Cardiac Output Calculator

Calculate cardiac output using Fick principle and thermodilution methods. Essential tool for medical professionals.

Fick Principle
Thermodilution

Fick Principle Formula: CO = VO₂ / (CaO₂ - CvO₂)

Where: CO = Cardiac Output, VO₂ = Oxygen Consumption, CaO₂ = Arterial Oxygen Content, CvO₂ = Venous Oxygen Content

Normal range: 200-300 mL/min at rest
Normal range: 95-100%
Normal range: 60-80%
Normal range: 12-16 g/dL (women), 14-18 g/dL (men)

Thermodilution Formula: CO = [V × (Tb - Ti) × K] / ∫ΔT dt

Where: CO = Cardiac Output, V = Injectate Volume, Tb = Blood Temperature, Ti = Injectate Temperature, K = Computation Constant

Typically 10 mL for adults
Normal body temperature: ~37°C
Typically room temperature or iced
Measured from thermodilution curve
Calculating...

Understanding Cardiac Output

Cardiac output (CO) is the volume of blood the heart pumps per minute. It is a crucial hemodynamic parameter that indicates how well the heart is functioning as a pump. Cardiac output is calculated as the product of heart rate (HR) and stroke volume (SV):

Formula: CO = HR × SV

Where: CO = Cardiac Output (L/min), HR = Heart Rate (beats/min), SV = Stroke Volume (mL/beat)

Normal Values

Parameter Normal Range Clinical Significance
Cardiac Output (CO) 4-8 L/min Indicates overall heart pumping efficiency
Cardiac Index (CI) 2.5-4.0 L/min/m² CO adjusted for body surface area
Stroke Volume (SV) 60-100 mL/beat Amount of blood pumped per beat
Heart Rate (HR) 60-100 beats/min Number of heartbeats per minute
Ejection Fraction (EF) 55-70% Percentage of blood ejected from ventricle

Measurement Methods

1

Fick Principle: Based on oxygen consumption and the arteriovenous oxygen difference. Considered the gold standard but requires invasive measurements.

2

Thermodilution: Uses temperature changes after injecting a cold solution. Commonly used with pulmonary artery catheters.

3

Echocardiography: Non-invasive method using ultrasound to measure blood flow through heart valves.

4

Pulse Contour Analysis: Estimates stroke volume from arterial pressure waveform analysis.

Clinical Applications

  • Heart Failure Assessment: Evaluating the severity of systolic dysfunction
  • Shock Management: Differentiating types of shock and guiding therapy
  • Postoperative Monitoring: Assessing cardiac function after major surgery
  • Medication Titration: Guiding inotropic and vasoactive drug therapy
  • Exercise Physiology: Evaluating cardiac response to physical stress

Factors Affecting Cardiac Output

Increasing Factors
  • Exercise
  • Fever
  • Anemia
  • Hyperthyroidism
  • Pregnancy
Decreasing Factors
  • Heart failure
  • Hypovolemia
  • Myocardial infarction
  • Beta-blockers
  • Hypothermia

Clinical Note: Cardiac output values should always be interpreted in the context of the patient's clinical condition, body size, and metabolic demands. Values outside the normal range require careful clinical evaluation.

Cardiac Index

Cardiac index (CI) is cardiac output normalized to body surface area (BSA), providing a more accurate assessment of cardiac function across different body sizes:

Formula: CI = CO / BSA

Where: CI = Cardiac Index (L/min/m²), CO = Cardiac Output (L/min), BSA = Body Surface Area (m²)

Frequently Asked Questions

Cardiac output is the absolute volume of blood pumped by the heart per minute, while cardiac index is cardiac output normalized to body surface area. Cardiac index provides a better comparison between individuals of different sizes.

The Fick method is considered the gold standard and is preferred in low cardiac output states, tricuspid regurgitation, or when thermodilution measurements are unreliable. Thermodilution is more commonly used in clinical practice due to its convenience.

Thermodilution accuracy can be affected by tricuspid regurgitation, intracardiac shunts, respiratory variations, improper injectate temperature or volume, and catheter position. Multiple measurements should be averaged for better accuracy.

During exercise, cardiac output can increase 4-5 times above resting values in healthy individuals. This is achieved through increases in both heart rate and stroke volume to meet the increased metabolic demands of working muscles.

For an average adult at rest, normal cardiac output ranges from 4 to 8 liters per minute. This corresponds to a cardiac index of 2.5 to 4.0 L/min/m² when adjusted for body surface area.