2018B01 Briefly describe the principles (50%) and sources of error (50%) in the measurement of
systemic arterial blood pressure using an automated oscillometric non-invasive monitor.

List:

· Device

· Functioning

· Considerations

Device:

Examples	· DINAMAP (device for indirect non-invasive mean arterial pressure) · Von Recklinghausen oscillotonometer
Components	· Cuff with an inflatable bladder · Port for air insufflation · Port for pressure transduction · Transducer in the module · Processor and display
Application and sizing	· Cuff width: covers 2/3 of arm length · Bladder length: encircle 80% of the arm’s circumference · Ensure cuff at level of right atrium

How it works:

Mechanism	· Cuff is inflated above estimated SBP then slowly released · Pulsatile flow through partially compressed artery · Oscillating pressure sensed by a strain gauge · Processor monitors: o Amplitude o ∆Amplitude / ∆Pressure  (not ∆Amplitude / Time)
Pressures	· Systolic pressure: max rate of ↑amplitude · Mean pressure: maximum amplitude (most accurate) · Diastolic pressure: several methods (least accurate) o Max rate of ↓amplitude o Calculated: DBP = 1.5 x mAP - 0.5 x SBP o Fixed ratio: 85% of max

Considerations:

Sources of error	Intrinsic: · Diastolic pressure less accurate · Inaccurate in arrhythmia (irregular amplitude of oscillations) · Inaccurate at extremes of BP (false falsely low if high, falsely high if low) · Improper calibration Sizing: · Poor fit · Too short or narrow -> falsely high · Too long or wide -> falsely low Cuff: · Movement artifact e.g. shivering · Cuff not at the level of RA (e.g. upper arm in lateral decubitus position -> ↓hydrostatic pressure) · Cuff inflation pain (↑SNS output -> ↑ BP)
Pros	· Non-invasive · Cheap · Easy to use · Can use for venipuncture
Cons	· Intermittent; may miss sudden change in BP · Many sources of error Repeated or prolonged inflation can cause neuropathy or limb ischaemia

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