Additionally, oxygen in a confined space can be consumed if carbon dioxide scrubbers are used without sufficient attention to supplementing the oxygen which has been consumed. Perfusion
Ventilation-perfusion mismatch
This refers to a disruption in the ventilation/perfusion equilibrium. Oxygen entering the lungs typically diffuses across the alveolar-capillary membrane into blood. However this equilibration does not occur when the alveolus is insufficiently ventilated, and as a consequence the blood exiting that alveolus is relatively hypoxemic. When such blood is added to blood from well ventilated alveoli, the mix has a lower oxygen partial pressure than the alveolar air, and so the A-a difference develops. Examples of states that can cause a ventilation-perfusion mismatch include:

Exercise. Whilst modest activity and exercise improves ventilation-perfusion matching, hypoxemia may develop during intense exercise as a result of preexisting lung diseases. During exercise, almost half of the hypoxemia is due to diffusion limitations (again, on average). Aging. An increasingly poor match between ventilation and perfusion is seen with age, as well as a decreased ability to compensate for hypoxic states. : 646 
Diseases that affect the pulmonary interstitium can also result in hypoxia, by affecting the ability of oxygen to diffuse into arteries. An example of these diseases is pulmonary fibrosis, where even at rest a fifth of the hypoxemia is due to diffusion limitations (on average). Diseases that result in acute or chronic respiratory distress can result in hypoxia. These diseases can be acute in onset (such as obstruction by inhaling something or a pulmonary embolus) or chronic (such as chronic obstructive pulmonary disease).
Papular purpuric gloves and socks syndrome is a cutaneous condition characterized by pruritus, edema, and erythema of the hands and feet, occurring primarily in teenagers and young adults. : 401 An association with parvovirus B19 has been described. It was discovered by a duo of medical students; Kishorkumar Osman and Sulaiman Saloojee, during a ward round. See also
List of cutaneous conditions


== References ==