Ketamine as a Unique Anesthetic Drug.

    Ketamine is a unique anesthetic drug that provides analgesia, hypnosis, and amnesia with minimal respiratory and cardiovascular depression. Ketamine produces a unique cataleptic trance known as disassociative anesthesia.

    Dissociative anesthesia is a unique anesthesia characterized by analgesia and amnesia with minimal effect on respiratory function. The patient does not appear to be anesthesized and can swallow and open eyes but does not process information.

    Ketamine was first tested in humans at the Parke Davis Research Unit of Jackson Prison in Michigan. The first human received the drug on August 3, 1964.By 1970, it was approved as an anesthetic agent by the US FDA.

Advantages and Precautions

• Ketamine induces significant increases in HR, mean arterial pressure, and plasma epinephrine levels. This sympathetic nervous system stimulation is centrally mediated. It can be harmful in patients with stenotic heart lesions or coronary artery disease.

•  Ketamine's mechanism for increasing cardiac output remains controversial though some studies have suggested that it is a direct myocardial depressant which augments cardiac output through indirect mechanisms such as potentiation of catecholamines. 

•  Ketamine may be advantageous in hypovolemia, major hemorrhage, for patients who have experienced severe acute blood loss or cardiac tamponade.

•  It allows humane obtundation of the hemodynamically unstable patient, giving the surgeon an opportunity to rapidly intervene and correct a life-threatening problem (e.g., cardiac tamponade). In these situations, skin preparation should be performed before induction

• Ketamine's mechanism for increasing cardiac output remains controversial though some studies have suggested that it is a direct myocardial depressant which augments cardiac output through indirect mechanisms such as potentiation of catecholamines. 

• The hemodynamic stimulatory effect of ketamine depends on the presence of a robust myocardium and sympathetic reserve. In the absence of either, hypotension may ensue from myocardial depression.

• Waxman et al. studied ketamine as an induction drug in a cohort of critically ill surgical patients (doses ranged from 25 mg to 140 mg) and found that ketamine increased heart rate and decreased total body oxygen consumption (VO₂). 

• Coronary blood flow may not be sufficient to meet the increased oxyg demands induced by sympathetic stimulation.

• Ketamine should be avoided in patients with elevated intracranial pressure.