CARDIORESPIRATORY EFFECTS OF INTRAVASCULAR INJECTIONS OF LIDOCAINE INTHE ANESTHETIZED RAT - COMPARISONS BETWEEN ARTERIAL AND VENOUS ROUTESOF ADMINISTRATION

The consequences of two types of intravascular injections of lidocaine 1.5 to 15 mg/kg on three cardiorespiratory parameters were studied in 16 anesthetized rats. Administration of the local anesthetic via eith er the internal carotid artery (n = 8) or the external jugular vein (n = 8) caused hypotension, bradycardia, and respiratory slowdown. Hypot ension was significantly greater after external jugular injections; th ese were also associated with larger reductions in heart rate. Respira tory attenuation was generally similar for both routes, but high lidoc aine doses (9 mg/kg) given via the external jugular were briefly the c ause of significantly more respiratory depression. When given via the external jugular, lidocaine 15 mg/kg proved lethal in seven of nine in stances. There were no lethal consequences when the same dose was admi nistered via the internal carotid artery. These results offer no evide nce in support of claims that the accidental retrograde flow of clinic al doses of local anesthetics to the brain via the internal carotid ar tery can be the cause of hitherto unsuspected high levels of toxicity, leading to respiratory depression and even death.