OSCILLOMETRIC BLOOD-PRESSURE MEASUREMENTS BY DIFFERENT DEVICES ARE NOT INTERCHANGEABLE

Blood pressure (BP) is frequently measured in patients by noninvasive blood pressure (NIBP) monitors. Values obtained by oscillometric devic es of different brands may appear in one patient's record as if they w ere interchangeable; their concordance, however, has not been establis hed. In 25 patients with major depression who were treated with electr oconvulsive therapy (ECT) BP was measured on either arm by devices man ufactured by SpaceLabs (SpL, 12 patients, 182 data points) and Marquet te (Marq, 13 patients, 193 data points), respectively, and comparisons were made with simultaneous measurements on the opposite arm by Dinam ap 1846SX (DIN), during the awake state and at 1-min intervals up to 5 -7 min after ECT. Because ECT is associated with an intense, but short -lasting hyperdynamic state, comparisons of BP values could be made ov er a wide range of pressures. Bland-Altman plots were constructed to s how the distribution of pressure differences at all pressures. Agreeme nts between two instruments were judged according to guide lines by th e American Association for Advancement of Medical Instrumentation (AAM I). The standard deviation of the difference (SDD) between two DIN dev ices was 7 nun Hg for systolic (SEP) and 6.3 mm Hg for diastolic blood pressure (DBP), whereas mean differences were 0.9 and 0.2 nun Hg, res pectively (P = not significant [NS]), thus showing reproducibility. Co rresponding SDD values SpL versus DIN were 9.1 for SEP and 8.3 nun Hg for DBP, while the mean differences were 1.6 (P = 0.026) and 7.3 (P = 0.0001) mm Hg, respectively. Corresponding SDD values for Marq versus DIN were 11.8 and 9.7 mm Hg with mean differences of 0.8 (P = NS) and 0.3 (P = NS) mm Hg. Whereas SEP differences DIN versus DIN exceeded 10 mm Hg in only 10% of observations, they exceeded that threshold in 31 % and 32% of observations for SpL versus DIN and Marq versus DIN, resp ectively. In view of the variability that exceeds the AAMI guidelines and the one out of three occurrence of individual SEP differences exce eding 10 mm Hg for comparisons of SpL or Marq versus DIN, measurements by these three oscillometric devices are not interchangeable.