Wong et al compared a PIEB (6 ml of bolus every 30 minutes) with CEI with the assumption that small frequent boluses may avoid wide fluctuations in sensory levels, commonly seen with traditional manually administered intermittent boluses and at the same time reduce the total anesthetic dose as in CEI. Chua and Sia showed that Pain scores were lower and the time to first manual epidural rescue bolus was longer in parturients assigned to intermittent boluses compared to continuous epidural infusion of the same solution in the intermittent group. Fettes and colleagues found that patients required a lower total drug dose and fewer manual bolus injections when epidural labor analgesia was maintained with automated intermittent boluses of ropivacaine compared to a continuous infusion. Solutions injected into the epidural space tend to spread more evenly when injected as a bolus, as compared to a continuous infusion. Furthermore, studies of epidural opioid analgesia suggest that epidural bolus administration of lipid soluble opioids (e.g., fentanyl) results in segmental spinal opioid analgesia, whereas continuous opioid epidural infusion results in systemic opioid analgesia. The analgesic effects of both epidural fentanyl infusion and epidural fentanyl bolus were evaluated using a volunteer, double blind, cross-over designs study. Taken together, the results of these studies suggest that further studies of automated intermittent bolus injections are indicated, in particular, studies of the optimal bolus time interval and volume. At one end of the spectrum, a short interval/low volume protocol may mimic a continuous infusion. At the other end of the spectrum, a long interval/large volume may negate the inherent safety of a continuous infusion. The purpose of the proposed study is to determine how manipulation of the programmed intermittent time interval and volume influences total drug use, quality of analgesia, and patient satisfaction during maintenance of labor analgesia.