Cardiac or central nervous system toxicity may result when standard lidocaine doses are administered to patients with circulatory failure. This may be due to the following reason –

Lidocaine is a rapidly acting drug because of its rapid distribution to well perfused tissues such as brain and heart. Circulatory failure is characterized by decreased cardiac output and a consequent decrease in hepatic blood flow. As a result metabolic clearance of Lidocaine in liver is diminshed and its elimination is increased. Consequently Lidocaine concentration is initially increased in these relatively well perfused tissues (brain and heart) even with usual doses and toxicity results.