-
160
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XYLAZINE AND KETAMIIW IN THE HORSE
P. M. Taylor and L. W. Hall Department of Clinical Veterinary Medicine, University of Cambridqe, Madinqley Road, Cambridqe.
General anaesthesia in the horse still presents a considerable challenge, and the search for improved methods continues. The use xylazine
-
Of
ketamine combinations in horses has been reported previously
(Brouwer et al., 1980; Ellis et al., 1977; Muir et al., 1977; Muir 1979). This paper is a summary of a clinical trial where xylazine and ketamine were administered on 100 occasions to horses admitted to the Cambridge Veterinary School for surgery. The breeds, ages and weights are summarised in tables 1 and 2. Surgery undertaken is summarised in tables 3 and 4. On seven occasions, the temperament of the animal necessitated the additional intramuscular administration of either acepromazine or xylazine
(table 5) to facilitate handling before the xylazine ketamine
combination was given. Xylazine was given by slow intravenous injection over a two minute period.
After a further two minutes ketamine was given intravenously
as a bolus. A record was made of the quality of induction, scoring from + (poor) to ++++(excellent) in terms of excitement and ataxia. The time taken for the horse to become recumbent was recorded in minutes. If prolonged anaesthesia was anticipated, intubation was performed, and halothane/oxygen administered by closed circuit. Arterial blood pressure, ECG, respiratory rate, pulse rate and blood gas values were recorded. The quality of surgical conditions
-
was recorded f r m
+
161
-
(surgery impossible) to
++++ (excellent conditions).
The length of time from disconnection from the anaesthetic machine (or from the ketamine injection if no halothane had been administered) to (a) first moving head, (b) first sitting on brisket, and (c) first standing up was recorded in minutes.
The quality of recovery was
recorded as for induction. To enable comparison, the same events were timed in a comparable group of 46 animals recovering from acepromazine/barbiturate/halothane anaesthesia. In 30 cases the combination of xylazine and ketamine was used as sole anaesthetic, and in 59 xylazine-ketaminewas used for induction only, anaesthesia being maintained with halothane and oxygen.
Other
intravenous agents were used in the remaining eleven cases, as described in table 6 .
This demonstrates the attempts made to prolong anaesthesia
intravenously. Results The two minute delay between the completion of the xylazine injection and the administration of the ketamine was sufficient to allow the full effect of the sedative to develop.
A s the trial
progressed it became apparent that the degree of sedation achieved with the xylazine was important to the quality of induction and the recumbent period such that if the sedation from the xylazine was judged to be insufficient, further xylazine was given to effect, and the dose Of
ketamine accordingly increased to maintain the xylazine
ratio 1
:
:
ketamine
2 (table 7 ) .
Mean time to recumbency ( 2 sd) after the ketamine injection was 85
2 30 seconds, the majority lying down quietly (table 8). Induction
was found to be quite different from that achieved after barbiturates. The horses remained standing longer, and the process of lying down was
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162
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slower and more controlled, although some staggering was seen. handling and a important.
Quiet
calm horse before induction were found to be particularly
In addition, twitching of the head and legs seen immediately
after the animal became recumbent was exacerbated if too much restraint was applied at this time. Anaesthesia appeared to deepen for a few minutes after the animal lay down, the jaw remained relatively tight, but once the mouth was opened intubation was easy. Where halothane was used to prolong anaesthesia transition was smooth in most cases.
It was necessary, however, to use very high
inspired concentrations initially, to ensure that the animal remained adequately anaesthetised as the effects of xylazine
-
ketamine wore off.
Early in the trial some difficulty was experienced in judging the depth of anaesthesia as the classical signs were not apparent; however, once familiar with the technique observation of eye position and movement was found to be reliable.
On three occasions under apparently quite
deep halothane anaesthesia spontaneous, aimless limb movements, not related to surgical stimulus were seen. These were depressed by the intravenous injection of small doses of thiopentone. Cardiovascular and respiratory parameters were well maintained (table 9).
Blood pressures were within acceptable limits, indeed, they
compare favourably with pressures commonly seen during barbiturate/ halothane anaesthesia. No dysrhythmias were recorded.
Respiratory
depression was minimal, and blood gas values were within acceptable limits.
Under
xylazine and ketamine alone an increase in respiratory
rate was seen, and some "periodic" breathing, with, however, no detriment to blood gas values. No untoward effect was noted in the animals which received additional premedication.
-
163
-
Surgical conditions were satisfactory in 27 out of the 30 cases where xylazine and ketamine were used alone, and lasted approximately
20 minutes (table lo), sufficient for most minor surgical procedures (table 4). The other 3 cases were early in the trial before the importance of quiet surroundings and adequate sedation was fully appreciated. They became recumbent, but muscle relaxation was poor, and duration of anaesthesia short.
Surgery was still possible, however,
since analgesia was adequate, and there was no response to surgical stimulus.
The end of surgical anaesthesia was often rather abrupt,
making intravenous prolongation of anaesthesia difficult. Where halothane/oxygen was used surgical conditions were satisfactory.
The spontaneous limb movements seen early in the
trial were easily depressed with thiopentone, and were avoided once greater familiarity with the technique was attained. All cases except three who sustained muscle damage during prolonged
(7 2
hours) surgery were able to stand at the first attempt.
Where
a good foothold was available e.g. grass or straw bedding, standing up was exceptionally well controlled.
Slightly more ataxia was seen
when halothane had been given, but recovery in the majority was satisfactory (table 11).
In all cases except one there was no
excitement, and the horses behaved normally within two to three minutes Of
regaining their feet.
Speed of recovery was also remarkable,
Particularly in comparison with barbiturate anaesthesia (Fig. 1). The one horse which showed excitement was poorly sedated after the xylazine and inadvertently received only a part of the calculated dose Of
ketamine.
Lateral recumbency was achieved, but muscle relaxation
was poor. and duration of anaesthesia short.
Following unsuccessful
attempts to prolong anaesthesia with two further doses of ketamine. the horse stood up and proceeded to stagger and roll around the field. When it regained its feet again, the impression was given that it might be hallucinating; normal behaviour was resumed within two hours.
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164
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The three horses which sustained.muscle damage all stood within a few hours. Conclusions The combination of xylazine and ketamine was found to provide an acceptable method for induction and short duration anaesthesia, with some advantages over other established techniques. The main disadvantages are the need to adjust to different techniques for handling and monitoring, the difficulties of adequately prolonging anaesthesia intravenously, and the cost.
However, once
familiar with the technique, the advantages of the lack of cardiovascular and respiratory depression, and above all the fast and quiet recovery outweigh the disadvantages. particularly for orthopaedic cases and for debilitated animals. The combination also shows considerable potential for short term total intravenous anaesthesia in the field. A more detailed account of this trial has been published
elsewhere (Hall and Taylor, 1981).
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165
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REFERENCES BROUWER, G . J . ,
HALL, L.W.,
KUCHEL, T . R .
E L L I S , R . G . , LOWE, J . E . , SWARK, W . S . M e d . and S u r g . , 1,259. HALL, L.W.
& TAYLOR,
P.M.
MUIR, W . W . , SKARDA, R . T . 38, 195.
-
MUTR, W . W .
(1979).
Am.
(1981). & MILNE,
J. V e t .
(1980).
h TAYLOR
Vet.
D.W.
Res.,
J.I. ( 1 9 7 7 ) .
Rec..
(1977).
40,
Vet. Rec.,
1518.
107, 241. J. E q u i n e
108, 489. Am.
J. V e t .
Res..
-
Breed
No.
Thoroughbred
32
Threequarterbred Halfbred
5
Hunter Arab Anglo Arab Hanovarian SUf f olk Punch Cob Lusitano Percheron PO10 pony Pony Donkey
9
166
-
Ages:
Weights:
6
-
9 months
140 meant
-
1270 kg. 447 kg.
8
1 3
Table 2 .
1 3 2 1 1
Overation
25
No. of cases
3
-
Debride f o o t Castration S u p e r f i c i a l surgery Ewradiography
LOO -
TOTAL
Table 1.
TOTAL
Orthopedic Abdaainal Thoracic
Table 4.
0.01
2
-
Xylazine + ketamine alone Xylazine, ketamine, halothane
59
100 -
Xylazine, ketamine. halothane. thiopentone during anaesthesia
3
8
Xylazine, ketamine, thiopentone, t h e n halothane Xylazine, ketamine, r e l a x a n t , halothane/thiopentrne Xylazine, ketamine, methohexitone Xylazine, ketamine, more ketamine Xylazine. ketamine, more ketamine. t h e n thiopentone
-
0.03 mg/kg
i/m
mg/kg
i/m
0.E
Table 6 .
Table 5 .
-
Surgery undertaken where xylazine and ketamine used a s sole anaesthetic.
29
Surgery undvrtaken.
0.4
-
10 13
TOTAL
Xylazine
30 -
9 9
Aceprmazine
17 5
1
Cryptorchid castration Castration Superficial surgery Hisc. EUAhadiopraphy
-
1 ?
19
ENT
Table 3.
19 years
6 years
meant
Premedication. Seven horses only.
-
30
2
2 2 1
1
100 -
Anaesthetic agents given.
Xylazine
1.1 mg/kg
Ketamine
2.2 mg/kg
167
-
initially
11 animals required further xylazine to achieve full sedation. Xylazine C
1.4 mg/kg
Ketamine &
2.E mg/kg
total dose **
maintaining
**
1 : 2 ratio
one donkey required 1.E m g h g xylazine
Table 7.
-
Induction.
Mean time (f sd) to assume lateral recumbency 85 2 30 secs.
Quality scores
Table 8.
-
+
++
+++
++++
O%(O)
2%(2)
15%(15)
E3%(83)
Induction.
-
Xylazine ketamine combination alone
Xylazine, ketamine, halothane, mygen
Pulse rate (+ sd) Beats per min
39
Arterial blood pressure ( 2 s d l nmHg
83 f 51
74 17 (TB) 64 % 18 (non TB)
Respiratory rate (f ad) Breaths per min
22 5 9
14
PaCo2 ( 2 sd) nnnHg
43
4
52
9
167
PaOz
1% s d l mnHs
PH
(range)
68
2
2
7.22
-
7.46
No dysrhythmias
ECG
Table 9.
40
9
-
Cardiovascular and respiratory parameters.
Quality score
+
++
+++
++++
3%(1)
7%(2)
17%(51
73%(221
Duration surgical anaesthesia (f sd) 20 f 7 mins. after Xylazine ketamine combination only
2 1
+5 7
2 73
-
Recovery from xvlazine Quality score
168
-
- ketamine
+
++
+++
****
O%(O)
W(0)
10%(3)
90%(27)
Times from ketamine injection to raising k a d sitting on brisket standing Recovery from xvlazine Quality score
canbination aim(
( 2 sd) 23 2 10 mins 26 33
9
mins
2 10 mins
- ketamine - halothane -
t
W(0) Times fran disconnection frm anaesthetic circuit ( 2 sd) to raising head sitting on brisket standing
++
+*+
**++
9%(6)
26%(17)
6SM42)
13 2 10 &M 1728 28 2 14 &M
plrina recovery (while in lateral recmbency) PaC02
( 2 sd)
47
2 7 mHg
Pa02
( 2 sd)
66
13 W
Table 11.
- Recovery.
axvaen
g
-
thiopentone
169-
methohexitone
xylazine
2 2 55 2
-
krtamine
Times taken tor-
:8
a ) r a i s e head
20
b ) 6ite on brisket
2 20 71 2 36 38
ci stand (minutes
17
12
13
2
29
13
17
2
8
22
28
2
14
10
sd)
T ..... .. :... ... .. Head
Xylazine
-
Brisket
Stand
ketamine
Acepromazine/thiopentone
Acepromazine/methohexitone Fiqure 1.
Xylazine-ketamine-oxygenhalothane with Acepromazine-thiopentoneoxygen-halothane and Accpromazine-rnethohexitoneoxygen-halothane Differences statistically significant according to student's t. test ( p < 0.05)
Recovery : Comparison