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 cell necrosis following hepatic cryosurgery, we determined the temperature necessary for induction of complete nutritive perfusion failure in cryothermia-treated rat livers. After localization of the cryoprobe with seven thermocouples and application of a single or double freeze-thaw cycle, in vivo fluorescence microscopy of the cryoinjured left lobe was performed over a 2-h period using a computer-controlled stepping motor, which guaranteed analysis of the identical liver tissue segments with exact allocation of the thermocouples and thus determination of tissue temperature. Cryothermia resulted in a central non-perfused part of injury, surrounded by a heterogeneously perfused peripheral zone. The non-perfused area after single and double freezing continuously increased over the first 90-min period due to a successive shutdown of perfusion within the peripheral border zone. Analysis of the 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-thaw cycle) distant from the centre of the cryoprobe, which exactly corresponds with the initial (30 min) expansion of the area with nutritive perfusion failure. The increased non-perfused tissue area at 2 h conformed a critical border temperature between 8.29 +/- 1.63 degrees C and 9.07 +/- 0.24 degrees C. From these findings, we conclude that freezing of liver tissue to temperatures 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 application of cryosurgery in hepatic tumour ablation.
Schüder
G
G
Department of General Surgery, University of Saarland, Homburg/Saar, Germany.
Pistorius
G
G
Fehringer
M
M
Feifel
G
G
Menger
M D
MD
Vollmar
B
B
D000818:Animals; D017679:Cryotherapy; D008099:Liver / Q000098:blood supply*; D008856:Microscopy, Fluorescence; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley