to Pregnancy Reviews
Blood pressure is a clinical
measurement and as such should be measured as accurately
as possible on all occasions. Early work carried out
on blood pressure measurement in pregnancy demonstrated
that the muffling of sounds (Korotkov phase IV), when
taking blood pressure using the standard technique,
with a mercury manometer, more accurately represented
the level of diastolic blood pressure. Normally in
the non-pregnant individual the diastolic blood pressure
is "read off" the manometer on the disappearance
of sounds, Korotkov phase V. There are many reasons
why this is a better measure in the non-pregnant individual.
However the early work referred to above claimed that
in pregnancy the muffling of sounds was frequently
heard down to zero on the mercury column(1,2).
In patients where K5 occurred the researchers claimed
that the gap between phase IV and phase V was so great
as to render phase V inaccurate. For many years, based
upon this work, Korotkov phase IV, the muffling of
sounds, was recommended by all bodies, such as the
WHO, ISSHP and ASSHP for the measurement of diastolic
blood pressure in pregnancy.
Subsequent research has revealed that these assertions
are wrong and that Korotkov phase V, the disappearance
of sounds, should be used as the measure of diastolic
blood pressure in pregnancy (3).
It was demonstrated that the muffling of sounds were
very rarely audible to the zero level (4)
on the mercury column. The research also showed that
the difference between phase IV and phase V was about
2 - 3 mmHg in pregnancy which is clinically insignificant.
Other work using intra-arterial measurements of blood
pressure also confirmed that Korotkov's phase V was
the most accurate measure of diastolic blood pressure
in pregnancy (5,6).
Recommendations for taking blood pressure:
- Blood pressure measurements need to be
both accurate and reproducible between observers.
Measurement devices such as sphygmomanometers
or automated devices should be well maintained
and regularly calibrated.
- The correct size upper arm cuff should
be used. The bladder of the cuff should encompass
80% of the upper arm, if the cuff size is
too small it could result in an over estimation
of blood pressure by up to 10 mmHg. A blood
pressure cuff which is too large could lead
to a similar under estimation.
- Be aware of the white coat effect. This
can be minimised by ensuring that the patient
is relaxed and comfortable before the blood
pressure measurements are taken.
- When measuring blood pressure in an individual
2 readings should be taken. The second reading
is nearly always lower that the first and
is a truer representation of blood pressure.
The British Hypertension Society produced
guidelines on the technique of blood pressure
measurement and should be referred to as
the gold standard of for blood pressure for
1. Davey DA. The classification and definition of
the hypertensive disorders of pregnancy. Am J Obstet
Gynecol 1988;58:892-8, Abstract
2. Wichman K. The influence of different positions and Korotkoff sounds on
the blood pressure measurements in pregnancy. Acta Obstet Gynecol Scand 1984;118(supp1):25-8, Abstract
3. Lopez MC. The measurements of diastolic blood pressure during pregnancy:
which Korotkoff phase should be used. Am J Obstet Gynecol 1994;170:574-8, Abstract
4. Walker SP. The diastolic debate: is it time to discard Korotkoff phase IV
in favour of phase V for blood pressure measurements in pregnancy? Med J Aust
5. Rattery EB. The indirect method of recording blood pressure. Cardiovasc.
6. Brown MA. Measuring blood pressure in pregnant women: a comparison of direct
and indirect methods. Am J Obstet Gynecol 1994;171:661-7, Abstract