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 druginduced cerebral blood flow changes (Δ CBF) using single-photon emission tomography (SPET) offers great in vivo possibilities but has to comply with demands on control of anaestesia-related influencing factors, such as PaCO2 changes. The model sought in this study and described here allows control of PaCO2, in the baboon under thiopentone anaesthesia by ventilation, and was evaluated for the functioal dependence of Δ CBF vs Δ PaCO2, 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 PaCO2 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 HMPAO 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 D CBF and the ensuing fall in PaCO2 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. (orig.)