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Abstract
Introduction
Combined monitoring of functional residual capacity (FRC) and compliance of the respiratory
system (Crs) at the bedside may allow alveolar recruitment and detect hyperinflation
[1]. The aims of this study were to evaluate the FRC by a modified nitrogen multiple
washout technique (NMBW) combined with the study of Crs, to set best PEEP on data
of FRC and Crs, and to evaluate by echocardiography study the cardiac response to
different levels of PEEP.
Methods
Thirty patients with ALI/ARDS were ventilated with an Engstrom carestation ventilator
(GE Healthcare, Helsinki, Finland) in accordance with the ARDS net guidelines. FRC
measurement was carried out with the COVX module integrated within the ventilator
(GE Healthcare) by the NMBW technique. Every patient had a basal FRC measurement and
then three measurements at PEEP 15/10/5 cm H2O during a de-recruiting maneuver. At
every step we studied the changes of FRC, Crs, PaO2/FIO2 ratio and performed a transthoracic
echocardiography (Agilent 5500; Hewlett and Packard) to evaluate the integral of velocity
time of left ventricular outflow tract (LVOT VTI). All data are reported as mean ±
SD. ANOVA was used to compare changes during the time.
Results
Table 1 presents the main results of the study. Best PEEP was set at 10 cmH2O, at
which level the decrease of FRC and improvement of Crs indicates the start of de-recruitment
and end of overdistention.
Table 1
PEEP 15
PEEP 10
PEEP 5
FRC ml
2,975 ± 644
2,412 ± 585*
2,059 ± 556**
Crs ml/cm
33 ± 8
39 ± 9*
45 ± 10**
PaO2/FIO2
310 ± 62
291 ± 78
185 ± 89†
LVOT VTI cm
16.3 ± 2
20 ± 3*
22 ± 6**
*P < 0.05. **P < 0.01 vs PEEP 15. †
P < 0.001 vs PEEP 15 and 10.
Conclusions
Increased levels of PEEP improve FRC. Combined monitoring of FRC and Crs may detect
hyperinflation. Hyperinflation impairs LV systolic function.