Cardiac rhythm disturbances due to caval occlusion during hepatic cryosurgery

Cryoablation is used to treat inoperable hepatic malignancy. We investigated the safety of cryoablation close to the inferior vena cava. Our sheep model showed that it was impossible to create an iceball around the inferior vena cava (IVC) unless this vessel was clamped. When subsequently the IVC was clamped and frozen for 30 min, the anesthetized spontaneously breathing sheep (n = 3) exhibited cardiac arrhythmias typical of hyperkalemia on release of the clamp. The plasma potassium in these sheep rose from a baseline mean (SD) of 5.0 (0.7) mmol/liter to 9.5 (0.9) mmol/liter after release of the clamp at the end of the freeze. These sheep also developed acute hypercapnoea and acidosis. These changes were avoided in subsequent sheep by assisting ventilation mechanically and hyperkalemia and arrhythmias were not seen in this group. Iceball cracking did not occur and the IVC remained intact in all cases. This work suggests that during hepatic cryotherapy of lesions close to the IVC, intraoperative monitoring of potassium is indicated, particularly if caval occlusion is required to achieve adequate iceball thermal distribution.