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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 2, March/April 2019
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AFRICA
to seven days.
73
Table 2 contains a list of automated home devices
validated in pregnancy.
Ambulatory blood pressure monitor
The ambulatory blood pressure monitor is a self-inflating device
programmed to frequently measure blood pressure at set time
intervals over 24 hours while the patient may be outside the
health facility. Given the multiple blood pressure measurements,
blood pressure variability is easily demonstrated.
The minimum amount of information to be included in
a clinical report of ambulatory blood pressure monitoring
measurements has been proposed.
102
Such information is aimed
at improving the interpretation of an ambulatory blood pressure
monitoring report irrespective of the make of the device and
the software used for analysis. This minimum information
includes: (1) the quality of the ambulatory blood pressure
monitor recording; (2) a list of each and every blood pressure
recorded; (3) a graphical representation of each reading; (4) a
graphical representation of the average systolic and diastolic
blood pressure per hour; (5) the 24-hour mean blood pressure,
pulse pressure and heart rate; (6) the mean values of the blood
pressure, pulse pressure and heart rate in daytime and night-time;
(7) maximum and minimum blood pressure, pulse pressure and
heart rate obtained during the entire period of measurement;
(8) standard deviation of the blood pressure, pulse pressure
and heart rate for the 24-hour, daytime and night-time periods;
(9) daytime minus night-time values of blood pressure, pulse
pressure and heart rate, and (10) percentage blood pressure load
in 24 hours, daytime and night-time.
102
A major role of the ambulatory blood pressure monitor in
the clinical management of pregnant women is in the detection
of blood pressure variability, aiding the diagnosis of white-coat
hypertension, chronic hypertension,
103
and masked hypertension.
For instance, in a pregnant woman with office hypertension
in the early stages of pregnancy, ambulatory blood pressure
monitoring will assist in distinguishing white-coat hypertension
from chronic hypertension.
103
Nonetheless, it is important to emphasise that up to 15%
of research participants using ambulatory blood pressure
monitoring may discontinue a study due to the discomfort
and sleep disturbances caused by the device.
104
However, a
recording with at least eight awake and four sleep readings
may be sufficient to give a valid result in a research setting.
105
Other drawbacks peculiar to ambulatory blood pressure
monitoring include limited availability of the device due to
cost, and challenges with reproducibility, particularly in the
absence of standardised procedures. Like most automated
devices, the presence of arrhythmia, high body mass index
and reaction to the environment where the monitoring is
performed may affect the results of the ambulatory blood
pressure monitor.
Notably, an ambulatory blood pressure monitor may also
be used in combination with an ambulatory electrocardiogram
(Holter monitoring) to discern blood pressure patterns as well
as to ascertain the presence and type of cardiac arrhythmia that
may predate an adverse event. For instance, Vasomedical-Biox
Model 2301 system is a combined ambulatory electrocardiogram
and blood pressure recorder approved by the US Food and Drug
Administration.
106
Doppler blood pressure-measurement device
Reflection of a sound wave by blood flow is the fundamental
principles of Doppler studies. A Doppler probe (made of
piezoelectric crystals) is placed on the skin where a vessel such as
the brachial artery transverse will produce a sound wave that is
reflected back by the distortion of blood flow and/or oscillating
arterial wall. This generates changes in frequency (Doppler
effect) that are detected by the transducer and used for the
assessment of blood pressure.
The use of Doppler for the assessment of blood pressure
is important in low-pressure structures where there may be
vascular insufficiency,
61
shocked patients and children. It may
also be valuable in a noisy environment.
81
The use of Doppler
for routine measurement of blood pressure in pregnancy has not
been extensively studied and its accuracy is difficult to confirm
or refute.
Blood pressure devices validated in pregnancy
To ensure that an accurate blood pressure reading is obtained, an
automated device should be validated, pass a baseline check and/
or have an equivalent listing. For instance, Mindray iMEC12
patient monitor (an automated blood pressure device) was listed
by the British and Irish Hypertension Society as being suitable
for clinical usage. This stems from the fact that Mindray iMEC12
patient monitor was a derivative of Mindray BeneView T5 (a
device previously validated).
107
A baseline check involves comparing the readings of an
unvalidated automated device with those of a mercury or
a calibrated aneroid sphygmomanometer.
6
A comprehensive
description on how to conduct such a baseline check was
recently described.
18
To date, not all automated devices have
been validated, especially in pregnancy and PE. Details of some
blood pressure devices validated in pregnancy and PE that are
listed in the dabl Education Trust website,
108
the British and Irish
Hypertension Society website,
107
and those validated without
protocol violation
109
are listed in Table 2.
It is important to note that at any particular blood pressure
range, the accuracy of a blood pressure reading is dependent on
the type of blood pressure device (whether or not the device is
validated and calibrated) and the adherence to recommended
techniques on how to use the device. However, the invasive blood
pressure devices may be more accurate than the non-invasive
devices,
110
but further studies are required to confirm this across
devices and different clinical conditions.
General precautions on blood pressure meas-
urement in pregnancy
To minimise the aorta–caval compressive effect of the gravid
uterus in a supine position, the blood pressure of pregnant
women should be measured in a sitting position. If this is not
possible, the left lateral decubitus position may be used. There
is a concern that the left lateral position may falsely lower the
blood pressure
49
because the cuff will be above the level of the
heart.
111
Manufacturer’s instructions should also be given due
consideration to ensure proper usage of the blood pressure
device. In the same vein, it is advised that newly employed
healthcare practitioners should be inducted on how to use