Effect of different CPAP levels on ultrasound-assessed lung aeration and gas exchange in neonates.

Background: Respiratory distress syndrome (RDS) and transient tachypnoea (TTN) are the two commonest neonatal respiratory disorders. The optimal continuous positive airway pressure (CPAP) to treat them is unknown. We aim to clarify the effect of different CPAP levels on lung aeration and gas exchange in patients with RDS and TTN.

Methods: Prospective, observational, pragmatic, physiological cohort study. CPAP was sequentially increased from 4 to 6 and 8 cmH₂O and backwards, with interposed wash-out periods. Lung aeration was assessed with a validated neonatal lung ultrasound score. Gas exchange was non-invasively evaluated with transcutaneous monitoring. Ultrasound score and PtcO₂/FiO₂ ratio were the co-primary outcomes. PtcCO₂ and other oxygenation metrics were the secondary outcomes.

Results: 30 neonates with RDS and 30 with TTN were studied. Each CPAP increment significantly (overall always p < 0.001) improved both lung aeration and oxygenation, but the increase from 6 to 8 cmH₂O achieved a small absolute benefit. In RDS patients, the absolute improvements were small and the diagnosis of TTN was significantly associated with greater improvement of lung aeration (β= -1.4 (95%CI: -2.4; -0.3), p = 0.01) and oxygenation (β = 39.6 (95%CI: 4.1; 75.1), p = 0.029). Aeration improved in 16 (53.3%) and 27 (90%) patients in the RDS and TTN groups, respectively (p = 0.034). Lung aeration showed significant hysteresis in TTN patients. Secondary outcomes gave similar results.

Conclusions: Increasing CPAP from 4 to 8 cmH₂O improves ultrasound-assessed lung aeration and oxygenation in RDS and TTN. The absolute improvements are small when CPAP is beyond 6 cmH₂O or for RDS patients.