THE EFFECT OF SENSOR MALPOSITIONING ON PULSE OXIMETER ACCURACY DURINGHYPOXEMIA

Background: Previous studies have shown that pulse oximeters whose sen sors are positioned improperly may yield erroneously low saturation (S p(O2)) values on normoxemic subjects. The behavior of oximeters with m alpositioned sensors during hypoxemia has not been studied. The curren t study is aimed at determining the behavior of several different puls e oximeters over a wide range of arterial oxygen saturation (Sa(O2)). Methods: In each of 12 healthy volunteers, a radial artery cannula was inserted, and eight different pulse oximeters, five of which had malp ositioned sensors, were applied. Subjects breathed controlled mixtures of nitrogen and oxygen to slowly vary their Sa(O2) from 100% to 70%. Arterial blood samples were analyzed and pulse oximeter data were reco rded at five stable Sa(O2) values for each subject. Results. The oxime ters with malpositioned sensors vary greatly in their behavior, depend ing on both the actual Sa(O2) and the manufacturer and model. One oxim eter underestimated saturation at all Sa(O2) values, while three other s underestimated at high Sa(O2) and overestimated at low Sa(O2). Linea r regression analysis shows a decrease in the slope of Sp(O2) versus S a(O2) in most cases, indicating a loss of sensitivity to Sa(O2) change s. Between-subject variation in response curves was significant. Concl usions. The calibration curves of the pulse oximeters studied were cha nged greatly by sensor malpositioning. At low Sa(O2) values, these cha nges could cause the oximeter to indicate that a patient was only mild ly hypoxemic when, in fact, hypoxemia was profound. It is recommended that sensor position be checked frequently and that inaccessible senso r locations be avoided whenever possible.