Measuring Oxygen Saturation
Kathy Lawrence, MSN, RNBC
Clinical Educator II
Educational Resource Center
Sue Simpson Johnson, BS, RRT
Manager, Pulmonary Care Services
Basically, a saturation of 97% of the total amount of hemoglobin in the body is filled with oxygen molecules. A range of 96% to 100% is generally considered normal. Anything below 90% could quickly lead to life-threatening complications. The margin between "healthy" saturation levels (95-98%) and respiratory failure (usually 85-90%) is narrow. If oxyhemoglobin is low (below 90%) inadequate amounts of oxygen will reach body cells!
Note: UTMB Pulmonary Care Services Oxygen Protocol requires titrating oxygen to maintain an SPO2 of 94% for most patients, and 92% for those who are CO2 retainers.
Pulse oximeters are used to monitor patients who have actual or potential respiratory problems. Although 100% saturation is not normal when breathing air, it can be achieved when supplementary oxygen is given. Oxygen, like any drug, can have toxic effects. So if oximetry consistently shows 100% saturation, patients may be receiving unnecessarily high levels of oxygen. However, 100% saturation may compensate for other problems of oxygen carriage, for example anemia, and you should consult medical staff to establish whether any change in oxygen therapy is appropriate.
As a rule of thumb, respiratory failure usually occurs when saturation (SpO2) falls to 90%, although some patients with chronic respiratory disease may tolerate lower saturations. Nurses should consider the patient's normal respiratory function and clarify the point at which medical staff needs to be informed of any changes. Alarm limits should be set at a level that identifies any significant change in saturation. Setting lower alarm limits of 90% may be appropriate when saturation is 95%, but inappropriate if saturation is fluctuating at 90-91%. If setting alarm limits below 90%, nurses should be cautious about the very narrow margin remaining before respiratory failure. Setting a lower alarm limit of 85% or less should always be avoided! Oxygen delivery to tissues, including vital organs, is likely to be inadequate at this level, and such low saturations usually require urgent medical intervention (intubation and artificial ventilation).
Oximetry may be used for 'spot checks' or a continuous measurement. Measurements should always be considered in the context of the whole person. A 'spot check' or single measurement of hemoglobin saturation might suggest respiratory problems. Example: a patient with no history of chronic respiratory disease who has a saturation of 90% may have an acute problem, such as a chest infection. But the value of isolated measurements is limited and trends are more important than absolute figures. Changes in saturation identify deterioration or improvement, caused either by changes in pathology, response to treatment, or both.
Note: UTMB Pulmonary Care Services Pulse Oximetry Protocol states that continuous pulse oximetry is recommended for patients who are requiring FIO2 of 40% or greater.
Monitor Your Pulse Rate and Blood Oxygen Saturation with our finger pulse oximeters and handheld pulse oximeters which features/benefits include:
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