For the purpose of assessing the utility and cautionary aspects of pulse oximetry of which use is rapidly increased, it was applied to the maladaptive child patients with sedative drugs and evaluated the results. When pulse oximeter was used alone for vital sign monitoring, it was thought impossible to exclude the false alarm or false silence by various causes. To minimize or remove these misunderstanding, operators should have a extensive knowledge not only on the factors affecting the operation of this apparatus but also on the potential of misoperation. To review the present status of increasing risk of hypoxia during the sedation, it was thought unreasonable to solely depend upon this apparatus for vital sign monitoring. By combining with more accurate and auxiliary monitoring devices, pulse oximetry will be of greater value and can meet the clinical needs and conveniences.