RESUMEN
<p><b>OBJECTIVE</b>To explore the best freezing time and the optimum analgesia modality.</p><p><b>METHODS</b>In dogs, intercostal nerves were froze at -70 degrees C at different time including 30, 60, 90, 120, 180 s. Samples were got at the operative day, in 10 days and 60 days respectively, then carried on the pathology exam. In clinical study, 150 patients undergoing thoracotomy were randomly designated into 5 groups, all patients were recorded the heart rate, blood pressure, SO2, VAS, the dosage of dolantin, and observed the complications and side effects.</p><p><b>RESULTS</b>At operative day, the freezing nerves appeared brown print macroscopically, and presented degeneration, necrosis of the nerve fiber microscopically with more than 90 s. After 10 days, nerves with more than 90 s became thinner than normal. After 60 days, all nerves had no obvious differentiation than normal. In clinical study, both 90 s group and 90 s with PCIA group were significantly better than 60 s group or PCIA group; The VAS of 90 s with PCIA group was significantly lower than 90 s group but had more side effects such as vomiting, nausea.</p><p><b>CONCLUSIONS</b>At -70 degrees C, the freezing time should be no less than 90 s. The freezing intercostal nerves can safely and effectively relieve postoperative chest pain. The effect of analgesia of 90 s with PCIA group is the best, but has many side effects.</p>