Plethysmograph and interrupter resistance measurements in prematurely born young children

Mark R Thomas ¹, Gerrard F Rafferty ¹, Richard Blowes ¹, Janet L Peacock ², Neil Marlow ³, Sandy Calvert ⁴, Anthony D Milner ¹ and Anne Greenough ^1*

¹ King's College, United Kingdom
² Brunel University, United Kingdom
³ University of Nottiingham, United Kingdom
⁴ St George's Hospital Medical School, United Kingdom

^* To whom correspondence should be addressed. E-mail: anne.greenough{at}kcl.ac.uk.

Accepted 14 October 2005

Abstract

Objective:Airways obstruction in prematurely born young children has frequently been assessed by plethysmographic measurements which require sedation. The interrupter (RINT) technique does not require sedation, but has rarely been examined in children under two years of age. Our aim was to compare RINT results to those of plethysmographic measurements of airway resistance 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. The baseline mean RINT values were higher than the baseline mean Raw results (3.45 vs 2.84kPa/[l/s], p = 0.006), limits of agreement for mean (RINT -Raw) -1.52 to 2.74 kPa(l/sec). Ten infants received salbutamol, after which their 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/sec).

Conclusion:The poor agreement we note between RINT and Raw results suggest that RINT measurements cannot substitute for plethysmographic measurements in sedated prematurely born infants.

Keywords: airways resistance, interrupter technique, plethysmography, premature

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