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Uncalibrated cardiac output determination in obese patients undergoing cardiac surgery
- Anthony C Smith (7 August 2009)
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Anthony C Smith, Specialist Registrar University Hospital North Staffordshire
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Editor- In their recent article Mayer and colleagues1 compared a new algorithm (version 1.10) of the FloTracTM/VigileoTM device with the bolus thermodilution technique. The authors have previously demonstrated acceptable reliability of this new algorithm in patients in sinus rhythm undergoing CABG. But they concluded that there was still a need to prove reliability in different clinical settings.2 Studies have suggested limitations of previous algorithms in the presence of altered SVRI and arrhythmias.3, 4 The authors state that arterial compliance has a large impact on the accuracy of CO calculation of the FloTracTM/VigileoTM device and that obese patients have altered arterial compliance.1 I agree that it would be useful to investigate the performance of the device under conditions of altered compliance such as obesity. Unfortunately, there was no significant difference in SVRI between the two groups. So, whilst this study may demonstrate acceptable reliability of the measurements in obese patients undergoing CABG, it does not demonstrate reliability of the device under conditions of altered compliance. Biancofiore and colleagues5 presented data in cirrhotic patients undergoing liver surgery using the new algorithm. By plotting bias against SVRI they demonstrated a log-linear relationship between SVRI and bias. They concluded that this highlighted a problem the FloTracTM/VigileoTM has with low peripheral resistance states. Mayer and colleagues2 have also previously noted differences in performance during the perioperative time course.2 In this study changes in performance are seen during the perioperative period, which appear to relate to changes in SVRI. Mayer and colleagues could have investigated further the relationship between SVRI and bias during the perioperative period. The study excluded all patients with arrhythmias and measurements were discarded if arrhythmias occurred. Compton and colleagues6 found poor performance of the new algorithm that could be as a result of arrhythmias. Arrhythmias are common in the critically ill so the FloTracTM/VigileoTM system needs to be assessed in this setting. With the new algorithm developed to improve accuracy, performance in patients with arrhythmias or altered compliance needs to be assessed further. AC. Smith* Stoke-on-Trent, UK *Email: Anthony-smith@doctors.org.uk 1 Mayer J, Boldt J, Beschmann R, et al. Uncalibrated arterial pressure waveform analysis for less-invasive cardiac output determination in obese patients undergoing cardiac surgery. Br J Anaesth 2009; 103: 185- 90 2 Mayer J, Boldt J, Wolf MW, et al. Cardiac output derived from arterial pressure waveform analysis in patients undergoing cardiac surgery: validity of a second generation device. Anesth Analg 2008; 106: 867-72 3 Sakka SG, Kozieras J, Thuemer O, et al. Measurement of cardiac output: a comparison between transpulmonary thermodilution and uncalibrated pulse contour analysis. Br J Anaesth 2007; 99: 337-42 4 Biais M, Noulette-Gaulain K, Cottenceau V, et al. Uncalibrated pulse contour-derived stroke volume variation predicts fluid responsiveness in mechanically ventilated patients undergoing liver transplantation. Br J Anaesth 2008; 101: 761-8 5 Biancofiore G, Critchley LAH, Lee A, et al. Evaluation of an uncalibrated arterial pulse contour cardiac output monitor system in cirrhotic patients undergoing liver surgery. Br J Anaesth 2009; 102: 47-54 6 Compton FD, Zukunft B, Hoffmann C, et al. Performance of a minimally invasive uncalibrated cardiac output monitoring system (FloTracTM/VigileoTM) in haemodynamically unstable patients. Br J Anaesth 2008; 100: 451-6 Conflict of Interest:None declared |
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