The purpose of this study is to determine if a new type of mechanical ventilation, or breathing machine (called neurally adjusted ventilatory assist or NAVA), will provide additional support to infants who were born prematurely. Investigators are looking to determine if in two hours infants who weighed less than 1500 grams or 3 pounds 5 ounces, will demonstrate a decrease in the amount of carbon dioxide (the gas that humans exhale) dissolved in their blood as compared to prior to starting the study. This will be accomplished by enrolling infants who are stable on their current type of mechanical breathing that provides a constant air flow into the infant. This type of mechanical support helps keep the lungs inflated but does not help remove carbon dioxide. This study will change the type of mechanical support to a type of support called neurally adjusted ventilatory assist or NAVA. This type of mechanical support detects when the infant is breathing in by having electrical sensors on a feeding tube that is placed into the stomach through the nose or mouth. These electrical sensors detect when the diaphragm or the muscle that helps humans breath is trying to take a breath in. When the NAVA ventilator senses the attempt to breath, it provides additional air flow to make the effort of breathing easier. The ventilator will be attached to a tube or cannula that is placed into the infant's nose. After two hours of being on the NAVA ventilator a repeat measure of carbon dioxide in the blood will be performed by taking a small amount of blood from the infant's heel.

Baseline Data Collection:

Demographic data: Patient gestational age at delivery, maternal betamethasone therapy, APGAR scores, admission weight, receipt of surfactant administered, age at extubation, time since extubation, current post menstrual age, and current weight.

Baseline vitals and ventilation mode: Heart rate, blood pressure, FiO2 (fraction of inspired oxygen), oxygen saturations, transcutaneous partial pressure of carbon dioxide (TCO2) and current mode of ventilation will be recorded four times in a one minute period and the values average to minimize normal variation. Intervention time will be manipulated to begin no later than one hour after the previous feeding, as to minimize interruption of feedings to no greater than 30 minutes.

Safety Safety: TCO2 monitor will be attached to the infant and the device will be calibrated according to protocol (reference TCO2 monitor manual). Carbon dioxide diffusion through the skin will be monitored continuously during the intervention (Bromley 08) to avoid periods of hypo or hypercarbia.

Edi (electrical activity of the diaphragm) Catheter placement: Edi catheter size will be selected according to infant's weight and length. It will be inserted according to manufacturer's guidelines and adjustments will be made to optimize positioning (reference NAVA manual).

NAVA settings:

Infants will be maintained on previous level of PEEP (positive end expiratory pressure) or calculated PEEP, rounding up to whole numbers. Initial NAVA level will be determined by starting with an initial NAVA level of 0.5 microvolts/cm of H20. The NAVA level will then be adjusted either by increasing or decreasing to generate a PIP that is a minimum of 8 cm of H2O greater than the current PEEP. Apnea alarm will be set at 5 seconds, which will initiate the NAVA back up setting if no electrical activity is detected by the Edi catheter. Back up NAVA settings will be set with a PIP of 12 cm of H20 greater than current PEEP, respiratory rate of 60 breaths per minute (RR) and inspiratory time of 0.5 seconds. Fraction of inspired oxygen (FiO2) will be adjusted to keep infant's oxygen saturations within previously established clinical parameters.

Study Intervention Procedure and Data Collection:

At initiation of intervention, and at time 30, 60, 90, and 120 minutes, heart rate (HR), respiratory rate (RR), tidal volume (TV), minute ventilation, FiO2, oxygen saturations, peak Edi and PIP will be recorded four times in a one minute period and the values average to minimize normal variation. Current NAVA settings, TCO2, and blood pressure (BP) will also be recorded. At 60 minutes of intervention if the TCO2 level has not decreased by 5 torr from baseline or has risen, the current NAVA level will be increased by 50%. At 90 minutes if the TCO2 level has not decreased by 5 torr from baseline or has risen; the NAVA level will be increased by 50% from the current level. At the completion of the study (120 minutes or pCO2 outside of established limits) the HR, RR, BP, TV, minute ventilation, FiO2, oxygen saturations, peak Edi and PIP will be recorded four times in a one minute period and the values average to minimize normal variation. A capillary blood gas will be obtained according to standard unit protocol with a warmed heel.

Inclusion Criteria:

• birth weight less than 1,500 grams
• Clinical history of respiratory distress syndrome treated with surfactant
• Chronological age greater than or equal to seven days
• 48 hours post-extubation or greater
• Medically stable per primary medical team
• Receiving ventilatory support on one of the following systems via nasal pharyngeal tube or nasal prongs:continuous positive airway pressure (CPAP), intermittent mechanical ventilation (IMV), or neutrally adjusted ventilatory assistance (NAVA)
• Receiving ventilatory support via high flow nasal cannula if the flow is large enough to provide a positive end expiratory pressure (PEEP) of 6 as defined by PEEP of 6 = 0.68 * weight (kg) + 0.92
• Capillary blood gas via heel stick within 24 hours that demonstrates a pH of less than or equal to 7.35 and/or a partial pressure of carbon dioxide (pCO2) greater than or equal to 45 mmHg

Exclusion criteria:

• Severe congenital abnormalities
• Grade III or IV interventricular hemorrhage.

Each subject was monitored for adverse events potentially attributable to the study intervention from the time of enrollment and completion of the study until their discharge from the hospital, which varied from 3 weeks to 3 months.