Background: Low hematocrit level is a hematological problem that is frequently encountered during cardiopulmonary bypass (CPB) in patients undergoing on-pump coronary artery bypass grafting (CABG). This study aimed to assess the impact of low hematocrit levels (≤22%) during CPB on the adverse outcomes of on-pump CABG in a large-scale, age- and sex-adjusted Bangladeshi population.

Materials and methods: This comparative cross-sectional study recruited 350 patients, age- and sex-matched, and divided them into two groups: Group A, comprising 175 patients with a hematocrit level of ≤22% on CPB, and Group B, comprising 175 patients with a hematocrit level of >22% on CPB. Univariate analysis curtailed the risk patterns, whereas multivariate logistic regression (LR) analysis observed independent predictors of postoperative adverse outcomes.

Results: The mean age was similar between Group A and Group B (57.82 ± 6.32 vs. 56.97 ± 6.49 years, P = 0.57), with a male predominance in both groups (135 (77.1%) vs. 130 (74.3%), χ² = 0.24, P = 0.78). Univariate analysis showed that Group A had longer mechanical ventilation hours (15.09 ± 2.64 vs. 12.57 ± 3.90, P = 0.002), required more blood transfusions (3.67 ± 1.48 vs. 1.94 ± 0.79 units, P = 0.001), and had longer ICU stays (5.05 ± 0.96 vs. 3.45 ± 1.12 days, P = 0.001) compared with Group B. Postoperative complications were also more frequent in Group A, including acute kidney injury (AKI) (34.3% vs. 14.3%, χ² = 17.96, P < 0.001), deep sternal infection (8.6% vs. 2.9%, χ² = 4.29, P = 0.03), and in-hospital mortality (5.7% vs. 2.9%, χ² = 1.11, P = 0.02). In age- and sex-adjusted multivariate LR analysis, a hematocrit level ≤22% during CPB was significantly associated with adverse outcomes: higher blood transfusion requirements (odds ratio (OR) = 5.95, 95% CI 1.21-9.83, P = 0.001), longer ICU stays (OR = 3.27, 95% CI 1.06-4.24, P = 0.02), AKI (OR = 3.13, 95% CI 1.19-8.14, P = 0.01), deep sternal infection (OR = 1.18, 95% CI 1.31-6.24, P = 0.04), and in-hospital mortality (OR = 1.56, 95% CI 1.17-7.28, P = 0.03). A receiver operating characteristic (ROC) curve analysis yielded an area under the ROC curve of 0.756 (95% CI 0.65-0.86; P < 0.001) for predicting adverse outcomes, with 80.0% sensitivity and 45.0% specificity at a 22% hematocrit threshold.

Conclusions: Hematocrit levels of 22% or lower during CPB are associated with increased morbidity and mortality following on-pump CABG. Maintaining hematocrit levels above 22% during CPB is therefore recommended to improve postoperative outcomes.