From the Guidelines
Pulse oximetry may not accurately reflect oxygenation in several clinical scenarios, including carbon monoxide poisoning, severe anemia, poor peripheral perfusion states, and certain environmental factors, as highlighted in the 2024 American Heart Association and American Red Cross guidelines for first aid 1.
Clinical Scenarios
Some of the key scenarios where pulse oximetry may be inaccurate include:
- Carbon monoxide poisoning, where carboxyhemoglobin is falsely read as oxyhemoglobin, resulting in normal-appearing oxygen saturation despite potentially severe tissue hypoxia 1
- Severe anemia, where pulse oximeters measure the percentage of hemoglobin that is saturated but not the absolute amount of oxygen in blood
- Poor peripheral perfusion states like shock, hypothermia, or vasoconstriction, which can prevent adequate signal detection
- Certain dyes (methylene blue, indigo carmine) and nail polish (particularly blue, black, or green), which can interfere with light absorption measurements
Limitations of Pulse Oximetry
Pulse oximetry has several limitations, including:
- Inaccuracy in patients with high levels of skin pigmentation, particularly those with darker skin tones, which can result in overestimation of oxygen saturation 1
- Environmental factors, such as motion artifact from shivering or seizures, which can disrupt readings
- Hyperbilirubinemia, which may cause falsely low readings, while methemoglobinemia typically causes readings to converge around 85% regardless of actual oxygenation
Reliable Oxygenation Assessment
In these situations, arterial blood gas analysis provides a more reliable oxygenation assessment, as it measures the actual amount of oxygen in the blood, rather than just the percentage of hemoglobin that is saturated 1.
From the Research
Examples of Inaccurate Pulse Oximetry Readings
- Sickle cell disease: Pulse oximetry may overestimate oxygen saturation in patients with sickle cell disease due to the presence of dyshemoglobin (methemoglobin and carboxyhemoglobin) 2.
- Chronic thromboembolic pulmonary hypertension: Pulse oximetry may not accurately detect hypoxemia in patients with chronic thromboembolic pulmonary hypertension, with different pulse oximeters having varying degrees of accuracy 3.
- Hypoxemic conditions: In hypoxemic conditions, pulse oximetry may not accurately reflect oxygen saturation, particularly in patients with sickle cell disease 4.
- Presence of carboxyhemoglobin and methemoglobin: The presence of these dyshemoglobins can affect the accuracy of pulse oximetry readings, although non-invasive pulse co-oximetry can provide relatively accurate measurements of carboxyhemoglobin and methemoglobin levels 5.
- Critically ill patients and newborns: Pulse oximetry may not be accurate in these populations, particularly when supplemental oxygen is being administered, due to the empirical calibration process and other limitations of the technology 6.
Factors Affecting Pulse Oximetry Accuracy
- Dyshemoglobins (methemoglobin and carboxyhemoglobin): These can affect the accuracy of pulse oximetry readings 2, 5.
- Low perfusion and motion artifacts: These can be partially rectified by sophisticated algorithms and reflection pulse oximetry 6.
- Empirical calibration process: This can lead to inaccuracies in certain populations, such as critically ill patients and newborns 6.