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

Epidural vein cannulation has long been recognized as a problem in parturients due to distension of epidural veins. Epidural vein engorgement is maximal when the pregnant woman is in the supine position and minimal in the lateral position. Following an initial observation of an apparently high incidence of epidural vein cannulation in the sitting position, a randomized trial was conducted to document whether such an association existed.

A total of 209 term parturients were randomized to either the sitting or lateral position (107 left lateral, 102 sitting). Epidural catheter placement was achieved using a loss of resistance to air technique with an 18-G Tuohy needle. A data sheet was completed for each patient recording patient position, patient characteristics data, stage in labour and the incidence of epidural vein cannulation. Poor labour analgesia was defined as a visual analogue scale (VAS) > 40 mm on a 0-100 mm pain intensity VAS.

The risk of epidural vein cannulation was significantly higher in the sitting group (16 of 102 = 15.7%) compared with the lateral position group (4 of 107 = 3.7%), P = 0.011. There was a significant association between epidural vein cannulation and poor analgesia (P = 0.006). These two variables remained independently significant on multiple regression analysis (position, P = 0.009; analgesia, P = 0.006).

We conclude that there is a direct correlation between the incidence of epidural vein cannulation and patient posture during epidural catheter insertion in parturients.