NAVA Helmet in Pediatric Respiratory Failure

Neurally Adjusted Ventilatory Assist (NAVA) is a new form of partial support wherein the machine applies positive pressure throughout inspiration in proportion to the electrical activity of the diaphragm (EAdi), as assessed by trans-esophageal electromyography (1). Because ventilator functioning and cycling are under control of the patient's respiratory drive and rhythm, NAVA has the potential to enhance patient-ventilator interaction ensuring synchrony and minimizing the risk of over-assistance. A high incidence of asynchrony events has been demonstrated to have a significant clinical impact by favouring weaning failure and longer duration of mechanical ventilation (2). NAVA has been implemented safely in animals, in healthy volunteers and in critically ill adults and has been shown to improve patient-ventilator synchrony, to limit excessive airway pressure and tidal volume, and to unload the respiratory muscles in tracheally intubated patients (1,3,4). Moreover NAVA was found to be effective in delivering non-invasive ventilation (NIV) even when the interface was excessively leaky (75% leak) with reduced positive end-expiratory pressure (3). With these conditions, NAVA was able to unload the respiratory muscles and preserve gas exchange, while maintaining synchrony to respiratory demand. Data from medical literature from our group demonstrate that the pediatric helmet was better tolerated than facial mask , required less sedation an allowed more prolonged ventilatory assistance due to better tolerance (5-6). To date, no data exist on the use of NAVA in infants during noninvasive ventilation. The aim of this physiological study is to compare patient-ventilator interaction in infants receiving NIV by NAVA and Pressure Support Ventilation (PSV). Equipment. NAVA and conventional PSV is provided by the Servo-I ventilator (Maquet Critical Care, Solna, Sweden). Electrical activity of the diaphragm (EAdi) is obtained using an array of nine miniaturized electrodes (spaced 6 mm apart) mounted on a conventional (5.5F) feeding tube (Maquet Critical Care AB, Solna, Sweden; Neurovent Research Inc, Toronto, Canada), and positioned in the lower esophagus at the level of the diaphragm. Confirmation of appropriate placement is achieved by viewing the online electrical displays from the catheter. The presence of a good quality EAdi trace with p waves displayed by the central electrodes indicates optimal positioning, with the array spanning the diaphragm equally in both caudal and cranial directions. A pediatric helmet is used as interface between the patient and the ventilator. Tidal volume , airway pressure and flow trace are recorded with the Servo I NAVA Tracker acquisition system.

Experimental protocol. Enrolled patients, after a stabilization period with oxygen therapy and standard medical treatment (antibiotics, steroids, Inhaled beta 2 agonists), receive two 60-minutes ventilatory trials delivered by pediatric helmet.

After a baseline trial on PSV conventional , children are allocated to receive 1 trial NAVA NIV and 1 trial PSV conventional. The sequence of the two ventilatory trials are randomized according to sealed opaque envelops.

Ventilatory trials are as follows:

1. NAVA-NIV
2. PSV conventional . The first 15 mins of each period are considered as a wash out period and patients are carefully observed for any reactions or problems occurring for the technique. After the first 15 mins period, data recording for the study are started.

NAVA and PSV level are set by the attending physician in order to obtain a Tidal Volume (TV) 6-8 ml/kg, peripheral oxygen saturation (SpO2) > 94%, Respiratory Rate (RR) < +/-2 SD for age. Sedation and analgesia are provided according to standardized PICU protocols, if needed and are not changed during the two study windows for the same patient.

Monitoring .All infants are monitored as follow: SpO2, and EKG continuously; arterial blood pressure every 15 min; arterial blood gases at enrolment and once for each trial. The total amount of drug needed for sedation and/or complications (intolerance to the interface, leaks, gastric distension) are also recorded.

Statistics. No data are available at the moment in medical literature in infants. Based on retrospective data from adult literature, the predicted reduction in the primary end point (AI) with NAVA versus Conventional flow triggered PSV, is around 20%. The power analysis indicated a sample size of 12 patients was needed to demonstrate a 20% reduction in the AI between the two ventilator modes with an alfa and beta risk of 005 and 0.2 respectively. Sample size calculation has been performed with GPower3.1.2 software (Kiel University, Germany)