The introduction of modern mechanical ventilation in neonatal medicine in the 1960s was followed shortly thereafter by its use in premature infants with hyaline membrane disease. Most premature infants born before 30 weeks' gestation receive some form of respiratory support, particularly those with fewer weeks of gestation.1 Although mechanical ventilation is frequently a life‐saving therapy, its use increases the risk of lung injury, particularly in preterm infants in whom the incidence of bronchopulmonary dysplasia (BPD) remains high.2
Before the current generation of neonatal ventilators, conventional mechanical ventilation (CMV) was provided mainly with time‐cycled pressure limited (TCPL) ventilators developed from adaptation of Ayre's T piece.3 This method, also known as intermittent mandatory ventilation (IMV), was and probably still is in many centres, the most common mode of ventilation.
During IMV mechanical breaths of fixed duration are delivered at predetermined time intervals. This frequently leads to asynchrony depending on the phase of the spontaneous breath when these IMV breaths are delivered. Inspiratory asynchrony occurring when a mechanical breath is delivered at the end of and extends beyond spontaneous inspiration can produce an inspiratory hold that limits the spontaneous respiratory rate or results in excessive lung inflation. Expiratory asynchrony occurring when a mechanical breath is delivered during exhalation can delay lung deflation and elicit active expiratory efforts against positive pressure producing large fluctuations in intrathoracic pressure. Asynchrony can affect gas exchange, and has been linked to increased risk of air leaks4,5 and intraventricular haemorrhage (IVH).6 As volume monitoring was lacking in most IMV devices, it was difficult to detect excessive lung inflation, gas trapping or hypoventilation.