Data describing the incidence of phosphate abnormalities in cardiac surgery patients and associated lactic acidosis are limited to single-center studies. This study aimed to determine the incidence of hypo- and hyperphosphatemia after procedures requiring cardiopulmonary bypass (CPB) in a multicenter cohort. We hypothesized that phosphate abnormalities would be associated with severe lactic acidosis.

This retrospective multicenter cohort study included patients ≥18 years undergoing procedures with CPB between January 2015 and December 2022 across 45 centers participating in the Multicenter Perioperative Outcomes Group. Only patients who had phosphate and lactate levels obtained within 6 h after the end of surgery were included. Multilevel logistic regression models were used to evaluate the association between phosphate abnormalities and severe lactic acidosis (lactate ≥4.0 mmol/L).

Among 34,953 cardiac surgery patients meeting inclusion criteria, 6863 (20%) had hypophosphatemia (phosphate <2.5 mg/dL) and 5013 (14%) had hyperphosphatemia (phosphate >4.5 mg/dL) within 6 h after surgery. After controlling for confounders, both hypophosphatemia and hyperphosphatemia were found to be associated with higher odds of severe lactic acidosis compared to patients with normal phosphate (OR 1.46, 95% CI: 1.33, 1.60 and OR 1.30, 95% CI: 1.16, 1.45, respectively). The odds were even higher (OR 2.53, 95% CI: 1.76, 3.63) in a subgroup of non-transplant patients with severe hypophosphatemia (phosphate <1.0 mg/dL).

Phosphate abnormalities in the immediate postoperative period after surgery with CPB are common and associated with a higher risk of severe lactic acidosis.