eMedinewS Editorial

5:11 am Health Care

Measuring blood pressure (Part 2)

  1. Even under optimal conditions, many patients are apprehensive when seeing a doctor. This causes an acute rise in BP. About 20–30% of patients with hypertension in the clinic are normotensive outside the clinic. This is called “white coat” or isolated office hypertension and should be suspected in any patient with marked high BP in the absence of end–organ damage or with normal ambulatory BP taken at work or at home.
  2. The presence of white coat hypertension can be diagnosed by 24–hour ambulatory BP monitoring or self–recorded readings or by having a nurse measure the BP.
  3. The white–coat effect can persist for years.
  4. Cuff placement: The BP cuff should be placed with the bladder mid line over the brachial artery pulsation, with the arm without restrictive clothing. The sleeve should not be rolled up as this may act as a tourniquet. Lower end of the BP cuff should be 2–3 cm above the antecubital fossa to minimize artifactual noise related to the stethoscope touching the cuff.
  5. The cuff should be inflated to a pressure 30 mm Hg greater than upper systolic, as estimated from the disappearance of the pulse in the brachial artery by palpation. In some patients, the Korotkoff sounds transiently disappear as the cuff is deflated. As an example, the Korotkoff sounds in a patient with a systolic pressure of 180 mm Hg may be first heard at 180 mm Hg, disappear at 165 mm Hg, and then be reheard at 140 mm Hg. This auscultatory gap is associated with increased arterial stiffness and carotid atherosclerosis.
  6. Neither the patient nor the doctor should talk during the measurement
  7. The BP should be taken with the patient’s arm supported at the level of the heart; allowing the arm to hang down when the patient is sitting or standing will result in the brachial artery being 15 cm below the heart. As a result, the measured BP will be elevated by 10 to 12 mm Hg due to the added hydrostatic pressure induced by gravity.
  8. The stethoscope should be placed lightly over the brachial artery. The use of excessive pressure can increase turbulence and delay the disappearance of sound. The lower diastolic pressure reading may be artifactually reduced by up to 10 to 15 mmHg.
  9. The cuff should be deflated slowly at a rate of 2 to 3 mm Hg per heartbeat. The systolic pressure is equal to the pressure at which the brachial pulse can first be palpated or at which the pulse is first heard by auscultation (Korotkoff phase I).
  10. As the cuff is deflated below the systolic pressure, the pulse continues to be heard until there is abrupt muffling (phase IV) and, approximately 8 to 10 mm Hg later, disappearance of sound (phase V).
  11. The diastolic pressure is generally equal to phase V. The point of muffling should be used in those patients in whom there is more than a 10 mm Hg difference between phases IV and V. This can occur in children, and in high-output states such as thyrotoxicosis (hyperfunction of the thyroid), anemia (low Hb), and aortic regurgitation (leaking valve).
  12. The BP should be measured initially in both arms.
  13. If there is a disparity between the two arm readings, the arm with higher pressure should be used. Normal difference between two arms can be 3–5 mm Hg.
  14. The BP should be taken twice on each visit, with the readings separated by 1 to 2 minutes to allow the release of trapped blood. If the second value is > 5 mm Hg different from the first, continued measurements should be made until a stable value is attained. The correct value is average of the last two measurements.
  15. There are occasional patients in whom the BP needs to be measured in the legs. The classic example is in cases of suspected coarctation of the aorta in which there is an arm–to–leg gradient.
  16. BP should be taken in the leg among women with breast cancer with bilateral axillary lymph node dissection. In unilateral axillary node dissection, BP should be taken in the opposite arm. The tourniquet effect may damage the lymphatics and exacerbate the arm edema. No precaution is needed if there has not been axillary node dissection.
  17. The systolic upper pressure in the leg is 10 to 20 % higher than that in the brachial (elbow) artery. Values > 10 % lower than brachial measurements are used to screen for significant peripheral vascular disease.
  18. Measurement of BP at the wrist may be more practical in obese people, since wrist diameter is not significantly affected.
  19. Systolic upper BP rises, and diastolic lower BP falls, in more distal arteries. In the wrist, the hydrostatic pressure related to the lower position of the wrist relative to the heart can result in a further false elevation of BP. This can be minimized by taking the BP with the wrist kept at the level of the heart.
  20. Errors can occur when the BP is taken at home or work by the patient or spouse, even when the instrument is accurate. The BP varies throughout the day. For monitoring therapy, the BP should be measured at roughly the same time each day and the relation to meals and medications noted. The patient should be instructed to wait to measure the BP if they have recently eaten a meal or exercised.
  21. Cuff inflation hypertension: A problem with self–measurement of BP is that the muscular activity used to inflate the cuff can acutely raise the BP by as much as 12/9 mm Hg. This dissipates within 5 to 20 seconds. Inflating the cuff to at least 30 mm Hg above supper BP and then allowing the mercury column to fall no more than 2 to 3 mm Hg per heartbeat is indicated both for accurate measurement and to permit this effect to disappear.
  22. One should take multiple BP measurements.
  23. In the absence of end–organ damage, the diagnosis of mild hypertension should not be made until the blood pressure has been measured on at least two additional visits, spaced over a period of one week or more. BP drops by an average of 10 to 15 mm Hg between the first and third visits in newly diagnosed patients, with a stable value not being achieved until more than six visits in some cases. Thus, many patients considered to be having high BP at the first visit may in fact be normal.
  24. If the BP is taken at home to diagnose or monitor treatment at least 12 to 14 measurements should be obtained, with both morning and evening measurements taken over seven workdays.

Dr KK Aggarwal
Editor in Chief

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