Blood pressure measurement

BMJ 2001; 323 doi: https://doi.org/10.1136/bmj.323.7316.805 (Published 06 October 2001) Cite this as: BMJ 2001;323:805

ABC shows absence of evidence in measuring blood pressure during pregnancy

  1. Martin Quinn, locum consultant in obstetrics and gynaecology (martin.quinn@hbhc-tr.anglox.nhs.uk)
  1. Hinchingbrooke Hospital, Huntingdon PE29 6NT
  2. St Bartholomew's Hospital, London EC1A 7BE
  3. Blood Pressure Unit, Beaumont Hospital, PO Box 1297, Dublin 9, Republic of Ireland
  4. University Department of Medicine, City Hospital, Birmingham B18 7QH
  5. University of Birmingham, Department of Public Health and Epidemiology, Birmingham B15 2TT

    EDITOR—In the short ABC on blood pressure measurement Beevers et al made several references to problems with measurement in pregnancy that have been discussed for many years without satisfactory resolution.1 There are four main points.

    1. Interestingly, the vascular sounds that are caused by vibration of the vessel wall are clearly modulated by consistent changes in patterns of flow in the brachial artery in pregnancy (figure).2

    Sequence of vascular sounds in normotensive pregnancy. Vascular sounds were recorded with microphone over brachial artery (Toshiba HSM-05B), with concomitant Doppler recording of brachial artery waveform (Toshiba PLF703ST)

    • (2) As the authors indicate, automated oscillometric devices may be inaccurate; they systematically under-record K1 (phase I; onset of sounds) and K4 (phase IV; muffling of sounds) in severe pre-eclampsia by up to 40 mm Hg.3 Other circulatory conditions characterised by reduced compliance may be susceptible to similar discordances.

    • (3) K5 (phase V; disappearance of sounds) may be the “most accurate measurement of diastolic blood pressure in pregnancy,” but academic precision may be less relevant than pragmatic thresholds in preventing the consequences of severe pre-eclampsia and eclampsia. Measurements of K1 and K4 of 140/90 mm Hg and 160/110 mm Hg may be difficult to improve on. Perhaps the authors have alternative techniques and thresholds in mind?

    • (4) In the British eclampsia survey 294 out of 383 patients with eclampsia had the characteristic symptoms associated with severe hypertension, although only 70 had a diastolic blood pressure >120 mm Hg before the seizure.4 The authors who reported the survey suggested that these observations …

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