ORIGINAL ARTICLE

Plethysmograph and interrupter resistance measurements in prematurely born young children

M R Thomas¹, G F Rafferty¹, R Blowes¹, J L Peacock³, N Marlow⁴, S Calvert², A Milner¹, A Greenough¹

¹ Department of Child Health, Guy’s, King’s and St Thomas’ Medical School, King’s College London, UK
² Department of Child Health, St George’s Hospital Medical School, London, UK
³ School of Health Sciences and Social Care, Brunel University, West London, UK
⁴ Academic Division of Child Health, School of Human Development, University of Nottingham, Nottingham, UK

Correspondence to:
Professor Greenough
Department of Child Health, 4th Floor Golden Jubilee Wing, King’s College Hospital, Bessemer Road, London SE5 9RS, UK; anne.greenough{at}kcl.ac.uk

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 –1.52 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 –0.28 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.

Abbreviations: Raw, airways resistance measured by total body plethysmography; Rint, interrupter resistance

Keywords: airways resistance; interrupter technique; premature; plethysmography

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