Cardiac Output Calculator
Use our free Cardiac output Calculator to get personalized health results. Based on validated medical formulas and clinical guidelines.
Formula
CO = HR x SV / 1000 (or) CO = VO2 / (CaO2 - CvO2)
Where CO = Cardiac Output in L/min, HR = Heart Rate in beats per minute, SV = Stroke Volume in mL per beat, VO2 = Oxygen Consumption in mL/min, CaO2 = Arterial Oxygen Content in mL/dL, CvO2 = Mixed Venous Oxygen Content in mL/dL. The HR x SV method is simpler while the Fick method is considered more accurate in clinical settings.
Worked Examples
Example 1: Standard HR x SV Calculation
Problem: A patient has a heart rate of 80 bpm and echocardiographic stroke volume of 65 mL. Calculate the cardiac output.
Solution: CO = HR x SV\nCO = 80 beats/min x 65 mL/beat\nCO = 5,200 mL/min = 5.2 L/min\nNormal range: 4.0-8.0 L/min\nThis value falls within the normal range.
Result: Cardiac Output: 5.2 L/min (Normal Range)
Example 2: Fick Method Calculation
Problem: A patient has VO2 of 280 mL/min, arterial O2 content of 20 mL/dL, and mixed venous O2 content of 14 mL/dL. Calculate CO using the Fick equation.
Solution: AV O2 difference = CaO2 - CvO2 = 20 - 14 = 6 mL/dL\nCO = VO2 / (AV O2 diff x 10)\nCO = 280 / (6 x 10) = 280 / 60\nCO = 4.67 L/min\nThe widened AV difference suggests mildly reduced CO.
Result: Cardiac Output: 4.67 L/min (Low-Normal)
Frequently Asked Questions
What is cardiac output and what does it measure?
Cardiac output (CO) is the total volume of blood the heart pumps per minute, measured in liters per minute (L/min). It represents the product of heart rate (beats per minute) and stroke volume (milliliters of blood ejected per beat). Normal resting cardiac output for an adult ranges from 4 to 8 liters per minute, meaning the entire blood volume of approximately 5 liters circulates through the body roughly once every minute. Cardiac output is a fundamental hemodynamic parameter used to assess overall cardiovascular function, guide treatment in critical care, and evaluate the severity of heart failure and shock states.
How does the Fick method for cardiac output work?
The Fick principle, first described by Adolf Fick in 1870, calculates cardiac output based on oxygen consumption and the difference between arterial and venous oxygen content. The formula states that CO equals oxygen consumption (VO2) divided by the arteriovenous oxygen content difference (CaO2 minus CvO2). For example, if a patient consumes 250 mL of oxygen per minute and the arteriovenous oxygen difference is 5 mL per deciliter, the cardiac output is 250 divided by 50, equaling 5 L/min. The Fick method is considered one of the most accurate techniques for measuring cardiac output, particularly when direct oxygen consumption measurements are available rather than estimated values.
What factors affect cardiac output in healthy individuals?
Multiple physiological factors influence cardiac output in healthy people. Exercise is the most potent stimulus, increasing cardiac output from a resting 5 L/min to over 25 L/min in trained athletes through increases in both heart rate and stroke volume. Body position affects venous return, with cardiac output being approximately 20 percent lower when standing compared to lying down. Emotional stress and anxiety activate the sympathetic nervous system, raising heart rate and contractility. Temperature elevation increases metabolic demand and consequently cardiac output by about 10 percent per degree Celsius. Pregnancy increases cardiac output by 30 to 50 percent by the second trimester. Age-related decline in maximum heart rate and myocardial compliance gradually reduces maximum achievable cardiac output.
What is the relationship between cardiac output and blood pressure?
Blood pressure is determined by the relationship between cardiac output and systemic vascular resistance (SVR), expressed as Mean Arterial Pressure equals Cardiac Output multiplied by SVR. This means blood pressure can be maintained through compensatory changes in either variable. In early heart failure, cardiac output declines but blood pressure may remain normal because SVR increases through vasoconstriction. Conversely, in septic shock, SVR drops dramatically but cardiac output initially increases to compensate. Understanding this relationship is critical for treatment selection: a hypotensive patient with low CO needs inotropic support, while one with low SVR needs vasopressors. This is why measuring cardiac output adds essential information beyond blood pressure alone.
How do clinicians measure cardiac output at the bedside?
Several methods exist for bedside cardiac output measurement, each with distinct advantages and limitations. Pulmonary artery catheter thermodilution involves injecting cold saline through a Swan-Ganz catheter and measuring the temperature change curve downstream, providing reliable measurements but requiring an invasive procedure. Transpulmonary thermodilution (PiCCO system) uses a central venous and arterial catheter to measure cardiac output with continuous monitoring capability. Echocardiographic methods use Doppler ultrasound to measure blood flow velocity through the left ventricular outflow tract, multiplied by the cross-sectional area. Non-invasive methods include bioimpedance cardiography and partial carbon dioxide rebreathing, though these are generally less accurate in critically ill patients.
What causes low cardiac output syndrome after cardiac surgery?
Low cardiac output syndrome (LCOS) occurs in 3 to 14 percent of patients following cardiac surgery and is defined by a cardiac index below 2.0 L/min/m2 with signs of end-organ hypoperfusion. Several factors contribute to LCOS in the postoperative period. Myocardial stunning from ischemia-reperfusion injury during cardiopulmonary bypass temporarily impairs contractility. Inadequate myocardial protection during aortic cross-clamping can cause direct cellular injury. Systemic inflammatory response triggered by the bypass circuit causes vasoplegia and myocardial depression. Pre-existing ventricular dysfunction compounds these acute insults. Treatment involves optimizing preload with fluids, using inotropes such as milrinone or dobutamine, and in refractory cases, mechanical circulatory support with an intra-aortic balloon pump or ventricular assist device.