Discussion
anesthesia-induced hypotension, venous vasodilation, hypotension, hypovolemia, Hypotension
ADVERSE EFFECTS, VASODILATION
This randomized controlled trial failed to demonstrate a significant difference in the incidence of hypotension after spinal anesthesia for elective cesarean delivery when using the SCVUS-based preloading protocol and the conventional fixed-volume fluid preload protocol. Although using SCVUS for patient-customized fluid treatment before spinal anesthesia during cesarean delivery did not lead to a decrease in the incidence of spinal anesthesia-induced hypotension, we observed a significant reduction in fluid preload when using the SCVUS-based preloading protocol. Moreover, reducing fluid preload neither increased the incidence of maternal and neonatal adverse effects nor increased the total vasopressor dose.Hypotension following spinal anesthesia for cesarean delivery has been thought to develop due to venous vasodilation; therefore, for many years, fluid-loading strategies have remained a major part of the anti-hypotensive strategy. A status of sufficient volume loading may reverse relative hypovolemia due to vasodilation and help maintain hemodynamic stability. However, there is still no consensus on fluid-loading strategies for obstetric patients. This study showed that the fixed-volume preload strategy recommended by the British guidelines (2011) [Good neonatal outcomes, as indicated by Apgar scores, were also similar in the two groups. We did not measure umbilical cord gases, as previous studies have demonstrated that fluid strategy does not influence neonatal acid-base status when maternal hypotension is treated [Ultrasonography has been used in adults as a rapid and objective tool for assessing intravascular status [This study had some limitations. First, the sample size was relatively small. Furthermore, we only included relatively stable patients to test our hypothesis, which may have affected the generalizability of this SCVCI index in special cases. Second, all ultrasonographic measurements of SVC diameter were performed by an anesthesiologist fully trained in ultrasonography, which might restrict the applicability of our findings in situations when ultrasonic exams are carried out by untrained doctors. Third, patients that receive more fluid may respond with higher urinary output. We didn’t measure the relationship between urine output with rehydration volume in our study. A previous study demonstrated that there was no association between increased fluid volume administration and augmented urinary output under general anesthesia [In conclusion, SCVUS-guided volume management did not ameliorate post-spinal anesthetic hypotension but reduced the volume of fluid preload required before spinal anesthesia. Reducing preload volume did not increase the incidence of maternal and neonatal adverse effects nor did it increase the total vasopressor dose. More importantly, reducing preload volume could relieve the heart burden of parturients, which has high clinical significance.Future studies should focus on the best practice of the combination of fluid-loading strategies and prophylactic use of vasopressors to prevent post-spinal anesthetic hypotension.