Anaesthesia for Pre-existing Conditions Flashcards
How is ICP increased in patients?
Increases in CSF or intracranial blood volume
What are our 2 main aims when anaesthetising animals with neurological/brain trauma?
Maintain cerebral blood flow
Reduce increases in ICP
What is normal ICP?
5-12mmHg
What clinical signs indicate increased ICP?
Papilledema
Abnormal pulsing of retinal vessels
Depression
Stupor
Coma
Why does the Cushings reflex occur?
Due to reduction in cerebral blood flow
To decrease intracranial volume/pressure
Describe the Cushings reflex.
Reduction in cerebral blood flow causes accumulation of CO2 as a result of poor perfusion
Detected by brainstem and sympathetic NS responds by increasing MAP (HYPERTENSION), which alerts baroreceptors and causes reflex BRADYCARDIA
How can we avoid increasing ICP?
Avoid coughing (anti-tussive?)
Harnesses to avoid pulling on leads
Careful intubation (adequate depth prior to attempt)
Avoid pressure on neck during restraint
Avoid jugular sampling
Avoid straining to defecate/urinate
What pre-op considerations should we have for neurological cases?
Pre-op assessment (may include bloods, electrolytes, glucose, PCV)
Modified Glasgow Coma Scale
Stabilisation if possible
Drug choice - not increase ICP or cause dramatic changes to MAP
What intra-op considerations should we have for anaesthetised neurological cases?
Pre-oxygenation
Adequate depth for intubation
Lateral intubation if neck instabilities
Isoflurane may slightly increase ICP - Sevo will not!
Maintain normocapnia
Fluid therapy
Mild head elevation to assist venous drainage
Monitor for seizure activity
Why might neurological cases be anaesthetised?
Imaging (MRI/myelography)
CSF tap
Spinal surgery (hemilaminectomy/ventral slot etc.)
Treatment of concurrent disease
Pre-existing neurological disease (e.g. epilepsy)
What considerations should we have for carrying out MRIs?
Careful positioning - lots of padding, patient must be straight
NO METAL - patient/staff/equipment
Temperature - can be cold, difficult to maintain
Remote monitoring
Describe CSF taps.
Common sites = cisterna magna or lumbar
Positioning - may need neck bent to chest (consider armoured ET tube)
How can we care for possible seizure patients?
Often unknown cause
IV catheter essential
Treat as if potential for increased ICP
On any current medication/anti-convulsant?
Close monitoring before/after anaesthesia
Capnography, BP
Risky post-op phase
What complications might we see in patients with neuromuscular disorders?
May be predisposed to regurgitation/aspiration - check gag reflex
Weakness may affect respiratory muscles
May require IPPV - capnography essential
Myasthenia gravis - exaggerated response to NMBs
What pre-op considerations should we have for a planned GI surgery e.g. oesophageal/GI FB?
Stabilise patient
May be dehydrated/anorexic
Acid-base disturbances
Potential for gastro-oesophageal reflux/aspiration pneumonia
Pain!
Limited access to head?
What intra-op considerations should we have for planned GI surgery patients?
Avoid drugs that may induce vomiting e.g. morphine
Pre-oxygenate
Suction available
Head elevated until ET tube inserted and cuff inflated
Removal per os or via thoracotomy
Rupture of oesophagus possible
Analgesia!
Care with heat preservation
What pre-op considerations should we have for emergency GI patients e.g. GDV?
IV access vital
Large volume fluid therapy
Stabilise but not much time!
Decompress stomach if possible
Arrhythmias common - monitor CVS
AIM - improved cardiovascular and pulmonary function prior to GA
What complications can we see with GDV patients?
Electrolyte and acid-base abnormalities
Clotting abnormalities
Potential pneumothorax
Blood pressure often okay BUT perfusion poor (reduced CO and increased systemic vascular resistance)
What arrhythmias are commonly seen in GDV patients?
Up to 40% of dogs will have arrhythmia
Commonly ventricular in origin
May last into post-op period
What pre-op considerations should we have for patients with pre-existing GI disease?
May require sedation/GA for diagnostics/surgery
Gastro-oesophageal reflux risk - starvation times crucial
May be on medication already
May need special diet
May have electrolyte/acid-base disturbances
What are the functions of the liver?
Substance production - urea/clotting factors/albumin
Bilirubin excretion
Biotransformation of drugs/toxins
Metabolism of carbs/proteins/fats
Glucose homeostasis - glycogen storage/gluconeogenesis
Major metabolic organ (heat!)
What are the possible dysfunctions of the liver?
Porto-systemic shunt
Biliary obstruction/trauma
Chronic disease
Acute failure
Neoplasia
What clinical signs of hepatic dysfunction can we see?
Ascites/oedema/pulmonary oedema
PUPD
Anaemia
Hypocalcaemia/hypoglycaemia
Hypothermia
Reduced clotting times
Acid-base disturbances
Jaundice
Encephalopathy
Why does hepatic encephalopathy occur?
Increased levels of toxins (inc. ammonia) in blood as liver cannot process properly
Toxins enter the CNS and result in encephalopathic signs
How do we treat hepatic encephalopathy?
Aim to reduce ammonia levels in the blood (via absorption or reduction)
Lactulose - transformed by colonic bacteria to organic acids, which trap ammonia ions and decreases ammonia absorption
What affects of liver dysfunction can we see on anaesthesia?
Prone to hypothermia/hypoglycaemia
Hypoalbuminaemia (reduced protein binding of drugs, harder to retain fluid in circulation)
Slower biotransformation of drugs?
Increased risk of surgical haemorrhage - coagulopathy risk
Electrolyte imbalances - sodium retention and decreased potassium
How can we manage hepatic patients before anaesthesia?
Stabilise (treat encephalopathy/seizures)
Minimal premed/cautious dosing/consider short-acting and antagonisable?
Induction - slow and use lowest possible dose
Analgesia
Avoid NSAIDs
Maintain body temp.
Monitor BG
Beware of coagulopathies!
How can we manage patients with coagulopathies?
Care with venepuncture - use peripheral veins!
Pressure after samples/IV catheters
Avoid rough handling/pulling leads
Avoid trauma e.g. excitable recoveries
What pre-anaesthetic lab tests can we do for hepatic patients?
Liver enzymes
Bile acids
Clotting function
Urea
Plasma proteins
Glucose
What is an insulinoma and what are the clinical signs?
Pancreatic islet cell tumour
Hypoglycaemia
What post-op complications may we see with insulinoma removal (laparotomy, partial pancreatectomy)?
Pancreatitis
Pain
Hyperglycaemia
What anaesthetic considerations should we have for patients having insulinoma surgery?
Monitor blood glucose
Avoid hyperglycaemia (stimulate insulin release) and hypoglycaemia
Consider neuromuscular blocking agents
What are the possible complications associated with diabetes mellitus patients?
Hyperglycaemia
Dehydration
Weight loss
Fatty liver
Ketosis
How can we manage diabetes mellitus patients prior to surgery?
Stabilise if elective
Find out routine from owner inc. favourite foods
First patient of the day
Monitor BG
Half dose insulin?
What anaesthetic considerations should we have for diabetes mellitus patients?
Short-acting drugs
Good analgesia
Avoid medetomidine (hyperglycaemia)
Fluids inc. glucose
Monitor BG!
Possibly second IV catheter?
Describe hyperthyroidism and its clinical signs.
Multi-organ dysfunction
Usually elderly cats
Thin
PUPD
Muscle weakness
Hypertrophic cardiomyopathy
What anaesthetic considerations should we have for hyperthyroid patients?
Avoid stress!
Consider sedating with opioid +/- ACP
?Avoid ketamine (increases myocardial workload and increases HR) and medetomidine (drops CO)
IV induction if possible
Monitor ECG
IV fluids
What considerations should we have for thyroidectomy surgery for hyperthyroid patients?
Monitor BP
Location of surgery!
Potential for laryngeal paralysis/hypocalcaemia post-op
Keep IV in and patent
What are the clinical signs of canine hypothyroidism?
May have megaoesophagus
Decreased GI motility
Obesity
Lethargy
Bradycardia and hypotension
Slow biotransformation of drugs
What causes hyperadrenocorticism (Cushing’s disease)?
Pituitary / adrenal tumour - glucocorticoid excess
May be iatrogenic
What are the clinical signs of hyperadrenocorticism (Cushing’s)?
Poor muscle tone
May be overweight and lethargic
Poor thermoregulation
Bruising
Risk of pulmonary thromboembolism - hypercoagulability
PUPD, Na retention/K excretion
Risk of wound infection
What are the clinical signs of hypoadrenocorticism (Addison’s disease)?
Unable to mount normal stress response - avoid stress!
Hyperkalaemia
Bradycardia
Dehydration
Weight loss
Weakness/lethargy
Non-specific clinical signs
What possible renal diseases can we see?
Acute kidney disease
Chronic kidney disease
Urinary tract obstruction/rupture - bladder/urethra/ureter
What complications can we see with renal disease?
Hypoproteinaemia
Uraemia
Metabolic acidosis
Hyperkalaemia
Anaemia
How can renal hypoproteinaemia affect anaesthesia?
Increased free fraction of drug
Decreased oncotic pressure
How can renal uraemia affect anaesthesia?
CNS depression
How can renal metabolic acidosis affect anaesthesia?
Decreased renal excretion of drugs
Myocardial dysfunction
How can renal hyperkalaemia affect anaesthesia?
Potentially life-threatening - acute vs chronic!
Measure potassium!
How can renal anaemia affect anaesthesia?
Oxygen-carrying capacity may be compromised
What considerations should we have for renal patients?
Pre-op bloods to ascertain current function of kidneys
Pre-op fluids? (maintain circulating volume and hydration)
Full clinical exam, avoid stress
Drugs with minimal effect of CVS and renal function/BP
Feed before going home!
