Anaesthesia - general Flashcards
What normally happens to urine output under anaesthesia?
decreased as ADH release from stress
When is an animal hypoxaemic?
PaO2< 60 mmHg
SpO2<90%
What can cause hypoxaemia / hypoxia?
low FiO2( fraction inspired O2) hypventilation V/Q mismatch CVS depression anaemia increased O2 demand
What can cause hypercapnia?
hypoventilation rebreathing high BMR tachycardia hypertension arrhythmias high intracranial pressure CVS depression resp acidosis
How can you correct hypoxia / hypercapnia?
-check depth
-check if rebreathing
-increase FiO2
IPPV
ventolin in horse
what is IPPV?
intermittent positive pressure ventilation
-get reduced venous return and CO as intrapleural pressure will be +ve
What do you aim for with IPPV?
Tidal vol : 10-15 ml/kg RR : 10-20 Inspire : expire : 1:2 - 1:3 ET CO2 : 35-45 mmHg Peak inspiratory pressure : <5cm H2O
What is classed as bradycardia?
What could be causing it?
What do you do?
<26bpm (horse)
- due to: high vagal tone, acid-base distrubance, hypothermia, a 2 agonists , hypertension, high ICP, too deep
- check : depthc, give atropine / glycopyrrolate
What is classed as tacchycardia?
What could be causing it?
What do you do?
> 180 bpm (SA), > 50 bpm (horse)
- due to: high catecholamines (pain, hypotension, hypovol, hypoxia, hypercapnia), hyperthermia, anaemia, drugs, tacchyarrhythmias
- check depth and treat cause
What do you do with an AV block?
if not due to a2 agonist then give atropine / glycopyrrolate
what do you do with a VPC?
lidocaine
treat if haemodynamically significant
What is cat, dog and horse blood volume?
dog and horse : 80-90 ml/kg
cat: 60-70 ml/kg
How do you correct hypvolaemia / hypotension?
fluids
Inotropes - dopamine, dobutamine
What fluid do you give for 10% blood loss?
crystalloid
what type of fluid do you give for 10-25% blood loss?
colloid
What type of fluid do you give for over 25% blood loss?
blood product
What are the consequences of hypothermia?
- decreased anaesthetic need
- prolonged recovery
- increased blood loss
- shivering increases oxygen need
- increased infection risk
how can you treat hypothermia?
warm fluid
warm lavage
bubble wrap
What effects does an increased intracranial pressure have?
high bp
bradycardia
How can you control high ICP?
hyperventilate
osmosis (mannitol, hypertonic saline, furosemide) to decrease blood viscosity and improve blood flow
What does pulse oximetry measure?
HbO2 sat, PaO2, Hr
used LED sensor to see how much oxygenated haemoglobin
Where is pulse ox measured?
tongue mammary gland toe prepuce ear
What are important things to consider with pulse ox?
- if anaemic can still have high saturation but be hypoxic as not enough Hb
- on 100% O2 cant hypoventilated enough to drop Pa02 so monitor during recovery and when not on O2
- CO will still read as high saturation
what does capnography measure?
expired CO2
what is a normal end tidal CO2?
35-45 mmHg
what can cause hypercapnia?
hypoventilation
high CO
hyperthermia
bicarb given
What can cause hypocapnia?
hyperventilation
low CO
hypothermia
what do you see on a capnograph if rebreathing?
non return to baseline
What reflexes can be tested for depth?
palpebral ocular position pupil diameter jaw tone lacrimation salivation nystagmus
what drug can interfere with reflex assessment of depth?
ketamine
Normal cat dog and horse bp?
dog = 100
cat =135
horse = 90
ok bp for anaesthetissed SA?
over 70
3 ways to measure bp?
doppler flow - sensor below cuff on limb / tail
oscillometric - automatic
direct - catheter in peripheral artery
How is central venous pressure measured?
catheter from jugular to vena cava
how ‘ full’ the circulation is
When do you intubate?
eyes rotated ventrally
minimal parapebral reflex
loose jaw tone
no swallowing reflex
what drug is used for intubation?
llidocaine spray
*careful as easy to overdose cat
what are the two type of ET cuff?
high pressure, low volume
low pressure, high volume
what are some problems with ET tubes?
- if too long then intubate one lung only
- mucus in tube can occlude it
- occlusion by tracheal wall prevented by murphy’s eye
- overinflated cuff - compress tube lumen or compress trachea and get necrosis
When do you extubate?
when swallowing reflex is back
what do you extubate earlier?
cats
who do you extubate later?
brachycephalic
vomiting risk
ruminants
How does anaemia affect anaesthesia?
- less Hb so although the Hb present may be fully saturated the oxygen content of the blood will be reduced
- CO will increase to maintain oxygen delivery to tissues
- be careful as most anaesthetic drugs decrease CO so can drop oxygen delivery to a critical level
- consider transfusion if acute and have ongoing blood loss
How does mitral valve disease affect anaesthesia?
- increased SV but ejection fraction is reduced so get forward failure and reduced CO
- compensatory increased ventricular filling and activation of RAAS
- get pulmonary congestion
- need to stabilise before anaesthesia
- want to avoid bradycardia as can cause valve regurgitation
How does pulmonary oedema affect anaesthesia?
- very high risk if animal cyanotic and dyspnoiec
- lungs wont expand as much and alveoli filled with fluid so will increase oxygen consumption as breathing is harder
- will be V/Q mismatch and shunting so reduced blood oxygen content
- treat before anaesthesia
When is an animal cyanotic?
Hb under 75-85% sat
how does hypoproteinaemia affect anaesthesia?
- affect amount of drugs free / bound
- will have more unbound drug so a greater response seen to a given dose
- risk of oedema as oncotic pressure is lower
How does azotaemia affect anaesthesia?
- increased free drug concentrations due to acidosis
- oxygen dissocation curve shifted to the right (reducing o2 affinity)
- changes in serum potassium affecting myocardial contractility
- pre-op fluids to increase GFR and induce diuresis
How does HCM affect anaesthesia?
-have extra heart muscle which due to vasodilation from anaesthesia wont be perfused so more likely to get arrhythmias and arrest
how is sepsis a complication with anaesthesia?
already hugely vasodilated
What is anaesthesia?
loss of sensation resulting form pharmacological depression of nerve function
What is a GA?
a state of unconsciousness produced by controlled reversible drug-induced intoxication of the CNS in which the patient neither receives or recalls noxious stimuli
What do we want from a Ga?
unconsciousness analgesia muscle relaxation amnesia homeostasis normal oxygen delivery
how long do you fast each species for pre-op?
cat and dog - 6 h
horse -12 h
cow - 24 h
rabbit - no
what can N2O exposure do?
inhibit DNA synthesis and cause CNS damage
