The following factors may cause inaccurate measurements during a SpO2 reading: Patient is in cardiac arrest or shock Excessive patient movement Bright light Sensor is too tight Moisture in the sensor Placement of a sensor on an extremity with a blood pressure cuff, arterial catheter, or intravascular line Incorrect sensor application or use Poor patient perfusion Arterial occlusion proximal to the sensor Venous pulsations Intravascular dyes such as indocyanine green or methylene blue Significant levels of dysfunctional hemoglobins (e.g., carboxyhemoglobin or methemoglobin) Fingernail polish (if finger sensor is used) Patient has hypotension, severe vasoconstriction, severe anemia, or hypothermia Exposure to excessive illumination, such as surgical lamps (especially ones with a xenon light source), bilirubin lamps, fluorescent lights, infrared heating lamps, or direct sunlight. Exposure to excessive illumination can be corrected by covering the sensor with a dark or opaque material.