The Use of NAVA vs. Pressure Support During Asynchrony in Children

Asynchrony during assisted ventilation in children is common because of the presence of uncuffed artificial airways and their rapid ventilatory rate with small volumes compared to adults.As a result, the most common approach to ventilatory support in children is pressure ventilation, since pressure targeted ventilation allows gas delivery to vary based on patient demand. In addition, many manufacturers have incorporated adjuncts designed to improve synchrony in pressure targeted ventilation. Most of today's ICU ventilators incorporate rise time and control of the breath termination criteria in pressure ventilation by either altering inspiratory time directly or adjusting the inspiratory flow termination criteria in pressure support ventilation. In addition, careful adjustment of trigger sensitivity, and insuring driving pressure is appropriately set to avoid large tidal volumes improves synchrony in many patients. However, in spite of all of these potential adjustments many pediatric patients are still asynchronous.

A recently released new mode of ventilation, NAVA (neurally adjusted ventilatory assist) is designed to reduce the asynchrony that exists between the ventilator and the patient. With NAVA, gas delivery from the mechanical ventilator is triggered, controlled and cycled by the diaphragmatic EMG signal (Edi). The ventilator is aware of the change in diaphragmatic EMG by the insertion of a specially designed nasogastric tube (NGT) with EMG electrodes that cross the diaphragm. This NGT also functions similar to any standard NGT. NAVA is used to control all aspects of assisted ventilatory support. A number of preliminary studies in neonates and pediatric patients have demonstrated that patient ventilator synchrony is improved with the application of NAVA. In general, tidal volumes delivered by the ventilator are decreased, respiratory rates increased and peak inspiratory pressures decreased. In these studies, triggering and cycling of the ventilator are controlled by the diaphragmatic EMG in more than 70 % of the time. If the EMG signal does not activate or terminate positive pressure backup flow/pressure/time signal, control gas delivery -as is customary in standard modes of ventilatory support- takes over.

We hypothesize that the use of NAVA will improve trigger and flow synchrony in children and insure that tidal volumes are normalized (6 to 8 ml/kg) in these patients.

Asynchrony will be studied in 12 mechanically ventilated pediatric patients in the Pediatric ICU at Hospital Universitario Materno-Infantil La Paz in Madrid, Spain.

The study protocol has 5 phases