A new system to record reliable pulse oximetry data from the Nellcor N-200 and its applications in studies of variability in infant oxygenation.

We have developed a simple system for internal validation of oximetry data collected over many hours from the Nellcor N-200 pulse oximeter (Nellcor, Inc., Hayward, CA). This system uses signals from the oximeter alone and a validation algorithm that is based in a computer connected to the oximeter. Unlike other validation systems, this system does not require connections to other monitors. The system was tested on 10 acutely ill newborns in an intensive care nursery over 16 hr of continuous recording for each infant (birthweight, 2.50 +/- 0.73 kg; age, 3.4 +/- 3.2 days). Oximetry data were accepted as valid using the new system if they surpassed a minimum level of quality (empirically derived, and equal to a 60% fractional success in pulse detection). The validated oximetry data were compared to data obtained using a conventional "compared to the electrocardiogram (ECG)" algorithm. For the new and the conventional algorithms, the distributions of validated SpO2 percents were nearly identical, with data rejection rates of 28.9% for the new system and 37.3% for the conventional system. In the newborns, the new system was used to demonstrate that as the mean saturations decreased, there were striking increases in variability about the reported mean saturation (p < 0.001). While variability in infant SpO2 is a well-known phenomenon, the amount seen here was unexpected. For example, the range of true saturations frequently recorded was quite wide at a reported mean SpO2 of 90% (from 81 to 94%; but, the range was only from 92 to 98% at a mean SpO2 of 96%). These findings demonstrate the usefulness of the new system and, if substantiated in more detailed studies, have important implications for the use of pulse oximeters to assess oxygenation in newborns.