Epidural chloroprocaine is often used in obstetrical anesthesia because of its fast onset and short duration. These properties make it an ideal drug to use for epidural anesthesia in patients undergoing postpartum tubal ligation. When epidural morphine is given after chloroprocaine, there is a decreased efficacy of analgesia as compared to lidocaine (1). Several studies have hypothesized a specific opioid receptor mediated antagonism of chloroprocaine (2,3). Karambelkar raised the question whether this decreased efficacy is due to a disparity between the time the chloroprocaine anesthesia resolves and the onset of epidural morphine analgesia, resulting in a time window of pain (2). The duration of action of epidural 2-CP anesthesia is 30-45 minutes and the onset of epidural morphine analgesia is 60-70 minutes, therefore the regression of sensory blockade before the onset of the morphine analgesia could result in a window of pain (2). Hess and colleagues studied epidural morphine analgesia and women who had a Cesarean delivery under spinal bupivacaine anesthesia (3). Subjects were randomized to receive epidural 2-CP and morphine or epidural saline and morphine. There was no difference in postoperative analgesia between the two groups (3 and personal communication, Dr. Philip Hess). A literature search cross referencing epidural chloroprocaine, using Pub Med, did not produce any articles comparing epidural morphine given before the procedure (in an attempt to time the onset of analgesia with the resolution of chloroprocaine anesthesia) to the standard administration time after the procedure.

Women undergoing post partum tubal ligation with an epidural in-situ will be randomly double blindedly selected into one of four groups for pain control. The groups are epidural 1) epidural morphine-choroprocaine 2) epidural chloroprocaine-morphine 3) epidural morphine-lidocaine 4) epidural lidocaine-morphine. Groups 1 and 3 will receive morphine 30 minutes prior to local anesthetic dosing followed by saline placebo after local dosing. Groups 2 and 4 will receive placebo 30 minutes prior to local anesthetic dosing followed by epidural morphine. Pain scores and supplemental analgesic requirements will be evaluated 30 minutes, 1hr, 2hr, 4hr and every 4 hrs for the first 24hrs.

• Labour
• Analgesia, Epidural

• Eisenach JC, Schlairet TJ, Dobson CE 2nd, Hood DH. Effect of prior anesthetic solution on epidural morphine analgesia. Anesth Analg. 1991 Aug;73(2):119-23.
• Karambelkar DJ, Ramanathan S. 2-Chloroprocaine antagonism of epidural morphine analgesia. Acta Anaesthesiol Scand. 1997 Jun;41(6):774-8.
• Camann WR, Hartigan PM, Gilbertson LI, Johnson MD, Datta S. Chloroprocaine antagonism of epidural opioid analgesia: a receptor-specific phenomenon? Anesthesiology. 1990 Nov;73(5):860-3.

Inclusion Criteria:

• All patients with an epidural catheter in situ for labor analgesia, status post a vaginal delivery, and scheduled for a postpartum tubal ligation under epidural anesthesia will be eligible

Exclusion Criteria:

• Allergy/hypersensitivity to morphine
• Allergy/hypersensitivity to ester-linked local anesthetics or para-amino benzoic acid (PABA)
• Body Mass Index >40 kg/m2
• Patients using chronic opioids
• History of obstructive sleep apnea
• Any contraindication to epidural anesthesia