High flow nasal cannula (HFNC) are introduced to clinical practice to improve oxygenation. Our group were the first to report the use of HFNC in extubated patients that showed comparable delivery of oxygen and improved comfort. These HFNC are subsequently shown to be useful in several clinical conditions in critically ill patients including respiratory failure due to hypoxia, hypercapnia (exacerbation of chronic obstructive lung disease), or post-extubation, pre-intubation oxygenation, and others.

Recently a new mode of high flow oxygen therapy has been presented on the market where the prongs of high flow have two different diameters. These two-nare size high flow nasal cannula are capable of delivering gases at a flow rate of 15-50 L/min, similar to the conventional HFNP but the difference in the diameters provide different levels of positive pressure as compared to conventional HFNP. This positive pressure could help in gas exchange of patients who need more oxygen. These devices are approved by the Therapeutic Goods Administration (TGA); the medicine and therapeutic regulatory agency of the Australian Government.

Our aim is to compare the two size nare high flow nasal cannula with conventional high flow nasal cannula in extubated patients in intensive care unit in a randomised crossover trial. The comparison will include arterial blood gasses, physiological data including heart rate, respiratory rate, saturations as well as comfort and tolerance of the patients to two size nare high flow nasal cannuale.

This is a randomised crossover study of ventilated patients suitable for extubation was conducted. Potential patients were clinically assessed for suitability of extubation and arterial blood gasses (ABG) were performed prior to extubation to ensure the patients had optimal gas exchange. If found to be suitable for extubation, patients were extubated and were provided with a high flow blend of oxygen and air by a high flow face mask at a rate of 40 litres per minute delivering an FiO2 to ensure an oxygen saturation of 93% + 1 for 30 minutes. At the end of this 30 minute stabilization, ABG were performed and heart rate, blood pressure, and Glasgow coma score (GCS) were recorded. If the patients remained stable they were randomized to either protocol A (Duet HFNP for 30 minutes followed by conventional HFNP for 30 minutes) or protocol B ( conventional HFNP for 30 minutes followed by Duet HFNP for 30 minutes). During both protocols gas flow rate and FiO2 were maintained at exactly the same settings as used during the stabilization period. Blood gases and other physiological observations (heart rate, blood pressure, and respiratory rate, saturations, GCS, comfort score and tolerance score) were recorded at the end of each protocol. The bed side nurse assessed comfort and tolerance of patients to both the devices by a 5-point Likert scale as shown below. For the purpose of this study only medium size cannulas were used to maintain consistency. Subgroup Comparisions will be performed between those with and without nasogastric tubes and between male and female patients. Randomization is performed using sequentially numbered, sealed, opaque envelope to maintain allocation concealment.

Determine patient's comfort:

Patients provided the comfort for both duet HFNP and conventional HFNP prongs using a 5-point Likert scale;

1. No discomfort,
2. Little bit discomfort,
3. Little more discomfort,
4. Whole lot more discomfort
5. Worst discomfort.

Determine patient's tolerance:

The bedside nurse documented the patient's tolerance using a 5-point Likert scale.

0 Patient never removes the apparatus and does not complain

1. Patient complains about keeping apparatus on
2. Patient request removal of the apparatus
3. Removal of the apparatus by the patient once
4. Removal of multiple times or non-compliance.

Inclusion Criteria:

• All intubated patients imminently requiring extubation with family consent for admittance into the trial that meet the follow criteria:
• P/F ratio between > 150 prior to extubation
• Has a functional arterial catheter to allow sample of arterial blood gasses.

Exclusion Criteria:

• Patients being extubated due to withdrawal of therapy Patients being extubated, that are expected to imminently die post extubation P/F Ratio :< 150 Patients extubated on to non-invasive ventilation Patients with known epistaxis or nasal surgery.