Gas Composition in the Hypopharynx During High-flow or Standard Oxygen Therapy Through Face Mask in Healthy Volunteers

Gas Composition in the Hypopharynx During High-flow Oxygen Therapy Through Nasal Cannula or Face Mask, or During Standard Oxygen Therapy Through a Non-Rebreather Face Mask in Healthy Volunteers

The COVID-19 pandemic has become a huge global problem, affecting all spheres of human life, resulting in enormous social, economic consequences and human tragedies. With very decent results of treatment of patients of average severity in the conditions of bed units, the results of treatment of the most severe category - patients of intensive care units who required tracheal intubation remain extremely unsatisfactory. According to different data, mortality in this category of patients reaches 80-90%. However, observational, randomized studies and their meta-analyses have shown high efficiency of high-flow oxygen therapy through nasal cannulas, reaching 50-60%. Some pilot bench studies (on manikins) have shown the advantages of high-flow oxygen therapy over standard oxygen therapy in reducing anatomical dead space and preserving a given inspiratory fraction of oxygen in the laryngeal pharynx of the manikin, but the actual state of the laryngeal pharyngeal gas composition was not studied. Some patients breathe through open mouth that decreases the efficacy oh high flow oxygen through nasal cannula. The aim of the study is to measure the inspiratory (FiO2) and expiratory (FeO2) oxygen fractions and the inspiratory and expiratory carbon dioxide fractions (FiCO2 and FeCO2, respectively) in the hypopharynx of healthy volunteers during high-flow oxygen therapy through nasal cannula and face mask, and during standard oxygen therapy through non-rebreather face mask under different physiological conditions.

Randomized controlled trials showed reduction of tracheal intubation in high- flow oxygen therapy through nasal cannula group in patients with acute respiratory failure as compared to standard oxygen therapy and noninvasive ventilation before Coronavirus disease-19 (COVID-19) pandemic.

The World Health Organization (WHO) declared the outbreak a pandemic of COVID-19 on March 11th, 2020. Since then observational, randomized studies and their meta-analyses have shown the high effectiveness of high-flow oxygen therapy through nasal cannulas (HFNC), reaching 50-60% in acute hypoxemic respiratory failure.

Bench studies showed the advantages of HFNC compared with standard oxygen therapy, consisting in reducing the anatomical dead space and maintaining a given inspiratory oxygen fraction in the hypopharynx of the mannequin, but the actual state of the gas composition of the hypopharynx during HFNC was not studied. Some patients breathe through open mouth that decreases the efficacy oh high flow oxygen through nasal cannula.

The aim of the study is to measure the inspiratory (FiO2) and expiratory (FeO2) oxygen fractions and the inspiratory and expiratory carbon dioxide fractions (FiCO2 and FeCO2, respectively) in the hypopharynx of healthy volunteers during high-flow oxygen therapy through nasal cannula and face mask, and during standard oxygen therapy through non-rebreather face mask under different physiological conditions.

Inclusion Criteria:

• Healthy Volunteers
• Age 18-50 years
• Written informed consent.

Exclusion Criteria:

• Any primary or secondary lung diseases (COPD, bronchial asthma, interstitial lung diseases, metastatic lung disease, lung cancer)
• Any chronic diseases that can cause respiratory disorders (chronic heart failure, liver cirrhosis, systemic connective tissue diseases, cancer, neuromuscular diseases etc)
• Heart rhythm disturbances
• Body mass index more than 30 kg/m2
• Swallowing disorders
• History of epileptic syndrome
• Recent head surgery or anatomy that precludes the use of nasal cannulas
• Pregnancy and lactation period
• Inability to cooperate with staff.