Monitoring cardiac output with Flo Trac VigileoTM
Pisa, Italy
* E-mail: f.guarracino{at}ao-pisa.toscana.it
Editor—In their recent article, Mayer and colleagues1 compared a new device for semi-invasive determination of cardiac output (CO) (Flo Trac/VigileoTM, Edwards Lifesciences, Irvine, CA, USA) with the bolus thermodilution technique, considered the clinical ‘gold standard’. They performed their measurements intraoperatively and after operation in patients undergoing cardiac surgery and concluded that the new device, based on arterial pressure waveform analysis, does not appear to adequately measure continuous CO and is not recommended for routine use. In fact, the authors found an overall percentage error of 45.9% in CO measurement compared with the ‘gold standard’ method.
We have been using the new device, Flo Trac/VigileoTM in the last 2 yr in medical and cardiac surgical patients requiring continuous CO monitoring during ICU stay. In our experience, VigileoTM and the thermodilution method show no significant differences in CO measurements in patients with ventricular dysfunction without valve disease.
We think that the different experience Mayer and colleagues report is due to several reasons. First, the authors included many patients (about 50% of study group) with mitral and aortic insufficiency, whose arterial compliance and impedance are of course different from patients without valve regurgitation. These differences lead to relevant changes in arterial waveform characteristics and in ventriculo-arterial coupling, which well explain the bias between VigileoTM technology and thermodilution described by Mayer. Secondly, they did not exclude the presence of tricuspid insufficiency in their study group, even in patients with mitral disease, so accepting a potential pitfall in thermodilution measurements.
In our opinion, Flo Trac sensor and pulmonary artery thermodilution catheter have different indications due to the different information they can provide. In severely haemodynamically compromised patients, we agree that pulmonary thermodilution catheter remains the best option for monitoring CO and cardiac pressures. Whereas in less compromised patients, requiring flow monitoring, in our experience the new device VigileoTM provides a valuable set of information, with reliable CO calculation by Flo Trac sensor plus ScO2 measurement if the Presep central venous oximetry catheter (Edwards Lifesciences) is added, with the great advantage of less invasiveness in comparison with pulmonary artery catheterization.
Ludwigshafen, Germany
* E-mail: j-mayer{at}gmx.de
Editor—We thank Guarracino and colleges for their interest in our article.1 We agree with the authors that the VigileoTM system and the pulmonary artery catheter (PAC) might have different clinical indications in the near future. Nevertheless, every new tool to measure CO has to be validated before it is introduced in clinical practice.
We disagree, however, with the valve theory as a possible explanation for the bias raised in their letter. First, it was described in the methods section of our article that patients undergoing mitral or aortic valve surgery were excluded from analysis if they showed echocardiographic signs of aortic or mitral dysfunction after surgery. Secondly, we did not state in the article that 50% of the included patients had mitral or aortic insufficiency. Patients scheduled for valve replacement in fact included aortic and mitral valve stenosis and insufficiency at about the same percentage. Thirdly, during preparation of our manuscript, we analysed patients undergoing valve surgery and coronary artery bypass grafting (CABG) separately. CABG patients (valve dysfunction before operation excluded) showed a percentage error of 45.1% with a bias of 0.44 litre min–1 m–2 and a precision of 1.24 litre min–1 m–2 which was comparable with patients undergoing valve surgery. Aortic and mitral valve dysfunction hence did neither bias thermodilution nor VigileoTM results in our study.
Unfortunately, the authors did not present own data to substantiate their experience. Other recently published validation studies are in good correlation with our results2 or show even worse results.3
References
1 Mayer J, Boldt J, Schollhorn T, Rohm KD, Mengistu AM, Suttner S. Semi-invasive monitoring of cardiac output by a new device using arterial pressure waveform analysis: a comparison with intermittent pulmonary artery thermodilution in patients undergoing cardiac surgery. Br J Anaesth (2007) 98:176–82.
2 Sander M, Spies CD, Grubitzsch H, Foer A, Muller M, von Heymann C. Comparison of uncalibrated arterial waveform analysis in cardiac surgery patients with thermodilution cardiac output measurements. Crit Care (2006) 10:R164.[CrossRef][Medline]
3 Opdam HE, Wan L, Bellomo R. A pilot assessment of the FloTracTM cardiac output monitoring system. Intensive Care Med (2007) 33:344–9.[CrossRef][Web of Science][Medline]
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