• Neonatology
• Intensive Care Units, Neonatal

We read with great interest the study of Maiwald et al,1 which compared pulse oximeter saturation (SpO₂) measurements and the proportion of time spent within the designated SpO₂ target range (90%–95%) using three Masimo sensors in extremely preterm infants. However, we disagree with the authors’ stated conclusions that Low Noise Cabled Sensors (LNCS) are preferable to Red Diamond Signal Extraction Technology (RD SET) sensors or that the data reveal a concern to clinical care in neonates. This interpretation is not supported by the data shown in the paper, which did not include arterial blood saturation (SaO₂) values, and is impacted by additional methodology shortcomings.

The authors’ conclusions de-emphasise the importance of sensor accuracy in SpO₂ targeting. Indeed, clinicians should adjust their management protocols to use the pulse oximeter sensor that most closely reflects the true SaO₂ values. The newer RD SET sensor is designed with improved accuracy specifications (1.5% root-mean-square error [A_RMS]), and has been validated against actual blood SaO₂ values. When targeting tighter ranges, higher precision is of importance.

Besides failure to use SaO₂ data to determine accuracy, the authors did not reference shielding measures. When comparing multiple sensors simultaneously, it’s important to use optical shielding to prevent sensor-to-sensor crosstalk.2 Furthermore, the data presented in supplemental figures raise concerns about SpO₂ stability and outlier treatment in the statistical methods used.

We did find the authors’ graphical illustration of counts for all SpO₂ values to be instructive. In review of this figure (annotated in figure 1), the RD SET sensor clearly shows a tighter distribution of SpO₂ values, that (contrary to authors’ conclusions) is most useful to safely guide fraction of inspired oxygen (FiO₂) titration in premature infants. The figure provided histograms of SpO₂ values from the three sensors studied, and showed RD SET (dashed line) provided a narrower distribution with a clearer peak in the histogram. In the absence of a true SaO₂ reference to make an accuracy statement, the tighter distribution of SpO₂ values using the RD SET implies that it would be best for SpO₂ targeting protocols, since FiO₂ values are titrated to changes in SpO₂ values.

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Figure 1

Counts of SpO₂ values per sensor in all infants. The peak count (mode) indicates the difference (bias) between sensors is ~1% (blue), and taking the top 10% of peak counts, the RD with higher precision shows an SpO₂ range spread of ~2% (green) versus ~4% for LNCS (red). Adapted from Maiwald et al, 2023.1

In summary, we found the conclusions stated by Maiwald et al 1 are prone to misrepresentation, potentially diverting clinician focus from recent performance improvements in pulse oximetry. In particular, they could drive neonatologists away from using RD SET, when neonatologists should be encouraged to use this sensor due to its increased accuracy. All three Masimo sensors (RD SET, LNCS and PPG) can be safely used to monitor neonates. However, RD SET represents industry leading accuracy (1.5% A_RMS), that has translated into a tighter distribution of SpO₂ values observed by these investigators in their SpO₂-targeting protocol.