An in-vitro evaluation of pressure generated by Programmed Intermittent Generated Bolus (PIEB) or Continuous Epidural Infusion (CEI)

PIEB has been reported as being superior to CEI for labor analgesia. The aim of this study was to measure the pressures generated by two commercially available pumps (CADD PIB, Smiths and Gemstar, Hospira) when delivering PIEB or CEI at 2 commonly used rates of infusion (10 or 5 mL). The two pumps were set to deliver fluid at four rates (CEI: 5 or 10 mL/h; PIEB: 5 or 10 mL every h) and connected to a pressure transducer (PCB Piezotronics 1500 connected to a NI USB-6251 Screw Terminal) to determine the pressures applied during each infusion. The peak pressure generated during the PIEB mode was consistently higher when compared to the CEI mode in both pumps. When comparing the two pumps in the PIEB 10 mL every hour mode, the peak pressures were approximately the same, while the pressure pattern differed. For each cycle the pressure generated by Gemstar oscillated from 25 mmHg to 0 mmHg; whereas with the CADD pump the baseline pressure was above 0. The Gemstar pump piston frequency (1.2 Hz) was twice as high as the CADD (0.5 Hz), so the volume delivered per cycle was lower. In the PIEB 5 mL every hour mode the peak pressures followed the same wave patterns. However, unlike the 10 mL mode, the pump piston frequency was approximately the same in both pumps. In both the CEI 5 or 10 mL/h modes, the CADD peak pressure was four times greater than the Gemstar. Both cycled between their respective peak pressures and 0 mmHg. Since the peak pressure of the CADD was approximately the same with PIEB and CEI, we speculated that the most important factor affecting the distribution of the solution in the epidural space was not the peak pressure per se, but the mode of delivery of the bolus.