Oxygen is a chemical element without which life on Earth would not be possible. Humans need oxygen for respiration, which takes place partly under the action of the respiratory center, and partly under the influence of the human will. The acid-base balance is responsible for determining the saturation and partial values of carbon dioxide and oxygen. Disorder of acid-base balance leads to the appearance of mechanical or respiratory alkalosis or acidosis. The main indication for oxygen therapy, i.e. oxygen therapy, is proven hypoxemia (when PaO2 <60 mmHg or SaO2 <90% in ordinary air). Oxygen therapy is recommended in medical emergencies and critical conditions, in serious diseases with hypoxemia, and in people who have worsening COPD. There are various techniques for administering oxygen through single or double nasal catheters, oxygen masks without a reservoir, oxygen masks with a reservoir and Venturi masks. Mechanical ventilation is used as an aid or replacement for spontaneous breathing and is divided into positive pressure ventilation and negative pressure ventilation (depending on the mode of inspiration) and invasive and non-invasive ventilation (depending on the existence of an artificial airway). Which oxygen application technique we choose depends on the flow required to achieve the optimal oxygen concentration. The most widespread therapy with high oxygen flows is through the nasal cannula. It is a non-invasive therapy that uses the method of heating and humidifying the inhaled gas and delivers oxygen at a flow rate of up to 60 l / min. It is most often used in the intensive care unit, emergency room and wake-up room. The nurse plays an important role in the therapy of a patient with a respiratory problem. Its task is to observe the patient's condition, identify deviations from normal, warn, record, respond in a timely manner and apply procedures to resolve problems or complications. The bachelors of defines current or potential nursing diagnoses to address the patient's emerging problems. In patients with Covid-19 infection, a high-flow nasal cannula (HFNC) is suggested as first-line therapy.