General Anaesthetics Flashcards
What is ketamine and how does it work?
A partially water soluble and highly lipid soluble phencyclidine derivative.
It produces a dissociative amnesic anaesthetic state characterised by: catatonia, amnesia, and analgesia without the loss of consciousness (hypnosis).
Differs from most IV anaesthetics in that it produces significant analgesia
Complex mechanism of action but the major effect is probably produced by inhibition of the NMDA receptor complex
The only IV anaesthetic that has low protein binding (12%)
What is the pharmacokinetics of ketamine?
A - Can be given IV or IM
D - High lipid solubility –> rapid onset of its effect.
M - Liver and involves the N-demethylation by the cytochrome P450 system.
E - Norketamine (the primary active metabolite) is less potent and subsequently hydroxylated and conjugated into water-soluble inactive metabolites that are excreted in urine.
What are the effects of ketamine?
CNS - Cerebral vasodilator –> increases cerebral blood flow; anticonvulsant effect; emergence reactions (vivid colourful dreams, hallucinations, out of body experiences, increased/distorted tactile, visual and auditory sensitivity)
- Ketamine can limit the emergence reactions and increase amnesia
CVS - Transient, but significant increase in SBP, HR, CO (sympathetic stimulation) –> increased cardiac workload and myocardial O2 consumption
Direct myocardial depressant - usually masked by sympathetic nervous system but may be apparent in critically ill patients.
Resp - It causes a decrease in respiratory rate but preserves respiratory reflexes and produces bronchodilation.
- Transient hypoventilation and in rare cases apnoea (large IV dose)
- Risk of laryngospasm because of increased salivation (in children)
