How should airways resistance be measured in young children: mask or mouthpiece?

The reproducibility and acceptability of airways resistance measurements us ing the interrupter technique (MicroRint) obtained using a mouthpiece were compared with those using a face mask. Fifty children aged 4-7 yrs performed four sets of six Rint measurements; t no using a mouthpiece and two using a face mask with integral mouthpiece. Complete data were obtained from 45 (90%) children using the mouthpiece and 43 (86%) children using the mask. The tno methods were equally repeatable with comparable intraclass correlation coefficients (ICC) and coefficients of variation. Mean Rint values obtained using the mouthpiece were significa ntly lo,rer than those using the face mask ((mean +/- SD) mouthpiece = 0.81 +/-0.18 kPa.L-1.s, mask = 0.88 +/-0.24 kPa.L-1.s p = 0.0002), Although the mean paired differences between the tno methods were small (0.07 kPa.L-1.s ), the ICC and limits of agreement confirmed that the two methods could not be used interchangeably. Sixty-seven per cent of children preferred the fa ce mask but this was more time-consuming (p = 0.03), Children did not produ ce more repeatable results using their preferred method, nor did they impro ve with practice. Repeatable airway resistance measurements using the interrupter technique r an be obtained from young children using either a mouthpiece or a face mask , but there are significant clinical and statistical differences between th e results obtained.