Pulse Ox Limitations

Purchasing a pulse oximeter can be done in a snap. However, there are limitations and usages to safeguard accurate measurements. Through understanding its limitations and usages, one can fully decipher its accuracy and reliability.

A pulse oximeter works by shining two lights though a translucent portion of the patient's body and measuring the variation in light absorption caused by the changes in blood flow. The result of arteriolar bed pulsations is caused by that total light absorbance.

The oximeter assumes that arterial blood is the only pulsatile absorber and other sources of fluctuations could contribute to wrong readings. Moreover, if the transparency and blood flow at the spot where the measurement is taken can affect the accuracy of a reading. For example, if the area is largely opaque or the blood flow is low or irregular, achieving accurate readings would be difficult. Understanding this is important to interpret a pulse oxymetry reading.

Extreme and low atmospheric pressures can also affect an oximeter reading. A low atmospheric pressure in high altitude has slight effect on an oximeter, while extreme low temperature and poor blood circulation would.

You should keep different factors in mind while taking pulse oximeter measurements. Carbon monoxide molecules can attach to the patient's hemoglobin replacing oxygen molecules. An oximeter cannot distinguish the differences; this will show a total saturation level of oxygen and carbon monoxide. For example, if 15% of hemoglobin has carbon monoxide and 80% has oxygen, the reading would be 95%. If that would be the case, then it is really dangerous. An oximeter should never use on people with smoke inhalation, heavy cigarette smoking, and carbon monoxide poisoning.

Moreover, having a low quantity of hemoglobin may also affect the oximeter result. The normal values for a person range from 11 - 18 g/dl. Conditions such as hypovolemia, hypotension, and hypothermia, may have satisfactory oxygen saturation, but low oxygen carrying capacity. The sensor may not be able to pick up adequately the pulsatile wav form resulting in no signal or loss of accuracy due to the reduction in blood flow. It is therefore challenging to take an oximeter measurement on sick patients with cold hands.

On the other hand, irregular signals can post problems for a fingertip pulse oximeter. This can be caused by irregular heartbeats of even by patient’s movements. If this is the case, then you can tell by looking at the waveform, which is available on some oximeter.