Hypoxemia defined in terms of reduced partial pressure of oxygen (mm Hg) in arterial blood, but also in terms of reduced content of oxygen (ml oxygen per dl blood) or percentage saturation of hemoglobin (the oxygen binding protein within red blood cells) with oxygen, which is either found singly or in combination. While there is general agreement that an arterial blood gas measurement which shows that the partial pressure of oxygen is lower than normal constitutes hypoxemia, there is less agreement concerning whether the oxygen content of blood is relevant in determining hypoxemia. This definition would include oxygen carried by hemoglobin.
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