative hematocrit level in predicting AKI following cardiopulmonary bypass.

Methods: It was a cross sectional study involving fifty patients who underwent cardiac surgery supported by cardiopulmonary bypass. Group A (25 patients) had hematocrit level ≥ 24 % and group B (25 patients) had hematocrit level <24% during cardiopulmonary bypass. Each patient was categorized by Acute Kidney Injury Network (AKIN) criteria based on creatinine changes within the first 48 hours. The independent impact of lower hematocrit on post-operative acute kidney injury was assessed.

Results:  In this study of the 50 patients, 30% were diagnosed with AKI. Among those 15 patients, 4 were from group A and 11 were from group B (p= 0.031). Most of the patients developed stage 1 AKI according to AKIN criteria (80%). None developed stage 3. Post-operative creatinine was significantly higher in group B than group A. When considering baseline characteristics, we found no difference in age, gender, pre-operative LVEF, diabetes and hypertension. Regarding the intraoperative characteristics, we found no relation with CPB time and cross clamp time (p value 0.982 and 0.596 respectively) with CSA-AKI. Postoperative urine output was not also significantly involved with post-operative AKI.

Conclusion: Patients with per-operative hematocrit level above 24% during cardiopulmonary bypass had good postoperative renal function than patients with per-operative hematocrit level below 24%.

Cardiovasc j 2024; 17(1): 40-44