CONTINUOUS NONINVASIVE BLOOD-PRESSURE MONITORING BY BRACHIAL-ARTERY DISPLACEMENT METHOD IN HIGH-RISK SURGICAL PATIENTS

Continuous non-invasive blood pressure (CNBP) measurements were compar ed to invasive radial artery pressure recordings in 26 patients with c ardiac, vascular and/or pulmonary disease. Patients were studied durin g general anaesthesia (n = 6), regional anaesthesia (n = 10), or combi ned technique (n = 10) for abdominal or transurethral surgery. CNBP wa s obtained from a cuff placed around the upper arm and simultaneously compared to invasive pressure from the ipsilateral radial artery. A CN BP device (7001 Cortronic) used intermittent oscillometric measurement for calibration. Through a cuff continuously inflated to a pressure o f 20 mmHg, a microprocessor-controlled electro-pneumatic acquisition s ystem sensed displacements of the brachial artery wall. Amplified, dig itally converted, filtered and transformed data were displayed as a co ntinuous pulse pressure waveform and digital pressure values on the sc reen. The CNBP method functioned without disturbances before surgery i n all patients. Intra-operative use of electrocautery or a spontaneous occurrence of warning on the screen repeatedly triggered oscillometri c recalibration, hence CNBP measurements were discontinued in nine pat ients. Coefficients of correlation (r) Of all invasive and CNBP pairs (n = 1111) were 0.68, 0.58 and 0.70 for systolic, diastolic, and mean blood pressures, respectively. Prediction errors (bias, mean +/- SD) w ere -13.6 +/- 22.5 mmHg (on average CNBP < invasive pressure) for syst olic, +13.0 +/- 12.4 mmHg (CNBP > invasive pressure) for diastolic and +5.0 +/- 13.9 mmHg (CNBP > invasive pressure) for mean CNBP, as compa red to radial artery pressure values. Absolute errors (precision) were 25.3 +/- 9.4 mmHg for systolic, 17.4 +/- 4.5 mmHg for diastolic, and 13.9 +/- 4.6 mmHg for mean CNBP. During anaesthesia induction (n = 672 ) the difference between consecutive measurements (trend of pressure c hanges) with invasive and CNBP method exceeded 20 mmHg in 90 (13.3%) i nstances for systolic, in 33 (4.9%) instances for diastolic, and in 45 (6.6%) instances for mean blood pressure. In conclusion, the CNBP met hod by brachial artery wall displacement failed to measure the blood p ressure reliably and to display the trend of pressure changes correctl y during anaesthesia induction. In its present form this CNBP method s hould not replace invasive blood pressure monitoring in high-risk pati ents neither for anaesthesia induction nor during non-thoracic surgica l procedures.