anaesthetics 1 - principles and pharmacology Flashcards
General anaesthesia
insensibility in whole body, usually causing unconsciousness
cantrally acting drugs - hypnotics, analgesics
Regional anaesthetic
insensibility in an area or region of the body
LA applied to nerves supplying relevant area
Local anaesthetic
insensibility in relevant part of the body only
LA applied directly to the tissues
How were bleeding, infection and pain in ancient surgery overcome?
bleeding - cautery, ligation, pressure, technique
infection - technique, germ theory
pain - herbs, opiates, restraint, alcohol
Early years inhaled therapies
ether and nitrous oxide found
How was anaesthesia given in the early years?
monotherapy - ether, chloroform
What provided the surgical conditions in early anaesthesia
deep planes of anaesthesia
how was ether administered in the early years?
schimmelbusch mask
Anaesthetic drugs in the modern era
inhaled, IV, muscle relaxants, analgesics, LA
Have the drugs or techniques improved more in anaesthetics?
techniques
technique and equipment improvements in the modern era
tracheal intubation ventilation fluid therapy regional anaesthetic monitoring USS, fibre optics, bis
Functions of modern anaesthetic machine
regulation of fresh gases and mixing to deliver precise concentrations
mechanical ventilation, microprocessor controlled
Triad of anaesthesia
analgesia
muscle relaxation
hypnosis
Which medications contribute most to each of the triad of anaesthesia?
Analgesia - opiates, LA
hypnosis - general anaesthetics
relaxation - muscle relaxants
Idea of balanced anaesthesia
different drugs do different jobs -enormous flexibility
titrate doses separately
avoid overdose
Problems with anaesthesia
polypharmacy - drug reaction/allergy
muscle relaxation - artificial ventilation and airway
separate relaxation and hypnosis - awareness
How do general anaesthetics work?
interfere with chloride ion channels which hyperpolarise and suppress excitatory synaptic activity
Explain the difference in how inhaled and IV general anaesthetics work
inhaled - dissolve in membrane - direct physical effect
IV - allosteric binding (GABA) open chloride channels
Chronology of what is “lost” with general anaesthesia
cerebral function lost top down - consciousness first
reflexes spared as small number of synapses
most complex pathways lost first - hearing near end
IV anaesthetics onset
rapid unconsciousness - 1 arm brain circulation time
IV anaesthetics recovery
disappear from circulation, redistribution, fat is poorly perfused
Inhaled anaesthetics
halogenated hydrocarbons - uptake and excretion by lungs
inhaled anaesthetics concentration gradient
lungs - blood - brain
MAC - what is it?
measure of potency
low number = high potency
minimum alveolar concentration
inhaled anaesthetics induction and waking up
slow induction, prolonged by maintenance
stop inhalation and washout to reverse concentration gradient
Usual way to induce and maintain general anaesthesia
IV - inhalation
IV general anaesthetics
Propofol
opiate - remifentanil
How general anaesthetics affect CVS - brief
depress cardiovascular centre
vasodilation and venodilation
negative ionotropic effect - weaken force of contraction
How general anaesthetics affect respiratory - brief
respiratory depressants and reduce hypoxic/hypercarbic drive
decreased tidial volume and increased rate
VQ mismatch
Indications for muscle relaxants
ventilation and intubation
body cavity surgery
immobility essential eg neurosurgery
Problems with muscle relaxants
awareness
incomplete reversal - airway obstruction
apnoea - dependence on airway and ventilatory support
Why give intraoperative analgesia
prevent arousal
opiates contribute to hypnotic effect
suppress reflex response to pain
Positives of regional anaesthesia
intense/complete analgesia
no direct hypnotic effect
Do local and regional anaesthetic affect resp and CVS function?
derange CVS but spare resp
Limiting factor of regional anaesthetic
toxicity - high absorption levels
Toxicity of regional/LA depends on what?
dose used
absorption
patient weight
drug
Toxicity of LA symptoms and signs
circumoral and lingual tingling and numb light headed coma muscular twitching coma cardiovascular depression cardiorespiratory arrest tinnitus, vision
How do LA display differential blockade?
motor fibres spared
pain fibres easily blocked
myelinated thick fibres are relatively spared
physiology of neuraxial block - CVS
venodilation and vasodilation due to sympathectomy
increasing physiological impact - anaesthetics
LA plexus block limb block neuraxial block epidural spinal
Physiology of neuraxial block - resp
expiratory function impaired
decrease FRC and increase VQ mismatch
