Validation and clinical feasibility of nitrogen washin/washout functional residual capacity measurements in children

Background The functional residual capacity (FRC) is an important parameter in pediatric respiratory monitoring but it is difficult to assess in the clinical setting. We have introduced a modified N(2) washout method utilizing a change of F(I)O(2) of 0.1 for FRC measurement in adult respiratory monitoring. This study validated the algorithm in a pediatric lung model and investigated the stability and feasibility in a pediatric peri-operative and intensive care setting. Methods The lung model was ventilated in combinations of ventilatory modes, CO(2) production, model FRC and respiratory rates. Sixteen children from 10 days to 5 years were studied peri-operatively with controlled ventilation using a Mapleson D system and in the intensive care unit using a Servo-i ventilator in a supported spontaneous mode. FRC was measured during stable metabolic, respiratory and circulatory periods at positive end expiratory pressure of 3-4 and 7-8 cmH(2)O. Results In the model and in the clinical setting, we found an excellent agreement between washout and washin measurements of FRC as well as acceptable coefficients of repeatability. Conclusion FRC was satisfactorily measured by a modified N(2) algorithm and may be included as a monitoring variable in pediatric respiratory care. Pediatric FRC monitoring demands strictly stable conditions as measurements are performed close to the limits of the monitor's specifications.