Acidemia is associated with a higher mortality independently of lactate levels in cardiac arrest patients

Abstract Background Acidemia is associated with a higher mortality risk in several shock types. In the current work, we analyzed the predictive value of pH additional to serum lactate levels in forecasting survival and neurological outcome of cardiac arrest (CA) patients following cardiopulmonary resuscitation (CPR). Methods The predictive accuracy of initial pH and lactate levels was retrospectively analyzed in non-traumatic CA patients admitted to a high-volume center in Germany. Independent association between these biomarkers and 30-day mortality was assessed using receiver operating characteristic (ROC) curves. Patients were stratified according to the Youden Index calculated for lactate, and the clinically established threshold of 7.2 for pH and 30-day mortality was assessed. An independent association between pH and survival was established using Cox regression analyses with adjustments for several CPR-related variables. Preliminary findings were validated in a database containing over 2000 patients from multiple intensive care units from the United States of America. Results Initial lactate and pH levels proved accurate independently in predicting in-hospital mortality (area-under-curve of 0.83 and 0.75, respectively, p0.0001). As expected, patients with pH levels≤7.2 had significantly higher mortality in each lactate stratification group. The hazard ratios (HR) for pH ranged between 0.1 – 0.3 and were significant after adjustment for lactate, age, CPR duration, and type of cardiac arrest (all p0.0001). When applying individual thresholds from this analysis to patients in the eICU database, a pH≤7.2 accurately distinguished groups at higher mortality risk in each analyzed lactate group. Cox regression showed here HR of 0.14 (p0.0001) for each pH unit after lactate, age, and initial creatinine level adjustment. No significant association was observed between initial pH levels and neurological outcomes in the German colective. Correlation analyses showed only a mild relationship between lactate and pH levels. Conclusion pH levels augment the predictive power of lactate, with values of pH≤7.2 marking a higher mortality risk in cardiac arrest patients, independently of lactate levels. pH does not accurately forecast neurological development in CPR survivors.