Editors' ChoiceAnesthesia

Is a Painless Labor Possible?

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Science Translational Medicine  10 Mar 2010:
Vol. 2, Issue 22, pp. 22ec40
DOI: 10.1126/scitranslmed.3001024

Despite relieving labor pain, epidural analgesia can also paralyze the pelvic muscles, prolonging labor and increasing the risk of fetal distress and cesarean delivery. On the other hand, an anesthetic agent that targets sensory nerves without impairing motor function would allow women in labor to push effectively without experiencing pain. Sensory-specific local anesthetics can be produced by coupling lidocaine with capsaicin, a molecule that binds to receptors found only on sensory nerves. However, these lidocaine-derived compounds invariably carry a positive charge, which limits their ability to penetrate the membrane of the nerve and reach their intracellular targets. Consequently, their potential clinical utility has been limited by low effectiveness and brief duration of action. In a recent report, Sagie and Kohane overcome this problem by using agents that enhance chemical permeation to increase drug concentrations inside the nerve cells and therefore achieve effective and long-lasting analgesia.

Chemical permeation enhancers, or CPEs, are known to improve drug delivery across the skin and the oral mucosa. To test the effects of surfactant CPEs on nerve blockade by lidocaine derivatives, the researchers co-injected the two compounds into the rat’s sciatic nerve, which supplies the main innervation of the hind limbs. The surfactant CPEs increased the ability of the lidocaine-derived molecules to block nerve function and produced anesthesia with a minimal degree of motor impairment. Furthermore, the animals exhibited prolonged sensory analgesia—for up to 14 hours with certain CPE compounds.

Sagie and Kohane have described a unique strategy by which to achieve prolonged sensory-selective nerve blockade. Although the safety of the surfactant CPEs used in this study has yet to be established, the co-administration of CPEs and lidocaine derivatives may be a potentially useful approach to effectively relieve pain in labor without placing the fetus at risk.

I. Sagie and D.S. Kohane, Prolonged sensory-selective nerve blockade. Proc. Nat. Acad. Sci. U.S.A. 107, 3740–3745 (2010). [Abstract]

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