SO2 pulse oximeter is a non-invasive way to measure a patient's blood oxygen saturation and heavily relies on the perfusion of blood vessel tissue. Therefore, its probe is usually placed at high-density blood vessel areas such as fingers, earlobes, or forehead. If peripheral perfusion is reduced, the measurement will be affected, resulting in inaccurate blood oxygen readings. Among these locations, the fingertip-style oximeter probe relies on perfusion from the radial artery to the finger artery, while the forehead relies on measurement of SpO2 from the supraorbital artery. Compared to the fingertip vascular system, the forehead vascular system has limited vasoconstriction ability. Therefore, in situations such as heart failure with high sympathetic output and low peripheral perfusion, placing the oximeter probe on the forehead may be more accurate than on the fingertip.
The forehead is the best position for measuring blood oxygen saturation with a pulse oximeter
A study on patients with low resting heart rate showed that a forehead-based oximeter is more accurate in determining blood oxygen saturation than a digital oximeter. Similarly, studies on surgical and trauma patients at risk of poor peripheral blood flow have shown that forehead oximeter probes are more accurate in measuring oxygen saturation. Although it has been shown that finger pulse oximeters are accurate under low perfusion, patients during transportation are affected by motion and ambient temperature, and measurement errors and failures using forehead oximeter probes when compared to finger placement are less common.
The same results have also been observed in clinical research experiments. Patients during and after surgery often experience mild hypothermia and vasoconstriction. The best tissue for measuring blood oxygen saturation used by researchers is the one with the least vascular activity, and the blood flowing to the forehead passes through the supraorbital artery, which is not easily affected by vasoconstriction caused by poor perfusion. In a hospital-based complementary study, the researchers examined the performance of the sensors on the patient's forehead, earlobe, and finger, which were initially in a normal state of temperature and vasoconstriction and then deliberately placed in a state of low temperature and vasodilation. In both states, the forehead was found to have "less vascular activity," so the researchers believed that the forehead may be the best position for measuring pulse oximeters.
The importance of correctly placing the oximeter saturimetro sensor
Although researchers found that the forehead may be the most accurate under low perfusion, they did not observe this in earlier experiments. They found that the reason may be that a headband used to secure the forehead sensor was not used in earlier studies, but was used in recent studies. They concluded that correctly placing the oximeter saturimetro sensor and using a headband are important considerations for the success of the forehead sensor. Proper placement means placing the sensor above the eyebrow, just outside the center of the iris. Considering its cost-effectiveness, researchers emphasized that forehead sensors are not ideal for general use but should be used more under low perfusion.
Therefore, the fingertip is still the best position for measuring blood oxygen saturation using oximeter probes in most situations, while under low saturation, to ensure accuracy, we can use a forehead oximeter probe.