Determination of the ED50 of Intrathecal Hydromorphone in Laboring Women Using the Up-and-down Sequential Allocation Method

This study will investigate the dose of hydromorphone which will relieve the pain of women in labor 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 4 out of 10 thirty minutes after intrathecal injection in 50% of women. Secondary objectives include determining this dose at five and ten minutes after injection. Thirty women admitted to labor and delivery for planned vaginal delivery desiring epidural placement 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 and the epidural is placed, visual analogue pain scores will be assessed 60 minutes following injection. 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, fetal heart rate, and any side effects will also be assessed.