Anaesthesia For Pre-exisiting Conditions Flashcards
what is stated by the Monroe Kellie hypothesis?
intracranial cavity is filled with brain, CSF and blood
in what ratios is the intracranial cavity filled?
brain - 80%
CSF - 10%
blood - 10%
what can disrupt the blood brain barrier?
trauma
inflammation
hypertension
what percentage of cardiac output does the brain receive?
~15%
why does the brain receive such a large percentage of cardiac output?
has high metabolic rate
what is the consequence of increases in CSF and intracranial blood volume?
raised / altered ICP
what is the brain reliant on to support metabolic rate?
maintenance of intracranial blood volume
what are the main aims when anaesthetising animals with neurological/brain trauma?
maintain cerebral blood flow
reduce or limit increases in ICPh
at is normal ICP?
5-12 mmHg
what are the clinical symptoms of riased ICP
papilledema
abnormal pulsing of retinal vessels
depression
stupor
coma
what is papilledema?
optic disc swelling
what happens if ICP increases?
compensatory mechanisms are initiated (e.g. cushings reflex)
what may happen if ICP continues to rise following initiation of compensatory mechanisms?
mechanisms may become exhausted
why does the cushings reflex occur?
because of the reduction in cerebral blood flow
what is the aim of of the cushings reflex?
decrease intracranial volume / pressure
how is the cushings reflex initiated?
reduction in blood flow causes an accumulation of CO2 as a result of poor perfusion
CO2 is detected by the brain stem and the sympathetic nervous system responds by increasing MAP to improve perfusion to the brain
what are the signs of the cushings reflex?
hypertension
reflex bradycardia
irregular breathing apnoea
what causes the signs of the cushings triad?
accumulation of CO2 as a result of poor perfusion
CO2 is detected by the brain stem and the sympathetic nervous system responds by increasing MAP to improve perfusion to the brain
how can an increase in ICP be prevented during patient care?
avoid coughing
avoid neck leads
adequate depth prior to intubation
avoid pressure on the neck during restraint
avoid jugular samples
avoid straining to urinate / defecate
avoid vomiting / gagging
how can coughing be avoided in patients at risk of raised ICP?
give anti-tussive
what may be involved in the pre-operative assessment of neurological patients?
haem and biochem
electrolytes
glucose
PCV
glasgow coma scale (MGCS)
what must be considered around drug choices when anaesthetising neurological patients?
should not increase ICP or cause dramatic change to MAP
are opioids indicated for use with neurological patients?
yes
what is the effect of opioids on ICP?
do not tend to alter cerebral blood flow or increase ICP too much
what are the effects of opioids on the cardiovascular and respiratory systems?
minimal, dose dependent, CV and respiratory depression
what opioid should be avoided in patients at risk of raised ICP and why?
morphine due to increased incidence of vomiting
are benzodiazepines indicated for use in patients at risk of raised ICP?
yes - no effect on ICP
what are the effects of benzodiazepines on the cardiovascular and respiratory systems?
no adverse effects
what are the effects of benzodiazepines?
reduction in anxiety but can be unreliable
is ACP contraindicated in patients at risk of raised ICP?
yes
why is ACP contraindicated in patients at risk of raised ICP?
may trigger seizures in patients with intracranial pathology
causes systemic vasodilation which causes hypotension and cerebral vasodilation
what effect does cerebral vasodilation have on ICP?
raises ICP as vessels take up more space
are alpha 2 agonists indicated for use in patients with a risk of raised ICP?
do not affect ICP but should be used very cautiously
why are alpha 2 agonists not indicated for use in patients with a risk of raised ICP?
can cause significant cardiopulmonary dysfunction
will cause an increase in MAP nd bradycardia so masking the cushings effect
can cause vomiting in cats
is ketamine indicated for use in patients at risk of raised ICP?
historically not as reported to increase ICP
now found to have neuroprotective properties and when used with other agents no increase in ICP seen
what can happen if ketamine is given alongside propofol?
reduction in ICP
what is the benefit of using ketamine in patients at risk of raised ICP?
thought to have neuroprotective properties
fewer CV and respiratory depressive effects
what are the main anaesthetic considerations for neuro patients?
preoygenate
ensure adequate depth before intubation
use sevolurane
monitor closely
maintain normocapnia
IVFT
mild head elevation
monitor for seizure activity
careful handling and restraint to avoid compression of jugular vein
avoid straining
why is sevoflurane better for patients at risk of raised ICP?
maintains cerebral perfusion pressure at higher MAC multiples
iso may slightly raise ICP
why is it important that normocapnia is maintained in neurological cases?
increased EtCO2 can lead to vasodilation
what is the purpose of elevation of the patient’s head if they are at risk of raised ICP?
aids venous drainage
why may patients with neurological issues need GA?
imaging
CSF tap
spinal surgery
treatment of non neuro issues
pre existing disease (epilepsy) but requires surgery
what are the main considerations for a patient undergoing MRI?
careful positioning (straightness)
no metal on patient/staff/equipment
safety
access for staff (remote, often outside hospital)
remote monitoring
temperature levels can be difficult to maintain as cold
what type of equipment is used for monitoring in MRI?
often specialised
fibreoptic
expensive!
long leads to reach outside unit and avoid metal in the room
what are the common CSF tap locations?
cisterna magna
lumbar
what is the anaesthetic consideration when a cisternal CSF sample is being taken?
need to bend the neck (nose on chest) to open up the vertebral space - monitor for signs of ET tube kinking
what equipment can be used to maintain patient safety during a cisternal CSF tap?
armored ET tube
what is the main consideration with using armored ET tubes?
not in MRI as contain metal!
what are the main airway considerations for a neurological patient?
lateral intubation may be necessary for neck or spine instability
avoid coughing - ensure anaesthetic plane is deep enough prior to intubation
positioning for cisternal CSF tap
what are the main anaesthetic considerations for a seizure patient?
often unknown cause
look at current medication and any interactions
treat as raised ICP
IV access essential
close monitoring pre and post anaesthesia
when is an especially risky phase of anaesthesia for seizure patients?
recovery as drugs wear off
what are the main anaesthetic considerations for a neuromuscular patient?
may be predisposed to regurgitation and aspiration - check gag reflex, suction ready
weakness of respiratory muscles possible so may need IPPV (check capnography)
rapid induction and recovery
exaggerated response to NMBA in myaesthenia gravis
consider local anaesthesia
what are the main areas to consider when planning for an anesthetic?
signalment
history and CE
presenting procedure
considerations
plan
what are the main brachycephalic considerations and how can they be mitigated?
airway - ETT selection, head up induction, cuff tube, on wedge, pre oxygenate
eyes - eye lube
skin - care with IV and CSF sampling if skin inflamed
joints - padding and support
GOR - fasting times, GOR, pre-op GI meds
what is the benefit of using butorphanol for a raised ICP patient?
anti-tussive
what is the benefit of using dexmedetomidine in a raised ICP patient?
vasoconstriction
antagonism possible
short acting
how can vasodilation be avoided in ICP patients?
VA low
good premed
consider drugs used
what must be considered about the breathing system used for ICP patients?
suitable for IPPV if become hypercapnic
what are some of the reasons that GI patients may present for anaesthesia?
planned abdominal surgery
acute abdomen surgery (e.g. GDV)
pre-existing GI condition
diagnostic procedures (e.g. endoscopy)
when may management of GI cases differ?
whether they are planned or emergencies
what are the main considerations for planned GI surgery?
stabilise patient (there is usually time)
pain management
reflux risk and so aspiration risk - suction and elevation of head until cuff inflated
may be limited access to head if oesophageal surgery
consider dehydration and anorexia
avoid drugs which induce vomiting
pre-oxygenate
may need access through the thorax - ventilation
heat preservation is key