Until recently, at Mount Sinai Hospital, epidural analgesia for labor pain was delivered with a pump that could only provide continuous infusion of the freezing medication in combination of pushes of medication activated by the patient, a technique called patient controlled epidural analgesia (PCEA). In the last decade or so, the literature has suggested that this continuous infusion of medication is not as effective as previously thought, and suggested that instead of continuous infusion, intermittent programmed pushes should be used. The investigators now have devices that are able to do that. Programmed intermittent epidural bolus (PIEB) is a new technological advance based on the concept that boluses of freezing medication in the epidural space are superior to continuous epidural infusion (CEI). The new pumps are able to deliver bolus of medication at regular intervals (PIEB), in addition to what the patient can deliver herself (PCEA). Studies have shown that delivering analgesia in this manner can prolong the duration of analgesia, diminish motor block, lower the incidence of breakthrough pain, improve maternal satisfaction and decrease local anesthetic consumption. Based on the information already available in the literature, this study aims to determine the best regimen of PIEB achievable with our standard epidural mixture.

The hypothesis of this study is that there is an optimal interval time between PIEB boluses of 30 to 60 minutes at a fixed volume of 10 ml of our standard epidural mixture that will provide women the necessary drug requirements, thus avoiding breakthrough pain and need for PCEA or physician intervention.

All studies involving PIEB to date have provided an analgesic regimen that delivered an amount of local anesthetic that was below the patient's requirement per hour, as the studies were done in the context of an association with PCEA (Patient controlled epidural anesthesia) as a rescue technique. As a result, PCEA requests were frequent and therefore these studies have not been able to truly understand the pharmacology of the bolus technique in the PIEB regimen, as the PCEA utilized by patients added an extra component to the regimen.

The ideal volume and interval time between PIEB bolus has not yet been established in the literature. Most likely the ideal volume and interval time between PIEB bolus will be specific for each epidural mixture.

At Mount Sinai Hospital, PIEB devices have been recently introduced. Currently our standard epidural mixture is bupivacaine 0.0625% with fentanyl 2mcg/ml. Our current epidural regimen consists of 10 ml continuous infusion per hour, with PCEA boluses of 5 ml and a lock out interval of 10 minutes, for a maximum of 20 ml of the epidural mixture per hour. In this study, the investigators will offer patients 10mL PIEBs of bupivacaine 0.0625% with fentanyl 2mcg/ml at 4 different intervals. PCEA bolus of 5mL of the same solution will also be available. The goal is to establish the ideal PIEB regimen that will be effective for our patient population with our standard epidural mixture.

Finding the best way of using the new device that will be able to provide analgesia for 90% of the parturients will represent a great improvement in labor analgesia. Moreover, there are expectations of having fewer side effects since the PIEB is more effective than CEI.

Inclusion Criteria:

• ASA I or II
• Full term (≥ 37 weeks gestation)
• nulliparous
• Singleton pregnancy, vertex presentation
• Regular painful contractions occurring at least every 5 minutes
• VAS Pain score at requesting analgesia > 5 (VNPS 0-10)
• Cervical dilatation < 5 cm

Exclusion Criteria:

• Refusal to provide written informed consent.
• Any contraindication to epidural anesthesia
• Accidental dural puncture
• Allergy or hypersensitivity to bupivacaine or fentanyl
• Use of opioids or sedatives within the last 4 hours.