the horse is handled too soon, good relaxation may not develop at all, and
it may even try to get up
•
For intermittent boluses, use a low dose of ketamine (⅓ of induction dose)
+ ½ your α-2 premed dose
•
If your surgery is likely to take longer than 45 min, consider using a triple
drip rather than intermittent boluses.
•
Hold the horse down at the end of anaesthetic until it is properly aware
•
If there is still severe nystagmus during the recovery period, give the
horse some diazepam or an α-2
•
If possible, don’t anaesthetize a horse with head trauma
Another scenario where ketamine becomes dangerous is a misplaced
catheter or intravenous injection. The ketamine is then presumably
absorbed erratically, causing excitation and panic. Overzealous “top up” of
ketamine during anaesthetic maintenance reduces the quality of recovery,
often causing early unco-ordinated attempts to stand.
Total intravenous anaesthesia has considerable attraction for horses,
as volatile agents cause so much cardiovascular and respiratory
depression. Respiratory depression may still occur with TIVA, and
oxygen supplementation should still be available. The major problem
with TIVA is that many of the agents used are cumulative, so that after
prolonged anaesthesia recovery can be slow and of poor quality.
Total Intravenous Anaesthesia and the triple drip
The TIVA technique most commonly used at present is the so-called
‘triple drip’. This is a combination of an α2 agonist, with guaiphenesin
and ketamine. It is most commonly used to prolong field anaesthesia in
a controlled manner. Cardiovascular and respiratory depression are
minimal, surgical conditions are good and recovery is usually smooth. It
is probably better restricted to procedures lasting less than 2 hours, as
beyond this guaiphenesin accumulates, leading to an ataxic recovery.
Head injury
Head injury is a more common presentation for emergency surgery in
foals than in adults. In creased intracranial pressure is to be avoided,
hence anything that increases cerebral blood flow is contraindicated. A
fatal case of apnoea and cardiac arrest following induction for traumatic
sinus injury repair has been recorded.
Post partum mares that tremble are in trouble
Anecdotally, 2 peripartum conditions seem to be more likely to cause
muscle trembling together with more universal signs of colic and
systemic compromise. In the author’s experience, mares that tremble
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
71