Cardiorespiratory effects of intravascular injections of lidocaine in the anesthetized rat. Comparisons between arterial and venous routes of 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 either the internal carotid artery (n = 8) or the external jugular vein (n = 8) caused hypotension, bradycardia, and respiratory slowdown. Hypotension was significantly greater after external jugular injections; these were also associated with larger reductions in heart rate. Respiratory attenuation was generally similar for both routes, but high lidocaine doses (9 mg/kg) given via the external jugular were briefly the cause of significantly more respiratory depression. When given via the external jugular, lidocaine 15 mg/kg proved lethal in seven of nine instances. There were no lethal consequences when the same dose was administered via the internal carotid artery. These results offer no evidence in support of claims that the accidental retrograde flow of clinical doses of local anesthetics to the brain via the internal carotid artery can be the cause of hitherto unsuspected high levels of toxicity, leading to respiratory depression and even death.