Background and aims Whether variations in end-expiratory lung volume (EELV) occur in stable infants receiving nasal CPAP is unknown. This study aimed to describe global and regional volumetric behavior over periods of hypopnoea (< 20 breaths/min over 15-secs) in preterm infants < 18 hours of age receiving nasal CPAP.
Methods Twenty infants < 32 weeks’ receiving CPAP were studied whilst supine. Clinicians set CPAP level at mean(SD) 6(1)cmH2O in FiO2 0.25(0.03). Relative ΔEELV and tidal volume (V T) [respiratory inductive plethysmography] ] and regional ΔEELV [electrical impedance tomography] were measured. 20-secs of data were analysed preceding and following episodes of hypopnoea and ΔEELV and ΔV T determined (expressed as average V T units at baseline). Breath-to-breath phase angles (Θ) and labored breathing index (LBI) were calculated post-hoc.
Results Ten episodes of hypopnoea lasting mean(SD) 26(11)s were analyzed in 10 infants mean(SD) GA 29(1) weeks and BW 1119 (264)g. EELV and V T fell significantly from baseline by median(range) 0.3(–1.1, 0.5) and 0.2 (0.3)V T units(p<0.05) during episodes of hypopnoea. Both non-dependant and dependant halves of the chest contributed equally to global loss in EELV during hypopnoea. During recovery, the non-dependant hemi-thorax recovered median (range)70 (9,100)% and dependant 63 (4,100)% of the loss of EELV in those regions respectively. No changes were seen in HR, oxygen saturations, FiO2, LBI and thoraco-abdominal asynchrony during these episodes.
Conclusions A significant loss in EELV may occur during hypopneic phases of respiration in infants considered stable on CPAP. Further work is needed to determine the significance of these observations.