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Department of Anaesthesiology and Intensive Care Medicine; University Hospital Schleswig-Holstein; Campus Kiel, Germany; renner{at}anaesthesie.uni-kiel.de
To the Editor:
Charron et al. (1) addressed the impact of tidal volume on pulse pressure variation (
% Pp) and on the aortic velocity–time integral (
%VTIAo). The authors used a small volume of hydroxyethyl starch (100 mL over 60 s) as a volume challenge, although there was no change of left ventricular end diastolic area index (LVEDAi). The authors refer to a study that applied an "equivalent fluid challenge" of 500 mL over 5–10 min (2). We question whether a rapid infusion of 100 mL hydroxyethyl starch 6% over 60 s is equivalent to 500 mL applied over 5–10 min.
Hemodynamic variables were collected during three 15-min time intervals while the depth of tidal volume (VT) was varied. It has been shown previously that after an infusion of 20 mL/kg hydroxyethylstarch 6% over 15 min, <50% of the volume initially infused remains in the intravascular space (3). This suggests that following the first period of data collection, a large proportion of the initially applied volume disappeared. This is supported by lack of change in LVEDAi, suggesting an insufficient volume challenge.
The absence of significant changes in
%VTIAo with changes tidal volume is counterintuitive. A close relationship exists between VTIAo as a surrogate parameter of stroke volume and VT (4). It is surprising that authors used VTIAo as their index, given the technical limitations, rather than using thermodilution, the clinically accepted gold standard (5).
REFERENCES
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C. Charron, C. Fessenmeyer, C. Cosson, J.-L. Hebert, D. Benhamou, J. X. Mazoit, and A. Edouard Dynamic Variables of Fluid Responsiveness may be Related to the Type of Volume Challenge Performed Anesth. Analg., June 1, 2007; 104(6): 1603 - 1603. [Full Text] [PDF] |
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