Comparison of Two SpO 2 Targets With Two Different Oximeters: Significant Impact on Oxygen Flow and on Oxygenation Parameters

Abstract

Background:

The choice of SpO₂ target significantly influences oxygen utilization. It was recently shown that oximeter brand influenced the SpO₂ measurements, with differences between oximeters of up to 4%. The objectives of the study were to evaluate the impact of the combination of SpO₂ target and oximeter brand on O₂ utilization, O₂ weaning, high O₂ flow requirements, occult hypoxemia and occult hyperoxemia.

Methods:

We have conducted a randomized cross-over study in 20 stable ICU patients requiring oxygen therapy delivered through nasal canula after cardiac surgery. Patients without adequate SpO₂ signal were excluded. Four randomized periods of 10 min were conducted in all patients with different SpO₂ targets (90 and 94%) and different oximeters (Nonin and Philips). For each period we collected the oxygen flow and oxygen blood gases at the end of the period. We compared the O₂ flow, the rate of occult hypoxemia (SaO₂ below 90% with SpO₂ ≥ 90%) and occult hyperoxemia (SaO₂ above 96% with SpO₂ ≤ 96%), O₂ partial weaning (below 0.5 L/min) or complete weaning and the rate of high O₂ flow requirements (above 5 L/min).

Results:

20 patients were studied (mean age 68 ± 8 years, 16 were men, all had light skin pigmentation (Fitzpatrick skin scale 1 or 2) reflecting our local population, none had shock). At baseline, SpO₂ was 93.4 ± 1.8% and oxygen flow was 2.1 ± 1.4 L/min. O₂ flow requirements and oxygenation parameters in the different study periods are displayed in the Figure 1. Differences in mean O₂ flow during monitoring with the Nonin with an SpO₂ target of 90% and Philips with an SpO₂ target of 94% were not statistically different (P = .74). However, all other comparisons for the O₂ flow were statistically different. The rate of complete O₂ weaning was 55% in the Philips 90% period and 0 to 5% in other periods. Oxygenation parameters (SaO₂, PaO₂) were similar during Nonin 90% and Philips 94%. Conversely, there were statistically significant differences for oxygenation parameters and for other comparisons.

Conclusions:

In patients requiring conventional oxygen therapy, the SpO₂ target, the oximeter brand and even more the combination of both have major impact on O₂ utilization, O₂ weaning and both occult hypoxemia and hyperoxemia. Patients managed with Nonin with SpO₂ target of 90% and Philips with SpO₂ target of 94% had similar O₂ flow and similar arterial oxygenation parameters. These data underline the necessity to use corrected SpO₂ targets rather than universal SpO₂ targets to manage O₂ therapy.

Mean oxygen flow utilization in the different study conditions comparing two SpO₂ targets (90 and 94%) and two oximeters brand (Philips and Nonin): Philips 90, Nonin 90, Philips 94, and Nonin 94. SpO₂ targets of 90% are represented with hatched bars while SpO₂ targets of 94% are represented with plain bars. Nonin conditions are represented with blue bars while Philips conditions are represented with light orange bars. Oxygen Ratio were 1.2 (Philips 94/Nonin 90), 4.0 (Nonin90/Philips90), 3.0 (Nonin94/Philips94), 3.6 (Nonin94/Nonin90), 4.7 (Philips94/Philips90) and 14.1 (Nonin94/Philips90).