A Pilot Animal Experimental Study Of Applying Thermo-sensitive Hydrogel In Protecting Surrounding Organs During Percutaneous Renal Radiofrequency Ablation

Objective:To assess the feasibility, effectiveness and safety of using thermo-sensitive hydrogel made from Poloxamer407 (P407) as the insulation to minimize collateral thermal injury of the surrounding organs such as bowels during renal percutaneous radiofrequency ablation (PRFA).Methods:1. Characterization of hydrogel and heat insulation effect study in vitro.2. In animal study, thirty rabbits were randomly divided into four groups:group "A", group "B", group "C" and group "D". In the experimental group A, hydrogel was instilled into the right perirenal space of 10 rabbits under CT guidance to separate kidney from adjacent bowels before PRFA was performed in the renal parenchyma. For the control group B, PRFA was performed in the similar areas of 10 rabbits without instillation of hydrogel. Immediately after the procedure in experimental and control groups, the distribution of gel was evaluated and the dimension of ablation zone, thermal injury of bowels were compared between the experimental and control groups at open laparotomy. The dimension of ablation zone was compared by direct measurement of the largest diameter. The degree of bowel thermal injury was graded by a three-point scoring system according to histologic analysis.3. In group C, hydrogel was instilled into the left perirenal space of 5 rabbits before PRFA, but in group D there was no instillation before left kidney RPFA. To assess the safety of hydrogel, rabbits in these two groups were followed up by CT scan every two days, gross anatomy and histopathological examination were used to evaluate gel absorption and thermal damage in the 5th day.Results:1. The characterization and heat insulation effect of hydrogel was good. In vitro study, temperature on gel-air interface was obviously lower than gel-renal interface(P<.05), and the temperature gradient had positive correlation with gel thickness.2. In vivo study, instillation of hydrogel was achieved successfully with a single puncture in all rabbits in the Gel group. The kidney-to-bowel distances in Gel group ranged from 0.5 to 1.8 cm, and was significantly larger than that in Control group which were 0.1 to 0.4 cm. There was no difference in the size of the RF ablation zones in the kidney between the Gel and control group (P>.05). Thermal injury in the adjacent bowel was observed significantly more serious in the control group compared with the Gel group (P<.05).3. All the rabbits with hydrogel instillation in the follow-up period were generally in good condition and gel was absorbed gradually.Conclusions:Thermo-sensitive hydrogel instillation is safe and effective for protecting the bowel adjacent to ablation area from thermal injury during percutaneous renal radiofrequency ablation.