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Pulse Oximeter
| Directory: Knowledge Base | Pulse Oximeter |
Limitations in Using a Pulse Oximeter
Under various conditions, a pulse oximeter would give inaccurate readings. Keep these factors in mind while taking measurements. Carbon MonoxideCarbon monoxide molecules, even in a small amount, can attach to the patient's hemoglobin replacing oxygen molecules. A pulse oximeter cannot distinguish the differences and the reading will show the total saturation level of oxygen and carbon monoxide. If 15% of hemoglobin has carbon monoxide and 80% has oxygen, the reading would be 95%.
This can be dangerous. A pulse oximeter should not be used on people with smoke inhalation, carbon monoxide poisoning, and heavy cigarette smoking. Hemoglobin Deficiency (Anemia)Low quantity of hemoglobin may affect the result. The normal values for a person is 11 - 18 g/dl. Blood Volume DeficiencyConditions, such as hypovolemia, hypotension, and hypothermia, may have adequate oxygen saturation, but low oxygen carrying capacity. Due to the reduction in blood flow, the sensor may not be able to pick up adequately the pulsatile waveform resulting in no signal or loss of accuracy. Irregular SignalsIrregular signals can post problems for a pulse oximeter. The problem signals can be caused by irregular heart beats or by patient's movements. External InterferenceExposure to strong external light while taking measurement may result in inaccurate readings. Shield the sensors from bright lights.
Strong electro-magnetic fields may also affect readings. Fingernail Polish and Pressed on NailsNail polish and pressed-on nails may interfere with readings. Remove them. Skin PigmentationDark skin pigmentation can give over-estimated SpO2 readings when it is below 80%. Find a place where the skin color is lighter. Intravenous DyesIntravenous dyes (such as methylene blue, indigo carmine, and indocyanine green) can cause inaccurate readings. MethaemoglobinMethaemoglobin is a form of haemoglobin that does not carry oxygen. It is normal to have 1-2% of haemoglobin in this form. A high level of methaemoglobin would cause a pulse oximter to have a reading of around 85% regardless of the actual oxygen saturation level.
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