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Author: Jake Toy, DO
PGY1 Emergency Medicine, Harbor UCLA Medical Center
Modern Resident Blog Editor-in-Chief
The management of intravascular volume in critically ill patients is a challenge we face daily in the emergency department (ED). Since the beginning of our training, hypotension and shock have often been synonymous with rapid fluid resuscitation. Yet at present, fluid resuscitation remains largely empiric in nature.
Though past recommendations often touted early, rapid fluid resuscitation in critically ill patients in order to improve organ perfusion and reduce mortality,[1, 2] an increasing body of evidence suggests that liberal intravenous fluid resuscitation may lead to complications and increased mortality.[3, 4] Previous studies further demonstrates that approximately 50% of patients might not be responsive to fluids. Fluid responsiveness has previously been defined as an increase in cardiac output by 10 to 15%. The Frank-Starling curve elucidates the relationship between changes in preload and cardiac output and can be used to predict patient response to a fluid challenge or aggressive early fluid resuscitation. However, the predictive ability of this curve is limited by varying disease states, such as systolic or diastolic heart failure, that impact the shape of each individuals curve and their ability to respond to fluid resuscitation. As such, it is difficult to accurately predict each patient’s capacity to respond prior to the administration of a fluid bolus or boluses.
Multiple static and dynamic hemodynamic parameters exist— central venous pressure, pulmonary artery occlusion pressure, inferior vena cava measurements, pulse pressure, and stroke volume variation—that offer varying degrees of insight toward assessing and predicting fluid responsiveness in the ED. Previous studies have evaluated these parameters before and after volume challenge (e.g. fluid resuscitation or passive leg raise [PLR] that delivers a reversible “auto-bolus”) in order to determine their predictive value. However, these methods are limited by their poor predictive outcomes, invasive nature, availability, feasibility, and factors that limit their accuracy such as mechanical ventilation and cardiac arrhythmias.[7,8] In order to overcome these limitations, carotid Doppler flow measurements via bedside ultrasound in combination with PLR represents a noninvasive, accurate, and safe method to guide fluid responsiveness within the ED.
Carotid Doppler flow ultrasound
Multiple studies exist that assess the use of carotid Doppler flow ultrasound to predict fluid responsiveness.
Citation: Marik PE, et al. The use of bioreactance and carotid Doppler to determine volume responsiveness and blood flow redistribution following passive leg raising in hemodynamically unstable patients. Chest. Feb 01 2013;143(2):364-370.
Objective: To determine the predictive value of PLR-induced stroke volume index (SVI) changes as measured by carotid ultrasound as a predictor of volume responsiveness.
Design: Prospective trial (n=34) performed in the intensive care unit (ICU) on hemodynamically unstable patients.
Results: A total of 53% of patients were volume responders after fluid challenge. PLR-induced changes in SVI noted on carotid ultrasound had a sensitivity and specificity of 94% and 100%, respectively, for predicting volume responsiveness (Increase in SVI >10% was considered a volume responder.). A correlation between percent change in SVI by PLR and the associated percent change in carotid blood flow (CBF) on carotid Doppler flow ultrasound was also noted. An increase in carotid blood flow of 20% after PLR correlated with a sensitivity and specificity of 94% and 86%, respectively, for predicting volume responsiveness.
Conclusions: Noninvasive carotid Doppler ultrasound used to measure SVI coupled with PLR is correlated with increased CBF and is a simple and accurate method to predict fluid responsiveness in critically ill ICU patients.
Citation: Ma IWY, et al. Correlation of carotid blood flow and corrected carotid flow time with invasive cardiac output measurements. Crit Ultrasound J. 2017;9.
Objective: To compare corrected carotid flow time (CFT) and CBF with cardiac output as measured by pulmonary artery catheterization following PLR.
Design: Prospective trial (n=51) of patients who had underwent right heart catheterization in the cardiac catheterization lab.
Results: Single- and three-waveform CBF measurements correlated with cardiac output. Three-waveform corrected CFT correlated weakly with cardiac output, while single-waveform corrected CFT showed no correlation.
Conclusions: Changes in CBF after PLR correlate with changes in cardiac output as measured by pulmonary artery catheterization.
Carotid Doppler flow ultrasound technique to measure CBF before and after passive leg raise
Procedure: The first carotid ultrasound measurements are taken with the patient in a supine position. The second measurements are taken between one to five minutes after leg lift to 45-degrees. Variations include initial positioning in a 45-degree semi-recumbent position.
Carotid Doppler flow study: The operator will use the linear transducer to determine the CBF via obtaining measurements of the common carotid artery (CCA) diameter and velocity time integral (VTI) of carotid blood flow in combination with the patient’s heart rate at the time of study. The following formula may be used to calculate CBF: Blood flow per minute = π x (CCA diameter)2/4 x VTI x heart rate (may be calculated automatically depending on ultrasound machine type).
First, an image of the CCA is obtained in the short-axis view. Second, a longitudinal axis view is obtained, and pulse wave Doppler should be activated. The sample gate (aka sample volume) must be placed directly below the carotid bulb, most often found 2-3 centimeters below the carotid bifurcation. The correction angle should be adjusted to run parallel to the carotid lumen. The angle of insonation must be greater than 60-degrees to obtain an accurate measurement. VTI is then measured in centimeters. The CCA diameter from intima to intima can then be measured in centimeters. Notably, CCA diameter and VTI should be measured at the same location on the CCA.
Check out this video for step-by-step carotid ultrasound: https://www.youtube.com/watch?v=YRFweWHCjsQ
Utilization of carotid Doppler flow to predict volume responsiveness represents a promising noninvasive method to guide fluid resuscitation in the ED. Carotid Doppler flow may provide important information to guide fluid administration specifically in, but not limited to, septic hypotensive patients. However, the feasibility of this method may be questionable, especially due to the busy nature of ED workflow and operator dependent limitations of this technical exam. At present, larger, ED-based investigations are needed prior to widespread use of this technique.
1. Rivers E, Nguyen B, Havstad S, et al. Early Goal-Directed Therapy in the Treatment of Severe Sepsis and Septic Shock. New England Journal of Medicine. 2001;345(19):1368-77.
2. Dellinger RP, Levy MM, Rhodes A, et al. Surviving sepsis campaign: international guidelines for management of severe sepsis and septic shock: 2012. Crit Care Med. 2013 Feb;41(2):580-637.
3. Wang CH, Hsieh WH, Chou HC, et al. Liberal versus restricted fluid resuscitation strategies in trauma patients: a systematic review and meta-analysis of randomized controlled trials and observational studies*. Crit Care Med. 2014 Apr;42(4):954-61.
4. Boyd JH, Forbes J, Nakada TA, Walley KR, Russell JA. Fluid resuscitation in septic shock: a positive fluid balance and elevated central venous pressure are associated with increased mortality. Crit Care Med. 2011 Feb;39(2):259-65.
5. Marik PE, Levitov A, Young A, Andrews L. The use of bioreactance and carotid Doppler to determine volume responsiveness and blood flow redistribution following passive leg raising in hemodynamically unstable patients. Chest. 2013 Feb 01;143(2):364-70.
6. Bendjelid K, Romand JA. Fluid responsiveness in mechanically ventilated patients: a review of indices used in intensive care. Intensive Care Med. 2003 Mar;29(3):352-60.
7. Monnet X, Marik PE, Teboul JL. Prediction of fluid responsiveness: an update. Ann Intensive Care. 2016;6.
8. Mackenzie DC, Noble VE. Assessing volume status and fluid responsiveness in the emergency department. Clin Exp Emerg Med. 2014 Dec;1(2):67-77.
9. Cavallaro F, Sandroni C, Marano C, et al. Diagnostic accuracy of passive leg raising for prediction of fluid responsiveness in adults: systematic review and meta-analysis of clinical studies. Intensive Care Med. 2010 Sep;36(9):1475-83.