Respiratory mechanics measured by forced oscillations during mechanical ventilation through a tracheal tube.

The forced oscillation technique (FOT) allows the measurement of respiratory mechanics in the intensive care setting. The aim of this study was to compare the FOT with a reference method during mechanical ventilation through a tracheal tube. The respiratory impedance spectra were measured by FOT in nine anaesthetized pigs, and resistance and compliance were estimated on the basis of a linear resistance-compliance inertance model. In comparison, resistance and compliance were quantified by the multiple linear regression analysis (LSF) of conventional ventilator waveforms to the equation of motion. The resistance of the sample was found to range from 6 to 21 cmH(2)O s l(-1) and the compliance from 12 to 32 ml cmH(2)O(-1). A Bland-Altman analysis of the resistance resulted in a sufficient agreement (bias -0.4 cmH(2)O s l(-1); standard deviation of differences 1.4 cmH(2)O s l(-1); correlation coefficient 0.93) and test-retest reliability (coefficient of variation of repeated measurements: FOT 2.1%; LSF 1.9%). The compliance, however, was poor in agreement (bias -8 ml cmH(2)O(-1), standard deviation of differences 7 ml cmH(2)O(-1), correlation coefficient 0.74) and repeatability (coefficient of variation: FOT 23%; LSF 1.7%). In conclusion, FOT provides an alternative for monitoring resistance, but not compliance, in tracheally intubated and ventilated subjects.