Anaesthesia for Pre-existing Conditions Flashcards

1
Q

what is contained in the intracranial cavity?

A

brain (80%)
CSF (10%)
blood (10%)

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2
Q

what might disrupt the blood-brain barrier?

A

trauma
inflammation
hypertension

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3
Q

how much of the total cardiac output does the brain receive?

A

15%

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4
Q

why do increases in CSF or intracranial blood volume have such an effect on ICP?

A

the skull is a fixed space and unable to expand

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5
Q

what can an increase in CSF or intracranial blood pressure result in?

A

increase in ICP

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6
Q

why is the brain reliant on maintenance of intracranial blood volume?

A

to support the brains high metabolic rate

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7
Q

what supports the brains high metabolic rate?

A

the maintenance of intracranial blood volume

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8
Q

what are the main aims when anaesthetising animals with neurological/brain trauma?

A

maintenance of cerebral blood flow

reduce increases in ICP

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9
Q

what is the normal ICP?

A

5-12 mmHg

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10
Q

what are the signs of high ICP?

A

papilledema, abnormal pulsing of retinal vessels, depression, stupor, coma

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11
Q

can compensatory mechanisms for ICP continue indefinitely?

A

they can become exhausted if ICP continues to build (e.g. haemorrhage)

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12
Q

what is the cushings reflex?

A

a response to raised ICP

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13
Q

what is involved in the cushings reflex?

A

reflex bradycardia and hypertension

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14
Q

what can also be seen in addition to bradycardia and hypertension in the cushings reflex?

A

irregular breathing/apnoea

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15
Q

why does the cushings reflex occur?

A

because of the reduction in cerebral blood flow

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16
Q

what is the aim of the cushings reflex?

A

decrease intracranial volume/pressure

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17
Q

what physiological marker triggers the cushings reflex?

A

a reduction in blood flow causes an accumulation of CO2 as a result of poor perfusion - increased in CO2 is detected by the brainstem

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18
Q

which branch of the nervous system involves the cushings reflex?

A

sympathetic

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19
Q

how does the sympathetic nervous system respond in the cushings reflex?

A

increases MAP, which in turn alerts baroreceptors and causes a reflex bradycardia

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20
Q

how can we avoid/control ICP?

A

avoid coughing (consider antitussives)
avoid neck leads
careful intubation
avoid pressure on neck during restraint
avoid jugular sampling
avoid straining to pass faeces/urine

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21
Q

what are the broad considerations for anaesthetising a neurological case?

A

thorough pre-operative assessment

use of mGCS

stabilisation pre-anaesthetic

consider drug choices carefully - should not increase ICP or cause dramatic change to MAP

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22
Q

what are the advantages of using opioids for neurological cases?

A

don’t tend to alter cerebral blood flow or increase ICP much
have minimal CVS and respiratory effects

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23
Q

which opioid should be avoided in neurological cases and why?

A

morphine/hydropmorphone - may increase incidence of vomiting

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24
Q

what are the advantages of using benzodiazepines in neurological cases?

A

no adverse effects on ICP, respiratory or CVS system

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25
what effect do benzodiazepines have on anxiety in neurological cases?
can reduce anxiety (but somewhat unpredictable)
26
is ACP a good drug of choice in neurological cases?
no
27
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
28
what effect does vasodilation have on ICP?
increases
29
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
30
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
31
which drugs make it difficult to observe the cushings reflex?
a2 agonists
32
can ketamine be used in neurological cases?
it is historically reported to increase ICP and so avoided for these purposes
33
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
34
what has ketamine been reported to do when given with propofol?
reduce ICP
35
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
36
which inhalational anaesthetic is better for neurological cases?
sevoflurane - iso may slightly increase ICP
37
what is the highest acceptable ETCO2 in neurological cases?
45mmHg
38
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
39
what are the common CSF tap sites?
cisterna magna lumbar
40
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
41
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
42
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
43
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
44
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
45
what drugs should be avoided in GI cases?
drugs that may induce vomiting e.g. morphine
46
how can we reduce risk of GOR/AP in GI patients?
always have suction available head elevated until ET tube inserted and cuff inflated
47
why should nitrous be avoided in GI cases?
will find its way into gas-filled spaces
48
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'
49
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
50
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
51
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
52
what is hepatic encephalopathy?
a collection of neurological abnormalities which can occur due to hepatic disease
53
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
54
what is the aim of medical management of hepatic encephalopathy?
reduce ammonia levels in the blood (via absorption or reduction)
55
what can be used for treatment/stabilisation of hepatic encephalopathy?
lactulose
56
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
57
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+
58
what are the pre-anaesthetic considerations for hepatic cases?
stabilise patient i.e. treat encephalopathy/seizures
59
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
60
how should induction of anaesthesia be performed in hepatic cases?
slow and titrate - use lowest possible dose
61
what class of drugs should be avoided in management of hepatic cases under anaesthesia?
avoid NSAIDs - coagulation issues, hepatic/renal effects
62
what parameters are important to monitor under anaesthesia for hepatic cases?
body temperature blood glucose
63
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
64
what pre-anaesthetic lab tests should ideally be done in patients with hepatic disease?
liver enzymes bile acids clotting factors urea plasma proteins glucose
65
what is an insulinoma?
pancreatic islet cell tumour
66
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
67
what should occur before anaesthesia for elective procedures surrounding diabetes mellitus?
stabilisation
68
which aspects of diabetes mellitus which may affect anaesthesia?
hyperglycaemia dehydration weight loss fatty liver ketosis
69
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
70
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
71
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
72
what are good drugs of choice for premed for patients with hyperthyroidism?
opioid +/- ACP
73
which drugs should be avoided in patients with hyperthyroidism and why?
ketamine - increases myocardial workload and increases HR medetomidine - drops cardiac output
74
how should patients with hyperthyroidism ideally be induced?
IV if possible - avoids stress of IM and patient being left unwatched after IM drugs (risky)
75
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
76
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
77
what is hyperadrenocorticism usually caused by?
pituitary or adrenal tumour - leads to glucocorticoid excess
78
patients with cushings disease often have poor muscle tone - why is this a problem?
respiratory muscle weakness can affect ventilation
79
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
80
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
81
what factors need to be considered when anaesthetising patients with kidney disease?
effects of hypoproteinaemia, uraemia, metabolic acidosis, hyperkalaemia, anaemia
82
what is the effect of hypoproteinaemia on anaesthesia?
increased free fraction of drug and decreased oncotic pressure means accidental overdose is possible
83
what is the effect of uraemia on anaesthesia?
causes CNS depression
84
what is the relevance of metabolic acidosis on anaesthesia of patients with kidney disease?
decreased renal excretion of drug myocardial dysfunction
85
what is the relevance of hyperkalaemia on anaesthesia of patients with kidney disease?
potentially life-threatnening - measure potassium throughout
86
what is the relevance of anaemia on anaesthesia of patients with kidney disease?
oxygen-carrying capacity may be compromised
87
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
88