Pharmacology of Anaesthesia Flashcards
What is the aim of general anaesthetics?
To produce insensibility in the whole body + unconsciousness
they are centrally acting drugs: hypnotics, analgesics
What are the aims of regional and local anaesthetics?
Regional= produce insensibility in an area of the body - applied to nerves supplying relevant area
Local= produce insensibility in only relevant part of the body
applied directly to the tissues
What techniques and equipment is used?
Tracheal intubation Ventilation Fluid therapy Regional anesthesia Monitoring
What is the triad of anaesthesia?
Analgesia- pain relief
Hypnosis- unconsciousness
Muscle relaxation
Allows anaesthetic to be split into separate components as an individual may not require all three
What are the features of balanced anaesthesia?
Allows flexibility - allows different drugs and techniques to be used to tailor to each patient
Requires to titrate doses separately = more accurate and allows more control over components of the triad
Avoid overdosage
What are the problems of anaesthesia?
Polypharmacy: chance of drug reactions/allergies
Muscle relaxation: requires artificial ventilation
Separation of relaxation and hypnosis: awareness can occur
What are the mechanisms of general anaesthetics?
What are the 2 types of general anaesthetics?
Interfere with neuronal ion channels:
hyperpolarises neurones and suppresses neuronal activity
Inhalation agents dissolve in membranes (direct effect)
IV agents cause allosteric binding
In what order does general anaesthesia affect the body’s functions?
Interrupt cerebral function first (complex processes first)
LOC early, then hearing, then primitive functions (reflexes) later
What are the features of intravenous anaesthesia?
Rapid onset of unconsciousness
Rapid recovery (due to disappearance of drug from circulation)
What are inhalation anaesthetics?
Where is the uptake?
They are halogenated hydrocarbons
Both uptake + excretion is via lungs
Concentration gradients= lungs > blood > brain
What is MAC (minimum alveolar concentration)?
What is it used for
Concentration of drug in the alveoli required to produce anaesthesia
Can measure potency:
low number = high potency
What are the features of induction and awakening by inhalation anaesthetics?
Induction = slow
But good for maintenance of anaesthesia (prolongs duration, flexible)
Awakening= by stopping inhalation administration
+ washout to reverse concentration agent
What is the common sequence of administration of general anaesthesia?
IV induction the inhalation maintenance
What effects does CENTRAL general anaesthetic have on the cardiovascular system?
Depresses CVS centre:
- reduce sympathetic outflow
- negative inotropic effect on heart
- reduced vasoconstrictor tone leads to vasodilation
What effects does DIRECT general anaesthetic have on the cardiovascular system?
- negative inotropic effect
- vasodilation by decreased peripheral resistance
- venodilation: decreases velour return and cardiac output
What effects does general anaesthetic have on respiratory function?
Anaesthetic agents are respiratory depressants
- reduce hypoxic and hypercarbic drive
- decreases tidal volume
- increases resp rate
- paralyse cili
- decrease functional residual capacity
What are the effects of muscle relaxants?
Paralyse skeletal muscle
Respiratory and airway muscles are affected as much as any other
What are the indications for muscle relaxants?
Ventilation and intubation
When immobility is essential
Body cavity surgery access
What problems are there with muscle relaxants?
Awareness: when there is insufficient dosage so patient is awake but paralysed
Incomplete reversal: airway obstruction, ventilatory insufficiency
What is the purpose of analgesia?
What is the purpose of intraoperative analgesia?
Prevents feeling of unpleasant stimulus
Intraoperative analgesia:
Prevents arousal of patient due to pain
Contributes sedative effect
Suppresses reflex responses to painful stimuli
What is the purpose of local and regional analgesia?
Retain awareness/consciousness
Produces analgesia but no direct hypnosis
Does not have global effects of general anaesthesia
Spares respiratory function
What is the limiting factor of local anaesthetics?
Toxicity
When absorption > rate of metabolism = the anaesthetic agents cause high plasma level and vasoconstrictors reduce blood flow and reduce absorption
What are some signs and symptoms of local anaesthetic toxicity?
Numbness and tingling around mouth Tinnitus Visual disturbances Muscular twitching Drowsiness CVS depression Convulsions Coma Cardiorespiratory arrest
What does local anaesthetic toxicity depend on?
Dose used
Rate of absorption
Patient weight
Drug (some more toxic than others)
