Acid-base balance disturbance following toxic doses of local anesthetics.

The effect of equitoxic doses of three carbamate local anesthetics (pentacaine, carbisocaine and heptacaine), and a derivative of lidocaine (trimecaine) on the acid-base balance of blood was studied in conscious rabbits. In addition, changes in arterial blood pH induced by local anesthetics in relation to lipophilicity of the respective drugs were evaluated. All the drugs administered at the dose of half of LD50 induced a significant decrease in the arterial blood pH as well as in the plasma bicarbonate level and in the blood base excess. The observed acidosis was compensated within a 60 minute period by hyperventilation. The local anesthetic-induced decrease in the blood pH, expressed as AUC, correlated to some extent with the partition coefficient of these agents. These findings suggest that the acidifying effect of local anesthetics may be dependent on their lipophilicity.