Level of agreement between Nexfin and PiCCO cardiac output in morbidly obese patients undergoing laparoscopic surgery

Pieter Schraverus1,2, Chantal A. Boly1, Jan-Willem Coumou2, Christa Boer1, 
Simone van Kralingen 2

Department of Anesthesiology, 1VU University Medical Center, Institute for Cardiovascular Research, De Boelelaan 1117, 1081 HV, Amsterdam, the Netherlands, 2Sint Lucas Andreas Hospital, Jan Tooropstraat 164, 1061 AE Amsterdam, the Netherlands
p.schraverus@vumc.nl 

Background: Morbidly obese patients are at increased risk for intraoperative hemodynamic instability, which requires intensive monitoring. While the non-invasive Nexfin® blood pressure monitor may be used in these patients to monitor cardiac output (CO), it is unknown whether the weight-based algorithm of this device also applies to patients with extreme body weight. We therefore investigated the agreement between Nexfin CO and thermodilution-based CO in morbidly obese patients undergoing laparoscopic surgery. 
Materials and methods: In 30 patients (BMI>35 kg/m2) undergoing laparoscopic gastric bypass surgery, CO was simultaneously measured by Nexfin and thermodilution-based PiCCO on 12 consecutive perioperative time points. Data analysis included Bland-Altman level of agreement, Clarke’s Error Grid analysis for clinical accuracy and a polar plot.
Results and discussion: The average BMI was 44.6±6 kg/m2. Bland Altman analysis revealed a bias of 0.60±1.62 L/min with limits of agreement from -2.67 to 3.86 L/min. The precision error was 46% and ranged outside the Critchley criteria for agreement of CO devices with a gold standard. Clarke’s error grid analysis showed that 72% of values were located in a clinically acceptable zone. Polar plot analysis resulted in an angular bias of 2.61° with radial limits of agreement of -60.08° to 49.82°. Angular concordance rate was 77%, with ranges outside the Critchley criteria for trending.
Conclusion: The present study shows a low level of agreement and insufficient trending of CO measurements by the Nexfin compared to PiCCO in morbidly obese patients.

Level of agreement between Nexfin and thermodilution cardiac output in morbidly obese patients undergoing bariatric surgery