Uncalibrated arterial pressure waveform analysis for less-invasive cardiac output determination in obese patients undergoing cardiac surgery

Abstract

Background: Uncalibrated arterial waveform analysis (FloTrac/ Vigileo™) uses standard arterial access to determine cardiac output (CO). Calculations are based on arterial waveform characteristics in combination with patient characteristic data to estimate individual arterial compliance. It has been shown that obesity is associated with altered arterial compliance independently of other risk factors. We conducted this study to assess the validity of measuring CO by the FloTrac/Vigileo™ device in obese patients undergoing cardiac surgery in comparison with bolus thermodilution technique. Methods: Fifteen obese patients with a BMI of ≥30 and 23 non-obese patients (BMI 18-25) undergoing coronary artery bypass grafting (CABG) were included. Simultaneous CO measurements by bolus thermodilution and the FloTrac/Vigileo™ device (software version 1.10) were obtained intraoperatively after induction of anaesthesia, before cardiopulmonary bypass (CPB), after CPB, and after sternal closure. Measurements in the intensive care unit (ICU) were performed upon arrival in the ICU, after 4, 8, and 24 h after surgery. CO was indexed to the body surface area (cardiac index, CI). Results: The analysis of 262 data pairs revealed a bias and precision of 0.19 and ±0.66 litre min-1 m-2, resulting in a percentage error of 26.6%. Thermodilution CI values ranged from 1.1 to 4.2 litre min -1 m-2 [mean 2.4 (0.52) litre min-1 m -2]. Subgroup analysis resulted in a percentage error of 29.8% in obese patients and 24.4% in patients with normal BMI. Conclusions: The semi-invasive FloTrac/Vigileo™ device was found to adequately agree with bolus pulmonary artery thermodilution in both obese and non-obese patients undergoing CABG. © The Author [2009]. Published by Oxford University Press on behalf of The Board of Directors of the British Journal of Anaesthesia. All rights reserved.