Measurement and repeatability of interrupter resistance in unsedated newborn infants

Interrupter resistance (R(int)) is a useful measure of airway caliber in young children, but has not been well characterized in infants-in whom there are concerns about the accurate measurement of driving pressure. This study aimed to assess the feasibility and repeatability of measuring R(int) in unsedated newborn infants, and to explore alternative algorithms for calculating driving pressure. R(int) measurement was attempted in 28 healthy term newborn infants during natural sleep using the MicroRint device. Paired R(int) measurements were achieved in 24 infants, but after screening of waveforms only 15 infants had at least 5 technically acceptable waveforms on both measurements. R(int) values obtained were comparable with reported values for airflow resistance in newborns using other methods. However, the repeatability coefficient (CR) was much higher than reported values in preschool children using standard back-extrapolation algorithms, with CR 2.47 KPa L(-1) sec (unscreened) and 2.93 KPa L(-1) sec (screened). Other algorithms gave only marginally better repeatability, with all CR values over 50% of the mean R(int) value. Using current commercially available equipment, R(int) is too poorly repeatable to be a reliable measurement of airflow resistance in newborn infants. Lower deadspace equipment is needed, but anatomical and physiological factors in the infant are also important.