Table 1: Comparison of non-invasive and invasive BP monitoring [20,21].

Non-Invasive (Oscillometric) Invasive (Arterial Line)

• American Society of Anesthesiology minimal standard: every 5 min while under general anesthesia

• continuous monitoring

• unstable patients

• strict BP control

• controlled hypotension

• anticipated volatility in BP

• obtaining frequent labs

• suspected NIBP inaccuracy


• cuff inflated above systolic BP and incrementally deflated while amplitudes of cuff pressure oscillations measured by pressure transducer

• systolic BP obtained when amplitude of oscillations increases by 25-50% of maximum

• MAP is point of maximum oscillations

• diastolic BP obtained when amplitude of oscillations decrease by 80% or disappear

• time versus pressure graph constructed whereby systolic and diastolic BPs are mathematically-derived

• fluctuations of vascular pressure cause pulsation of saline column

• displacement of electromanometer diaphragm

• mechanical to electrical transduction

• Fourier analysis for waveform construction

Factors that may affect accuracy

• patient movement/external pressure

• obesity

• poor perfusion

• poor pulsatility (e.g. mechanical cardiac support)

• extremes of BP

• bradycardia or irregular pulse

• improperly selected cuff size

• arterial stiffness

• regional vascular disease

• excessive tubing length, compliance, or caliber

• improper zeroing

• wrong transducer leveling (transducer should be at the level of the heart -aiming 5 cm behind the sternum in a supine patient)

• over- or under-dampening of the pressure tracing

• arterial spasm or thrombosis

• extremes of BP


• delayed therapeutic intervention

• soft tissue injury

• phlebitis

• neuropathy

• compartment syndrome

• intravenous line infiltration/occlusion

• interference with pulse oximetry

• thrombosis

• embolism

• infection

• neuropathy from hematoma/compression

• vascular injury

• limb loss


• ensure proper cuff size/circumference

• ensure regular pulse

• consider arterial stiffness

• inspect for device malfunction (air leak, tubing kink, external pressure)

• reassess at different extremities

• assess waveform quality

• re-zero/calibrate

• level transducer with heart

• remove catheter/tubing kinks

• ensure pressure bag full

• consider arterial stenosis/spasm

• remove air bubbles/clot

• correct hypothermia