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

Background

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.

Methods

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.

Results

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 MAP_AT compared with MAP_AL was +3.97 mm Hg (SAP_AT +3.45 mm Hg; DAP_AT +3.66 mm Hg) with limits of agreement for MAP_AT of –14.47 and +22.41 mm Hg (SAP_AT –22.0 and +28.9 mm Hg; DAP_AT –15.7 and +23.1 mm Hg). Percentage error for MAP_AT was 23.5% (23.4% for SAP_AT; 30.5% for DAP_AT). Trending ability for MAP, SAP, and DAP revealed a concordance of 0.74, 0.72, and 0.71, respectively.

Conclusions

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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