Study of Respiratory Physiology During High Flow Nasal Cannula Treatment in Preterm Neonates.

Purpose and design

Design: Prospective randomised crossover study.

Purpose:

• Raising airway pressure is one of the most important interventions at the disposal of clinicians treating patients with respiratory failure. In premature infants Continuous Positive Airway Pressure (CPAP) and High Flow Nasal Cannula (HFNC) are noninvasive techniques to raise mean airway pressure when intubation is not required. It is not clear how clinicians choose between these techniques and there is little data comparing the physiological effect of these treatments.
• A composite physiological assessment of babies on HFNC and CPAP treatment is required to understand how HFNC works. It is important to answer this question to understand how best to use HFNC in babies.
• This proposal is designed to provide information on physiological effects of both therapies in same population of babies across different weight categories. The study protocol involves use of same HFNC device that is currently being used in neonatal unit.

Interventions:

1. A small plastic catheter tip transducer (Gaeltec) will be placed in upper breathing passage (nasopharynx or oropharynx) using standard methods. From this we will measure airway pressures and respiratory gas concentrations.

The catheter will be removed soon after the study is completed. This procedure will be done once during the study.

2. Breathing markers (Tidal breathing indices) will be measured by non invasive method using Volusense method where a vest will be applied over the chest and abdomen like a layer of clothing. The Volusense vest will be removed soon after the procedure. This process is done once during the study.

3. Blood carbon dioxide (CO2) levels will be measured by a non invasive transcutaneous sensor applied to the skin (Tosca Radiometer). This skin sensor will be removed soon after the study is completed.

1. The baby must be clinically stable for preceding 12 hours on noninvasive breathing support (not meeting exit criteria). The babies will be randomised to either group 1 (CPAP first followed by HFNC) or group 2 (HFNC first followed by CPAP) by computerised software programme.
2. The measuring devices namely nasopharyngeal catheter, Volusense vest and transcutaneous CO2 sensor are placed as per standard methods.
3. After ensuring babies' clinical stability the measurements are recorded at HFNC gas flow rate range from 2 litres to 8 litres per minute and in CPAP of 6 cm of water pressure level.
4. The study lasts about 2 hours. The baby spends 10 minutes at each HFNC flow rate level and 30 minutes of equilibration period when support will be changed between HFNC and CPAP.
5. Routine measurement of heart rate, respiratory rate and oxygen saturations will be done as per standard neonatal practice. The above data will be recorded electronically for analysis with total study duration around 120 minutes.
6. Respiratory support can be terminated at any point if clinically not indicated.

The researcher is an experienced neonatal registrar who will be directly observing the baby throughout the study.

Measurements would be discontinued if any pre set exit criteria is noted.

Statistics: A total of 45 babies (15 babies in each weight category: <1000 grams, 1001500 grams and >1500 grams) will be studied.