Uterine contractions and the spread of local anesthetics in the epidural space.

Local anesthetics injected into the epidural space during a uterine contraction are commonly believed to produce a higher than usual level of anesthesia. This was evaluated in 34 parturients undergoing continuous lumbar epidural labor analgesia. The patients were divided into two equal groups. In group A, the inducing dose (2% chloroprocaine, 8 ml) was injected during an active uterine contraction and the top-up dose was injected between contractions. In group B, the injection sequence was reversed. Irrespective of the time of injection, in relation to uterine contractions, approximately 16 dermatomal segments were blocked in both groups. It is concluded that uterine contractions do not affect spread of local anesthetic solution in the epidural space.