Page 452 - WSAVA2018
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    Stage 3
  Progressive depression of respiration, circulation, protective reflexes, muscle tone. Divided into 4 planes
Plane 1
· Respiration: regular, full use of intercostals muscles & diaphragm
· Pupils: constricted, slow nystagmus may be present
· rd eyelid partially protruding
· Salivation and lacrimation and pharyngeal and laryngeal
reflexes persist. Can intubate a horse or dog but not a cat.
· Muscle tone still present.
· Painful stimuli cause limb retraction and elevation in HR, RR
and blood pressure.
Plane 2
· Respiration: slight decrease in tidal volume (intercostals not working as well) and increase in respiratory rate.
· Eye: eccentrically fixed with halothane, centrally fixed with ether and methoxyflurane, centrally fixed with halothane in the horse.
· Lateral nystagmus still present in the horse.
· Surgical stimulation produces HR, BP and RR.
· Oropharynx reflexes abolished in dog but not completely in
the cat.
· Deep tracheal reflexes persist.
· Muscle tone lessens. Plane 3
· Deep Surgical Anaesthesia
· Respiration: The intercostal muscles weaken and lag behind
the diaphragm contraction. This unevenness creates a rocking
boat type respiratory movement.
· Abdominal muscles are relaxed.
· Eye: eyeball is slightly downwardly rotated in a ventro-medial
direction
· Palpebral reflex: absent in dog and cat but only slowed in the
horse.
· Corneal reflex: absent in dog and cat but present in the horse.
· Lacrimation, salivation, oropharynx and laryngeal relaxes all
abolished but deep visceral pain and vagal responses remain.
· Muscle relaxation is good. Plane 4
· Too Deep
· Respiration: only diaphragmatic breathing. Tidal volume is reduced.
THE INSPIRATORY DIAPHRAGMATIC CONTRACTION MAY PRODUCE A TRACHEAL TUG WHICH IS AN EXAGGERATED MOVEMENT OF THE TRACHEA AND LARYNX AND EVEN THE MANDIBLE, ALL OF WHICH CAN BE INCORRECTLY (AND DANGEROUSLY) INTERPRETED AS LIGHTENING OF ANAESTHESIA.
· This plane starts with the paralysis of the intercostal muscles and ends in apnoea.
· Eye: cornea is dry and dull. Pupils are dilated.
· Corneal reflex vanishes in the horse.
· Heart rate and blood pressure fall.
PLANE 4 IS A DANGEROUS AND UNNECESSARY DEPTH OF ANAESTHESIA.
 Stage 4
   The period between respiratory arrest and cardiovascular collapse and arrest. The length of this period depends on the anaesthetic used, degree of oxygenation at the beginning of respiratory arrest and the species, i.e. this time is zero for birds!
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25-28 September, 2018 | Singapore
To achieve surgical anaesthesia we must maintain the animal at Stage 3 between Planes 2 and 3. The deeper Plane 3 will be needed for painful procedures that require good muscle relaxation – eg, orthopaedic and ophthalmic operations. If the patient is being maintained at Stage 3, Plane 3 careful monitoring and I/V fluid support, if the procedure is prolonged will be required.
Monitoring Of Anaesthesia
Early detection of adverse events and evaluation of corrective intervention’s the aim of the game. Various pieces of equipment are of use but reliance should not be placed on just one item. For example, the apnoea alert. By the time this alarm sounds to signal that the animal is no longer breathing, irreversible damage has occurred to the heart and brain. YOU ARE TOO LATE!
Remember these important rules:
· Monitor the patient not the equipment;
· Check the patient before checking the equipment;
· A machine should not replace a skilled anaesthetist.
A machine is primarily directed at the body systems that are essential for the maintenance of life - the central nervous system and the cardiovascular system. Thus we need to monitor the following:
· Central nervous system – reflexes, depth of anaesthesia.
· Cardiovascular system – heart rate, perfusion.
· Pulmonary system & airway
· Oxygenation
· Temperature – this is difficult to maintain and subnormal temperatures will slow metabolic rate and lengthen recovery and post anaesthetic complications.
Note: Never over interpret one piece of information. The aim of anaesthetic monitoring is to obtain data from a number of different body systems that will allow an overall picture of the patient to emerge. The most important monitor is the operator’s senses – sight, hearing, touch etc.
Monitoring of Central Nervous System Reflexes
Basic reflexes and muscle tone are the method of monitoring whether the brain still functions. Under anaesthesia most of the central nervous system undergoes a selective, dose dependent reversible depression caused by the anaesthetic drugs at their site of action. Basic reflexes are:
· Spontaneous motor activity
· Jaw tone
· Palpebral reflex
· Corneal reflex
· Lacrimation
43RD WORLD SMALL ANIMAL VETERINARY ASSOCIATION CONGRESS AND 9TH FASAVA CONGRESS
































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