A pulse oximeter is a small, non-invasive device, often resembling a clip, that is placed on a person’s fingertip. Its purpose is to estimate the oxygen saturation level in the blood, a measurement known as SpO2. This technology is used in medical environments like hospitals and clinics, and has also become common for individuals to use at home to monitor their oxygen levels.
How Pulse Oximeters Measure Oxygen
The technology behind pulse oximetry relies on the transmission of light through the body. A pulse oximeter works by emitting two distinct wavelengths of light, red and infrared, from one side of the device. These light beams pass through the fingertip, where a sensor on the opposite side measures how much light gets through. This measurement is based on how hemoglobin, the oxygen-carrying protein in red blood cells, interacts with these specific types of light.
Oxygenated hemoglobin and deoxygenated hemoglobin absorb red and infrared light differently. Specifically, hemoglobin rich in oxygen absorbs more infrared light while allowing more red light to pass through. In contrast, hemoglobin without oxygen absorbs more red light and lets more infrared light through. The device calculates the ratio between the absorption of red and infrared light to estimate the percentage of oxygen saturation in the blood.
The Impact of Skin Pigmentation on Accuracy
The accuracy of pulse oximeters can be influenced by the amount of melanin in the skin. Melanin, the pigment responsible for skin color, absorbs light. In individuals with darker skin tones, the higher concentration of melanin can interfere with the light beams from the oximeter, scattering or absorbing some light before it reaches the blood vessels. This interference can disrupt the device’s ability to accurately calculate the ratio of oxygenated to deoxygenated hemoglobin.
This interference often leads to an error where the pulse oximeter overestimates the amount of oxygen in the blood. Research has demonstrated that these devices can display a normal oxygen saturation level, while the true level in the person’s arterial blood is much lower. This discrepancy is clinically referred to as occult hypoxemia, meaning a hidden state of low oxygen.
The Food and Drug Administration (FDA) has issued safety communications acknowledging that pulse oximeters may be less accurate in people with darker skin pigmentation. Numerous studies have confirmed these findings, highlighting a public health concern. The data show that Black patients are more likely than white patients to experience occult hypoxemia that is not detected by pulse oximetry.
Health Implications of Inaccurate Readings
Missed diagnoses of hypoxemia due to inaccurate pulse oximeter readings carry substantial health risks. When a patient’s low oxygen levels go undetected, they may not receive necessary medical interventions in a timely manner. This can lead to delays in treatment and result in poorer health outcomes.
For instance, a patient with a severe respiratory illness like COVID-19 or pneumonia might be sent home from an emergency department based on a falsely reassuring oximeter reading. This could lead to a worsening of their condition at home. Similarly, individuals with chronic conditions such as chronic obstructive pulmonary disease (COPD) or heart failure rely on accurate oxygen monitoring. An overestimated reading could prevent them from receiving the supplemental oxygen they need.
The failure to detect low oxygen levels can delay treatments and interventions. In a hospital setting, an inaccurate reading can lead clinicians to withhold oxygen therapy or other life-saving treatments. This directly impacts patient safety and increases the risk of adverse events.
Patient Guidance and Future Directions
Given the potential for inaccurate readings, do not depend solely on the number displayed by a pulse oximeter. Individuals monitoring their oxygen levels at home should also pay close attention to physical symptoms that can indicate low oxygen. These signs include:
- Difficulty breathing or shortness of breath
- A rapid heart rate
- Confusion or lightheadedness
- A bluish discoloration of the lips, face, or nail beds
If any of these symptoms are present, it is important to seek medical attention, regardless of what the oximeter shows.
Patients should feel empowered to discuss any concerns about their pulse oximeter readings with their healthcare providers. Informing a doctor about your concerns, especially if you have a darker skin tone, can provide important context for your medical care. This communication can help ensure that clinical decisions are not based on flawed data from a single device.
The medical and scientific communities are actively working to resolve this issue. There is a growing demand for medical device manufacturers to test their products on a more diverse range of skin tones to ensure accuracy. Regulatory bodies are also re-evaluating the standards for these devices, with the goal of developing new technologies that are not affected by skin pigmentation. These efforts aim to ensure everyone can rely on these medical tools for accurate information.