In vivo lung uptake of lidocaine in pigs

A mixture of 14C-labelled lidocaine and indocyanine green dye (IG) (Cardiogreen) was injected as a bolus into the pulmonary artery in pigs (15-25 kg). Time-concentration curves for both substances were constructed from 20s blood samples taken from the common carotid artery for approximately 20s. The extraction of lidocaine in each sample and the 95% first passage uptake (FPU) were calculated, assuming that IG is inert with respect to the lung and that it remains within the vascular compartment. The IG curves were also used to calculate cardiac output. The acid-base status and arterial blood pressure or ECG were also followed. Each animal was given two injections. When 0.5 mg/kg b.w. lidocaine was injected, FPU was 41 +/- 3%; at a dose of 2 mg/kg b.w., FPU was 28 +/- 3% (P less than 0.05). The initial extraction during the first 2 s after appearance of the substances was approximately 80%. This level declined with subsequent samples, and the decline was equally rapid at both dose levels.