Effects of the pregnant uterus on the extradural venous plexus in the supine and lateral positions, as determined by magnetic resonance imaging.

Abstract

To clarify the effects of the pregnant uterus on the extradural venous plexus in the supine and lateral positions, we studied magnetic resonance (MR) images of the lumbar spine in three parturients. T2-weighted axial MR images were obtained with the parturient in the supine and lateral positions. On each slice level in the same subject, the MR images were compared with the control MR images obtained before pregnancy. When the parturient lay supine, the pregnant uterus compressed the inferior vena cava and almost totally obstructed it; the extradural venous plexus was engorged. On turning the parturient into the lateral position, the inferior vena cava was free from compression, and the engorged extradural venous plexus was found to shrink to the level of the non-pregnant state.

Major impact of body position on arterial stiffness indices derived from radial applanation tonometry in pregnant and nonpregnant women

“…It has been known for decades that, in advanced pregnancy, the force exerted in the supine position by the uterus on the inferior vena cava leads to its almost complete obliteration [28]. The impact on venous return, cardiac output and arterial BP is variable, depending on the functionality of parallel venous channels, notably the paravertebral sinuses [29]. In a minority of cases, cardiovascular collapse may ensue (the supine hypotensive syndrome), relieved by moving the patient from dorsal to lateral decubitus [28,30].…”

Spinal anesthesia with sequential administration of plain and hyperbaric bupivacaine provides satisfactory analgesia with hemodynamic stability in cesarean section

“…Because the gravid uterus compresses the inferior vena cava with engorgement of the epidural venous plexus, turning a parturient to the supine position causes bulk movement of CSF and enhances rostral spread regardless of baricity. [12][13][14][15][16] After such bulk movement, hyperbaric solutions will redistribute because of gravity and move to the lowest point of the thoracic curve, situated around T6-7 in pregnant, 17 while isobaric solutions mix with CSF with little further spread. Therefore, hyperbaric solutions are more predictable and controllable than isobaric solutions in their spread with posture adjustment just as in non-obstetric patients.…”

Influence of posture on the incidence of vein cannulation during epidural catheter placement

“…Epidural vein cannulation, however, continues to be a particular problem in parturients due to distension of epidural veins [1]. Epidural vein engorgement is maximal when the pregnant woman is in the supine position and minimal in the lateral position [2]. The incidence of epidural vein cannulation varies between 5% and 12% depending on the size of the Tuohy needle and the type of epidural catheter used [3].…”