January 2002 / Volume 47 / Number 1 / Page 48
The Effects of Motion Artifact and Low Perfusion on the Performance of a New Generation of Pulse Oximeters in Volunteers Undergoing Hypoxemia
INTRODUCTION: Motion artifact and low perfusion often lead to faulty or absent pulse oximetry readings in clinical practice. OBJECTIVE: Determine the impact of motion artifact and low perfusion on newly introduced pulse oximetry technologies during hypoxemic episodes in healthy volunteers. METHODS: Five different pulse oximeters from 4 manufacturers (the Datex Ohmeda 3900P; the Agilent; the Nellcor N-3000; the Nellcor N-395; and the Schiller OX-1, which is the European version of the Ivy SatGuard 2000 with Masimo SET) were compared with respect to their ability (separated or in combination) to provide accurate readings in the presence of motion artifact and low perfusion. Four of these oximeters represent the latest available oximetry technology, and one (the N-3000) represents a previous generation of oximeters. Oxygen saturation values (SpO2) and pulse rate from the oximeters were recorded during episodes of induced hypoxemia in 10 healthy volunteers. Standardized and repeatable motion artifacts were generated by a motion machine and by having the test subject perform tapping and scratching motions. Perfusion to the finger was reduced by an inflatable balloon impinging on the brachial artery. The pulse oximetry readings from the test oximeters were compared to readings from control pulse oximeters on the unperturbed reference hand. The pulse rates from the test oximeters were compared to the electrocardiographically-measured heart rate. RESULTS: The frequency of faulty readings was increased by increasing motion interference and decreasing perfusion. The SpO2 deviation was within ± 3% of the reference reading > 95% of the time for all instruments during the control desaturation period in the absence of motion and with normal perfusion. With the combination of motion and low perfusion, the SpO2 error was within ± 3% less than 62% of the time for all oximeters tested. A significant difference in the frequency of large SpO2 errors was observed only in the direct comparison of the N-395 and N-3000. The N-395 exhibited less frequent SpO2 error exceeding 6% of SpO2 in the combination of the most challenging situations (motion and motion with reduced perfusion). In the same situation the Datex-Ohmeda 3900P and Nellcor N-3000 showed significantly higher pulse rate errors than the other devices (Datex-Ohmeda 3900P 53% of the time and N-3000 37% of the time). CONCLUSIONS: The established model of creating motion artifact and low perfusion is capable of simulating a hierarchy of severe clinical situations. With solely motion or solely reduced perfusion the percentage of errors exceeding ± 3% of SpO2 increased by 20% and 10%, respectively, compared to the control period. Simultaneous presence of motion and reduced perfusion leads to a relative incidence of > 35% of errors > 3% of SpO2 for the various oximeters. In this situation the N-3000 and the Datex-Ohmeda 3900P exhibited differences between estimated pulse rate and electrocardiographically-measured heart rate > 25 beats/min > 37% of the time.
Key words: pulse oximetry, artifact simulation, motion, reduced perfusion, desaturation, monitoring.
[Respir Care 2002;47(1):48-60]
Pulse oximetry is part of routine basic monitoring in anesthesia, along with electrocardiographic (ECG) and blood pressure monitoring. Pulse oximetry is commonly employed in nearly all areas where patients are at risk of hypoxemia.
In clinical practice, pulse oximetry has to cope with many factors that influence SpO2 accuracy. In a randomized study of pulse oximetry performance, the pulse oximetry failure rate (temporarily and completely abandoned pulse oximetry monitoring) was 2.5% of all monitored patients, and it increased to 7.2% in patients with American Society of Anesthesiology status 4. The main reasons (59%) for temporary and complete pulse oximetry failure in that study were restricted peripheral perfusion and movement artifacts due to patient restlessness. Minor reasons (41%) for pulse oximetry failure were technical or practical problems (not further defined) and unknown.
In a retrospective study by Reich et al, the incidence of intraoperative loss of pulse oximetry readings for > 10 minutes was 9.2%. Predictors of pulse oximetry failure included American Society of Anesthesiology status 3, 4, and 5 patients undergoing vascular or cardiac surgery, and restricted finger perfusion caused by hypothermia or hypotension.
The conditions that are most challenging for pulse oximeters are patient motion and low perfusion, which can be present in critical situations such as surgery, during patient transport, in emergency departments, and in neonatal intensive care units. We believe that a clinically relevant performance test of pulse oximeters should include a standardized simulation of motion and restricted perfusion during changes in arterial oxygen saturation. So under those conditions we tested instruments from the most recently introduced generation of pulse oximeters from 4 manufacturers. Our goal was to address the question, "Do the new oximeters improve the accuracy of tracking SpO2 and pulse rate during induced patient hypoxemia in the presence of motion artifact and low perfusion?"
The new-generation instruments we tested were: the 3900P, software version 2.000/04.000 (Datex Ohmeda, Helsinki, Finland); the Agilent with CMS monitor software Rev B.0 (Philips Medical Systems, Böblingen, Germany); Nellcor N-395 with OxiSmart XL (software version 184.108.40.206) (Tyco Healthcare Group, Pleasanton, California); the Ivy SatGuard 2000 with Masimo Signal Extraction Technology (SET) (Model 2000, Ivy 2356-00-04 REV 01 DSP 220.127.116.11, MS1:HW REV: A ID:2 SMC: 18.104.22.168, sold by the Swiss company Schiller as model OX-1) (Ivy Biomedical Systems, Branford, Connecticut; Masimo, Irvine, California). The Nellcor N-3000 (software version 3.03 001) was also tested as a representative of the previous generation of oximeters.