From the Department of Anesthesia, St Luke's International Hospital, Tokyo, Japan.
Department of Anesthesiology, Tokyo Women's Medical University, Tokyo, Japan.
Anesth Analg. 2019 Jun;128(6):1217-1222. doi: 10.1213/ANE.0000000000004166.
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.
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.
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%).
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.
尽管现有的教条认为接受脊髓麻醉下剖宫产的女性应采用 15°左侧倾斜位，但在最初的几项研究中，实际上患者被置于右侧倾斜位。右侧与左侧倾斜位对下腔静脉最佳容积的优越性尚不清楚。我们使用磁共振成像比较了右侧和左侧倾斜位对妊娠妇女腹主动脉和下腔静脉容积的影响。
13 名单胎妊娠且孕周为 31-39 周的孕妇接受磁共振成像检查，分别处于仰卧位、左侧（15°和 30°）和右侧（15°和 30°）倾斜位，通过在身体两侧放置 1.5 米长的聚乙烯泡沫来维持倾斜位。使用磁共振图像测量 L1-L2 椎间盘和 L3-L4 椎间盘之间的腹主动脉和下腔静脉容积。
在检查的任何位置，主动脉容积均无显著差异。30°左侧倾斜位的下腔静脉容积明显大于 15°右侧倾斜位（10.7 ± 7.5 比 5.9 ± 5.1 mL；平均差异，4.8；95%置信区间，1.2-8.5；P =.002）和 30°右侧倾斜位（10.7 ± 7.5 比 5.9 ± 2.5 mL；平均差异，4.8；95%置信区间，1.2-8.4；P =.002）。15°左侧倾斜位的下腔静脉容积与 15°右侧倾斜位（平均差异，0.4；95%置信区间，-3.2 至 4.0；P = 1.000）或 30°右侧倾斜位（平均差异，0.4；95%置信区间，-3.3 至 4.0；P = 1.000）无显著差异。仰卧位的下腔静脉容积仅与 30°左侧倾斜位（5.2 ± 3.8 比 10.7 ± 7.5 mL；平均差异，5.5；95%置信区间，1.8-9.1；P <.001）有显著差异。13 名受试者中有 9 名（70%）在 30°左侧倾斜位观察到最大的下腔静脉容积，3 名（23%）在 30°右侧倾斜位观察到最大的下腔静脉容积。
与仰卧位相比，30°左侧倾斜位最能减轻子宫对下腔静脉的压迫。与 30°左侧倾斜位相比，右侧倾斜位的任何角度都不会增加孕妇的下腔静脉容积。然而，在一部分患者中，30°右侧倾斜位实现了最佳的下腔静脉容积。需要进一步研究以了解这种变异性。
