- Email: [email protected]
STEROID ANAESTHESIA FIVE YEARS ON
73.
STEROID ANAESTHESIA FIVE YEARS ON
J. M. Evans, GLAXOVET LIMITED, GREENFORD, MIDDLESEX
Usaqe and Benefits of Steroid Anaesthesia Information gleaned by Dodman (1977) as a result of a BSAVA Regional exercise showed that the steroid anaesthetic "Saffan"*, is used in cats as an induction agent by some 63% of veterinary surgeons and that 52% of practitioners use it for the maintenance of anaesthesia.
From our records
we calculate that currently about 30,000 cats are anaesthetised with "Saffan" each month.
There is no doubt therefore that
within the relatively short period of time since its launch in 1972 the anaesthetic has become extremely popular in feline practice.
The success of the anaesthetic in this
respect probably stems f r o m five important characteristics. 1.
The extremely high therapeutic index of at least three to one means that it is virtually fail-safe.
In
practical terms veterinary surgeons will be unable to kill the average healthy cat unless it is approached with a 10 ml syringe full of anaesthetic; a most unlikely situation. 2.
Lack of cumulation means that it can be safely used to maintain
anaesthesia without unduly prolonging
recovery and without fear of toxicity.
* Glaxovet Limited, Greenford, Middlesex
74.
3.
Complete recovery and r a p i d r e t u r n t o a p p e t i t e . I n p r a c t i c a l t e r m s t h i s b e n e f i t means less c l u t t e r e d recovery cages and c a u s e s owners less concern.
4.
Good muscle r e l a x a t i o n and l i t t l e r e s p i r a t o r y depression. The f a c t t h a t c a t s b r e a t h e normally w i t h f u l l expansion and c o n t r a c t i o n of t h e c h e s t d u r i n g a n a e s t h e s i a and t h a t t h e r e i s good muscle r e l a x a t i o n means t h a t v e t e r i n a r y surgeons can r e l a x and a r e t h e r e f o r e more l i k e l y t o be a b l e t o c o n c e n t r a t e on t h e s u r g i c a l procedures i n hand.
5.
Lack of l o c a l i r r i t a n c y and subcutaneous a c t i v i t y makes it p o s s i b l e t o d i s r e g a r d i n a d v e r t e n t p e r i v a s c u l a r i n j e c t i o n a s f a r a s sloughing o r t h e e f f e c t on subsequent d o s e s a r e concerned. A l l t h e s e p r o p e r t i e s a r e i n marked c o n t r a s t t o
t h i o p e n t o n e which was t h e s t a n d a r d i n d u c t i o n agent f o r c a t s b e f o r e "Saffan" was launched and d o u b t l e s s t h e y a r e t h e major reasons f o r v e t e r i n a r y surgeons changing t o , and s t a y i n g w i t h , t h e s t e r o i d a n a e s t h e t i c . Problems Associated w i t h S t e r o i d Anaesthesia (a)
General S i d e - E f f e c t s Of course t h e usual side-effects
of u r i n a t i o n ,
d e f e c a t i o n , muscle tremor, paddling d u r i n g recovery and s a l i v a t i o n have been r e p o r t e d , b u t t h e s e s e e m t o occur no more f r e q u e n t l y t h a n w i t h o t h e r a n a e s t h e t i c s .
75.
(b) Oedema/Hyperaemia It is known that oedema, or hyperaemia, of the ears and feet occurs in a percentage of cats.
Despite an
in-depth investigation during which the rate of administration, breeds of cat, type of syringe used and many other factors were looked at, it was not possible to identify why some veterinary surgeons encounter this more frequently than others. Currently, it has to be accepted that this side-effect results from an individual idiosyncracy in some cats to some ingredient in the product.
Because such cats cannot be
identified in advance, it is recommended that if a veterinary surgeon is seeing a lot of cats that react in this way, and needs to operate on paws or ears, then a premedicant dose of an antihistamine should be given before induction.
There is
no doubt that it would be preferable if this effect did not occur but the current informed opinion is that generally it is without clinical significance. (c) Deaths/Respiratory Failure Because it is well known and accepted that deaths can result from the use of barbiturates, often the anaesthetic agent is blamed by veterinary surgeons for a death without some lateral thought as to other possible causes.
"Saffan" may similarly be blamed without the real
cause coming to mind.
Occasionally we receive unsolicited
cadavers through the post with a cryptic note saying "Please establish why this cat died as a result of "Saffan" administration".
Quite often this is despite the fact
76.
that other agents have been given in conjunction with the steroid anaesthetic.
Most frequently, no post-mortem
has been carried out in the surgery and usually we find very obvious causes of death such as gross abdominal haemorrhage
and ruptured diaphragms, in no way related
to the anaesthetic agent,
that anaesthetic supplements
have been inappropriately used, or recommended dosages have not be given.
There is no doubt a need to educate
veterinary surgeons to look for other reasons for apparent anaesthetic deaths and to be critical of their technique before they apportion blame.
This is particularly
in respect of respiratory failure.
SO
Veterinary surgeons
may blame the induction agent when in fact respiratory failure has been brought about by poor intubation techniques or because some underlying lung pathology has affected lung compliance under anaesthesia.
The use of inappropriate
anaesthetic machines or anaesthetic circuits has also been identified, following an in-depth investigation, as the cause of problems. Cases of respiratory arrest reputely associated with lung oedema have been reported, though it must be emphasised that such diagnoses are based simply on clinical observation and are mostly unsupported by necropsy findings. An analysis of our records of adverse reactions reveal that to date we have had 189 cases reported to us in sufficient detail to make an analysis of the cause possible.
Of these,
rather less than one-third are related to respiratory problems and in less than half of these (30 cases) was lung oedema suspected or confirmed histologically.
A
picture surely that is hardly commensurate with a product which is the cause of such a problem.
A closer look
77 *
at the reports indicates further that they stem from a very few practitioners, indicating that it may well be an administration or administrator associated problem. Apart from this, cats medicated for long term toxicity studies have not shown such changes and neither have those which have received large amounts of the anaesthetic by intermittent injection; sometimes as much as 300 mg per kg has been given (Hall (1976).
It
is obvious, therefore, that more attention should be paid to the other causes of lung oedema and respiratory embarrassment which are listed below, since they are much more likely to be at the root of the problem (Table I).
The first four items are well recognised by
veterinary anaesthetists but nevertheless need explanation and emphasising to veterinary surgeons in practice.
The
remaining two possible causes necessitate further comment since they have been recognised only comparatively recently. Table I Possible Causes of Respiratory Embarrassment/Lunq Oedema Obstruction of the airway Fear Pre-existing lung lesions: parasitic, viral, bacterial, neoplastic Fat embolism Neurogenic pulmonary oedema A primed complement system
78.
( i ) Neuroqenic Pulmonary Oedema I t h a s been shown i n man and e x p e r i m e n t a l a n i m a l s
t h a t b r a i n damage a s s o c i a t e d w i t h head wounds o r anoxia can c a u s e a massive c e n t r a l l y - m e d i a t e d discharge.
sympathetic
T h i s can r e s u l t i n a s h i f t of blood from
t h e h i g h r e s i s t a n c e s y s t e m i c c i r c u l a t i o n t o t h e low r e s i s t a n c e pulmonary c i r c u l a t i o n .
Marked i n c r e a s e s
i n pulmonary v a s c u l a r p r e s s u r e and r e s u l t leading t o lung
oedema
pulmonary blood volume
because of t h e h y d r o s t a t i c
e f f e c t of i n c r e a s e d pulmonary c a p i l l a r y p r e s s u r e . (Theodore and Robin ( 1 9 7 6 ) , Moss ( 1 9 7 4 ) ) .
I t i s possible
t o t h e o r i s e t h a t a s a r e s u l t of v e r y r a p i d i n j e c t i o n , any intravenous agent, including t h e s t e r o i d a n a e s t h e t i c "Saffan" could remain a s a b o l u s i n t h e c i r c u l a t i o n and b r i n g about such n e u r a l damage i n chance c i r c u m s t a n c e s . I t i s however, more l i k e l y t h a t temporary anoxia
connected w i t h problems a t i n d u c t i o n , and p o s s i b l y associated with intubation, o r a s a
r e s u l t of r e b r e a t h i n g ,
w i l l be t h e c a u s e of such an o c c u r r e n c e .
This i s a
r e l a t i v e l y new s u b j e c t and w e c e r t a i n l y do n o t know how f r e q u e n t l y i t o c c u r s , b u t it i s worthwhile b e a r i n g such a p o s s i b i l i t y i n mind when a c a s e of r e s p i r a t o r y a r r e s t i n c a t s occurs.
( i i ) Primed Complement S y s t e m R e c e n t l y some human a n a e s t h e t i s t s have drawn a t t e n t i o n t o t h e f a c t t h a t immunopathological c o n d i t i o n s i n v o l v i n g c i r c u l a t o r y immune complexes, a s can occur i n c h r o n i c i n f e c t i o n s , may prime complement systems making them s u s c e p t i b l e t o a c t i v a t i o n by any i n t r a v e n o u s l y a d m i n i s t e r e d
79.
compound.
(Watkins, Padfield and Alderson (1978)).
The
subsequent anaphylactoid response could cause lung lesions and lead to pulmonary oedema, a situation that
is not
appreciated generally and particularly by veterinary surgeons in practice. Prevention of Problems In the light of all the factors mentioned previously some 'rule of thumb' procedures are suggested below (Table 2) which if followed are likely to lead to even safer anaesthesia in the average practice situation. Table 2 Advocated Procedure for those not Familiar with Steroid Anaesthesia 1.
Dose to effect.
2.
Only use intracheal tubes for dental operations and where positive pressure ventilation is required.
3.
When tubes are used: (a) Take care to use correct size and length (b) Avoid use of detergents, including centrimide and other quaternary ammonium compounds, to clean intracheal tubes. (c) Don't 'overspray' the larynx.
4.
Use an anesthetic machine and circuit appropriate to cats if anaesthesia is to be maintained with gaseous anaesthetics.
5.
If possible, treat chronic infections before an
anaesthetic is given. 6.
Tranquillise excited or fearful cats before anaesthesia
is induced. 7.
Observe and care for cats during recovery.
80.
To put the occurrence of problems into context it has to be said that the incidence of side-effects, bearing in mind the extremely large usage of the product, is really minimal.
Even if all the reported deaths are taken as
being due to the administration of the steroid anaesthetic, the mortality rate is of the order of 1 in 10,000 cats anaesthetised. There is no doubt that this represents a real improvement and a positive advantage to veterinary surgeons in practice.
In short, the introduction of steroid
anaesthesia has offered many advantages to the veterinary surgeon in practice and indeed overall it has made anaesthetising cats a much safer procedure.
Steroid
anaesthesia goes a long way towards taking the 'worry out of anaesthesia' but it is important to realise that it does not remove the responsibility.
It behoves those who have charge
of cats under such circumstances to ensure that animals are properly observed and cared for during induction, anaesthesia, and importantly during the recovery period.
No matter
how safe an anaesthetic is, if the basic care of animals under anaesthesia is neglected then deaths will occur. Intramuscular Injection It is well known that some difficulties were encountered during the original clinical investigation with this route of administration. However, now more and more veterinary surgeons are adopting the technique of giving the product by 'infusion' into the quadriceps muscle mass, fewer difficulties are being reported. Despite this
81.
p o s s i b l e usage of t h e p r o d u c t , t h e r e i s no doubt t h a t t h e prime r o l e of "Saffan" i s a s an i n t r a v e n o u s i n d u c t i o n a g e n t o r a s a t o t a l a n a e s t h e t i c u s i n g an i n c r e m e n t a l dosage technique. More Recent I n f o r m a t i o n (a)
Safety Recent work h a s confirmed t h e wide t h e r a p e u t i c i n d e x of
"Saffan".
I n a recent study t o re-evaluate acute
i n t r a v e n o u s t o x i c i t y i n c a t s , no a n i m a l s were k i l l e d i n t h e group when u s i n g d o s e s of 27 mg p e r kilogram o r less.
In
f a c t t h e LD50 was c a l c u l a t e d a s b e i n g 36 mg p e r kilogram. (b)
Dose Dependence I n t e r e s t i n g l y t o o , t h e s e s t u d i e s showed t h a t t h e
d u r a t i o n of a n a e s t h e s i a was d o s e dependent b u t o n l y up t o 18 mg p e r k i l o g r a m a f t e r which a p l a t e a u was r e a c h e d , t h u s t h e r e i s no r a t i o n a l e f o r g i v i n g more t h a n 18 mg p e r k i l o g r a m a s a s i n g l e dosage. (c)
A d m i n i s t r a t i o n t o Doqs Perhaps more i n t e r e s t i n g i s t h e work r e p o r t e d by
C o r b e t t (1977) i n A u s t r a l i a i n r e s p e c t of t h e u s e of "Saf f a n " i n dogs. A l l t h e genus Canis show a d o s e r e l a t e d a n a p h y l a c t o i d
t y p e of r e a c t i o n t o s u r f a c t a n t s s u c h a s Cremophor EL, a c o n s t i t u e n t of t h e v e h i c l e used i n "Saffan".
Dr.
Corbett
h a s d e v i s e d a p r a c t i c a l regime which overcomes t h i s problem u s i n g a premedicant m i x t u r e of acepromazine and c h l o r p h e n i r a m i n e b e f o r e "Saffan" i s a d m i n i s t e r e d .
If t h i s
p r o c e d u r e is f o l l o w e d he c l a i m s t h a t i n d u c t i o n is p l e a s a n t ,
82.
anaesthesia is of good quality and recovery is rapid and quiet.
The method is considered to be particularly
advantageous in breeds such as Greyhounds, Afghans and the like, and in the caesarian section case; all indications where barbiturates can present problems.
The
rapid, smooth and complete recovery that he obtains allows him, he claims, to continue operating until later in the afternoon and yet still return animals to their owners that day. The Future (a) Other Species More and more experience is being gained concerning the use of steroid anaesthesia in many species other than the cat and the agent is providing a useful addition to the veterinary surgeon's armamentarium. There is, however, still some work to be done in a number of areas to identify the best dosage regimes and methods of administration. addition more information is required
In
in respect of the
possibility of combining the steroid anaesthetic with other agents. Infusion Techniques Because of the concern over atmospheric pollution with anaesthetic gases there seems to be a small but perceptible swing back from gaseous to intravenous anaesthetics.
It is a real possibility (especially in view
of this particular concern, the safety of steroid anaesthesia, the availability of motor driven syringes and the escalating cost of maintaining Boyles machines) that intravenous infusion techniques to maintain anaesthesia at a level
83.
pre-determined by t h e surgeon a s i s done r o u t i n e l y i n l a b o r a t o r i e s , w i l l come t o v e t e r i n a r y p r a c t i c e i n t h e near f u t u r e .
The method i s s i m p l e and c o n s e r v i n g i n
r e s p e c t of t h e amount of a n a e s t h e t i c used.
I t would
seem most l i k e l y t h a t a n i m a l s w i l l be induced w i t h an i n t r a v e n o u s d o s e of a s t e r o i d a n a e s t h e t i c and t h e n immediately connected t o a motorised s y r i n g e p r e f i l l e d w i t h a d i l u t e d volume of a n a e s t h e t i c .
This apparatus
would be f i t t e d w i t h a l e v e r which could be a d j u s t e d t o c o n t r o l t h e speed of d e l i v e r y t o g i v e t h e r e q u i r e d d e p t h of a n a e s t h e s i a a s t h e o p e r a t i o n p r o g r e s s e s .
A l l
t h a t i s needed i s a l i t t l e c a p i t a l i n v e s t m e n t and t h e courage t o adopt a new t e c h n i q u e . Conclusion The advent of s t e r o i d a n a e s t h e t i c h a s no doubt made a s i g n i f i c a n t impact on s m a l l animal p r a c t i c e and r e p r e s e n t s a major advance i n a n a e s t h e s i a i n v e t e r i n a r y practice.
Doubtless i t i s h e r e t o s t a y and i n t i m e
newer and even b e t t e r compounds w i l l be d i s c o v e r e d and u t i l i s e d t o advantage i n b o t h human and v e t e r i n a r y medicine.
84.
REFERENCES
CORBETT, H. ( 1 9 7 7 ) . 184-188.
Australian Practitioner,
2,
DODMAN N. ( 1 9 7 7 ) .
The U s e of "Saf f a n " i n t h e C a t . J o u r n a l of S m a l l Animal P r a c t i c e , 18, 653-658. ' F e l i n e Anaesthesia Survey'.
HALL, L. ( 1 9 7 6 ) . 17, 661-668. MOSS,
G.
(1974).
J o u r n a l of Small Animal P r a c t i c e , 'Prolonged A n a e s t h e s i a ' . Hospital Practice
THEODORE, J. and R O B I N , E.D. of R e s p i r a t o r y D i s e a s e ,
9.
77-86.
(1976). American Review 405-411.
113,
WATKINS, J . , PADFIELD, A. and ALDERSON, J . D . , B r i t i s h M e d i c a l J o u r n a l , 1, 1180-1181.
(1978).
STEROID ANAESTHESIA FIVE YEARS ON
J. M. Evans, GLAXOVET LIMITED, GREENFORD, MIDDLESEX
Usaqe and Benefits of Steroid Anaesthesia Information gleaned by Dodman (1977) as a result of a BSAVA Regional exercise showed that the steroid anaesthetic "Saffan"*, is used in cats as an induction agent by some 63% of veterinary surgeons and that 52% of practitioners use it for the maintenance of anaesthesia.
From our records
we calculate that currently about 30,000 cats are anaesthetised with "Saffan" each month.
There is no doubt therefore that
within the relatively short period of time since its launch in 1972 the anaesthetic has become extremely popular in feline practice.
The success of the anaesthetic in this
respect probably stems f r o m five important characteristics. 1.
The extremely high therapeutic index of at least three to one means that it is virtually fail-safe.
In
practical terms veterinary surgeons will be unable to kill the average healthy cat unless it is approached with a 10 ml syringe full of anaesthetic; a most unlikely situation. 2.
Lack of cumulation means that it can be safely used to maintain
anaesthesia without unduly prolonging
recovery and without fear of toxicity.
* Glaxovet Limited, Greenford, Middlesex
74.
3.
Complete recovery and r a p i d r e t u r n t o a p p e t i t e . I n p r a c t i c a l t e r m s t h i s b e n e f i t means less c l u t t e r e d recovery cages and c a u s e s owners less concern.
4.
Good muscle r e l a x a t i o n and l i t t l e r e s p i r a t o r y depression. The f a c t t h a t c a t s b r e a t h e normally w i t h f u l l expansion and c o n t r a c t i o n of t h e c h e s t d u r i n g a n a e s t h e s i a and t h a t t h e r e i s good muscle r e l a x a t i o n means t h a t v e t e r i n a r y surgeons can r e l a x and a r e t h e r e f o r e more l i k e l y t o be a b l e t o c o n c e n t r a t e on t h e s u r g i c a l procedures i n hand.
5.
Lack of l o c a l i r r i t a n c y and subcutaneous a c t i v i t y makes it p o s s i b l e t o d i s r e g a r d i n a d v e r t e n t p e r i v a s c u l a r i n j e c t i o n a s f a r a s sloughing o r t h e e f f e c t on subsequent d o s e s a r e concerned. A l l t h e s e p r o p e r t i e s a r e i n marked c o n t r a s t t o
t h i o p e n t o n e which was t h e s t a n d a r d i n d u c t i o n agent f o r c a t s b e f o r e "Saffan" was launched and d o u b t l e s s t h e y a r e t h e major reasons f o r v e t e r i n a r y surgeons changing t o , and s t a y i n g w i t h , t h e s t e r o i d a n a e s t h e t i c . Problems Associated w i t h S t e r o i d Anaesthesia (a)
General S i d e - E f f e c t s Of course t h e usual side-effects
of u r i n a t i o n ,
d e f e c a t i o n , muscle tremor, paddling d u r i n g recovery and s a l i v a t i o n have been r e p o r t e d , b u t t h e s e s e e m t o occur no more f r e q u e n t l y t h a n w i t h o t h e r a n a e s t h e t i c s .
75.
(b) Oedema/Hyperaemia It is known that oedema, or hyperaemia, of the ears and feet occurs in a percentage of cats.
Despite an
in-depth investigation during which the rate of administration, breeds of cat, type of syringe used and many other factors were looked at, it was not possible to identify why some veterinary surgeons encounter this more frequently than others. Currently, it has to be accepted that this side-effect results from an individual idiosyncracy in some cats to some ingredient in the product.
Because such cats cannot be
identified in advance, it is recommended that if a veterinary surgeon is seeing a lot of cats that react in this way, and needs to operate on paws or ears, then a premedicant dose of an antihistamine should be given before induction.
There is
no doubt that it would be preferable if this effect did not occur but the current informed opinion is that generally it is without clinical significance. (c) Deaths/Respiratory Failure Because it is well known and accepted that deaths can result from the use of barbiturates, often the anaesthetic agent is blamed by veterinary surgeons for a death without some lateral thought as to other possible causes.
"Saffan" may similarly be blamed without the real
cause coming to mind.
Occasionally we receive unsolicited
cadavers through the post with a cryptic note saying "Please establish why this cat died as a result of "Saffan" administration".
Quite often this is despite the fact
76.
that other agents have been given in conjunction with the steroid anaesthetic.
Most frequently, no post-mortem
has been carried out in the surgery and usually we find very obvious causes of death such as gross abdominal haemorrhage
and ruptured diaphragms, in no way related
to the anaesthetic agent,
that anaesthetic supplements
have been inappropriately used, or recommended dosages have not be given.
There is no doubt a need to educate
veterinary surgeons to look for other reasons for apparent anaesthetic deaths and to be critical of their technique before they apportion blame.
This is particularly
in respect of respiratory failure.
SO
Veterinary surgeons
may blame the induction agent when in fact respiratory failure has been brought about by poor intubation techniques or because some underlying lung pathology has affected lung compliance under anaesthesia.
The use of inappropriate
anaesthetic machines or anaesthetic circuits has also been identified, following an in-depth investigation, as the cause of problems. Cases of respiratory arrest reputely associated with lung oedema have been reported, though it must be emphasised that such diagnoses are based simply on clinical observation and are mostly unsupported by necropsy findings. An analysis of our records of adverse reactions reveal that to date we have had 189 cases reported to us in sufficient detail to make an analysis of the cause possible.
Of these,
rather less than one-third are related to respiratory problems and in less than half of these (30 cases) was lung oedema suspected or confirmed histologically.
A
picture surely that is hardly commensurate with a product which is the cause of such a problem.
A closer look
77 *
at the reports indicates further that they stem from a very few practitioners, indicating that it may well be an administration or administrator associated problem. Apart from this, cats medicated for long term toxicity studies have not shown such changes and neither have those which have received large amounts of the anaesthetic by intermittent injection; sometimes as much as 300 mg per kg has been given (Hall (1976).
It
is obvious, therefore, that more attention should be paid to the other causes of lung oedema and respiratory embarrassment which are listed below, since they are much more likely to be at the root of the problem (Table I).
The first four items are well recognised by
veterinary anaesthetists but nevertheless need explanation and emphasising to veterinary surgeons in practice.
The
remaining two possible causes necessitate further comment since they have been recognised only comparatively recently. Table I Possible Causes of Respiratory Embarrassment/Lunq Oedema Obstruction of the airway Fear Pre-existing lung lesions: parasitic, viral, bacterial, neoplastic Fat embolism Neurogenic pulmonary oedema A primed complement system
78.
( i ) Neuroqenic Pulmonary Oedema I t h a s been shown i n man and e x p e r i m e n t a l a n i m a l s
t h a t b r a i n damage a s s o c i a t e d w i t h head wounds o r anoxia can c a u s e a massive c e n t r a l l y - m e d i a t e d discharge.
sympathetic
T h i s can r e s u l t i n a s h i f t of blood from
t h e h i g h r e s i s t a n c e s y s t e m i c c i r c u l a t i o n t o t h e low r e s i s t a n c e pulmonary c i r c u l a t i o n .
Marked i n c r e a s e s
i n pulmonary v a s c u l a r p r e s s u r e and r e s u l t leading t o lung
oedema
pulmonary blood volume
because of t h e h y d r o s t a t i c
e f f e c t of i n c r e a s e d pulmonary c a p i l l a r y p r e s s u r e . (Theodore and Robin ( 1 9 7 6 ) , Moss ( 1 9 7 4 ) ) .
I t i s possible
t o t h e o r i s e t h a t a s a r e s u l t of v e r y r a p i d i n j e c t i o n , any intravenous agent, including t h e s t e r o i d a n a e s t h e t i c "Saffan" could remain a s a b o l u s i n t h e c i r c u l a t i o n and b r i n g about such n e u r a l damage i n chance c i r c u m s t a n c e s . I t i s however, more l i k e l y t h a t temporary anoxia
connected w i t h problems a t i n d u c t i o n , and p o s s i b l y associated with intubation, o r a s a
r e s u l t of r e b r e a t h i n g ,
w i l l be t h e c a u s e of such an o c c u r r e n c e .
This i s a
r e l a t i v e l y new s u b j e c t and w e c e r t a i n l y do n o t know how f r e q u e n t l y i t o c c u r s , b u t it i s worthwhile b e a r i n g such a p o s s i b i l i t y i n mind when a c a s e of r e s p i r a t o r y a r r e s t i n c a t s occurs.
( i i ) Primed Complement S y s t e m R e c e n t l y some human a n a e s t h e t i s t s have drawn a t t e n t i o n t o t h e f a c t t h a t immunopathological c o n d i t i o n s i n v o l v i n g c i r c u l a t o r y immune complexes, a s can occur i n c h r o n i c i n f e c t i o n s , may prime complement systems making them s u s c e p t i b l e t o a c t i v a t i o n by any i n t r a v e n o u s l y a d m i n i s t e r e d
79.
compound.
(Watkins, Padfield and Alderson (1978)).
The
subsequent anaphylactoid response could cause lung lesions and lead to pulmonary oedema, a situation that
is not
appreciated generally and particularly by veterinary surgeons in practice. Prevention of Problems In the light of all the factors mentioned previously some 'rule of thumb' procedures are suggested below (Table 2) which if followed are likely to lead to even safer anaesthesia in the average practice situation. Table 2 Advocated Procedure for those not Familiar with Steroid Anaesthesia 1.
Dose to effect.
2.
Only use intracheal tubes for dental operations and where positive pressure ventilation is required.
3.
When tubes are used: (a) Take care to use correct size and length (b) Avoid use of detergents, including centrimide and other quaternary ammonium compounds, to clean intracheal tubes. (c) Don't 'overspray' the larynx.
4.
Use an anesthetic machine and circuit appropriate to cats if anaesthesia is to be maintained with gaseous anaesthetics.
5.
If possible, treat chronic infections before an
anaesthetic is given. 6.
Tranquillise excited or fearful cats before anaesthesia
is induced. 7.
Observe and care for cats during recovery.
80.
To put the occurrence of problems into context it has to be said that the incidence of side-effects, bearing in mind the extremely large usage of the product, is really minimal.
Even if all the reported deaths are taken as
being due to the administration of the steroid anaesthetic, the mortality rate is of the order of 1 in 10,000 cats anaesthetised. There is no doubt that this represents a real improvement and a positive advantage to veterinary surgeons in practice.
In short, the introduction of steroid
anaesthesia has offered many advantages to the veterinary surgeon in practice and indeed overall it has made anaesthetising cats a much safer procedure.
Steroid
anaesthesia goes a long way towards taking the 'worry out of anaesthesia' but it is important to realise that it does not remove the responsibility.
It behoves those who have charge
of cats under such circumstances to ensure that animals are properly observed and cared for during induction, anaesthesia, and importantly during the recovery period.
No matter
how safe an anaesthetic is, if the basic care of animals under anaesthesia is neglected then deaths will occur. Intramuscular Injection It is well known that some difficulties were encountered during the original clinical investigation with this route of administration. However, now more and more veterinary surgeons are adopting the technique of giving the product by 'infusion' into the quadriceps muscle mass, fewer difficulties are being reported. Despite this
81.
p o s s i b l e usage of t h e p r o d u c t , t h e r e i s no doubt t h a t t h e prime r o l e of "Saffan" i s a s an i n t r a v e n o u s i n d u c t i o n a g e n t o r a s a t o t a l a n a e s t h e t i c u s i n g an i n c r e m e n t a l dosage technique. More Recent I n f o r m a t i o n (a)
Safety Recent work h a s confirmed t h e wide t h e r a p e u t i c i n d e x of
"Saffan".
I n a recent study t o re-evaluate acute
i n t r a v e n o u s t o x i c i t y i n c a t s , no a n i m a l s were k i l l e d i n t h e group when u s i n g d o s e s of 27 mg p e r kilogram o r less.
In
f a c t t h e LD50 was c a l c u l a t e d a s b e i n g 36 mg p e r kilogram. (b)
Dose Dependence I n t e r e s t i n g l y t o o , t h e s e s t u d i e s showed t h a t t h e
d u r a t i o n of a n a e s t h e s i a was d o s e dependent b u t o n l y up t o 18 mg p e r k i l o g r a m a f t e r which a p l a t e a u was r e a c h e d , t h u s t h e r e i s no r a t i o n a l e f o r g i v i n g more t h a n 18 mg p e r k i l o g r a m a s a s i n g l e dosage. (c)
A d m i n i s t r a t i o n t o Doqs Perhaps more i n t e r e s t i n g i s t h e work r e p o r t e d by
C o r b e t t (1977) i n A u s t r a l i a i n r e s p e c t of t h e u s e of "Saf f a n " i n dogs. A l l t h e genus Canis show a d o s e r e l a t e d a n a p h y l a c t o i d
t y p e of r e a c t i o n t o s u r f a c t a n t s s u c h a s Cremophor EL, a c o n s t i t u e n t of t h e v e h i c l e used i n "Saffan".
Dr.
Corbett
h a s d e v i s e d a p r a c t i c a l regime which overcomes t h i s problem u s i n g a premedicant m i x t u r e of acepromazine and c h l o r p h e n i r a m i n e b e f o r e "Saffan" i s a d m i n i s t e r e d .
If t h i s
p r o c e d u r e is f o l l o w e d he c l a i m s t h a t i n d u c t i o n is p l e a s a n t ,
82.
anaesthesia is of good quality and recovery is rapid and quiet.
The method is considered to be particularly
advantageous in breeds such as Greyhounds, Afghans and the like, and in the caesarian section case; all indications where barbiturates can present problems.
The
rapid, smooth and complete recovery that he obtains allows him, he claims, to continue operating until later in the afternoon and yet still return animals to their owners that day. The Future (a) Other Species More and more experience is being gained concerning the use of steroid anaesthesia in many species other than the cat and the agent is providing a useful addition to the veterinary surgeon's armamentarium. There is, however, still some work to be done in a number of areas to identify the best dosage regimes and methods of administration. addition more information is required
In
in respect of the
possibility of combining the steroid anaesthetic with other agents. Infusion Techniques Because of the concern over atmospheric pollution with anaesthetic gases there seems to be a small but perceptible swing back from gaseous to intravenous anaesthetics.
It is a real possibility (especially in view
of this particular concern, the safety of steroid anaesthesia, the availability of motor driven syringes and the escalating cost of maintaining Boyles machines) that intravenous infusion techniques to maintain anaesthesia at a level
83.
pre-determined by t h e surgeon a s i s done r o u t i n e l y i n l a b o r a t o r i e s , w i l l come t o v e t e r i n a r y p r a c t i c e i n t h e near f u t u r e .
The method i s s i m p l e and c o n s e r v i n g i n
r e s p e c t of t h e amount of a n a e s t h e t i c used.
I t would
seem most l i k e l y t h a t a n i m a l s w i l l be induced w i t h an i n t r a v e n o u s d o s e of a s t e r o i d a n a e s t h e t i c and t h e n immediately connected t o a motorised s y r i n g e p r e f i l l e d w i t h a d i l u t e d volume of a n a e s t h e t i c .
This apparatus
would be f i t t e d w i t h a l e v e r which could be a d j u s t e d t o c o n t r o l t h e speed of d e l i v e r y t o g i v e t h e r e q u i r e d d e p t h of a n a e s t h e s i a a s t h e o p e r a t i o n p r o g r e s s e s .
A l l
t h a t i s needed i s a l i t t l e c a p i t a l i n v e s t m e n t and t h e courage t o adopt a new t e c h n i q u e . Conclusion The advent of s t e r o i d a n a e s t h e t i c h a s no doubt made a s i g n i f i c a n t impact on s m a l l animal p r a c t i c e and r e p r e s e n t s a major advance i n a n a e s t h e s i a i n v e t e r i n a r y practice.
Doubtless i t i s h e r e t o s t a y and i n t i m e
newer and even b e t t e r compounds w i l l be d i s c o v e r e d and u t i l i s e d t o advantage i n b o t h human and v e t e r i n a r y medicine.
84.
REFERENCES
CORBETT, H. ( 1 9 7 7 ) . 184-188.
Australian Practitioner,
2,
DODMAN N. ( 1 9 7 7 ) .
The U s e of "Saf f a n " i n t h e C a t . J o u r n a l of S m a l l Animal P r a c t i c e , 18, 653-658. ' F e l i n e Anaesthesia Survey'.
HALL, L. ( 1 9 7 6 ) . 17, 661-668. MOSS,
G.
(1974).
J o u r n a l of Small Animal P r a c t i c e , 'Prolonged A n a e s t h e s i a ' . Hospital Practice
THEODORE, J. and R O B I N , E.D. of R e s p i r a t o r y D i s e a s e ,
9.
77-86.
(1976). American Review 405-411.
113,
WATKINS, J . , PADFIELD, A. and ALDERSON, J . D . , B r i t i s h M e d i c a l J o u r n a l , 1, 1180-1181.
(1978).