46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
89
Factors that increase VO2 in colic horses:
1. Pain (increased sympathetic tone and metabolism)
2. Hyperthermia (especially septic horses)
3. Shock (increased sympathetic tone)
Derangements in DO2 and VO2 will depend on the severity of clinical signs; very
severe colic episodes may increase the OER to > 30% (Cambier et al. 2008) in
horses undergoing initial medical management. This may mean that DO2 could
become flow dependant, especially if there is severe hypovolaemia.
While the horse is under general anaesthesia it is imperative to ensure adequate
perfusion of oxygenated blood to metabolically active tissue, especially the cardiac
tissue. Hypoxemia is the leading cause of cardiac arrest under general anaesthesia in
colic horse (Boesch 2013). The main mechanisms of hypoxemia in a colic horse
under general anaesthesia are: V/Q mismatching, hypoventilation, and severe rightto-left (lung-to-systemic) shunting of blood (meaning that blood moves through the
lungs without absorbing O2) (Boesch 2013).
Recognising cardiovascular issues
There are a number of techniques used to monitor the cardiovascular system. The
techniques mentioned here should be considered a basic requirement for adequate
monitoring of perfusion under general anaesthesia (Tranquilli et al. 2007):
1. Mucous Membrane Colour – very subjective. A general rule is that if it looks
normal than this information tells you nothing. However, abnormal mucous
membrane colour could indicate a severe peripheral perfusion disturbance
that may even include the central systemic perfusion. Very pale, brick red,
congested (bright red) and bluish coloured mucous membranes can indicate a
perfusion issue.
2. Capillary refill time – Very subjective. Should target < 2 seconds. However,
very prolonged CRT could be due to drugs such as alpha2-adrenoreceptor
agonists (xylazine, detomidine). Very rapid CRT could indicate hyperdynamic
shock and delayed CRT could indicate hypodynamic shock.
3. Pulse quality – very subjective. When this technique is used, there are two
parameters that can be determined. The first is the pulse quality (feeling
systolic – diastolic arterial blood pressure) and rhythm. It should be an easily
palpatable and matched to every heartbeat. The second is the arterial tone.
Intense arterial vasoconstriction feels like a tight band that has a ticking pulse,
while vasodilation causes the artery to collapse easily thus making it difficult
to feel. Ideally you want to feel a pulsating band. This information subjectively
assesses the volume status and blood vessel tone. Peripheral arteries include
the facial, transverse facial.
4. ECG – may detect arrhythmias. Tachyarrhythmias are arguably the most
common finding during the presentation phase prior to surgery.
5. Blood pressure monitoring – Non-invasive (indirect) techniques are least
preferred in colic surgery. However, if only oscillometric blood pressure
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