title: Effect of lateral tilt angle on the volume of the abdominal aorta and inferior vena cava in pregnant and nonpregnant women determined by magnetic resonance imaging.
abstract: BACKGROUND
  Left-lateral tilt position is used to reduce assumed aortocaval compression by the pregnant uterus.
  
  
  METHODS
  Magnetic resonance images of 10 singleton parturients at full term and 10 healthy nonpregnant women were obtained for measurement of the abdominal aorta and inferior vena cava volume between the L1-L2 disk and L3-L4 disk levels in both the supine and left-lateral tilt positions (15°, 30°, and 45°) maintained by insertion of a 1.5-m-long polyethylene foam placed under the right side of the parturient's body.
  
  
  RESULTS
  Aortic volume did not differ significantly between parturients and nonpregnant women in the supine position (12.7 ± 2.0 vs.12.6 ± 2.1 ml, mean ± SD; mean difference, -0.1; 95% confidence interval [CI], -2.0 to 1.9; P = 0.95). Inferior vena cava volume in the supine position was significantly lower in parturients than in nonpregnant women (3.2 ± 3.4 vs.17.5 ± 7.8 ml; mean difference, 14.3; 95% CI, 8.3-20.2; P < 0.001). Aortic volume in parturients did not differ among left-lateral tilt positions. Inferior vena cava volume in the parturients was not increased at 15° (3.0 ± 2.1 ml; mean difference, -0.2; 95% CI, -1.5 to 1.2; P > 0.99), but was significantly increased at 30° (11.5 ± 8.6 ml; mean difference, 8.3; 95% CI, 2.3-14.2; P = 0.009) and 45° (10.9 ± 6.8 ml; mean difference, 7.7; 95% CI, 2.2-13.1; P = 0.015).
  
  
  CONCLUSIONS
  In parturients, the aorta was not compressed, and a 15° left-lateral tilt position did not effectively reduce inferior vena cava compression.
authors.affiliation: From the Department of Anesthesiology, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Higuchi
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takagi
authors.forename: Kan
authors.initials: K
authors.lastname: Zhang
authors.forename: Ikue
authors.initials: I
authors.lastname: Furui
authors.forename: Makoto
authors.initials: M
authors.lastname: Ozaki
mesh_terms: D000328:Adult; D001012:Aorta, Abdominal / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D056888:Patient Positioning; D011247:Pregnancy; D016683:Supine Position; D014599:Uterus / Q000033:anatomy & histology; D014682:Vena Cava, Inferior / Q000033:anatomy & histology*; D055815:Young Adult