The assessment of circulating capacity and rehydration needs is the basis for recovery, but remains largely empirical. Recently, several arterial Doppler ultrasonography markers have been used to assess preoperative intravascular volume status in non-obstetric patients.14 However, assessing the intravascular volume of obstetric patients with spontaneous respiration remains a challenging task (Preau et al.,2017).
As we know, evaluation of common carotid artery (CCA) blood flow can provide valuable information regarding the hemodynamic status of a patient. In the recent years, the carotid artery VTI as well as measures of their variation induced by the respiratory cycle, have demonstrated a direct correlation with aortic VTI and have been proposed as fast and easy to obtain ultrasound measures for assessing fluid responsiveness in intensive care unit patients (Pace et al.,2021). Importantly, Sidor et al. confirmed that total carotid flow (TCF) calculated based on volume-time integral (VTI) in the carotid artery showed positive correlation to cardiac output and carotid systolic VTI was one of the most promising indicators to assess fluid responsiveness and help fluid management in hemodynamically stable participants (Sidor et al.,2020). Interestingly, during passive leg raising (PLR), an increase of the VTI of subaortic blood flow (ΔVTI) above 12% predicted the response with a sensitivity and specificity of 75 [95% confident interval (CI): 0.42–0.95] and 100% (95% CI: 0.72–1.00), respectively, ΔVTI combined with PLR could accurately predict fluid responsiveness in the specific setting of severe preeclampsia (SP) (Brun et al.,2013). In addition, measurement of the subaortic variation in the velocity time integral (VTI) after passive leg raising allows prediction of fluid responsiveness (Zieleskiewicz et al.,2018). In this context, our study showed that fluid challenge markedly increased VTI in both non-responders and responders groups and the area under the ROC curve to predict fluid responsiveness for VTI was 0.821, the sensitivity and specificity for carotid artery blood flow and VTI are 67%, 90%, with the cut-off values is 8.7 cm/s. Based on our findings, ultrasound measurements of VTI is displayed as an effective indice for predicting fluid responsiveness in pregnant women, suggesting that carotid artery VTI provides characterisation of the risk of capacity overload or insufficient during elective caesarean section under spinal anaesthesia, and therefore may allow individualised strategies for prevention and management. Further work is needed to validate the correlations of ΔVTI and stroke volume (SV) and cardiac index (Ci) and utilize these acquired carotid parameters to guide fluid management and predict fluid responsiveness in pregnant women.
Up to now, emerging evidence showed that carotid blood flow measurements correlated moderately with cardiac output and may be a better marker of cardiac output and less subject to measurements issues than corrected carotid flow time (Ma et al.,2017). Accordingly, carotid blood flow (CBF), which was calculated based on both systolic VTI and total VTI, correlated very strongly with SV, indicating that Doppler ultrasonography of the left common carotid artery (CCA) is able to estimate the SV and cardiac index (Ci) of critically ill children and therefore, the carotid Doppler ultrasonography may be considered as an alternative for estimating Ci when transthoracic echocardiography (TTE) is not feasible or available (Rubio et al.,2022). Of note, Gassner et al. found that intraclass correlation coefficient (ICC) analysis demonstrated almost perfect correlation (0.8152) between measurements of CO via ultrasound vs. invasive modalities, while the ICC between POCUS and the invasive measurement via PCA was 0.84 and via PA catheter 0.74, which showed a basic consistency between ultrasound and the two invasive devices and indicated that common carotid artery POCUS offers a non-invasive method of measuring the CO in the critically ill population (Gassner et al.,2014). As our results indicated, the predictability of carotid artery blood flow was comparable to that of carotid artery VTI with excellent interobserver agreement. Moreover, carotid artery blood flow yielded a cut-off value with the highest sensitivity and specificity. We also showed fluid challenge significantly increased carotid artery diameter and carotid artery blood flow in both two groups after the fluid challenge, suggesting their strong association with preload. Unfortunately, our findings were not consistent with previous study which stated that in patients with suspected sepsis, a fluid challenge did not result in a significant change in CBF, the reason may be due to the patient style and PLR (Liteplo et al.,2021). In the present study, we comprehensively evaluated the ability of the carotid artery to predict volume responsiveness from both the carotid artery VTI and blood flow, which can provide more favorable evidence for the clinical use of the carotid artery in evaluating volume state. Thus, it remains to be verified through further studies and more clinical experience and identify the key limiting factors in using carotid ultrasound to determine fluid responsiveness.
This study has some limitations. First of all, in our study, only 72 women who chose elective cesarean section were enrolled. We will recruit more obstetric patients to explore the best ultrasound technique and the cutoff points for predicting fluid responsiveness and avoid overestimating the predictive power of these indices in our future studies. Second, this study was not conducted in women with gestational hypertension, preeclampsia, or emergency cesarean section, who are currently considered to be at high risk for hemodynamic instability. Future studies will determine the reliability and feasibility of ultrasonic techniques in predicting fluid responsiveness in pregnant women. Third, carotid artery blood flow and VTI are negatively correlated with systemic vascular resistance and are affected by left ventricular preload and myocardial strength. Therefore, many other factors that alter afterload also affect VTI and carotid artery blood flow (Sidor et al.,2020). In future studies, the predictive power of VTI and carotid blood flow in different populations and clinical settings should be evaluated. Fourth, in this study, ultrasound technology was only applied to perioperative parturients to accurately measure carotid artery blood flow and VTI to predict fluid responsiveness. Future studies will use ultrasound measurements of other peripheral arteries, such as the radial or brachial arteries, to predict fluid reactivity in pregnant women. Our study demonstrated that ultrasound evaluation of VTI and carotid artery blood flow appeared to be the accurate indicators of fluid responsiveness in pregnant women. Future researches should focus further on the accuracy and reliability of carotid artery blood flow and VTI, as well as their relations to other sonographic predictive measurements.