Correlation of Carotid Blood Flow and Carotid Flow Time With Invasive Cardiac Output Measurements

Abstract

There is increasing interest in using noninvasive ultrasound measures such as carotid blood flow and carotid flow time as predictors of volume responsiveness. While these measures are easy to obtain at the bedside, their correlation with cardiac output (CO) from invasive measures has not been previously demonstrated. This study seeks to compare carotid blood flow and carotid flow time measurements with invasive CO. METHODS: Consenting adult patients at Massachusetts General Hospital cardiac catheterization laboratory undergoing right heart catheterization between Feb and Mar 2016 were invited to participate. Carotid ultrasound images were obtained concurrently with CO both pre-and post-passive leg raise (PLR) maneuvers. CO measurements were obtained by the thermodilution method in the absence of severe tricuspid regurgitation and by the Fick oxygen method in the presence of severe tricuspid regurgitation. PLR was performed using a standardized protocol with a 30 0 foam wedge. Post-PLR measurements were performed within one minute after PLR. Carotid blood flow was calculated as: p x (carotid artery diameter) 2 / 4 x velocity time integral x heart rate. Carotid flow time was calculated as systole time / square-root of cycle time. Pre-and post-PLR parameters were compared using paired t-tests and Wilcoxon signed rank tests, as appropriate. Carotid parameters and CO measurements were correlated using Pearson's correlation coefficients. RESULTS: Forty patients (33 men, 7 women) were included. The mean age of patients was 59 years AE 17 (mean AE SD). PLR did not alter CO (pre vs. post PLR 5.3 AE 1.7 vs. 5.3 AE 1.6 L/min, p¼0.88), carotid blood flow (644.0 AE 308.9 vs. 620.5 AE 256.5 mL/ min, p¼0.50) or carotid flow time (330 AE 56 vs. 338 AE 40 msec, p¼0.23). Carotid blood flow significantly correlated with CO both pre-PLR (r ¼ 0.33, 95% CI 0.02-0.58; p¼0.04) and post-PLR (r ¼ 0.34, 95% CI 0.03-0.59; p ¼ 0.03). Carotid flow time did not correlate with CO either pre-(r ¼ 0.15, 95% CI-0.17 to 0.44, p¼0.37) or post-PLR (r ¼ and 0.22, 95% CI-0.09 to 0.50, p¼0.16, respectively). CONCLUSIONS: The correlation between carotid blood flow and invasive CO was moderate and significant, while carotid flow time did not correlate significantly with CO. CLINICAL IMPLICATIONS: Although the lack of CO increase with PLR in our patient population precluded conclusions regarding fluid responsiveness, our results suggest that carotid blood flow may be a better predictor of CO than carotid flow time.