ETHYL CHLORIDE.
Chemically this drug has the formula C_{2}H_{5}Cl. It is a colourless
fluid so volatile that it boils at ordinary room temperature. Its
vapour is highly explosive, and the fluid itself very inflammable. The
drug is supplied by the makers in small tubes with a metal end which
can be opened by pressing a little lever (_see_ Fig. 40), varying
in type with the brands made by various makers. Two brands are sold
by each firm; one is chemically pure, intended for use as a general
anæsthetic; the other is not so pure, and is only sold for local
anæsthesia. Such a product is not suitable for inhalation.
[Illustration: FIG. 40.--Tube of Ethyl Chloride.]
Physiology.
The special points in the physiology of ethyl chloride may be briefly
summarised as follows:--
1. After a trifling preliminary rise, the effect of the drug
is to lower the blood pressure appreciably. In the human adult
subject, this fall becomes appreciable when more than 3 c.c.
have been given; if the dose exceed 5 c.c. a fall of 30 to 40
mm. of Hg. is probable,--occurring as it does within a period of
perhaps twenty or thirty seconds, such a fall cannot be regarded
as safe.
2. The cause of this fall is diminished cardiac output from
weakening of heart muscle. The vagus though not paralysed, does
not appear to be unduly irritable, as it does with chloroform.
3. The respiratory centre is at first perceptibly stimulated,
and respiration is therefore deeper and quicker than normal. The
stimulant effect rapidly passes away and gives place to a stage
of depression.
In the majority of cases, death appears to take place from paralysis
of the respiratory centre, the heart still showing a little power of
contraction after respiration has ceased. There is therefore a fair
prospect of recovery if artificial respiration be resorted to promptly.
Methods of Administration.
OPEN METHOD.
The extreme volatility of the drug has discouraged most anæsthetists
from giving it upon an open mask. Hornabrook, of Melbourne, advocates
this system, however. His mask fits the face accurately, and his whole
method is strictly perhalational. He uses some 4–6 c.c. of the drug
for a child, 6–8 c.c. for an adult, and achieves his anæsthesia in a
minute to a minute and a half. He also advocates open ethyl chloride
as a preliminary to open ether. For some twelve months, the author
adopted the method. At the end of that time he came to the conclusion
that while it greatly facilitated the induction stage of open ether,
it appeared to increase the after sickness. He therefore abandoned it,
though rather reluctantly.
CLOSED METHOD.
This is the usual means employed. A variety of inhalers have been
produced on the market, one of which is shown in Fig. 41. Essentially
all consist of:--
(_a_) A face-piece which must fit the face with reasonable
accuracy.
(_b_) A one-gallon rubber bag attached to the mask by a
T-piece.
(_c_) A glass vial, with numerals from 1 to 5 marked on the
outside to facilitate the measurement of the drug in c.c. Into
this the drug is squirted from the makers’ tube. The vial is
attached to the T-piece (or alternatively the bottom of the bag)
by a rubber tube.
[Illustration: FIG. 41.--Ethyl Chloride Inhaler.]
Administration.
To use such an inhaler, the glass vial is first detached from the
rubber tube, and the chosen dose of drug squirted into it. A child
of five or six will require 3 c.c., an adult up to 5 c.c.; this dose
should never be exceeded. The vial is then rapidly reconnected with
the inhaler. The face-piece is adapted to the face, care being first
taken to place between the teeth a mouth prop or a gag. This enables
one to get immediate access to the mouth when the inhaler is removed.
The patient is then told to breathe deeply once or twice. During the
inspiration the mask is lifted slightly, and the ensuing expiration is
then caught in the bag by pressing down the mask on to the face. To
volatilise the drug there are two alternative methods. In the one, part
or the whole of the dose is tipped into the rubber bag by elevating the
vial. A far better is the “Vapour” method, almost universally used in
Edinburgh owing to the advocacy of Dr Logan Turner. A tumbler is filled
with hot water, and the bottom of the glass vial is allowed first to
touch, and after a few seconds to be immersed in it. Some thirty to
forty seconds suffice to vapourise the whole of the dose.
Ethyl chloride given by itself should always be administered to a
patient in the recumbent position. A dose sufficient to produce
anæsthesia without the aid of nitrous oxide or ether will not be safe
in the erect posture. The case is quite different where a small dose
only is given, to assist the action of nitrous oxide, or facilitate the
induction stage of ether.
Signs of Anæsthesia.
Ethyl chloride is very rapid in its action, some sixty seconds
availing to produce quite a deep anæsthesia. _Respiration_ is
at first deepened and quickened: as full anæsthesia is attained it
remains rather deeper than normal, and is accompanied usually by light
snoring. The colour should remain perfectly good: the pupils show
marked dilatation, the corneal reflex is abolished, and good muscular
relaxation is attained.
With no anæsthetic is it so essential as with this, to become
acquainted with the type of respiration normally to be expected, and to
watch for any departure therefrom with cat-like vigilance. The other
danger signal is the pupil. It should be dilated, but a rim of iris
should still be perceptible.
Once anæsthesia is established, the inhaler should be removed, and the
surgeon may begin his work. He will have for its completion some 80–90
seconds against the 40–50 available after nitrous oxide. With ethyl
chloride there is a somewhat prolonged “analgesic” stage. The patient
is partly conscious and may even be phonating, but seems unconscious of
the infliction of pain unless very severe measures are being used.
The Scope of Ethyl Chloride.
When first introduced, it was expected by enthusiasts that the
lightness and portability of the drug itself and of the necessary
inhaler, would enable ethyl chloride to oust nitrous oxide from its
recognised place in surgery and dentistry. These high expectations
have for several reasons not been fulfilled. In the first place, this
drug is essentially a “single dose” anæsthetic. Most authorities view
coldly all attempts to prolong anæsthesia by repeated or continued
administration. Secondly, ethyl chloride has a mortality rate very
much greater than nitrous oxide if doses sufficient in themselves to
produce anæsthesia are habitually used (_vide supra_). The introduction
of the “vapour” method has done much to mitigate the risks, but even
then, this anæsthetic cannot approach the high level of safety rightly
credited to N_{2}O. Moreover, it leads to after vomiting much more
commonly than its rival.
In many schools these considerations have been held so powerful that
ethyl chloride has been entirely abandoned. It is, however, a very
valuable drug for the following purposes:--
(1) The removal of tonsils and adenoids. For this operation,
the speed with which the patient (usually a child) loses
consciousness, the pleasant type of anæsthesia and absence of
all serious asphyxial phenomena, and the rapid re-appearance
of the cough reflex when once the inhaler is removed, are all
strong recommendations.
(2) As an adjuvant to gas, or gas oxygen (_see_ Chapter
XIII.).
(3) As a help to the speedy and comfortable induction of “closed
ether” (_see_ Chapter XV.).