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 74 mg (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.