What is the dye dilution method for measuring cardiac output (Cardiac Output, CO)?

From the Guidelines

The dye dilution method for measuring cardiac output involves injecting a known amount of indicator dye into the venous circulation and measuring its concentration over time as it passes through the arterial system, with the cardiac output calculated using the Stewart-Hamilton equation: CO = (amount of dye injected)/(area under the concentration-time curve) 1.

Key Components of the Dye Dilution Method

• A small bolus of dye, typically indocyanine green, is rapidly injected into a central vein or the right side of the heart.
• Blood samples are continuously drawn from an arterial site to measure dye concentration.
• The technique requires careful timing, precise dye injection, and accurate concentration measurements.
• The method works based on the principle that the more blood flowing through the heart, the more diluted the dye becomes, resulting in a lower peak concentration and a shorter duration of the dye curve for higher cardiac outputs.

Clinical Application and Limitations

• While largely replaced by thermodilution techniques in modern practice, dye dilution remains valuable for research and in situations where thermal methods are contraindicated.
• The method provides a reasonably accurate assessment of cardiac output but requires specialized equipment and expertise to perform correctly.
• Other methods, such as foreign gas rebreathing and CO2 rebreathing, have also been explored for measuring cardiac output, but the dye dilution method is specifically focused on the principle of dye concentration over time 1.
• The choice of method may depend on the clinical context, patient condition, and availability of resources, with the goal of accurately assessing cardiac output to guide patient management and improve outcomes.

From the FDA Drug Label

In the performance of dye dilution curves, a known amount of dye is usually injected as a single bolus as rapidly as possible via a cardiac catheter into selected sites in the vascular system A recording instrument (oximeter or densitometer) is attached to a needle or catheter for sampling of the dye‑blood mixture from a systemic arterial sampling site. The usual doses of IC‑GREEN™ which have been used for dilution curves are as follows: Adults ‑ 5.0 mg Children ‑ 2.5 mg Infants ‑ 1. 25 mg To quantitate the dilution curves, standard dilutions of IC‑GREEN™ in whole blood are made Ear Densitometry: Ear oximetry has also been used and makes it possible to monitor the appearance and disappearance of IC‑GREEN™ without the necessity of withdrawal and spectrophotometric analysis of blood samples for calibration

The dye dilution method for measuring Cardiac Output (CO) involves:

• Injecting a known amount of indocyanine green (IC-GREEN™) as a single bolus into the vascular system
• Using a recording instrument to sample the dye-blood mixture from a systemic arterial site
• Quantifying the dilution curves using standard dilutions of IC-GREEN™ in whole blood
• Optionally, using ear densitometry to monitor the appearance and disappearance of IC-GREEN™ without blood sample analysis 2 Key points:
• Dye injection: a single bolus of 5.0 mg (adults), 2.5 mg (children), or 1.25 mg (infants) of IC-GREEN™
• Recording instrument: oximeter or densitometer attached to a needle or catheter
• Sampling site: systemic arterial site
• Quantification: using standard dilutions of IC-GREEN™ in whole blood
• Alternative method: ear densitometry for monitoring IC-GREEN™ appearance and disappearance 2

From the Research

Dye Dilution Method for Measuring Cardiac Output

The dye dilution method is a technique used to measure cardiac output (CO) by injecting a dye, typically indocyanine green (ICG), into the bloodstream and measuring the resulting concentration curve over time. This method is based on the principle that the concentration of the dye in the blood is inversely proportional to the cardiac output.

Principles of the Dye Dilution Method

• The dye is injected into a central vein, and its concentration is measured at a downstream site, usually in the aorta or pulmonary artery.
• The resulting concentration curve is analyzed to determine the cardiac output, which is calculated using the Stewart-Hamilton equation 3, 4.
• The dye dilution method can be performed using various techniques, including pulse dye densitometry (PDD) and fiberoptic catheters 4, 5.

Advantages and Limitations of the Dye Dilution Method

• The dye dilution method is a less invasive alternative to the thermodilution technique, which requires a pulmonary artery catheter 3.
• However, the dye dilution method can be affected by various factors, such as signal detection failure and systematic bias, which can limit its accuracy and reliability 3, 4.
• The method has been shown to be accurate and reliable in certain patient populations, such as those undergoing cardiac surgery, but may not be suitable for all patients, such as those on venovenous extracorporeal lung assist 4, 6.

Comparison with Other Methods

• The dye dilution method has been compared to other methods for measuring cardiac output, including thermodilution, radiolabeled microspheres, and electromagnetic flow methods 4, 5.
• The results of these studies suggest that the dye dilution method can provide accurate and reliable measurements of cardiac output, but may not be as accurate as other methods in certain situations 4, 5.
• The choice of method for measuring cardiac output depends on various factors, including the patient population, the clinical setting, and the availability of equipment and expertise 7.