Pharmacology - CNS Flashcards
Define general anaesthesia in clinical applications
Loss of consciousness, analgesia, muscle relaxations, amnesia
Name 3 commonly used inhalation anaesthetics
Isoflurane, Sevoflurane, Nitrous oxide
What is the general mechanism of action of inhalation anaesthetics?
Inhibit glutamate receptors and increase GABA activity
List 5 factors that influence the potency and rate of induction and recovery from inhalation anaesthetics
- Conc of anaesthetic in inspired air
- Alveolar ventilation and resp rate
- Solubility of anaesthetic in blood
- Cardiac output and lung perfusion
- Lipophilicity of anaesthetic
True or false: a higher MAC = lower potency
True
List some things that will DECREASE the MAC
- Hypothermia
- Hyponatraemia
- Pregnancy
- CNS depressants
- Anaemia and hypotension
- Hypoxia
- Respiratory acidosis
List some things that will INCREASE the MAC
- Hyperthermia
- Hypernatraemia
- CNS stimulants
- Decreased brain perfusion
Is Isoflurane and analgesic?
NO!!!
List some of the unique features of Nitrous oxide as an inhalation anaesthetic
- low potency and high MAC
- BUT has ANALGESIC properties –> via NMDA receptors
- minimal direct adverse effects on cardiovasc and resp system
- prolonged use inhibits methionine synthatase –> folate deficiency and bone marrow defects
List 5 types of injectable anaesthetics with examples
- Barbituates e.g thiopental, phenobarbital
- Propofol
- Alphaxalone
- Benzodiazepines e.g midazolam, diazepam
- Dissociative anaesthetics e.g ketamine, tiletamine
Describe the mechanism of action of injectable anaesthetics (aside from dissociative)
Enhance the efficacy of GABA at different sites of GABAa receptors
Describe the mechanism of action of dissociative anaesthetics
Glutamate antagonist, binds non-competitively to NMDA receptor to inhibit excitatory effects of glutamate = ANALGESIC
Weak action on GABA receptors
Describe the distribution-redistribution phenomenon of injectable anaesthetics
- Once administration is stopped, rapid dist of drug into vessel rich organs, slowly in poorly vasc tissue
- Anaesthetic then redistributes out of brain to re-est. equilibrium with plasma conc –> decreasing CNS effects
Why do you need to use ketamine with a muscle relaxant?
Dissociative anaesthetics maintain skeletal muscle tone incl. protective reflexes such as coughing and swallowing
Define the following:
Tranquiliser
Sedative
Neuroleptanalgesia
Tranquiliser: relieve anxiety w/o undue drowsiness
Sedative: cause sedation or drowsiness
Neuroleptanalgesia: combo of tranquiliser/sedative with an opioid to achieve pain relief