TY - JOUR T1 - Interpretation of passive respiratory mechanics in infants: Should we normalise by body weight? JF - European Respiratory Journal JO - Eur Respir J VL - 38 IS - Suppl 55 SP - p2013 AU - The Thanh Diem Nguyen AU - Ah-Fong Hoo AU - Sooky Lum AU - Angie Wade AU - Janet Stocks Y1 - 2011/09/01 UR - http://erj.ersjournals.com/content/38/Suppl_55/p2013.abstract N2 - Introduction: Tidal volume (VT) and respiratory compliance (Crs) are commonly normalised for body weight; whether this is appropriate beyond the neonatal period or in weight restricted children remains unclear.Aim: To examine the relationship between VT, Crs and growth in healthy infants.Methods: The Jaeger BabyBody (v4.6) was used to assess lung function (LF) in healthy, sedated term Caucasian infants.Results: Technically satisfactory VT and Crs from 140 infants [median (range) age: 38 (3-105) w] were available on 192 & 84 occasions respectively (Table).View this table:Table 1The average relationship between VT or Crs and weight was constant over time but between-subject variability increased with growth (Fig. 1a&b). 95% Limits based on VT/kg or Crs/kg would over-estimate predicted range in the youngest and under-estimate it in older infants, leading to potential misdiagnosis. VT/kg or Crs/kg were inversely related to weight z-score (Fig. 1c&d); light-for-age babies had higher values than those who were heavier. This again may lead to misdiagnosis especially in those with impaired growth (eg, CF).Figure 1Conclusions: Reporting infant LF/kg body weight is inappropriate. Equipment-specific regression equations are needed to avoid misinterpretation; for this a larger dataset is required. We would welcome contributions of similar data from other centres. ER -