Pulse oximeters are a type of oxygen monitor that measure the amount of oxygen in a person’s blood. Although they are accurate, like all technology, they do have limitations which can prevent them from obtaining an accurate reading. If the user is aware of the limitations, a more accurate and reliable reading can be obtained.
1. The first and easiest limitation to fix is poor positioning of the oximeter. To obtain a quality reading both sides of the sensor should have contact with the skin.
2. Nail polish, especially red polish can cause false low readings. To prevent finger nail polish from interfering, the user can twist the oximeter so the sensors are side to side on the finger instead of top to bottom. The position will allow the light to pass through the finger without making contact with the polish.
3. Any issues which may cause poor tissue perfusion such as hypovoliemia, hypotension, cold extremities, hypothermia, or cardiac arrest. Oximeters cannot function without pulsing circulation. If the tissue is cold, you can attempt to warm the extremity. Hypotensive and hypovoliemic causes must be corrected with improving circulation and blood volume.
4. Some Cardiac valvular defects can cause venous pulsation resulting in a finger pulse oximeter reading venous blood and recording low SpO2 levels. Tricuspid regurgitation is one defect. Unfortunately, there is no fix for such defects in terms of obtaining an accurate reading.
5. Finger pulse oximeters accuracy decreases as the value decreases. Readings below 70 percent are not reliable. Most oximeters are fairly accurate down to around 75 percent. Anything lower should not be considered accurate, especially if the individual is not showing any obvious signs of respiratory distress.
6. Cardiac arrhythmias that alter arterial pulsation can disrupt the finger pulse oximeter from recording an accurate reading. Heart rhythms such as atrial fibrillation and frequent PVC’s can alter the steady pulsitile rhythm oximeters use to determine arterial circulation. The result can be frequent variations in the oximeters readings. If the individuals pulse is irregular or frequent changes are noted on the oximeter, this could be the cause.
7. Carbon monoxide poisoning causing carboxyhaemoglobin cannot be distinguished from oxygen resulting in finger pulse oximeters giving false readings of 100%. Finger pulse oximeters should not be utilized when carbon monoxide poisoning is suspected
8. Abnormal haemoglobins such as methaemoglobinaemia, for example following overdose of prilocaine, cause readings to tend towards 85%. Resolution of the cause is the only fix for this.
9. Skin pigmentation can cause inaccurate readings. Like the red nail polish, darker skin can alter the way an oximeter absorbs and interprets light. Finding a lighter area of skin can frequently improve the accuracy of the readings.
10. Operator error. Like all electronic devices, users must know how to operate the equipment and have a good knowledge of how to interpret the results. Oximetry is just an assessment tool used to augment other clinical assessment findings. Just because an individual can read a number, does not mean they understand the meaning of the number. Medical professionals are trained to understand, which is why if you have concerns you should seek their professional wisdom.
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