title: [Prospective double-blind randomized trial of cryoanalgesia: experimental and clinical study].
abstract: OBJECTIVE
  To alleviate and prevent postthoracotomy severe chest pain.
  
  
  METHODS
  In dogs, intercostal nerves were freezed at -50 degrees C at different times. Pathological changes and repair process of the nerves were observed while identifying the best freezing time that could be used clinically. Prospective double-blind randomized trial in 200 patients who had undergone thoracotomy was carried out from January 1996 to June, 2000. Cryoanalgesia(Cryo group) and control group consisted of 100 patients. Before closing chest, 4 routes of costal nerves (incision, above and below incision, and one for inserting drainage tube) were freezed for 1.5 minutes separately. Postoperative incision pain was recorded by VAS(visual analogue scales) including recording the dosage of narcotics, pulmonary function on 3, 7, 15, 30, 90 postoperative days.
  
  
  RESULTS
  Pathological changes of the axons and myelin sheaths progressed along with freezing time from 30 seconds to 2 minutes, but recovered in about one month. As the best freezing time, 1.5-minute freezing provided effective analgesia and quick recovery. Clinical application showed strong analgesia effect. VAS score of the cryo-group and control group was 2.29, and 7.24 (P < 0.001) respectively. In the cryo-group, no pain (0 degree) was observed in 22 patients (22%), very slight pain (1-2 degrees) in 44(44%), slight pain (3-4 degrees) in 20 (20%), and moderate pain (5-6 degrees) in 8 (8%). The total effective rate (0-6 degrees) was 94%. Dosage of dolantin in the cryo- and control groups was 41.3 mg and 185 mg, respectively(P < 0.001). The changes of pulmonary function for the two groups were not significant.
  
  
  CONCLUSIONS
  Freezing intercostal nerves during thoracotomy can effectively prevent postoperative chest pain. The pathological changes of nerves are reversible.
authors.affiliation: Department of Thoracic Surgery, China-Japan Friendship Hospital, Beijing 100029, China.
authors.forename: F
authors.initials: F
authors.lastname: Zhao
authors.forename: Y
authors.initials: Y
authors.lastname: Tian
authors.forename: D
authors.initials: D
authors.lastname: Liu
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000698:Analgesia / Q000379:methods; D000818:Animals; D002637:Chest Pain / Q000209:etiology / Q000517:prevention & control; D004285:Dogs; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced / Q000379:methods / Q000639:trends; D007367:Intercostal Nerves / Q000473:pathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D010149:Postoperative Pain / Q000517:prevention & control*; D011446:Prospective Studies; D020127:Recovery of Function; D012129:Respiratory Function Tests / Q000379:methods; D013908:Thoracotomy / Q000009:adverse effects* / Q000379:methods