Preoperative inferior vena cava-abdominal aorta ultrasound examination to guide the positioning of spinal anesthesia to reduce post-spinal hypotension: a prospective, randomized trial

Haixing Wu¹Ting Chen¹Xiyuan Xie¹Jin Ning²Han Yupeng¹Suren SOORANNA³Qiuxia Huang²Han Wu²Rong Lin²Li Li⁴Liang Lin^2*Xiaodan Wu^1,2*

• ¹Department of Anesthesiology, Fujian Provincial Hospital, Shengli Clinical Medical College of Fujian Medical University, Fujian Medical University, Fuzhou, China
• ²Fujian Provincial Hospital, Fuzhou, China
• ³Imperial College London, London, United Kingdom
• ⁴Fujian Maternal and Child Healthcare Hospital, CHINA, China

Background: The effectiveness of a 15° left-lateral tilt for alleviating the inferior vena cava (IVC) compression caused by a gravid uterus has been questioned. This study assessed the benefits of conducting pre-spinal anesthesia IVC-abdominal aorta ultrasound examinations and utilizing the IVC to abdominal aorta (IVC/Ao) ratio as a guide for post-spinal anesthesia positioning. Methods: 200 parturients undergoing cesarean section were randomized 1:1 into an ultrasound-guided and a control group (groups U and C, respectively). The parturients in group C were positioned with a 15° left-lateral tilt, while those in group U had the operating table tilted to achieve the maximum IVC:Ao diameter, as determined by preoperative ultrasound, which indicated the maximum IVC:Ao diameter. The primary endpoint was the incidence of hypotension in parturients, defined as the period from the completion of intrathecal drug injection (time A) to when they were placed in the supine position (time B). Secondary outcomes included total vasopressor use, umbilical cord blood parameters (such as the pH and base excess values of the umbilical artery) immediately after birth, and Apgar scores at 1 and 5 minutes for the neonate. Results: The incidence of hypotension from the end of spinal anesthesia until the supine position was lower in group U (60.8%, n = 79) compared to group C (80%, n = 80) for the parturients included in the statistical analysis (risk difference = -0.192 (95% CI -0.325 to -0.050), P=0.010. Furthermore, the usage of the vasoactive drug, metaraminol, in group U was lower than in group C (1 (0, 1.5) vs. 1 (0.5, 1.5), with a mean difference of 0.283 (95% CI 0.044 to 0.522), P=0.012. Conclusions: Conducting an IVC-abdominal aorta ultrasound examination before spinal anesthesia in parturients and using the IVC/Ao ratio to guide post-spinal anesthesia positioning reduced the incidence and frequency of hypotension as well as the dose of vasopressors required after surgery. Clinical trial registration: ChiCTR2200059888. (https://www.chictr.org.cn/showproj.html?proj=166587)