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
what type of GI surgery may be planned?
oesophageal or GI foreign body
what is an example of an emergency GI surgery?
GDV
what is needed on GDV arrival?
IV access
IVFT - large volume, fast
what is the aim of GDV stabilisation prior to GA?
improved CV and respiratory function prior to GA
how may a GDV patient be stabilised prior to GA?
decompress stomach if able (percutaneous or stomach tube)
IVFT
CVS monitoring
how is GDV treated?
decompression surgery and gastropexy
what altered parameter is often seen in GDV patients?
ventricular arrhythmias
where do arrhythmias seen in GDV patients originate from?
ventricles
what are the common intraoperative considerations / risks with GDV surgery?
pressure on diaphragm from distended viscera can alter respiration
electrolyte and acid base abnormalities
clotting abnormalities
possible pneumothorax due to stomach position in cranial abdomen
what is the issue with blood pressure monitoring during GDV surgery?
BP reads ok but perfusion is poor
why may BP read as normal in GDV patients when perfusion is poor?R
cardiac output reduced due to hypovolaemia and dehydration
SVR increased due to pressure on great vessels by stomach reducing blood flow return to the heart
how is BP calculated?
BP= SVR x CO
what must be monitored in GDV patients in the post op period?
ECG to check for ventricular arrhythmia
pain - adequate analgesia
what percentage of dogs with GDV may have arrhythmias pre, peri or post op?
up to 40%
where should GDV patients recover?
ICU / intensive monitoring
what drugs should be avoided in GDV patients?
any that suppress the CVS
what is a significant risk in patients with pre-exisiting GI disease?
GOR
what is crucial when managing patients at risk of GOR?
starvation times
what are the main considerations for patients with pre-existing GI disease?
starvation times due to GOR risk
may be chronic disease - research
current medication
may be on a special diet
may have electrolyte or acid base disturbance so pre-op blood sensible
what are some of the considerations for lower GI scope?
long starvation time
Kleanprep and enema
bloods and electrolytes checked
place cephalic IVC NOT saphenous for IVFT
keep warm
tail wrapped and area clipped for cleanliness
loss of access for rectal temperatures
what is the function of the liver?
production of substances
bilirubin excretion
biotransformation of drugs or toxins
metabolism of carbs, proteins and fats
glucose homeostasis
metabolism and so heat production
what substances are produced by the liver?
urea
clotting factors
albumin
how is the liver involved with glucose homeostasis?
glycogen storage
gluconeogenesis
what can cause hepatic dysfunction?
porto-systemic shunt
biliary obstruction or trauma
chronic disease
acute failure
neoplasia
what symptoms may be seen with hepatic dysfunction?
ascites / oedema
PUPD
anaemia
hypocalcaemia
hypoglycaemia
hypothermia
reduced clotting times
acid base disturbences
jaundice
encephalopathy
why is liver dysfunction associated with ascites and oedema?
due to hypoproteineamia and hypoalbuminaemia
what is hepatic encephalopathy?
a collection of neurological abnormalities which can occur due to hepatic disease
what causes the signs of hepatic encephalopathy?
increased toxins (ammonia) in the blood as the liver is unable to process them properly so they build up.
these toxins then access the CNS and result in encephalopathic signs
what are the signs of hepatic encephalopathy?
altered demenour
confusion (increasing in severity)
inappetance
disorientation
blindness
occassional aggressive, uncontrolled behaviour
seizures
unrousable
coma
death
what are the stages of hepatic encephalopathy?
stage 1-4
what is the aim of medical management of hepatic encephalopathy?
reduce ammonia levels in the blood through absorption or reduction
what drug is often used in hepatic encephalopathy patients?
lactulose
how does lactulose work?
transformed by colonic bacteria into organic acids
results in trapping of ammonia ions and so decrease in absorption of ammonia
what ion contributes to hepatic encephalopathy signs?
ammonia
what are liver dysfunction patients prone to under GA?
hypothermia
hypoglycaemia
why are liver dysfunction patients prone to hypothermia under GA?
liver is massive producer of heat due to metabolism
why are liver dysfunction patients prone to hypoglycaemia under GA?
liver involved in glucose homeostasis
what are the effects of low albumin on anaesthesia?
reduced protein binding of drugs
oncotic pressure of blood reduced so fluids will not remain in circulation (fluid rescuss more difficult)
what is the effect of reduced protein binding of drugs?
drug action longer lasting as larger free fraction
overdose effects exacerbated
what are the effects of liver dysfunction on anaesthesia?
slower biotransformation of drugs
increased risk of haemorrhage due to reduction in clotting factors
electrolyte imbalances
fluid rescussitation more challenging due to reduced oncotic pressure
how should hepatic patient’s be managed for GA?
stabilisation
cautious and minimal premedication
slow induction with lowest possible dose
analgesia
avoid NSAIDs
maintain temp
monitor glucose
be aware of coagulopathies
why should NSAIDs be avoided in hepatic patients?
coagulation issues
hepatic and renal excretion (extra work for kidneys)
what are the main nursing care points for patients with coagulopathies?
care with venepuncture (no jugular sticks)
pressure applied well after samples or IVC removal
avoid rough handling
avoid trauma (e.g. excitable recovery)
what pre-anaesthetic blood may be needed for hepatic patients?
liver enzymes
bile acids
clotting times
urea
plasma proteins
glucose
what is an insulinoma a tumour of?
pancreatic islet cells
what are the main indications for insulinoma?
hypoglycaemia
why do insulinomas make patients hypoglycaemic?
over production of insulin
how can insulinoma be treated?
medical - preds, glucose, diazoxide
surgery to remove - may include partial pancreatectomy
what should be monitored for following insulinoma removal?
pancreatitis
pain
hyperglycaemia or hypoglycaemia - regular BG
what additional technique may be used during insulinoma surgery to facilitate removal?
NMBA
how should diabetic patients be managed when having surgery?
stabilise for GA whenever possible
find out routine and try to stick to it
first patient of the day and then home ASAP
monitor glucose
feed as soon as possible in recovery and give insulin
what complications can be seen with diabetic patients?
hyperglycaemia
dehydration
weight loss
fatty liver
ketoacidosis
how may diabetics be managed in terms of starvation times?
half meal and half insulin in the moring if vet is happy
what drug considerations should be made for patients with diabetes?
short acting
good analgesia
IVFT
what drug should be avoided for diabetic patients?
medetomidine
why should medetomidine be avoided in diabetic patients?
hyperglycaemia is a risk
why may a second IVC be useful in diabetic patients?
glucose monitoring
in what cats is hyperthyroidism often seen?
elderly
what are the main presenting signs of hyperthyroidism?
highly strung
thin
PUPD
muscle weakness
why is muscle weakness of note when anaesthetising a patient?
may need ventilation if unable to breathe adequately themselves
what is often seen alongside hyperthyroidism?
hypertrophic cardiomyopathy
how should hyperthyroid cats be managed pre GA?
avoid stress
IV induction where possible
ECG
IVFT
what drugs should be avoided in hyperthyroid cats?
ketamine
medetomidine
why should ketamine be avoided in hyperthyroid cats?
increases myocardial workload and increases HR
why should medetomidine be avoided in hyperthyroid cats?
drops CO
what may create monitoring challenges in thyroidectomy surgery?
access to patient due to surgical site
what should patients be monitored for post thyroidectomy?
laryngeal paralysis
hypocalcaemia
BP changes
what must remain patent at all times in hyperthyroid cats?
IVC
in what patients is hypothyroidism often seen?
elderly dogs
what concurrent condition may be seen in many patients with hypothyroidism?
megaoesophagus
what are some of the anaesthetic considerations for hypothyroidism?
decreased GI motility
obesity may affect ventilation
lethargy
prone to bradycardia and hypotension
slow biotransformation of drugs common
what is hyperadrenocorticism caused by?
pituitary or adrenal tumour leading to glucocorticoid excess
can also be iatrogenic
what are the main anaesthetic considerations for hyperadrenocorticism patients?
poor muscle tone - may affect ventilation
may be overweight and lethargic
poor thermoregulation
high risk of bruising
risk of PE
PUPD
higher risk of wound infection
may be on medical management
why are hyperadrenocorticism patients at risk of PE?
hypercoagulability
why are hyperadrenocorticism patients at higher risk of wound infections?
due to increased glucocorticoids
what is the main consideration of patients with hypoadrenocorticism?
avoid stress
unable to mount normal stress response
need stabilisation pre GA
what electrolyte imbalances are commonly seen with hyperadrenocorticism patients?
Na retention
K excretion
what electrolyte imbalances are commonly seen with hypoadrenocorticism patients?
hyperkalaemia
what are the main signs of hypoadrenocorticism?
bradycardia
dehydration
weight loss
weakness
lethargy
non-specific
what are the main types of renal disease seen?
AKI
CKD
urinary tract obstruction or rupture (bladder, ureter or urethra)
what are the main effects of kidney disease which can affect anaesthesia?
hypoproteinaemia
uraemia
metabolic acidosis
hyperkalaemia
anaemia
how does hypoproteinaemia affect anaesthesia?
increased free fraction of drug so more to take effect
decreased oncotic pressure to hold fluids in intravascular space
how does uraemia affect anaesthesia?
CNS depression
how does metabolic acidosis affect anaesthesia?
decreased renal excretion of drugs
myocardial dysfunction
how does potassium disturbance affect anaesthesia?
potentially life threatening
may be high or low in kidney patients
what can happen to potassium levels in acute kidney injury?
increase rapidly as excretion stopped
what can happen to potassium levels in CKD?
low due to continual potassium leakage
how does anaemia affect anaesthesia?
potential for reduced O2 carrying capacity
what should be done before anesthesia of renal patients?
pre op bloods to check current function
IVFT pre op?
full clinical exam
why may pre op fluids be helpful for renal patients?
maintain circulating volume and hydration to support kidneys
what drugs should be used for renal patients?
minimal CV, BP and renal effects
what are the main effects on GA of renal disease?
decreased GFR
ADH release
aldosterone activation
effect on prostaglandins
