🫀 Modified Shock Index (MSI)
The Modified Shock Index (MSI) is the ratio of heart rate to mean arterial pressure, a simple early marker of circulatory instability that outperforms the conventional shock index in some cohorts.
Modified Shock Index (MSI)
Heart rate (bpm)
Systolic BP (mmHg)
Diastolic BP (mmHg)
When to use
Enter heart rate and systolic/diastolic blood pressure; the tool computes MAP and MSI. A higher MSI signals greater hemodynamic compromise and worse outcomes.
How it works
MAP = (SBP + 2×DBP)/3. MSI = HR / MAP. Reference: < 0.7 low normal · 0.7–1.3 normal · > 1.3 suggests hypoperfusion / increased mortality risk.
Key points
- Because MAP weights diastolic pressure, MSI captures both pump rate and perfusion pressure, making it more sensitive than HR/SBP for occult hypoperfusion. (original synthesis · not guideline verbatim)
- MSI > 1.3 has been associated with higher mortality and ICU admission across trauma, sepsis, and obstetric-hemorrhage cohorts.
- It is confounded by beta-blockers, pacing, and pre-existing hypertension; treat it as a trend and trigger, not a standalone diagnosis.
References
- Liu YC, et al. Modified shock index and mortality rate of emergency patients. World J Emerg Med. 2012;3(2):114-117.
- Singh A, et al. Utility of the Shock Index and Modified Shock Index. J Emerg Trauma Shock. 2014;7(2):84-89.
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.