From the Guidelines
Noninvasive carotid flow monitoring is not recommended for cardiac output assessment due to its limitations and potential inaccuracies, particularly in patients with carotid artery disease or hemodynamic instability. This approach, although noninvasive, has significant drawbacks, including operator dependency and the fact that it measures flow in only one vessel as a surrogate for total cardiac output. According to the 2019 guidelines on cardiopulmonary bypass in adult cardiac surgery 1, minimally invasive haemodynamic monitors using pulse contour analysis have poor agreement with the gold standard pulmonary artery catheter (PAC), with a mean percentage error of 41%. The use of noninvasive carotid flow monitoring may be considered in stable patients or in settings where more invasive monitoring is unavailable or unwarranted, but its accuracy and reliability are limited. In complex situations, such as severe ARDS or sepsis-associated disorders, advanced hemodynamic monitoring, including pulmonary artery catheterization or transpulmonary thermodilution, may be more appropriate 1. Key considerations for cardiac output monitoring include:
- Accuracy and reliability of the method
- Invasiveness and potential risks
- Patient stability and complexity of the clinical situation
- Availability and expertise with different monitoring techniques. Given the limitations of noninvasive carotid flow monitoring, it is not a recommended method for cardiac output assessment in most clinical situations, particularly when accurate and reliable measurements are crucial for patient management.
From the Research
Noninvasive Carotid Flow Monitoring for Cardiac Output
- Noninvasive measures of cardiac output, such as carotid blood flow and corrected carotid flow time, have been studied for their correlation with invasive cardiac output measurements 2.
- Carotid blood flow measurements have been found to correlate moderately with cardiac output, regardless of whether single waveform or an average of three waveforms are used 2.
- Another study introduced a novel approach to estimate cardiac output and central systolic blood pressure from noninvasive measurements of peripheral cuff-pressure and carotid-to-femoral pulse wave velocity 3.
- The study found that the proposed framework can potentially be used to obtain central aortic hemodynamic parameters in a noninvasive and accurate way, with low biases reported for cardiac output and central systolic blood pressure predictions 3.
- However, other studies have found poor correlations between noninvasive techniques, such as bioreactance, and invasive measurements of cardiac output 4.
- A review of cardiac output measurement technologies found that invasive techniques are more accurate, but noninvasive devices can be useful in certain clinical situations, such as when invasive monitoring is not feasible 5.
- Another study found that carotid Doppler flowmetry correlates poorly with thermodilution cardiac output following cardiac surgery, and that changes in carotid Doppler flow following passive leg raising correlated with baseline arterial resistance but not with compliance or effective elastance 6.
Key Findings
- Carotid blood flow measurements may be a better marker of cardiac output than corrected carotid flow time 2.
- Noninvasive measurements of peripheral cuff-pressure and carotid-to-femoral pulse wave velocity can be used to estimate cardiac output and central systolic blood pressure 3.
- Bioreactance devices may not be reliable for measuring cardiac output in critically ill patients 4.
- Invasive techniques, such as pulmonary artery catheter thermodilution, are considered the gold standard for measuring cardiac output, but noninvasive devices can be useful in certain clinical situations 5.
- Carotid Doppler flowmetry may not be a reliable method for monitoring cardiac output and volume responsiveness in post-operative cardiac surgery patients 6.