Objective:

To investigate the time-dependent interplay between early metabolic failure and delayed systemic inflammatory response in 24-h conditional survivors of post-cardiac arrest syndrome (PCAS) and to develop a non-linear risk stratification tool using CART analysis based on serial lactate and procalcitonin (PCT) kinetics.

Approach:

• Study Design: Retrospective cohort study including 158 24-h conditional survivors of PCAS, monitoring arterial lactate and PCT levels at specified time points.
• Data Handling: Missing data were managed using multiple imputation by chained equations (MICE).
• Primary Endpoint: In-hospital mortality was the primary endpoint, with a landmark analysis performed at 24 h to address immortal time bias.

Key Findings:

• In-hospital mortality rate was 70.9%.
• Non-survivors had higher rates of non-shockable rhythms, longer CPR durations, and higher APACHE II scores.
• Persistent hyperlactatemia at 48 h was a significant independent predictor of mortality (OR: 1.92; 95% CI: 1.22–3.01).
• CART analysis identified a high-risk phenotype (T0 lactate >5 mmol/L AND T24 PCT > 5.5 ng/mL) associated with a 92% mortality risk.

Interpretation:

Persistent metabolic debt at 48 h is an independent biochemical indicator of poor outcome in 24-h conditional survivors of PCAS, and integrating serial lactate and PCT kinetics through CART analysis identifies a high-risk phenotype.

Limitations:

• Retrospective nature of the study may introduce bias.
• Single-center study limits generalizability of findings.

Conclusion:

The CART model may assist in identifying high-risk patients.