Calculate cardiac output using the Fick principle or thermodilution. Includes cardiac index, stroke volume, and systemic vascular resistance.
Cardiac output (CO) — the volume of blood pumped by the heart each minute — is a fundamental hemodynamic parameter that directly reflects the heart's ability to meet the body's metabolic demands. Normal resting CO in adults ranges from 4 to 8 L/min, but it can increase fourfold during vigorous exercise or decrease dramatically in heart failure and shock states.
The **Fick principle**, first described by Adolf Fick in 1870, remains one of the most physiologically sound methods for determining CO. It is based on the concept that the oxygen consumed by the body must equal the oxygen delivered by the heart minus the oxygen returned to it. The calculation uses oxygen consumption (VO₂), hemoglobin concentration, and the difference between arterial and mixed venous oxygen saturations.
The **thermodilution method**, performed via a pulmonary artery (Swan-Ganz) catheter, measures CO by injecting a known volume of cold saline and detecting the resulting temperature change downstream. This technique remains widely used in ICU settings, though its use has declined with the rise of non-invasive monitoring technologies.
This calculator computes CO via either method and derives the cardiac index (CI = CO/BSA), stroke volume (SV = CO/HR), stroke volume index (SVI = SV/BSA), and systemic vascular resistance (SVR). These derived parameters provide a comprehensive hemodynamic profile essential for managing patients with heart failure, septic shock, cardiogenic shock, and valvular disease.
Understanding cardiac output and its derived parameters is essential for managing critically ill patients in ICU and cardiology settings. This calculator provides a comprehensive hemodynamic assessment from basic physiologic measurements. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain. Use this clarification to avoid ambiguous interpretation. Align this note with review checkpoints.
Fick Cardiac Output: CO = VO₂ / [(SaO₂ − SvO₂) × Hb × 1.34 × 10], where VO₂ = O₂ consumption (mL/min), Hb = hemoglobin (g/dL), SaO₂/SvO₂ = arterial/mixed venous O₂ saturation (fraction). Cardiac Index: CI = CO / BSA. Stroke Volume: SV = (CO × 1000) / HR. SVR = [(MAP − CVP) / CO] × 80.
Result: 5.14 L/min
With VO₂ of 250 mL/min, Hb 14 g/dL, SaO₂ 98%, and SvO₂ 75%, the arteriovenous O₂ difference is 4.31 mL/dL, yielding a CO of ~5.14 L/min (CI 2.71 L/min/m²), which is within normal range.
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Normal resting cardiac output in adults is 4–8 L/min. Cardiac index (CO divided by body surface area) of 2.5–4.0 L/min/m² is considered normal.
The Fick principle states that cardiac output equals oxygen consumption divided by the arteriovenous oxygen content difference. It requires measurement of VO₂ and arterial and mixed venous oxygen saturations.
Cardiac index normalizes CO for body size, allowing comparison between patients of different sizes. A CI < 2.2 L/min/m² indicates critically reduced cardiac function regardless of the patient's size.
Elevated SVR (> 1200 dyn·s/cm⁵) suggests increased afterload, seen in cardiogenic shock, hypertension, or hypothermia. Low SVR occurs in septic shock and anaphylaxis.
Normal SvO₂ is 60–80%. Values < 60% suggest inadequate oxygen delivery (low CO, anemia, or increased oxygen demand). Values > 80% can indicate sepsis or left-to-right shunts.
Both have limitations. Fick is considered more accurate at low cardiac outputs, while thermodilution may be more practical and reproducible. Significant tricuspid regurgitation can make thermodilution unreliable.