Determination of the ED50 of Intrathecal Hydromorphone for Post-cesarean Section Pain Relief

This study will investigate the dose of hydromorphone which will relieve the pain of women following a cesarean section when delivered directly in the area around the spinal cord (i.e., intrathecal injection). The primary objective is to determine the dose of intrathecal hydromorphone that results in a pain score of less than 3 out of 10 12 hours after intrathecal injection in 50% of women. Secondary objectives include determining the average amount of time patients obtain pain relief after injection. Other secondary objectives include determining the frequency and severity of side-effects associated with intrathecal administration of hydromorphone, including: bradycardia, hypotension, respiratory depression, apnea, pruritus, rash, nausea, vomiting, and drowsiness. Thirty women admitted to labor and delivery for planned cesarean section desiring will be consented for the study. The starting dose of intrathecal hydromorphone will be 6 mcg. The up-and-down sequential allocation method of statistical analysis will be used, meaning that each subsequent dose will be dependent upon the result obtained from the prior dose - ergo, if the initial subject has pain relief, the second subject will receive 4 mcg (2 mcg less), but if the initial subject does not have pain relief, the second subject will receive 8 mcg (2 mcg more) of hydromorphone.

After the intrathecal injection is given, patients will undergo their cesarean section. The patient's pain will be assessed at 6, 12, and 18 hours post-injection using a questionnaire. The patient's medical record will be reviewed to determine when she first requested supplemental pain medication. A pain score of less than three will be a positive result. A pain score of three or greater will be a negative result. Blood pressure, heart rate, arterial oxygen saturation, 5 and 10 minute APGAR scores, and any side effects will also be assessed.