Is applanation tonometry a reliable method for monitoring blood pressure in morbidly obese patients undergoing bariatric surgery?

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The aim of this study was to evaluate the validity of non-invasive continuous BP measurement by applanation tonometry in morbidly obese patients undergoing bariatric surgery.


Arterial blood pressure (AP) was recorded intraoperatively both by applanation tonometry (AT) (T-Line 200pro, Tensys Medical®, USA) and an arterial line (AL) after radial cannulation in obese patients undergoing bariatric surgery. Discrepancies between the two methods were assessed as bias, limits of agreement and percentage error. Mean, systolic, and diastolic arterial pressures were assessed (MAP, SAP, DAP respectively). Trending ability was assessed by concordance based on four-quadrant plotting.


Mean (sd) BMI of the 28 patients was 49.4 (9.7 kg m−2). A total of 201 907 time points were available for analysis. Bias for MAPAT compared with MAPAL was +3.97 mm Hg (SAPAT +3.45 mm Hg; DAPAT +3.66 mm Hg) with limits of agreement for MAPAT of −14.47 and +22.41 mm Hg (SAPAT −22.0 and +28.9 mm Hg; DAPAT −15.7 and +23.1 mm Hg). Percentage error for MAPAT was 23.5% (23.4% for SAPAT; 30.5% for DAPAT). Trending ability for MAP, SAP, and DAP revealed a concordance of 0.74, 0.72, and 0.71, respectively.


Continuous BP assessment by applanation tonometry is feasible in morbidly obese patients undergoing bariatric surgery. However, despite a low mean difference, 95% limits of agreement and trending ability indicate that the technology needs to be improved further, before being recommended for routine use in this group of patients.

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