Displacement of lidocaine from the lung after bolus injection of bupivacaine

The purpose of this study was to determine whether lidocaine was displaced from the lung after bolus injection of bupivacaine. Fourteen anaesthetized rabbits were randomly assigned to either a bupivacaine or a control group. Lidocaine was infused at a rate of 10 mg · kg^?1 hr^?1. After one hour of infusion, a bolus of bupivacaine (1 mg · kg^?1) in normal saline (0.2 ml · kg^?1) was injected into the central venous circulation in the bupivacaine group. The control group was injected with normal saline. After bolus injection, arterial blood samples were collected serially from an internal carotid artery at 1.2-sec intervals for 24 sec. The baseline concentration of lidocaine was 3.0 ±0.1 μg · ml^?1 in the bupivacaine group and 3.2 ±0.1 μg · ml^-1 in the control group (NS). Arterial concentrations of lidocaine increased to a maximum of 4.7 ±0.2 μg · ml^?1 in the bupivacaine group (P = 0.0001). No increases were seen in the control group. These findings indicate that lidocaine was displaced from the lung into the blood after bolus injection of bupivacaine. The amount of lidocaine displaced during the first passage of bupivacaine through the lung was calculated to be 92.3 ±9.7 μg. It is concluded that lidocaine is displaced from the lung after bolus injection of bupivacaine.