Oxygen saturation (medicine) approaches 100% at partial oxygen pressures of >10 kPa. A pulse oximeter relies on the light absorption characteristics of saturated hemoglobin to give an indication of oxygen saturation. The body maintains a stable level of oxygen saturation for the most part by chemical processes of aerobic metabolism associated with breathing. Using the respiratory system, red blood cells, specifically the hemoglobin, gather oxygen in the lungs and distribute it to the rest of the body. The needs of the body's blood oxygen may fluctuate such as during exercise when more oxygen is required or when living at higher altitudes. A blood
Packed red blood cells the red blood cells using special equipment, such as the IBM 2991 cell processor in a similar manner to washing RBCs. The processing (often termed "manufacture", since the end result is deemed a biologic biopharmaceutical product) and the storage can occur at a collection center and/or a blood bank. RBCs are mixed with an anticoagulant and storage solution which provides nutrients and aims to preserve viability and functionality of the cells (limiting their so-called "storage lesion"), which are stored at refrigerated temperatures for up to 42 days (in the US), except for the rather unusual long-term storage in which case