Introduction: The experience with cryosurgery of irresectable liver metastases shows that the freezing capacity in close proximity to the inferior vena cava (IVC) is inadequate due to the blood flow and heat flux in this vessel. This is also frequently the basis for local recurrence. As demonstrated by Morris, caval occlusion is required to achieve adequate iceball thermal distribution close to the IVC, which may, however, result in lifethreatening cardiac arrythmias. The objective of this non-survival animal model experiment, therefore, was to investigate the hepatic perfusion conditions (changes of blood flow in the IVC or hepatoduodenal ligament) under which a freezing temperature of -50°C can be achieved in liver tissue close to the intrahepatic wall of the IVC without acute life-threatening complications.
Material and Methods: Under thiopentone anesthesia and controlled ventilation, 8 pigs were subjected to hepatic cryosurgery with the ERBE CRYO 6 (Erbe, FRG). Using ultrasound guidance, 2 cryoprobes were placed at I cm distance from the intrahepatic IVC, and 2 thermocouples introduced into defmed positions (one directly adjacent to the caval wall). Arterial blood pressure, pulse rate, and ECG were monitored continuously throughout. Arterial blood gases, central venous pressure, pulmonary arterial pressure wedge pressure, heart-time volume, IVC pressure, and caval and right ventricular temperature were recorded at regular intervals. The pigs were divided into three groups: group 1: freeze without clamping (n=2), group 2: freeze with infrahepatic IVC clamping and portal inflow occlusion (n-=3), group 3: freeze with portal inflow clamping only (n=3). Clamping was maintained until completion of the freezing process.
Results: The minimum temperature reached at the caval wall during a freezing period of 15 min in group I was -8°C with a mean fall in IVC and right ventricular blood temperature of 2.3°C. Caval and portal clamping (group 2) resulted in intravascular ice formation already after a freezing-time of 5 min, the intracaval temperature being -70°C. In this group, the temperature in the right ventricle fell by 1.5°C. During thawing, when IVC flow recommenced, the temperature in the right ventricle decreased by 5.6°C, and the pigs developed severe hypotension and lethal ventricular arrythmias. During the portal inflow clamping (Pringle-manoeuvre, group 3), a temperature of -50°C was measured at the caval wall after a freezing period of I I min, however, without intravascular ice formation. IVC blood temperature fell by 4°C, and right ventricular temperature by 1.4°C. This group recovered quickly after thawing and survived the 4 hour post procedure observation time without major complications.
Summary: Reduction of hepatic perfusion via portal inflow occlusion during cryotherapy of hepatic tissue adjacent to the IVC allows adequate freezing at the caval wall to -50°C without intracaval ice formation or clinically threatening decrease of intracardial temperature. Possible effects on the vascular wall with secondary necrosis, hemorrhage or thrombosis need further assessment in survival experiments.