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
what effect do benzodiazepines have on anxiety in neurological cases?
can reduce anxiety (but somewhat unpredictable)
is ACP a good drug of choice in neurological cases?
no
why isn’t ACP an appropriate choice for neurological cases?
may seizure trigger activity
causes systemic vasodilation –> hypotension and cerebral vasodilation
vasodilation will increase ICP
what effect does vasodilation have on ICP?
increases
can a2 agonists be used in neurological cases?
don’t appear to affect ICP but can cause significant cardiopulmonary dysfunction - use with caution
can cause vomiting in cats
why is it difficult to observe the cushings reflex when an a2 agonists has been given?
alpha 2s also cause an increase in MAP and bradycardia
which drugs make it difficult to observe the cushings reflex?
a2 agonists
can ketamine be used in neurological cases?
it is historically reported to increase ICP and so avoided for these purposes
what are the possible advantages of using ketamine in neurological cases?
may have neuroprotective properties and have fewer CVS and respiratory depressive effects than some other drugs
what has ketamine been reported to do when given with propofol?
reduce ICP
what considerations should be made for neurological cases on induction of anaesthesia
pre-oxygenation likely beneficial if doesn’t cause extra stress
ensure adequate depth prior to intubation to reduce risk of coughing
mild head elevation to assist with venous drainage may be helpful
which inhalational anaesthetic is better for neurological cases?
sevoflurane - iso may slightly increase ICP
what is the highest acceptable ETCO2 in neurological cases?
45mmHg
what are the main issues involved in monitoring MRI cases?
careful positioning
no metal (patient/staff/equipment)
difficult to maintain temperature
remote monitoring can be less detailed
often separate from main building - less staff if something goes wrong
what are the common CSF tap sites?
cisterna magna
lumbar
why is it important to monitor the patient closely during a cisterna magna CSF tap
head must be bent towards chest and ET tube can become kinked
what are the airway considerations for neurological cases?
lateral intubation may be needed if neck instabilities
avoid coughing - ensure deep plane of anaesthesia before attempt intubation
consider ET tube positioning when performing CSF tap
what specific considerations are there for patients who have a history of seizures?
often unknown cause - treat as if potential for raised ICP
establish any current medications/anticonvulsants
IV catheter essential
close monitoring before and after GA - post-op period most risky
what considerations are there for cases with neuromuscular disorders?
may be pre-disposed to regurgitation/aspiration
weakness may affect respiratory muscles
aim for rapid induction and recovery
careful drug choices with myasthenia gravis
IPPV likely required - ensure capnography available
what risks should be considered when anaesthetising a patient for planned GI surgery?
stabilise patient beforehand
may be dehydrated/anorexic
may have acid/base disturbances
potential for GOR/AP
likely painful
what drugs should be avoided in GI cases?
drugs that may induce vomiting e.g. morphine
how can we reduce risk of GOR/AP in GI patients?
always have suction available
head elevated until ET tube inserted and cuff inflated
why should nitrous be avoided in GI cases?
will find its way into gas-filled spaces
why is blood pressure not a good indicator of perfusion in GDV cases?
BP = CO x SVR
cardiac output reduced by dehydration and hypovolaemia
SVR increased due to compression of CVC, restricting blood flow to heart
combined these make BP appear ‘normal’
why is close post-op monitoring required in GDV cases?
arrythmias common (40%) - may last 24hrs into post-op period
will likely be very painful - good analgesia required
what is important to consider when anaesthetising patients with a pre-existing GI condition?
risk of GOR - shorter starvation times
if chronic disease, important to research and understand it well
consider medications and diet
may have electrolyte/acid base disturbances - pre-op bloods sensible
name some things which can be associated with hepatic dysfunction which may affect anaesthesia
ascites/oedema/pulmonary oedema (hypoproteinaemia/hypoalbuminaemia)
pu/pd
anaemia
hypocalcaemia
hypoglycaemia
reduced clotting times
hypothermia risk
acid base disturbances
jaundice
encephalopathy
what is hepatic encephalopathy?
a collection of neurological abnormalities which can occur due to hepatic disease
what are the signs of hepatic encephalopathy?
signs associated with increased levels of toxins (inc ammonia) in the blood - the liver cannot process it properly and they build up in the bloodstream, access the CNS and result in encephalopathic signs
what is the aim of medical management of hepatic encephalopathy?
reduce ammonia levels in the blood (via absorption or reduction)
what can be used for treatment/stabilisation of hepatic encephalopathy?
lactulose
how does lactulose help treat hepatic encephalopathy?
it is transformed by colonic bacteria into organic acids - this results in trapping of the ammonia ions and a decrease in the absorption of ammonia
what are the main effects of liver dysfunction on anaesthesia?
prone to hypothermia and hypoglycaemia
low albumin - reduced protein binding of drugs means may have more of an effect
potentially slower biotransformation of drugs
risk of surgical haemorrhage due to coagulopathies
electrolyte imbalances - sodium retention and lower K+
what are the pre-anaesthetic considerations for hepatic cases?
stabilise patient i.e. treat encephalopathy/seizures
what should be considered when choosing a premedicant for hepatic cases?
minimal premedication - cautious with dosing
consider short-acting drugs
consider drugs which can be antagonised
how should induction of anaesthesia be performed in hepatic cases?
slow and titrate - use lowest possible dose
what class of drugs should be avoided in management of hepatic cases under anaesthesia?
avoid NSAIDs - coagulation issues, hepatic/renal effects
what parameters are important to monitor under anaesthesia for hepatic cases?
body temperature
blood glucose
what special considerations are there for nursing patients with coagulopathies?
care with venepuncture - use peripheral veins
ample pressure after samples/IV catheters
avoid rough handling/pulling on leads
avoid trauma - consider in excitable/dysphoric recoveries
what pre-anaesthetic lab tests should ideally be done in patients with hepatic disease?
liver enzymes
bile acids
clotting factors
urea
plasma proteins
glucose
what is an insulinoma?
pancreatic islet cell tumour
what are the considerations for anaesthesia for insulinoma?
painful during and after surgery - adequate analgesia
monitor blood glucose closely post-operatively
possibility for pancreatitis post-op
consider using NMBA
what should occur before anaesthesia for elective procedures surrounding diabetes mellitus?
stabilisation
which aspects of diabetes mellitus which may affect anaesthesia?
hyperglycaemia
dehydration
weight loss
fatty liver
ketosis
what are the nursing considerations for anaesthesia for diabetes mellitus?
find out routine from owner inc favourite foods
1st patient of day so they can get back to normal routine ASAP
monitor glucose throughout entire stay
consider half-dose insulin at start of day, feed as soon as possible after anaesthesia with remaining insulin dose
what specific anaesthesia considerations are there for patients with diabetes mellitus?
use short-acting drugs
avoid medetomidine (can cause hyperglycaemia)
monitor blood glucose - consider second IV catheter for blood glucose sampling
fluids inc glucose
what factors are there to consider when anaesthetising patients with hyperthyroidism?
multi-organ dysfunction
consider temperament - usually highly strung, try to avoid stress
thin, low BCS
PU/PD
muscle weakness
hypertrophic cardiomyopathy
what are good drugs of choice for premed for patients with hyperthyroidism?
opioid +/- ACP
which drugs should be avoided in patients with hyperthyroidism and why?
ketamine - increases myocardial workload and increases HR
medetomidine - drops cardiac output
how should patients with hyperthyroidism ideally be induced?
IV if possible - avoids stress of IM and patient being left unwatched after IM drugs (risky)
what are the specific considerations for thyroidectomy?
monitor blood pressure closely
location of surgery - lose access to head end of patient, limited depth checking
potential for laryngeal paralysis post-op
monitor for hypocalcaemia post-op
keep IV catheter in and patent
what factors are there to consider when anaesthetising a canine patient with hypothyroidism?
often geriatric patients - consider additional risks
may have megaoesophagus - care with induction and intubation
decreased GI motility
lethargy and obesity common
bradycardia and hypotension
likely slow biotransformation of drugs
what is hyperadrenocorticism usually caused by?
pituitary or adrenal tumour - leads to glucocorticoid excess
patients with cushings disease often have poor muscle tone - why is this a problem?
respiratory muscle weakness can affect ventilation
what considerations are there for patients with cushings disease?
poor muscle tone (ventilation)
may be overweight + lethargic
poor thermoregulation - monitor temp
risk of pukmonary thromboembolism - hypercoagulability
PUPD (Na+ retention, K+ excretion)
risk of wound infection, bruising
what factors are important to consider when anaesthetising a patient with hypoadrenocorticism (addisons)?
unable to mount normal stress response - avoid stress!
hyperkalaemia
bradycardia
dehydration
weight loss, weakness/lethargy
important to stabilise before anaesthesia
what factors need to be considered when anaesthetising patients with kidney disease?
effects of hypoproteinaemia, uraemia, metabolic acidosis, hyperkalaemia, anaemia
what is the effect of hypoproteinaemia on anaesthesia?
increased free fraction of drug and decreased oncotic pressure means accidental overdose is possible
what is the effect of uraemia on anaesthesia?
causes CNS depression
what is the relevance of metabolic acidosis on anaesthesia of patients with kidney disease?
decreased renal excretion of drug
myocardial dysfunction
what is the relevance of hyperkalaemia on anaesthesia of patients with kidney disease?
potentially life-threatnening - measure potassium throughout
what is the relevance of anaemia on anaesthesia of patients with kidney disease?
oxygen-carrying capacity may be compromised
what are the anaesthetic considerations for renal patients?
pre-op bloods important to ascertain current function of kidneys, full clinical exam
pre-op planning - fluids to maintain circlating volume and hydration
avoid stress
select drug which have minimal effect of CVS and renal function/BP
careful patient monitoring throughout
