The effect of lidocaine when used as a local anesthetic or by intravenous injection

The efficacy profile of lidocaine as a local anesthetic is characterized by a rapid onset of action and an intermediate duration of efficacy. Therefore, lidocaine is suitable for infiltration, block, and surface anesthesia. Longer-acting substances such as bupivacaine are sometimes given preference for spinal and peridural anesthesias, however, lidocaine, on the other hand, has the advantage of a rapid onset of action. Adrenaline supplements could delay the resorption and the duration of efficacy could be doubled. Lidocaine is the most important class 1B antiarrhythmic drug: it is used intravenously for the treatment of ventricular arrhythmias (for acute myocardial infarction, digitalis poisoning, cardioversion, or cardiac catheterization). However, a routine prophylactic administration is no longer recommended for acute cardiac infarction. The overall benefit of this measure is not convincing. Lidocaine has also been efficient in refractory cases of status epilepticus.

Management of digoxin poisoning

Despite a gradual decline in the clinical use of digitalis glycosides, digitalis toxicity continues to be responsible for substantial morbidity and mortality, particularly among the elderly. Digitalis poisoning may occur acutely, after intentional overdose, but is more often seen as the result of chronic intoxication among patients receiving digitalis therapy. Clinical findings in chronic digitalis poisoning are often subtle. The astute clinician will enquire about digitalis use in older patients with vague complaints and will not be dissuaded from considering digitalis toxicity in the face of a ‘therapeutic’ digitalis blood concentration. Two digitalis preparations continue to be used with frequency, depending on geography. Digoxin is the digitalis glycoside of choice in the USA, while digitoxin prevails in some parts of Europe. While the methods and half-lives of elimination differ markedly for these two substances, the approach to poisoning by either is similar. Advanced age, underlying cardiovascular disease, and severe hyperkalaemia represent poor prognostic factors in digitalis poisoning. Early administration of digitalis Fab fragments should be undertaken when life-threatening symptoms are present. Prophylactic therapy with reduced doses of Fab fragments should be strongly considered for less serious toxicity.

Calcium role in digitalis acute poisoning – between myth and evidence-based medicine

Digitalis poisoning is still frequently encountered in medical practice, either as acute or chronic overdosage. Toxic mechanism is represented by Na+/K+ ATP-ase blockade, followed by an increase in intracellular Na+ and hiperkalemia. Hiperkalemia increases mortality in digitalis poisoning, having a complementary effect to digitalis toxicity. Calcium salts are indicated for cardiac protection in hyperkalemia. Traditionlly, calcium was contraindicated in digitalis poisoning. A careful analisys of available studies demonstrates that calcium salts are useful in treatment of severe hyperkalemia, with electrocardiogram changes, associated with acute digitalis poisoning. Management issues for digitalis poisoning are presented in the end.