**1.3 Devices of oxygen delivery**

Oxygen (O2); is an inert gas essential for life, being inspired through the airway and transported via the lungs towards the blood to be used in cellular respiration and delivery of energy needed for body metabolism. Human body uptake of oxygen in concentration of 20.95% from air by natural airways; nose and mouth, transported down along the conductive airways to be resting in the alveoli where the gas exchange happening. Physiological and pathological conditions required an increased FIO2 to meet the body oxygen requirement and its high demand. Devices are designed to facilitate oxygen delivery from artificial oxygen sources in correspond to the target of FIO2, patient's breathing effort and patient's device compliance [3].

All critically ill patients must have high-flow oxygen delivery device (15 L/min), until stable status achieved, then oxygen requirement could be individually determined depending on the existing pathology. Patient's breathing effort is the primary determinant for the oxygen delivery device selection. Critically ill patients might be one of two groups; spontaneous breathing group or assisted ventilation one and each group has a preference in oxygen delivery system [4].
