Cardiac Index - CO divided by BSA

A cardiac index calculator is a clinical tool that turns a measured cardiac output and a body surface area into a single size-normalised number, the cardiac index in L/min/m^2. The page covers the formula, a worked example, the adult reference range, and the limitations.

• • Bedside review: Drop in a measured CO and the patient's height and weight, then read the indexed value next to the raw output.
• • Sepsis and shock workup: Use the L/min/m^2 value to spot a low-output picture, then pair it with MAP and lactate.
• • Heart failure and transplant follow-up: Use it when cardiology wants a size-normalised number or when donor-recipient matching calls for a CI value.
• • Teaching and review: Use the side-by-side CO, BSA, and CI display to teach the size-normalisation step.

The cardiac index is what cardiology and intensive care teams quote for a fair comparison between a small adult, a large adult, and an athlete. Cardiac output alone is a number, so a 5 L/min reading in a 60 kg adult and a 5 L/min reading in a 110 kg adult do not mean the same thing. Dividing by BSA puts them on the same scale.

The result is a planning estimate. Decisions about inotropes, fluids, or a different line of treatment sit with the clinical team that has the full picture.

The size-normalisation step is the same one the Body Surface Area Calculator uses to return BSA in m^2 from height and weight.

The form works in three short steps. It reads the cardiac output from the selected source, computes the body surface area from the height and weight, and divides the two to return the cardiac index in L/min/m^2 with a severity band.

• CO: Cardiac output in L/min, the volume of blood the left ventricle pumps per minute.
• SV: Stroke volume in mL, the blood volume ejected by one heartbeat.
• HR: Heart rate in bpm, used with SV or the LVOT Doppler branch to compute CO.
• LVOT_diameter: Inner-edge LVOT diameter in cm at the aortic annulus on a parasternal long-axis view.
• LVOT_VTI: Velocity-time integral of the pulsed-wave Doppler signal in the LVOT, traced from the apical five-chamber view.
• BSA: Body surface area in m^2, computed from height and weight with Haycock, Mosteller, or DuBois.

The arithmetic is small. The hard part is picking the CO source that matches your data and the BSA formula that matches the worksheet. Haycock is the default on most haemodynamic worksheets, Mosteller the most common in adult dosing, and DuBois the 1916 reference still seen on older cath-lab reports.

According to StatPearls - Physiology, Cardiac Index (Patel et al., 2024), cardiac index is the cardiac output in L/min divided by the body surface area in m^2 and expressed in L/min/m^2, with a normal resting adult value of 2.5 to 4.0 L/min/m^2.

According to StatPearls - Cardiogenic Shock (Kosaraju et al., 2023), the haemodynamic criterion for cardiogenic shock includes a cardiac index at or below 2.2 L/min/m^2 with a pulmonary-capillary wedge pressure above 15 mmHg, which is why the calculator flags any reading under 2.0 L/min/m^2 as the cardiogenic shock range.

The LVOT Doppler branch uses the same continuity-equation step the Aortic Valve Area Calculator uses to return AVA from LVOT diameter and LVOT VTI.

Four concepts drive the result. Naming them keeps the L/min/m^2 value from being read as a single lab number.

The cardiac index calculator makes one core distinction visible. CO is a raw L/min number, CI is that same value divided by BSA, so the same L/min/m^2 value can be compared across body sizes and studies.

The form works from the data the bedside team or worksheet already has. Type the value that was actually measured.

1. 1 Pick the cardiac output source: Choose Direct cardiac output if the L/min value is in hand. Choose SV and HR for echo, or LVOT Doppler for a non-invasive bedside echo.
2. 2 Type the cardiac output inputs: Type the L/min value for Direct, the SV in mL and HR in bpm for SV and HR, or the LVOT diameter, VTI, and HR for LVOT.
3. 3 Enter height and weight: Type the patient's height in cm and weight in kg so the body surface area can be computed from the selected formula.
4. 4 Pick the BSA formula: Use Haycock as the default. Switch to Mosteller or DuBois if the rest of the chart uses a different formula.
5. 5 Read the result panel: Read the cardiac index, the cardiac output used, the body surface area, the severity band, and the active source.

A reader with SV 70 mL, HR 64 bpm, height 169 cm, and weight 70 kg on Haycock BSA can read CI 2.46 L/min/m^2, BSA 1.82 m^2, and severity band Low normal on the same row.

A small form that turns CO and BSA into a single L/min/m^2 value has practical advantages.

• • Three input paths: A single dropdown moves between direct CO, SV*HR, and LVOT Doppler, covering the cath-lab, the bedside echo, and the clinic worksheet.
• • Three BSA formulas: Haycock, Mosteller, and DuBois are all available, so the result aligns with the worksheet where the value will be written.
• • Severity band on the result: The 2.0 L/min/m^2 cardiogenic shock threshold, the 2.5 to 4.2 L/min/m^2 adult range, and the elevated range are returned as a clear label.
• • Active source disclosure: The result panel labels the source that produced the cardiac output.
• • Cardiovascular context: A size-normalised number sits next to the wider haemodynamic workup, including the rate from a strip, MAP from a cuff reading, and the rest of the ICU context.

The side-by-side display of CO, BSA, and CI makes the cardiac index calculator useful as a teaching aid, since the size-normalisation step stays visible.

The heart rate input sits inside the SV*HR cardiac output branch, and the ECG Heart Rate Calculator returns the rate in beats per minute from a 10-second strip or an R-R interval for the same patient.

Several factors shape the result. The most important ones sit inside the form, and a small set of caveats belong outside.

• • The calculator does not measure cardiac output. It is a planning tool that turns a measured CO into a size-normalised value, so the final decision depends on how the CO was measured.
• • The result is a single number. It does not replace MAP, lactate, central venous pressure, or the rest of the shock workup, and it is not a stand-alone resuscitation trigger.

The reference range is a starting point, not a hard threshold. A reading just below 2.5 L/min/m^2 in an athlete at rest is normal, while the same reading in a septic patient is a concern. Read the value next to the full haemodynamic picture and the trend over time.

According to ASEcho practice guidelines on valve disease and LVOT Doppler, CO is computed by multiplying the LVOT VTI by the LVOT cross-sectional area, the same continuity-equation step the cardiac index calculator uses for the LVOT Doppler input.

A low CI in a septic or shock workup pairs with a metabolic read, and the Anion Gap Calculator returns the gap from sodium, chloride, and bicarbonate.