Continuous Noninvasive Arterial Pressure Monitoring Using the Vascular Unloading Technique (CNAP System) in Obese Patients During Laparoscopic Bariatric Operations

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Increasing rates of obesity create new challenges for hemodynamic monitoring in the perioperative phase. Continuous monitoring of arterial pressure (AP) is important in severely obese patients who are at particular risk for cardiovascular complications. Innovative technologies for continuous noninvasive AP monitoring are now available. In this study, we aimed to compare continuous noninvasive AP measurements using the vascular unloading technique (CNAP system; CNSystems, Graz, Austria) compared with invasive AP measurements (radial arterial catheter) in severely obese patients during laparoscopic bariatric surgery.


In 29 severely obese patients (mean body mass index 48.1 kg/m2), we simultaneously recorded noninvasive and invasive AP measurements over a period of 45 minutes and averaged the measurements using 10-second episodes. We compared noninvasive (test method) and invasive (reference method) AP measurements using Bland-Altman analysis and 4-quadrant plot/concordance analysis (2-minute interval).


We observed a mean of the differences (±SD, 95% limits of agreement) between the AP values obtained by the CNAP system and the invasively assessed AP values of 7.9 mm Hg (±9.6 mm Hg, −11.2 to 27.0 mm Hg) for mean AP, 4.8 mm Hg (±15.8 mm Hg, −26.5 to 36.0 mm Hg) for systolic AP, and 9.5 mm Hg (±10.3 mm Hg, −10.9 to 29.9 mm Hg) for diastolic AP, respectively. The concordance rate was 97.5% for mean AP, 95.0% for systolic AP, and 96.7% for diastolic AP, respectively.


In the setting of laparoscopic bariatric surgery, continuous noninvasive AP monitoring with the CNAP system showed good trending capabilities compared with continuous invasive AP measurements obtained with a radial arterial catheter. However, absolute CNAP- and arterial catheter–derived AP values were not interchangeable.

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