Objective:

To develop and externally validate a model based on the lactate-to-invasive diastolic blood pressure ratio (LDR) for predicting 28-day mortality in septic shock patients with invasive arterial monitoring, emphasizing its potential impact on clinical decision-making.

Key Findings:

• 28-day mortality was 29.7% in the development cohort and 26.0% in the validation cohort.
• LDR × 100 showed AUCs of 0.726 (95% CI 0.657–0.786) and 0.714 (95% CI 0.674–0.753) for the development and validation cohorts, respectively.
• LDR × 100 improved AUC compared to lactate alone, though the improvement was small in external validation (ΔAUC +0.029, 95% CI +0.006 to +0.051).
• External validation showed calibration drift, indicating local recalibration is necessary for absolute risk estimates.

Interpretation:

LDR × 100 serves as a simple bedside marker for risk stratification in septic shock patients with invasive monitoring, particularly in the lactate gray zone, with implications for addressing calibration drift.

Limitations:

• Calibration drift observed in external validation.
• Selection bias due to exclusion of patients without invasive DBP measurements, which may affect generalizability.
• Observational design necessitates prospective validation before clinical adoption.

Conclusion:

LDR × 100 is a complementary tool for risk assessment in septic shock patients with invasive monitoring, requiring further validation for clinical use, particularly due to calibration drift and selection bias.