blood pressure measurement

Last reviewed 08/2021

The blood pressure is measured with a sphygmomanometer.

• use a machine with validated accuracy that is calibrated and properly maintained
• the systolic pressure is the maximum pressure in an artery just after left ventricular contraction. The diastolic pressure is the minimum pressure in an artery during left ventricular filling
• the blood pressure is usually measured with the pressure cuff around the upper arm and the stethoscope placed over the brachial artery in the antecubital fossa. The patient should be sitting with the arm at the level of the heart
• as the pressure in the cuff is reduced from above the systolic pressure down to zero, five characteristic Korotkoff sounds are heard. The pressure at which a sound is first heard is the systolic pressure (Korotkoff I). The pressure at which silence begins corresponds to the diastolic pressure (Korotkoff V)
• the pressure should be measured to the nearest 2 mmHg
• to determine the extent of the hypertension the blood pressure should be recorded twice per visit
  • blood pressure should initially be measured in both arms as a significant number of patients, particularly the elderly, have large between arm differences
  • (>10 mmHg) and the arm with the highest value used for subsequent measurements and this recorded. Two measurements (1-2 minutes apart) should be taken on each occasion, the initial value being discarded if there is a large (>10 mmHg) difference between the first and subsequent readings and further measurements made
  • in order to assess orthostatic BP changes, particularly in elderly or diabetic patients and in those with symptoms suggesting postural hypotension, measurements should be repeated after the patient has been standing for 1-3 minutes, again with the arm supported
• while undergoing evaluation of mild hypertension and assessment of overall cardiovascular risk, paired BP recordings should be repeated on two or three further visits over the subsequent 2-3 months. For those with moderate or severe hypertension on initial recordings, and/or evidence of target organ damage further assessments should be made over a shorter period e.g. 3 to 4 weeks, as prolonged periods of observation before starting treatment are unnecessary and unwarranted (2)
• all adults, aged 40 years or more, should have their blood pressure measured routinely at least every 5 years until age 80

If the person has severe hypertension, consider starting antihypertensive drug treatment immediately, without waiting for the results of ABPM or HBPM

Confirming the Diagnosis

• if the clinical BP is 140/90 mmHg or Higher, Offer ABPM to confirm the diagnosis
• if the patient is unable to tolerate ABPM, HBPM to confirm the diagnosis of HTN
• while waiting to confirm the diagnosis, carry out investigations for target organ damage and formal CVD assessment
• CVD Assessment:
  • test for Presence of protein in urine, Albumin: Cr Ratio, Hematuria
  • Bloods for Plasma Glucose, Electrolytes, Cr, GFR, Serum total cholesterol & HDL cholesterol
  • Fundi for Retinopathy
  • ECG

Ambulatory blood pressure monitoring

• when using ABPM to confirm a diagnosis of hypertension, ensure that at least two measurements per hour are taken during the person's usual waking hours (for example, between 08:00 and 22:00)
• use the average value of at least 14 measurements taken during the person's usual waking hours to confirm a diagnosis of hypertension

Home blood pressure monitoring

• when using home blood pressure monitoring (HBPM) to confirm a diagnosis of hypertension, ensure that:
  • for each blood pressure recording, two consecutive measurements are taken, at least 1 minute apart and with the person seated and
  • blood pressure is recorded twice daily, ideally in the morning and evening
  • blood pressure recording continues for at least 4 days, ideally for 7 days
  • discard the measurements taken on the first day and use the average value of all the remaining measurements to confirm a diagnosis of hypertension

Notes:

• multiple recordings are required in atrial fibrillation to obtain an accurate estimation of blood pressure levels (2)
• when heart rates are below 50 beats/min, even if the rhythm is regular, some of the newer semi-automatic devices are unable to reduce their deflation rate accordingly such that too rapid a fall in cuff pressure results in underestimation of systolic blood pressure and overestimation of diastolic blood pressure (2)
• in pregnancy, diastolic blood pressure is best measured as the disappearance of Korotkoff V sounds. However, in some cases the sounds may persist when the cuff is completely deflated, in which case Phase IV should be used (2)
• refer immediately patients with accelerated (malignant) hypertension (BP more than 180/110 mmHg with signs of papilloedema and/or retinal haemorrhage) or suspected phaeochromocytoma (possible signs include labile or postural hypotension, headache, palpitations, pallor and diaphoresis) (3)
• to identify hypertension (persistent raised blood pressure, above 140/90 mmHg), ask the patient to return for at least two subsequent clinics where blood pressure is assessed from two readings under the best conditions available (3)
• measurements should normally be made at monthly intervals. However, patients with more severe hypertension should be re-evaluated more urgently (3)

Reference:

1. BMJ 1999; 319: 630-635.
2. British Heart Foundation Factfile (October 2005). Blood Pressure Measurement.
3. NICE (November 2016). Management of hypertension in adults in primary care.