G6ii: NIBP Monitoring – Auscultation with Sphygmomanometer

Equipment

  • A sphygmomanometer = pneumatic cuff, inflating valve, release valve, mercury manometer
  • Stethoscope for auscultation

Method

  • Cuff placed over peripheral vessel
  • Cuff inflated to occlude pulse of limb
  • Stethoscope placed over artery to listen for Korotkoff sounds as cuff pressure is released
  • Korotkoff sound I = SBP
    • = Onset of turbulent flow as cuff pressure falls below SBP
  • Korotkoff sound II = DBP
    • = No sound, sound disappears as flow is ‘smooth’

Sources of Error

  • Wrong cuff size
    • Should be:
      • Width = 40% circumference of limb
      • Length = twice this width
    • Small cuff → overestimates
    • Large cuff → underestimates
  • Inter observer variability → Large variation
  • Origin of Korotkoff sounds uncertain → so doesn’t actually correlate well with IABP
  • Over rapid deflation & bradycardia

Advantages

  • Simple
  • Cheap
  • Reliable

Disadvantages

  • Inaccurate