Cardiac output (CO) is a fundamental measurement in cardiovascular physiology and clinical medicine. It reflects the efficiency of the heart in pumping blood and delivering oxygen to the body.
🔍 Definition of Cardiac Output
Cardiac Output (CO) is the volume of blood the heart pumps per minute.
Formula:
javaCopyEditCardiac Output = Heart Rate (HR) × Stroke Volume (SV)
- Heart Rate (HR): Number of heartbeats per minute
- Stroke Volume (SV): Amount of blood ejected with each heartbeat
For example, if HR = 75 bpm and SV = 70 mL:
CO = 75 × 70 = 5,250 mL/min (5.25 L/min)
📊 Normal Cardiac Output Values
| Population | Cardiac Output (L/min) | Cardiac Index (L/min/m²) |
|---|---|---|
| Average Adult (at rest) | 4.0 – 8.0 | 2.5 – 4.0 |
| Trained Athlete | 5.0 – 9.0 | 3.0 – 4.5 |
| Elderly | 3.5 – 6.0 | 2.0 – 3.5 |
| During Intense Exercise | Up to 30.0 | Up to 12.0 |
| Severe Heart Failure | < 3.5 | < 2.0 |
Cardiac Index (CI) adjusts CO to body size:
iniCopyEditCI = CO / Body Surface Area (BSA)
💡 Why is Cardiac Output Important?
Understanding and monitoring CO helps clinicians:
- Diagnose heart failure, shock, and cardiac tamponade
- Optimize fluid therapy, vasopressors, and inotropes
- Predict outcomes in critically ill patients
- According to the American Heart Association, cardiac output plays a vital role in blood pressure regulation and oxygen delivery.
Low cardiac output → Tissue hypoxia, organ dysfunction
High cardiac output → Possible sepsis, anemia, or AV fistulas
🧪 How is Cardiac Output Measured?
Several techniques are available:
| Method | Invasiveness | Accuracy | Notes |
|---|---|---|---|
| Fick Method | High | ✅ Gold Standard | Requires O₂ consumption + arterial/venous blood gases |
| Thermodilution | High | ✅ | Via pulmonary artery catheter |
| Echocardiography | Low | ⚠️ Operator-dependent | Uses Doppler and LVOT diameter |
| Pulse Contour Analysis | Moderate | ⚠️ | Based on arterial waveform |
| Bioimpedance/Bioreactance | Low | ⚠️ | Non-invasive but less reliable |
| Cardiac MRI | Low | ✅ Highly accurate | Expensive, not widely available |
👉 Use our Fick Calculator to estimate cardiac output using the gold-standard method.
📉 What Causes Abnormal Cardiac Output?
Low CO:
- Heart failure
- Cardiogenic or hypovolemic shock
- Tamponade or severe arrhythmias
High CO:
- Sepsis or systemic vasodilation
- Anemia
- Hyperthyroidism
- Pregnancy
🧠 Key Takeaways
- Cardiac Output = Heart Rate × Stroke Volume
- Normal CO ≈ 4–8 L/min in adults at rest
- CO is critical in managing cardiac and critically ill patients
- Use accurate methods like the Fick equation when precision matters