Anaesthetic drugs Flashcards
Define anaesthetia?
What is an anaesthetic?
A reversible drug-induced absence of sensation and awareness
Any lipid-soluble agent that causes depression of the brain in a predictable order: cortex, midbrain, spinal cord, medulla
Outline the stages of effects of Ethanol
Tranquillization Excitation Dysarthria - slurred speech Ataxia- lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes and abnormalities in eye movements Sedation/hypnosis Anaesthesia Coma Medullary depression DEATH
How do anaesthetics work?
Lipid-soluble
Stereo-selective
Modulation of ligand gated channels
Act on cell membrane:
- interaction with membrane proteins
- stimulation of inhibitory receptors, GABA/glycine
- inhibition of excitatory receptors
CAUSE GLOBAL DEPRESSION IN NEURONAL ACTIVITY
How are GABAa receptors involved in anaesthetic drug action?
The GABAa receptor is a pentomer and is the most abundant fast inhibitory neurotransmitter receptor in the CNS
-ligand gated ion channel selective for single amino acids causing influx of Cl- which leads to hyperpolarisation
Oxygen is used in anaesthesia.
At what temperature is it a gas? Where is it derived from? How is it stored? Method of administration? Side effects?
Gas >-119 degrees c
Derived from distilled air
Supports combustion, not flammable in itself. Stored in black cylinder with white shoulders
Inhaled
SIDE EFFECTS:
- Oxygen free radicals
- CNS convulsions
- Pulmonary oxygen toxicity
- Retrolental fibroplasia
- CO2 narcosis
GENERALLY GOOD FOR YOU
Nitrogen oxide is used in anaesthesia.
What does it look like? When is it a vapour? Method of administration? Analgesic or anaesthetic? Side effects?
Odourless, gas stored in blue cylinder Vapour at 44bar Inhaled agent Poor anaesthetic (MAC 105%), Good analgesic Quick onset and offset CARDIO RESPIRATORY DEPRESSANT Side effects: neuropathy/bm depression
State the physical properties to be considered for inhalation agents
Cost Chemical stability Non-flammable/explosive Vapourizable Environmentally stable
State the chemical properties to be considered for inhalation agents
Non-toxic Non-irritant Low blood: gas solubility High potency (MAC) Minimal side effects (pharmacodynamics) Biotransformation (pharmacokinetics)
Consider the older anaesthetic agents. What was wrong with them?
- Ether
- Chloroform
- Cyclopropane
- Methoxyflurane
- Halothane
- Enflurane
Ether- emetic
Chloroform- dysrhythmia
Cyclopropane- VERY explosive
Methoxyflurane- F- (bad for kidneys)
Halothane- Liver failure/hepatitis
Enflurane- prone to fitting
Describe Isoflurane
What is it?
Physical and chemical properties?
Side effects?
GENERAL ANAESTHETIC-inhaled Halogenated ether Relatively cheap Stable and non-flammable Vapourizable at 49degrees c Relatively potent (MAC 1.1%) 0.2% metabolised
Side effects: irritable to airway
Describe Sevoflurane
What is it?
Physical and chemical properties?
Side effects?
GENERAL ANAESTHETIC-inhaled Halogenated ether Non-irritable Quick onset/offset MAC 2% 5% metabolised (few bad breakdown products) CVS stability Expensive \$\$
Side effects: emergence phenomena
Describe Desflurane
What is it?
Physical and chemical properties?
Side effects?
GENERAL ANAESTHETIC- inhaled Halogenated ether Very quick onset/offset 0.02% metabolised Moderately expensive Needs a specialised vapouriser due to boiling point MAC 6.35%
Side effect: irritant
Describe Thiopentone
What is it?
Physical and chemical properties?
Side effects?
Intravenous general anaesthetic
- Thiobarbituate
- Antiepileptic
- Powder
- Smells like garlic
- Causes CVS and RS depression
- Anaphylaxis/arterial
- Half life 10 hours
What can be said intravenous general anaesthetics?
NEWER Uses induction agent/ IV opiate Rapid and unpleasant Lipid soluble Wear off by redistribution -this is when you wake up(moves from brain to fat and muscle) Metabolised Cause CVS and RS depression
Describe Propofol
What is it?
Redistribution and elimination half lives?
Side effects?
Solvent -General anaesthetic -Anti emetic -Anti epileptic Redistribution half life: 4 minutes Elimination half life: 4 hours
Minimal accumulation
SIDE EFFECTS:
Painful to inject (use carrying agent and local anaesthetic), abnormal movemenets, SEVERE CVS depression
What other anaesthetic agents exist?
Ketamine- anaesthetic and analgesic
Etomidate
Mildazolam- any administrayion,sedation in ICU, induction agent
Muscle relaxants are used only be anaesthetics. Why is that?
Indication?
VERY DANGEROUS
Muscle paralysis
Facilitates intubation (endotracheal tube entry)
Maintains paralysis for surgery/ventilation
2 Types depolarising and non-depolarising
Give an example of a depolarising muscle relaxant
Where does it act?
Physical and chemical properties?
Side effects?
e.g. Suxemethonium
Act on post-synaptic membrane, plasma cholinesterase. Mimics ACh
Rapid onset and offset
Short half life = 2 mins
MULTIPLE SIDE EFFECTS such as anaphylaxis
Consider non-depolarising muscle relaxants
Where do they act?
Physical and chemical properties?
Side effects?
Compete with ACh
ACh moiety blocks Na channels with size
Duration is variable
Slower onset/offset
Steroid group
Benzylisoquinoliniums
What is pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
Briefly outline the gate theory
C fibres transmit pait information
Ab fibres stimulate inhibitory neurons
Descending pathways prevent central passage
How can we score pain?
Linear?
Smiley/sad faces?
Mild/moderate/severe/excrutiating
Consider the pain ladder. What types of drugs are used at each stage?
NSAIDs/paracetamol
Weak opiates (e.g. codeine) / local anaesthetics
Strong opiates
Give an example of an opioid
Where do they act/where are its receptors?
Side effects?
Morphine
Receptors in pons/midbrain Peripheral tissue Spinal cord posterior horn 1 and 2 GIT PAQ Grey matter
Respiratory depression/airway loss
Nausea and vomiting
Constipation and pruritis
Miosis (excessive contriction of pupil)
Where does ketamine act?
What is it?
Side effects?
NMDA receptors
Kappa and delta receptors (not GABA)
Local and general analgesic
Anaesthetic
Side effects: emergence phenomena
What are NSAIDs?
Where do they act?
Use?
Side effects?
Non-steroidal anti-inflammatory drugs
Act by inhibiting COX1 and 2
Analgesic, antipyretic, anti-inflammatory
Side effects: bronchospasms, renal impairment, platelet dysfunction (ASPIRIN)
Aspirin is an example of a….
Mechanism of action?
Side effects?
NSAIDS
Oxidative phosphorylation
Air hunger, reyes syndrome, platelet dysfunction
What is the Ramsay sedation scale?
A sedation scoring system used in ICU
Describe the mechanismof action of benzodiazepines and barbituates in sedation
What other sedatives are there?
Benzodiazepines (Midazolam, Diazepam, Lorazepam), Baribituates
Bind to GABAa receptor at different allosteric sites
Facilitates GABA action
Barbituates increase duration and Benzos increase frequency of Cl- channel opening
Membrane hyperpolarisation
CNS depression
Low dose vapours (Isoflurane/Sevoflurane/Desflurane),Ketamine, Hyoscine, Propofol low dose, major tranquillisers, alpha-2 agonists
What are the side effects of benzodiazepines
- Over sedation
- Loss of airway
- Respiratory depression
