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Response to the letter of Dr. Bein
- Daniel A. Reuter, Jens C. Kubitz (14 August 2007)
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VALIDATION OF PULSE CONTOUR DERIVED STROKE VOLUME VARIATION
- Berthold Bein, Jochen Renner, Patrick Meybohm, Jens Scholz (19 July 2007)
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Daniel A. Reuter , Jens C. Kubitz
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We appreciate the interest of Dr Bein and colleagues in our recent article. We would like to take the opportunity to give a short statement. First, they are correct that Critchley and Critchley suggested a very useful approach to “quantify acceptable limits of agreement between two measurement techniques” (1). From a meta-analysis comparing absolute values of clinical cardiac output measurement techniques they concluded that combined limits of agreement should not be above 30 % according to an error-gram, as correctly stated by Dr Bein. This is a possible point of discussion; however, in contrast to our investigation, this was focussed on absolute values of cardiac output and a comparison of two clinical methods versus each other. Secondly, there is no analysis of changes in SVV provided in our article, as no change in SVV occurred following alteration of mean arterial pressure. Thirdly, the influence of tidal volume on functional preload indices is indeed well known for a long time (2,3,4). This is, why tidal volume has not been altered in our study and, accordingly, the recent work of Dr Bein’s group, confirming those previous results, has not been cited. Jens C. Kubitz, Daniel A. Reuter Literature: 1. Critchley LA, Critchley JA. A meta-analysis of studies using bias and precision statistics to compare cardiac output measurement techniques. J Clin Monit Comput. 1999; 15: 85-91 2. Szold, Pizov A, Segal E, Perel A. The effect of tidal volume and intravascular volume state on systolic pressure variation in ventilated dogs. Intensive Care Med 1989; 1989;15: 368-71 3. Reuter DA, Bayerlein J, Goepfert MS, et. al. Influence of tidal volume on left ventricular stroke volume variation measured by pulse contour analysis in mechanically ventilated patients. Intensive Care Med. 2003; 29: 476-80 Conflict of Interest:None declared |
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Berthold Bein University Hospital Schleswig-Holstein, Campus Kiel, Department of Anaesthesiology and Intensive Car, Jochen Renner, Patrick Meybohm, Jens Scholz
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EDITOR: We read the article by Dr. Kubitz and colleagues reporting their results comparing stroke volume variation (SVV) derived by different methods of stroke volume (SV) determination with great interest [1]. The authors should be commended for this study, that for the first time compared SVV derived from the widely used PiCCO monitor (Pulsion Medical Systems, Mu- nich, Germany) to a true reference standard, i.e. aortic transit time ultrasound. Though their approach is ambitious, however, some methodological remarks are necessary. Firstly, the authors state that there was good agreement between SVV derived from pulse contour analysis and that derived from the aortic flow signal. This conclusion, however, is not supported by the data presented. Following the introduction of Bland Altman plots for method comparison in 1986 [2], for more than a decade the judgement of bias and limits of agreement was left to the clinician, and identical values were interpreted differently. The pivotal work by Critchley for the first time suggested a comprehensive mathematically derived criterion for assessment of observed variability [3]. Given an inherent variability of ±20% for each method under comparison, the combined variability (i.e. limits of agreement) should not exceed ±30% of the mean SVV. Applying these strict criteria to the data, agreement of methods studied by the authors was unacceptable. Secondly, the authors compared SV derived from different methods at specified experimental conditions. Unfortunately, no information is provided as to the ability of methods to reflect changes of SVV consistently. It has been suggested recently to analyse the change in a variable after a specific intervention also with a Bland Altman plot, comparing the mean per-cent change of both methods against the difference [4]. This analysis would have revealed quickly, if methods under comparison do track ensuing changes of SVV in a comparable fashion. This is an very important issue, since changes of SVV are thought to reflect a change in the fluid responsiveness of an individual patient. Thirdly, the authors compared methods during a single tidal volume (12 ml∙kg-1). This is quite surprising, in as much there is evidence that mechanical ventilation has an important impact on SVV, and consequently agreement between methods may be influenced by depth of tidal volume applied [5]. References 1. Kubitz JC, Annecke T, Forkl S et al. Validation of pulse contour derived stroke volume variation during modifications of cardiac afterload. Br J Anaesth 2007; 98: 591-7 2. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 307-10. 3. Critchley. A meta-analysis of studies using bias and precision statistics to compare cardiac output measurement techniques. J Clin Monit 1999; 15: 85-91 4. Linton NW, Linton RA. Is comparison of changes in cardiac output, assessed by dif-ferent methods, better than only comparing cardiac output to the reference method? Br J Anaesth 2002; 89: 336-7 5. Renner J, Cavus E, Meybohm P et al. Stroke volume variation during hemorrhage and after fluid loading: impact of different tidal volumes. Acta Anaesthesiol Scand 2007; 51: 538-44 Conflict of Interest:None declared |
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