The effect of changes in arterial CO <Subscript>2 </Subscript> tension on plasma lidocaine concentration

The authors studied the effect of changes in arterial carbon dioxide tension on plasma tidocaine concentrations dltring a constant lidocaine infusion in eight healthy volunteers. With a PaC02 of 41.4 : 0.9 mmttg (mean • SE). total plasma lido. caine concentrations were 3.97 ~0.20 tzg.ml t. There was no significant change associated with hypercarbia (PaCO 2 = 55~7 • 1.5 mmtfg, lidoeaine = 3.93 • 0.18 I~g'ml-J)orhypocarbia (PaC02 = 19.5 +1.4mmJtg, tidocaine = 4.29 +-0.25 I.Lg' ml-~ ). despite the known effects of change.r in C02 tension on hepatic blood flow and lidocaine protein binding. During hyperc~rbia, plasma lidoeaine binding decreases while total plasma lidocaine remains essentially constant; therefore, increased C02 tensions cauld cause toxicity Jf total lidocaine concentrations were in the high therapeutic range (5 Izgml; ). Four subjects experienced transient symptoms of mild lidocaine toxicity during acute increases in carbon dioxide tension.