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The Influence of Acid‐Base Changes on Central Nervous System Toxicity of Local Anaesthetic Agents I: An Experimental Study in Cats

A method is described of stabilising the metabolic and respiratory acid‐base status of 90 cats in which 127 local anaesthetic toxicity studies were performed. Nine different local anaesthetic agents were studied. These agents were infused intravenously at a constant rate until the appearance of generalised seizure activity in the EEG from the cortex and amygdala via implanted electrodes. A fall in Paco2, or hydrogen ion activity (aH+) was found to decrease local anaesthetic toxicity, such that a linear correlation was found between the log of the toxic dose and Paco2 and aH+. No correlation was found to the metabolic variable chosen (“non‐respiratory” hydrogen activity, aH+NR). The conclusion was that both hydrogen ion activity and Paco2 are of importance in modifying the CNS toxic threshold dose of local anaesthetic agents.