The Article: Shokoohi H, Berry GW, Shahkolahi M, King J, King J, Salimian M, Poshtmashad A, Pourmand A. The diagnostic utility of sonographic carotid flow time in determining volume responsiveness. J Crit Care. 2017 Apr;38:231-235. doi: 10.1016/j.jcrc.2016.10.025. Epub 2016 Nov 9. PMID: 27987483.
The Idea: Determining volume status and fluid responsiveness in patients with volume depletion is a critical but challenging task. Carotid Flow Time (FTc) is a noninvasive method that has been evaluated and shown to be a tool to predict volume status. However, even when volume status is known, about 50% of hypotensive, critically ill patients fail to improve cardiac output after IV fluid administration; and there are increasing data showing that excessive fluid administration may be harmful and associated with increased mortality. Physicians are hoping to find data to support the use of FTc as a method of predicting fluid responsiveness as well.
The Study: A prospective, observational study conducted at a health fair event at a Tertiary academic medical center in Washington, DC in July, 2015.
Inclusion Criteria: Participants were recruited from a convenience sample of attendees who were observing a prolonged fast (due to Ramadan).
Exclusion Criteria: Pregnancy; medical history significant for cardiovascular or renal disease; fasting for less than 12 hours; <18 years of age; found to be in a-fib during the study; or did not return for ultrasound measurements in the non-fasting state.
139 participants were screened for enrollment, with 16 excluded due to above criteria. 123 had FTc measurements taken both in the fasting and non-fasting states. The prolonged fasting state was assumed to be a dehydrated state, and the non-fasting state assumed to be a normal hydration state. Flow time was measured from the onset of systolic time until the dichrotic notch and then the measurements were repeated following a PLR maneuver.
Primary outcome: the diagnostic accuracy of change in FTc and the optimal cutoff value of a relative increase in FTc in regard to the hydration status and after a PLR maneuver at predicting fluid status.
Secondary outcomes: correlation of FTc values following PLR and oral fluid rehydration, covariate-adjusted changes in FTc as measure in the semi-Fowler position by fluid status, and the reliability of FTc measurements based on agreements between two independent physicians’ measurements.
Results: Changes in FTc by Fluid status: FTc was significantly lower in the fasting state compared with non fasting state (312 +/- 22 vs 345 +/- 25ms, P < 0.001), an absolute difference of -33ms (95% CI, -29 to -38). This difference remained significant after adjusting for other variables. Diagnostic Accuracy of change in FTc with PLR: A relative increase of 5% following PLR was 73% sensitive and 82% specific for predicting fluid status. As baseline FTc increased, there were an increase in specificity and decrease in sensitivity of the test to detect volume status. Change in FTc following PLR was significantly correlated with FTc in the rehydrated state.
The Takeaway: This study confirms data from previous studies that the FTc can be a reliable predictor of volume status when using a cutoff of a change of 5% from baseline after PLR maneuver. However, sensitivity and specificity are impacted by the baseline FTc of the patient, with a profound volume depletion leading to higher sensitivity of the test. The data did not provide any correlation for the utility of FTc measurements in predicting Volume responsiveness and further studies, preferably randomized controlled trials, are needed to investigate this possibility.
Summary by: Daniel Guillory, MS4