Understanding Anesthesiology - The Global Regional Anesthesia ...

KETAMINE
Class
Phencyclidine derivative. Can be used as an induction
agent (usually in hemodynamically-compromised 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. Pretreat-
126