Background: The inferior vena cava (IVC) in the parturients is compressed by enlarged uterus, which is thought to be one of the causes of hypotension after subarachnoid local anesthetic injection (SI). Therefore, aortocaval decompression maneuvers, such as left lateral tilt of 15° or leftward manual uterine displacement (MUD)1, are widely adopted during Caesarian section (CS) to reduce assumed IVC compression by the pregnant uterus in the supine position. However, a recent magnetic resonance imaging study2 shows that a 15° left lateral tilt is not a sufficient relief from the IVC compression in term parturient, and the dogma is in controversy. The MUD is another measure to avoid IVC compression, however, there is no study showing IVC decompression by it under spinal anesthesia for CS. The purpose of this study is to uncover the effect of MUD by measuring IVC cross-section area (IVCCA) using ultrasonography in parturients who undergoes spinal anesthesia for caesarean section. 
Materials and methods: 88 full term pregnancies receiving elective CS under spinal anesthesia were included in this study from January to November 2017. We measured end-expiratory IVCCA “before anesthesia (supine position)”, “3 minutes after SI”, “after applying MUD (3-6 minutes after SI)”, and “after operation”. To obtain IVCCA, we used planimetry with sector probe (S-NerveTM FUJIFILM SonoSite Japan) at epigastric fossa. We defined 20% change of IVCCA or more compared to the prior one as significant.
Results and Discussion: We were able to obtain the data of IVCCA in 73 patients “before anesthesia” and “3 minutes after SI”. IVCCA of “3 minutes after SI” became significantly small (P = 0.0234). In 65 patients, we were able to compare “3 minutes after SI” and “after applying MUD”. MUD was effective in 26 patients (40%), but there was no significant difference between the two measures (1.00(0.65-1.58) v.s. 1.15 (0.57-1.85) cm2, P = 0.63). On the other hand, MUD was effective in 17 of 29 patients (59%) whose IVCCA at “3 minutes after SI” was decreased by more than 20% from the “before anesthesia”. In those patients, the IVCCA of “3 minutes after SI” and “after applying MUD” were 0.69 (0.44-1.15) and 1.33(0.49-1.91), respectively. 
Conclusions: We measured IVCCA in full term parturients during anesthetic management for elective CS. Although MUD was considered to be effective in parturients whose IVCCA decreased after SI, IVCCA was not increased in general by MUD. 


02 / Manual uterine displacement does not always increase the inferior vena cava cross-section area after subarachnoid injection of local anesthetics for Caesarean section