['Delivery room cardiopulmonary resuscitation is rare. Recent evidence suggests that effective ventilation may be compromised during chest compressions (CC).', 'To determine whether trained neonatal personnel can assess effective ventilation during CC in the setting of changing lung compliance.', 'Neonatal providers (n=30) provided CC using a 3:1 CC to ventilation ratio performed for 2\u2005min, with lung compliance adjusted every 30\u2005s from 0.5 (low) to 1.0\u2005mL/cmH2O (normal), followed by face mask ventilation (FMV) alone for 1\u2005min. A neonatal lung simulator connected to a neonatal manikin was used to simulate the volume/pressure relation at low and normal compliance.', 'Group analysis showed no difference in peak inflating pressure (PIP) at low versus normal compliance, but a threefold increase in tidal volume (TV) (p=0.00005) during synchronised CC. Paired analysis demonstrated minimal change in PIP, but a significant decrease in TV at low versus normal compliance. During FMV only, a significant decrease in PIP and increase in TV was noted with improved compliance. The face mask was incorrectly applied in 12 (40%) cases and in 20/30 (67%) providers did not perceive a change in compliance. During FMV only, 7/30 (23%) took corrective steps to achieve chest rise.'] Is assessment of effective face mask ventilation compromised during synchronised chest compressions?