Many women experience severe pain during labour. There are many forms of pain relief methods available to women in developed countries. Labour epidural analgesia remains the most effective form of pain relief. It is also the least depressive to the central nervous system of the mother and the baby. After initiating epidural analgesia, there are many regimens that can be employed to maintain analgesia for the duration of labour.

Traditionally, epidural analgesia (using low dose mixtures of local anaesthetic and opioid) has been administered by nurse or midwife-controlled manual boluses or as continuous infusion via a dedicated epidural pump (once the epidural catheter has been placed by an anaesthetist). Although these regimens provide an effective form of labour analgesia, patient satisfaction is not always achieved because of the associated lower limb motor block (leg weakness) and the increased risk of requiring instrumental delivery such as a forceps delivery. Due to recent advances in medical technology, new epidural pumps, which allow patient controlled epidural analgesia (PCEA) boluses and programmed intermittent epidural (PIEB) boluses, are now available.

Bolus injection through an epidural catheter may result in better distribution of anaesthetic solution in the epidural space when compared with continuous infusion of the same low dose local anaesthetic / opioid mixture. Capogna et al carried out a randomized double-blind study to compare the effects of a programmed intermittent epidural bolus (PIEB) regimen with a continuous epidural infusion (CEI). Motor block was reported in 37% in the CEI group and in only 2.7% in the PIEB group (P \< 0.001). The incidence of instrumental delivery was 20% for the CEI group and 7% for the PIEB group (P = 0.03). The total local anaesthetic consumption, number of patients requiring additional PCEA boluses, and mean number of PCEA boluses per patient were also found to be lower in the PIEB group (P \< 0.001). There were no differences in pain scores and duration of labour analgesia. (Capogna et al, 2011) Another randomized controlled study published by Wong et al compared total local anaesthetic (bupivacaine was used in this study) consumption, need for supplemental epidural analgesia, quality of analgesia, and patient satisfaction in women who received programmed intermittent epidural boluses (PIEB) compared with continuous epidural infusion (CEI) for maintenance of labour epidural analgesia. The median total bupivacaine dose per hour of analgesia was significantly less in the PIEB (n = 63) (10.5 mg/h; 95% confidence interval, 9.5-11.8 mg/h) when compared with the CEI group (n = 63) (12.3 mg/h; 95% confidence interval, 10.5-14.0 mg/h) (P \< 0.01). Patient satisfaction scores were also higher in the PIEB group. The authors concluded that PIEB combined with patient controlled epidural analgesia (PCEA) provided similar analgesia, but with a smaller bupivacaine dose and better patient satisfaction compared with CEI with PCEA for maintenance of epidural labour analgesia. (Wong et al, 2006) Wong et al carried out another study to evaluate bupivacaine consumption and other analgesic outcomes when the programmed intermittent bolus time interval and volume were manipulated during the maintenance of epidural labour analgesia. They found that extending the programmed intermittent bolus interval and volume from 15 minutes to 60 minutes, and 2.5 mL to 10 mL, respectively, decreased bupivacaine consumption without decreasing patient comfort or satisfaction. (Wong et al, 2011) In our study, we aim to compare the effects of different combinations of PIEB bolus volume and PIEB time interval on the number of PCEA demands / clinician boluses, pain score, local anaesthetic consumption and patient satisfaction in order to find the optimal PIEB volume and PIEB time interval for labour pain relief when used together with a fixed (pre-determined) PCEA regimen.