Corrected Flow Time in the Carotid Artery as a Predictor of Fluid Responsiveness in Mechanically Ventilated Patients With Low Tidal Volume in the Intensive Care Unit

Corrected carotid artery flow time is measured using 6-13 MHz linear probe on a portable ultrasound machine. On the two-dimensional image, the optimal image of the long-axis view is obtained at the left common carotid artery. The sample volume is placed on the center of the lumen, 2 cm proximal to the bulb, and a pulsed wave Doppler examination was performed while the Doppler beams were adjusted to ensure \< 60° of angle for the best signal. Then, cardiac cycle time and carotid flow time is measured. Carotid flow time is measured between the upstroke of the flow tracing and the dicrotic notch, and it is corrected for pulse rate by dividing flow time by the square root of the cardiac cycle time to calculate corrected carotid artery flow time (flow time/√cycle time).