Keep these factors in mind while taking measurements. Carbon 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.
This can be dangerous. A pulse oximeter should not be used on people with smoke inhalation, carbon monoxide poisoning, and heavy cigarette smoking. Low quantity of hemoglobin may affect the result. Conditions, 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. Taking measurement on sick patients with cold hands can be challenging. Irregular signals can post problems for a pulse oximeter. The most important number, oxygen saturation level, is usually abbreviated SpO 2 , and is presented as a percentage. The pulse rate similar to heart rate is abbreviated PR, and sometimes there is a third number for strength of the signal.
Oxygen saturation levels are also generally slightly lower for those living at higher altitudes. Pulse oximeters have limitations and a risk of inaccuracy under certain circumstances. In many cases, the level of inaccuracy may be small and not clinically meaningful; however, there is a risk that an inaccurate measurement may result in unrecognized low oxygen saturation levels.
Therefore, it is important to understand the limitations of pulse oximetry and how accuracy is calculated and interpreted. FDA-cleared prescription pulse oximeters are required to have a minimum average mean accuracy that is demonstrated by desaturation studies done on healthy patients. However, real-world accuracy may differ from accuracy in the lab setting.
While reported accuracy is an average of all patients in the test sample, there are individual variations among patients. The SpO 2 reading should always be considered an estimate of oxygen saturation. Due to accuracy limitations at the individual level, SpO 2 provides more utility for trends over time instead of absolute thresholds. Many patient factors may also affect the accuracy of the measurement. In the recently published correspondence by Sjoding, et.
It is important to note that this retrospective study had some limitations. It relied on previously collected health record data from hospital inpatient stays and could not statistically correct for all potentially important confounding factors.
However, the FDA agrees that these findings highlight a need to further evaluate and understand the association between skin pigmentation and oximeter accuracy. All premarket submissions for prescription use oximeters are reviewed by the FDA to ensure that clinical study samples are demographically representative of the U. Although these clinical studies are not statistically powered to detect differences in accuracy between demographic groups, the FDA has continued to review the effects of skin pigmentation on the accuracy of these devices, including data from controlled laboratory studies and data from real world settings.
The FDA is committed to the continued evaluation of the safety, effectiveness, and availability of medical devices, especially devices in high demand during the COVID pandemic. To obtain FDA labeling for "medical use," the manufacturers must submit their devices to rigorous testing on human volunteers. Accurate pulse oximeters utilize correction factors based on the in vivo comparison of arterial hemoglobin oxygen saturation obtained from direct measurement of arterial blood gases with what the pulse oximeter obtains over a wide range of oxygen saturations.
These correction factors help account for causes of known variability, including anemia, light scattering, venous and tissue pulsation by mechanical force from nearby arteries, pulsatile variations in tissue thickness in the light path other than in the arteries, nail polish, and skin pigmentation. Because they lack validation by such rigorous testing, the relatively inexpensive pulse oximeters sold in drugstores or over the internet are specifically labeled not for medical use NMU.
Although I can't find any NMU statement on the box or the manufacturer's website , the Zacurate-brand NMU pulse oximeter I purchased says in slightly bold letters near the front of the instruction manual:. It is intended for non-medical use by healthy people to monitor their pulse rate and blood oxygen levels.
People who need SpO2 and pulse rate measurements because of a medical condition should consult with their physician. Exactly how one would use the pulse oximeter in sports is not clear to me: The devices become extremely inaccurate with any motion of the fingers.
When I wore my NMU pulse oximeter with even slow walking, it told me my oxygen saturation had dropped into the 80s. This study has been widely reported as demonstrating that NMU pulse oximeters are inaccurate and unreliable. A sister product to one of those accurately-performing NMU pulse oximeters, Contec's CMS50D, was selected in a study in the South African Medical Journal and compared to a much more expensive gold-standard, bedside pulse oximeter.
The reference medical-grade monitor cost times that of the CMS50D. Again, once the oxygen levels dropped, however, the NMU pulse oximeter values differed from the reference, with the researchers writing that "accuracy deteriorated with progressive hypoxaemia.
0コメント