MONITORING RENAL CRYOSURGERY - PREDICTORS OF TISSUE NECROSIS IN SWINE

Purpose: To examine parameters for monitoring renal cryosurgery and co rrelate with histopathologic necrosis in a porcine model. Parameters i nclude: 1) tissue temperature, 2) distance of tissue from the cryosurg ical probe insertion site, and 3) inclusion of tissue by the visible i ceball. Materials and Methods: Following midline incision, 6 healthy k idneys from 3 domestic pigs were treated using a nitrogen-based cryosu rgical system with 3.4 mm outer diameter cryoprobe. Temperatures were monitored at 6 sites in each kidney using prototype thermocouples. Gro ss and histologic analysis was performed on tissue harvested from each thermosensor site 24 hours postoperatively. Results: All animals surv ived to complete the full protocol. Post-procedure bleeding was manage d surgically. Histopathology revealed that complete ablation was unifo rmly produced at temperatures of -19.4C or lower in 13/13 tissue sampl es. Within 16 mm. of the probe insertion site, cells were uniformly ab lated in 17/17 samples while degree of tissue death varied widely beyo nd this margin. Cell death was more likely found at points encompassed by the visible iceball (16/18, 89%) than those beyond it (2/18, 11%) [p <0.0001, Chi-square] while 2/18 (11%) of samples harvested from wit hin the iceball margin were partially viable. Conclusions: Temperature monitoring using thermocouples during porcine renal cryosurgery demon strated complete homogenous necrosis of tissues reaching -19.4C or low er. Distance beyond 16 mm. from the cryoprobe and direct visualization of the iceball proved to be less reliable predictors of tissue necros is. Management of bleeding post-thaw was necessary in every case.