Influence of intravenously administered lidocaine on cerebral blood flow in a baboon model standardized under controlled general anaesthesia using single-photon emission tomography and technetium-99m hexamethylpropylene amine oxime

The baboon under general anaesthesia as a model to assess drug-induced cerebral blood flow changes ( CBF) using single-photon emission tomography (SPET) offers great in vivo possibilities but has to comply with demands on control of anaesthesia-related influencing factors, such as P _aCO₂ changes. The model sought in this study and described here allows control of P _aCO₂, in the baboon under thiopentone anaesthesia by ventilation, and was evaluated for the functional dependence of CBF vs P _aCO₂, using SPET technetium-99m hexamethylpropylene amine oxime (HMPAO) and the split-dose method together with controlled ventilation. During the experiment the model was validated for normal reactivity to P _aCO₂ changes, and subsequently applied to investigate the mechanisms (still uncertain) of CBF increase known to follow administration of the local anaesthetic lidocaine. Six baboons received 6 mg/kg lidocaine intravenously. CBF was measured between two consecutive SPET acquisitions (split-dose method) respectively relating to HM-PAO distributions in the brain before and after the injection of lidocaine. Meanwhile the animals were maintained at constant respiratory rate and volume. The results indicate that the correlation between CBF and the ensuing fall in P_aCO₂ deviated from the baseline pattern from the model and confirmed a cerebrovascular contribution to the lidocaine-induced CBF increase. This agreed well with mean and systolic blood pressure changes and heart rate. Correspondence to: I.C. Dormehl