METHODS OF ANÆSTHETISING.
Certain terms such as “open method,” “closed method,” etc., are used in
describing different systems of anæsthetising, and it will save time
later if these are now defined.
The OPEN METHOD is one in which the drug is dropped or poured upon
a fabric stretched on a mask which does not lie in close apposition
to the face. If the student will experiment with such a mask as
Schimmelbusch’s, he will find that by no effort can he make its whole
circumference touch his face at the same time. Anæsthetics vapourised
from such masks must of necessity be inhaled freely diluted with fresh
air. These masks are only suitable for use with chloroform.
The PERHALATION METHOD.--This term is not used often, but it is the
most strictly correct name to give to the process commonly called
“open ether.” If the student will examine Bellamy Gardner’s open ether
mask (Fig. 27) he will find that it is deliberately shaped to lie
over its entire circumference in close apposition to the face of the
average patient. In actual use it is well however to make sure of this
apposition by the use of a ring of gauze as shown in Fig. 28A. Upon the
mask is stretched gauze of a thickness just as great as will permit
free respiration to take place through its layers. The whole bulk of
the respired air must pass _through the fabric_, none escaping between
the face and mask.
The term “SEMI-OPEN” is applied to various methods now rarely seen. One
of the best known of these was the anæsthetic cone, still used by a few
for C.E. mixture (_see_ Fig. 45).
The term “CLOSED METHOD” is applied to one in which the patient
breathes in and out of a closed bag. The Clover and Ormsby inhalers are
“closed” instruments. With this method the patient rapidly uses up the
oxygen of the contained air, and accumulates considerable CO_{2}; life
could not be sustained for any long period of time under such a system.
Oxygen must be supplied from time to time by permitting say one breath
in five to be taken from the fresh air instead of from that in the bag.
Alternatively, oxygen from a cylinder may be supplied by an accessory
pipe into the inhaler.
* * * * *
This method is also referred to as the RE-BREATHING METHOD.
* * * * *
The VALVED METHOD is used only with “gas” or “gas-oxygen.” The
facepiece fitting accurately, the patient draws all the volume of
his inspiration from the inhaler: his expirations he propels through
a valve, into the general atmosphere of the room. If nitrous oxide
unmixed with oxygen is being given, the patient suffers from oxygen
starvation even more rapidly and completely than in the re-breathing
method. During the induction period of gas anæsthesia, such oxygen
starvation is practised deliberately, and if not pushed too far is
harmless. It cannot, however, be continued for more than a brief space
of time. The admixture of oxygen to the vapour being breathed entirely
abolishes this unfavourable feature of the valved method.
There is, however, another consequence of the use of “valves” which
is unaffected by the addition of oxygen. Reference has already been
made to _Yandell Henderson’s acapnic theory_, and if under any form
of anæsthesia the patient can be reduced to a condition _of CO_{2}
starvation_, it will be when the valved system of administration is in
operation for a prolonged period. As a matter of experience, patients
breathing “on the valves” do often exhibit shallow respirations and
slight pallor which is rapidly and very strikingly remedied by turning
to the rebreathing method. One can hardly doubt that the improvement
is due to a gradual re-accumulation of carbon di-oxide in the blood and
tissues.
Two other terms referring not to the type of inhaler but to the method
of supplying the drug, are in use.
By the “DROP” METHOD, we mean one in which the anæsthetic is supplied
in a steady series of drops. The flow may be quick or slow, but it
always arrives on the mask in isolated drops of uniform size. Such a
method demands more constant attention than the next to be described,
but it is capable of yielding that even uniformity of vapour strength
so desirable in open methods.
THE DOUCHE METHOD is unfortunately far more commonly used by those
whose attention has never been drawn to the significance of the
difference between the two. Supplies of the drug rendered, say, every
twenty seconds cannot possibly give an even vapour strength.
“SINGLE DOSE” methods are of use chiefly in dental surgery. The patient
is charged up with the anæsthetic, and the operator has to begin his
work as soon as the mask is withdrawn from the face, ceasing as soon as
the patient shows any signs of recovering consciousness of pain.
Single dose anæsthetics are in a class by themselves. In order to
achieve success with them, special experience on the part of the
administrator and mutual confidence between operator and anæsthetist
are essential.
The period of anæsthesia available to the operator which any particular
“single dose” anæsthetic may be expected to yield is obviously a matter
of the first importance, and the table given in Chapter XIX.
will be found helpful in this connection.