T1 L23 Anaesthetic drugs Flashcards
What is anaesthesia?
Defect of sensation
Reversible drug-induced absence of sensation & awareness
Any lipid-soluble agent that causes depression of the brain in a predictable order: cortex –> midbrain –> spinal cord –> medulla
Describe effects of ethanol with increasing dose
Tranquillisation Excitation Dysarthria Ataxia Sedation Anaesthesia Coma Medullary depression Death
What was used for anaesthesia in the past?
Alcohol Opium Hemp Cold Concussion Compression Nitrous oxide
How do anaesthetics work?
Diverse range of pharmacology Many are lipid soluble Cell membrane Stereo-selectivity Interaction with membrane proteins Modulation of ligand-gated ion channels Global depression in neuronal activity
What is the current theory of the mechanism of anaesthetics?
Stimulation of inhibitory receptors
Inhibition of excitatory receptors
Describe the effect of anaesthetics on stimulation of inhibitory receptors
GABA(A) - pentameric, single amino acid change stops it working. Chloride ions cause hyperpolarisation –> unable to deal with any more electrical activity
Glycine
What excitatory receptors are inhibited by anaesthesia?
Nicotinic
Serotonin
Glutamate / NMDA
Describe oxygen
Gas above –119C
Distill air to get it
Supports combustion - not flammable
Black cylinders & white shoulders 137 bar
Piped VIE = stored under pressure & at low temperature
What are the side effects of oxygen?
O2 free radicals CNS convulsions Pulmonary oxygen toxicity Retrolental fibroplasia CO2 narcosis
Describe nitrous oxide
Odourless gas in blue cylinder Liquid / vapour at 44 bar Poor anaesthetic - MAC 105% Good analgesic Quick onset / offset Cardio respiratory depressant Neuropathy / BM depression 35X more soluble than N2
What are the ideal physical properties of an anaesthetic drug?
Cost Chemical stability Non-flammable / explosive Vapourisable Environmentally stable
What are the ideal chemical properties of an anaesthetic drug?
Non-irritant Low blood: gas solubility High potency MAC Minimal side effects Biotransformation Non-toxic
Describe isoflurane
Halogenated ether Relatively cheap Stable & non-flammable Vaporisable BP Irritable to airway Relatively potent MAC 1.1% Side effects: CVS / RS
Describe sevoflurance
Non-irritable Quick onset / offset MAC 2% 5% metabolised CVS stability Emergence phenomena Expensive
Describe desflurance
Very quick onset / offset 0.02% metabolised Moderately expensive Irritant Special vaporiser
