3455 In vivo characterization of colonic thermal injury by the argon plasma coagulator.

Abstract

The Argon Plasma Coagulator (APC) is a new instrument for non-contact delivery of monopolar electrical energy to mucosal surfaces. It has rapidly gained acceptance for obliteration of vascular lesions and superficial tumors. Depth of injury is thought to be limited through preferential discharge of energy to non-dessicated tissue. However, injury induced by this device has not been well characterized <i>in vivo</i>. Aim: To characterize APCinduced colonic injury in a porcine model. Methods: Swine weighing 50kg were used. Under general anesthesia, a laparotomy was performed and a colotomy incision was made on the antimesenteric border. Burns were made with an APC probe perpendicular to the mucosa at gas-flow 2.4L/min. Variables studied were power (45, 60 & 75W) and duration (1, 2 or 3 seconds), n ≥ 11 for each power/time permutation. Injury was graded histologically as the percentage of coagulation sites per setting yielding severe injury to the superficial circular muscle layer (CML) and deep longitudinal muscle layer (LML). Injury was expressed as the number of burns to CML or LML. Results: The mean surface area of lesions increased with coagulation duration (45W for 1,2 & 3 seconds:184±7mm², 215±1mm², 234±8mm², respectively). CML injury was predicted by power (p=0.01) and duration of burn (p=0.001) and correlated strongly with total energy delivered (r²=0.92). Severe damage to the LML correlated strongly with time of burn (r²=0.99), but poorly with power (r²=0.15); correlation with total energy was less apparent than with CML (r²=0.72). Conclusions: Deep injury correlates more closely with <i>duration</i> of coagulation than total energy delivered. Power setting does not correlate with deep injury. Surface area of the lesion is not proportional to energy delivered. Implication: Limitation of depth of injury with the APC may have been previously overstated, "protective" arcing to non-dessicated tissue does not appear to be significant <i>in vivo</i>. Transmural injury may occur at recommended settings (eg: 45W) if coagulation duration is excessive.