Respiratory Systolic Variation Test to predict fluid responsiveness
Editor—Priesman and colleagues1 have published an interesting study showing that the Respiratory Systolic Variation Test (RSVT) is an accurate way of predicting fluid responsiveness. They state that it demands a complex respiratory manoeuvre and off-line measurements and calculations. We note that they use three airway pressures and use linear regression to calculate the slope of a line of best fit. Using linear regression with three points, the middle value has no effect on the slope of the line of best fit. The same accuracy can therefore be obtained using two ventilator pressures, at 10 and 30 cm H2O. This then makes the respiratory manoeuvre much simpler and a screen capture can be used to measure the two lowest systolic pressures whilst switching from 10 to 30 cm H2O breaths. The slope is then given by the equation (lowest systolic pressure at 10 cm H2O)–(lowest systolic pressure at 30 cm H2O)/20. Using their calculated cut-off value of –0.52 cm/H2O gives an even easier calculation: if the lowest systolic pressure falls by greater than 10.2 mm Hg when switching from 10 to 30 cm H2O breaths then fluid responsiveness is implied. This simple modification makes the RSVT a simple bedside test using a standard ventilator and a standard monitor which allows screen capture.J. Brown*
O. Chappell
Bristol, UK
*E-mail: Jules.brown{at}nbt.nhs.uk
Editor—We thank Drs Brown and Chappell for their interest in our study. They correctly state that the slope of the line of best fit for the RSVT would not be affected by the addition of a middle value and that the same accuracy may be achieved by a manoeuvre composed of two consecutive breaths. We used three consecutive incremental airway pressures in our study to avoid any erroneous blood pressure measurement resulting from occasional extrasystoles, spontaneous respiratory effort, etc. If the manoeuvre had been of only two breaths, it would have been difficult to identify such abnormalities and discard them from measurement. We did not encounter such a situation in our clinical studies but it did occur in our preliminary animal experiments.
Thus, in our opinion, it is worthwhile to use three breaths with incremental pressures during the RSVT manoeuvre to identify and reject artifacts.
S. Preisman*
A. Perel
Tel-Aviv, Israel
*E-mail: preisman{at}netvision.net.il
References
1 Preisman S, Kogan S, Berkenstadt H, Perel A. Predicting fluid responsiveness in patients undergoing cardiac surgery: functional haemodynamic parameters including the Respiratory Systolic Variation Test and static preload indicators. Br J Anaesth 2005; 95:746–55
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