Ultrasound Assessment of the Change in Carotid Corrected Flow Time in Fluid Responsiveness in Undifferentiated Shock

Patrick Siegele, MS4

The article: Barjaktarevic, Igor, et al. “Ultrasound Assessment of the Change in Carotid Corrected Flow Time in Fluid Responsiveness in Undifferentiated Shock.” Critical Care Medicine, vol. 46, no. 11, 2018.

The Idea: In the resuscitation of shock, fluid responsiveness assessments are used to evaluate an increase in cardiac output (CO) in response to preload augmentation. One preload augmentation technique is the passive leg raise (PLR) which creates intravascular fluid shifts thus increasing venous return and ultimately enabling assessment of CO change. Currently, CO monitoring technology is expensive, not widely available, and imprecise. However, the use of carotid Doppler ultrasound is already widely used in ICUs and can effectively evaluate fluid responsiveness. Changes in corrected carotid flow time (ccFT) are thought to reflect changes in stroke volume. This study compares ccFT to the reference standard of Noninvasive cardiac output monitoring (NICOM, Cheetah Medical, Newton Center, MA) which has been validated with PLR in the literature.

The Study: Prospective, noninterventional study taking place between May 2016 and April 2017.

Design: Study took place in medical and surgical ICUs in a single academic quaternary care center. Consent was obtained prior to enrollment. ccFT was measured via ultrasound before and after PLR. Predicted fluid responsiveness was defined as greater than 10% increase in stroke volume on NICOM following PLR. Fluid responsiveness status was defined as greater than or equal to 10% increase in stroke volume with NICOM. Images and measurements were reanalyzed by a second, blinded physician.

  • Inclusion criteria: adult patients admitted to medical or surgical ICUs with new (less than 24 hours), undifferentiated shock, and vasopressor requirements despite fluid resuscitation greater than 1 L of IV fluids

  • Exclusion criteria: significant cardiac disease (heart failure, pulmonary hypertension, cardiac arrhythmia, significant peripheral vascular disease, increased intracranial pressure, recent abdominal surgery, recent venous thromboembolism, and BMI less than 15 or greater than 40) and conditions that precluded adequate passive leg raising

  • Primary Endpoints: Compare the ability to of ccFT to predict changes in stroke volume to the reference standard of NICOM. 

Results: 77 patients were enrolled with 54 classified as fluid responders by NICOM.

  •  NICOM cutoff of 10% increase in stroke volume was used to define fluid responders

  • Fluid responsive patients had an average increase in ccFT after PLR of 14.1 ms

  • Non-fluid responsive patients had an average decrease of 4.0 ms

  • Cutoff of 7ms increase in ccFT had specificity of 97%, sensitivity of 68%, positive predictive value of 97% and accuracy of 82%

  • Area under curve of 88% suggests it can be used as alternative to NICOM.

The Takeaway:

Corrected carotid Flow Time can predict fluid responsiveness status after passive leg raise maneuver. Further utility of this technique is the fact that there were no changes found when subgroup analyses were performed on mechanical ventilation, respiratory rate, and PEEP greater than 5.

  • Limitations: Passive leg raise does not only measure preload, but also heart rate, inotropy and afterload conditions. Exclusion of patients with heart failure decreases generalizability.