Background: A number of therapeutic settings have lately utilised the high-flow nasal cannula (HFNC) to oxygenate people. When compared to low-flow oxygen systems or non-invasive ventilation, HFNC has several benefits. These include making the patient more comfortable, making expectoration easier by humidifying secretions, washing out the nasopharyngeal dead space to make ventilation more efficient, providing a small positive end-inspiratory pressure effect, and quickly and accurately delivering a fraction of inspired oxygen (FiO2) by minimising room air entrainment. Hypercapneic respiratory failure (an aggravation of chronic obstructive lung disease), hypoxemic respiratory failure, post-extubation respiratory failure, pre-intubation oxygenation, and other disorders have all been effectively treated using HFNC in critically ill patients. While there is some evidence of benefit, it is mostly subjective and based on physiological factors; furthermore, the signs are not conclusive. This study delves into the practical and clinical uses of HFNC in adults, including topics such as its distinct impact on respiratory physiology, device settings, and clinical indications.