Pulse oximeter readings can become inaccurate in the presence of carbon monoxide, which falsely elevates oxygen saturation levels. Nitrogen and high blood pressure do not influence the device's accuracy. Therefore, the correct answer is carbon monoxide.
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A pulse oximeter can give inaccurate readings in the presence of carbon monoxide, which falsely elevates oxygen saturation levels. Nitrogen and high blood pressure do not affect the accuracy of the pulse oximeter readings. Thus, carbon monoxide is the correct choice among the options given. ;