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 N₂ washout method utilizing a change of F_IO₂ 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, CO₂ 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 cmH₂O. 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 N₂ 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.