Regional anesthesia is commonly used for elective and emergency cesarean delivery. It provides numerous safety advantages when compared to general anesthesia for both the mother and fetus1. Epidurals also have the added benefit of being able to provide pain relief throughout labor and in the event of cesarean delivery, epidural analgesia can be "extended" to provide surgical anesthesia. Numerous studies have been performed to assess the onset times of various local anesthetics when administered through an epidural catheter. Attempts to reduce anesthetic onset time and improve the quality of intraoperative analgesia have been attempted by using different local anesthetic solutions and by the addition of other drugs to the epidural solution (such as epinephrine, fentanyl and sodium bicarbonate).

Regional anesthesia is commonly used for elective and emergency cesarean delivery. It provides numerous safety advantages when compared to general anesthesia for both the mother and fetus1. Epidurals also have the added benefit of being able to provide pain relief throughout labor and in the event of cesarean delivery, epidural analgesia can be "extended" to provide surgical anesthesia. Numerous studies have been performed to assess the onset times of various local anesthetics when administered through an epidural catheter. Attempts to reduce anesthetic onset time and improve the quality of intraoperative analgesia have been attempted by using different local anesthetic solutions and by the addition of other drugs to the epidural solution (such as epinephrine, fentanyl and sodium bicarbonate).

A recent meta-analysis concluded that the optimum local anesthetic solution for extending a labor epidural from analgesia to surgical anesthesia has yet to be determined 2. In 1994, a retrospective study compared 1.5% lidocaine/bicarbonate/epinephrine mixture to 3% chloroprocaine in parturients with pre-existing epidural catheters for urgent cesarean delivery3. It was found that the chloroprocaine group had a significantly faster onset of anesthesia compared to the lidocaine group. Both drugs provided excellent anesthesia. However a high quality study comparing 3% chloroprocaine with 2% lidocaine/ epinephrine/ bicarbonate/ fentanyl (LEBF) in terms of anesthetic onset times has yet to be performed.

Women in labor frequently request an epidural to provide pain relief. Epidural pain relief is commonly provided by the administration of a low concentration of local anesthetic and opioid solution through an epidural catheter. This solution is delivered by an automated epidural infusion pump. In the event that a cesarean delivery is required, the pre-existing epidural is frequently used to administer a higher concentration anesthetic solution to allow pain free cesarean delivery. This is commonly referred to as an "epidural top up" or as an "extension of the epidural block." Standard practice at University of Arkansas for Medical Sciences (UAMS) for an epidural top up is Lidocaine, Epinephrine, Bicarbonate and Fentanyl (LEBF) or 3% chloroprocaine. These two mixtures are routinely and almost exclusively used for epidural cesarean delivery. The decision on which mixture to use is based solely on physician preference. It is likely that the LBEF mixture is used more frequently but the investigators consider both local anesthetic mixtures as equals and the standard of care at UAMS. The investigators do not use any other local anesthetics (unless there are very specific reasons).

Inclusion Criteria:

• ≥ 18 years of age for the mother
• Singleton pregnancy
• Gestation > 36 weeks
• American Society of Anesthesiologist (ASA) class II
• Provides written consent
• Infant of mother

Exclusion Criteria:

• Patient refusal
• Non-elective or urgent/emergent cesarean sections
• ASA class III or above
• Unable to understand English
• Significant back surgery or scoliosis
• Known fetal abnormality
• Weight > 120 kg
• Height < 150 cm
• Allergy to local anesthetics
• Concurrent use of sulfonamides

Any mother requiring an elective cesarean section.

During inpatient admission, approximately three days

local anesthetic systemic toxicity (LAST), post-dural puncture headache (PDPH) and high spinal (defined as upper limb weakness)