Anaesthesia Flashcards
what problems can occur in general anaesthesia?
> polypharmacy so higher chance of reaction
muscle relaxation
- requires artificial ventilation
- airway management
separation of relaxation and hypnosis can lead to awarness
what do genera anaesthetics act on?
the neuronal ion channels opening up cl channels hyper polarising them
what tissues do IV anaesthetic agents pass though?
first the blood the into the viscera then into the muscle then into the fat
what is the MAC?
the maximum alveolar concentration, a measure of potency (low number high potency)
what is the affect of general anaesthesia on the central cardiovascular system?
depresses it
> decreased sympathetic outflow
> negative inotropic effect on the heart
> vasodialtion
what is the direct effect of general anaesthesia on the cardiovascular system?
> negatively inotropic
vasodilation decreasing the peripheral vascular resistance
vasodilation decreasing the venous return and cardiac output
what is the effect of general anaesthesia on the respiratory system?
> paralyses cilia
decreases the FRc (lower lung volumes, VQ mismatch)
resp. depressants (decreased hypoxic and hypercarbic drive, decreased tidal volume, increased uptake)
when are muscle relaxants indicated?
> ventilation and intubation
immobility is essential (microscopic and neurosurgery)
body cavity surgery
what problems occur with muscle relaxants?
> awareness
incomplete reversal causing airway obstruction
apnoea- dependence on ventilation and support
why is intra-operative analgesia often needed?
> prevents arousal
opiate contribute to hypnotic effects of GA
suppression of the reflex response to painful stimuli (tachycardia, hypertension)
what does toxicity of local or regional anaesthesia depend on?
> dose
rate of absorption
patient weight
drug
how might local anaesthetic toxicity present?
> coma > drowsiness > numbness and tingling > light headedness > tinnitus > visual disturbance > muscle twitching > CVS depression > cardiopulmonary arrest
what is differential blockade?
there is different penetration to different nerve types (myelinated thick fibres are spared and pain fibres are blocked easily)
what is the physiological affect of a neuroaxial block?
> inspiratory function spared
expiratory function relatively impaired
decreased FRC
increased V/Q match
what agents can be used in induction of general anaesthesia?
> Propofol
> thiopentone
how are conscious levels monitored?
> movement
resp. pattern
processed EEG
is the airway is open and unobstructed it is……….?
maintained
what airway complications can occur in general anaesthesia?
> obstruction
- ineffective triple airway manoeuvre
- airway device malposition
- laryngospasm (forced reflex adduction of the vocal cords)
> aspiration
- gastric contents
- blood
- surgical debriment
what triple airway manoeuvre is used to maintain the airway?
> head-tilt
chin lift
jaw thrust
why might you intubate?
> protect airway from gastric contents
need for muscle relaxation
need for tight control of blood gases
restricted access to airway (maxfax)
what risks are there for the unconscious patient?
> airway > temperature > loss of protective reflexes > consent and identification > pressure areas > venous thromboembolism risk
how is the unconscious patient monitored?
> FiO2 > ECG > ETO2 > SPO2 > resp. parameters > agent monitoring > temperature > venous and arterial monitoring > processed ECG > urine output
what is the process of emergence?
> muscle relaxant is reversed
resumption of spontaneous respiration
return of airway reflexes/control
extubation
what is the role of anaesthetists preop assessment?
> identify risk > optimise > minimise risk > inform and support he patient > consent (reducing complications, delays, anxiety, mortality and length of stay)
what would you want to illicit from a preop history?
> known comorbidities and their severity > unknown comorbidities > drugs and allergies > previous surgery and anaesthesia > family history and rarities (malignant hyperpyrexia and cholinesterase deficiency)
describe an ASAS grade 1
healthy
describe an ASAS grade 2
mild to moderate systemic disturbance
describe an ASAS grade 3
severe systemic disturbance
describe an ASAS grade 4
life threatening disease
describe an ASAS grade 5
moribund patient
describe an ASAS grade 6
organ retrieval
what does the cardiac risk index involve?
> high risk surgery > ischaemic heart disease > congestive heart failure > cerebrovascular disease > diabetes > renal failure
what medication would not carry on as normal throughout a GA?
> antidiabetic medication
> anticoagulants
describe an endotracheal tube?
> balloon at one end stopping it going down into the lungs
cuff so high pressure air enters the lungs
triggers gag reflex so sedation and anaesthesia is needed
what is the effect of beta blockers on the heart rate?
decrease in rate
what is the affect of chronotropes on the heart rate?
increases the rate
what do inotropes drive?
contractility
what do vasopressors drive?
afterload
define chronic pain
pain lasting more than 3 months
lasting beyond normal healing
no identifiable cause
describe cancer pain
progressive and a mixture of acute and chronic
what is nociceptive pain?
> obvious tissue pain or illness
physiological/inflammatory pain
protective pain
well localised
describe neuropathic pain
> nervous system damage/abnormality
tissue injury may not be obvious
serves no protective function
not well localised
describe the physiology of pain in the periphery
there is tissue injury leading to a release of chemicals (prostaglandins) which stimulate the nociceptors.
the signal travels up the a-omega and c fibres.
what analgesia can be given for peripheral pain?
> RICE
> NSAIDS
describe the pathway of a pain signal when it reaches the spinal cord
the first relay station is the dorsal horn where a omega and c fibres synapse with a second nerve and travel up the contralateral side of the spinal cord
what analgesics can intervene at the spinal cord?
> TENS
opioids
ketamine
where is the second pain relay station?
the thalamus
what analgesics work on the modulation pathways?
> psychological > paracetamol > opioids > amitriptyline > clonidine
what pathological mechanisms are there in neuropathic pain?
> increased receptor number
chemical changes in the dorsal horn
abnormal sensitisation of the nerves
loss of normal inhibitory modulation
what is a disadvantage of paracetamol?
liver damage in overdose
what are the advantages of paracetamol?
> cheap
many routes
safe
what are the advantages of NSAIDS?
> cheap
> good for nociceptive pain with paracetamol
what are the disadvantages of NSAIDS?
> GI side effects
renal
sensitive asthmatics
what are the advantages of codeine?
> cheap
> good for mild/moderate acute nociceptive pain with paracetamol
what are the disadvantages of codeine?
> constipation
> not good for chronic pain
name some anticonvulsants
> gabapentin
sodium valproate
carmabezopeine
what are anticonvulsants good for?
neuropathic pain
what is the action of anticonvulsants?
reduce abnormal firing of nerves
what is the action of amitriptyline?
decrease in inhibitory signals
what are the advantages of amitriptyline?
> cheap
treats depression
neuropathic pain
what are the disadvantages of amitriptyline?
anticholinergic side effects
what are the advantages of morphine?
> cheap
effective if given regularly
good for chronic cancer pain or moderately severe nociceptive pain
what are the disadvantages of morphine?
> controlled drug
> resp. depression at high doses
what is the action tramadol?
it has a weak opioid effect plus inhibitor of serotonin and noradrenaline reuptake
what are the advantages of tramadol?
> less respiratory depression
not a controlled drug
can be used with opioids and simple analgesics
what are the disadvantages?
> nausea
> vomiting
how would you assess pain?
> verbal rating score > numerical rating score > visual analogue scale > smiley faces > abbey pain score
what non-pharmacological treatment is there for pain?
Physical > RICE > surgery > acupuncture > massage
Psychological
> explanation
> reassurance
> counselling
describe the WHO analgesic ladder
> mild/moderate pain: non-opioids
moderate/severe pain: mild opioids +/- non-opioids
severe pain: strong opioids +/- non-opioids
