Clinical experience with continuous epidural infusion of bupivacaine at 6 ml per hour in obstetrics

Maintenance of continuous epidural analgesia for obstetrics by slow infusion is a feasible alternative to maintenance by intermittent injection. The method described by Davies and Fettes using 0.25 per cent bupivacaine through a 6 ml/hr capillary flow device (Intraflo), with the fast-flush cut-off, is simple and convenient. However, failure of the fast-flush valve, resulting in a high flow rate, has been reported. It is therefore imperative that, prior to connecting the pressurized system to the epidural catheter, correct function of the device be verified by observing the flow rate in the microdrip chamber. We have used this method for the past year and found the equipment reliable, but in order to achieve more satisfactory analgesia the concentration of the infusion was increased initially to 0.375 per cent, and then reduced to 0.30 per cent. The records of the first 187 patients were reviewed retrospectively. Group I (n = 99) received an infusion of 0.25 per cent bupivacaine, Group II (n = 49) received 0.30 per cent and Group II (n = 39) received 0.375 per cent. Significantly more patients in Group I (30 per cent) required supplementary top-ups (in addition to the infusion) for the first stage of labour than in either Group II (10 per cent), or Group III (13 per cent). Top-ups for delivery were given to 55 per cent of patients in Group I, 64 per cent in Group II and 48 per cent in Group III. The incidence of motor block was significantly higher in Group III (21 per cent) than in either Group I (1 per cent) or Group II (2 per cent). For continuous epidural infusion at 6 ml/hr, 0.30 per cent bupivacaine combines optimum analgesia with minimal side-effects.