Accuracy and Trending Ability of Cardiac Index Measured by the CNAP System in Patients Undergoing Abdominal Aortic Aneurysm Surgery.

OBJECTIVES: The CNAP system is a noninvasive monitor that provides a continuous arterial pressure waveform using an inflatable finger cuff. The authors hypothesized that dramatic changes in systemic vascular resistance index during abdominal aortic aneurysm (AAA) surgery might affect the accuracy of noninvasive pulse contour monitors. The aim of this study was to evaluate the accuracy and trending ability of cardiac index derived by the CNAP system (CICN) in patients undergoing AAA surgery. DESIGN: Prospective clinical study. SETTING: Cardiac surgery operating room in a single cardiovascular center. PARTICIPANTS: Twenty patients who underwent elective AAA surgery. INTERVENTIONS: CICN and cardiac index measured using 3-dimensional images (CI3D) were determined simultaneously at 8 points during the surgery. At aortic clamping and unclamping, the authors tested the trending ability of CICN using 4-quadrant plot analysis and polar plot analysis. MEASUREMENTS AND MAIN RESULTS: The authors found a wide limit of agreement between CICN and CI3D (percentage error: 85.0%). The cubic splines, which show the relationship between systemic vascular resistance index and percentage CI discrepancy [(CICN-CI3D)/CI3D], were sloped positively. Four-quadrant plot analysis showed poor trending ability for CICN at both aortic clamping and unclamping (concordance rate: 29.4% and 57.9%, respectively). In the polar plot analysis, the concordance rates at aortic clamping and unclamping were 15.0% and 35.0%, respectively. CONCLUSIONS: CICN is not interchangeable with CI3D in patients undergoing AAA surgery. The trending ability for CICN at aortic clamping and unclamping was below the acceptable limit. These inaccuracies might be secondary to the high systemic vascular resistance index during AAA surgery.