Background and Goal of Study: Arterial pressure-based cardiac ouput monitors are increasingly used as alternatives to thermodilution. It seems that arterial compliance, which has been shown altered in obese patients, has a large impact on the accuracy of CO calculation of the Flo Trac/Vigileo device. Our goal was to investigate the agreement between FloTrac-Vigileo and thermodilution through pulmonary artery catheter (PAC) to CO measurement in morbid obese (MO) patients before bariatric surgery (BS).
Materials and Methods: Under the IRB approval, we realized a prospective study in MO patients(BMI ≥ 35 Kg/m2) in the context of a wider study conducted to investigate the causes of hypoxemia in MO patients by ventilation-perfusion study. Exclusion criteria were cardiovascular and pulmonary diseases and obstructive sleep apnea syndrome. PAC (Opticath catheter, Hospira, Inc., Lake Forest, IL) and radial artery catheter were inserted. Data sets of thermodilution PAC-based and arterial pressure-based cardiac output were obtained simultaneously at predefined time points: breathing air (A) and pure oxygen (O2), and in both sitting (S) and lying (L) position. At least 3 consecutive injections of 10 mL of cold-temperature normal saline through PAC at defined time points were performed and the results were accepted and averaged if the shape of the thermodilution curve was consistent. The arterial cannula was connected to a FloTrac pressure transducer (FloTrac sensor, Edwards Lifesciences) for continuous CO display and data were registered simultaneously. We analyzed data base through Blant Altman plot and Lin's corcondance coefficient to measure the accuracy and precision magnitude.
Results and Discussion: Eight MO patients (7F/1M; 51±9 years old) with BMI 44±4,4 Kg/m2 were included. One hundred and thirty-two pairs of measurements were registered, 69 (51.9%) pairs while breathing A (32 S and 37 L) and 63 (48.1%) pairs while breathing O2 (35 S and 28 L).The analysis of these 132 data pairs revealed, through Bland Altman plot and Lin's corcondance coefficient (LCC), inadequately correlation between these two devices, LCC=0.299. When data pairs obtained in S and L position were analyzed separately, LCC remained inadequately (S=0.291 and L=0.291).
Conclusion(s): The semi-invasive Flo Trac/Vigileo device was found to inadequately agree with bolus pulmonary artery thermodilution in obese patients.