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
- Should be:
- 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