A blood oxygen level is the percentage of oxygen saturation either in arterial or venous blood, and can be measured by oximetry or through blood tests. By measuring the percentage of oxygen-carrying hemoglobin, doctors can determine arterial blood saturation, or Sa02; venous oxygen saturation, or Sv02; or the peripheral oxygen saturation, or Sp02. According to the Mayo Clinic, an Sa02 value of less than 90 percent indicates hypoxemia, or a low blood oxygen level.
Oxygen Saturation of Arterial Blood
An arterial blood gas, or ABG, test will accurately assess the Sa02, and often uses blood from the radial artery. An ABG test measures the pH and partial pressure of oxygen and carbon dioxide, as well as the bicarbonate level, various electrolytes, oxyhemoglobin, carboxyhemoglobin and methemoglobin. These measurements will help the physician in diagnosing and treating various pulmonary disorders.
Oxygen Saturation of Venous Blood
Measuring the Sv02 provides valuable information regarding the body's ability to utilize the oxygen that the hemoglobin is carrying. According to Harvard Medical School, ischemia--or restricted blood supply--occurs if the Sv02 drops below 60 percent. The Sv02 is often monitored in the critical care setting as well as during extracorporeal circulation, or blood circulating outside of the body through procedures such as cardio-pulmonary bypass or dialysis.
Oxygenation
Oxygenation occurs through the process of respiration. According to the Cleveland Clinic, just as the body needs oxygen to function, too much oxygen can become toxic, leading to tissue, brain, and organ damage, as well as death. Hypoxia or hypoxemia is the lack of oxygen, which can also lead to complications such as shortness of breath, nausea, headache and fatigue. Severe hypoxemia can cause seizures, coma and even death.
Pulse Oximetry
Pulse oximetry provides a painless, non-invasive method of estimating the Sp02 by attaching a small device to the finger, earlobe or toe. A pulse oximeter emits an infrared light that measures the percentage of hemoglobin because blood cells saturated with oxygen will absorb and reflect light. Normal ranges for a healthy, non-smoking adult are between 95 and 100 percent.
Hemoglobin
Oxygen binds to the hemoglobin contained in the red blood cells through the process of respiration. Hemoglobin found outside of the red blood cells does not carry and transport oxygen. Before the hemoglobin can pick up fresh oxygen molecules, carbon dioxide, which also binds to the protein found on hemoglobin, must be dropped off in the lungs and exhaled. Several health conditions can occur when this process malfunctions.
