Sonographic Assessment of the Effects of Mechanical Ventilation on Carotid Flow Time and Volume

Background Corrected carotid flow time (CFTc) and carotid blood flow (CBF) are sonographic measurements used to assess fluid responsiveness in hypotension. We investigated the impacts of mechanical ventilation on CFTc and CBF. Materials and methods Normotensive patients undergoing cardiac surgery were prospectively enrolled. Carotid ultrasound (US) was performed pre and post-intubation. Post-intubation measurements took place after the initiation of mechanical ventilation. To measure CFTc and CBF, a sagittal carotid view was obtained with pulse wave-Doppler (maximum angle 60°). CFTc was calculated with the Bazett formula (CFTc = systolic time/√cycle time). CBF was calculated using CBF (mL/min) = area (cm (2 )) x time average mean velocity (TAMEAN) (cm/sec) x 60 (sec/min). The maximum carotid diameter was measured at the level of the thyroid. Results Twenty patients were enrolled. Mean CFTc pre-intubation was 328 ms (SD 43.9 ms) compared to CFTc post-intubation 336 ms (SD 36 ms). There was no significant difference between pre and post-intubation CFTc (mean differences=-0.008; t(19)=-0.71, p=.49). Mean CBF pre-intubation was 487 mL/min (SD 176 mL/min) compared to CBF post-intubation 447 mL/min (SD 187 mL/min). There was no significant difference between pre and post-intubation CBF (mean differences= 40; t(19)=1.24, p=.23). Conclusions In this study of normotensive patients, there were no detected differences in CFTc or CBF pre and post-intubation with mechanical ventilation.