Plethysmograph and interrupter resistance measurements in prematurely born young children

Abstract

Background: Airways obstruction in premature infants is often assessed by plethysmography, which requires sedation. The interrupter (Rint) technique does not require sedation, but has rarely been examined in children under 2 years of age. Objective: To compare Rint results with plethysmographic measurements of airway resistance (Raw) in prematurely born, young children. Design: Prospective study. Setting: Infant and Paediatric Lung Function Laboratories. Patients: Thirty children with a median gestational age of 25-29 weeks and median postnatal age of 13 months. Interventions and main outcome measures: The infants were sedated, airway resistance was measured by total body plethysmography (Raw), and Rint measurements were made using a MicroRint device. Further Raw and Rint measurements were made after salbutamol administration if the children remained asleep. Results: Baseline measurements of Raw and Rint were obtained from 30 and 26 respectively of the children. Mean baseline Rint values were higher than mean baseline Raw results (3.45 v 2.84 kPa/l/s, p = 0.006). Limits of agreement for the mean difference between Rint and Raw were 21.52 to 2.74 kPa/l/s. Ten infants received salbutamol, after which the mean Rint result was 3.6 kPa/l/s and mean Raw was 3.1 kPa/l/s (limits of agreement 20.28 to 1.44 kPa/l/s). Conclusion: The poor agreement between Rint and Raw results suggests that Rint measurements cannot substitute for plethysmographic measurements in sedated prematurely born infants.

Interrupter technique in infancy: Higher airway resistance and lower short‐term variability in preterm versus term infants

“…Diverging results might be due to differences in study age, data acquisition, and analysis software, occlusion time, and quality control. In another study, Rint measured during peak inspiratory flow in sedated preterm infants at 1 year was lower than in our study. Previous methodological work compared Rint measurements completed during inspiration and expiration in preschool children, and reported a higher Rint during expiration .…”

“…Previous methodological work compared Rint measurements completed during inspiration and expiration in preschool children, and reported a higher Rint during expiration. 7,26 This methodological impact on Rint values may be one reason for a higher Rint in our study compared to the study by Thomas et al 18 Several studies from children reported that Rint decreases with increasing age and height. 7,27,28 In regards to Rint measurements in infants, it is still unclear which factor is a more relevant predictor in this age group.…”

“…The awareness of the high variability of Rint measurements at early infancy is essential, since the technique was used already in follow-up studies of preterm infants. 18 Further development in hardware and software to improve Rint measurement quality was asked for already years ago, 12 but no substantial changes in the technical equipment used in this study were performed until now. On the other hand, it may be even more likely that the variability of measurements is less dependent on the equipment, but on physiological factors, for example, the unstable breathing pattern of infants.…”

“…10,11 These findings indicate that, especially in infants, Rint measurements require further quality assessment. Further understanding of variability of Rint also seems relevant, given that Rint was previously used to assess bronchodilator response in children with asthma, Cystic Fibrosis 16,17 and former preterm children, 18 as well as to study methacholine induced bronchoconstriction in preschool children. 19 Based on studies reporting increased airway resistance in former preterm born children in early childhood, 4…”

Impact of ethnicity and extreme prematurity on infant pulmonary function

“…The finding of relatively better pulmonary function in boys than girls was unexpected, as most previous studies have reported worse morbidity in male infants following preterm birth. 4 , 33 , 34 Given that investigation of sex differences was not an a priori hypothesis and the relatively small sample size once subsets were examined according to ethnic group, gestational age sex and sex, this finding needs to be interpreted with caution, as it may simply reflect a chance finding due to sampling. In addition, these findings may be biased by the fact that a larger proportion of SGA infants were recruited to the PTC than EP group (possibly reflecting the fact that such children rarely survive if born EP) and that of these children, twice as many were girls.…”