The effect of intra-neural local anaesthetic infusion on pain following major lower limb amputation

Background Critical lower limb ischaemia has an annual incidence of 500 - 1000 per million and around a quarter will undergo a major lower limb amputation. Post operative pain and phantom pain are recognised complications. Aim The aim of this study was to assess the role of postoperative intraneural infusion of local anaesthetic in patients under-going major lower limb amputation. Methods Between May 1998 and July 2001, following amputation patients either had standard post-operative analgesia or had an intra-neural infusion of 0.5% bupivicaine via an infant feeding catheter connected to a standard syringe pump (Alaris). This was a retrospective review and clinical notes of these patients were analysed to assess their post operative course, analgesic requirements and to ascertain phantom limb pain/sensation rates. All the data collected was from standard drug charts, case note entries and out-patient letters. Results During this time period 64 patients had a major lower limb amputation (31 patients treated routinely and 33 patients had an intra-neural anaesthetic (INA) catheter placed). In the INA group median post-operative opioid analgesia requirement was 10mg versus 74mg (p=0.0002, Mann-Whitney U) and post-operative prescription of amitriptyline for phantom pain was less common (4 patients versus 11 patients; p=0.0281, Mann-Whitney U). There was no obvious increase in complications or significant adverse events. Conclusions Postoperative intra-neural local anaesthetic infusion is a safe and effective technique. It reduces post-operative opioid analgesia requirement and seems to reduce phantom pain development.