Mechanical ventilation has been used for decades in preterm infants to provide respiratory support in patients with respiratory insufficiency. There are multiple modes of conventional ventilation in neonates, which mainly use a flow trigger to synchronize the ventilator with the patient's spontaneous breathing effort. Synchronization is important because asynchrony can cause volutrauma,1,2 fluctuations in cerebral blood flow with risk of intraventricular haemorrhage (IVH),3,4 respiratory distress, and suboptimal ventilation and oxygenation.5 Synchronized intermittent mandatory ventilation (SIMV) and assist control (A/C) ventilation are the two most widely used modes of conventional mechanical ventilation. In SIMV a user-selected number of breaths is supported by mechanical inflations, while the rest are either unsupported or augmented with a flow-cycled, pressure-controlled amount of pressure, known as pressure support (PS). In A/C all spontaneous breaths are supported, resulting in more even tidal volume. Synchronization has been shown to reduce the work of breathing compared with intermittent mandatory ventilation, with A/C having been shown to unload the diaphragmatic workload more than SIMV.6 Trigger systems that detect flow (or pressure) changes are adversely affected by leak around uncuffed endotracheal tubes and can lead to asynchrony with the mechanical inflations due to insufficient sensitivity or delayed trigger response, and consequently lead to missed spontaneous breaths, triggering on expiration, or inappropriate triggering (auto-cycling) due to artefactual signals.7

Neurally adjusted ventilatory assist (NAVA) and proportional assist ventilation (PAV) are two novel modes of ventilation that use the diaphragmatic electrical activity (Edi) and the airflow changes detected by a pneumotachograph (PNT), respectively, to adjust the inflation pressure continuously in response to the ongoing breathing effort of the patient. Thus, the patient controls the support of the ventilator throughout the respiratory cycle and defines both the peak inflation pressure and inspiratory time. The focus of this review is the physiology, limitations and evidence behind the proposed benefits of these modes of ventilation as applied in neonates.