Korean J Radiol.  2009 Feb;10(1):43-50. 10.3348/kjr.2009.10.1.43.

Does Artificial Ascites Induce the Heat-Sink Phenomenon during Percutaneous Radiofrequency Ablation of the Hepatic Subcapsular Area?: an in vivo Experimental Study Using a Rabbit Model

• Kim YS
• Rhim H
• Choi D
• Lim HK

• KMID: 1088677
• DOI: http://doi.org/10.3348/kjr.2009.10.1.43

Abstract

OBJECTIVE
To evaluate the effect of the heat-sink phenomenon induced by artificial ascites on the size of the ablation zone during percutaneous radiofrequency (RF) ablation of the hepatic subcapsular area in an in vivo rabbit model. MATERIALS AND METHODS: A total of 21 percutaneous rabbit liver RF ablations were performed with and without artificial ascites (5% dextrose aqueous solution). The rabbits were divided into three groups: a) control group (C, n = 7); b) room temperature ascites group (R, n = 7); and c) warmed ascites group (W, n = 7). The tip of a 1 cm, internally cooled electrode was placed on the subcapsular region of the hepatic dome via ultrasound guidance, and ablation was continued for 6 min. Changes in temperature of the ascites were monitored during the ablation. The size of the ablation zones of the excised livers and immediate complications rates were compared statistically between the groups (Mann-Whitney U test, Kruskal-Wallis test, linear-by-linear association, p = 0.05). RESULTS: One rabbit from the "W" group expired during the procedure. In all groups, the ascites temperatures approached their respective body temperatures as the ablations continued; however, a significant difference in ascites temperature was found between groups "W" and "R" throughout the procedures (39.2 +/- 0.4 degrees C in group W and 33.4 +/- 4.3 degrees C in group R at 6 min, p = 0.003). No significant difference was found between the size of the ablation zones (782.4 +/- 237.3 mL in group C, 1,172.0 +/- 468.9 mL in group R, and 1,030.6 +/- 665.1 mL in group W, p = 0.170) for the excised liver specimens. Diaphragmatic injury was identified in three of seven cases (42.9%) upon visual inspection of group "C" rabbits (p = 0.030). CONCLUSION: Artificial ascites are not likely to cause a significant heat-sink phenomenon in the percutaneous RF ablation of the hepatic subcapsular region.

Keyword

Radiofrequency (RF) ablation; Liver, interventional procedure; Ascites; Carcinoma, Hepatocellular; Neoplasm, Metastasis

MeSH Terms

Animals
*Ascites
*Body Temperature
Burns/etiology/prevention & control
*Catheter Ablation/adverse effects/methods
Diaphragm/injuries
Glucose/administration & dosage
Liver/pathology/*surgery
Rabbits
Solutions

Figure

• 

  Fig. 1 Experimental setting which will determine effect of heat-sink phenomenon induced by artificial ascites during percutaneous radiofrequency ablation. Abdomen of New Zealand white rabbit is distended due to previously injected artificial ascites. 20-gauge, 32-mm sheath (arrow) with tip located in gastrohepatic space via right subcostal area and wire thermocouple (arrowheads) inserted through sheath lumen. Internally-cooled radiofrequency electrode was also inserted via epigastric abdomen.

• 

  Fig. 2 US images of experimental setting before and after percutaneous radiofrequency ablation. A. Shaft of radiofrequency electrode is shown as hyperechoic line (arrows), with its tip is barely noted (abutting hepatic capsule). Anechoic artificial ascites are filled in subphrenic peritoneal space separating liver (arrowheads) from diaphragm (open arrowheads) by more than 1.0 cm. B. After applying radiofrequency energy for 6 minutes, hyperechoic change measuring about 1.5 cm is produced. Separation between (arrows) diaphragm and hepatic capsule is still identifiable.

• 

  Fig. 3 Representative photographs of gross specimens from excised liver after radiofrequency ablation in groups "C" (A), "R" (B), and "W" (C). No significant difference is detected for either area on hepatic capsule or volume on cross section of radiofrequency-ablated zone. Small penetrations (arrows) of hepatic capsule made by tip of electrode are noted in some specimens (A, B).

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