🫀 Fick Cardiac Output / Cardiac Index
Estimates cardiac output (CO) and cardiac index (CI) by the indirect Fick principle from oxygen consumption and the arteriovenous oxygen content difference.
Fick Cardiac Output / Cardiac Index
Oxygen consumption VO₂ (mL/min)
Hemoglobin (g/L)
Arterial oxygen saturation SaO₂ (%)
Mixed venous oxygen saturation SvO₂ (%)
Body surface area (optional, for CI) (m²)
When to use
Enter VO2 (or an estimate), hemoglobin, and arterial/mixed-venous oxygen saturations; the tool returns CO and CI. Useful at the bedside or in the cath lab when thermodilution is unavailable or unreliable.
How it works
CaO2−CvO2 = 1.34 × Hb × (SaO2 − SvO2) × 10 (mL/L). CO = VO2 / (CaO2 − CvO2). CI = CO / BSA. Estimated VO2 commonly uses 125 mL/min/m² × BSA (or 110 in the elderly).
Key points
- The indirect Fick relies on an assumed VO2, which can err by 25% or more — direct measurement of VO2 is preferred when accuracy is critical (e.g., shunt or PVR calculation). (original synthesis · not guideline verbatim)
- Accuracy degrades at high cardiac output (the narrow a-v difference amplifies measurement error) and with intracardiac shunts.
- Use true mixed-venous (pulmonary artery) saturation; a central-venous (SVC) sample is a substitute that introduces additional error.
References
- LaFarge CG, Miettinen OS. The estimation of oxygen consumption. Cardiovasc Res. 1970;4(1):23-30.
- Narang N, et al. Inaccuracy of estimated resting oxygen uptake in the clinical setting. Circulation. 2014;129(2):203-210.
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.