Blood pressure

Auscultatory Gap

  • As illustrated below, if the cuff is inflated  only to the initial disappearance of the sound, the actual SBP maybe underestimated.
  • Cause is a mystery.
  • Avoided by palpating the disappearance of the pulse by inflation of cuff before using stethoscope to estimate the SBP. Cuff should be inflated 20-30 mmHg higher than the estimated SBP.

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Level of arm

  • Should be at the level of heart
  • Too high: the readings will be lower
  • Too lower: the readings will be higher
  • Due to hydrostatic effect

Blood pressure deficits between left and right arm

  • Normal is <10 mmHg, >20 mmHg is abnormal
  • Ddx:
    – Subclavian steal syndrome
    – Aortic dissection

BP deficits between arms and legs

  • Chronic ischemia of lower extremities
  • Coarctation of aorta (aorto-femoral delay in pulse)

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Orthostatic hypotension

  • 500 mL of blood shifts to lower body on standing up.
  • Defined as drop in SBP >20 mmHg or drop in DBP >10 mmHg
  • Orthostatic hypotension happens when:
    – Excessive loss of fluid
    – Lack of compensatory mechanism (autonomic dysfunction)
  • Evidence showed that
    – Finding of postural drop in SBP has no proven value
    – The better findings are postural increment of pulse >30/min OR dizziness on standing up

Blood pressure and impaired consciousness

  • Cushing reflex – normally due to increased ICP (structural lesions)
  • Cushing triad: 3B: Blood pressure increases, Bradycardia, Breathing irregular

Pathogenesis of Cushing Reflex

Cushing’s Triad and Cushing’s Reflex

Reference:

Steven McGee, Evidence Based Physical Diagnosis, pg 153-160

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