Neurally Adjusted Ventilatory Assist vs Proportional Assist Ventilation

Despite improvements in survival rates of extremely preterm born infants, the incidence of bronchopulmonary dysplasia (BPD) remains unchanged over the last two decades. As invasive ventilation is frequently necessary and indeed life saving, numerous ventilator strategies have been developed to reduce damage to the developing lung. Synchronisation of mechanical breaths with the patient's respiratory effort offers the theoretical benefit of improving oxygenation and ventilation, requiring lower ventilator pressures, fewer air leaks and increased patient comfort.

Recently, novel modes of ventilation have been introduced that aim to improve upon conventional ventilation. During both proportional assist ventilation (PAV) and neurally-adjusted ventilatory assist (NAVA), respiratory support is servo-controlled based on continuous input from the baby's respiratory effort. Both aim to improve synchronization of the timing of the respiratory cycle and also to vary the level of support offered breath-to-breath in proportion to the respiratory effort of the patient.

During proportional assist ventilation (PAV), the ventilator can vary inflation pressure in phase with both volume change and flow change in order to offload both elastic and resistive components of the work of breathing. We have previously shown that PAV, compared to ACV, reduces the oxygenation index and improves respiratory muscle strength in infants born prematurely who remain ventilated at or beyond one week of life .

Neurally adjusted ventilatory assist (NAVA) utilises the electrical activity of the diaphragm to trigger the ventilator. A modified nasogastric feeding tube with a series of electrodes allows monitoring of the diaphragmatic electromyogram (Edi). The waveform of the Edi is used to trigger and control ventilator support. We have recently shown that NAVA compared to ACV results in a lower oxygenation index in infants born prematurely who remain ventilated at or beyond one week of life.

Both PAV and NAVA have been shown to have advantages above conventional triggered ventilation in neonates, but they have not been compared to each other. Our aim is to determine whether NAVA or PAV is more effective in prematurely born neonates with evolving or established BPD.

Inclusion criteria

• Born at less than 32 weeks gestation
• ventilated at or beyond one week of life

Exclusion criteria

• major congenital abnormalities