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Y3 - anaesthetic s > principles of pharmacology > Flashcards

principles of pharmacology Flashcards

1
Q

what is a general anaesthetic

A

loss of consciousness and global lack of awareness

achieved using general anaesthetic agents

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2
Q

what is a regional anaesthetic

A

producing insensibility in an area or region of the body

local anaesthetics applies to nerves supplying relevant area

e.g. nerve and plexus blocks incl. central neuraxial block (spinal and epidural)

effect is remote from the injection

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3
Q

what is local anaesthetic

A

insensibility in only the relevant area of the boy

applied directly to the tissues

effect is at the site of inkection

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4
Q

GA vs sedation

A

GA - patient is completely unaware of what is occurring

sedation - some awareness but not necessarily recall

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5
Q

regional anaesthesia vs analgesia

A

regional anaesthesia - little to no sensation of any sort from the blocked area

regional analgesia - only pain sensation need be removed or reduced, other sensations may be retained to varying extents

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6
Q

functions of modern anaesthetic machine

A

regulation of fresh gases and mixing to deliver precise concentrations of gaseous agents

addition of precise concentrations of inhaled anaesthetic gases

CO2 removal to allow recirculation of inhaled gases

mechanical ventilation

monitoring is integrated

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7
Q

safety of anaesthesia

A

overall operative mortality 4% - includes all anaesthetic and surgical mortality from all emergency and elective surgery and all patient groups, includes all deaths within 30 days of surgery

anaesthetic mortality 0.00024%

ASA system - mortality is concentrated in ASA groups 3-5

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8
Q

3 components of anaesthesia

A

hypnosis
analgesia
relaxation

an individual anaesthetic may consist of varying contributions from all 3 but doesn’t require all 3

different drugs do different jobs, some do more than one:

GA agents - relaxation, hypnosis (analgesia)
opiates - hypnosis, analgesia
muscle relaxants - muscle relaxants
LA agents - analgesia, relaxation

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9
Q

3 components of anaesthesia - hypnosis

A

unconsciousness

necessary component of any GA

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10
Q

3 components of anaesthesia - analgesia

A

removal of pain and perception of unpleasant stimulus

if patient is unconscious and unaware of pain, still required to suppress reflex autonomic responses to painful stimulus

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11
Q

3 components of anaesthesia - relaxation

A

skeletal muscle relaxation

necessary to provide immobility for certain procedures, allow access to body cavities and permit artificial ventilation

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12
Q

what is balanced anaesthesia and what are the benefits

A

different drugs do different jobs

great degree of control over the individual components of the triad

titrate doses separately and therefore more accurately to meet individual requirements

avoid over dosage of individual drugs

enormous flexibility

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13
Q

problems with balanced anaesthesia

A

polypharmacy - drug interactions, reactions, allergies

muscle relaxation - requirement for artificial ventilation and airway control

separation of relaxation and hypnosis - awareness (possibility of being awake and paralysed and unable to communicate)

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14
Q

general anaesthetic agents - what do they do

A

inhaled and IV

provide unconsciousness as well as a small degree of muscle relaxation

may to differing extents provide analgesia - negligible for all except ketamine

potent drugs - separates them from sedatives - low doses of a potent agent e.g. propofol may be used to provide sedation

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15
Q

how do general anaesthetic agents work

A

suppress neuronal activity in a dose dependent fashion

open chloride channels which hyperpolarise the neurons - suppresses excitatory synaptic activity

neurons become reversibly hyperpolarised and therefore less able to likely to reach their threshold potential and fire

–> globally suppressed neuronal activity

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16
Q

how do IV and inhalational GA agents work

A

inhalational agents - dissolve in membranes, direct physical effects

IV agents - allosteric binding, GABA receptors - open chloride channels

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17
Q

loss of function with GA

A

cerebral function lot from top down

  • most complex processes interrupted first
  • LOC early, hearing later
  • more primitive functions lost later

spinal reflexes relatively spared - primitive and small number of synapses

allows unconscioussness while preserving some autonomic and automatic functions e.g. respiration and BP homeostasis (impaired in dose dependent fashion)

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18
Q

management of a patient under GA

A 
ABC - long drawn out resuscitation 
mandates airway management 
impairment of resp function and control of breathing 
CV impact 
care of the unconscious patient
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18
Q

management of a patient under GA

A 
ABC - long drawn out resuscitation 
mandates airway management 
impairment of resp function and control of breathing 
CV impact 
care of the unconscious patient
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19
Q

IV anaesthesia - unconsciousness and recovery

A

rapid onset unconsciousness
1 arm - brain circulation time

rapid recovery - due to disappearance of drug from circulation, redistribution V’s metabolism

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20
Q

how do IV anaesthetic agents work so rapidly

A

highly fat soluble drugs and cross basement membranes extremely quickly

cross the blood brain barrier rapidly and get into neural tissues very quickly

leave the circulation very quickly - a bolus only causes temporary unconsciousness

metabolism contributes very little to the immediate termination of action when given as a bolus

21
Q

examples of IV GA agents

A

thiopentone

propofol

22
Q

IV anaesthetics - blood concentration over time

A

brain concentration (effect of the drug) follows blood concentration very closely

blood level is very high initially but falls quickly as drug moves into highly perfused tissues

Muscle picks up the drug more slowly but the effect is large because of the relative high mass of skeletal muscle in the body.

Fatty tissue picks up drug even more slowly but given lengthy enough exposure can store large amounts due to the high fat solubility - large amounts stored after a length procedure, leaches out slowly over a long time period

23
Q

what is a TCI pump system

A

target controlled infusion pump system

with total IV anaesthesia (TIVA) we can’t measure the drug conc in real time so use calculations to make estimates

allows very accurate infusion to achieve specific blood or brain concentrations of agents - calculations and assumptions about physiology based on age, sex and size

24
what are inhalational anaesthetics
halogenated hydrocarbons
25
uptake and excretion of inhalational anaesthetics
uptake and excretion via lungs partial pressure gradient - lungs > blood > brain (patient given a relatively high concentration of the agent at induction to breath in, gas moves down pressure gradient to produce unconsciousness) cross alveolar BM easily arterial PP equates closely to alveolar PP
26
what is MAC
minimum alveolar concentration the concentration of the drug required in the alveoli to produce anaesthesia with any particular agent i.e. measure of potency low MAC value = potent agent e.g. halothane (MAC 0.8%) is more potent than desflurane (6%) because it takes less concentration of the agent to produce the same effect
27
process of inhalational anaesthetics
induction - slow, can be good when this is desirable maintenance of anaesthesia - prolong duration, very flexible awakening - stop inhalational admin, washout - reversal of conc grad
28
when can a slow induction with inhalational anaesthesia be desirable
e.g. potentially obstructing airway
29
what is the main role of inhalational agents
extension or continuation of anaesthesia patient breathes gas mixture containing inhalational agent for duration of procedure and will remain unconscious for as long as the anaesthetic is administered
30
metabolism of inhalational agents
undergo very little actual metabolism in the bdoy breathed back out again almost completely unchanged
31
sequence of GA
induction - IV/inhalational maintenance - inhalational more modern agents allow IV maintenance (propofol, opiate - remifentanil) - better recovery +/- additional regional anaesthesia/analgesia
32
physiology of GA: CVS - central effects
adverse effects are almost universally depressant (ketamine is the exception) central effects arise due to depressant effects of the agent on CV centres and nuclei in brainstem reduced symp nerve activity direct -ve chronotropic and inotropic effects on the heart reduced vasoconstrictor tone --> venous and arterial vasodilation
33
physiology of GA: CVS - direct effects
direct effects of anaesthetic on vascular smooth muscle and myocardium - compounds the effects of the reduced symp activity vasodilation --> decreased peripheral resistance venodilation - decreased venous return, decreased CO -vely inotropic - worsen the fall in CO
34
physiology of GA: resp
all anaesthetic agents are resp depressants (excl ketamine) - reduce hypoxic and hypercarbic drive (depression of brainstem resp centres), decreased tidal volume and increase rate paralyse cilia decrease FRC - lower lung vol, VQ mismatch
35
opiate resp depression
preserves tidal vol low resp rate
36
why is post-op oxygen often required
fall in lung vol due to anaesthetic and VQ mismatch persists into post-op period can persist for several days so patients can require post-op O2 for several days
37
what are muscle relaxants and what is required at the same time
paralyse skeletal muscle indiscriminate - resp and airway muscles are also affected unconsciousness must also be provided with systemic muscle relaxants
38
indications for muscle relaxants
ventilation and intubation when immobility is essential e.g. microscopic surgery, neurosurgery body cavity surgery - access
39
problems with muscle relaxants
awareness - due to the separation of unconsciousness from relaxation in the triad incomplete reversal - airway obstruction, ventilatory insufficiency in immediate post-op period, unlikely to persist apnoea - dependence on airway and ventilatory support
40
analgesia in anaesthesia - what is used alongside it
if analgesia is good enough then there is no need for unconsciousness e.g. regional anaesthesia which can be used alone or part of a combined technique most commonly used in conjunction w/ unconsciousness as part of a balanced GA technique w/ or w/o relaxation Regional techniques usually provide reasonable muscle relaxation by blocking motor nerves so spinal or epidural analgesia may not require additional muscle relaxation.
41
why is intra-operative analgesia used
prevention of arousal from pain of surgery opiates contribute to hypnotic effect of GA suppression of reflex responses to painful stimuli e.g. tachycardia, HT, gross movement regional anaesthesia has no direct sedative effect but can allow lighter levels of GA to be used
42
examples of opiate analgesics
fentanyl morphine, oxycodone remifentanil
43
fentanyl uses
short acting potent intra-operative analgesia
44
morphine, oxycodone and conventional opiate uses
intra-operative analgesia which we want to continue into the post-op period
45
remifentanil uses
very highly potent and extremely short acting has to be given by infusion high potency - allows use as a very potent adjunct to inhalation and IV agents, allowing them to be used in lower doses - faster recovery doesn't provide any post-op analgesia
46
examples of local anaesthetics
lignocaine bupivacaine ropivacaine
47
how do local anaesthetics work
analgesia w/o hypnosis block Na+ channels and prevent axonal AP from propagating effects on every tissue, toxic if delivered wrong (e.g. IV)
48
effects of local and regional anaesthesia
retain awareness/consciousness lack of global effects of GA derangement of CVS physiology - proportional to site of anaesthetised area relative sparing of resp function - preferred technique in pts w/ concomitant resp problems
49
US guided regional anaesthesia
US used to guide needle placement safer and more effective delivery of LA drug w/ less likelihood of going intravenously or direct nerve/vascular injury

Y3 - anaesthetic s (5 decks)

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