Motion resistant pulse oximetry in neonates.

Background: Pulse oximetry is widely used in neonates. However, its reliability is often affected by motion artefact. Clinicians confronted with questionable oxygen saturation (Sp[O.sub.2]) values often estimate the reliability by correlating heart rate (HR) obtained with the oximeter with that obtained by electrocardiogram.

Objective: To compare the effects of motion on Sp[O.sub.2] and HR measurements made with Masimo signal extraction technology and those made with a Nellcor N-200.

Design: Continuous pulse oximetry and HR monitoring were performed in 15 healthy, term infants (mean (SD) birth weight 3408 (458) g) undergoing circumcision, using Masimo and Nellcor pulse oximeters and a standard HR monitor (Hewlett-Packard). Simultaneous minute by minute behavioural activity codes were also assigned. Baseline data were collected for 10 minutes when the infant was quietly asleep and then continued during and after circumcision for a total duration of one hour. The oximeter HR and Sp[O.sub.2] values were compared and related to HR values obtained by ECG during all three periods. The effect of behavioural activity on Sp[O.sub.2] and HR was also evaluated.

Results: When compared with results obtained with the Nellcor, the mean Sp[O.sub.2] and HR were higher and the incidence of artefact lower with the Masimo during all three periods. Masimo HR more accurately predicted HR obtained with a standard monitor, with lower residual error. Sp[O.sub.2] and HR values obtained with the Nellcor were lower and more variable during all behavioural states, especially crying, when excessive motion artefact was most likely.

Conclusions: The data suggest that Masimo signal extraction technology may offer improvement in pulse oximetry performance, particularly in clinical situations in which extreme motion artefacts are likely.

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Pulse oximetry is now the standard non-invasive method of measuring blood oxygenation in neonates. Pulse oxygen saturation (Sp[O.sub.2]) is measured so commonly that it is now generally accepted as the fifth vital sign. (1) Although trials have shown that Sp[O.sub.2] measurements obtained by conventional pulse oximetry correlate very closely with blood oxygen saturation (2) and quite accurately predict Pa[o.sub.2], (3) they may be affected by subject motion. (4)

Motion artefact limits accurate assessment of oxygenation and may lead to inappropriate responses by clinicians, including both overtreatment and undertreatment. (5-8) Various strategies have evolved to adjust measurements for presumed motion artefact, such as freezing the display on values thought to be correct or reporting zero. (9-11) These methods produce misleading information. Faced with suspicious measurement, clinicians usually wait for the motion to stop and then compare the heart rate (HR) value obtained with the oximeter with that obtained by electrocardiogram (ECG). If the two agree, the assumption is that the data are reliable. These periods of absent or inaccurate Sp[O.sub.2] values resulting from motion artefact are not insignificant. Recent reports have shown that movement affects up to 50% of the recorded tracings in preterm and term infants. (12)

Reduction in the number of false alarms and provision of reliable oximeter readings, even in the presence of patient motion, are two major goals for pulse oximetry in intensive care. Conventional pulse oximetry, based on the ratio of the absorbancy patterns of red and infrared light, is unable to correct the interference caused by patient motion and low perfusion. The Masimo Corporation (Irvine, California, USA) has developed a new electronic signal processing technique and sensor design, called signal extraction technology, which is said to improve the …