CAL: How do we anaesthetise this animal? Flashcards
Why is anaemia a problem in anaesthesia? Actions?
The oxygen content of the blood will be reduced and CO will need to be increased to maintain adequate oxygen delivery. Most anaesthtics reduce CO and this may reduce oxygen delivery to a critical level in anaemic patients. Blood transfusion may be necessary - depends on underlying cause, acute/chronic anaemia and whether there is ongoing blood loss.
Are acute or chronic anaemic patients likely to be more tolerant of anaesthesia?
Chronic - due to a rightward shift in the oxyhaemoglobin dissociation curve (due to increased 2,3-diphosphoglycerate levels).
What would you have to do to anaesthetise a patient with MVD resulting in CHF?
The ondition should be stabilized before anaesthesia. Anaesthesia should aim to produce mild reductions in systemic vascular resistance (to promote forward flow of blood and reduce regurgitant fraction), mild increases in HR, with avoidance of bradycardia and hypertension.
When can cyanosis be detected clinically?
clinically when haemoglobin is 75-85% saturated, but at least 5g deoxyHb/100ml blood is a requirement (so not obvious in anaemia). Clinical detection also depends on lighting conditions, skin/MM pigmentation and perfusion of the area examined.
Will pulmonary oedema affect the risk of anaesthesia?
Yes
What actions should you take to anaesthetise a patient with pulmonary oedema?
find out and treat the cause of the pulmonary oedema (often CHF) before anaesthesia is induced, usually diuretic Tx. Pre-oxygenation is essential, (flow-by, facemask, or oxygen cage).
When does hypoproteinaemia usually become clinically detectable?
in very severe cases only
How does hypoproteinaemia affect anaesthesia? 2
- Changes in albumin concentrations will affect the amount of free/bound drugs. Many anaesthetic agents are highly protein bound (e.g. propofol is 98% albumin bound) and hypoalbuminaemia will increase the amount of free (unbound) drug greater response with a given dose.
- Also, plasma proteins maintain colloid oncotic pressure, so that there is a risk of oedema if albumin concentrations are < 20g/litre.
Define azotaemia
is blood urea ~>10mmol/litre OR creatinine ~>200mmol/litre
When do you see azotaemia? 2
renal failure
dehydration
How does acidosis due to azotaemia affect anaesthesia?
Concurrent acidosis increases free drug concentrations, changes resting membrane potential (resulting in myocardial depression), O2 dissociation curve shifted to the right (reducing oxygen affinity). There may also be changes in serum K+ concentrations, which will also affect myocardial contractility and excitability
What might you need to do preoperatively in patients with azotaemic patient?
give IV fluids (to increase GFR and induce diuresis)
What could be the cause of oxygen pressure gauages pointing to zero? 2
no oxygen left in any of the attached tanks OR neither valve has been turned on to allow the oxygen to flow into the machine
What analgesia might be provided in addition to the anaesthetics for a dog castrate? 3
- an opioid in the pre-anaesthetic medication (such as buprenorphine)
- a NSAID (such as carprofen)
- intratesticular injection of lidocaine once asleep.
What is a T piece?
a part of anaesthetic equipment connecting the 2 pipes.
What patients are T pieces suitable for?
ideal for animals ~<5kg) because it has minimal apparatus deadspace and resistance to breathing
Define FGF
Fresh gas flow
What is the FGF for a T piece?
must exceed 2.5 times the patient’s MV otherwise expired gas will be rebreathed. Rapid RRs and short expiratory pauses may require even higher flow rates (e.g. over 3 times the MV).
How would you calculate the FGF for a particular breathing system?
FGF = RR * tidal volume * circuit factor.
How do you calculate the minute volume (MV)?
MV = RR * estimated TV (10ml/kg)
What size of animal is Bain system used for?
adequate for animals >10kg but becomes uneconomical and very expensive for animals weighing more than 30-35kg.
What size of animal is a standard parallel lack system used for?
adequate for animals >10kg but becomes uneconomical for animals >45-50kg.
What size of animal is a Magill system used for?
suitable for animals >10kg but uneconomical for animals >45-50kg. Considerable wasted gas.
What size of animal is a circular breathing system used for?
adequate for animals weighing ~> 10kg
Name a re-breathing system
Circular breathing system (these are the most economical types of system)
What CO2 absorbent if often used for circular breathing systems?
soda lime
Generally what type of gas is carried in the green and clear anaesthetic tubes?
There are exceptions to this rule but generally the green tube – gas coming AWAY from the machine. Other tube (white) is gas going TOWARDS the machine.
What does an ETT size refer to?
The inside diameter of the endotracheal tube (some have a Murphy’s eye to provide an additional alternative opening.
Why are laryngeal masks used for human surgery rather than ETT?
to reduce the tracheal trauma
What size laryngeal mas will fit into a cat?
Sizes 0-1
