Prognostic performance of the oxygenation-modified shock index in predicting in-hospital mortality in acute pulmonary embolism.

BACKGROUND: This study evaluated the prognostic performance of the Oxygenation-Modified Shock Index (O-MSI) compared with conventional SI for predicting in-hospital mortality in hospitalized PE patients. METHODS: We conducted a retrospective observational study including 358 adults hospitalized with confirmed PE between January 1, 2024, and January 1, 2026. SI (heart rate/systolic blood pressure) and O-MSI (SI divided by oxygen saturation) were calculated. RESULTS: Of 358 patients, 58 (16.2%) died during hospitalization. Non-survivors were older, more frequently had active malignancy, and showed higher heart rate, lower blood pressure, higher PESI scores, elevated troponin, BNP, lactate, and larger right ventricular diameter. Median SI and O-MSI were significantly higher in non-survivors (0.926 vs. 0.716 and 0.0106 vs. 0.00784, respectively; P < 0.001). In multivariable analysis, increasing age (OR 1.108 per year; 95% CI 1.037-1.182; P = 0.002) and higher O-MSI×1000 values (OR 1.257; 95% CI 1.079-1.465; P = 0.003) were independently associated with in-hospital mortality. O-MSI demonstrated a modestly higher discriminatory performance than SI (AUC 0.741; 95% CI 0.672-0.810) compared with SI (AUC 0.722; 95% CI 0.650-0.793; ΔAUC 0.019; P = 0.019). At optimal cut-offs, O-MSI showed sensitivity 63.2%, specificity 75.6%, and negative predictive value 91.4%. CONCLUSION: The O-MSI is a simple, bedside-applicable tool that integrates circulatory and oxygenation parameters. O-MSI demonstrated a modest but statistically significant improvement over conventional SI for predicting in-hospital mortality. As a simple bedside measure integrating circulatory and oxygenation parameters, O-MSI may provide incremental prognostic value in hospitalized patients with acute PE.