Asymmetrical HFNCO vs Standard HFNCO Post Cardiac Surgery Patients

High-flow oxygen therapy has been applied after extubation in cardiac surgery patients with a well-known successful efficacy. The current authors plan to conduct a prospective, randomized, controlled study of the Asymmetrical device Nasal Cannula High Flow Oxygenation (HFNCO) application on high flow (60L/min) with 60% fiO2 administration versus Conventional device Nasal Cannula High Flow Oxygenation (HFNCO) application on high flow (60L/min) with 60% fiO2 administration and versus Conventional oxygen treatment (Venturi mask) after extubation of patients undergoing elective or non-elective cardiac surgery.

Over the last decade, High Flow Nasal Cannula Oxygenation,(HFNCO) has proven successfully its capability in the management of hypoxemic respiratory failure patients post cardiac surgery. Efficient oxygenation has been recorded in meta-analyses on study population research with BMI \> 30 . Moreover, in a recent meta-analysis, it has been documented that the use of HFNCO required less need for upgrade of respiratory support . Similar findings were documented in a study of two different variations of HFNCO treatment as compared with Conventional oxygen therapy (Venturi mask) .

A modified version (Asymmetrical) of HFNCO came on the surface recently whereas the (L) nasal prong has a larger diameter compared with the (R) prong of the nasal cannula.

Research results on hypoxemic patients and laboratory models also revealed interesting measurements on specific respiratory parameters such as minute volume ventilation, respiratory rate, and work of breathing as compared with conventional HFNCO. In addition, there were documented higher resistance flow rates which achieved higher PEEP rates in favor of lung alveoli.

On the other hand, there exists documentation with positive aspects that support the use of a non-rebreathing mask / Venturi mask or surgical mask fixed on top of nasal prongs of HFNCO to augment the fiO2 which finally ends up on the patient.

Aim of the study. The primary goal of the study is the efficacy of the Asymmetrical HFNCO on cardiac surgical patients post-extubation as compared with Conventional HFNCO The secondary goal of the study is the comparison of initial Asymmetrical HFNCO parameters versus a) the avoidance of upgrading Asymmetrical HFNCO supported by a non-rebreathing mask fixed on top of that, versus b) the avoidance of upgrading Asymmetrical HFNCO to Non-Invasive Ventilation (NIV).

The tertiary goal of the study is the comparison of all three patient groups; a) Asymmetrical HFNCO, 60L/min, FiO2 60%, b) Conventional HFNCO 60l/min, FiO2 60%, c) Conventional oxygen therapy Venturi mask 12l/min, FiO2 60% regarding the use of treatment on patients with ΒΜΙ \> 30 and regarding respiratory parameters (respiratory rate, pO2/ FiO2, spO2, use of accessory muscles, dyspnoea, comfort and tolerance by using the visual analog scale).

Additional goals of the study are to compare all three patient groups regarding ICU Length of Stay, Hospital Length of Stay, rates of ICU re-admission and re-intubation, and any other respiratory / non-respiratory complications and adverse events ( respiratory-chest infection, pneumothorax, delirium, grand mal, acute renal failure, major bleeding - tamponade, cardiac arrest) . Moreover, the rate of failure of the initial treatment will be recorded (as a major measure of treatment efficacy).

Method This is a prospective, non-blinded, randomized study in post-extubated cardiac surgery patients. The study population will consist of three patient groups;

1. Asymmetrical HFNCO, 60l/min, FiO2 60%,
2. Conventional HFNCO 60l/min, FiO2 60%,
3. Conventional oxygen therapy Venturi mask 12l/min, FiO2 60%

Treatment "failure" will be defined as any crossover from one treatment to another due to the patient's respiratory distress and discomfort. To be more specific, switch from Asymmetrical HFNCO to Conventional HFNCO, or switch from Asymmetrical HFNCO to Conventional oxygen therapy supported by a non-rebreathing mask fixed on top of a nasal cannula, or need for more advanced respiratory support such as non-invasive ventilation or invasive mechanical ventilation

Any implemented treatment would also be defined as "failure" when any irreversible (for at least 48 hours) FiO2/gas-mixture flow escalation might be needed, either it is being recorded in study groups 1 \& 2 or control group.

"Failure" would also defined as any irreversible (\> 48 hours) crossover from either the HFNCO group to standard practice (Venturi mask) or the need for more advanced respiratory support such as non-invasive ventilation or invasive mechanical ventilation.

An initial power analysis was based on a predicted, average failure rate of 15% in the HFNCO groups and a failure rate of 51% in the control group; this analysis yielded the need for enrollment of a total of 41 HFNCO patients and 21 controls for alpha = 0.05 and power=0.80. To ensure equal numbers of patients in each one of the 2 HFNCO groups, the authors decided to enroll 42 HFNCO patients (n=21 for each NHF group) and 21 controls, resulting in a total enrollment of 63 patients

Eligibility Criteria:
Inclusion Criteria:

* Cardiac ICU adult patients
* \>18 years
* After elective or urgent cardiac surgery
* Successful Spontaneous Breathing Trial (SBT) with T-piece and FiO2=60%.
* pO2/ FiO2 \<150
* Hemodynamically stable (160\>SAP\>90mmHg)

Exclusion Criteria:

* Obstructive Sleep Apnea Syndrome supported by CPAP mask on ventilator
* COPD, officially diagnosed, respiratory failure - on exacerbation with serum blood pH \<7,35.
* Patients with tracheostomy,
* DNR status,
* Glasgow Coma Scale score \< 13,
* Insufficient knowledge of the Greek Language
* Visual or hearing impairment.