Combined spinal epidural anesthesia (CSE) is a very effective technique to provide labor analgesia. One of the disadvantages of this technique is the delay in recognizing an error in the position of the epidural catheter because of the effects of the spinal component. Eventually in case of a misplaced catheter, the patient will experience pain or discomfort requiring a repeat procedure after the effect of drug given during the spinal wears off. Low current electrical stimulation test, or the Tsui test, has been used successfully to confirm catheter location in the epidural space. The investigators' objective in this study is to test the usefulness of the Tsui test to confirm the correct placement of the epidural catheter during CSE in laboring patients.

CSE is a widely used technique to provide analgesia in laboring patients. One of the disadvantages of the CSE is the delay in recognizing the mal-position of the epidural catheter, which is initially masked due to the effects of the spinal component. A mal-positioned epidural catheter can cause unnecessary maternal discomfort and dissatisfaction, as it requires a repeat procedure when the effect of spinal drug wears off. Additionally, in the event of emergency caesarean delivery, it would be advantageous to know that the catheter is properly placed. Low current electrical stimulation test, or the Tsui test, has been used successfully to confirm catheter location in the epidural space. Our objective in this study is to test the usefulness of the Tsui test to confirm the correct placement of the epidural catheter during CSE in laboring patients.

Two groups of patients will be studied. In the first group, after the placement of the epidural catheter and noting the electric current required to elicit a motor response (maximum current used is 20 mA), a spinal needle is introduced one inter vertebral space below the space where the epidural catheter is inserted and 0.7 ml of 0.25% isobaric bupivacaine and 15 mcg of fentanyl is injected intrathecally. The epidural catheter is then re-stimulated and the magnitude of the current required to reproduce the motor response is noted. The stimulation is repeated after 5, 10, and 15 minutes. The second group consists of patients with accidental dural puncture. An intrathecal catheter is inserted and the Tsui test performed (maximum current used is 2 mA), followed by the injection of same mixture of local anesthetic and opioid as used in the first group. The Tsui test is repeated at 5, 10 and 15 minute intervals, similar to what is done in the epidural group. After 15 minutes, patients in both groups are managed as per departmental policy. In both the groups, the Tsui test will be repeated after 120 minutes during the maintenance of labor analgesia to determine the change in intensity of current required to elicit the motor response.

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) 1 or 2
• Full term pregnancy
• Patients requesting epidural in early labor

Exclusion Criteria:

• Any contraindication to regional anesthesia
• Allergy or hypersensitivity to lidocaine, bupivacaine, or fentanyl
• Received prior sedatives or opioids
• Abnormal vertebral anatomy
• Neurological disorders with lumbar involvement
• Patients with implanted electronic devices