Ventilatory Response to CO2Following Intravenous and Epidural Lidocaine

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Abstract
The effects of i.v. infusion and epidural administration of lidocaine on the control of ventilation was determined in 2 groups of 8 healthy unpremedicated subjects. In the i.v. group, an injection of 1.5 mg/kg lidocaine was followed by an infusion at a rate of 60 .mu.g .cntdot. kg-1 .cntdot. min-1 for 30 min. The slope of the ventilatory response to CO2 was significantly increased (P < 0.05) from its control value (2.65 .+-. 1.22 1 .cntdot. min-1 .cntdot. mm Hg-1 [mean .+-. SD]) at the end of the infusion (58%), while plasma lidocaine level was at 3.14 .+-. 0.82 .mu.g/ml. The correlation between individual plasma lidocaine levels and the changes in the slope of the ventilatory response to CO2 was significant (r = 0.58, n = 24, P < 0.01). In the epidural group, after the administration of 5 mg/kg of lidocaine, the slope of the ventilatory response to CO2 increased significantly (P < 0.05) from its control value (1.52 .+-. 0.75 l .cntdot. min-1 .cntdot. mm Hg-1) at 15 (+22%) and 25 min (+42%), while plasma lidocaine levels were at 1.79 .+-. 0.42 and 2.22 .+-. 0.47 .mu.g/ml, respectively. In both groups, resting minute ventilation and end-tidal CO2 values remained unchanged. Epidural lidocaine has a stimulating effect on the ventilatory control mechanisms that results from the systemic effect of the drug.