What causes pulse oximeter readings to be inaccurate?
The most common problem is the oximeter probe not consistently registering the pulsatile arterial flow through the skin. This is often caused by movement, poor perfusion of the skin, or bright ambient light. Careful attention to the graphical display of pulsatile flow on the pulse oximeter can almost always distinguish a falsely low saturation due to poor signal capture from true hypoxemia. Occasionally, hemoglobin is abnormal. Carboxyhemoglobinemia will cause a falsely elevated measurement of oxygen saturation by pulse oximetry; methemoglobinemia in significant concentrations will cause a modest lowering.
Lee WW, Mayberry K, Crapo R, et al: The accuracy of pulse oximetry in the emergency department. Am J Emerg Med 2000;18:427.