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chloroform with air and the restriction of the amount of chloroform vapour to a certain per
- c e n t a g e d o n o t n e c e s s a r i l y p r o v e a s a f e g u a r d a g a i n s t t h e s p e e d y i n t a k e o f a n o v e r d o s e . F o r a i r
containing a sufficient percentage of chloroform vapour, for safe and effective anæsthesia dur
- i n g e a s y b r e a t h i n g , w i l l , d u r i n g d e e p a n d r a p i d r e s p i r a t i o n , s u p p l y a v a s t l y g r e a t e r a m o u n t o f
chloroform to the pulmonary capillaries. I am not able to state precise amounts for the volumes
of air taken in during easy breathing and exaggerated breathing in the case of the cat. But
we know that in man the quantity of air taken in at each respiration during easy breathing is
about 20 cubic inches: whereas, during a very deep breath, about 100 cubic inches may be
inspired. Thus five times as much air is taken in at a very deep breath as by an ordinary in
- s p i r a t i o n ; b u t , i n a d d i t i o n t o t h e d i f f e r e n c e b e t w e e n o r d i n a r y b r e a t h i n g a n d d e e p b r e a t h i n g , w e
have to consider the results of acceleration..
In addition to a change in depth we have often a great change in rate. The rate may
be doubled or trebled at the same time that the depth is increased. Hence it is evident that
the amount of chloroform taken in during a period (for example, 10 seconds) of deep rapid
breathing may be at least ten or fifteen times as much as during a similar period (10 seconds)
of easy breat hi ng. And, i f t here i s a fi xed percent age of chl oroform vapour i n t he ai r al l t he t i me
i t i s obvi ous t hat t en or f i f t een t i mes as much chl or of or m wi l l be admi t t ed i nt o t he l ungs i n t he
one period as in the other. Now, it will readily he understood that—especially if chloroform
is already present and exerting its influence to some extent in the circulation—an overdose
may be very speedily given in this way, and evidences of dangerous collapse may present
themselves with striking suddenness.
The chloroform taken in will, of course, tend to lower the blood-pressure, and so tend to
retard the access of the drug to the vital organs; but, as we have seen the heart often shows
signs of dilatation before there has been sufficient time for the fall of blood-pressure to be
brought about; hence in all probability in some cases an amount of chloroform suf-
ficient to cause disastrous results may be taken in before a protective fall of pressure
can come efficiently into play. Especially when deep rapid respiration is accompanied
by a high or tolerably high blood-pressure, the amount of the anæsthetic rapidly taken
in is apt to prove dangerous; and a fairly high pressure may be present for a time,
even though a good deal of chloroform has been taken in. For example, when
—
although a considerable amount of the drug has been administered—the anæsthesia is not suffi-
ciently sensory irritation (for example, operative interference, or the intro
-duction of too concentrated chloroform vapour into the air passages) can induce a marked rise
of blood-pressure. The blood-pressure rises under the influence of sensory irritation, even
though there is in the circulation an amount of chloroform sufficient to maintain a pronounced
l owe r i ng of pr e s s ur e i n t he a bs e nc e of s e ns or y s t i mul a t i on.
Further disturbances of the breathing and the occurrence of deep rapid inspirations
are apt to he excited by sensory excitation during imperfect anæsthesia, when the influence of
t he chl or of or m i s not s uf f i ci ent l y gr eat t o pr event t he r es pi r at or y cent r e bei ng r ef l exl y af f ect ed
in this way. In this condition then there may he suddenly developed the conditions that are
most favourable to the rapid intake of an overdose of chloroform, namely, quick gaspmg respi
-ration, accompanied by a high blood-pressure.