[Pulse oximetry in the air rescue service. 1: Quantitative detection of interfering factors on the method]

The introduction of pulse oximetric monitoring in prehospital emergency medicine considerably contributed to emergency patients' safety, stability and protection. As inherent in any method of measurement, certain factors can interfere with it and limit its practical application. The emergency helicopter service at Ulm, in a prospective study involving 400 patients, systematically collected data on these limiting factors and evaluated them. The index "S" was established to quantify the time lost due to malfunctioning. Within the study group, the index average was S = 0.269, that is 26.9% of measurement time was subject to interference. The major cause was motion artifacts (68%) sensor probe dislocation (15%), low perfusion (14%) and radiation (3%). Regarding the volume of time lost due to specific interfering factors, motion artifacts (61.8%) and low perfusion (25.5%) were dominant, followed by sensor probe dislocation (10.3%) and radiation (2.4%). Interference therefore, both in time and frequency was primarily due to motion artifacts and low perfusion. The conclusions from this study led to the evaluation of two methods by which the interfering factors could be reduced: 1. ECG-synchronisation of the pulse oximetric signal; 2. The use of adhesive sensors.--The degree of increase in pulse oximetric measurement stability achieved by these two methods will be investigated in part 2 of this study.