Dose-dependent depth of tissue injury with carbon dioxide cryotherapy in porcine GI tract

Background: Cryotherapy is a method of endoscopic mucosal ablation that involves delivery of a cryogen to result in tissue destruction by extreme low temperature. Its effects are influenced by the dosage of cryogen and thawing of ice. There are limited data on the tissue effects of multiple freeze and thaw cycles of carbon dioxide (CO₂) cryotherapy on GI tissues. Objective: To investigate the extent of tissue injury due to escalating doses of CO ₂ cryotherapy on the esophagus, stomach, and colon of pigs. Design: Animal experiment. Intervention: Varying doses of CO₂ cryotherapy with increasing number of freeze-thaw cycles were applied to each site. The animals were allowed to survive for 48 hours. Main Outcome Measurements: Depth of tissue injury assessed in blinded fashion by varying doses of cryotherapy on a defined area of porcine esophagus, stomach, and colon. Results: There was a dose-dependent relationship of CO₂ cryogen and depth of injury (P =.0001 and P =.002, respectively). In the stomach, the dose-response relationship was significant (P =.007), but the average grades of injury across the various doses were lower when compared with the esophagus at comparable cryogen doses (P =.0004). The estimated depth of tissue injury from the mucosal surface in the porcine esophagus and colon tissue ranged from 1.2 to 2.5 mm and 1.3 to 2.5 mm, respectively. Limitations: The study was performed in a normal porcine model. Conclusion: There was a dose-dependent relationship between the dose of CO₂ cryotherapy and the depth of tissue injury in the porcine esophagus, stomach, and colon.