An oxygen meter, or an oxygen monitor, is used to measure this oxygen saturation and an oxygen saturation monitor is also available for home use. This is a device intended for the non-invasive measurement of arterial blood oxygen saturation and pulse rate. Typically it uses two LEDs generating red and infrared lights through a translucent part of the body. Bone, tissue, pigmentation, and venous vessels normally absorb a constant amount of light over time. Oxygenated blood and deoxygenated blood have significantly different absorption patterns. Pulse oximetry does not provide information on the oxygen content of the blood nor ventilation and thus care is needed in the presence of anaemia and in patients developing respiratory failure due to carbon dioxide retention, for example.
The role of an oxygen saturation monitor
- Diagnosing and managing a severe exacerbation of chronic obstructive pulmonary disease (COPD) in the community.
- Grading the severity of an asthma attack. Where oxygen saturations are less than 92% in air, consider the attack potentially life-threatening.
- Assessing severity and oxygen requirements for patients with community-acquired pneumonia.
- Assessing severity and determining management in infants with bronchiolitis.
- Resting readings should be taken for at least 5 minutes.
- Poor perfusion (due to cold or hypotension) is the main cause of an inadequate pulse wave..
- If a finger probe is used, the hand should be rested on the chest at the level of the heart rather than the affixed digit held in the air in order to minimise motion artefact.
- Checking that the displayed heart rate correlates to a manually checked heart rate generally rules out significant motion artefact.
- Emitters and detectors must oppose one another and light should not reach the detector except through the tissue. Ensure the digit is inserted fully into the probe and that flexible probes are attached correctly. Appropriately sized probes should be used for children and infants.