Abstract

Background: Hypophosphatemia is a common occurrence following cardiac surgery. Hypophosphatemia is often clinically insignificant due to its mild severity and brief duration during intensive care unit (ICU) admission. Evidence to support hypophosphatemia treatment for mild and moderate hypophosphatemia remains scarce.

Objectives: This retrospective cohort study aimed to determine the prevalence of hypophosphatemia, assess the impact of phosphate supplementation on postoperative serum phosphate changes over time and identify patient characteristics that may predispose patients to hypophosphatemia in an elective on-pump cardiac surgical population.

Design: This retrospective analysis involved 1003 patients who underwent elective on-pump cardiac surgery as part of a single-center cohort, spanning surgeries performed between January 1st, 2019 and January 2nd, 2022.

Setting: At the General Hospital Maria Middelares, Gent, Belgium.

Patients: Adults undergoing elective on-pump cardiac surgery between January 1, 2019, and January 2, 2022.

Interventions: Patients were categorized into three groups based on their serum phosphate concentrations: no hypophosphatemia (> 0.8 mmol l-1), hypophosphatasemia with and without phosphate supplementation.

Main outcome measure: The primary outcome was the postoperative change in serum phosphate concentration within the first 48 hours after ICU admission.

Results: Phosphate supplementation resulted in a greater increase in serum phosphate concentration on day 1 (estimate: +0.237 ± 0.026; P < 0.001) and a less pronounced decrease on day 2 (+0.082 ± 0.030; P = 0.006). Postoperative hypophosphatemia occurred in 63.3% of this patient cohort. Higher baseline serum phosphate concentrations, female sex and longer surgical duration were associated with significant changes in postoperative serum phosphate concentrations.

Conclusion: This retrospective cohort study acknowledges hypophosphatemia as a common occurrence in adults undergoing on-pump cardiac surgery. A clear benefit of phosphate supplementation could however not be demonstrated, as serum phosphate concentrations seem to normalize, regardless of the severity of hypophosphatemia. Certain patient characteristics predispose patients to more pronounced changes in postoperative serum phosphate concentrations. Future research is needed to explore the role of these patient characteristics and to determine whether phosphate supplementation should be limited to patients with severe hypophosphatemia.

Keypoints:

• Postoperative hypophosphatemia is a common occurrence in adults undergoing on-pump cardiac surgery.
• Regardless of the severity of hypophosphatemia, phosphate supplementation appears ineffective as serum phosphate concentrations seem to normalize.
• Preoperative serum phosphate concentration, female sex, and duration of surgery were identified as significant predictors of postoperative changes in serum phosphate concentration.