The Validity of Eadyn in Spontaneously Breathing Patients

To the Editor Recently, Cecconi et al.1 showed that in spontaneously breathing patients in the intensive care unit, noninvasively derived dynamic arterial elastance (Eadyn) can predict an increase in arterial blood pressure after fluid administration. Included patients were assumed preload-dependent, and hemodynamics were assessed using the volume clamp technique (Nexfin®, BMEYE, Amsterdam, The Netherlands). Eadyn, assumed as a functional measure of arterial elastance, represents the ratio of pulse pressure variation (PPV; pressure-related) to stroke volume variation (SVV; flow-related), PPV/SVV.2–4 Although it is well known that spontaneous ventilation renders PPV and SVV useless in the prediction of fluid responsiveness,5 the authors’ reason that this is not true for the validity of Eadyn in assessing arterial elastance. The authors state that “as long as the magnitude of PPV and SVV allows reliably depicting the slope of arterial pressure–volume relationship,” the validity of Eadyn is not hindered by spontaneous ventilation because PPV and SVV should be equally affected by the inhomogeneous respiratory-induced variations.1 Although compelling, this assumption is unproven and requires more detailed elaboration. The authors’ results do not prove its correctness; neither does the report by Pinsky4 to which the authors refer. Therefore, we kindly ask the authors to elaborate the exact reasoning behind this issue. In addition, mathematical coupling among the measured variables might partly explain the observed results. We believe that SVV and PPV should have been measured independently of each other to exclude this. Jaap Jan Vos, MD, PhD Thomas W. L. Scheeren, MD, PhD Department of Anesthesiology University of Groningen University Medical Center Groningen Groningen, The Netherlands [email protected] Alain F. Kalmar, MD, PhD Department of Anesthesiology and Intensive Care Medicine Maria Middelares Hospital Ghent, Belgium