Thermo-sensitive hydrogel for preventing bowel injury in percutaneous renal radiofrequency ablation

Percutaneous radiofrequency ablation (PRFA) has been used to ablate renal neoplasms with good outcome. However, if bowel lies adjacent to a tumor, ablation increases the risk of thermal bowel injury, and the consequences could be fatal. We describe the technique, effectiveness and safety of using thermo-sensitive hydrogel as insulation to displace the bowel away during PRFA.

The study was divided into two main parts: the in vitro and in vivo studies. In in vitro study, to explore the heat insulation of hydrogel, the rabbit kidney was entirely embedded in hydrogel, and then radiofrequency ablation was performed; the temperature on the gel-air and gel-kidney interfaces was measured. In in vivo study, hydrogel of poloxamer 407, 25 % concentration (w/v), was instilled into the perinephric space of 10 rabbits under CT guidance to separate the kidney from adjacent bowel before PRFA performed in the targeted parenchyma in the gel group. For the control group, PRFA was performed in similar portions of 10 rabbits without instillation of hydrogel. Some parameters were recorded such as kidney-to-bowel and electrode-to-bowel distance. Immediately after PRFA, distribution of hydrogel was evaluated and the dimension of radiofrequency ablation zone was measured; bowel thermal injury was compared between the gel and control groups by gross anatomy and histopathological examination. To assess safety, two additional follow-up groups with 10 rabbits in each were set; after PRFA, CT scan was performed every 2 days; gel absorption, thermal damage and some other complications were evaluated during the period.

In in vitro study, temperature was significantly lower at the gel-air than gel-kidney interface (P < .05), and the temperature gradient was positively associated with gel thickness. In in vivo study, hydrogel was instilled successfully in all rabbits in the gel group. The kidney-to-bowel and electrode-to-bowel distances were larger in the gel than control group [(1.1 ± 0.6 cm vs 0.1 ± 0.0 cm, P < .01), (1.8 ± 0.4 cm vs 0.5 ± 0.1 cm, P < .01), respectively]. The gel and control groups did not differ in size of the ablation zones (0.80 ± 0.2 cm vs 0.75 ± 0.3 cm, P > .05). Thermal injury in adjacent bowel was more serious in the control than gel group (P < .01). As for the follow-up, rabbits with gel instillation showed good condition and gel was absorbed gradually within 5 days. Those rabbits with no bowel displacement by gel got significantly lower survival rate and high complication rate (P < .01).

Hydrogel-dissection by means of thermo-sensitive hydrogel instillation is valuable for protecting the bowel adjacent to ablation area against thermal injury during PRFA.