Understanding Anesthesiology - The Global Regional Anesthesia ...

Ketamine
Class
Phencyclidine derivative. Can be used as an induction agent (usually in hemodynamicallycompromised
patients) or for sedation during painful procedures.
Mechanism of action
Acts at numerous central nervous system receptor sites, including the N-methyl-D-aspartate
(NMDA) receptor.
Dose
Induction of anesthesia: 2 mg/kg IV
Induction of anesthesia: 5 mg/kg IM
Onset
Within one arm-brain circulation time (approximately 20 seconds).
Duration
Approximately 10-15 minutes after single induction dose, with full orientation occurring after
15-30 minutes.
Elimination
Redistribution from central nervous system (CNS) to inactive tissue sites accounts for termination
of unconsciousness. Ultimate clearance is via hepatic metabolism and renal excretion.
Effects
CNS:
Produces “dissociative anesthesia” with patient in a cataleptic state. Ketamine provides a
state of unconsciousness and intense analgesia however the patient’s eyes may remain open
and roving, and their limbs may move purposelessly. Cerebral metabolic rate and intracranial
pressure are increased.
CVS
Ketamine increases sympathetic outflow from the CNS leading to increased heart rate, blood
pressure and cardiac output. Because of this effect, ketamine plays an important role in the
management of patients with hypovolemic shock or cardiac tamponade. However, ketamine
does possess direct myocardial depressant effects which may lead to worsened hypotension
in patients in a prolonged shock state.
Respiratory
Some degree of airway protection is maintained. The patient may cough or swallow. Airway
secretions increase. Bronchodilatory effect is secondary to increased sympathetic tone. Apnea
is rare as respiratory drive is maintained.
Misc.
Undesirable psychological reactions are common on emergence: vivid, unpleasant dreams,
excitement, confusion, fear. They tend to occur in the first hour of emergence and abate
within one to several hours. Pretreatment with benzodiazepines may help minimize this effect.
Contraindications
Raised intracranial pressure, coronary ischemia, psychiatric disease, eye surgery.
Related Glossary Terms
Etomidate, Induction, Propofol, Shock, Sodium Thiopental
Index
Find Term
Chapter 3 - General Anesthesia
Chapter 6 - Drug Finder
Chapter 6 - Induction Agents