LAUSR

BACKGROUND: CPAP improves respiratory function in prematurely born infants by establishing and maintaining functional residual capacity, but the level of CPAP that optimizes respiratory function has not been adequately described. We compared ventilation efficiency and respiratory muscle function at different levels of CPAP. METHODS: We studied spontaneously breathing, intubated convalescent premature infants at King's College Hospital NHS Foundation Trust and calculated the ventilation efficiency index and the respiratory muscle time constant of relaxation (τ) at the end of 3 consecutive 5-min periods at 4, 6, and 8 cm H2O of CPAP delivered in random order. RESULTS: Between February 2016 and August 2016, 38 infants with a median gestational age of 27 (interquartile range [IQR], 25−30) weeks and a median birthweight of 0.88 (IQR, 0.73–1.02) kg were studied. At a CPAP level of 6 cm H2O, the median ventilation efficiency index was higher (1.52 [IQR, 1.02–2.27]) and median τ was lower (15.6 [IQR, 10.1–21.3]) s/cm H2O] compared with the median ventilation efficiency index (0.75 [IQR, 0.56–1.03]) and median τ (23.3 [IQR, 15.4–35.2] sec/cm H2O) at CPAP of 4 cm H2O (P < .001 for both). At a CPAP level of 8 cm H2O, median ventilation efficiency index was significantly lower (1.27 [IQR, 1.04–1.91]) and median τ was not significantly different (11.2 [IQR, 8.3–18.9] s/cm H2O) compared with ventilation efficiency index and τ at CPAP of 6 cm H2O (P < .001 and P = .12, respectively). After multiple logistic regression, the level of CPAP was independently associated with the ventilation efficiency index (adjusted P < .001) and τ (adjusted P = .003). CONCLUSIONS: Increasing the level of CPAP from 4 to 6 cm H2O was associated with enhanced ventilation efficiency and respiratory muscle function in convalescent premature infants on ventilation, but there was no further benefit from increasing the pressure >6 cm H2O.