Michael PiagnerelliPatrick Biston

End-tidal carbon dioxideand arterial pressurefor predicting volumeresponsiveness by the passiveleg raising test: a commentary

Accepted: 20 March 2013Published online: 25 April 2013� Springer-Verlag Berlin Heidelberg andESICM 2013

A reply to this comment is available atdoi:10.1007/s00134-013-2920-1.

Dear Editor,We read with interest the manuscriptby Monnet et al. [1] concerning therole of end-tidal carbon dioxide(etCO2) in predicting volumeresponsiveness by the passive legraising (PLR) test. If we agree withthese distinguished experts that it isimportant to study indices of preloaddependence, in order to limit thedeleterious effects of overfilling ofcritically ill patients, we just want todraw readers’ attention to some limi-tations of this study. Indeed, webelieve that the inclusion criteria forpatients were not optimal to reach thesame conclusions as the authors.First, the authors included 65 patientsof which 17 % had arrhythmias [1].We agree with the authors that theaim of this work is not to study theprediction of volume responsiveness

by the pulse pressure analysis and, asreported by the authors [1] as well asin a meta-analysis [2], the sensitivityof PLR remains good despitearrhythmia. However, a comparisonof results between patients with orwithout arrhythmia could enhance thebenefit of etCO2 on volume respon-siveness by the PLR test. In addition,the article does not mention the pro-portion of patients with arrhythmiathat were included in the PLR test.

Second, 97 % of the patientsincluded were in septic shock withARDS [1]. As described by the sameauthors in other works, introductionof or change in norepinephrine dos-age could influence the cardiacpreload and minimize the variation ofpulse pressure. Were modifications ofnorepinephrine between measure-ments in the patients studied?Moreover, do we see the same resultsin patients without norepinephrine?

Third, the tidal volume used(6.4 ± 0.8 ml/kg of predicted bodyweight) in these patients was in therange recommended for this particu-lar population. However, it isimportant to remember the effects ofmechanical ventilation on the mea-surement of the pulse pressurevariation as a low tidal volume [3],impaired respiratory system compli-ance or elevated respiratory rate [4],as all these patients should certainlyhave had. In other words, the resultsobtained were perhaps different inpatients without ARDS. The authorsshould be commended for theirexcellent work, and as mentioned inthe discussion, for the importance of

these findings in treating the veryspecific population studied [1]. Fur-ther studies on other categories ofpatients (severe sepsis, without lowtidal volume) may confirm the inter-est of etCO2 as a measure of preloaddependence in critically ill patients.

Conflicts of interest The authors declareno conflict of interest.

References

1. Monnet X, Bataille A, Magalhaes E,Barrois J, Le Corre M, Gosset C, GuerinL, Richard C, Teboul JL (2013) End-tidalcarbon dioxide is better than arterialpressure for predicting volumeresponsiveness by the passive leg raisingtest. Intensive Care Med 39:93–100.doi:10.1007/s00134-012-2693-y

2. Cavallaro F, Sandroni C, Marano C, LaTorre G, Mannocci A, De Waure C,Bello G, Maviglia R, Antonelli M (2010)Diagnostic accuracy of passive legraising for prediction of fluidresponsiveness in adults: systematicreview and meta-analysis of clinicalstudies. Intensive Care Med36:1475–1483

3. De Backer D, Heenen S, Piagnerelli M,Koch M, Vincent JL (2005) Pulsepressure variations to predict fluidresponsiveness: influence of tidalvolume. Intensive Care Med 31:517–523

4. De Backer D, Taccone FS, Holsten R,Ibrahimi F, Vincent JL (2009) Influenceof respiratory rate on stroke volumevariation in mechanically ventilatedpatients. Anesthesiology 110:1092–1097

M. Piagnerelli ()) � P. BistonIntensive Care Unit, CHU-Charleroi,Universite Libre de Bruxelles,6000 Charleroi, Belgiume-mail: michael.piagnerelli@chu-charleroi.be

Intensive Care Med (2013) 39:1164DOI 10.1007/s00134-013-2913-0 CORRESPONDENCE