Volume Responsiveness, Carotid Ultrasound, and the PLR
Passive Leg Raise (PLR) is accomplished by starting with the patient at a 45’ semi recumbent position, lowering the body to horizontal, passively raising the patients legs to 45’ for 30-90 seconds, then returning the patient to the semi-recumbent position.
To assess volume responsiveness using PLR, you must assess cardiac output (CO) and not simply look at the changes in blood pressure or heart rate.
Previous papers have shown EtCO2 to be a reasonable surrogate of CO with PLR when ventilation is unchanged.
Another option for measuring CO is carotid ultrasound. One study demonstrated good correlation between carotid ultrasound and invasive measurements on ICU patients. It is calculated using the equation Diameter * VTi, where VTI is the velocity time integral.
Take Home Point - Be sure to measure CO with a PLR to help determine volume responsiveness- EtCO2 or carotid ultrasound can be considered as surrogates of CO.
References
Gassner M, Killu K, Bauman Z, Coba V, Rosso K, Blyden D. Feasibility of common carotid artery point of care ultrasound in cardiac output measurements compared to invasive methods. Journal of Ultrasound. 2015;18(2):127-133.
