Interpretation of readings

It is important to recognize that the pulse oximeter only identifies the ercentage of the hemoglobin that is bound to oxygen and not the total amount of oxygen that is being delivered. In other words, if a patient had an oxygen saturation of 100 per cent but was anemic, he or she could still be receiving only half the oxygen that the tissues need. The same situation could occur if the saturation were 100 per cent but the cardiac output was low. Thus with normal levels of dyshemoglobins and adequate signal strength (adequate perfusion at the probe site), we only know for sure that the hemoglobin is being properly loaded with oxygen and therefore that the lungs must also be reasonably well perfused and exchanging gas properly.

On the otherwise healthy patient, arterial oxygen saturation should typically be about 96 per cent and quite stable. If the oximeter is reading less than the normal oxygen saturation levels, the source of the low readings should be investigated (e.g. ventilation-perfusion mismatch or inadequate fraction of inspired oxygen, possibly because of faulty or incorrectly set-up gas mixers; various hemoglobinopathies, such as sickle cell hemoglobin, can reduce the ability of hemoglobin to bind with the available oxygen).

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