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A Comparison of Some Anaesthetic Techniques in Young Calves
Brit. vet.]. (1g66),
122,
65
A COMPARISON OF SOME ANAESTHETIC TECHNIQUES IN YOUNG CALVES By].
BERGER
Wellcome Research Laboratory (East Mrica), Kabete, Kenya
============= SUMMARY Ten methods of anaesthesia in preparation for splenectomy were compared in groups of ten calves. Barbiturates, chloral hydrate and an antagonist were used. Of these methods, that using chloral hydrate was found to be the best for routine splenectomies. INTRODUCTION
Splenectomy of calves at this Laboratory has been described by Brown ( 1 g63) and the technique for chloral hydrate anaesthesia has been recorded by Wilde (I g62). This anaesthetic method has proved entirely satisfactory, but the need to splenectomize calves every week gave an opportunity to compare it with other anaesthetic techniques. MATERIALS AND METHODS
All the calves were high-grade European/Boran crossbreds from two to five weeks old and weighing 25 to 52 ·s kg. Any one trial method was carried out on ten calves, and anaesthesia was obtained with one or a combination of two of the following drugs:Pentobarbitone sodium (Sagatal, May & Baker, Ltd.) as a 6·48 per cent solution (I grain in 1 mi.). If used in conjunction with another drug, a pause of three minutes was allowed before pentobarbitone sodium induction began. Chlorpromazine hydrochloride (Largactil, May & Baker Ltd.) as a I ·25 per cent solution (so mg. in 4 mi.) administered intravenously in approximately 30 seconds. . Promazine hydrochloride (Sparine, John Wyeth and Brother Ltd.) as a I per cent or 5 per cent solution administered intravenously. Thiopentone sodium (Intraval Sodium, May & Baker Ltd.) as a 5 per cent solution (I g. in 20 ml.). Megimide sodium (Megimide, Aspro-Nicholas Ltd.) (P-methyl P-ethylglutarimide) as a o·s per cent or a ro per cent solution by the intravenous route. Pethidine lrydrochloride as a 5 per cent solution in a dose of I or 2 ml. given intramuscularly 20 to 30 minutes before a second drug. Diethylthiambutene hydrochloride (Themalon, Burroughs W ellcome & Co.) as a I per cent solution given intravenously in 1 ·25 to I ·s minutes. Chloral hydrate as a 40 per cent solution.
66
BRITISH VETERINARY JOURNAL,
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Food and water were withheld from the calves from 4 p.m. on the evening before the anaesthetic was to be given, and a standard dose of o ·I grain atropine sulphate was administered 20 to 30 minutes before the start of induction between 8.30 a.m. and 10.30 a.m. All intravenous injections were given with 5, 10, or 20 ml. syringes, and It inch, I6 BWG needles were found best. Figures given for pulse and respiration are rates per minute calculated from single counts over half a minute. Observations on respiratory rates were recorded in groups 1 and 2, and on pulse and respiratory rates in all other groups, for comparison with mean rates of similarly aged calves at rest. (Mean respiratory rate 25 and pulse rate So.) Respiration was recorded as diphasic or triphasic in cases where there was a double or treble expiratory effort, although any small interposed inspiratory effort may not have been detected. The term "medium" anaesthesia indicates perfect analgesia with complete relaxation of abdominal muscles. "Light" anaesthesia describes a condition suitable for surgery but in which there was some twitching of abdominal muscle bundles at incision. "Very light" anaesthesia indicates that there was pronounced muscular response to interference. Induction continued until anaesthesia suitable for splenectomy was obtained, anaesthetic depth being assessed from jaw relaxation, palpebral, corneal and "ear pinch" reflexes. A fingernail pinch to the edge of the ear provokes an anterior (extensor) movement of the forelimb in the deeply narcotized animal, and, as light anaesthesia deepens to surgical anaesthesia, marked twitching of the brachiocephalic muscle gives way to a slight tensing of the muscle. In observing recovery, particular note was made of the sleeping time, i.e. the time from completion of the operation until the calf could keep its head up in response to stimulus. It was not possible to observe all calves until the end of recumbency. RESULTS
The results are summarized in Table I. ( 1) Pentobarbitone sodium Induction took approximately ten miJ:?.utes without excitement. The calves subsided to the ground when between one-third and one-half of the final dose had been given. Respiratory volume remained good; the rate slowed to a mean of 20 by the time anaesthesia was completed and changed little during the operation. Light to medium anaesthesia lasted one to two hours. Most of the calves were unable to drink their 4 p.m. milk ration, and two were still unsteady the following morning.
(2) Chlorpromazine hydrochloride and pentobarbitone sodium Eight calves remained standing but unsteady following administration of chlorpromazine hydrochloride. Respiratory rate increased but decreased during the course of pentobarbitone induction (mean at completion of anaesthesia,
0
TABLE I
0
~
SUMMARY OF RESULTS OBTAINED USING TEN DIFFERENT METHODS O F ANAE STHETIZING CALVES
2
Mean weight (kg.) 38 "4 42"2
3
37 "6
4 5
37"7 38·2
6
42 "4
7
40"9
8
38•7
9
35"8
10
43"7
Group
Drugs used Pentobarbitone sodium Chlorpromazine HCl Pentobarbitone sodium Promazine HCl Pentobarbitone sodium Thiopentone sodium Thiopentone sodium Megimide (antagonist) Pethidine HCl Thiopentone sodium Diethylthiambutene HCI Thiopentone sodium Promazine HCl Thiopentone sodium Chloral·hydrate Thiopentone sodium Chloral hydrate (rapid primary) (slow final) • See Table II.
Mean Depth of dbse anaesthesUJ (mg.fkg. ) Very light to deep 19"9 I•! Light to deep 18·8 J •2 Light to deep 15·8 Light to medium 17"0 18•1 Light to medium 1"9 21"2 2"0 14"3 1"0 !8•7 116·o 6 ·8 158·o 105"0 53"0
Mean sleeping time 5"4 >5"7 > 5"2 2"95
•
Shortest (hr. )
Period of Recumbency Longest Mean (hr.) (hr. )
6·5 >7•0
>9 >8
> 7"75 >7 •7
7"0
>9
>7·8
3 "0
>8
>5 ·9
•
•
No. of deaths 2
3"25
5"0
>7
> 6·1
1"7
2"0
>6
> 4"9
Light to medium
4"3
3"0
>9
> 7"3
Very light to medium Very light to medium
1"75
4"0
>7
>4"9
1"3
1"5
>6
> 2"75
C/l
0
z
0
"1
~ ~
...,C/l :I: ...,t'l
•
Very light to medium Light to medium
-~
0
~
...,t'l 2
:I: 0
tl
C/l
z 0
~
< t'l C/l
68
BRITISH VETERINARY JOURNAL,
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33 ·5) and increased again by completion of splenectomy (mean 39). There was a tendency to excessive haemorrhage at the operation site during surgical interference. Only four calves took their 4 p.m. milk feed, and two were unsteady on their feet at 24 hours. Two deaths occurred during anaesthesia. One animal, although apparently deeply anaesthetized, groaned several times when the spleen was handled. Reflexes appeared to be returning at 3 ·5 hours, but death occurred at 5 hours. The second showed apnoea as the administration of pentobarbitone was completed, but I5 seconds' manual compression of the thorax provoked fast shallow respiration. Five minutes later respiration failed again. The animal responded to intravenous nikethamide, but there was considerable regurgitation of watery mucus. Soon after completion of splenectomy apnoea recurred. Though manual compression . restored respiration it remained very shallow and the pulse was very fast until death at I ·5 hours. Autopsy showed no factor likely to have contributed to anaesthetic intolerance. (3) Promazine hydrochloride and pentobarbitone sodium Promazine hydrochloride as a 5 per cent solution was administered in I ·5 to 3 minutes. Total induction with pentobarbitone varied from 5 to 15 minutes (mean 8·5 minutes). At the completion of promazine injection three calves subsided to the ground. The others could sti11 stand and walk unsteadily. Four calves actively resisted the restraint necessary for induction with pentobarbitone, although only one had exhibited excitability before promazine injection. The seven calves given pentobarbitone while they were standing subsided to the ground when between one-third and one-half of the final dose had been injected. Respiratory rates increased following promazine premedication (mean 6 I). Rates of I40 in two calves account for the high mean. Following pentobarbitone administration the rate dropped (mean 34) and changed little by the completion of splenectomy (mean 32). Pulse rate was noticeably increased following promazine (mean I 33), remained steady during pentobarbitone anaesthesia (mean I34), and showed a moderate rise by completion of splenectomy (mean I48). Five calves showed marked changes in pulse and respiration during interference with the spleen. Cardiac function of calf no. 2 I became so weak that no activity could be detected by palpation for some 20 seconds and respiration was very shallow. Both returned to normal a minute later. In calf no. 22 not only was it impossible to detect cardiac function for 40 seconds but there was also temporary apnoea, followed by shallow respiration. Two minutes later both were normal. In calf no. 24, pulse and respiration became weak and slow for about 30 seconds. In calf no. 26, for I 5 seconds after ligation of the splenic artery, cardiac function became weak, and an obvious pause after every two ventricular systolic thuds and an exaggerated jugular pulse were evident. In calf no. 28, pulse rate slowed for I o seconds, became undetectable for 5 and recovered normal function during the next 10 seconds. Assessment of anaesthesia by reflex activity proved difficult : for instance,
COMPARISON OF ANAESTHETIC METHODS IN CALVES
6g
calf no. 25 showed corneal and ear pinch reflexes throughout medium anaesthesia. Two calves were unable to take their 4 p.m. milk feed and three still showed an unsteady gait at 24 hours.
(4) Thiopentone sodium Calves subsided to the ground 45 to 6o seconds after thiopentone sodium induction started. Total induction time varied from 7 to I5 minutes (mean I I). Some calves responded to operative interference and more of the drug had to be given. However, induction was quiet, the animals subsiding when between a quarter and a half of the total dose had been given. In three calves respiration became triphasic or diphasic for 2 to 5 minutes during the latter half of induction. Four calves groaned on expiration during the last stages of induction and splenectomy. Handling of the spleen appeared temporarily to decrease ventilation. Respiration slowed during induction. The respiration rates recorded at the start of surgical interference varied from 20 to 52 per minute (mean 34), tending to fall by the completion of splenectomy (mean 32). Pulse rate at the start of the surgical interference was moderately increased (mean ISO) and showed little change at its completion (mean _r55). Although the majority were still recumbent all calves took their 4 p.m. milk feed. Three were still unsteady at 24 hours.
(5) Thiopentone sodium and antagonist megimide sodium The results in this group of calves are recorded individually in Table II, as there was a large variation in the dose rate of megimide. All calves subsided quietly to the ground in 45 to 6o seconds when between aquarter and a half of the total dose of anaesthetic had been given. Total induction time varied from 4 to 9 minutes (mean 5 minutes). Anaesthesia was satisfactory and only temporary minor variations in cardiac or respiratory functions were shown. Megimide sodium was administered at completion of the operation, injection taking between o·s and 5 minutes. Delay occurred when animals showed convulsive symptoms. Obvious resuscitation resulted from doses of 7 ·s to IOO mg./kg. megimide, swallowing movements and twitching of facial muscles being evident soon after the start of injection. At the same time cardiac function slowed and strengthened, while respiration accelerated and increased in depth. Temporary convulsive symptoms in some calves given higher dosage levels necessitated manual restraint of the head and limbs, but the calf given the largest dose (100 mg. /kg.) exhibited only continuous subacute spasms with two periods of temporary apnoea. Mean rate of respiration at the end of splenectomy was 24 and this was followed by a rise to a mean of 3 I a few minutes after completion of megimide injection. Over the same period a mean pulse rate of I6o dropped to IOO. No calf relapsed into a comatose state once the head was held off the ground voluntarily, but two calves thrashed about the loose-box in an attempt to stand before they were able to do so.
BRITISH VETERINARY JOURNAL, 122, 2
70
TABLE II RESULTS
OBTAINED
WHEN
USING
THIOPENTONE IN GROUP
SODIUM AND ANTA GO NIST MEGIMIDE SODIUM
(5)
Megimide mg./kg.
Depth of anaesthesia
Sleeping time
Period of recumbency
37 31 40 40 45 50
Thiopentone sodium mg.fkg. !8•2 12'9 19'4 21'2 17•8 19'0
2'7 3'2 7'5 15'0 22 '2 25 '0
7 hr. 4 hr. 30 min. 1 min. 5 min. 30 min.
8 hr. 8 hr. 4 hr. 2 hr. 2·5 hr. 4 hr.
38 38 38 25
15·8 19'0 19'7 18·o
42'1 50'0 64'5
Medium Medium Light Medium Medium Light/ medium Medium Medium Medium Medium
Calf no.
Wtight (kg.)
41 42 43 44 45 46 47 48 49 50
wo·o
10 min. < I min. < I min. < I min.
30 min. 30min. Iomin. 30min.
(6)Pethidine hydrochloride and thiopentone sodium Pethidine hydrochloride premedication was followed by thiopentone sodium induction in IO to 15 minutes (mean I2·5 minutes), primary injection until the calf subsided being carried out in 45 to 50 seconds. One calf was excited prior to thiopentone injection and two calves resisted restraint during in. duction. The calves subsided to the ground when between one-fifth and onethird of the final dose had been given. Four calves exhibited expiratory groaning during the operation and one continued to do so afterwards. Handling of the spleen provoked decreased heart rates in three calves, with marked loss offorce in one. Diphasic respiration was recorded at the completion of the operation in three calves. There was little effect on respiratory rates when anaesthesia (mean 26) and splenectomy (mean 26) were completed. Pulse rates increased at completion of anaesthesia (mean I 72) and showed a slight decrease by completion of splenectomy (mean 162). In three calves the eye reflexes disappeared before light anaesthesia was attained, although the ear pinch stimulated a refle.l_{. All ten calves took their 4 p.m. milk feed. One calf still exhibited an unsteady gait at 24 hours. ( 7) Diethylthiambutene hydrochloride and thiopentone sodium All ten calves subsided to the ground o to I 20 seconds after completion of thiambutene injection and a pause of 3 minutes was allowed before thiopentone induction was begun. If the animals were allowed to sit up they remained quiet, but, with one exception, they resisted restriction in the lateral position and some bellowed. Total induction time with thiopentone was 5 to IO minutes (mean 6·3 minutes). Respiratory rates increased following the thiambutene injection (mean 35), slowed by the time anaesthesia by thiopentone was completed (mean 29), and increased by the time splenectomy was completed (mean 36). Pulse rates increased following thiambutene injection (mean I 53), showed further increase by completion of anaesthesia (mean I6I ), but slowed again by completion of
COMPARISON OF ANAESTHETIC METHODS IN CALVES
71
splenectomy (mean 145). Four calves temporarily showed marked diphasic expiratory effort at full anaesthesia. Calf no. 62, although judged satisfactorily anaesthetized by assessment of reflexes, showed strong leg movements when the abdominal muscles were incised, and yet adequate relaxation followed without more thiopentone. Calf no. 65 reacted similarly, received more thiopentone, and exhibited occasional periods of expiratory groaning during surgery. Half to 2 hours after completion of splenectomy it made excited efforts to raise its head, its respiration was stertorous and it had to be restrained manually. Calf no. 70 died 24 hours after splenectomy, having shown little lightening of anaesthesia. Soon after thiopentone anaesthesia was completed the pulse rose to a rate impossible to count, slowed, nearly stopped, and then increased again. This was immediately followed by apnoea which responded to intravenous nikethamide and artificial respiration. After a few inspiratory efforts there was a second failure for nearly a minute before further nikethamide induced respiration. Splenectomy followed without further crisis. Four hours later there were signs of reflex activity returning, but from this point there was no improvement despite attempted resuscitation. Autopsy revealed no abnormality to account for anaesthetic intolerance. The other calves took their 4 p.m. feed, but one calf was still unsteady at 24 hours.
(8) Promazine 4ydrochloride and thiopentone sodium Promazine chloride as a 1 per cent solution was injected in two minutes and thiopentone followed after a pause of 3 minutes. Total induction time varied from 6 to 15 minutes (mean 8·8 minutes). After the promazine injection seven calves remained standing. These subsided to the ground when one-third to one-half the total dose had been injected. Respiratory rates were little affected by the promazine premedication (mean 25); they increased by the time anaesthesia with thiopentone was completed (mean 35) and showed little change when splenectomy was completed (mean 36). Pulse rates were moderately increased by the promazine premedication (mean 122) and again by the completion of anaesthesia (mean 152) but started to decrease when splenectomy was completed (mean 145). Calf no. 72 showed diphasic respiration following promazine injection and a period of apnoea lasting ten seconds in which cardiac function became almost imperceptible, during thiopentone induction and again when the spleen was handled. Calf no. 76 exhibited a temporary slowing of the heart rate when the spleen was handled, and this was followed by "thumping" heart beats for two minutes. Calf no. 8o showed apnoea when three-quarters of the final dose of thiopentone had been given. Respiration was re-established a minute later on administration of nikethamide and artificial respiration. During handling of the spleen there was a further short period of apnoea and very weak cardiac function which responded to a further injection of nikethamide. There were two deaths during anaesthesia. In calf no. 75, whose pulse had become almost imperceptible when the spleen was ligated, anaesthesia
BRITISH VETERINARY JOURNAL,
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appeared to be lightening satisfactorily an hour after the operation, but the animal died one hour later. Autopsy showed no factor likely to contribute to anaesthetic intolerance. In calf no. 78, in which respiration was shallow during splenectomy, anaesthesia appeared to be lightening satisfactorily one hour after completion of the operation, but the animal died half an hour later. Autopsy revealed enteritis and two myocardial lesions which might have contributed to anaesthetic intolerance. The order in which reflexes disappeared varied in these calves, making assessment of anaesthesia difficult.
(g) Chloral hydrate and thiopentone sodium Induction with chloral hydrate took 2 to 5 minutes, using 53 to 75 per cent of the dose necessary for anaesthesia with chloral hydrate alone. All calves subsided quietly to the ground when between 40 and 70 per cent of the estimated full dose had been given. After a three-minute wait, thiopentone solution was injected in 3 to 8 minutes. Respiratory rates rose by the time chloral hydrate narcosis was completed (mean 45), fell again when anaesthesia with thiopentone sodium was completed (mean 38), and rose again by the end of splenectomy (mean 47). Pulse rate was increased by the time chloral hydrate narcosis was completed (mean I6o) and continued to rise until the completion of anaesthesia by thiopentone sodium (mean I 9 I). In seven calves the pulse rate had dropped by the end of splenectomy (mean I 6o). Assessment of the depth of anaesthesia by reflex activity was difficult. For instance, calf no. 77 had lost eye and ear-pinch reflexes before even light anaesthesia~ had been achieved. In calf no. 7 I eye reflexes disappeared long before that from the ear pinch. During transition from light to medium anaesthesia two calves exhibited groaning respiration. There was a tendency to excessive haemorrhage at the operation site during surgical interference. All calves took their 4 p.m. milk feed and were bright and steady at 24 hours. (I o) Chloral hydrate, primary rapid induction Two-thirds of the estimated full dose of chloral hydrate necessary to produce anaesthesia at the normal speed of injection (I76 mg./kg.) (Wilde, Ig62) was administered in I5 to 30 seconds (mean 24 seconds). After a 3- to 5-minute wait, induction was continued slowly until satisfactory anaesthesia was attained. The mean primary dose was 68 per cent of the mean total dose. All calves subsided to the ground 10 to 30 seconds after the primary rapid injection. Nine calves could only be considered narcotized 3 to 5 minutes later, the ear pinch provoking violent muscular movement. Pressure on the ventral aspect of the tongue usually induced jaw movements. In calf no. 97 and calf no. gg, two minutes after completion of the primary rapid injection, respiration became stertorous and heart rate slowed to 30 and 40 respectively, cardiac function becoming scarcely perceptible by palpation of the thoracic wall. In both cases nikethamide provoked an immediate response. Chloral hydrate was then given slowly until satisfactory anaesthesia was obtained.
COMPARISON OF ANAESTHETIC METHODS IN CALVES
73
In calf no. 97 this was not until after ligation of the splenic vessels. An initial, markedly increased respiratory rate during injection, slowed to give a mean rate of 50 at the completion of anaesthesia. A further decrease by the completion of the operation gave a mean figure of 45· Pulse rate at the start of the operation was increased (mean I57) but insufficient figures were recorded to give a mean rate at the completion of surgical interference. Haemorrhage during surgical interference was minimal. All ten calves took their 4 p.m. feed and were bright and steady at 24 hours.
Other techniques It was intended to use methohexital sodium (Brevane, Corn States Laboratories), but initial results in 5 calves given 9 to I 2 ·2 mg. /kg. as a 2 ·s per cent solution were so unsatisfactory that the series was discontinued. During induction there were marked muscular spasms and only a short, light anaesthesia was obtained, lasting 3 to IO minutes. These results contrast with those of Robertshaw (I964), who was using older and larger calves. Evidently the necessary dose rate rises rapidly in very young animals. Results following intravenous injection of phencyclidine (Sernylan, Parke Davis & Co.) were unsatisfactory and no further attempts were made to assess its value. In all, 93 calves weighing 28 ·2 to 57 ·3 kg. were anaesthetized with the standard technique (Wilde, I962) on the same days as those in the ten groups of ten recorded above. The mean dose rate of chloral hydrate used was I 89 mg./kg. with a range of I24 to 27I mg. /kg. Two deaths occurred during anaesthesia. CONCLUSION
Chloral hydrate anaesthesia proved superior to all the others tested in respect of ease of induction, absence of haemorrhage, recovery, safety and cost. Thiopentone sodium was considered to be the second best. ACKNOWLEDGEMENTS
The technical assistance of Mr. W. G. Revil is gratefully acknowledged. Thanks are due to Dr. J. K. H. Wilde and Miss M. E. Watts for assistance in the preparation of this paper. REFERENCES
BRoWN, C. G. D. (1963) . Bull. epi;:oot. Dis. Ajr., n, 23. RoBERTSHAW, D. (1964). Vet. Rec., 76, 13, 357· WILDE, J. K. H. ( 1962). Br. vet. J., :u8, 206. (Accepted for publication 8 October, 1965)
122,
65
A COMPARISON OF SOME ANAESTHETIC TECHNIQUES IN YOUNG CALVES By].
BERGER
Wellcome Research Laboratory (East Mrica), Kabete, Kenya
============= SUMMARY Ten methods of anaesthesia in preparation for splenectomy were compared in groups of ten calves. Barbiturates, chloral hydrate and an antagonist were used. Of these methods, that using chloral hydrate was found to be the best for routine splenectomies. INTRODUCTION
Splenectomy of calves at this Laboratory has been described by Brown ( 1 g63) and the technique for chloral hydrate anaesthesia has been recorded by Wilde (I g62). This anaesthetic method has proved entirely satisfactory, but the need to splenectomize calves every week gave an opportunity to compare it with other anaesthetic techniques. MATERIALS AND METHODS
All the calves were high-grade European/Boran crossbreds from two to five weeks old and weighing 25 to 52 ·s kg. Any one trial method was carried out on ten calves, and anaesthesia was obtained with one or a combination of two of the following drugs:Pentobarbitone sodium (Sagatal, May & Baker, Ltd.) as a 6·48 per cent solution (I grain in 1 mi.). If used in conjunction with another drug, a pause of three minutes was allowed before pentobarbitone sodium induction began. Chlorpromazine hydrochloride (Largactil, May & Baker Ltd.) as a I ·25 per cent solution (so mg. in 4 mi.) administered intravenously in approximately 30 seconds. . Promazine hydrochloride (Sparine, John Wyeth and Brother Ltd.) as a I per cent or 5 per cent solution administered intravenously. Thiopentone sodium (Intraval Sodium, May & Baker Ltd.) as a 5 per cent solution (I g. in 20 ml.). Megimide sodium (Megimide, Aspro-Nicholas Ltd.) (P-methyl P-ethylglutarimide) as a o·s per cent or a ro per cent solution by the intravenous route. Pethidine lrydrochloride as a 5 per cent solution in a dose of I or 2 ml. given intramuscularly 20 to 30 minutes before a second drug. Diethylthiambutene hydrochloride (Themalon, Burroughs W ellcome & Co.) as a I per cent solution given intravenously in 1 ·25 to I ·s minutes. Chloral hydrate as a 40 per cent solution.
66
BRITISH VETERINARY JOURNAL,
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Food and water were withheld from the calves from 4 p.m. on the evening before the anaesthetic was to be given, and a standard dose of o ·I grain atropine sulphate was administered 20 to 30 minutes before the start of induction between 8.30 a.m. and 10.30 a.m. All intravenous injections were given with 5, 10, or 20 ml. syringes, and It inch, I6 BWG needles were found best. Figures given for pulse and respiration are rates per minute calculated from single counts over half a minute. Observations on respiratory rates were recorded in groups 1 and 2, and on pulse and respiratory rates in all other groups, for comparison with mean rates of similarly aged calves at rest. (Mean respiratory rate 25 and pulse rate So.) Respiration was recorded as diphasic or triphasic in cases where there was a double or treble expiratory effort, although any small interposed inspiratory effort may not have been detected. The term "medium" anaesthesia indicates perfect analgesia with complete relaxation of abdominal muscles. "Light" anaesthesia describes a condition suitable for surgery but in which there was some twitching of abdominal muscle bundles at incision. "Very light" anaesthesia indicates that there was pronounced muscular response to interference. Induction continued until anaesthesia suitable for splenectomy was obtained, anaesthetic depth being assessed from jaw relaxation, palpebral, corneal and "ear pinch" reflexes. A fingernail pinch to the edge of the ear provokes an anterior (extensor) movement of the forelimb in the deeply narcotized animal, and, as light anaesthesia deepens to surgical anaesthesia, marked twitching of the brachiocephalic muscle gives way to a slight tensing of the muscle. In observing recovery, particular note was made of the sleeping time, i.e. the time from completion of the operation until the calf could keep its head up in response to stimulus. It was not possible to observe all calves until the end of recumbency. RESULTS
The results are summarized in Table I. ( 1) Pentobarbitone sodium Induction took approximately ten miJ:?.utes without excitement. The calves subsided to the ground when between one-third and one-half of the final dose had been given. Respiratory volume remained good; the rate slowed to a mean of 20 by the time anaesthesia was completed and changed little during the operation. Light to medium anaesthesia lasted one to two hours. Most of the calves were unable to drink their 4 p.m. milk ration, and two were still unsteady the following morning.
(2) Chlorpromazine hydrochloride and pentobarbitone sodium Eight calves remained standing but unsteady following administration of chlorpromazine hydrochloride. Respiratory rate increased but decreased during the course of pentobarbitone induction (mean at completion of anaesthesia,
0
TABLE I
0
~
SUMMARY OF RESULTS OBTAINED USING TEN DIFFERENT METHODS O F ANAE STHETIZING CALVES
2
Mean weight (kg.) 38 "4 42"2
3
37 "6
4 5
37"7 38·2
6
42 "4
7
40"9
8
38•7
9
35"8
10
43"7
Group
Drugs used Pentobarbitone sodium Chlorpromazine HCl Pentobarbitone sodium Promazine HCl Pentobarbitone sodium Thiopentone sodium Thiopentone sodium Megimide (antagonist) Pethidine HCl Thiopentone sodium Diethylthiambutene HCI Thiopentone sodium Promazine HCl Thiopentone sodium Chloral·hydrate Thiopentone sodium Chloral hydrate (rapid primary) (slow final) • See Table II.
Mean Depth of dbse anaesthesUJ (mg.fkg. ) Very light to deep 19"9 I•! Light to deep 18·8 J •2 Light to deep 15·8 Light to medium 17"0 18•1 Light to medium 1"9 21"2 2"0 14"3 1"0 !8•7 116·o 6 ·8 158·o 105"0 53"0
Mean sleeping time 5"4 >5"7 > 5"2 2"95
•
Shortest (hr. )
Period of Recumbency Longest Mean (hr.) (hr. )
6·5 >7•0
>9 >8
> 7"75 >7 •7
7"0
>9
>7·8
3 "0
>8
>5 ·9
•
•
No. of deaths 2
3"25
5"0
>7
> 6·1
1"7
2"0
>6
> 4"9
Light to medium
4"3
3"0
>9
> 7"3
Very light to medium Very light to medium
1"75
4"0
>7
>4"9
1"3
1"5
>6
> 2"75
C/l
0
z
0
"1
~ ~
...,C/l :I: ...,t'l
•
Very light to medium Light to medium
-~
0
~
...,t'l 2
:I: 0
tl
C/l
z 0
~
< t'l C/l
68
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33 ·5) and increased again by completion of splenectomy (mean 39). There was a tendency to excessive haemorrhage at the operation site during surgical interference. Only four calves took their 4 p.m. milk feed, and two were unsteady on their feet at 24 hours. Two deaths occurred during anaesthesia. One animal, although apparently deeply anaesthetized, groaned several times when the spleen was handled. Reflexes appeared to be returning at 3 ·5 hours, but death occurred at 5 hours. The second showed apnoea as the administration of pentobarbitone was completed, but I5 seconds' manual compression of the thorax provoked fast shallow respiration. Five minutes later respiration failed again. The animal responded to intravenous nikethamide, but there was considerable regurgitation of watery mucus. Soon after completion of splenectomy apnoea recurred. Though manual compression . restored respiration it remained very shallow and the pulse was very fast until death at I ·5 hours. Autopsy showed no factor likely to have contributed to anaesthetic intolerance. (3) Promazine hydrochloride and pentobarbitone sodium Promazine hydrochloride as a 5 per cent solution was administered in I ·5 to 3 minutes. Total induction with pentobarbitone varied from 5 to 15 minutes (mean 8·5 minutes). At the completion of promazine injection three calves subsided to the ground. The others could sti11 stand and walk unsteadily. Four calves actively resisted the restraint necessary for induction with pentobarbitone, although only one had exhibited excitability before promazine injection. The seven calves given pentobarbitone while they were standing subsided to the ground when between one-third and one-half of the final dose had been injected. Respiratory rates increased following promazine premedication (mean 6 I). Rates of I40 in two calves account for the high mean. Following pentobarbitone administration the rate dropped (mean 34) and changed little by the completion of splenectomy (mean 32). Pulse rate was noticeably increased following promazine (mean I 33), remained steady during pentobarbitone anaesthesia (mean I34), and showed a moderate rise by completion of splenectomy (mean I48). Five calves showed marked changes in pulse and respiration during interference with the spleen. Cardiac function of calf no. 2 I became so weak that no activity could be detected by palpation for some 20 seconds and respiration was very shallow. Both returned to normal a minute later. In calf no. 22 not only was it impossible to detect cardiac function for 40 seconds but there was also temporary apnoea, followed by shallow respiration. Two minutes later both were normal. In calf no. 24, pulse and respiration became weak and slow for about 30 seconds. In calf no. 26, for I 5 seconds after ligation of the splenic artery, cardiac function became weak, and an obvious pause after every two ventricular systolic thuds and an exaggerated jugular pulse were evident. In calf no. 28, pulse rate slowed for I o seconds, became undetectable for 5 and recovered normal function during the next 10 seconds. Assessment of anaesthesia by reflex activity proved difficult : for instance,
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calf no. 25 showed corneal and ear pinch reflexes throughout medium anaesthesia. Two calves were unable to take their 4 p.m. milk feed and three still showed an unsteady gait at 24 hours.
(4) Thiopentone sodium Calves subsided to the ground 45 to 6o seconds after thiopentone sodium induction started. Total induction time varied from 7 to I5 minutes (mean I I). Some calves responded to operative interference and more of the drug had to be given. However, induction was quiet, the animals subsiding when between a quarter and a half of the total dose had been given. In three calves respiration became triphasic or diphasic for 2 to 5 minutes during the latter half of induction. Four calves groaned on expiration during the last stages of induction and splenectomy. Handling of the spleen appeared temporarily to decrease ventilation. Respiration slowed during induction. The respiration rates recorded at the start of surgical interference varied from 20 to 52 per minute (mean 34), tending to fall by the completion of splenectomy (mean 32). Pulse rate at the start of the surgical interference was moderately increased (mean ISO) and showed little change at its completion (mean _r55). Although the majority were still recumbent all calves took their 4 p.m. milk feed. Three were still unsteady at 24 hours.
(5) Thiopentone sodium and antagonist megimide sodium The results in this group of calves are recorded individually in Table II, as there was a large variation in the dose rate of megimide. All calves subsided quietly to the ground in 45 to 6o seconds when between aquarter and a half of the total dose of anaesthetic had been given. Total induction time varied from 4 to 9 minutes (mean 5 minutes). Anaesthesia was satisfactory and only temporary minor variations in cardiac or respiratory functions were shown. Megimide sodium was administered at completion of the operation, injection taking between o·s and 5 minutes. Delay occurred when animals showed convulsive symptoms. Obvious resuscitation resulted from doses of 7 ·s to IOO mg./kg. megimide, swallowing movements and twitching of facial muscles being evident soon after the start of injection. At the same time cardiac function slowed and strengthened, while respiration accelerated and increased in depth. Temporary convulsive symptoms in some calves given higher dosage levels necessitated manual restraint of the head and limbs, but the calf given the largest dose (100 mg. /kg.) exhibited only continuous subacute spasms with two periods of temporary apnoea. Mean rate of respiration at the end of splenectomy was 24 and this was followed by a rise to a mean of 3 I a few minutes after completion of megimide injection. Over the same period a mean pulse rate of I6o dropped to IOO. No calf relapsed into a comatose state once the head was held off the ground voluntarily, but two calves thrashed about the loose-box in an attempt to stand before they were able to do so.
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TABLE II RESULTS
OBTAINED
WHEN
USING
THIOPENTONE IN GROUP
SODIUM AND ANTA GO NIST MEGIMIDE SODIUM
(5)
Megimide mg./kg.
Depth of anaesthesia
Sleeping time
Period of recumbency
37 31 40 40 45 50
Thiopentone sodium mg.fkg. !8•2 12'9 19'4 21'2 17•8 19'0
2'7 3'2 7'5 15'0 22 '2 25 '0
7 hr. 4 hr. 30 min. 1 min. 5 min. 30 min.
8 hr. 8 hr. 4 hr. 2 hr. 2·5 hr. 4 hr.
38 38 38 25
15·8 19'0 19'7 18·o
42'1 50'0 64'5
Medium Medium Light Medium Medium Light/ medium Medium Medium Medium Medium
Calf no.
Wtight (kg.)
41 42 43 44 45 46 47 48 49 50
wo·o
10 min. < I min. < I min. < I min.
30 min. 30min. Iomin. 30min.
(6)Pethidine hydrochloride and thiopentone sodium Pethidine hydrochloride premedication was followed by thiopentone sodium induction in IO to 15 minutes (mean I2·5 minutes), primary injection until the calf subsided being carried out in 45 to 50 seconds. One calf was excited prior to thiopentone injection and two calves resisted restraint during in. duction. The calves subsided to the ground when between one-fifth and onethird of the final dose had been given. Four calves exhibited expiratory groaning during the operation and one continued to do so afterwards. Handling of the spleen provoked decreased heart rates in three calves, with marked loss offorce in one. Diphasic respiration was recorded at the completion of the operation in three calves. There was little effect on respiratory rates when anaesthesia (mean 26) and splenectomy (mean 26) were completed. Pulse rates increased at completion of anaesthesia (mean I 72) and showed a slight decrease by completion of splenectomy (mean 162). In three calves the eye reflexes disappeared before light anaesthesia was attained, although the ear pinch stimulated a refle.l_{. All ten calves took their 4 p.m. milk feed. One calf still exhibited an unsteady gait at 24 hours. ( 7) Diethylthiambutene hydrochloride and thiopentone sodium All ten calves subsided to the ground o to I 20 seconds after completion of thiambutene injection and a pause of 3 minutes was allowed before thiopentone induction was begun. If the animals were allowed to sit up they remained quiet, but, with one exception, they resisted restriction in the lateral position and some bellowed. Total induction time with thiopentone was 5 to IO minutes (mean 6·3 minutes). Respiratory rates increased following the thiambutene injection (mean 35), slowed by the time anaesthesia by thiopentone was completed (mean 29), and increased by the time splenectomy was completed (mean 36). Pulse rates increased following thiambutene injection (mean I 53), showed further increase by completion of anaesthesia (mean I6I ), but slowed again by completion of
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splenectomy (mean 145). Four calves temporarily showed marked diphasic expiratory effort at full anaesthesia. Calf no. 62, although judged satisfactorily anaesthetized by assessment of reflexes, showed strong leg movements when the abdominal muscles were incised, and yet adequate relaxation followed without more thiopentone. Calf no. 65 reacted similarly, received more thiopentone, and exhibited occasional periods of expiratory groaning during surgery. Half to 2 hours after completion of splenectomy it made excited efforts to raise its head, its respiration was stertorous and it had to be restrained manually. Calf no. 70 died 24 hours after splenectomy, having shown little lightening of anaesthesia. Soon after thiopentone anaesthesia was completed the pulse rose to a rate impossible to count, slowed, nearly stopped, and then increased again. This was immediately followed by apnoea which responded to intravenous nikethamide and artificial respiration. After a few inspiratory efforts there was a second failure for nearly a minute before further nikethamide induced respiration. Splenectomy followed without further crisis. Four hours later there were signs of reflex activity returning, but from this point there was no improvement despite attempted resuscitation. Autopsy revealed no abnormality to account for anaesthetic intolerance. The other calves took their 4 p.m. feed, but one calf was still unsteady at 24 hours.
(8) Promazine 4ydrochloride and thiopentone sodium Promazine chloride as a 1 per cent solution was injected in two minutes and thiopentone followed after a pause of 3 minutes. Total induction time varied from 6 to 15 minutes (mean 8·8 minutes). After the promazine injection seven calves remained standing. These subsided to the ground when one-third to one-half the total dose had been injected. Respiratory rates were little affected by the promazine premedication (mean 25); they increased by the time anaesthesia with thiopentone was completed (mean 35) and showed little change when splenectomy was completed (mean 36). Pulse rates were moderately increased by the promazine premedication (mean 122) and again by the completion of anaesthesia (mean 152) but started to decrease when splenectomy was completed (mean 145). Calf no. 72 showed diphasic respiration following promazine injection and a period of apnoea lasting ten seconds in which cardiac function became almost imperceptible, during thiopentone induction and again when the spleen was handled. Calf no. 76 exhibited a temporary slowing of the heart rate when the spleen was handled, and this was followed by "thumping" heart beats for two minutes. Calf no. 8o showed apnoea when three-quarters of the final dose of thiopentone had been given. Respiration was re-established a minute later on administration of nikethamide and artificial respiration. During handling of the spleen there was a further short period of apnoea and very weak cardiac function which responded to a further injection of nikethamide. There were two deaths during anaesthesia. In calf no. 75, whose pulse had become almost imperceptible when the spleen was ligated, anaesthesia
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appeared to be lightening satisfactorily an hour after the operation, but the animal died one hour later. Autopsy showed no factor likely to contribute to anaesthetic intolerance. In calf no. 78, in which respiration was shallow during splenectomy, anaesthesia appeared to be lightening satisfactorily one hour after completion of the operation, but the animal died half an hour later. Autopsy revealed enteritis and two myocardial lesions which might have contributed to anaesthetic intolerance. The order in which reflexes disappeared varied in these calves, making assessment of anaesthesia difficult.
(g) Chloral hydrate and thiopentone sodium Induction with chloral hydrate took 2 to 5 minutes, using 53 to 75 per cent of the dose necessary for anaesthesia with chloral hydrate alone. All calves subsided quietly to the ground when between 40 and 70 per cent of the estimated full dose had been given. After a three-minute wait, thiopentone solution was injected in 3 to 8 minutes. Respiratory rates rose by the time chloral hydrate narcosis was completed (mean 45), fell again when anaesthesia with thiopentone sodium was completed (mean 38), and rose again by the end of splenectomy (mean 47). Pulse rate was increased by the time chloral hydrate narcosis was completed (mean I6o) and continued to rise until the completion of anaesthesia by thiopentone sodium (mean I 9 I). In seven calves the pulse rate had dropped by the end of splenectomy (mean I 6o). Assessment of the depth of anaesthesia by reflex activity was difficult. For instance, calf no. 77 had lost eye and ear-pinch reflexes before even light anaesthesia~ had been achieved. In calf no. 7 I eye reflexes disappeared long before that from the ear pinch. During transition from light to medium anaesthesia two calves exhibited groaning respiration. There was a tendency to excessive haemorrhage at the operation site during surgical interference. All calves took their 4 p.m. milk feed and were bright and steady at 24 hours. (I o) Chloral hydrate, primary rapid induction Two-thirds of the estimated full dose of chloral hydrate necessary to produce anaesthesia at the normal speed of injection (I76 mg./kg.) (Wilde, Ig62) was administered in I5 to 30 seconds (mean 24 seconds). After a 3- to 5-minute wait, induction was continued slowly until satisfactory anaesthesia was attained. The mean primary dose was 68 per cent of the mean total dose. All calves subsided to the ground 10 to 30 seconds after the primary rapid injection. Nine calves could only be considered narcotized 3 to 5 minutes later, the ear pinch provoking violent muscular movement. Pressure on the ventral aspect of the tongue usually induced jaw movements. In calf no. 97 and calf no. gg, two minutes after completion of the primary rapid injection, respiration became stertorous and heart rate slowed to 30 and 40 respectively, cardiac function becoming scarcely perceptible by palpation of the thoracic wall. In both cases nikethamide provoked an immediate response. Chloral hydrate was then given slowly until satisfactory anaesthesia was obtained.
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In calf no. 97 this was not until after ligation of the splenic vessels. An initial, markedly increased respiratory rate during injection, slowed to give a mean rate of 50 at the completion of anaesthesia. A further decrease by the completion of the operation gave a mean figure of 45· Pulse rate at the start of the operation was increased (mean I57) but insufficient figures were recorded to give a mean rate at the completion of surgical interference. Haemorrhage during surgical interference was minimal. All ten calves took their 4 p.m. feed and were bright and steady at 24 hours.
Other techniques It was intended to use methohexital sodium (Brevane, Corn States Laboratories), but initial results in 5 calves given 9 to I 2 ·2 mg. /kg. as a 2 ·s per cent solution were so unsatisfactory that the series was discontinued. During induction there were marked muscular spasms and only a short, light anaesthesia was obtained, lasting 3 to IO minutes. These results contrast with those of Robertshaw (I964), who was using older and larger calves. Evidently the necessary dose rate rises rapidly in very young animals. Results following intravenous injection of phencyclidine (Sernylan, Parke Davis & Co.) were unsatisfactory and no further attempts were made to assess its value. In all, 93 calves weighing 28 ·2 to 57 ·3 kg. were anaesthetized with the standard technique (Wilde, I962) on the same days as those in the ten groups of ten recorded above. The mean dose rate of chloral hydrate used was I 89 mg./kg. with a range of I24 to 27I mg. /kg. Two deaths occurred during anaesthesia. CONCLUSION
Chloral hydrate anaesthesia proved superior to all the others tested in respect of ease of induction, absence of haemorrhage, recovery, safety and cost. Thiopentone sodium was considered to be the second best. ACKNOWLEDGEMENTS
The technical assistance of Mr. W. G. Revil is gratefully acknowledged. Thanks are due to Dr. J. K. H. Wilde and Miss M. E. Watts for assistance in the preparation of this paper. REFERENCES
BRoWN, C. G. D. (1963) . Bull. epi;:oot. Dis. Ajr., n, 23. RoBERTSHAW, D. (1964). Vet. Rec., 76, 13, 357· WILDE, J. K. H. ( 1962). Br. vet. J., :u8, 206. (Accepted for publication 8 October, 1965)