Establishment of functional residual capacity at birth: Observational study of 821 neonatal resuscitations

Abstract

Aim of the study: Establishing functional residual capacity (FRC) during positive pressure ventilation (PPV) of apnoeic neonates is critical for survival. This may be difficult due to liquid-filled airways contributing to low lung compliance. The objectives were to describe initial PPV, changes in lung compliance and establishment of FRC in near-term/term neonates ≥36 weeks gestation at birth.

Methods: Observational study of all neonatal resuscitations between 01.07.13 and 30.06.18 in a Tanzanian referral hospital. Perinatal events and characteristics were observed and recorded by trained research assistants. PPV were performed using self-inflating bag-masks without positive end-expiratory pressure (PEEP). Ventilation signals (pressure/flow), expired CO₂ (ECO₂) and heart rate were recorded by resuscitation monitors.

Results: 19,587 neonates were born, 1451 received PPV, of these 821 of median (p25, p75) birthweight 3180 (2844, 3500) grams and gestation 38 (37, 40) weeks had ≥20 ventilations and complete datasets. There was a significant increase in expired volume (from 3.3 to 6.0 ml/kg), ECO₂ (0.3-2.4%), lung compliance (0.13-0.19 ml/kg/mbar) and heart rate (109-138 beats/min) over the first 20 PPVs. Inflation volume, time, and peak inflation pressure (PIP) were stable around 12-13 ml/kg, 0.45 s, and 36 mbar, respectively.

Conclusions: The combination of increasing expired volumes, ECO₂, and heart rate with decreasing inflation/expired volume ratios and constant PIP, suggests establishment of FRC during the first 20 PPVs in near-term/term neonates using a self-inflating bag-mask without PEEP, the most common device worldwide for ventilating non-breathing neonates. Initial lung compliance is low, and with short inflation times, higher than recommended PIP seem necessary to deliver adequate tidal volumes.

Keywords: Functional residual capacity; Lung compliance; Neonatal resuscitation; Positive pressure ventilation; Resuscitation monitor.