Severity and Timing of Elevated Lactate Correlates with Mortality after Cardiac Surgery

Extreme serum hyperlactatemia is common after cardiac surgery but can portend organ ischemia and demise. Thus, we sought to determine what lactate thresholds should raise concern at various timepoints after cardiac surgery. We hypothesized that post-cardiac surgery lactate correlates with operative mortality and is most worrisome outside of the immediate post-bypass period.

All adult patients at a quaternary institution undergoing CABG 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 2012-2024 were included for analysis. The correlation between lactate and operative mortality was modeled using log-PROM adjusted logistic regression.

In total, 7,292 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<0.001) 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 post-operatively. On adjusted analysis, later lactate peaks demonstrated greater model discrimination than peak lactates collected in the first post-operative 24 hours (>24 Hours AUC: 0.94; ≤24 Hours 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 are less concerning, while after the first 24 hours postoperatively, there is a strong correlation between peak lactate and mortality.