Complete shutdown of microvascular perfusion upon hepatic cryothermia is critically dependent on local tissue temperature

Since microvascular dysfunction with complete circulatory arrest and, thus, prolongation of tissue ischaemia is considered a potential mechanism for c ell necrosis following hepatic cryosurgery, we determined the temperature n ecessary for induction of complete nutritive perfusion failure in cryotherm ia-treated rat livers. After localization of the cryoprobe with seven therm ocouples and application of a single or double freeze-thaw cycle, in vivo f luorescence microscopy of the cryoinjured left lobe was performed over a 2- h period using a computer-controlled stepping motor, which guaranteed analy sis of the identical liver tissue segments with exact allocation of the the rmocouples and thus determination of tissue temperature. Cryothermia result ed in a central non-perfused part of injury, surrounded by a heterogeneousl y perfused peripheral zone. The non-perfused area after single and double f reezing continuously increased over the first 90-min period due to a succes sive shutdown of perfusion within the peripheral border zone, Analysis of t he thermocouples' temperature at the end of freezing revealed the 0 degrees C-front at 11.7 mm (single freeze-thaw cycle) and 12.1 mm (double freeze-t haw cycle) distant from the centre of the cryoprobe, which exactly correspo nds with the initial (30 min) expansion of the area with nutritive perfusio n failure. The increased nonperfused tissue area at 2 h conformed a critica l border temperature between 8.29 +/- 1.63 degrees C and 9.07 +/- 0.24 degr ees C. From these findings, we conclude that freezing of liver tissue to te mperatures of at least < 0 degrees C causes complete/irreversible perfusion failure, which consequently will result in cell death and tissue necrosis, and may thus be supposed as a prerequisite for the safe and successful app lication of cryosurgery in hepatic tumour ablation. (C) 2000 Cancer Researc h Campaign.