Limitations of Pulse Oximeters

Oxygen is vital for human survival. Because of this, health professionals need ways to ensure their patients have sufficient amounts of oxygen in their bodies. A pulse oximeter is one way to do this. A pulse oximeter is a device that measures oxygen saturation, or the oxygen-carrying capacity by the red blood cells that attach to hemoglobin molecules. However, a pulse oximeter isn't fool proof; it does have limitations that can prevent accuracy.

Poor Perfusion

• Pulse oximeters don't detect if enough blood is getting to the tissues. Poor perfusion occurs in conditions such as hypovolemia (low blood volume), hypotension (low blood pressure) and hypothermia (low body temperature). However, despite low perfusion in these conditions, there still may be an adequate oxygen saturation level, but with low oxygen-carrying capacity. The reduction in blood flow causes the arterial pulsations to become less detectable, thus causing no signal in the pulse oximeter, or an inaccurate reading.

Skin Color

• Pulse oximeters give overestimated readings at saturations below 80 percent when done on patients with dark skin color. However, according to dentists George Mardirossian and Ronald Schneider, "skin color is not a limiting factor in pulse oximetry" because the oximeter is meant to cover a wide array of skin pigmentation. To err on the side of caution, though, health care professionals should typically place the oximeter in areas, like a finger or earlobe, that contain less pigmentation.

Shivering or Shaking

• Pulse oximeters rely on the pulsations from the arterial blood flow to provide accurate readings. If a patient is cold and subsequently shaking or shivering, it affects the pulse oximeter's results by influencing the pulse rate display and saturation readings. The health care professional can place warm blankets over the patient, or the patient can be warmed by covering up with the sheets on the hospital bed.

Nail Polish

• A pulse oximeter senses light wavelengths and anything that interferes with the detection of this light results in inaccurate readings. This includes both nail polish and fake nails. Health care professionals can attach the oximeter to an earlobe or have the patient remove the nail polish.

Anemia

• Anemia is a type of hemoglobin deficiency where there aren't enough red blood cells to carry the proper amount of oxygenated-hemoglobin to the tissues. Normal hemoglobin values range from 11 to 18 g/dl. A patient having a low quantity of hemoglobin also affects pulse oximeter readings.