Cirrhosis can be complicated by refractory hypoxemia due to high rates of blood flow through the lung, resulting in ventilation-perfusion mismatch. Fat embolism syndrome, in which fat droplets are deposited in the pulmonary capillary bed. Shunting
Shunting refers to blood that bypasses the pulmonary circulation, meaning that the blood does not receive oxygen from the alveoli. In general, a shunt may be within the heart or lungs, and cannot be corrected by administering oxygen alone. Shunting may occur in normal states:

Anatomic shunting, occurring via the bronchial circulation, which provides blood to the tissues of the lung. Shunting also occurs by the smallest cardiac veins, which empty directly into the left ventricle. Physiological shunts, occur due to the effect of gravity. The highest concentration of blood in the pulmonary circulation occurs in the bases of the pulmonary tree compared to the highest pressure of gas in the apexes of the lungs. Alveoli may not be ventilated in shallow breathing.Shunting may also occur in disease states:

Acute respiratory distress syndrome (ARDS). Alveolar collapse, which can increase the amount of physiological shunting, may be managed through a combination of increasing oxygenation as well as positive pressure to recruit collapsed alveoli. Pathological shunts such as patent ductus arteriosus, patent foramen ovale, and atrial septal defects or ventricular septal defects. These states are when blood from the right side of the heart moves straight to the left side, without first passing through the lungs. This is known as a right-to-left shunt, which is often congenital in origin.
A decreased respiratory drive can also be the result of metabolic alkalosis, a state of decreased carbon dioxide in the blood
Central sleep apnea. During sleep, the breathing centers of the brain can pause their activity, leading to prolonged periods of apnea with potentially serious consequences. Hyperventilation followed by prolonged breath-holding. This hyperventilation, attempted by some swimmers, reduces the amount of carbon dioxide in the lungs. This reduces the urge to breathe. However, it also means that falling blood oxygen levels are not sensed, and can result in hypoxemia. Physical states
A variety of conditions that physically limit airflow can lead to hypoxemia. Suffocation, including temporary interruption or cessation of breathing as in obstructive sleep apnea, or bedclothes may interfere with breathing in infants, a putative cause of SIDS. Structural deformities of the chest, such as scoliosis and kyphosis, which can restrict breathing and lead to hypoxia. Muscle weakness, which may limit the ability of the diaphragm, the primary muscle for drawing new air into lungs, to function. This may be a result of a congenital disease, such as motor neuron disease, or an acquired condition, such as fatigue in severe cases of COPD. Environmental oxygen
In conditions where the proportion of oxygen in the air is low, or when the partial pressure of oxygen has decreased, less oxygen is present in the alveoli of the lungs. The alveolar oxygen is transferred to hemoglobin, a carrier protein inside red blood cells, with an efficiency that decreases with the partial pressure of oxygen in the air. Altitude.