week 13 Flashcards
(22 cards)
Definition of MAC
(mean alveolar concentration)
Alveolar concentration of agent at 1atm that prevents movement in 50% of patients in response to surgical stimulus
What does MAC indicate?
Potency of Inhaled anaesthetic drugs.
Lower MAC = more potency
what decreases MAC
Age, CNS depressants, hypothermia
in relation to inhaled anaesthetic agents what is the blood:gas partition coefficient
Reflects the solubility in blood.
Lower value = faster onset and offset
mechanism of action of inhaled anaesthetic agents
- GABA – a receptor Chloride channel
- activated at high concentration and facilitate GABA action at low concentration
- inhibitory synaptic transmission
- Hyperpolarization via activation of K channels
- Decrease time of nicotinic receptor opening.
what class of drug is sodium thiopentone
IV anaesthetic induction agent.
Ultra short acting barbituate.
mechanism of action of sodium thiopentone
Binds to GABA receptors.
enhances GABA mediated chloride influx.
Causes hyperpolarisation.
Causes CNS depression
onset of sodium thiopentone
Rapid onset ~30seconds
due to high lipid solubility
Duration and elimination of sodium thiopentone
short duration 5-10minutes.
Due to redistribution not metabolism.
Hepatic metabolism with slow elimination.
Adverse reactions of sodium thiopentone
Can cause tissue necrosis if extravasated.
low BP, apnoea.
Decreased ICP (good in neurotrauma).
anaphylaxis
when is sodium thiopentone contraindicated
Porphyria
(genetic disorder in making heme)
mechanism of action propofol
potentiates GABA-A.
Increases Chloride conductance.
causes hyperpolarisation.
CNS depression
why is propofol used in neurotrauma
It is neuroprotective.
Decreases ICP and cerebral metabolism
when is propofol contraindicated
in egg and soy allergies
mechanism of action of ketamine
NMDA receptor antagonist.
Also interacts with opioid receptors, monoaminergic and muscarinic systems.
contraindications to ketamine
suspected or raised ICP
acute psychosis or schizophrenia
uncontrolled HTN
IHD
mechanism of action of Benzodiazepines
enhance GABA-A receptor activity.
Increase frequency of chloride channel opening.
Causes hyperpolarisation and CNS depression
Reversal agent of Benzos and risk of using it.
Flumazenil - a competitive antagonist to GABA-A receptor.
May precipitate seizures.
mechanism of action of Etomidate
Enhances GABA-A receptor activity.
Increase chloride influx causing hyperpolarisation.
causes CNS depression.
adverse effects of Etomidate
Adrenal suppression
Myoclonus
nausea/vomiting
pain on injection
no analgesia effects
mechanism of action of dexmetadomidine
selective alpha-2 agonist in the brainstem.
reduces noradrenaline release.
causes sedation, anxiolysis, bradycardia
adverse effects of dexmetadomidine
bradycardia
hypotension
dry mouth
withdrawal symptoms
