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

Abstract

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 min 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.

Conclusion: 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: https://www.chictr.org.cn/showproj.html?proj=166587, identifier ChiCTR2200059888.

Keywords: IVC:Ao diameter; cesarean delivery; hypotension; left uterine displacement; spinal anesthesia.

Figure 1

Ultrasound images of the inferior vena cava and abdominal aorta. (A) Ultrasound probe in the right mid-axillary line to measure the position of the inferior vena cava; (B) Ultrasound probe in the subxiphoid process to measure the position of the abdominal aorta; (C) maximum and minimum values of the inferior vena cava and inferior vena cava diameter at the end of expiration and inspiration; (D) two consecutive measurements of the inferior vena cava and inferior vena cava diameter during calm breathing; (E) abdominal aorta and abdominal aorta diameter. IVC, inferior vena cava. IVCmax, maximum value of inferior vena cava diameter at the end of expiration; IVCmin, minimum value of inferior vena cava diameter at the end of inspiration; IVCave, average value of inferior vena cava diameter on two consecutive occasions during calm breathing; Ao, abdominal aorta.

Figure 2

Flow chart for the protocol after the eligible parturients enter the preoperative waiting area.

Figure 3

Flow diagram of the study participants.

Figure 4

Perioperative hemodynamic variables indicators. (A) SBP; (B) DBP; (C) MAP; (D) HR. A generalized estimation equation to analyze the hemodynamics at 18 min post-anesthesia. T1, immediately after spinal anesthesia; T2, T3, T4, T5, T6, T7, T8, T9 and T10 at 2, 4, 6, 8, 10, 12, 14, 16 and 18 min after spinal anesthesia, respectively. * represents p < 0.05. SBP, systolic blood pressure; DBP, diastolic blood pressure; MAP, mean arterial pressure; HR, heart rate.