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Calcimator

Cardiac Output Calculator

Calculate cardiac output using the Fick equation and stroke volume method. Also estimates cardiac index and systemic vascular resistance.

About this calculator

This calculator computes cardiac output two independent ways so they can be cross-checked against each other, plus two commonly derived hemodynamic figures. Cardiac Output (Fick) applies the Fick principle -- CO = VO2 / [(CaO2 - CvO2) x 10] -- where oxygen consumption divided by the arteriovenous oxygen content difference (converted from mL/dL to L/min) gives the blood flow needed to deliver that much oxygen to the tissues. Cardiac Output (HR x SV) instead multiplies Heart Rate by Stroke Volume directly and is entirely independent of the Fick inputs -- it uses none of Oxygen Consumption, Arterial O2 Content, or Venous O2 Content, and the Fick side of the calculation is likewise unaffected by Heart Rate or Stroke Volume. In real clinical use these two methods should roughly agree; a large discrepancy between them usually signals a measurement error in one of the five inputs rather than a genuine physiological finding.

Cardiac Index divides Cardiac Output (Fick) by a fixed 1.8 m² body surface area assumption rather than the patient's own calculated BSA, and SVR (estimated) uses a fixed assumed MAP (80 mmHg, the low-normal end of the typical ~70-100 mmHg range) and CVP (5 mmHg) rather than the patient's actual measured pressures -- both of those downstream figures are only as meaningful as how close the real patient's BSA, MAP, and CVP happen to be to those textbook averages, and even at this calculator's own default inputs, SVR can land right at the edge of the "Normal: 800-1200" range it displays rather than comfortably inside it. If Venous O2 Content is entered equal to or greater than Arterial O2 Content -- physiologically impossible, since venous blood cannot carry more oxygen than arterial blood, but not blocked by these two inputs' independent ranges -- Cardiac Output (Fick), Cardiac Index, and SVR (estimated) all show "N/A" instead of a number, since the Fick equation has no valid answer for a non-positive arteriovenous difference. This calculator is an educational and cross-checking aid, not a substitute for clinical judgment or a validated bedside monitor; any value outside normal physiological ranges warrants direct clinical assessment.

Inputs

Results

Cardiac Output (Fick)

5 L/min

Cardiac Output (HR x SV)5.04 L/min
Cardiac Index2.78 L/min/m²
SVR (estimated)1,200 dynes·s/cm⁵
Assumed MAP (fixed, not calculated)80 mmHg
How to Use This Calculator
  1. Enter oxygen consumption (VO₂) in mL/min from Fick measurement or estimate.
  2. Input arterial oxygen content (CaO₂) and venous oxygen content (CvO₂) in mL/dL from blood gas data.
  3. Enter heart rate in beats per minute and stroke volume in mL.
  4. Review the two Cardiac Output values (L/min) — one from the Fick equation, one from the HR × SV method — plus the estimated Cardiac Index, SVR, and MAP.
  5. Use these values alongside clinical assessment — values outside normal ranges require physician review.

What each input means

Oxygen Consumption (mL/min)
VO₂: total body oxygen consumption. Normal resting: 200-300 mL/min.
Arterial O₂ Content (mL/dL)
CaO₂: oxygen content of arterial blood. Normal: 18-21 mL/dL.
Venous O₂ Content (mL/dL)
CvO₂: oxygen content of mixed venous blood. Normal: 13-16 mL/dL.
Heart Rate (bpm)
Heart rate in beats per minute.
Stroke Volume (mL)
Volume of blood ejected per heartbeat. Normal: 60-100 mL.

What each result means

Cardiac Output (Fick)
Normal: 4-8 L/min.
Cardiac Index
Normal: 2.5-4.0 L/min/m². Divides Cardiac Output (Fick) by a fixed 1.8 m² body surface area assumption, not your patient's actual measured BSA.
SVR (estimated)
Normal: 800-1200 dynes·s/cm⁵. Uses a fixed assumed MAP (80 mmHg) and CVP (5 mmHg), not your patient's actual measured pressures -- see the MAP output below.
Assumed MAP (fixed, not calculated)
A fixed textbook average (80 mmHg, the low-normal end of the typical ~70-100 mmHg range) used only as the MAP term in the SVR estimate above -- this number never changes and is not derived from anything you enter. Substitute your patient's real measured MAP when calculating SVR by hand.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    5 parameters
    Oxygen Consumption (mL/min) = 250, Arterial O₂ Content (mL/dL) = 20, Venous O₂ Content (mL/dL) = 15, Heart Rate (bpm) = 72, Stroke Volume (mL) = 70 = 5 input(s) provided
  2. Calculate Cardiac Output
    Cardiac Output
    5 = 5
  3. Calculate Cardiac Output
    Cardiac Output
    5.04 = 5.04
  4. Calculate Cardiac Index
    Cardiac Index
    2.78 = 2.78

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why are there two different Cardiac Output values, and should they match?

Cardiac Output (Fick) and Cardiac Output (HR x SV) are two independent ways of arriving at the same physiological quantity -- one from oxygen delivery, one from the heart's own stroke mechanics -- computed from entirely separate sets of inputs. In a real patient they should land reasonably close to each other; a large gap between them more often points to an error or artifact in one of the five measurements (blood gas sampling, oxygen consumption estimate, or hemodynamic monitoring) than to two genuinely different true cardiac outputs.

Why does Cardiac Index use a fixed 1.8 m² instead of my patient's actual body surface area?

This calculator doesn't collect height or weight, so it applies 1.8 m², a commonly cited population-average adult BSA, rather than computing your specific patient's real BSA from a formula like DuBois. For a patient who is notably larger or smaller than average, the true Cardiac Index will differ meaningfully from what this calculator shows -- recompute it using the patient's actual measured or calculated BSA before relying on it clinically.

Where do the MAP and CVP values used in the SVR calculation come from?

They're fixed textbook averages (80 mmHg, the low-normal end of the typical ~70-100 mmHg range, for MAP; 5 mmHg for CVP) built into the formula, not values derived from anything you enter -- this calculator has no MAP or CVP input at all. Even with these fixed low-normal figures, SVR (estimated) at this calculator's own default inputs lands right at the top edge of the "Normal: 800-1200" range it displays, so a real patient's actual MAP and CVP -- which can run higher -- may push the estimate above normal even when Cardiac Output itself is unremarkable; substitute the patient's real MAP and CVP when calculating SVR for actual clinical use.

Does Heart Rate or Stroke Volume affect the Fick-based Cardiac Output?

No -- Cardiac Output (Fick) is computed entirely from Oxygen Consumption, Arterial O₂ Content, and Venous O₂ Content, and does not reference Heart Rate or Stroke Volume anywhere in its formula. Likewise, Cardiac Output (HR x SV) does not use any of the three Fick inputs -- the two methods are calculated completely independently from separate physiological data.

Is this calculator a substitute for a bedside hemodynamic monitor or clinical judgment?

No -- it's an educational tool for practicing the Fick and stroke-volume calculation methods and cross-checking them against each other, not a validated clinical device. Several of its outputs (Cardiac Index, SVR) lean on fixed population-average assumptions rather than a specific patient's actual measurements, so any result outside normal physiological ranges, or any large mismatch between the two Cardiac Output values, warrants direct clinical assessment rather than being acted on alone. If you enter a Venous O2 Content equal to or greater than Arterial O2 Content -- physiologically impossible, since venous blood can't carry more oxygen than arterial blood -- Cardiac Output (Fick), Cardiac Index, and SVR (estimated) all show "N/A" rather than a misleading zero, since the Fick equation has no valid answer at that input combination.

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