BLOOD PRESSURE IN ITS CLINICAL APPLICATIONS
It is well to bear constantly in mind the point made over and over in
this work, that blood pressure is only one of many methods of acquiring
information. He who worships his sphygmomanometer as a thing apart and
infallible will sooner or later come to grief. Judgment must be used in
interpreting changes in blood pressure just as judgment is essential in
properly evaluating any instrumental help in diagnosis. One must not
forget the personal equation which enters into even accurate
instrumental recording in medicine and surgery.
In this chapter there will be no attempt to quote largely from what
others have said or thought. Every one has his own opinion as to the
value of certain methods after he has worked with them for a long time.
The ideas here expressed, except in cases where no opportunity has
offered to make personal studies, are those gathered from personal
experience.
=Blood Pressure in Surgery=
Careful estimation of the blood pressure in surgical cases has, at
times, great value. In all surgical diseases the most important fact to
know is not the systolic pressure, but the pulse pressure. If the pulse
pressure keeps within the range of normal, does not drop much below 30
mm. in an adult, then so far as we can tell the circulation is being
carried on. When the systolic pressure is gradually falling and the
diastolic remains the same, the circulation is failing and unless the
pulse pressure can be established again the patient will die. Again we
see the value of the pulse pressure.
All prolonged febrile diseases tend to produce a lowering of the blood
pressure picture. The diastolic does not fall to the same extent as the
systolic so that there is a pulse pressure smaller than normal. This is
to be expected from what we know of the general depression of the
circulation in fevers. The blood pressure reading is only a graphic
record of what we have long known, and enables us from day to day
accurately to measure the general circulation.
=Head Injuries=
It was claimed that in fracture of the skull or in concussion much could
be gained by frequent estimations of the blood pressure. This seemed
probable in the light of experiments on compressing the brains of dogs
by the use of bags inserted through trephine openings (Cushing). In the
clinic, however, it has not been found of any material value. It has a
value in differentiating a simple fracture, let us say, from a case of
uremia which is picked up on the street with a bump on the head. There
the high pressure usually found would at once direct attention to the
kidneys and the newer methods of blood examination would at once settle
the question. Naturally uremics may also have skull fracture. There the
diagnosis would be complicated. A decompression done at once would be
indicated. If the skull fracture happened in a uremic, the decompression
would probably do no harm. In fact, there are some who advise
decompression for uremia.
=Shock and Hemorrhage=
In shock the blood pressure picture is low but the pulse pressure drops
to abnormally low figures. It seems to me that the blood pressure
instrument has its greatest value in surgery in the warning it gives to
the operating surgeon in cases of impending shock.
It is well known that the first effect of ether, the commonly used
anesthetic, is to raise the blood pressure and quicken the pulse rate.
The whole blood pressure picture is at first elevated (Fig. 54). Soon
the whole pressure falls slightly but continues at a higher level than
normal. The diastolic pressure drops back nearly to normal and the
increased pulse pressure is due almost entirely to the slight rise in
the systolic pressure. Now the whole duty of the anesthetist is to
administer the ether so that this ratio of systolic and diastolic is
maintained throughout the operation. Warning comes to him of impending
shock before it comes to any one in the neighborhood (Fig. 55). Any
sudden change in the pressure is a signal for increased watchfulness.
Should the pressure all at once drop he can immediately notify the
surgeon and institute measures to resuscitate the patient.
[Illustration: Fig. 54.--Blood pressure record from a normal reaction to
ether. Note that the systolic and diastolic rise and fall together. At
the end of the anesthetization the pulse pressure is practically the
same as at the beginning. Compare this with the record in Fig. 55, where
the operation had to be discontinued on account of the onset of shock.]
[Illustration: Fig. 55.--Beginning of operative shock. Chart showing the
method of recording blood pressure during operation.
Note that the pulse and respiration show no remarkable changes, but the
blood pressure steadily fell, the systolic more than the diastolic so
that the pulse pressure was gradually reaching the danger point. Further
work on this case was stopped following the warning given by the blood
pressure. The patient was returned to the ward and a week later
anesthesia was again given, the operation was completed, and the patient
had a satisfactory convalescence.]
A method which is widely used is as follows: The anesthetist wraps the
cuff of one of the dial instruments around the patient's arm, and
arranges the dial so that it can easily be seen by him at all times.
This does not in any way interfere with the work of the surgeon. Over
the brachial artery below the cuff is the bell of a binaural stethoscope
held in place by the strap attachment now on the market. The tubes of
the stethoscope are long enough to reach conveniently to the ear pieces.
A watch is pinned to the sheet of the table. He has a chart, as
illustrated (Fig. 56) on a board and makes a dot in every space for five
minute intervals. By joining the lines a curve is obtained which tells
at a glance what the circulation is doing. I feel sure that more
attention and care exercised on the part of the anesthetist would be the
means of conserving many lives lost from shock following operation.
[Illustration: Fig. 56.--Showing method of using blood pressure
instrument during operation without interfering with the operator or
assistants. Sheet thrown back to show cuff on arm of patient.
Anesthetist has chart on table beside him, dial pinned to pad in full
view, bulb near hand. Extra tubing must be put on the blood pressure
instrument.]
A sudden drop in the pressure picture may mean a large hemorrhage. The
gradual return of the pressure picture means that the vasomotor
mechanism has acted to keep up the pulse pressure. Should the diastolic
pressure continually fall, it may mean that the hemorrhage is still
taking place (Wiggers).
=Blood Pressure in Obstetrics=
One might affirm almost without fear of contradiction that the constant
determination of blood pressure during pregnancy is more important than
the examination of the urine. Within recent years a number of observers
having access to a large material, have given the results of their
findings. There is a striking unanimity of opinion, although now and
then a difference in minor details.
The blood pressure should be taken frequently during pregnancy. The
usual and highly essential precautions in taking pressure in general
apply most particularly in these cases. Towards the end of pregnancy the
pressure should if possible be taken daily and oftener if necessary.
Pressure in women is usually below 120 mm. Many patients have a
temporary rise in blood pressure during pregnancy, due oftenest to
constipation, without developing other symptoms. This is common to all
conditions and has no significance. Some think that an abnormally low
pressure, that is, a systolic below 90 mm., suggests that the patient is
likely to react unduly to the strain of labor. This is denied by others.
Among 1000 cases (Irving) the pressure was below 90 in only one case. A
gradually rising pressure precedes albuminuria, as a rule. If there is
albumin without change in pressure the albumin may usually be
disregarded. Some think that a pressure over 130 mm. systolic should be
carefully watched. The danger limit is set by some at 150 mm. If the
blood pressure from the very first is high, it may mean only that that
was the patient's normal pressure. This calls for increased
watchfulness. It is held by some that high blood pressure favors
hemorrhage and probably explains the hemorrhagic lesions in the placenta
and some viscera in eclampsia and albuminuria.
All are agreed that the most significant change is the gradual but sure
rise from a low pressure. When this is combined with albuminuria the
danger of toxemia is imminent. The high blood pressure in those under
thirty years of age seems to be a more certain sign of approaching
toxemia than the same pressure in those older. The pressure falls within
a few days to its normal after delivery in the toxic cases.
Although the emesis gravidarum is held to be a sign of a toxemia of some
unknown nature, the blood pressure is never raised even in the
pernicious form.
=Infectious Diseases=
In all infectious diseases the blood pressure tends to be lower than
normal. During chills the systolic may rise to great height due to the
violent muscular contractions.
We found the blood pressure of great value in giving information
concerning the circulation. Again we repeat that it is not the systolic
alone or the diastolic alone but the pulse pressure which we wish to
keep informed about. In pneumonia we have tried out Gibson's law only to
discard it. This so-called law is that in pneumonia the systolic
pressure in millimeters should remain above the figure for the pulse
rate. When the figure in mm. of pressure is equalled by or exceeded by
the pulse rate the prognosis is grave.
In typhoid fever we have made many estimations at various stages of the
disease. We can only say that the pressure picture tends to fall during
the course. The systolic falls more than the diastolic so that it is not
uncommon to see pulse pressures of 20 mm. at the beginning of
convalescence in spite of the high caloric feeding practiced. At the
time of perforation the systolic pressure may be raised. This is only
the reflex from the initial pain. Soon the pressure falls and if
peritonitis sets in, the pressure is exceedingly low and the pulse
pressure gradually falls until the circulation can no longer be carried
on. In large hemorrhage the pressure suddenly falls. If only one
hemorrhage has occurred a gradual rise takes place, but the general
pressure picture remains at a lower level for days, gradually returning
where it was before the hemorrhage.
In beginning failure of the circulation we found elevation of the foot
of the bed about nine inches to be of such value that we felt there must
be some increase in blood pressure. Numerous readings were made covering
a period of several months. Although we felt certain that the
circulation was improved, we rarely needed cardiac stimulation, we never
could prove any increase of blood pressure with the sphygmomanometer.
In all infectious diseases there is no help offered by blood pressure
estimations in diagnosis. The sole and important use is that of keeping
track of the circulation.
=Valvular Heart Disease=
No rules can be laid down for blood pressure in valvular heart disease.
Aortic stenosis, the rarest of the valvular lesions, is practically
always accompanied by high pressure picture. Mitral stenosis on the
contrary usually shows a low pressure picture. Mitral insufficiency may
show an exceedingly low picture or an exceedingly high picture. Aortic
insufficiency also may be accompanied by a high systolic or by a normal
systolic pressure. It depends on the etiology. Practically all the
rheumatic cases have low pressure, the syphilitic cases have a high
pressure. It is characteristic of all cases of aortic insufficiency that
the diastolic pressure is low, even as low as 30 mm. The pulse pressure
is invariably high. Usually there is no difficulty in determining the
diastolic pressure. The intense third tone suddenly becomes dull at the
point of diastolic pressure and frequently the dull sound can be
distinctly heard over the artery down to the zero of the scale. If
difficulty is found in reading the diastolic as the pressure is reduced,
the estimation may be reversed and the pressure gradually increased from
zero to the point where the dull tone suddenly becomes loud and clear.
These points always coincide.
=Kidney Diseases=
This has already been discussed somewhat fully in Chapter III and will
receive more consideration later. It might be remarked in passing that
in a case of seeming coma where albumin is found in the urine but where
the blood pressure is low or normal, I have found at autopsy in several
cases pyonephrosis and not chronic nephritis. The blood pressure may be
useful in differentiating uremic coma from the coma of pyonephrosis.
Also in the cases of coma with anasarca, either the acute, subacute or
chronic form the blood pressure is not raised as a rule. Other diseases
of the kidney, as tuberculosis, cancer, infection with pyogenic
organisms, are not accompanied with any notable changes in blood
pressure.
=Other Diseases, Liver, Spleen, Abdomen, etc.=
Blood pressure is only of value in the above diseases in affording
information concerning the state of the circulation. There is nothing
characteristic about the pressure in any of these diseases.