Differential flow from multihole epidural catheters

The pressures used in vivo to administer epidural doses of local anaesthetic were recorded for 16- and 18-gauge multihole catheters. Observations were made on 10 patients in labour for each catheter gauge. The pressure range for the 16-gauge catheters was 39.9-266 kPa, with a mean of 167.2 kPa, and for 18-gauge, a range of 53.2-266 kPa, mean, 159 kPa. Similar pressures were then applied in vitro to 10 catheters of each gauge, and the flow of fluid observed from the three holes. For each size of catheter, with increasing pressure, flow appeared at the proximal, then the middle, and finally the distal hole. This emphasises that the effect of epidural doses can vary depending on the pressure of injection, especially if the catheter had been passed partially through the dura.