摘要BACKGROUND: Cryoanalgesia at -50℃ for 90 seconds yields effective pain relief following thoracotomy. In China, -50℃ is a common temperature for intercostal cryoanalgesia following thoracotomy. However, experimental results vary.OBJECTIVE: To explore intercostal nerve pathological changes at -70℃ for various freezing times by studying canines, and to evaluate long-term clinical efficacy of intercostal nerve cryoanalgesia for postoperative pain relief based on the animal experiments.DESIGN, TIME AND SETTING: A comparative animal study was performed at the Animal Experimental Center of the General Hospital of the People's Liberation Army. Based on results from the animal study, a randomized, controlled, clinical trial was performed at the Department of Thoracic Surgery of the General Hospital of the People's Liberation Army between October 2006 and October 2008.PARTICIPANTS: A total of 120 patients undergoing posterolateral single incision Iobectomy at the Department of Thoracic Surgery of PLA General Hospital between October 2006 and October 2008 were selected. Nervous system diseases were excluded.METHODS: Animal experiment: 8 anaesthetized, mixed-breed dogs were used. The intercostal nerves (costal bone 6-10) were frozen at -70℃ for varying times (30, 60, 90, 120, and 180 seconds). Clinical study: 120 patients were randomly assigned to 2 groups (n=60). In the cryoanalgesia group, the intercostal nerves were frozen prior to chest closure, and 4 costal nerves (1 at incision level, 2 above and below incision, and 1 at drainage tube level) were frozen for 90 seconds at -70℃, respectively. Intercostal nerves were not frozen in the control group patients.Dolantin was used to relieve postoperative pain in patients from both groups.MAIN OUTCOME MEASURES: Pathological changes in frozen intercostal nerves were examined at days 1, 10, 30, and 60 following freezing. Following surgery, the degree of postoperative pain in all patients was evaluated by visual analogue scale at days 1,3, 5, 9, 30, 60, 90, and 180. Dolantin doses at days 1, 3, 5, 9 post-surgery and postoperative complications were noted.RESULTS: Nerve damage progressively increased with length of freezing time at -70℃, and recovery time from damage was gradually increased. After freezing for 90 seconds, the nerves exhibited obvious histopathological damage, and then completely recovered. In addition, after freezing for 180 seconds, the histopathological changes in nerves were reversible. In the clinical study, visual analogue scale scores were significantly less in the cryoanalgesia group compared with the control group (P<0.01), which was maintained over 30 days. In the cryoanalgesia group, the mean dolantin dose administered and postoperative complications were significantly reduced compared with the control group (P<0.01).CONCLUSION: Freezing of the intercostal nerve at -70℃ for 90 seconds is a safe and long-term effective method for relieving post-thoracotomy pain.