Research
Accuracy and precision of end-expiratory lung-volume measurements by automated nitrogen washout/washin technique in patients with acute respiratory distress syndrome
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* Corresponding author: Jean Dellamonica jean.dellamonica@inserm.fr
1 Réanimation Médicale, AP-HP, Centre Hospitalier Albert Chenevier, Henri Mondor, avenue Marechal de Lattre de Tassigny, Créteil, 94000, France
2 Réanimation Médicale, CHU de Nice, Hôpital L'Archet, Université de Nice Sophia Antipolis, Route de St Antoine de Ginestière, Nice 06200, France
3 Réanimation Médicale, AP-HP, Hôpital Européen Georges Pompidou, rue Leblanc, Paris 75015, France
4 Réanimation Médicale, CHU Angers, rue Larrey, Angers 49100, France
5 Réanimation Médicale & UPRES EA 3830, CHU Charles Nicolle, rue Germont, Rouen 76031, France
6 Pneumologia Ospedale San Paolo, Universita degli Studi di Milano, via A. di Rudini 8, Milano 20142, Italy
7 Servei de Medicina Intensiva, Hospital de Sant Pau, C. Sant Quinti 89, Barcelona, 08041, Spain
8 Réanimation Polyvalente, AP-HP, Hôpital Pitié Salpêtrière, UPMC, Université Paris 6, Boulevard de l'Hôpital, Paris 75014, France
9 INSERM U-955, Université Paris EST, avenue Marechal de Lattre de Tassigny, Créteil 94000, France
10 Intensive Care Department, University Hospital and University of Geneva, rue Gabrielle Perret-Gentil, Geneva 1211, Switzerland
Critical Care 2011, 15:R294 doi:10.1186/cc10587
Published: 7 December 2011Abstract
Introduction
End-expiratory lung volume (EELV) is decreased in acute respiratory distress syndrome (ARDS), and bedside EELV measurement may help to set positive end-expiratory pressure (PEEP). Nitrogen washout/washin for EELV measurement is available at the bedside, but assessments of accuracy and precision in real-life conditions are scant. Our purpose was to (a) assess EELV measurement precision in ARDS patients at two PEEP levels (three pairs of measurements), and (b) compare the changes (Δ) induced by PEEP for total EELV with the PEEP-induced changes in lung volume above functional residual capacity measured with passive spirometry (ΔPEEP-volume). The minimal predicted increase in lung volume was calculated from compliance at low PEEP and ΔPEEP to ensure the validity of lung-volume changes.
Methods
Thirty-four patients with ARDS were prospectively included in five university-hospital intensive care units. ΔEELV and ΔPEEP volumes were compared between 6 and 15 cm H2O of PEEP.
Results
After exclusion of three patients, variability of the nitrogen technique was less than 4%, and the largest difference between measurements was 81 ± 64 ml. ΔEELV and ΔPEEP-volume were only weakly correlated (r2 = 0.47); 95% confidence interval limits, -414 to 608 ml). In four patients with the highest PEEP (≥ 16 cm H2O), ΔEELV was lower than the minimal predicted increase in lung volume, suggesting flawed measurements, possibly due to leaks. Excluding those from the analysis markedly strengthened the correlation between ΔEELV and ΔPEEP volume (r2 = 0.80).
Conclusions
In most patients, the EELV technique has good reproducibility and accuracy, even at high PEEP. At high pressures, its accuracy may be limited in case of leaks. The minimal predicted increase in lung volume may help to check for accuracy.