The Flotrac-Vigileo system appears to have become the first line haemodynamic monitor in Galway. How did this happen, and is it just a toy?
Over the past 2 decades there have been considerable advances in minimally invasive cardiovascular monitoring. This results from a greater acceptance of the flow-model approach to fluid resuscitation,1 a cultural shift away from pulmonary artery catheters (rightly or wrongly),2 and the now widespread acceptance that central venous pressure (CVP) does not predict fluid responsiveness.3 In essence, critical care practitioners now tend to combine data on arteriolar compliance (blood pressure), cardiac performance (stroke volume) and oxygen delivery-consumption (SvO2) when making decisions about fluids and vasopressors. The most popular non invasive devices to date are – oesophageal Doppler (useful, but huge user variability), PiCCO – which requires the placement of a femoral arterial line, and NiCCO – which uses the Fick principle to measure cardiac output from rebreathing CO2. None of these are simple to use, nor can they utilize monitors already in place. Hence, a device that measures stroke volume from a standard arterial line would appear to be a major step forward: assuming, of course, that it is accurate.
The Flotrac (sensor)-Vigileo monitor (Edwards Lifesciences, Irvine, Ca) calculates stroke volume and cardiac output from a single sensor attached to an arterial line at any site. Unlike PiCCO/PulseCO/LiDCO, it does not require external calibration, or the presence of a central line or specialized catheter. Since its introduction in 2006, the device has seen several software upgrades, with progressive improvement in accuracy: with time we can expect this device to improve further. We are now using the third generation of software,4 and this appears to be more accurate than previous versions.5
Flotrac-VIgileo combines rapid analysis in real time of the arterial pressure waveform with demographic data (such as gender, age, weight and height) applied to an evolving algorithm to calculate cardiac output. Arterial pulsatility is directly proportional to stroke volume. As changes in vascular tone and compliance occur dynamically, the device appears capable of correcting for this by analyzing skewness and kurtosis of the arterial waveform (more information here ). These correction variables are updated every 60 seconds and the arterial waveform is analyzed and averaged over 20 seconds, thus eliminating artifacts, jitter and premature contractions. Cardiac output is calculated utilizing the arterial waveform and the heart rate.
In addition to cardiac output, Flotrac-VIgileo (F/V) also calculates stroke volume variability, and hence fluid responsiveness.
An increasing number of studies have investigated this system. With each software update the device appears to be becoming more accurate. Mayer and colleagues6 meta-analysed studies to date. Earlier studies demonstrated poor correlation between F/V and thermodilution methods; with newer software the correlation has improved.7 It should be borne in mind, however, that thermodilution methods, although considered the gold standard, are not ideal devices to compare with F/V: measurement intervals and averaging times are substantially longer with all thermodilution methods. Hence it is possible that F/V is more sensitive to dynamic changes in cardiovascular activity. Conversely, it is likely the F/V is severely limited in patients with aortic valve disease (PMID: 21823375), those with intra-aortic balloon pumps in situ, those rewarming from induced hypothermia and patients with intra-cardiac shunts.
Recent studies have suggested that F/V is quite accurate at measuring changes in cardiac output associated with volume expansion (preload sensitivity)8 but not with changes associated the vasopressor use.9-11 In patients undergoing open abdominal aortic aneurysm surgery, the F/V system was highly inaccurate during the critical phases of clamping/unclamping.12 It is likely that the accuracy also depends on the patient having a regular cardiac rhythm and minimal variability in tidal volume.13;14
So a mixed report on the Flotrac. Clearly, in terms of simplicity it is unbeatable: simplicity of placement, lack of observer error, continuity of data and the lack of need for secondary vascular access. In terms of accuracy– assuming that the patient is in a regular rhythm and has a reasonably stable respiratory pattern, it appears fairly reliable. I cannot see this being a device used intraoperatively, in the way the oesophageal Doppler has found its niche, due to significant inaccuracy in dynamic conditions. Nevertheless, in the ICU, in patients where haemodynamic monitoring may be beneficial – such as early sepsis, this is a useful tool. Is it better than a Swan? No, is anything? That will be topic of a future post.
1. Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B, Peterson E, Tomlanovich M: Early goal-directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med 2001; 345: 1368-77
2. Connors AF, Jr., Speroff T, Dawson NV, Thomas C, Harrell FE, Jr., Wagner D, Desbiens N, Goldman L, Wu AW, Califf RM, Fulkerson WJ, Jr., Vidaillet H, Broste S, Bellamy P, Lynn J, Knaus WA: The effectiveness of right heart catheterization in the initial care of critically ill patients. SUPPORT Investigators. JAMA: The Journal of the American Medical Association 1996; 276: 889-97
3. Marik PE, Baram M, Vahid B: Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares. Chest 2008; 134: 172-8
4. Vasdev S, Chauhan S, Choudhury M, Hote M, Malik M, Kiran U: Arterial pressure waveform derived cardiac output FloTrac/Vigileo system (third generation software): comparison of two monitoring sites with the thermodilution cardiac output. Journal of Clinical Monitoring and Computing 1-6
5. De Backer D, Marx G, Tan A, Junker C, Van Nuffelen M, H++ter L, Ching W, Michard Fdr, Vincent JL: Arterial pressure-based cardiac output monitoring: a multicenter validation of the third-generation software in septic patients. Intensive Care Medicine 2011; 37: 233-40
6. Mayer J, Boldt J, Poland R, Peterson A, Manecke GR, Jr.: Continuous arterial pressure waveform-based cardiac output using the FloTrac/Vigileo: a review and meta-analysis. J Cardiothorac Vasc Anesth 2009; 23: 401-6
7. Mayer J, Boldt J, Beschmann R, Stephan A, Suttner S: Uncalibrated arterial pressure waveform analysis for less-invasive cardiac output determination in obese patients undergoing cardiac surgery. Br J Anaesth 2009; 103: 185-90
8. Zhang Z, Lu B, Sheng X, Jin N: Accuracy of stroke volume variation in predicting fluid responsiveness: a systematic review and meta-analysis. Journal of Anesthesia 2011; 25: 904-16
9. Meng L, Phuong Tran N, Alexander BS, Laning K, Chen G, Kain ZN, Cannesson M: The Impact of Phenylephrine, Ephedrine, and Increased Preload on Third-Generation Vigileo-FloTrac and Esophageal Doppler Cardiac Output Measurements. Anesthesia & Analgesia 2011; 113: 751-7
10. Monnet X, Anguel N, Jozwiak M, Richard C, Teboul JL: Third-generation FloTrac/Vigileo does not reliably track changes in cardiac output induced by norepinephrine in critically ill patients. British Journal of Anaesthesia 2012;
11. Metzelder S, Coburn M, Fries M, Reinges M, Reich S, Rossaint R, Marx G, Rex S: Performance of cardiac output measurement derived from arterial pressure waveform analysis in patients requiring high-dose vasopressor therapy. British Journal of Anaesthesia 2011; 106: 776-84
12. Kusaka Y, Yoshitani K, Irie T, Inatomi Y, Shinzawa M, Ohnishi Y: Clinical Comparison of an Echocardiograph-Derived Versus Pulse CounterGÇôDerived Cardiac Output Measurement in Abdominal Aortic Aneurysm Surgery. Journal of Cardiothoracic and Vascular Anesthesia 2012; 26: 223-6
13. Khwannimit B, Bhurayanontachai R: Prediction of fluid responsiveness in septic shock patients: comparing stroke volume variation by FloTrac/Vigileo and automated pulse pressure variation. European Journal of Anaesthesiology (EJA) 2012; 29:
14. Saraceni E, Rossi S, Persona P, Dan M, Rizzi S, Meroni M, Ori C: Comparison of two methods for cardiac output measurement in critically ill patients. British Journal of Anaesthesia 2011; 106: 690-4