SEQUENCES.
By a sequence we mean a method in which anæsthesia is partially or
wholly induced by one anæsthetic or one method, and maintained by
another. The methods mentioned in Chapter XIII. as devised
by Dr Guy for dental purposes are examples which have already been
sufficiently described.
C.E. Mixture--Ether Sequence.
Of the method of inducing anæsthesia by _C.E._, and turning later to
_open-ether_, we have also already spoken. One thing remains to be
said in this connection. Learn to judge the appearance of the type of
patient who will require this alternative to open-ether induction, and
use the sequence to such patients from the beginning. Don’t start off
with open-ether, and find out in a few minutes that the patient is too
obstreperous. A change from mixture to ether is harmless, the reverse
process needs much care.
The sequence of _C.E. to closed ether_ was advocated by Hewitt as a
means of dealing with very alcoholic men, and for this purpose has
great merits. The mixture is given until the stage of struggling is
just about to commence, a point which experience enables one to fix
with considerable accuracy. The remainder of the induction is conducted
by a closed-ether inhaler, either the Hewitt wide-bore or preferably
the Ormsby. The ether indicator which stands at about one when the
inhaler is first applied, may be advanced very rapidly full ether
strength being attained within a minute or two. As soon as rebreathing
is begun with either of these instruments, it is very striking to watch
the rapid and apparently safe subsidence into anæsthesia of the most
troublesome patient. The struggling is cut short and greatly minimised
in violence, and a stage which under CHCl_{3} might have presented some
considerable risk of secondary syncope, is thus eliminated.
Nitrous Oxide and Ether Sequences.
This is a method greatly superior to the induction by closed-ether
described on p. 79. Instead of the 1-gallon bag of the Clover or Hewitt
instrument, the valve piece and 2-gallon bag of a gas apparatus are
attached to the head of the ether inhaler (Fig. 23, on page 77).
Once the gas bag is inflated from the cylinder, the supply of gas may
be cut off. A few breaths of gas “upon the valves” are given, until the
bag is half empty; the valve tap is then pushed over to “no valves” and
rebreathing begun. Ether may be turned on a few seconds later, and the
strength of the vapour may be increased more rapidly. Three-quarter
strength of ether may be attained as a rule in ninety seconds. There is
very little likelihood of struggling in this method.
Ethyl Chloride and Ether.
This is a valuable method for short operations, being easily portable,
speedy and safe in action, and fairly agreeable to the patient. Some
anæsthetists use this induction method as a prelude to open-ether.
The Clover (or Hewitt wide-bore) instrument is interposed between the
face-piece and the T. of the ethyl chloride inhaler, as shown in Fig.
47. A small dose of ethyl chloride only is requisite; for an adult, 3
c.c. is enough. This is vapourised over hot water in the usual way; a
very light anæsthesia is induced in some sixty seconds, and the ether
can then be turned on at a much quicker rate than if the induction be
conducted by that drug alone.
Scope.
The gas-ether and ethyl chloride-ether sequences are most useful
methods. They are quick, safe, and powerful.
[Illustration: FIG. 47.--Clover’s Inhaler adapted
for the Ethyl Chloride-Ether sequence.]
Either may be used as “single dose” anæsthetic, the ether being pushed
quickly up to “full” and the inhaler then withdrawn. If, however, no
access to the mouth is required by the surgeon, ether anæsthesia may,
by occasional breaths of fresh air be prolonged for as long as desired.