Effect of Right-Lateral Versus Left-Lateral Tilt Position on Compression of the Inferior Vena Cava in Pregnant Women Determined by Magnetic Resonance Imaging

Abstract

BACKGROUND: Despite the existing dogma that women undergoing cesarean delivery under spinal anesthesia should be positioned with a 15° left-lateral tilt, the patients were actually positioned in a right-lateral tilt position in several of the original studies. The superiority of right versus left positioning for optimal inferior vena cava volume is unknown. We used magnetic resonance imaging to compare the effects of right-lateral and left-lateral tilt positions on abdominal aortic and inferior vena cava volumes in pregnant women. METHODS: Thirteen women with singleton pregnancies and gestational age 31–39 weeks underwent magnetic resonance imaging while in the supine position, and in the left-lateral (15° and 30°) and right-lateral tilt (15° and 30°) positions, which were maintained by placing a 1.5-m–long piece of polyethylene foam under either side of the body. Abdominal aorta and inferior vena cava volume were measured between the L1–L2 disk and L3–L4 disk levels using magnetic resonance images. RESULTS: Aortic volume did not differ significantly among any of the positions examined. Mean inferior vena cava volume was significantly greater in the 30° left-lateral tilt position than in the 15° right-lateral tilt (10.7 ± 7.5 vs 5.9 ± 5.1 mL; mean difference, 4.8; 95% CI, 1.2–8.5; P = .002) and 30° right-lateral tilt (10.7 ± 7.5 vs 5.9 ± 2.5 mL; mean difference, 4.8; 95% CI, 1.2–8.4; P = .002) positions. Mean inferior vena cava volume in the 15° left-lateral tilt position did not differ significantly from that in the 15° right-lateral tilt (mean difference, 0.4; 95% CI, −3.2 to 4.0; P = 1.000) or 30° right-lateral tilt (mean difference, 0.4; 95% CI, −3.3 to 4.0; P = 1.000) positions. Mean inferior vena cava volume in the supine position only differed significantly from that in the 30° left-lateral tilt position (5.2 ± 3.8 vs 10.7 ± 7.5 mL; mean difference, 5.5; 95% CI, 1.8–9.1; P < .001). The greatest inferior vena cava volume was observed in the 30° left-lateral tilt position in 9 of 13 subjects (70%), and in the 30° right-lateral tilt in 3 subjects (23%). CONCLUSIONS: The 30° left-lateral tilt position most consistently reduced inferior vena cava compression by the gravid uterus compared with the supine position. Mean inferior vena cava volume in pregnant women was not increased at either angle of the right-lateral tilt position compared with the 30° left-lateral tilt position. However, in a subset of patients, the 30° right-lateral tilt position achieved the optimal inferior vena cava volume. Further investigation to understand this variability is warranted.

The Transverse Diameter of Right Common Femoral Vein by Ultrasound in the Supine Position for Predicting Post-spinal Hypotension During Cesarean Delivery

“…Many studies have demonstrated that velocities or diameters of the compressed IVC and AA could indicate the degree of aortocaval compression by the gravid uterus, and could change dramatically in the supine position during late pregnancy using magnetic resonance imaging (MRI). 10,11,12,13 Lee et al also demonstrated a dramatic change in cardiac output on suprasternal Doppler with patients in the supine position in late pregnancy. 14 However, none of these studies further clari ed the relationship between the degree of aortocaval compression and the incidence of hypotension after spinal anesthesia during cesarean delivery.…”

The transverse diameter of right common femoral vein by ultrasound in the supine position for predicting post-spinal hypotension during cesarean delivery

“…Many studies have demonstrated that the velocity or diameter of the compressed IVC could indicate the degree of aortocaval compression by the gravid uterus, and could change dramatically in the supine position during late pregnancy using magnetic resonance imaging (MRI) [12][13][14][15]. Lee et al also demonstrated a significant decrease in cardiac output on suprasternal Doppler, in late pregnancy, with parturients in the supine position, owing to IVC compression by the uterus [16].…”

The transverse diameter of right common femoral vein by ultrasound in the supine position for predicting post-spinal hypotension during cesarean delivery.

“…Many studies have demonstrated that velocity or diameter of the compressed IVC could indicate the degree of aortocaval compression by the gravid uterus, and could change dramatically in the supine position during late pregnancy using magnetic resonance imaging (MRI) [12][13][14][15]. Lee et al also demonstrated a signi cant decrease in cardiac output on suprasternal Doppler with patients in the supine position in late pregnancy due to the IVC compression by the uterus [16].…”