Lung uptake of lidocaine in healthy volunteers

Eleven patients with no known history of heart or lung disease received an i.v. bolus injection of a mixture of lidocaine and indocyanine green dye (Cardiogreen). The dose of lidocaine, given once (or twice 10 min apart), was 0.5 mg/kg b.w. Time concentration curves from the appearance of indocyanine green were constructed for both substances from blood samples taken from the common femoral artery for approx. 50 s at the rate of one sample every 1.2 s. The extraction of lidocaine in each sample and the uptake of lidocaine, when 95% of the injected dose of indocyanine green had been recovered, were calculated. Nine patients showed an initial plateau of high extraction, which was 0.92 +/- 0.02 (mean +/- s.e mean) and 0.91 +/- 0.02 for the first and second injections, respectively, for the entire material. In two cases, however, a short plateau and a rapid decline in the extraction curve were observed. The 95% first pass uptake was 60 +/- 5% in the first injection and 55 +/- 12% for the second injection. Extraction of lidocaine dominated over back diffusion for the approximately 25 s. It is concluded that: (1) The described technique for studying lung uptake gave consistent and reproducible results in human volunteers; (2) Lung uptake of lidocaine in healthy man exceeds that previously observed in anaesthetized pigs; (3) The initial uptake during the first 5 s after appearance of indocyanine green in the arterial samples was more than 90%. (4) The lungs thus have a dampening effect on the arterial concentration, which might be of importance if lidocaine is accidentally injected intravenously.