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Medical Emergencies · single question

While taking a patient's blood pressure, the assistant lets the patient's arm hang BELOW the level of the heart. How will this affect the reading?

  1. No effect as long as cuff size is correct
  2. Falsely lowered (lower than the true value)
  3. Falsely elevated (higher than the true value)
  4. Systolic falsely high but diastolic falsely low
Show answer and explanation

Correct answer: C. Falsely elevated (higher than the true value)

  • A. Arm position is an independent source of error even with a correctly sized cuff. Cuff size, arm position, back/feet support, and talking are all separate error sources.
  • B. The opposite is true — an arm held ABOVE heart level produces a falsely LOW reading.
  • C. Correct. When the arm is BELOW heart level, hydrostatic pressure adds to the measured pressure and the reading is falsely HIGH (roughly 2 mmHg error per inch of vertical displacement, both systolic and diastolic). The arm must be supported at heart level (mid-sternum / 4th intercostal space).
  • D. Hydrostatic error shifts systolic and diastolic in the SAME direction — both are falsely elevated.

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