Shock Index Calculator

The standard Shock Index (SI) is calculated by dividing the patient's heart rate (HR) by their systolic blood pressure (SBP): SI = HR / SBP. A normal adult resting shock index typically ranges from 0.5 to 0.7. Values climbing above 0.9 often signal significant hypovolemia or occult shock, prompting urgent intervention. Additional advanced metrics include the Modified Shock Index (MSI), which substitutes systolic pressure with Mean Arterial Pressure (MAP), and the Age-Adjusted Shock Index (ASI), which multiplies the baseline SI by the patient's age to account for physiological aging and baseline medication use.

Consider an emergency department patient presenting with a heart rate of 110 beats per minute and a systolic blood pressure of 100 mmHg. First, we calculate the standard Shock Index by dividing 110 by 100, which yields 1.10. Because this value exceeds the normal threshold of 0.7, it immediately alerts the medical team to underlying circulatory compromise. Next, if the patient's diastolic blood pressure is 70 mmHg, we calculate Mean Arterial Pressure as MAP = (2(70) + 100) / 3 = 80 mmHg. The Modified Shock Index then becomes 110 / 80 = 1.37, further emphasizing the severity of the hemodynamic instability.

Always interpret shock index values within the context of the patient's baseline medications, such as beta-blockers, which can artificially blunt heart rate responses. Serial measurements provide far more diagnostic utility than a single isolated reading; tracking the trajectory of the index over time highlights whether resuscitation efforts are succeeding. Finally, integrate the age-adjusted index when evaluating older adults, as normal age-related cardiovascular stiffening can mask standard warning signs.