Principles and Pharmacology of Anaesthetics Flashcards
What are the three main kinds of anaesthetic?
General
Regional
Local
What are the characteristics of general anaesthetic?
Produces insensibility in the whole body
Usually with loss of consciousness
Uses centrally acting drugs such as hypnotics or anaelgesics
What are the characteristics of regional anaesthetic?
Produces insensibility in an area or region of the body Involves application of local anaesthetic to nerves supplying the relevant area
What are the characteristics of local anaesthetic?
Produces insensibility in only the relevant part of the body
Involves application of local anaesthetic directly to the tissue.
What is the triad of anaesthetic?
Analgesia
Hypnosis
Relaxation
What aspects of the triad of anaesthetic do opiates act on?
Analgesia and hypnosis
What aspects of the triad of anaesthetic do local anaesthetics act on?
Analgesia and relaxation
What aspects of the triad of anaesthetic do muscle relaxants act on?
Relaxation
What aspects of the triad of anaesthetic do general anaesthetic agents act on?
Hypnosis and relaxation
Analgesia to a lesser degree
What is balanced anaesthesia?
Balanced anaesthesia involves using multiple drugs, each with altering functions. This allows a degree of control over the individual components of anaesthesia and helps keep the dosage of individual drugs down
What are the problems with balanced anaesthesia?
- Increased risk of drug interactions due to polypharmacy
- Muscle relaxation- requires airway maintenance
- Separation of relaxation and hypnosis- awareness possible
What is the physiology of general anaesthetic?
General anaesthetic agents interfere with neuronal ion channels, hyperpolarising them and making them less likely to fire
What is the difference in physiology between inhalational and intravenous anaesthetic agents?
Inhalational agents dissolve in the membranes and have a direct physical effect
Intravenous agents act via allosteric binding to GABA receptors, opening the chloride channels
What additional management must be given with general anaesthetic?
Airway management vital
Care should be taken to reduce cardiopulmonary impact
How does the uptake of intravenous anaesthetic vary in different body tissues?
Initially the blood level is very high but falls as the drug moves into highly perfused tissues
Muscle picks up the drug more slowly but the effect is large because of the relative mass of skeletal muscle in the body
Fatty tissue picks up drug even more slowly but can store large amounts due to the high fat solubility of these drugs
What is the benefit of using a target-controlled infusion pump?
It allows for very accurate concentrations of anaesthetic to be delivered to the blood and brain
How do inhalational anaesthetics work?
Halogenated hydrocarbons taken up and excreted by the lungs
Concentration gradient where lungs > blood > brain
What is the minimum alveolar concentration in terms of anaesthetic?
A measure of potency
A low concentration corresponds to a high potency
How is inhaled anaesthetic reversed?
Inhalational administration is stopped so the concentration gradient is reversed
What physiological changes occur with the administration of general anaesthetic?
- Depress cardiovascular centre (reduce sympathetic outflow, negative inotropic effect on heart, vasodilation)
- Direct vasodilation and venodilation
- Respiratory depressant (reduced hypoxic and hypercarbic drive, decrease tidal volume and increase rate, paralyse cilia)
- Decreases functional residual capacity
What are the indications for muscle relaxants?
- Ventilation & Intubation
- When immobility is essential (microscopic surgery, neurosurgery)
- Body cavity surgery (access)
What are the problems with muscle relaxants?
- Awareness
- Incomplete reversal
- Apnoea
- Relax skeletal muscle indiscriminately and so respiratory and airway muscles are also affected
For what reasons can intraoperative analgesia be given?
- Prevention of arousal
- Opiates contribute to hypnotic effect of GA
- Suppression of reflex responses to painful stimuli (e.g. tachycardia , hypertension)
What are the characteristics of local and regional anaesthetic?
- Retain awareness / consciousness
- Lack of global effects of GA
- Derangement of CVS physiology- proportional to size of anaesthetised area
- Relative sparing of respiratory function
