This suggests that during motion the N-200 has a greater tendency to yield erroneous SpO 2values, whereas the N-3000 is more likely to fail and provide no values. On the other hand, the N-200 demonstrated the greatest SpO 2errors of any instrument (E7 = 29%), also during condition B. In fact, the N-3000 exhibited the highest dropout rate of any instrument (DR = 46%) for condition B, motion beginning before oximeter connection.
Although the N-3000 performed better than the N-200 for condition A (PI = 87% compared with 76%), this relationship was reversed for conditions B and C. The N-3000 and N-200 also differed significantly from one another in their motion performance. The lowest performance index for the Masimo was 95%, compared with 46% for the N-3000 and 68% for the N-200. The most obvious is that the Masimo SET exhibited much lower error rates and dropout rates than did the other two oximeters for all three test conditions. The performance of the three instruments during motion differed in several ways. The other two instruments did not track control SPO 2in this case. The Masimo SET tracked the control SpO 2well during the desaturation but exhibited some lag during the rapid resaturation. Figure 2shows a similar plot for a rapid desaturation and resaturation that occurred during continuous tapping motion (protocol 3). The Masimo SET displayed an SpO 2value at all times but underestimated saturation by 3% to 6% during hypoxemia and motion.
The N-3000 failed to display an SpO 2value after a disconnection-reconnection for both motions. For this participant in both normoxemia and hypoxemia, the N-200 underestimated saturation by 5% to 18% during motion. The durations of the two motions are indicated on the bottom of Figure 1, as are the times when the sensors were disconnected and reconnected. The figure depicts the normoxemia and gradual desaturation to SpO 2= 75% sections of the protocol (1 and 2). Each plot compares one test oximeter during the two motion conditions with the N-200 control on the stationary hand. ( Figure 1) shows typical single-subject plots of SpO 2versus time for the three pulse oximeters tested: Nellcor N-200, Nellcor N-3000, and Masimo SET. Sensors were located on the index, middle, and ring fingers, and the specific fingers for each instrument were rotated among the volunteers. Data obtained from the test hand during various motion protocols were compared with simultaneous data from a similar oximeter whose sensor was located on the stationary control hand. The Masimo sensor, provided by the manufacturer, was similar in appearance to the Nellcor disposable. All sensors used in the study were disposable, tape-on adult finger sensors they were firmly attached to the finger and all had the same low mass. ) Additional N-200 and Masimo SET sensors were placed on the cannulated or control hand. (The C-lock feature of the N-200 was not used during this study because it actually deteriorated performance in the preliminary motion study. Three pulse oximeter sensors were then attached to the test hand (the hand opposite the radial cannula): Nellcor N-200, Nellcor N-3000 “Symphony,” and Masimo SET prototype. After giving informed consent, each participant had a 20-gauge, 1.5-inch cannula placed in the radial artery of the nondominant wrist. Participants included seven men and three women, whose average age was 26.6 + 6.7 yr (range, 19 to 42 yr) all were nonsmokers with no evidence of vascular or other systemic disease.
Ten healthy volunteers participated in this study, which was reviewed and approved by the Human Subjects Review Committee. To avoid confusion, we use the term data dropout to describe any interruption in continuous SpO 2data, and dropout rate as the percentage of time when SpO 2data are not provided by the oximeter. A recent intraoperative study defined data failure as the presence of a gap of more than 10 min in continuously recorded SpO 2data. Use of the term failure rate is problematic, because nearly every published study has applied a different definition. The term failure was defined in this study as a gap of more than 15 minutes in the anesthesia record without pulse oximetry (SpO 2) data. A prospective study in the operating room in 1991 found an overall incidence of oximeter failure near 1%. Continuous monitoring of arterial hemoglobin oxygen saturation by pulse oximetry has been a standard of care in the operating room since 1990 and in the recovery room since 1992.* Despite universal agreement on the importance of pulse oximetry monitoring, little progress has been made in reducing the incidence of failure to display valid data.
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