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Cardiac Output Calculator

Calculate cardiac output, cardiac index, stroke volume, SVR, and PVR using Fick, thermodilution, or HR×SV methods with BSA-indexed values.

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bpm
mL/beat
mL/min
g/dL
%
%
mmHg
mmHg
L/min
bpm
Body Surface Area (for indexing)
kg
cm
Vascular Resistance Inputs (optional)
mmHg
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About

Cardiac output (CO) quantifies the volume of blood ejected by the left ventricle per minute, typically 4 - 8 L/min in adults at rest. Errors in hemodynamic assessment propagate directly into fluid management, vasopressor titration, and mechanical support decisions. A 15% measurement error in CO can reverse the clinical interpretation of a shock state from distributive to cardiogenic. This calculator implements three standard methods: the Fick principle using arteriovenous oxygen difference, the indicator-dilution (thermodilution) integral, and the direct heart-rate - stroke-volume product. All results are indexed to body surface area (BSA) via the DuBois formula to yield cardiac index (CI) and stroke volume index (SVI).

Derived resistances - systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) - require mean arterial pressure, central venous pressure, mean pulmonary artery pressure, and pulmonary capillary wedge pressure inputs. Note: this tool assumes steady-state conditions, no significant intracardiac shunt, and stable hemoglobin concentration. In tricuspid regurgitation, thermodilution systematically underestimates CO. Always correlate computed values with clinical context.

cardiac output cardiac index fick method hemodynamics stroke volume SVR PVR BSA thermodilution critical care

Formulas

The heart-rate - stroke-volume method computes cardiac output directly:

CO = HR × SV1000

where CO is in L/min, HR is heart rate in bpm, and SV is stroke volume in mL/beat.

The Fick principle relates oxygen consumption to arteriovenous oxygen difference:

CO = VO2CaO2 − CvO2

Oxygen content is computed as:

CaO2 = (1.34 × Hb × SaO2100) + (0.003 × PaO2)

where 1.34 is Hüfner's constant in mL O2/g Hb and 0.003 accounts for dissolved oxygen. The venous content CvO2 uses SvO2 and PvO2 analogously.

Body surface area follows the DuBois formula:

BSA = 0.007184 × W0.425 × H0.725

where W is weight in kg and H is height in cm. Cardiac index and stroke volume index are then:

CI = COBSA    SVI = SVBSA

Vascular resistances use the hydraulic analogue of Ohm's law, multiplied by 80 to convert mmHg⋅min/L to dyn⋅s/cm5:

SVR = (MAP − CVP) × 80CO    PVR = (MPAP − PCWP) × 80CO

Reference Data

ParameterSymbolNormal RangeUnitClinical Context
Cardiac OutputCO4.0 - 8.0L/minGlobal LV pump function
Cardiac IndexCI2.5 - 4.0L/min/m2BSA-normalized output
Stroke VolumeSV60 - 100mL/beatVolume per contraction
Stroke Volume IndexSVI33 - 47mL/beat/m2BSA-normalized SV
Heart RateHR60 - 100bpmSinus rhythm assumed
Body Surface AreaBSA1.5 - 2.2m2DuBois formula standard
Systemic Vascular ResistanceSVR800 - 1200dyn⋅s/cm5Afterload marker
Pulmonary Vascular ResistancePVR20 - 120dyn⋅s/cm5RV afterload
Mean Arterial PressureMAP70 - 105mmHgOrgan perfusion driver
Central Venous PressureCVP2 - 8mmHgRV preload surrogate
Mean PA PressureMPAP9 - 18mmHgPulmonary hypertension cutoff ≥ 20
PCWP / Wedge PressurePCWP6 - 12mmHgLV filling pressure surrogate
O2 ConsumptionVO2200 - 250mL/minFick method input, often assumed
HemoglobinHb12 - 17g/dLOxygen-carrying capacity
Arterial O2 SaturationSaO295 - 100%Pulse oximetry or ABG
Mixed Venous O2 SaturationSvO265 - 75%PA catheter sample
Left Ventricular Stroke Work IndexLVSWI50 - 62g⋅m/m2LV work per beat per BSA
Right Ventricular Stroke Work IndexRVSWI5 - 10g⋅m/m2RV work per beat per BSA

Frequently Asked Questions

Hemoglobin (Hb) directly scales oxygen content via Hüfner's constant (1.34 mL O2/g Hb). In severe anemia (Hb < 7 g/dL), the arteriovenous O2 difference narrows, producing a mathematically higher CO. This is physiologically real: the heart compensates with increased output. However, if VO2 is assumed rather than measured (common in clinical practice), the computed CO may overestimate true output by 10 - 25%.
The conversion factor 80 transforms Wood units (mmHg⋅min/L) into CGS units (dyn⋅s/cm5). Specifically, 1 mmHg = 1333 dyn/cm2 and 1 L = 1000 cm3, so the exact factor is 79.9, rounded to 80 by convention. Some institutions report in Wood units directly (divide SVR by 80), where normal SVR is approximately 10 - 15 Wood units.
Thermodilution accuracy degrades in three scenarios: (1) tricuspid regurgitation causes indicator recirculation, underestimating CO by up to 30%; (2) intracardiac shunts (VSD, ASD) create aberrant indicator transit; (3) very low cardiac output states (CI < 1.5 L/min/m2) produce prolonged thermodilution curves with high signal-to-noise ratios. In these cases, the Fick method with measured VO2 is preferred.
The Lafarge-Miettinen regression is commonly used: VO2 ≈ 138.1 − (11.49 × ln(age)) × BSA for males, and 138.1 − (17.04 × ln(age)) × BSA for females. A simpler rule-of-thumb uses 125 mL/min/m2 × BSA. Both introduce ±10 - 15% error. In critically ill, septic, or febrile patients, assumed VO2 values are unreliable.
The DuBois formula (0.007184 × W0.425 × H0.725) was derived from only 9 subjects in 1916 but remains the reference standard. Mosteller's simplified formula (√H × W / 3600) agrees within ±2% for adults with BMI 18 - 30. Divergence increases at extremes of body habitus: morbid obesity or cachexia. This calculator uses DuBois, consistent with most PA catheter lab protocols.
Cardiogenic shock typically shows elevated SVR (> 1400 dyn⋅s/cm5) with low CI (< 2.2 L/min/m2) as the vasculature compensates for diminished output. Distributive shock (sepsis) shows low SVR (< 800 dyn⋅s/cm5) with normal or elevated CI. Mixed shock states produce intermediate values. Always interpret SVR alongside CI, lactate, and clinical assessment.