Use of the vasodilator sodium nitroprusside to increase tumour temperature during loco-regional hyperthermia with a capacitive ring applicator in a rat tumour model.

The influence of sodium nitroprusside (SNP) induced hypotension (to a mean arterial pressure of 60 mmHg) on tumour and normal tissue temperature during hyperthermia (HT) was examined. Loco-regional HT was given to the calf of BD IX rats by external radiofrequency heating from a capacitive ring applicator. In experiments in rats with subcutaneous BT(4)An tumours, the mean tumour temperature increased by 0.49 degrees C from 42.36 to 42.85 degrees C, on average, during SNP-hypotension. This represented 58% of the increase in tumour temperature found in the same rats when the tumour circulation was stopped completely by sacrificing the rats. SNP-hypotension resulted in a decrease in mean muscle temperature from 41.73 to 41.23 degrees C. The temperature difference between the tumour and the underlying muscle thereby increased by approximately 1 degrees C, indicating that SNP can increase tumour temperature during HT without increasing the risk of heat-related damage to skeletal muscle. Experiments in rats without tumours were also done to further examine the effect of SNP-hypotension on muscle temperature under different treatment conditions (variation of radiofrequency energy deposition and water bolus temperature). It was found that SNP decreased the muscle temperature during HT in two experiments where the average muscle temperature was 42.1 and 42.6 degrees C, respectively. In an experiment where the muscle temperature was 43.0 degrees C, on average, before SNP infusion, the muscle temperature increased during SNP-hypotension. This finding indicates that SNP-hypotension during HT may increase the risk of skeletal muscle necrosis with muscle temperatures at this level.