| PaO2 | Arterial oxygen tension, or partial pressure |
|---|---|
| PAO2 | Alveolar oxygen tension, or partial pressure |
| PaCO2 | Arterial carbon dioxide tension, or partial pressure |
| PACO2 | Alveolar carbon dioxide tension, or partial pressure |
| PvO2 | Oxygen tension of mixed venous blood |
| P(A-a)O2 | Alveolar-arterial oxygen tension difference. The term formerly used (A-a DO2) is discouraged. |
| P(a/A)O2 | Alveolar-arterial tension ratio; PaO2:PAO2 The term oxygen exchange index describes this ratio. |
| C(a-v)O2 | Arteriovenous oxygen content difference |
| SaO2 | Oxygen saturation of the hemoglobin of arterial blood |
| SpO2 | Oxygen saturation as measured by pulse oximetry |
| CaO2 | Oxygen content of arterial blood |
| pH | Symbol relating the hydrogen ion concentration or activity of a solution to that of a standard solution; approximately equal to the negative logarithm of the hydrogen ion concentration. pH is an indicator of the relative acidity or alkalinity of a solution |
Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. It means that not all the air in each breath is available for the exchange of oxygen and carbon dioxide. Mammals breathe in and out of their lungs, wasting that part of the inhalation which remains in the conducting airways where no gas exchange can occur.