Noninvasive continuous blood pressure measurement: A clinical evaluation of the Cortronic APM 770

The Cortronic APM 770 (Cortronic, Ronkonkoma, NY) is a commercial device that claims to measure blood pressure noninvasively and continuously with the use of a standard blood pressure cuff. The aim of our study was to assess the performance of the continuous-mode blood pressure readings of the Cortronic during anesthesia and surgery. We recorded blood pressure in 5 patients bilaterally. An intraarterial pressure (IAP) curve was recorded from 1 arm and the Cortronic pressure curve (CPC) was recorded from the other. For statistical analysis the period between 2 Cortronic recalibrations was defined as the intercalibration interval. The duration of these intervals ranged from 20 to 0.5 minutes. Four paired samples were drawn from each interval. The first sample in an interval represented the recalibration blood pressure; the other samples represented the continuous blood pressure. A total of 1,232 samples were taken, of which 308 were recalibration. The median of the differences and the 2.5th and 97.5th percentile limits of agreement were determined. Their respective values for diastolic and systolic recalibration measurements were 5, –17, and 34 mm Hg, and 6, –12, and 38 mm Hg. Their values for continuous measurements were 4, –23.5, and 32 mm Hg, and 6, –30, and 70 mm Hg. Changes in CPC were evaluated against changes in the corresponding IAP by plotting them in 4-quadrant graphs. In these graphs the Spearman rank correlations were betweenr=–0.17 andr=0.01. We observed opposite CPC and IAP trends on 24 occasions during this study. We performed a simple simulation study to better understand the measurement method of the Cortronic. The study showed a positive relationship between pulsation volume and CPC amplitude, and between pulsation rate and CPC amplitude. We conclude that during anesthesia and surgery continuous-mode blood pressure readings of the Cortronic are unreliable, and suggest that the phenomenon of the two pressures' moving in opposite directions is inherent to the measurement principles of the device.