Extreme serum hyperlactatemia is common after cardiac surgery but can portend organ ischemia and mortality. Thus, we sought to determine which lactate thresholds warrant concern at various time points after cardiac surgery. We hypothesized that post–cardiac surgery lactate correlates with operative mortality and is most strongly associated with risk outside of the immediate post–bypass period.

All adult patients at a quaternary institution undergoing coronary artery bypass graft and/or valve procedures with recorded Society of Thoracic Surgeons Predicted Risk of Mortality (PROM) scores, peak postoperative lactate, and time to postoperative peak lactate from 2012 to 2024 were included for analysis. The correlation between lactate and operative mortality was modeled using logit-transformed PROM (log-PROM)–adjusted logistic regression.

In total, 7292 patients (PROM score, 2.4%) met inclusion criteria (median lactate, 2.3 mmol/L). The operative mortality rate was 1.4% (n = 103). On log-PROM–adjusted analysis, a postoperative peak lactate >5 mmol/L (P < .001) was associated with increased mortality risk (mortality rate, 9.8% [66/672]). Moreover, mortality risk dramatically increased with a postoperative peak lactate ≥7 mmol/L (mortality rate, 17.5% [52/297]). Only 6% (n = 444) of patients experienced peak hyperlactatemia >24 hours postoperatively. On adjusted analysis, later lactate peaks demonstrated greater model discrimination than peak lactates collected in the first postoperative 24 hours (>24-hour area under curve [AUC], 0.94; ≤24-hour AUC, 0.79).

Peak lactate values >5 mmol/L correlate with increased mortality risk. Mortality risk increases drastically at lactates above 7 mmol/L. Early hyperlactatemia is less concerning, while after the first 24 hours postoperatively, there is a strong correlation between peak lactate and mortality.