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BJA Advance Access originally published online on November 3, 2009
British Journal of Anaesthesia 2009 103(6):828-832; doi:10.1093/bja/aep301
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 BJA: December 2009
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© The Author [2009]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournal.org

Respiratory impedance during weaning from mechanical ventilation in a mixed population of critically ill patients

J. Sellares1,2, I. Acerbi3,4, H. Loureiro1,2, R. L. Dellaca4, M. Ferrer1,2, A. Torres1,2, D. Navajas2,3,5 and R. Farre2,3,*

1 Servicio de Neumología, Instituto Clínico del Tórax, Hospital Clínic de Barcelona - Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Universidad de Barcelona (UB), Villarroel 170, 08036 Barcelona, Spain
2 Centro de Investigación Biomedica En Red-Enfermedades Respiratorias (CibeRes), Instituto de Salud Carlos III, Ministerio de Ciencia e Innovacion, Spain
3 Unitat de Biofísica i Bioenginyeria, Facultat de Medicina, University of Barcelona—IDIBAPS, Casanova 143, 08036 Barcelona, Catalonia, Spain
4 Bioengineering Department, Politecnico di Milano, Milan, Italy
5 Institut de Bioenginyeria de Catalunya, Barcelona, Spain

* Corresponding author. E-mail: rfarre{at}ub.edu, URL: www.idibapsrespiratoryresearch.org

Background: Worsening of respiratory mechanics during a spontaneous breathing trial (SBT) has been traditionally associated with weaning failure, although this finding is based on studies with chronic obstructive pulmonary disease patients only. The aim of our study was to assess the course of respiratory impedance non-invasively measured by forced oscillation technique (FOT) during a successful and failed SBT in a mixed population.

Methods: Thirty-four weaning trials were reported in 29 consecutive mechanically ventilated patients with different causes of initiation of ventilation. During the SBT, the patient was breathing through a conventional T-piece connected to the tracheal tube. FOT (5 Hz, ± 1 cm H2O, 30 s) was applied at 5, 10, 15, 20, 25, and 30 min. Respiratory resistance (Rrs) and reactance (Xrs) were computed from pressure and flow measurements. The frequency to tidal volume ratio f/Vt was obtained from the flow signal. At the end of the trial, patients were divided into two groups: SBT success and failure.

Results: Mixed model analysis showed no significant differences in Rrs and Xrs over the course of the SBT, or between the success (n=16) and the failure (n=18) groups. In contrast, f/Vt was significantly (P<0.001) higher in the failure group.

Conclusions: Worsening of respiratory impedance measured by FOT is not a common finding during a failed SBT in a typically heterogeneous intensive care unit population of mechanically ventilated patients.

Keywords: ventilation, high frequency oscillation; ventilation, mechanical; ventilation, respiratory impedance


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