The Association Between Hypophosphatemia and Lactic Acidosis After Cardiac Surgery With Cardiopulmonary Bypass: A Retrospective Cohort Study

Abstract

Objectives: The clinical significance of hypophosphatemia in cardiac surgery has not been investigated extensively. The aim of this study was to evaluate the association of postoperative hypophosphatemia and lactic acidosis in cardiac surgery patients at the time of intensive care unit (ICU) admission.

Design: A retrospective cohort study.

Setting: At a single academic center.

Participants: Patients who underwent nontransplant cardiac surgery with cardiopulmonary bypass between August 2009 and December 2020.

Interventions: None.

Measurements and main results: Serum phosphate and lactate levels were measured upon ICU admission in patients undergoing nontransplant cardiac surgery with cardiopulmonary bypass. There were 681 patients in the low-phosphate (<2.5 mg/dL) group and 2,579 patients in the normal phosphate group (2.5-4.5 mg/dL). A higher proportion of patients in the low phosphate group (26%; 179 of 681; 95% CI: 23-30) had severe lactic acidosis compared to patients in the normal phosphate group (16%; 417 of 2,579; 95% CI: 15-18). In an unadjusted logistic regression model, patients in the low phosphate group had 1.9-times the odds of having severe lactic acidosis (serum lactate ≥4.0 mmol/L) when compared to patients in the normal phosphate group (95% CI: 1.5-2.3), and still 1.4-times the odds (95% CI: 1.1-1.7) after adjusting for several possible confounders.

Conclusions: Hypophosphatemia is associated with lactic acidosis in the immediate postoperative period in cardiac surgery patients. Future studies will need to investigate it as a potential treatment target for lactic acidosis.

Keywords: cardiopulmonary bypass; hypophosphatemia; insulin; lactate; lactic acidosis; phosphate.