CHLOROFORM.
Physical Characteristics.
Chloroform is chemically trichlor-methane, CHCL_{3}. It is a
colourless, transparent fluid, with a specific gravity of 1·491 at
17°C. Its vapour is even heavier than that of ether, approximately
four times heavier than air. It is not inflammable, but the action of
an open fire or naked flame tends to break it up into hydrochloric
acid and phosgene, both of which are highly irritant gases to all who
breathe them. The patient suffers, but since all the other occupants of
the theatre are also affected, warning is given before serious harm has
been inflicted.
Chemically pure chloroform is a somewhat unstable product, but the
addition invariably made to it by the producers, of a trace of
alcohol, prevents any serious risk of decomposition in bulk. It should
be neutral in reaction and have an agreeable non-irritating odour:
departure from the normal in either respect indicates the possibility
of the presence of acids or aldehydes, and the necessity for referring
a specimen to the laboratory.
Like ether, chloroform may be obtained from pure ethyl alcohol or from
methylated spirits, and the remarks made in the chapter upon ether
apply to the case of chloroform also. A third source of supply is
acetone, from which perfectly good chloroform can be produced.
Physiology.
Chloroform is an irritant to the skin and mucous membranes. A drop left
on the skin and covered over with impermeable material will produce a
deep and painful blister. A drop falling into the eye, if not instantly
washed away, produces a very powerful inflammatory reaction, and many
eyes have been totally lost from carelessness in this respect. Such
incidents are of course actionable, and heavy damages may be given.
[Illustration: FIG. 35.--Diagrammatic representation of
various blood pressure curves obtainable with chloroform.
Line ABA′ represents curve desired in normal chloroform
administration.
Line ABCB′ represents gradual overdosage.
Line ABCC′ represents recovery by inversion.
DD′ represents syncope from vagal inhibition: in its course,
one attempt of the heart to “escape” is shown.]
The special peculiarities of the action of chloroform upon the nervous
system have already been emphasised in the account given of the
physiology of ether (see page 75). Its action upon the _circulatory
and respiratory systems_ has been the subject of many researches,
and of much embittered controversy. The literature is therefore very
extensive, and the account of it must be severely condensed. The
following may be taken as a brief resumé of present day opinion (_see_
Fig. 35):--
(1) In every case of chloroform administration, there is a fall
of blood pressure.
(2) If the drug be presented in weak concentration (less than 2
per cent. vapour strength), the fall is gradual and even (line
AB).
(3) If the same strength (say 2 per cent.) of vapour as produced
the above effect be prolonged unduly, the respiration will cease
at a time when blood pressure is still well above zero (line
ABCB′).
(4) The fall of pressure is due to diminished force of cardiac
action, and at a later stage also to vaso-motor paresis.
(5) The cessation of respiration is due partly to fall of
blood pressure in the vessels supplying the medullary centre;
partly to gradual poisoning of the centre itself by the drug.
That the fall of B.P. in the cerebral vessels is in itself one
explanation of the cessation of respiration, was proved many
years ago by Leonard Hill in his inversion experiments. Just
at the stage when respiration had ceased, the anæsthetic was
withdrawn, and the animal inverted into the head-down position.
The B.P. in the carotid at once began to rise, and natural
respiration was resumed (line A′BCC′).
The above conclusions refer to chloroform given in moderate vapour
strength; other effects are produced if higher percentages are
administered:--
(6) With high concentration of chloroform vapour, the fall
of blood pressure is rapid, and is apt to become suddenly
precipitous (line DD′).
(7) The cause of these sudden falls is inhibition of the
heart by over-activity of the vagus: cutting the vagi always
terminates the effect unless delayed so long that the animal is
dead: in an animal fully under atropine, these vagal actions
cannot be produced.
(8) If the heart is inhibited by vagal action, the respiration
ceases at once, usually after one deep inspiratory sigh.
(9) An inhibited heart may “escape” from vagal action before the
animal is dead: frequently, however, the inhibition persists and
the animal dies.
(10) Struggling and breath-holding in the early stages of
induction cause sudden falls of blood pressure. Many observers
believe that these falls also are due to vagal activity, others
hotly deny this. All are united in believing that to _press_
chloroform upon a patient who is struggling and holding the
breath, is fraught with grave risk of causing sudden syncope.
(11) The abnormal irritability of the vagus above referred to is
a feature mainly of the induction stage, disappearing once full
anæsthesia is developed.
(12) It is an undoubted clinical fact that there is a risk
of sudden arrest of heart’s action if the operation is begun
before the stage of full anæsthesia is reached. A reasonable
explanation of such accidents is furnished by supposing a reflex
inhibition acting through the vagal centre already rendered
hyper-sensitive by partial chloroformisation.
Views of Goodman Levy.
This worker has demonstrated in animals that the heart is sometimes
thrown by chloroform into the condition of fibrillation--a delirium
of the cardiac muscle, from which recovery is rare. It occurs in
the early stage, before full anæsthesia has been reached, and is
predisposed to by the infliction of trauma. The practical outcome of
this is that the induction stage of chloroform should not be unduly
prolonged, and that the operation should not be begun until the third
stage is fully developed.
So far as the author understands the views of Dr Levy, his explanation
of chloroform syncope need not be taken as introducing any new
principle into the administration of the drug. Even those who lay most
emphasis upon the danger of using vapours of too high a percentage
strength would admit the force of Levy’s contentions. As usual, safety
lies in steering between two extremes.
During his work on this subject, Levy further demonstrated that
the introduction into the circulation of _adrenalin_ during
incomplete chloroform anæsthesia was very liable to induce fatal
cardiac fibrillation. He thus furnished the explanation of a number
of deaths which had occurred in the practice of nose and throat
specialists. Since the publication of Levy’s work, the rule has been
absolute that if _adrenalin_ is to be used in a case requiring
chloroform anæsthesia, the adrenalin must _precede, not follow_
the anæsthetic.
Administration.
Basing upon these views as to the action of chloroform, and upon the
lessons of practical experience, we may formulate definite rules for
giving the drug.
General Principles for giving Chloroform.
(1) Give chloroform evenly, not spasmodically.
(2) Increase the vapour strength of chloroform gradually from
zero until 2 per cent. or at most 2½ per cent. is reached at the
end of two or three minutes; maintain that strength until full
anæsthesia is obtained; thereafter, drop down to 1–1·5 per cent.
This will result in a B.P. curve corresponding to the line ABA′
in the diagram (Fig. 35).
(3) Be guided chiefly by the patient’s respiration. Chloroform
kills by stopping the heart, but in the immense preponderance
of cases, evidence of failure of respiration appears in ample
time to give warning of approaching circulatory failure. The eye
reflexes give confirmatory evidence of the depth of anæsthesia,
but the superlatively important thing is to _maintain a free
airway, and be sure the patient is using it_.
(4) If serious struggling and breath-holding occur, withdraw the
anæsthetic until the patient “resumes normal.”
Methods of Administration.
The logical application of such general principles would be to use an
instrument which gives a definite and known percentage of chloroform,
variable at the wish of the administrator. Many such machines have
been brought forward, and while none of them have obtained general
acceptance, a description of the best known instrument will be given,
as the reader may as a house-surgeon meet with it, and with a surgeon
who wishes it to be used.
Vernon Harcourt’s Inhaler.
In principle, this is a “draw-over” instrument; the patient’s own
inspirations are the motive power. Passing over the surface of the
fluid drug, the inspired air picks up from it a known percentage of
vapour. The other system available for the construction of percentage
chloroform instruments is the “plenum”; in this the vapour is propelled
to the patient by a pump.
[Illustration: FIG. 36.--Vernon Harcourt’s Percentage
Chloroform Inhaler.]
In appearance, the inhaler resembles the letter T, with a rubber
face-piece attached to the lower end of the vertical limb (_see_ Fig.
36). The T portion itself is made of metal tubing of a definite size
in cross section. One end of the horizontal limb admits pure air, the
other, air which has passed over chloroform and picked up from it a
certain proportion of vapour. The proportion of the total inspired
volume of air which passes through each of the ends is regulated by
a lever seen at the junction of horizontal and vertical limbs, and
the exact percentage of chloroform being inhaled is indicated by a
series of numerals marked on the dial over which the lever moves. These
figures are correct provided:--
(1) The chloroform receptacle is not shaken (this would greatly
increase the percentage).
(2) The temperature of the chloroform is not allowed to fall
below 13° centigrade. To ensure that this cannot take place
without the knowledge of the administrator, two coloured beads
are thrown into the chloroform. At the desired temperature of
the chloroform (13°–15°C) the blue bead sinks to the bottom,
the red one nearly to the bottom. Below 13°C, the red bead also
touches bottom, and when this is observed, the chloroform vial
is warmed up in the palm of the hand. At the point 15°C, both
beads float, and the warming must then stop, or an undesirable
addition to the vapour strength yielded will occur.
The face-piece is made of rubber, and must be closely adapted to the
face; in its side is seen the expiratory valve. Inspiratory valves are
present at each end of the horizontal limb.
The great advantage of this instrument, to the author’s mind, is for
teaching or demonstration purposes. If the student _sees_ the lever
gradually being moved over from ·2 to 2 per cent., then slipped back to
about 1·5 per cent. after full anæsthesia has been obtained, he begins
to appreciate what it is he is aiming at when giving chloroform by the
ordinary open method.
[Illustration: FIG. 37.--Schimmelbushch’s mask.]
Open Method.
The appliances requisite are:--
(1) A mask. Schimmelbushch’s is the best known (Fig. 37): as
elsewhere explained, it does not accurately fit the face.
(2) Material to stretch on the mask. The best is two layers of
domette or one of flannelette: surgical gauze is so light that
heavy drops of chloroform are apt to “spark” through it and burn
the skin of the face: lint rapidly becomes sodden; the drug
drips away from its edge instead of vapourising properly.
(3) A good drop bottle, of which many varieties are marketted
(Fig. 38): it is essential that it should be capable of
producing definite _drops_: the old method of intermittent
“douching” of chloroform is to be condemned as violating the
first general principle for giving the drug.
[Illustration: FIG. 38.--Chloroform drop bottles.]
It is not possible by the open method to be mathematically accurate
with percentages, but the necessary appliances are simple, easily
transported, and practically always at hand. If the student learns to
use it, and while doing so _to think in percentages_, he will
achieve as good results as or better than he will with percentage
instruments. While he may not have in front of his eyes a dial which
shows the percentage graphically, observation of the patient will
inform him whether the percentage being given should be maintained,
raised, or lowered. The only remaining point for him to realise, then,
is how in practice such regulations of percentage strength can be
achieved by the open method. The strength of the vapour will depend
upon three factors:--
(1) Nature of the material used on the mask.
(2) Closeness with which the mask is adapted to the face.
(3) Amount of chloroform exhibited on the mask.
To ensure uniformity of result, two of these factors should be kept
constant, and the necessary increase or decrease of vapour strength
achieved by varying the third. Always use the same type and thickness
of material on the mask, and allow the mask to lie lightly on the face.
If the amount of chloroform is then regulated by a strictly “drop”
method, results of great uniformity may be obtained by the open method.
The Junker Inhaler.
This instrument was originally introduced as an attempt to achieve a
percentage method. Air is pumped through a certain depth of chloroform
contained in a bottle, and the vapour brought to the patient in the
face-piece shown in Fig. 39. The calculations by which it was sought
to establish this as a reliable dosimetric or percentage method are of
no great value. From that standpoint the instrument has not achieved
success. It delivers to the patient a _small quantity of high
percentage vapour_ which is diluted by a much larger quantity of
air inspired by the patient from the general atmosphere, and the final
percentage inhaled by the patient is therefore no more accurately known
to the administrator than in the open method.
The instrument is, however, of considerable value for tongue and jaw
cases, where anæsthesia has to be maintained for some considerable
time after the mask with which anæsthesia has been induced has had to
be removed, to give access to the surgeon.
[Illustration:
FIG. 39.--Junker’s Chloroform Inhaler showing hand
bellows, bottle and mask. Alternatively to the latter, the
nasal tube shown above, may be used.]
The Figure 39 shows the instrument as usually marketed. It consists
of:--
(1) A hand-bellows.
(2) Chloroform bottle. A mark cut on this shows the level to
which it is to be filled: if more than the proper quantity be
poured in, droplets of fluid chloroform are apt to be blown
along the exit tube, with dangerous results.
For convenience and neatness, it is usual to make the exit surround
the inlet tube. The entering air bubbles through the chloroform,
and a stream of air and chloroform vapour passes out from the exit
tube.[10] It is unnecessary to give a detailed account of the use of
the instrument, but the student must remember the following points:--
(1) The amount of chloroform vapourised will depend on the
vigour of the pumping, the depth of fluid, and the temperature
of the chloroform. In order to achieve uniform results, it
is therefore necessary to keep up a steady but not excessive
pumping, to warm up the bottle occasionally by holding it in the
palm of a disengaged hand, and to watch that the level of the
chloroform does not fall too low.
(2) The pumping should be timed to synchronise with inspiration:
a puff of vapour delivered during an expiration will be wasted.
Advantages and Disadvantages of Chloroform.
The light portable appliances which are alone necessary for chloroform
anæsthesia, the comparative cheapness of the method, and the _apparent_
ease with which its administration may be conducted, are all great
temptations to its use. Those who feel the temptation strong upon them
are advised to remember the following quotation from the writings of
Professor Leonard Hill:--
“Chloroform is a drug used by the young anæsthetist with the utmost
hardihood, and until he has had the misfortune in his practice to meet
with a death caused by it, he derides the danger of the drug, and
asserts that its safety merely depends on the care and skill of the
administrator. After losing his patient, he falls to descanting on the
unavoidable dangers of the drug, dangers which he is now the first to
maintain cannot be met by any degree of skill in administration.”
The most distressing and probably the most common chloroform fatalities
are exemplified in administration given for the most trifling
conditions, such as opening abscesses or extracting teeth.
In general, we use chloroform if for any reason ether is not
applicable. For examples of cases of this description, the reader is
referred to the chapter upon the choice of anæsthetics.