anaesthetics intro Flashcards
general anaesthesia
produces insensibility in whole body, usually causing unconsciousness
centrally acting drugs
regional anaesthesia
producing insensibility in an area/region of body
local anaesthetics applied to nerves supplying relevant area
anaesthetic agent applied to nerve and anaesthesia produced in distal site served by that nerve
local anaesthesia
insensibility only in relevant part of body
local anaesthetics applied directly to tissues
unlike regional anaesthesia, anaesthesia produced at site of injection
regional analgesia vs anaesthesia
regional anaesthesia patient should have little or no sensation of any sort from blocked area: warmth, proprioception, light touch, vibration, pain
regional analgesia only pain sensation needs to be removed/reduced. Other sensation may be retained to varying extents
different categories of anaesthetic drugs
inhalational anaesthetics intravenous anaesthetics muscle relaxants local anaesthetics analgesics
different techniques and equipment
tracheal intubation ventilation fluid therapy regional anaesthesia monitoring
functions of modern anaesthetic machine
- deliver precise concentrations of gaseous agents
- addition of precise concentrations oh inhaled anaesthetic gases
- co2 removal to allow recirculation of inhale gases
- mechanical ventilation
- most monitoring
ASA system
mortality concentrated in ASA groups 3-5
fit healthy patients are at very little risk indeed
ASA 1
normal, fit, healthy patient
ASA 2
patient with mild systemic disease
ASA 3
patient with severe systemic disease
ASA 4
patient with severe systemic disease that is a constant threat to life
ASA 5
moribund patient, not expected to survive
surgery carried out in desperation
ASA 6
patient declared brain dead, usually undergoing organ retrieval
triad of anaesthesia
hypnosis
analgesia
relaxation
triad of anaesthesia: hypnosis
unconsciousness
necessary component of any general anaesthetics
triad of anaesthesia: analgesia
pain relief, removal of perception of unpleasant stimulus
if pt unconscious and so unaware of pain, analgesia usually required to suppress reflex autonomic responses to painful stimuli
triad of anaesthesia: relaxation
refers to skeletal muscle relaxation necessary to provide immobility for certain procedures
allow access to body cavities and to permit artificial ventilation
balanced anaesthesia
use different drugs to do different jobs
titrate doses separately + so more accurately to requirements
avoid over-dosage
enormous flexibility
problems with balanced anaesthesia
polypharmacy - increasing chance of drug reactions/allergies
muscle relaxation
separation of relaxation and hyponosis –> awareness: possible to have patient paralysed with muscle relaxant yet insufficiently anaesthetised so aware
general anaesthetic agents
provide unconsciousness as well as a small degree of muscle reactions
they may also provide some analgesia, but for all except ketamine, analgesia is negligible
how to general anaesthetic agents work
- interfere with neuronal ion channels
- hyper-polarise neurones = less likely to fire
suppress neuronal activity
inhalational agents dissolve in membranes - direct physical effect
IV agents - allosteric binding: GABA receptors - open chloride channels
IV anaesthetics
rapid onset of unconsciousness
rapid recovery
target controlled infusion pump system
allows very accurate infusion to achieve specific blood or brain concentrations of agents
inhalational anaesthetics
halogenated hydrocarbons
uptake and excretion in lungs - partial pressure gradient
inhalational anaesthetics: minimum alveolar concentration
measure of potency
low number = high potency
concept of the concentration of drug required in the alveoli which is required to produce anaethesia
main role of inhalational agents
extension or continuation of anaesthesia
sequence of general anaesthesia
IV induction followed by inhalational maintenance
more modern agents with more sophisticated infusion techniques allow use of IV maintenance
physiology of GA: CVS
reduce sympathetic outflow
negative iontropic/chronotropic effect on heart
reduced vasoconstrictor tone –> vasodilatoin
decreased peripheral resistance, venous return and cardiac output.
physiology of GA: repsiratory
reduce hypoxic and hypercarbic drive decreased tidal volume+ inc rate paralyse cilia decrease functional residual capacity -lower lung volumes -VQ mismatch
indications for muscle relaxants
ventilation + intubation
when immobolity is essential e.g. microscopic surgery, neurosurgery
body cavity surgery (access_
how do muscle relaxants work
work on NMJ in skeletal muscle
do not effect cardiac or smooth muscle
problems with muscle relaxants
awareness: separation of unconsciousness from hypnosis in triad
incomplete reversal: may lead to airway obstruction
apnoea: dependence on airway and ventilatory support
intraoperative analgesia
prevention of arousal - pain wakes you up
opiates contribute to hypnotic effect of GA
suppression of reflex response to painful stimuli e.g. tachycardia
regional anaesthesia
intense/complete analgesia
no direct hypnotic effects
can allow lighter levels of GA to be used by eliminating painful surgical stimuli
local analgesia
analgesia with no hypnosis, little bit of muscle relaxation too
work by blocking Na+ channels and preventing axonal AP from propagating
pharmacologically filthy with effects on every tissue so is toxic if delivered wrongly
