Anaesthetics- Principles of Pharmacology Flashcards
What is general anaesthesia?
A state of controlled unconsciousness.
How is General anaesthetic administered?
Via centrally acting drugs, such as Hypnotics or Analgesia
What does regional anaesthesia do?
Produce insensibility in an area or region of the body
How does regional anaesthesia work?
- Nerve and plexus blocks
* Applied to nerves supplying relevant areas
What does local anaesthesia do?
• Produces insensibility on the relevant part of the body
Applied directly to the tissue
What is the ASA score used for?
To work out if someone is healthy enough for anaesthesia and surgery
What is the triad of anaesthesia?
What is the triad of anaesthesia?
Hypnosis
Analgesia
Relaxation
What is hypnosis?
Unconsciousness.
Done via opiates or general anaesthetic agents (main)
What is analgesia?
Pain relief.
Done via opiates, local anaesthetic and general anaesthetics
What is relaxation?
Skeletal muscle relaxation.
Done via muscle relaxants (mainly), general anaesthetic agents and local anaesthetic agents
What are the 3 main problems of anaesthetics?
Polypharmacy
Muscle relaxation
Separation of relaxation and hypnosis
What is the problem with polypharmacy?
Increases chances of drug reactions and allergies
What is the problem with muscles relaxation?
Artificial ventilation, patients airways need managed
What is the problem of Separation of relaxation and hypnosis?
Awareness
What is the main effect of general anaesthetic agents?
Hypnosis/ unconsciousness
How do general anaesthetic agents work?
- Interfere with neuronal ion channels
* Hyperpolarise neurones- Less likely to fire
How do general anaesthetic inhalation agents work?
Dissolve in membranes
Have a direct physical effect
How do general anaesthetic IV agents work?
Allosteric binding
GABA receptors open chloride channels
What type of drugs are used for intravenous anaesthesia?
Fat soluble drugs
Why are fat soluble drugs used for IV anaesthesia?
Rapid onset of unconsciousness
Rapid disappearance of drug from circulation
How is the onset of unconsciousness measured?
1 arm-brain circulation time
What type of drug are inhalation anaesthetics?
Halogenated hydrocarbons
How are inhalation anaesthetics taken up and excreted?
Via the lungs
Why are inhalation anaesthetics given in high concentrations?
To create a partial pressure gradient between the lungs > blood > brain
What does MAC stand for?
Minimum alveolar pressure
What is MAC?
The concentration of inhaled agent that is required to achieve a certain level of anaesthesia
What is MAC a measure of?
Potency- high number, low potency
Is the induction of inhalation slower or faster than IV?
Slower
It takes longer to build up effective concentrations
Is the duration of inhalation longer or shorter than IV?
Longer-prolonged duration
What effect does general anaesthetic have on the cardiovascular system?
Depress cardiovascular system
What are the central effects of general anaesthesia on the CVS?
- Reduce sympathetic outflow
- Negative iontropic/chronotropic effect on the heart
- Reduced vasoconstrictor tone->Vasodilation
What are the direct effects of general anaesthesia on the CVS?
- Negatively inotropic
- Vasodilation- Decreased peripheral resistance
- Venodilation- Decreased venous return and decrease cardiac output
What is the effect of general anaesthesia on the respiratory system?
All anaesthetic agents are respiratory depressants
• Reduce hypoxic and hypercarbic drive
• Decreased tidal volume & increase rate
Paralyse cilia
Decrease FRC- Lower lung volumes, VQ mismatch
What are the indications for using muscle relaxants?
- Ventilation & Intubation
- When immobility is essential-microscopic surgery, neurosurgery
- Body cavity surgery
What are the problems of muscle relaxants?
- Awareness
- Incomplete reversal → airway obstruction, ventilatory insufficiency in immediate post op period
- Apnoea = dependence on airway and ventilatory support
What are the effects of local and regional anaesthesia?
- Retain awareness/ consciousness
- Lack of global effect of G?
- Derangement of CVS physiology
- Relative sparing of respiratory function
