Prognostic Significance of Plasma Lactate Levels in Postcardiotomy Patients

Although plasma lactate levels have established prognostic value in cardiac critical care, current shock thresholds are largely derived from nonsurgical cardiogenic shock populations and may not apply to postcardiotomy patients.

The objectives of the study were to examine the association between plasma lactate levels during the first 5 postoperative days (PODs) and in-hospital mortality in postcardiotomy patients, and to compare the discriminative performance with the SCAI (Society of Cardiovascular Angiography and Interventions) SHOCK classification.

This retrospective, multicenter study included consecutive adult postcardiotomy patients from 2 academic centers between 2015 and 2024. Plasma lactate levels were measured every 6 hours, with levels of >2.0 mmol/L considered elevated. The primary endpoint was in-hospital mortality.

Among the 8,519 patients, the median age was 68 years (Q1-Q3: 59-74 years) and 72% were males. Overall in-hospital mortality was 2%. The highest levels of plasma lactate were observed on POD 2, with 46% of patients having elevated plasma lactate, declining thereafter. In-hospital mortality increased significantly at plasma lactate levels ≥5.0 mmol/L. Every 1 mmol/L increase in plasma lactate was independently associated with higher in-hospital mortality risk after multivariable adjustment. The SCAI SHOCK classification demonstrated higher discriminative performance to predict in-hospital mortality compared to plasma lactate on POD 1 (area under the curve: 0.81 vs 0.75; P = 0.050), whereas values were comparable on the following PODs.

Elevated plasma lactate levels were common after cardiac surgery and independently associated with in-hospital mortality, with risk rising exponentially from ≥5.0 mmol/L. No statistically significant differences in discriminative performance between plasma lactate, SCAI SHOCK classification, and EuroSCORE (European System for Cardiac Operative Risk Evaluation) II were observed.