From the Guidelines
Fick's method is a technique used to calculate cardiac output by measuring oxygen consumption and the difference in oxygen content between arterial and venous blood, and it is considered the gold standard for cardiac output measurement, as stated in the most recent study 1. The formula for Fick's method is: Cardiac Output = Oxygen Consumption ÷ (Arterial Oxygen Content - Venous Oxygen Content). To perform this method, you need to measure the patient's oxygen consumption over time (typically using a metabolic cart or Douglas bag), and obtain blood samples from both arterial and mixed venous blood to determine their oxygen content difference. The principle behind Fick's method is based on conservation of mass - the amount of oxygen consumed by the body must equal the amount of oxygen delivered to the tissues, which is the product of blood flow (cardiac output) and the arteriovenous oxygen difference. Some key points to consider when using Fick's method include:
- It requires arterial and pulmonary artery catheterization to obtain the necessary blood samples, making it impractical for routine clinical use, as noted in 1 and 1.
- It is invasive and technically demanding, but remains valuable in research settings and for calibrating other cardiac output measurement techniques, as stated in 1 and 1.
- The accuracy of the method can be affected by various factors, such as the presence of a systemic-to-pulmonary shunt, as mentioned in 1.
- Alternative methods, such as thermodilution, may be used in certain situations, as discussed in 1. Overall, Fick's method is a reliable and accurate technique for measuring cardiac output, but its use is limited by its invasiveness and technical demands.
From the Research
Fick's Principle Method
Fick's principle method is a technique used to determine cardiac output, which is the volume of blood the heart pumps per minute. The method is based on the Fick principle, which states that the rate of blood flow through an organ is equal to the rate of uptake or release of a substance by that organ divided by the difference in concentration of the substance between the arterial and venous blood [ 2, 3, 4, 5, 6 ].
Key Components of Fick's Principle Method
The Fick's principle method involves the following key components:
- Measurement of oxygen consumption (VO2) [ 2, 4, 5, 6 ]
- Measurement of arterial and venous oxygen saturations [ 2, 3, 4, 5 ]
- Calculation of cardiac output using the Fick equation: CO = VO2 / (Ca - Cv), where CO is cardiac output, VO2 is oxygen consumption, Ca is arterial oxygen content, and Cv is venous oxygen content [ 2, 3, 4 ]
Advantages and Limitations of Fick's Principle Method
The Fick's principle method has several advantages, including:
- It is a direct and accurate method for measuring cardiac output [ 2, 4 ]
- It can be used to measure cardiac output in a variety of clinical settings [ 2, 3, 4, 5 ] However, the method also has some limitations, including:
- It requires measurement of oxygen consumption, which can be difficult to obtain accurately [ 6 ]
- It requires insertion of a pulmonary artery catheter, which can be invasive and carries risks [ 2, 3, 4 ]
Comparison with Other Methods
The Fick's principle method has been compared with other methods for measuring cardiac output, including thermodilution [ 2, 3, 4 ] and bioimpedance [ 3 ]. The results of these studies have shown that the Fick's principle method is a reliable and accurate method for measuring cardiac output, but it may not always agree with other methods [ 2, 3, 4 ].