The specific aims of this study are to evaluate the amount of high flow nasal cannula (HFNC) gas flow required to generate an equivalent positive distending pressure as that provided by nasal continuous positive airway pressure (NCPAP) of 6 cm H2O, assess the relationships between positive distending pressure, gas flow, oxygen requirement, and patient weight, and lastly, develop an appropriate protocol to be used in the NICU for transitioning patients from NCPAP to an equivalent amount of HFNC.

In the face of exogenous surfactant and use of antenatal steroids, respiratory distress syndrome (RDS) remains a leading cause of morbidity and mortality in premature infants. RDS is the result of a series of complex, interrelated events, including atelectasis, ventilation-perfusion mismatching, and lung inflammation/injury (1). The cascade of events which typifies RDS and its long-term counterpart, chronic lung disease (CLD), is rooted in the intrinsic deficits of the premature lung as well as exacerbated by mechanical ventilation, a mainstay of therapy. For this reason, scientists and clinicians alike continue to search for treatment modalities which will not only treat RDS but also decrease the incidence of chronic lung disease.

The use of non-invasive ventilatory strategies, such as nasal continuous positive airway pressure (NCPAP), in the treatment of RDS is thought to provide positive distending pressure while minimize lung inflammation and injury associated with mechanical ventilation (2). Avoidance of intubation and increased use of NCPAP to treat respiratory distress syndrome has been shown to decrease the incidence of chronic lung disease (3,4). However, NCPAP does have some common clinical limitations. First, the administration of NCPAP has inherent mechanical difficulties in appropriately maintaining the nasal prong apparatus within the small neonatal nose. Secondly, the nasal prongs used to deliver NCPAP can cause nasal septal trauma. Lastly, some premature infants do not tolerate the NCPAP apparatus which must be tightly affixed to their nose and face. This intolerance is often demonstrated by increased patient movement, and subsequently, the risk of mechanical difficulties and septal trauma increase during these times. Although NCPAP continues to be used in most neonatal intensive care units (NICUs), due to its aforementioned drawbacks, we continue to look for other effective, non-invasive modes of ventilation to provide support to premature infants with respiratory distress.

Humidified high flow nasal cannula (HFNC) has recently been introduced into neonatal respiratory care as a means of providing positive distending pressure to the neonate with respiratory distress. HFNC aims to maximize patient tolerance by employing heated, humidified gas flow through the standard neonatal nasal cannula that is used routinely in neonatal intensive care units. HFNC provides positive distending pressure by using high gas flow (>1 liter per minute) (5). Although numerous neonatal intensive care units are using HFNC, including both NICUs at Children's Hospitals of Minnesota, there are very few studies regarding its use in this population. Anecdotally, the premature babies tolerate the administration of HFNC quite well. However, like any new therapy, there are many unknowns.

There is only one study to date which investigates HFNC versus NCPAP in the preterm neonate (6). Sreenan and colleagues found HFNC to be as effective as NCPAP in the management of apnea of prematurity and also demonstrated that the positive distending pressure provided by HFNC varied with the patient's weight. Sreenan's study as well as preliminary data presented in abstract form cite HFNC use with various amounts of gas flow, ranging from 1 liter per minute up to 6 liters per minute (6,7,8). The choice of how much gas flow to use with the HFNC system is unclear. This decision is actually a three-fold question: 1) the initial amount of liter flow to use, 2) what does a particular liter flow provide for positive distending pressure to that patient, and 3) are these values system-specific? We aim to evaluate these questions in our study. Until recently, NCPAP has been the mainstay of non-invasive ventilatory support for premature babies. However, as HFNC is better tolerated and uses a nasal cannula that is less prone to mechanical mishaps than NCPAP, it is clear that we need more information to accurately treat babies with HFNC. The results of this study will help guide the use of HFNC in preterm babies with respiratory insufficiency, as knowledge of the positive distending pressures derived from the HFNC system are crucial in minimizing barotrauma to the fragile, premature lung.

Inclusion Criteria:

• 1) receiving NCPAP ventilatory support at > 72 hrs. of age and 2) requiring FiO2 21-50% on NCPAP.

Exclusion Criteria:

• FiO2 >50%, presence of pneumothorax or pleural effusion, anatomical abnormalities of the airway, lungs, or esophagus, or cyanotic congenital heart defect.