Page 453 - WSAVA2018
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· Pupil position
· Respiratory effort (intercostal/diaphragmatic)
Summary of Central Nervous Monitoring
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If it is longer than 2 seconds AND the colour is muddy, then the animal is shunting blood away from the periphery of the body because of a drop in blood pressure – alert the veterinarian immediately
Heart Rate
Although mechanical monitoring is often implemented by the use of a pulse oximeter or similar, it is always best to listen to the heart rate. This can be achieved by using a stethoscope (as long as it does not interfere with the surgical site) or by use of an oesophageal stethoscope.
External auscultation
Place the stethoscope on the left hand side where the elbow lies against the chest. Reposition slightly to give best hearing of heart sounds. The apex of the heart points downwards and lies near the sternum at the level of rib 7.
Listen to the heart sounds. The normal sound is described as being a “lub, dup” sound. The sound that we hear is caused by the snapping closed of certain heart valves as the chambers contract and start to eject blood.
The heart should have a regular beat, if you are concerned that the beat is irregular ask the veterinarian to listen.
Listen to the rhythm. Normally the heat beats will
have the same interval between them or has a sinus arrhythmia. This means there is a regular irregularity. The heart speeds up slightly as the animal inhales and slows down slightly as it exhales.
If there is an abnormal arrhythmia there will be irregular gaps between heat beats. This irregularity can be heard
To calculate the heart rate, count the beats for 15 seconds then multiply by four to gain heart per minute.
Oesophageal Stethoscope
The oesophageal stethoscope is passed down the oesophagus to the level of the heart. It enables constant monitoring of the heart beat either via the ear pieces or can be amended to attach to small speakers.
Heart rate & anaesthetic Depth
General indicators:
· Increased heart rate – tachycardiac – decreasing depth of anaesthesia – becoming lighter
· Decreased heart rate – bradycardia – increasing depth of anaesthesia – becoming too deep
Arterial Blood Pressure
Arterial blood pressure is useful in providing continuous information on the performance of the cardiovascular system and indirectly on the depth of the anaesthetic. However, it is important to remember that good blood
 Jaw Tone
   Absent following induction - by Stage 3
   Palpebral reflex
 Absent by Stage 3 plane 2 - 3 in dog and cat Slowed in horse at Stage 3 plane 3
 Corneal reflex
   Very dulled, almost absent by Stage 3 plane 3
   Pedal reflex
 Absent by Stage 3 plane 2
 Lacrimation
   Absent by Stage 3 plane 3
   Eye position
 Stage 3 plane 1 – located in medial canthus with 3rd eyelid partially protruding Stage 3 plane 3 – ventral medial direc- tion Stage 3 plane 4 – central and fixed, eye dry and dull
 Pupil Position
   Stage 3 plane 1 – pupils constricted Stage 3 plane 3 – pu- pil mid-point Stage 3 plane 4 – pupils dilated *remember certain drugs affect pupil size*
   Laryngeal reflex
  Absent in the dog by stage 3 plane 2 (can intubate dog at stage 3 plane 1) Reduced (but not absent) in cat at stage 3 plane 2 Absent in cat at stage 3 plane 3
   Respiration
  Stage 3 plane 1 – regular with full use of muscles & dia- phragm Stage 3 plane 2 – slight decrease in tidal volume & slight increase in respiratory rate Stage 3 plane 3 – intercostals muscles weaken and lag behind diaphragm contraction; creates unevenness & a ‘rocking’ boat type respiratory movement Stage 3 plane 4 – only diaphrag- matic breathing Stage 4 - apnoea
  Monitoring the Cardiovascular system
The aim of the cardiovascular system is the maintenance of adequate tissue perfusion with oxygenated blood. The aim of intraoperative monitoring of the cardiovascular system is to ensure that it is achieving this and intervene if it is not.
Mucous Membrane Colour
The colour of the mucous membranes (gums, conjunctiva, vagina etc) provides information on the adequacy of oxygenation of blood in the lungs, adequacy of blood volume, cardiac output and the delivery of oxygenated blood to the tissues.
· Pink – good perfusion and oxygenation.
· Pale – poor perfusion. This may be the result of (a) poor perfusion from low cardiac output – cardiac problem, low venous return; (b) poor perfusion from vasoconstriction – PAIN; (c) low blood volume – haemorrhage.
· White – severe blood loss, hypovolaemia etc – immediate action required
· Cyanotic – slight blue / grey tinge to mucosa – immediate action required
· Muddy – this indicates both poor oxygenation and poor perfusion. Beware, this animal is in trouble and the oxygen concentration in the blood is below normal!
Capillary Refill Time
Place firm digital pressure on a mucous membrane. This will push all blood from the capillary bed. The speed at which it returns is relative to blood pressure and blood volume. A normal rate is less than 2 seconds.
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