BACKGROUND: Cryoanalgesia at -50 ℃ for 90 seconds yields effective pain relief followingthoracotomy. In China, -50 ℃ is a common temperature for intercostal cryoanalgesia followingthoracotomy. However, experimental results vary.OBJECTIVE: To explore intercostal nerve pathological changes at-70 ℃ for various freezing timesby studying canines, and to evaluate long-term clinical efficacy of intercostal nerve cryoanalgesia forpostoperative pain relief based on the animal experiments.DESIGN, TIME AND SETTING: A comparative animal study was performed at the AnimalExperimental Center of the General Hospital of the People’s Liberation Army. Based on results fromthe animal study, a randomized, controlled, clinical trial was performed at the Department ofThoracic Surgery of the General Hospital of the People’s Liberation Army between October 2006and October 2008.PARTICIPANTS: A total of 120 patients undergoing posterolateral single incision Iobectomy at theDepartment of Thoracic Surgery of PLA General Hospital between October 2006 and October 2008were selected. Nervous system diseases were excluded.METHODS: Animal experiment: 8 anaesthetized, mixed-breed dogs were used. The intercostalnerves (costal bone 6-10) were frozen at -70 ℃ for varying times (30, 60, 90, 120, and 180seconds). Clinical study: 120 patients were randomly assigned to 2 groups (n = 60). In thecryoanalgesia 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 90seconds 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 atdays 1, 10, 30, and 60 following freezing. Following surgery, the degree of postoperative pain in allpatients was evaluated by visual analogue scale at days 1,3, 5, 9, 30, 60, 90, and 180. Dolantindoses 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 ℃, andrecovery time from damage was gradually increased. After freezing for 90 seconds, the nervesexhibited obvious histopathological damage, and then completely recovered. In addition, afterfreezing for 180 seconds, the histopathological changes in nerves were reversible. In the clinicalstudy, visual analogue scale scores were significantly less in the cryoanalgesia group compared withthe control group (P < 0.01), which was maintained over 30 days. In the cryoanalgesia group, themean dolantin dose administered and postoperative complications were significantly reducedcompared with the control group (P< 0.01).CONCLUSION: Freezing of the intercostal nerve at -70 ℃ for 90 seconds is a safe and long-termeffective method for relieving post-thoracotomy pain. However, experimental results vary. OBJECTIVE: To explore intercostal nerve pathological changes at -70 ° C for various freezing timesby studying canines, and to evaluate long-term clinical efficacy of intercostal nerve cryoanalgesia forpostoperative pain relief based on the animal experiments. DEIGNIGN, TIME AND SETTING: A comparative animal study was performed at the Animal Experimental Center of the General Hospital of the People’s 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 ° C for varying times Clinical studies: 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 ° C, 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 allpatients was evaluated by visual analogue scale at days 1,3, 5,9, 30, 60, 90, and 180. Dolantindoses 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 ° C, and recover from damage 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 The cryoanalgesia group compared with the control group (P <0.01), which was maintained over 30 days. In the cryoanalgesia group, themean dolantin dose administered and postoperative complications were significantly reducedcompared with the control group (P <0.01) .CONCLUSION: Freezing of the intercostal nerve at -70 ° C for 90 seconds is a safe and long-termeffective method for relieving post-thoracotomy pain.