Predictive value of venous bicarbonate levels for survival to hospital discharge in out-of-hospital cardiac arrest patients.

Abstract

Background: Acid-base disturbances significantly impact cardiac function and prognostic outcomes in cardiac arrest. Previous studies have highlighted the correlation between pH levels from arterial blood gas (ABG) analyses during cardiopulmonary resuscitation (CPR) in out-of-hospital cardiac arrest (OHCA) and survival outcomes. However, ABG measurements are often impractical in resource-limited settings. This study explores the relationship between serum bicarbonate levels and survival outcomes in patients with OHCA.

Methods: This retrospective cohort study examined patients with OHCA who presented at Srinagarind Hospital (Thailand) between 2015 and 2021. We analyzed venous bicarbonate levels and other laboratory markers (Na+, K+, BUN, Creatinine). Demographic and clinical data were extracted from electronic medical records. The primary objective was to assess the association between venous bicarbonate levels and survival and to determine the optimal cutoff values for predicting survival in these patients.

Results: Of the 461 identified patients, 19% survived hospital discharge. Survivors exhibited higher bicarbonate and BUN levels but lower potassium levels. Bicarbonate levels ≥ 12.6 demonstrated a sensitivity of 74% and specificity of 47%, with an 88.44% negative predictive value (NPV) for survival. A sensitivity analysis, which reclassified patients who left against medical advice as non-survivors, revealed that a bicarbonate cutoff of 13.9 mmol/L yielded the best predictive value, with a sensitivity of 93.8% and a specificity of 52.1%. Factors associated with increased survival included BUN ≥ 19.5, bicarbonate ≥ 12.6, private transport, and initial PEA or VT/VF rhythms, while potassium ≥ 5.1 decreased survival likelihood.

Conclusion: Bicarbonate levels, particularly with a threshold greater than 12.6 mmol/L, may be effective prognostic indicators. Other factors influencing survival include BUN, potassium levels, private transport, and initial cardiac rhythm. These insights can help clinicians improve resuscitation strategies and prognosis assessment, especially in resource-limited settings.