Anaesthetic drugs Flashcards
What is anaesthesia
• A reversible drug induced absence of sensation and awareness
What is an anaesthetic agent
• Any lipid soluble agent that causes depression of the brain in a predictable order: Cortex Midbrain Spinal cord Medulla
Effects of ethanol
- Tranquillization
- Excitation
- Dysarthria
- Ataxia
- Sedation/hypnosis
- Anaesthesia
- Coma
- Medullary depression
- Death
How do anaesthetics work
- Diverse range
- Lipid solubility
- Cell membrane
- Stereo-selectivity
- Interaction with membrane proteins
- Modulation of ligand gated ion channels
- Global depression in neuronal activity
Biochemical effects of anaesthetics
• Stimulation of inhibitory receptors
- GABAA
- Glycine
• Inhibition of excitatory receptors
- Nicotinic
- Serotonin
- Glutamate/NMDA
Effect of anaesthetic on GABAa receptors
- Pentameric
- Single amino acids
- Chloride ions
- Hyperpolarisation
Examples of inhalational anaesthetic agents
- Oxygen
- Nitrous oxide
- Ideal properties
- Isoflurane
- Other volatile agents
Features of oxygen
- Priestly 1777
- Gas above -119C
- Distilling air
- Supports combustion – not flammable
- Black cylinders and white shoulders 137 bar
- Piped VIE
Side effects of oxygen
- O2 free radicals
- CNS convulsions
- Pulmonary oxygen toxicity
- Retrolental fibroplasia
- CO2 narcosis
Features of nitrous oxide
- Odourless gas in blue cylinder
- Liq/vapour at 44bar
- Poor anaesthetic MAC 105%
- Good analgesic
- Quick onset/offset
- Cardio respiratory depressant
- Neuropathy/BM depression
- 35x more soluble than N2
Physical properties of inhalational agents
- Cost
- Chemical stability
- Non-flammable/explosive
- Vapourizable
- Environmentally stable
Chemical properties of inhalational agents
- Non irritant
- Low blood:gas solubility
- High potency MAC
- Minimal side effects (pharmacodynamics)
- Biotransformation (phamacokinetics)
- Non-toxic
Older agents
- Ether
- Chloroform
- Cyclopropane
- Methoxyflurane
- Halothane
- Enflurane
Features of isoflurane
- Halogenated ether
- 1965
- Relatively cheap
- Stable and non flammable
- Relatively potent MAC 1.1% B:G co 1.4
- 0.2% metabolised
Vapourizable BP of isoflurane
Vapourizable BP 49C
Effect of isoflurane on airway
- Irritable to airway
Side effects of isoflurane
- CVS/RS
Features of sevoflurane
- Non irritable
- Quick onset/offset
- MAC 2%
- 5% metabolised
- CVS stability
- Emergence phenomena
- Expensive
Features of desflurane
- Very quick onset/offset
- 0.02% metabolised
- Moderately expensive
- Irritant
- Special vaporizer
- MAC 6.35%
What is MAC(minimum alveolar concentration)
- Minimum alveolar concentration or MAC is the concentration of a vapour in the lungs that is needed to prevent movement (motor response) in 50% of subjects in response to surgical (pain) stimulus
Features of intravenous agents
• Shorter history • Induction agents/iv opiate • Rapid and pleasant • Lipid soluble • Redistribution short acting • Metabolised CVS/RS depression
features of thiopentone/thiobarbituate
- Powder
- Smell of garlic
- Antiepileptic
- CVS/RS depression
- Anaphylaxis/ arterial
Half life of thiobarbituate
- 10 hours
Redistribution half life of 2,6-diisopropylphenol
4 minutes
Elimination half life of 2,6-diisopropylphenol
4 hours
Features of 2,6-diisopropylphenol
Solvent • Anti emetic • Anti epileptic • Painful to inject • Abnormal movements • CVS/RS effects
Other examples of intravenous anaesthestic agents
- Ketamine
- Etomidate
- Midazolam
Features of muscle relaxants
- Dangerous drugs
- Muscle paralysis
- Facilitate intubation
- Maintain paralysis for surgery/ventilation
- Depolarising
- Non depolarising
- Anaesthetists only
Features of depolarising agents with an example
- Suxamethonium
- Post-synaptic membrane
- Mimics acetylcholine
- Rapid onset offset
- Short half life ~ 2min
- Plasma cholinesterase
- Multiple side effects
Features of non-depolarising blockers
- Competitive with Ach
- Ach mostly blocks Na channel with size
- Duration is variable
- Slower onset
- Slower offset
- Steroid group rocuronium
- Benzylisoquinoliniums atracurium
Features of n-m blocking agents
- Intubation
- Surgery
- Ventilation
- Transfer
- Side effects
- Reversal