ASPHYXIA OR ANOXÆMIA.
Some degree of asphyxia is a common complication of inhalational
anæsthesia: indeed some small degree of it is almost unavoidable. It
is hardly too much to say that the difference between a good and a bad
anæsthetist is that the one recognises and deals with asphyxia in its
early stages, while the other allows it to assume serious proportions
before he becomes aware of its existence. The man who only realises
that asphyxia is present when the patient is deeply cyanosed and has
ceased to be able to draw any air at all into his chest may know much
of the physiology of anæsthetic drugs, and be well up in complicated
anæsthetic apparatus, but knows nothing of the proper practice of
anæsthesia.
Asphyxia arises during anæsthesia from several causes. In the first
place, the drug which the patient is inhaling and absorbing into the
blood, turns out from his red corpuscles a corresponding quantity
of oxygen. While this is only seen in its extreme form in the case
of nitrous oxide gas, it is a factor acting even in the case of
other anæsthetics. Secondly, during deep anæsthesia, the respiratory
centre may be somewhat depressed, and the force and frequency of the
respiratory act diminished. Thirdly, the respiratory passages may be
partially or wholly occluded from _mechanical_ causes. This is far
the most important type of asphyxia, being the most common, the most
fatal, and the most easily prevented.
Common Causes of Mechanical Asphyxia.
(1) CLENCHING OF THE JAWS arises not uncommonly during anæsthesia,
being specially frequent towards the end of the induction period.
Since a very large proportion of individuals have nasal passages
insufficient in bore to carry the full volume of respired air,
respiration must be obstructed if the jaws are clenched.
(2) FALLING BACK OF THE LOWER JAW AND BASE OF THE TONGUE OVER THE
EPIGLOTTIS.--This is always liable to happen after the muscles are
deeply relaxed.
(3) MUCOUS OR BLOOD OR A FOREIGN BODY IS DRAWN BY INSPIRATION INTO
THE AIR PASSAGES.--Changes of position of the head may release
mucous which has been gathering in some parts of the mouth or pharynx.
For instance, if the head has been lying on the side for some time, a
pool of mucous or saliva commonly gathers in the most dependent cheek,
and unless this is mopped out before the head is brought into the
mesial position, this pool will be suddenly tipped backwards, and very
probably drawn into the larynx. Again, in operations upon the nasal or
oral cavities, blood is always liable to be inspired, and not a few
teeth have found their way into the air passages in the practices of
dental surgeons who do not take precautions against this accident.
(4) SPASM OF THE ADDUCTORS OF THE VOCAL CORDS is one of the most common
and most baffling incidents in anæsthesia. It announces its presence by
the commencement of _laryngeal stridor_, a high-pitched crowing noise,
which is as annoying for the surgeon and anæsthetist to hear as it is
detrimental to the progress of a smooth anæsthesia. Inspired mucous or
blood almost invariably sets it up, and the two conditions of fluid
in the larynx and narrowing of the glottis from approximation of the
cords, add their effects together, with resulting obstruction of a high
degree.
Laryngeal stridor, however, frequently occurs even when no fluid
has been inspirated. It may be set up as a reflex from the area
of operation. Dilatation of the sphincter ani, and removal of the
prepuce in circumcision, are two common examples of this. It is also
undoubtedly sometimes caused by giving too strong a vapour during the
latter part of the induction stage. Stridor unfortunately sometimes
occurs from no obvious cause at all, or to speak more correctly,
from causes which are at present not known to us. It is the author’s
belief that one of these causes may prove to be _morphia_ given as a
preliminary to inhalational anæsthesia. In his experience, stridor
has been more frequent with morphia than without, particularly if
chloroform be the anæsthetic chosen. Beyond that he cannot at present
go.
(5) PRESSURE UPON THE AIR PASSAGES OF NEOPLASTIC OR INFLAMMATORY
SWELLINGS IN THE NECK.--In such cases any obstruction which may
exist before induction will probably become intensified during the
process, and a complete arrest of respiration is not uncommon. Large
goîtres are the most common type of neoplasm to give trouble, and all
acute inflammatory conditions in the neck which extend towards the
trachea are notorious for their tendency to give cause for anxiety
during anæsthesia.
The Physiology of Asphyxia.
An animal, subjected to asphyxia, either mechanically or otherwise,
shows the following signs:--
(_a_) _Increase of the force and frequency of the
respiratory movements of chest and abdomen._ Even though
there be a complete mechanical obstruction, increased efforts
to breathe will still be made for some moments, although air no
longer passes in and out of the chest.
(_b_) There is a considerable rise of blood pressure owing
to a high degree of vaso-construction.
(_c_) The pupils dilate.
(_d_) Generalised convulsions.
(_e_) The animal succumbs finally from cardiac failure.
No heart muscle can continue to function properly if supplied
by the coronary arteries with venous blood. Moreover, the
heart pump has to act against the greatly increased peripheral
resistance induced by vaso-constriction. It must therefore be a
matter of time only when the strongest and healthiest heart will
cease to contract under the abnormal conditions of asphyxia.
There are in asphyxia, two alterations in the blood-gasses, _i.e._
lack of oxygen and increase of CO_{2}. The action of these two
conditions have been differentiated by experimental work (Starling,
Kayala, Jerusalem), and one can say definitely that the excess of
CO_{2} is the cause of the increased activity of the respiratory
efforts, and that the remaining phenomena are due to oxygen starvation.
This point is of some importance in considering anæsthetic methods
in which re-breathing (breathing in and out of a bag) is practised.
The use of such methods has often been thoughtlessly condemned as
“poisoning the patient with his own CO_{2}.” Within the limits usually
practised, a re-breathing method does not involve any such risk,
provided oxygen starvation does not occur. This point is referred to
again in Chapter iv.
Clinical Signs of Mechanical Asphyxia in the Anæsthetised Subject.
The classical signs of asphyxia above described are hardly to be
expected in the operating theatre, but essentially the condition
of the patient who develops respiratory obstruction while under an
anæsthetic is similar to that produced experimentally in animals in the
laboratory. The changes most easily observed are as follows:--
(1) _Alteration of the colour._--Cyanosis shows itself earliest
in the lips, and the lobules of the ears,--later the whole face
becomes dusky.
(2) _Dilatation of the pupil_, which ceases to respond to the
stimulus of light.
(3) _The respiratory movements increase in depth and
frequency._--The chest and abdominal walls heave forcibly; but
(4) _The volume of air passing in and out of the glottis is
diminished._--In complete obstruction, of course, none passes
at all. In passing we may draw the moral that persistence of
chest movements is no proof of the passage of air in and out
of the chest: that can only be proved by hearing the movement
of air through glottis and mouth or nose, or feeling it on the
delicate skin of the back of the observer’s hand.
(5) _True convulsions are not seen_, unless we may consider
the jactitation of deep N_{2}O anæsthesia as such (see Chapter
VII.). Nevertheless, there are obvious and most valuable signs
of asphyxia to be found in the muscular system often quite
early. These consist in the incidence of _muscular rigidity_,
which is frequently observed first in the muscles of the
abdominal wall. A surgeon performing laparatomy will notice
at once the occurrence of this phenomenon, than which hardly
anything can complicate and delay his task more effectively.
The anæsthetist who knows his work will, upon hearing from the
surgeon a complaint as to the rigidity of the abdominal wall,
devote his attention first to securing a perfectly free air-way
before deciding that a deeper anæsthesia is required.
[Illustration: FIG. 5.--Vicious circle of asphyxia.]
Prevention and Treatment of Asphyxia.
Once asphyxia, especially mechanical asphyxia, has begun, it almost
invariably tends to get worse. The engorgement affects among other
venules, those which run under the mucous membrane of the respiratory
tract, still further obstructing the passage of air. The muscular
rigidity, moreover, soon manifests itself in the adductors of the
vocal cords and the muscles which close the jaws: the patient has
thus entered into a “vicious circle,” Fig. 5. It is evident that the
prevention of the earliest signs of asphyxia is to the anæsthetist a
matter of vital interest. The cardinal points to watch are as follows:--
(1) Keep the neck of the patient as far as possible in a natural
position, _i.e._ do not either flex or extend the head unduly
upon the body unless the nature of the operation demands such an
unusual position.
(2) Maintain a free passage for air either through the nose or
the mouth.
(3) Keep the lower jaw in good position throughout the
administration.
(4) Avoid turning the face from the lateral to the dorsal (face
up) position unless essential. If it has to be done, be careful
first to mop out any “pool” from the dependent cheek.
(5) Deal as effectively as possible with the earliest appearance
of laryngeal stridor.
Let us see how in a normal case, these rules can be applied. With
the patient lying (or, in exceptional circumstances, sitting) in a
comfortable position, the shoulders and head raised above the rest of
the body and the face looking upwards (or straight forwards, in the
case of the sitting patient), the anæsthetic is begun slowly, and the
patient encouraged to take his time and to breathe naturally. At this
stage the jaw needs no support, the muscles being neither relaxed by
deep anæsthesia, nor spastic from asphyxia. With the advent of muscular
relaxation, the head is turned to one side, that which is opposite to
the side on which the surgeon will be working, being usually chosen.
We must now determine whether the patient can breathe best through the
mouth or the nose, and make sure that the channel chosen is as free as
possible. In the majority of cases it will be found that respiration is
oral, and that all that is necessary is to support the lower jaw by a
finger hooked into the depression just below the symphysis mentes. The
hands of the anæsthetist, therefore, take up a position from which in
nine cases out of ten they will never require to be moved.
_The hand of the side toward which the patient’s face is turned_
supports the jaw and keeps the face-piece or mask adapted to the face.
The middle finger is pressed into the space below the symphysis mentis,
and _exercises traction forwards and a little upwards_, thus preventing
the jaw from slipping backwards; the index finger lies along the lower
part of the mask, maintaining adaptation between it and the chin; the
thumb bears on the mask higher up, keeping its upper part pressed
against the bridge of the patient’s nose, and also serving as a _point
d’appui_, or fulcrum, from which the jaw traction by the middle finger
can conveniently be exercised. This grip once learnt is not fatiguing
to the hand, and is in the author’s opinion one of the essential points
for the beginner to master (_see_ Fig. 28C, page 85).
_The opposite hand_ holds the drop bottle, if the method in use is
an open one, the wrist resting upon the uppermost side of the patient’s
head.
[Illustration: FIG. 6.--Hewitt’s dental props.]
Fig. 28C shows this grip in operation, while Fig. 28D shows the
alternative frequently adopted. This alternative has various
disadvantages. It covers up a larger part of the patient’s face than
the method recommended, and it tends to tilt the mask sideways. The
little finger is supposed to be hooking forward the jaw by pressing
behind its angle, but such a method is very fatiguing if in use for
more than a few moments.
In a proportion of cases, it is found that a free air-way cannot be
maintained by these simple measures. Upper or lower teeth (or both)
may be missing and traction upon the lower jaw only closes the mouth
the more firmly. In most of these cases, the difficulty can be met
by the use of the _dental prop_. These are made in various sizes and
shapes, of which the best known are Hewitt’s and Bellamy Gardner’s
(_see_ Figs. 6 and 7). The latter are made of aluminium and are of
small size only. They are the most convenient for cases with teeth
both in the upper and lower jaw, but who suffer from a receding lower
jaw not easily kept forward unless the prop is used as a rocker, as it
were, upon which it can be slid forward. Hewitt’s props are of plated
metal, with lead on the cups, to avoid injury to the teeth. They are
made in five sizes, of which the middle and larger are very convenient
for cases in which one or both rows of teeth are missing.
[Illustration: FIG. 7.--Bellamy Gardner’s Dental
Props.]
[Illustration: FIG. 8.--Phillips’ modification of
Hewitt’s artificial airway.]
For cases entirely without teeth, and in which a large flabby tongue
is prone to fall back over the epiglottis, the mouth tube (Fig. 8) is
very convenient. The rubber shank lies along the top of the tongue, the
metal end lies between the gums. As originally introduced by Hewitt,
the air-way was circular in cross section, but the flattened model
figured is a distinct improvement. It was introduced by Dr Phillips.
[Illustration: FIG. 9.--Silk’s nasal tubes.]
Occasionally one decides to facilitate nasal rather than oral
breathing, and if the natural passages are inadequate, recourse may be
had to the passage of a short piece of drainage tube of the calibre of
a number 10 catheter, and about 3 inches in length. With such a tube
in one or both sides of the nose, reaching from anterior to posterior
nares, nasal respiration is usually possible even in much obstructed
noses (Silk). (Fig. 9.)
[Illustration: FIG. 10A.--Bellamy Gardner’s
tongue-clip.]
[Illustration: FIG. 10B. Ring tongue
forceps.]
[Illustration: FIG. 10C. Glossotilt.]
[Illustration: FIG. 11A.--Boxwood wedge for
opening jaws.]
[Illustration: FIG. 11B.--Wedge for opening
jaws.]
[Illustration: FIG. 11C.--Mouth gag.]
If proper and timely use be made of one or other of these simple
devices, the use of the _tongue forceps_ is rarely necessary.
Occasionally, however, it may be required, and a suitable appliance
should always be at hand for an emergency. Fig. 10 shows two types. The
little clip of Mr Bellamy Gardner is preferable to the ring type, the
passage of the spike through the tongue substance producing less after
pain, than the bruising following the use of the other instrument. The
third drawing in Fig. 10 is of an instrument not much known outside
Edinburgh; it is called a glossotilt, and is intended to lever forward
the base of the tongue, as an alternative to nipping the tip of the
organ with forceps, and has, in the opinion of some, various advantages.
Before using either mouth prop or tongue forceps, it is occasionally
necessary to use some mechanical means to lever open a tightly clenched
jaw. The earlier one interferes in a case of mechanical asphyxia, the
less necessity will exist for the use of such means. Fig. 11 shows two
well-known mouth gags, and also a box-wood wedge, the use of which is
less liable to injure teeth than a metal instrument. If a gag is used,
the blades when closed should lie the one behind the other, not side
by side. This ensures a minimal thickness to be inserted between the
tightly clenched teeth.
Treatment of Laryngeal Stridor.
This is of necessity difficult since the causation of the condition is
in many cases obscure. _The error_ common to most beginners, and to
many who would resent such a title being applied to them, is to regard
the appearance of stridor as an indication to _deepen the anæsthesia_.
Whether the cause lie in local irritation of the laryngeal mucous
membrane or in some stimulus from the area of operation, the condition
is presumably always essentially a reflex spasm of the adductors of
the vocal cords, but it is a _reflex which may persist even in an
anæsthesia so deep that the vital medullary centres are in peril_.
The preventive treatment consists chiefly in following the other rules
set forth above for the prevention of asphyxia with such faithful care,
that the patient never enters into the vicious circle of asphyxia of
which stridor is so prominent a feature. Patience in the induction
stage--the avoidance of _forcing_ the anæsthetic upon the patient--is a
safeguard not to be forgotten.
Once the condition has arisen, it saves time to _withdraw the
anæsthetic_ altogether, and to allow the patient to breathe nothing
but fresh air. Brisk friction of the lips with a rough towel often
does good, presumably by setting up a “cross reflex.” In severe cases,
a most valuable measure is the inhalation of pure oxygen, a cylinder
of which should always be at hand in the operating theatre. Even an
obstructed air-way will convey enough undiluted oxygen to reduce the
venosity of the blood, and so cut across the “vicious circle.”
So much for the treatment of the early stages of asphyxia, the more
advanced stages constitute one of the “accidents of anæsthesia,” and
are dealt with in Chapter XVI.