Improved pain relief after thoracotomy: use of cryoprobe and morphine infusion.

In a randomised controlled trial carried out during the first to days after thoracotomy patients who had had intercostal nerves frozen with a cryoprobe or were given morphine by continuous intravenous infusion had significant less pain at rest than patients given intramuscular morphine. Differences between the groups with respect to pain on movement and during physiotherapy were not significant. Pain was estimated using visual analogue scales, and an arc sine transformation was carried out on values obtained from these scales before comparison using an analysis of variance. The trial did not distinguish between the cryoprobe and infusion treatment. The simplicity of the cryoprobe had much to commend it, but in units without access to this equipment a small infusion pump offers a satisfactory alternative.