Anaesthesia for Pre-existing Conditions Flashcards
what is contained in the intracranial cavity?
brain (80%)
CSF (10%)
blood (10%)
what might disrupt the blood-brain barrier?
trauma
inflammation
hypertension
how much of the total cardiac output does the brain receive?
15%
why do increases in CSF or intracranial blood volume have such an effect on ICP?
the skull is a fixed space and unable to expand
what can an increase in CSF or intracranial blood pressure result in?
increase in ICP
why is the brain reliant on maintenance of intracranial blood volume?
to support the brains high metabolic rate
what supports the brains high metabolic rate?
the maintenance of intracranial blood volume
what are the main aims when anaesthetising animals with neurological/brain trauma?
maintenance of cerebral blood flow
reduce increases in ICP
what is the normal ICP?
5-12 mmHg
what are the signs of high ICP?
papilledema, abnormal pulsing of retinal vessels, depression, stupor, coma
can compensatory mechanisms for ICP continue indefinitely?
they can become exhausted if ICP continues to build (e.g. haemorrhage)
what is the cushings reflex?
a response to raised ICP
what is involved in the cushings reflex?
reflex bradycardia and hypertension
what can also be seen in addition to bradycardia and hypertension in the cushings reflex?
irregular breathing/apnoea
why does the cushings reflex occur?
because of the reduction in cerebral blood flow
what is the aim of the cushings reflex?
decrease intracranial volume/pressure
what physiological marker triggers the cushings reflex?
a reduction in blood flow causes an accumulation of CO2 as a result of poor perfusion - increased in CO2 is detected by the brainstem
which branch of the nervous system involves the cushings reflex?
sympathetic
how does the sympathetic nervous system respond in the cushings reflex?
increases MAP, which in turn alerts baroreceptors and causes a reflex bradycardia
how can we avoid/control ICP?
avoid coughing (consider antitussives)
avoid neck leads
careful intubation
avoid pressure on neck during restraint
avoid jugular sampling
avoid straining to pass faeces/urine
what are the broad considerations for anaesthetising a neurological case?
thorough pre-operative assessment
use of mGCS
stabilisation pre-anaesthetic
consider drug choices carefully - should not increase ICP or cause dramatic change to MAP
what are the advantages of using opioids for neurological cases?
don’t tend to alter cerebral blood flow or increase ICP much
have minimal CVS and respiratory effects
which opioid should be avoided in neurological cases and why?
morphine/hydropmorphone - may increase incidence of vomiting
what are the advantages of using benzodiazepines in neurological cases?
no adverse effects on ICP, respiratory or CVS system