Respiratory impedance during weaning from mechanical ventilation in a mixed population of critically ill patients.
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 H(2)O, 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/V(t) 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/V(t) 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.
Sellares
J
J
Servicio de Neumología, Instituto Clínico del Tórax, Hospital Clínic de Barcelona - Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Universidad de Barcelona (UB), Barcelona, Spain.
Acerbi
I
I
Loureiro
H
H
Dellaca
R L
RL
Ferrer
M
M
Torres
A
A
Navajas
D
D
Farre
R
R
D000368:Aged; D000403:Airway Resistance / Q000502:physiology*; D003422:Critical Care / Q000379:methods; D016638:Critical Illness / Q000628:therapy*; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology; D008297:Male; D009991:Oscillometry / Q000379:methods; D011446:Prospective Studies; D012129:Respiratory Function Tests / Q000379:methods; D013990:Tidal Volume; D017211:Treatment Failure; D015300:Ventilator Weaning