Carotid ultrasound measurements for assessing fluid responsiveness in spontaneously breathing patients: corrected flow time and respirophasic variation in blood flow peak velocity

Background: This study evaluated the ability of two Doppler ultrasound-derived parameters, the carotid corrected flow time (FTc) and respirophasic variation in carotid artery blood flow peak velocity (Delta Vpeak), to predict fluid responsiveness in spontaneously breathing patients. Methods: A total of 53 spontaneously breathing patients were studied before anaesthetic induction for neurosurgery. Carotid FTc, Delta Vpeak, and haemodynamic data were measured before and after administration of 6 ml kg(-1) colloid. Fluid responsiveness was defined as a 15% or more increase in stroke volume index as assessed by transthoracic echocardiography after the fluid challenge. Results: Twenty-two (42%) patients were fluid responders. The areas under the receiver operating characteristic curves for FTc and Delta Vpeak were 0.842 [95% confidence interval (CI) 0.735-0.948, P<0.001] and 0.818 (95% CI: 0.701-0.935, P<0.001), respectively. The optimal cut-off values of FTc and Delta Vpeak for fluid responsiveness were 349.4 ms (sensitivity of 72.7%; specificity of 83.9%) and 9.1% (sensitivity of 72.7%; specificity of 87.1%), respectively. The grey zone for FTc was 346.9-361.0 ms and included 28% of the patients, and the grey zone for Delta Vpeak was 6.5-10.2% and included 50% of the patients. Conclusions: Using Doppler ultrasound-derived parameters measured at the carotid artery, FTc predicted fluid responsiveness in spontaneously breathing patients better than Delta Vpeak. However, further studies are warranted before these parameters are recommended for clinical use.