Correlation Between Doppler Derived Carotid Artery Corrected Flow Time and Pressure Transducer Derived Radial Artery Corrected Flow Time: A Prospective Observational Study.

Purpose: Carotid artery corrected flow time (cFT) derived from Doppler USG is a known predictor of volume responsiveness. However, it can't be obtained continuously, and is operator dependent. In this prospective study, correlation between Doppler derived carotid artery cFT and pressure transducer derived radial artery cFT was evaluated in adult patients undergoing surgery under general anaesthesia.
Methods: Doppler derived carotid artery cFT were obtained from n = 51 adult patients at n = 125 time points. Simultaneously, pressure transducer waveforms were saved at the time of measurement of carotid artery cFT. Later, images were analyzed by an image processing computer software; both pulse pressure variation and cFT were estimated from pressure transducer waveform.
Results: Radial artery flow times measured by two independent observers, were significantly correlated (r ²  = 0.99, p < 0.00001). Bland-Altman analysis found limits of agreement - 8.3 to 6.3 ms [mean difference (95% CI) - 0.98 (- 1.63, - 0.32)]. Doppler derived carotid artery cFT & pressure transducer derived radial artery cFT were also significantly correlated [r ²  = 0.78, p < 0.0001]. However, radial artery cFT was significantly higher than carotid artery cFT [p < 0.0001, paired sample t test]. Radial artery cFT > 404.4 ms had an sensitivity and specificity of 87.34% and 85% respectively with a grey zone was between 393.7 and 417 ms to predict PPV ≥ 12%.
Conclusion: Pressure transducer derived radial artery cFT correlated with Doppler derived carotid artery cFT and may be a reasonable predictor of volume responsiveness. Further studies are required to confirm its role in various clinical scenario for prediction of volume responsiveness.