Ventilator displays of tidal volume are often used to guide ventilator settings for patients receiving mechanical ventilation. It is therefore important that these volumes are accurately measured. However, as has been shown in several studies, the volumes displayed at the ventilator can be substantially different from volumes measured at the endotracheal tube. Especially when small tidal volumes are used, as with infants and children, such discrepancies may have significant adverse consequences for the patient.
Many ventilators measure tidal volumes at the expiratory valve of the ventilator. Such a measurement does not compensate for the compliance of the ventilator circuit, or for variations in the circuit setup, which may explain the aforementioned discrepancies between displayed and actual delivered tidal volume. In the Servoi ventilator (Maquet, Sweden) special software is installed to compensate for ventilator circuit compliance. It has been shown by Heulitt et al in healthy pigs, that volumes can be accurately measured at the expiratory valve of this ventilator by using this software. However, thus far it has not been verified in human infants or children with varying pulmonary disorders/conditions.
The main objective of our study is to compare tidal volumes measured at the expiratory valve of a Servoi ventilator equipped with the above-mentioned software with (expiratory) tidal volumes measured at the endotracheal tube with the use of a pneumotachometer (Novametrix Medical Systems, Wallingford, Connecticut, USA).
Infants and children (age 1 day–16 years) with varying pulmonary disorders receiving endotracheal mechanical ventilation with a Servoi ventilator will be included.
We hypothesise that, despite the use of the software compensating for ventilator circuit compliance, there will still be a difference between tidal volume measured at the expiratory valve and tidal volume measured at the endotracheal tube.
In October 2008 our first results will be presented at the 2nd Congress of the European Academy of Paediatrics.