The RIP Coils Were Aligned with the Nipples and Umbilicus, Respectively, and Tightly Fixed

ELECTRONIC SUPPLEMENTARY MATERIAL

PHYSIOLOGICAL RESPONSES DURING A T-PIECE WEANING TRIAL WITH A DEFLATED TUBE

Piero Ceriana*, Annalisa Carlucci*, Paolo Navalesi*, Georgios Prinianakis^, Francesco Fanfulla°, Monica Delmastro*, and Stefano Nava*

From: *Respiratory Intensive Care Unit, Fondazione S.Maugeri, IRCCS, Istituto Scientifico di Pavia, ITALY, °Respiratory Unit, Fondazione S.Maugeri, IRCCS, Istituto Scientifico di Montescano, ITALY and ^Intensive Care Unit Heraklion Hospital Crete, GREECE

Methods

The RIP coils were aligned with the nipples and umbilicus, respectively, and tightly fixed, although not taped, on the patient’s skin. A brief period (five minutes) of spontaneous ventilation through the pneumotachograph was performed in order to evaluate the patient’s tidal volume; this volume was used as a “baseline” reference value for the quantitative “off-line” preliminary calibration of the RIP; furthermore, during the first minutes of operation, the RIP performed an autocalibration (1) in order to determine the volume motion coefficients of the rib cage and abdominal coils.

Calibration was performed in the semirecumbent position, which the patients maintained for the whole duration of the test, with the torso flexed about 45° with respect to the horizontal plane. The calibration procedure was repeated at the beginning of each trial.

To avoid problem in the calculation of VT with RIP throughout the experimental procedures, we have performed a preliminary test on 5 patients, with the aim to assess the reliability of RIP calibration after 180 minutes of spontaneous breathing in the semi-recumbent position. The variation in VT was <10% (range 3% to 11%), at the end of the recording, compared to the baseline value, so that the measurement of VT using the RIP was considered reliable.

Since the tidal volumes obtained using the PT during the uncuffed cannula trial markedly underestimated those recorded using the RIP due to airleaks around the cuff (see fig. R1), all the measurements involving tidal volume recordings were calculated from the RIP signals. In order to assess the accuracy of tidal volume measurement with RIP, this method underwent a process of validation: during a preliminary spontaneous breathing trial, performed in all patients, the respiratory pattern was measured with both RIP and PT for a period of five minutes and tidal volume values obtained with the two methods were compared by means of simple linear Pearson’s correlation (fig. R2) and with Bland-Altman plot (fig.R3).

Correlation between tidal volume values recorded with the two different methods showed a high statistical significance (r= 0.84; p=<0.0001) (fig.R2) and the mean difference between the two measurements was 0.0049 ± 0.1 ml.

As shown in Bland-Altman plot (fig.R3), the difference between the two measurements never exceeded the two standard deviations.

Reference

1)  Sackner MA, Watson H, Belsito AS, Feinerman D, Suarez M, Gonzalez G, Bizousky F and Krieger B. (1989): Calibration of respiratory inductive plethysmograph during natural breathing. J. Appl. Physiol.; 66:410-420.

Legends

Figure 1R: Tidal volume measured with pneumotachograph (PT) and with Respiratory Inductive Pletismograph (RIP) with the cuff deflated

Figure 2R: Linear regression analysis between tidal volume measured with pneumotachograph (PT) and with Respiratory Inductive Pletismograph (RIP) with the cuff inflated

Figure 3R: Comparison with Bland-Altman plot between tidal volume measured with pneumotachograph (PT) and with Respiratory Inductive Pletismograph (RIP) with the cuff inflated