Brief report: a randomized controlled trial of Synera versus lidocaine for epidural needle insertion in labouring...

Skin infiltration with lidocaine, although brief, can be very stressful, painful, and may perpetuate anxiety. Synerat, a local anesthetic patch, which contains an oxygen-activated heating component to enhance the delivery of a eutectic mixture of lidocaine (70 mg) and tetracaine (70 mg), has provided analgesia for minor, dermatological procedures. We hypothesized that the analgesic effect of Synera, for pain in labouring parturients, would be superior to the traditional infiltration of lidocaine prior to epidural needle insertion.

With Institutional Review Board approval, we recruited women, who consented to epidural labour analgesia and who met the following criteria: older than 18 yr; body mass index less than 45 kg x m(-2); and with no history of hypersensitivity to any study medications. We randomized the labouring parturients into Synera (SS) or placebo (PL) groups. Group SS received the Synera patch and infiltration with saline prior to epidural needle insertion. Group PL received a placebo patch and infiltration with 2% lidocaine.

The groups were similar with respect to age, estimated gestational age, gravidity, parity, and body mass index. The subjects' pain, with epidural placement, was significantly greater in the SS group (P < 0.001). More SS subjects required additional, deep, local anesthetic infiltration compared to PL (P = 0.02).

The Synera patch provided inferior analgesia, for performing epidural labour analgesia in labouring parturients, compared to traditional infiltration with 2% lidocaine.