{
  "id": "shock-index",
  "version": "63a8f96da343",
  "status": "published",
  "name": "Shock Index Calculator",
  "question": "What is the shock index?",
  "summary": "Divides the heart rate by the systolic blood pressure to give the shock index, and shows where it sits against the 0.5 to 0.7 normal range and the 1.0 mark.",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/shock-index-calculator",
  "markdown": "https://www.acalculator.org/health/shock-index-calculator.md",
  "kind": "function",
  "method": "Shock index = heart rate (beats per minute) ÷ systolic blood pressure (mmHg), rounded once to 2 decimals, halves up; the range reads the rounded value.",
  "assumptions": [
    "The heart rate and the systolic pressure are taken at the same time.",
    "The 0.5 to 0.7 normal range and the 1.0 mark are for adults (Koch 2019); children have their own age-based marks.",
    "The index is worked from the exact typed values and rounded once to 2 decimals, halves up; the range reads the rounded value."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "hr": {
        "title": "Heart rate (beats per minute)",
        "description": "The pulse, 20 to 300 beats per minute.",
        "type": "number",
        "minimum": 20,
        "maximum": 300
      },
      "sbp": {
        "title": "Systolic, top number (mmHg)",
        "description": "The systolic blood pressure, 50 to 300 mmHg.",
        "type": "number",
        "minimum": 50,
        "maximum": 300
      }
    }
  },
  "outputs": {
    "si": {
      "label": "Shock index",
      "description": "Heart rate ÷ systolic pressure, to 2 decimals.",
      "format": "number"
    },
    "range": {
      "label": "Range",
      "description": "Where the shock index shown sits: under 0.5, 0.5 to 0.7, over 0.7 up to 1.0, or over 1.0.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "hr": 80,
      "sbp": 120
    },
    "outputs": {
      "si": 0.67,
      "range": "0.5 to 0.7 (normal range)"
    },
    "text": "A heart rate of 80 beats per minute and a systolic pressure of 120 mmHg give a shock index of 0.67."
  },
  "examples": [
    {
      "given": {
        "hr": 80,
        "sbp": 120
      },
      "expect": {
        "si": 0.67,
        "range": "0.5 to 0.7 (normal range)"
      },
      "source": "Koch 2019: SI = HR ÷ SBP; 80 ÷ 120 = 0.667, shown as 0.67 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "hr": 120,
        "sbp": 100
      },
      "expect": {
        "si": 1.2,
        "range": "Over 1.0"
      },
      "source": "Koch 2019: 120 ÷ 100 = 1.20, over 1.0 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "hr": 100,
        "sbp": 100
      },
      "expect": {
        "si": 1,
        "range": "Over 0.7, up to 1.0"
      },
      "source": "Band edge: 100 ÷ 100 = 1.00 is not over 1.0 (Koch 2019) (hand calculation in content.mdx)"
    },
    {
      "given": {
        "hr": 105,
        "sbp": 150
      },
      "expect": {
        "si": 0.7,
        "range": "0.5 to 0.7 (normal range)"
      },
      "source": "Band edge: 105 ÷ 150 = 0.70, the top of the 0.5 to 0.7 range (Koch 2019) (hand calculation)"
    },
    {
      "given": {
        "hr": 141,
        "sbp": 200
      },
      "expect": {
        "si": 0.71,
        "range": "Over 0.7, up to 1.0"
      },
      "source": "Rounded once to 2 decimals, halves up: 141 ÷ 200 = 0.705, shown as 0.71 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "hr": 50,
        "sbp": 125
      },
      "expect": {
        "si": 0.4,
        "range": "Under 0.5"
      },
      "source": "50 ÷ 125 = 0.40, under 0.5 (hand calculation in content.mdx)"
    }
  ],
  "sources": [
    "Koch E, Lovett S, Nghiem T, Riggs RA, Rech MA. Shock index in the emergency department: utility and limitations. Open Access Emerg Med. 2019;11:179-199 (abstract and introduction: SI = HR ÷ SBP, unitless, normal 0.5 to 0.7, SI above 1.0 and higher mortality; tables 1 and 2: modified, age and pediatric indices; limitations; conclusion). https://doi.org/10.2147/OAEM.S178358 (full text: https://pmc.ncbi.nlm.nih.gov/articles/PMC6698590/, retrieved 2026-10-19)"
  ],
  "related": [
    "mean-arterial-pressure",
    "pulse-pressure"
  ],
  "changelog": [
    {
      "date": "2026-11-01",
      "note": "Published after this site's editorial review against the cited sources (no clinician review); the page notices say so."
    }
  ]
}