Quantitative assessment of carotid diameter measurements in parallel versus rotated and tilted orientation using ultrasound in the operating room: a comparative analysis

Introduction. Hemodynamic monitoring is of utmost importance when treating critically ill patients, but the currently used techniques are invasive and related with catheter-related complications. Over the last two decades, carotid artery ultrasound (US) was investigated as a non-invasive alternative for hemodynamic monitoring, including cardiac output estimation. Both vessel diameter and blood velocity are needed to compute blood flow in a vessel. Traditionally, carotid flow
measurements are performed with the US probe oriented in the long-axis (LA) view [1]. Assuming a circular cross-section of the vessel and a parabolic flow profile, the probe should be properly positioned along the mid-axis to obtain an accurate blood flow estimation. However, obtaining and maintaining this mid-axis parallel view is difficult and literature describes that operator experience may impact the reliability of carotid flow measurements [2]. While the short-axis (SA) view allows for measurement of the true diameter, it does not allow for velocity estimation as the Doppler frequency shift approaches 0 degrees. Another way of assessing the cross-section of the carotid artery is by rotating and tilting (RT) the probe, a view that is easier to visualize and assess for sonographers. Regarding velocity measurements, preliminary research showed that the RT view was more robust to motion and less operator-dependent than the LA view [3]. To our knowledge, there is no literature regarding clinical diameter estimates with the RT view.Objectives. To evaluate the use of the RT view in a clinical setting, and to compare it with the LA and SA views using systolic diameter and spread of systolic diameter estimates per acquisition. The spread of systolic diameter values serves as a measure of robustness.Methods. We performed 30 s US acquisitions of the carotid artery in adult cardiac surgery patients, with a LA, SA, and RT probe orientation. The 30 s US recordings were analyzed to derive a diameter waveform. From this, we computed the systolic diameter values and a measurement of spread (calculated as the IQR of the systolic diameter estimates per acquisition) and investigated for potentially significant differences between views. Results. US acquisitions were performed in 29 patients. The median systolic diameter (IQR) per 30 s acquisition was 7.08 (1.59) mm, 7.22 (1.20) mm, and 6.95 (1.77) mm for the LA, SA, and RT views, respectively (Fig. 1). The median spread (IQR) per 30 s acquisition was 0.12 (0.13) mm, 0.10 (0.10) mm, and 0.09 (0.10) mm for the LA, SA, and RT views, respectively. Normality was checked using the Shapiro–Wilk test and Friedman tests showed no statistically significant difference between the views for either the median (p=0.142) or spread (p=0.786) of systolic diameter per 30 s acquisition. Conclusions. It was feasible to acquire data and derive diameter estimates using the three probe orientations. The median and spread in systolic diameter values per 30 s acquisition were comparable for the LA, SA, and RT views, suggesting that the different views result
in evenly robust measurements and can be used interchangeably to obtain diameter estimates. This study opens the path for further investigation of the newly introduced RT view for new applications and possibilities, such as hands-free measurements.