MIXTURES OF NITROUS OXIDE AND ETHYL CHLORIDE.
Dr Guy, Dean of the Edinburgh Dental School, introduced some years
ago a method of giving ethyl chloride in mixture with nitrous oxide.
Guy’s objective was to utilise the many excellent features of the drug
without incurring the risks which are apparently inherent in it when
a dose sufficient in itself to induce full narcosis is used. Given in
mixture with gas, a much smaller dose suffices.
[Illustration: FIG. 42.--Guy’s inhaler for N_{2}O and Ethyl
Chloride.]
His original apparatus is shown in Fig. 42, the details are shown in
Fig. 43. The horizontal limb of a 3-way gas tap is prolonged half an
inch. In each side of the prolongation is a hole. The bag mount has
in its side also one hole, which is connected by a universal ball and
socket joint, with the rubber tube to which the ethyl chloride vial is
attached. An indicator on the outside of the bag mount and a mark upon
the outside of the horizontal limb of the 3-way tap, serve by their
apposition or the reverse to show whether the ethyl chloride vial is in
direct continuity with the interior of the inhaler. For purposes of
description, Dr Guy calls these two positions, “in register” and “out
of register.”
To use the instrument, the ethyl chloride vial is removed, and the side
pipe attached to a cylinder of nitrous oxide. The indicator of the
3-way tap is put at “air” and the bag mount “in register.” The bag is
then filled with gas by opening the head of the cylinder. The bag mount
is now put “out of register,” and the side tube disconnected with the
cylinder. The bag, being closed, remains full of gas.
[Illustration: FIG. 43.--Guy’s Instrument for Gas and Ethyl
Chloride. Details of valve piece and bag mount, showing side
tube for attachment of Ethyl Chloride vial.]
A suitable dose of ethyl chloride is now squirted into the vial. To
an adult, Dr Guy gives 3 c.c.: on no account is this dose exceeded:
children take 1½–2 c.c.--even adults often get less than 3 c.c. The
vial is now attached to the side tube again, and the inhaler is ready
for use.
After application of the mask to the face, the 3-way tap is at once
pushed over to “no valve” and the patient rebreathes the gas in and out
of the bag for some six or eight respirations. The bag mount is now
turned round “into register,” and the ethyl chloride tipped into the
bag. In a further twenty-five seconds the mask may be removed and the
operation begun.
The available period of anæsthesia is eighty to ninety seconds,
counting from the instant of the removal of the inhaler.
This method was in use for some years at the Dental Hospital of
Edinburgh; no instance of danger to life was ever seen. With so small a
dose of ethyl chloride, the erect position necessary for the purposes
of dentistry is perfectly safe.
[Illustration: FIG. 44.--Diagram of the method
introduced by Dr Guy and the author for giving Nitrous Oxide
and Oxygen, with or without Ethyl Chloride.]
This inhaler, of course, will serve admirably for giving ethyl chloride
without gas, and the author habitually uses it for giving the drug by
the “vapour” method.
In 1911, Dr Guy and the present author modified the method so as to
permit the use of oxygen with the nitrous oxide. The inhaler which
they then introduced serves also for nitrous oxide and oxygen, unaided
by ethyl chloride, and the author has by its means given gas-oxygen
to a considerable number of major surgical cases. He now, however,
limits its use to short anæsthesias, and uses a sight-feed or a Clarke
apparatus for long cases.
[Illustration: FIG. 45.--The Guy-Ross Inhaler for
Nitrous Oxide and Oxygen, with or without Ethyl Chloride.]
In Fig. 44 will be found a diagram showing the method by which the
oxygen is introduced. The 1-gallon oxygen bag is either attached
directly to a cylinder, or suspended on an upright as shown in Fig.
45. In either case, the bag is, before the administration, moderately
filled with oxygen: one bagful will suffice for a short anæsthesia, and
the supply of the oxygen from the cylinder is therefore turned off at
once. For long cases, of course, a small trickle of oxygen into the bag
is required to replace the gas used.
In the outlet pipe from the oxygen bag is placed a ball syringe of 2
ounces capacity. A valve in the pipe obliges the flow of oxygen to take
place in one direction only when the bulb is squeezed, viz. from oxygen
bag to inhaler.
The remainder of the apparatus is identical with Guy’s original
inhaler, except that the bag is of 2-gallon capacity, and is perforated
at its base by a =Y=-tube, one limb of the fork bringing in the
nitrous oxide, the other the oxygen.
Method of Use.
A few breaths of pure nitrous oxide gas are usually allowed “on the
valve.” Rebreathing is then instituted, and the addition of oxygen
begun. The amount required to each type of patient can only be learnt
with experience, but the average is one full compression of the bulb
every ten seconds. If anæsthesia is not complete at the end of one
minute, put the indicator to “valves” again, and allow the patient
nearly to empty the bag. Then push back the indicator to “no valves,”
and refill the bag with nitrous oxide by opening the cylinder with the
foot key. Some four to six compressions of the bulb are made while the
nitrous oxide is running in. The time will now have come to add the
dose of ethyl chloride if it be judged necessary at all. This will have
been placed in the vial before the administration is begun. After
emptying the ethyl chloride into the bag of the inhaler, anæsthesia
should be complete in twenty-five seconds.
The same small doses of ethyl chloride are used as is the case with
Guy’s original method.
After a little practice under supervision, students at the Dental
Hospital learn to use this method safely and well. No example of risk
to life has arisen after eight years’ daily experience.[11]