Publications

Introduction: Several prior studies have suggested that baseline SpO2 in healthy adults may differ between females and males. However, most research has been limited by small sample sizes or the absence of concurrent arterial blood gas (ABG) measurements. Our study aims to assess potential sex-based differences in SpO2 and SaO2 in a controlled laboratory environment with simultaneous SpO2 and SaO2 collection.

Methods: We analyzed prospectively collected data from healthy, non-smoking, non-pregnant adults enrolled in controlled desaturation studies at the UCSF Hypoxia Lab. Variables included age, body mass index (BMI), body surface area (BSA), heart rate (HR), finger diameter, SpO2 and pulsatility amplitude measured using the Nellcor PM1000N oximeter with the DS-100A1 probe. Additional measurements included total hemoglobin (tHb), carboxyhemoglobin (COHb), methemoglobin (MetHb), partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), and arterial oxygen saturation (SaO2), obtained via ABG analysis using the Radiometer ABL90. All values were recorded while participants breathed room air. Skin color was assessed with individual typology angle (ITA) measured by the Konica Minolta Cm-700d spectrophotometer. Statistical analyses included the Mann-Whitney U test and Fisher’s exact test for subject-level covariates, univariate generalized linear mixed effects and generalized estimating equations for measurement-level covariates.

Results: We enrolled 90 females (median age: 25.7) and 77 males (median age: 26.6). Of these participants, 91 participants (46 females and 45 males) made repeat visits, resulting in a total of 502 paired SpO2-SaO2 samples (277 from females and 225 from males). As shown in Table 1, median SpO2 and SaO2 were not statistically different between females (99.0% and 98.5%) and males (98.0% and 98.1%) (p = 0.08 and p = 0.21). Females had significantly lower height, BMI, BSA, percent modulation, finger diameter, PaCO2, tHb, and had an ITA distribution with a larger proportion of lightly pigmented individuals than did the male cohort (p < 0.05). Conclusions: We did not detect a difference in SpO2 or SaO2 between healthy females and males. However, we observed several differences in our female cohort, including smaller stature, lower pulsatility amplitude, BMI, finger size, skin color, PaCO2, and tHb. While some of these factors could potentially contribute to previously observed differences in SpO2, further investigations are needed with larger sample sizes and more balanced variables to clarify how these factors may affect SpO2 and SaO2 and to determine if there is a sex-linked difference.

The OpenOximetry Dataset stores clinical and lab pulse oximetry data. It supports measurements of arterial oxygen saturation (SaO2) by arterial blood gas co-oximetry and pulse oximetry (SpO2), alongside processed and unprocessed photoplethysmography (PPG) data and other metadata. This includes skin color measurements, finger diameter, vital signs (e.g., arterial blood pressure, end-tidal carbon dioxide), and arterial blood gas parameters (e.g., acid-base balance, hemoglobin concentration). All data, from desaturation studies to clinical trials, are collected prospectively to ensure accuracy. A common data model and standardized protocols for consistent archival and interpretation ensure consistent data archival and interpretation. The dataset aims to facilitate research on pulse oximeter performance across diverse human characteristics, addressing performance issues and promoting accurate pulse oximeters. The initial release includes controlled lab desaturation studies (CLDS), with ongoing updates planned as further data from clinical trials and CLDS become available.

Background: Some pulse oximeters perform worse in people with darker skin, and this may be due to inadequate diversity of skin pigment in device development study cohorts. Guidance is needed to accurately and equitably characterize skin pigment to ensure diversity in research cohorts. We tested multiple methods for characterizing skin pigment to assess comparability and impact on cohort diversity.

Objectives: The objectives of this study were to assess reliability and comparability of common skin pigment measurement methods, compare findings from different anatomical sites and demonstrate that pigment cannot be assumed from US National Institutes for Health (NIH) race categories.

Methods: We used three subjective methods [perceived Fitzpatrick (pFP) scale, Monk Skin Tone (MST) scale and Von Luschan (VL) scale] and two objective methods [Konica Minolta CM-700d spectrophotometer and Delfin Skin Color Catch (DSCC) colorimeter] for individual typology angle (ITA) across multiple measurement sites in adults. We calculated ΔE to estimate operator perceptibility thresholds for subjective methods and to determine reproducibility for objective methods. We used each method to categorize participants as ‘light, medium or dark’ and compared the impact of method selection on cohort diversity.

Results: We studied 789 participants, with 33 856 assessments. The MST had the widest luminosity range, and the VL scale had the least discernible adjacent categories. With ‘dark’ defined as ITA < -30°, 14% of participants were categorized ‘dark’ as compared with 26% by pFP or 16% by MST. Approximately half of the ‘dark’ cohort had an ITA < -50°. With an ITA threshold < -50°, only 7% of the cohort was categorized as ‘dark’. When ‘Black or African American’ self-identification was used to define ‘dark’, 23% of the cohort was categorized as such. Each self-assigned NIH race category included a wide range of ITA and subjective scale categories. Both ITA and L* from the KM-700d and DSCC demonstrated strong correlation (ρ > 0.7).

Conclusions: Common methods for skin pigment characterization, especially the use of race or subjective scales, have significant limitations. When applied to the same cohort, different methods yield significantly different results and some may overestimate diversity. Previously published ITA thresholds for defining ‘dark’ skin are too light and lead to under-representation of people with darker skin.

Functional testers are designed to evaluate select pulse oximeter characteristics but are often misused to validate device accuracy, potentially providing false reassurance. This study evaluated whether the Fluke ProSim8 (FPS8) could accurately predict oximeter performance during human controlled desaturation studies or identify performance differences under low signal conditions. 12 oximeters were tested using two FPS8 protocols: (1) an ‘SpO₂ plateau’ protocol which mimicked controlled desaturation studies by evaluating device performance over a range of simulated SpO2 (70-100%), and (2) a ‘signal space’ protocol designed to assess device accuracy under varying modulation and transmission conditions. Each device also underwent controlled desaturation testing in healthy adults. Six of the 12 oximeters passed (ARMS ≤ 3%) the SpO₂ plateau protocol; however, three of these failed (ARMS > 3%) human testing. At lower simulated saturations, most devices overestimated SpO₂. In the signal space protocol, oximeters performed well under high signal conditions, but many failed to produce readings or showed SpO₂ errors > 3% under low signal conditions. On average, oximeters failed to generate a reading 20.2 ± 7.2 times out of 60 attempts. Ten devices passed (ARMS < 3%) the signal space protocol, but two of these failed human testing. Oximeter performance on the FPS8 did not correlate with human performance (R² = 0.08 for the plateau protocol; R² = 0.01 for the signal space protocol). The FPS8 did not reliably predict oximeter accuracy in human desaturation studies or under low signal conditions; current functional tester protocols are limited in predicting real-world oximeter performance.

Rationale 

Pulse oximeter performance may vary by skin pigmentation, but most data are retrospective with key limitations.

Objective

To quantify pulse oximeter bias [mean difference between pulse oximeter oxygen saturation (SpO2) and arterial blood functional oxygen saturation (SaO2)], and average root mean square error (ARMS) and estimate adjusted effects of skin pigment on bias or ARMS in critically-ill adults

Methods

Prospective single-center study of 631 ICU patients (2022–2024) directly observed SpO and SaO pairs. Skin pigment was assessed using the subjective Monk Skin Tone Scale and objective spectrophotometry measurement (Individual Typology Angle [ITA]). Adjusted effects were estimated with targeted maximum likelihood estimation.

Main Results

Among 1,760 paired measurements from 631 critically-ill adults, median SaO2 was 98% (IQR 96%, 99%) with 40 episodes of stable hypoxemia (SpO2<90%). SpO2 systematically underestimated SaO2 [median bias= −1.70 IQR (−2.84, −0.50)]. Bias was less negative in patients with darker skin (ITA <-30°) [−1.05 (−2.44, −0.10)] vs lighter skin (ITA >30°) [−2.01 (−3.34, −1.00)] and remained significantly different in adjusted analyses. ARMS was 3.87 (95% CI 3.25, 4.53) overall and 4.49 (95% CI 2.63, 7.07) in patients with darker skin. Ear probes performed worse than finger probes [bias: −2.20 vs. −1.60; ARMS: 4.90 vs. 2.70].

Conclusions

In this large ICU cohort, hypoxemia was rare, pulse oximeters systematically underestimated SaO, performance varied by skin pigment and probe site. Bias was less negative in patients with darker skin. Pulse oximeter inaccuracies in ICU patients may be more substantial than clinicians recognize.

Question

Does pulse oximeter bias in critically-ill adults differ by skin pigmentation?

Findings

In this prospective, single-center study of 631 critically-ill adults, oximeter mean bias was negative for all patients but relatively less negative for patients with darker pigment. Bias variation by pigment was nonlinear and larger in ear than finger probes.

Meaning

Pulse oximeter bias varies with skin pigmentation and may not always be positive in patients with darker pigmentation. Pulse oximeter inaccuracy may be larger than clinicians appreciate. Additional studies with multiple oximeter brands and more stable hypoxemia are needed to further understand bias variation with skin pigment.

Background

Fingertip pulse oximeters are widely available, inexpensive, and commonly used to make clinical decisions in many settings. Device performance is largely unregulated and poorly characterised, especially in people with dark skin pigmentation.

Methods

Eleven popular fingertip pulse oximeters were evaluated using the US Food and Drug Administration (FDA) Guidance (2013) and International Organization for Standardization Standards (ISO, 2017) in 34 healthy humans with diverse skin pigmentation utilising a controlled desaturation study with arterial oxygen saturation (SaO 2) plateaus between 70% and 100%. Skin pigmentation was assessed subjectively using a perceived Fitzpatrick Scale (pFP) and objectively using the individual typology angle (ITA) via spectrophotometry at nine anatomical sites.

Findings

Five of 11 devices had a root mean square error (ARMS) > 3%, falling outside the acceptable FDA performance range. Nine devices demonstrated worse performance in participants in the darkest skin pigmentation category compared with those in the lightest category. A commonly used subjective skin colour scale frequently miscategorised participants as being darkly pigmented when compared to objective quantification of skin pigment by ITA.

Interpretation

Fingertip pulse oximeters have variable performance, frequently not meeting regulatory requirements for clinical use, and occasionally contradicting claims made by manufacturers. Most devices showed a trend toward worse performance in participants with darker skin pigment. Regulatory standards do not adequately account for the impact of skin pigmentation on device performance. We recommend that the pFP and other non-standardised subjective skin colour scales should no longer be used for defining diversity of skin pigmentation. Reliable methods for characterising skin pigmentation to improve diversity and equitable performance of pulse oximeters are needed.

Funding

This study was conducted as part of the Open Oximetry Project funded by the Gordon and Betty Moore Foundation, Patrick J McGovern Foundation, and Robert Wood Johnson Foundation. The UCSF Hypoxia Research Laboratory receives funding from multiple industry sponsors to test the sponsors’ devices for the purposes of product development and regulatory performance testing. Data in this paper do not include sponsor’s study devices. All data were collected from devices procured by the Hypoxia Research Laboratory for the purposes of independent research. No company provided any direct funding for this study, participated in study design or analysis, or was involved in analysing data or writing the manuscript. None of the authors own stock or equity interests in any pulse oximeter companies. Dr Ellis Monk’s time utilised for data analysis, reviewing and editing was funded by grant number: DP2MH132941.

Background

Retrospective clinical trials of pulse oximeter accuracy report more frequent missed diagnoses of hypoxemia in hospitalized Black patients than White patients, differences that may contribute to racial disparities in health and health care. Retrospective studies have limitations including mistiming of blood samples and oximeter readings, inconsistent use of functional versus fractional saturation, and self-reported race used as a surrogate for skin color. Our objective was to prospectively measure the contributions of skin pigmentation, perfusion index (PI), sex, and age on pulse oximeter errors in a laboratory setting.

Methods

We enrolled 146 healthy subjects, including 25 with light skin (Fitzpatrick class I and II), 78 with medium (class III and IV), and 43 with dark (class V and VI) skin. We studied 2 pulse oximeters (Nellcor N-595 and Masimo Radical 7) in prevalent clinical use. We analyzed 9763 matched pulse oximeter readings (pulse oximeter measured functional saturation [Spo2]) and arterial oxygen saturation (hemoximetry arterial functional oxygen saturation [Sao2]) during stable hypoxemia (Sao2 68%-100%). PI was measured as percent infrared light modulation by the pulse detected by the pulse oximeter probe, with low perfusion categorized as PI < 1%. The primary analysis was to assess the relationship between pulse oximeter bias (difference between Sao2 and Spo2) by skin pigment category in a multivariable mixed-effects model incorporating repeated-measures and different levels of Sao2 and perfusion.

Results

Skin pigment, PI, and degree of hypoxemia significantly contributed to errors (bias) in both pulse oximeters. For PI values of 1.0% to 1.5%, 0.5% to 1.0%, and <0.5%, the P value of the relationship to mean bias or median absolute bias was <.00001. In lightly pigmented subjects, only PI was associated with positive bias, whereas in medium and dark subjects bias increased with both low perfusion and degree of hypoxemia. Sex and age was not related to pulse oximeter bias. The combined frequency of missed diagnosis of hypoxemia (pulse oximeter readings 92%-96% when arterial oxygen saturation was <88%) in low perfusion conditions was 1.1% for light, 8.2% for medium, and 21.1% for dark skin.

Conclusions

Low peripheral perfusion combined with darker skin pigmentation leads to clinically significant high-reading pulse oximeter errors and missed diagnoses of hypoxemia. Darkly pigmented skin and low perfusion states are likely the cause of racial differences in pulse oximeter performance in retrospective studies.

Anemia and hypoxemia are common clinical conditions that are difficult to study and may impact pulse oximeter performance. Utilizing an in vitro circulation system, we studied performance of three pulse oximeters during hypoxemia and severe anemia. Three oximeters including one benchtop, one handheld, and one fingertip device were selected to reflect a range of cost and device types. Human blood was diluted to generate four hematocrit levels (40%, 30%, 20%, and 10%). Oxygen and nitrogen were bubbled through the blood to generate a range of oxygen saturations (OHb) and the blood was cycled through the in vitro circulation system. Pulse oximeter saturations (SpO) were paired with simultaneously-measured OHb readings from a reference CO-oximeter. Data for each hematocrit level and each device were least-squares fit to a 2nd-order equation with quality of each curve fit evaluated using standard error of the estimate. Bias and average root mean square error were calculated after correcting for the calibration difference between human and in vitro circulation system calibration. The benchtop oximeter maintained good accuracy at all but the most extreme level of anemia. The handheld device was not as accurate as the benchtop, and inaccuracies increased at lower hematocrit levels. The fingertip device was the least accurate of the three oximeters. Pulse oximeter performance is impacted by severe anemia in vitro. The use of in vitro calibration systems may play an important role in augmenting in vivo performance studies evaluating pulse oximeter performance in challenging conditions.

It has long been known that many pulse oximeters function less accurately in patients with darker skin. Reasons for this observation are incompletely characterized and potentially enabled by limitations in existing regulatory oversight. Based on decades of experience and unpublished data, we believe it is feasible to fully characterize, in the public domain, the factors that contribute to missing clinically important hypoxemia in patients with darkly pigmented skin. Here we propose 5 priority areas of inquiry for the research community and actionable changes to current regulations that will help improve oximeter accuracy. We propose that leading regulatory agencies should immediately modify standards for measuring accuracy and precision of oximeter performance, analyzing and reporting performance outliers, diversifying study subject pools, thoughtfully defining skin pigmentation, reporting data transparently, and accounting for performance during low-perfusion states. These changes will help reduce bias in pulse oximeter performance and improve access to safe oximeters.

Background

Currently, no reliable method exists for continuous, noninvasive measurements of absolute cerebral blood flow (CBF). We sought to determine how changes measured by ultrasound-tagged near-infrared spectroscopy (UT-NIRS) compare with changes in CBF as measured by transcranial Doppler (TCD) in healthy volunteers during profound hypocapnia and hypercapnia.

Methods

Ten healthy volunteers were monitored with a combination of TCD, UT-NIRS (c-FLOW, Ornim Medical), as well as heart rate, blood pressure, end-tidal PCO2 (PEtCO2), end-tidal O2, and inspired O2. Inspired CO2 and minute ventilation were controlled to achieve 5 stable plateau goals of EtCO2 at 15-20, 25-30, 35-40, 45-50, and 55-60 mm Hg, for a total of 7 measurements per subject. CBF was assessed at a steady state, with the TCD designated as the reference standard. The primary analysis was a linear mixed-effect model of TCD and UT-NIRS flow with PEtCO2, which accounts for repeated measures. Receiver operating characteristic curves were determined for detection of changes in CBF.

Results

Hyperventilation (nadir PEtCO2 17.1 ± 2.4) resulted in significantly decreased mean flow velocity of the middle cerebral artery from baseline (to 79% ± 22%), but not a consistent decrease in UT-NIRS cerebral flow velocity index (n = 10; 101% ± 6% of baseline). Hypercapnia (peak PEtCO2 59.3 ± 3.3) resulted in a significant increase from baseline in both mean flow velocity of the middle cerebral artery (153% ± 25%) and UT-NIRS (119% ± 11%). Comparing slopes versus PEtCO2 as a percent of baseline for the TCD (1.7% [1.5%-2%]) and UT-NIRS (0.4% [0.3%-0.5%]) shows that the UT-NIRS slope is significantly flatter, P < .0001. Area under the receiver operating characteristic curve was significantly higher for the TCD than for UT-NIRS, 0.97 (95% confidence interval, 0.92-0.99) versus 0.75 (95% confidence interval, 0.66-0.82).

Conclusions

Our data indicate that UT-NIRS cerebral flow velocity index detects changes in CBF only during hypercarbia but not hypocarbia in healthy subjects and with much less sensitivity than TCD. Additional refinement and validation are needed before widespread clinical utilization of UT-NIRS.

Objective

To describe the association between intraoperative tissue oxygenation and postoperative troponin elevation in patients undergoing major spine surgery. We hypothesised that a decrease in intraoperative skeletal muscle tissue oxygenation (SmO) was associated with the peak postoperative cardiac troponin value.

Design

This is a prospective cohort study.

Setting

Single-centre, University of California San Francisco Medical Center.

Participants

Seventy adult patients undergoing major elective spine surgery.

Primary and secondary outcome measures

High-sensitivity troponin T (hsTnT) was measured in plasma preoperatively and on the first and second day after surgery to assess the primary outcome of peak postoperative hsTnT. Secondary outcomes included MINS and intensive care unit (ICU) admission within 30 days. Skeletal cerebral tissue oxygenation and SmO was measured continuously with near-infrared spectroscopy during surgery. The primary exposure variable was time-weighted area under the curve (TW AUC) for SmO.

Results

Mean age was 65 (33-85) years and 59% were female. No significant association was found between TW AUC for SmO and peak hsTnT (Spearman’s correlation, r=0.17, p=0.16). A total of 28 (40%) patients had MINS. ICU admission occurred in 14 (40%) in lower vs 25 (71%) in upper half of patients based on TW AUC for SmO, p=0.008.

Conclusions

Decrease in SmO was not a statistically significant predictor for peak troponin value following major spine surgery but is a potential predictor for other postoperative complications.

Trial registration number

NCT03518372.

Background

Pulse oximetry is used as an assessment tool to gauge the severity of COVID-19 infection and identify patients at risk of poor outcomes. The pandemic highlights the need for accurate pulse oximetry, particularly at home, as infection rates increase in multiple global regions including the UK, USA and South Africa. Over 100 million Samsung smartphones containing dedicated biosensors (Maxim Integrated Inc, San Jose, CA) and preloaded Apps to perform pulse oximetry, are in use globally. We performed detailed in human hypoxia testing on the Samsung S9 smartphone to determine if this integrated hardware meets full FDA/ISO requirements for clinical pulse oximetry.

Methods

The accuracy of integrated pulse oximetry in the Samsung 9 smartphone during stable arterial oxygen saturations (SaO) between 70% and 100% was evaluated in 12 healthy subjects. Inspired oxygen, nitrogen, and carbon dioxide partial pressures were monitored and adjusted via a partial rebreathing circuit to achieve stable target SaO plateaus between 70% and 100%. Arterial blood samples were taken at each plateau and saturation measured on each blood sample using ABL-90FLEX blood gas analyzer. Bias, calculated from smartphone readings minus the corresponding arterial blood sample, was reported as root mean square deviation (RMSD).

Findings

The RMSD of the over 257 data points based on blood sample analysis obtained from 12 human volunteers tested was 2.6%.

Interpretation

Evaluation of the smartphone pulse oximeter performance is within requirements of <3.5% RMSD blood oxygen saturation (SpO) value for FDA/ISO clearance for clinical pulse oximetry. This is the first report of smartphone derived pulse oximetry measurements that meet full FDA/ISO accuracy certification requirements. Both Samsung S9 and S10 contain the same integrated pulse oximeter, thus over 100 million smartphones in current global circulation could be used to obtain clinically accurate spot SpO measurements to support at home assessment of COVID-19 patients.

Severe hypoxemia presents variably, and sometimes silently, without subjective complaints of dyspnea. The adequacy of cardiovascular compensation for oxygen delivery to tissues should be a focus in all hypoxemic patients.

Unlabelled

Lundeberg, Jenny, John R. Feiner, Andrew Schober, Jeffrey W. Sall, Helge Eilers, and Philip E. Bickler. Increased cytokines at high altitude: lack of effect of ibuprofen on acute mountain sickness, physiological variables or cytokine levels. High Alt Med Biol. 19:249-258, 2018.

Introduction

There is no consensus on the role of inflammation in high-altitude acclimatization.

Aims

To determine the effects of a nonsteroidal anti-inflammatory drug (ibuprofen 400 mg every 8 hours) on blood cytokines, acclimatization, acute mountain sickness (AMS, Lake Louise Score), and noninvasive oxygenation in brain and muscle in healthy volunteers.

Materials and methods

In this double-blind study, 20 volunteers were randomized to receive ibuprofen or placebo at sea level and for 48 hours at 3800 m altitude. Arterial, brain, and leg muscle saturation with near infrared spectroscopy, pulse oximetry, and heart rate were measured. Blood samples were collected for cytokine levels and cytokine gene expression.

Results

All of the placebo subjects and 8 of 11 ibuprofen subjects developed AMS at altitude (p = 0.22, comparing placebo and ibuprofen). On arrival at altitude, the oxygen saturation as measured by pulse oximetry (SO) was 84.5% ± 5.4% (mean ± standard deviation). Increase in blood interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10), tumor necrosis factor-α (TNF-α), and granulocyte-macrophage colony-stimulating factor (GM-CSF) levels occurred comparably in the placebo and ibuprofen groups (all not significant, univariate test by Wilcoxon rank sum). Increased IL-6 was associated with higher AMS scores (p = 0.002 by Spearman rank correlation). However, we found no difference or association in AMS score and blood or tissue oxygenation between the ibuprofen and placebo groups.

Conclusions

We found that ibuprofen, at the package-recommended adult dose, did not have a significant effect on altitude-related increases in cytokines, AMS scores, blood, or tissue oxygenation in a population of healthy subjects with a high incidence of AMS.

Detecting life-threatening common dyshemoglobins such as carboxyhemoglobin (COHb, resulting from carbon monoxide poisoning) or methemoglobin (MetHb, caused by exposure to nitrates) typically requires a laboratory CO-oximeter. Because of cost, these spectrophotometer-based instrument are often inaccessible in resource-poor settings. The aim of this study was to determine if an inexpensive pocket infrared spectrometer and smartphone (SCiO®Pocket Molecular Sensor, Consumer Physics Ltd., Israel) accurately detects COHb and MetHb in single drops of blood. COHb was created by adding carbon monoxide gas to syringes of heparinized blood human or cow blood. In separate syringes, MetHb was produced by addition of sodium nitrite solution. After incubation and mixing, fractional concentrations of COHb or MetHb were measured using a Radiometer ABL-90 Flex® CO-oximeter. Fifty microliters of the sample were then placed on a microscope slide, a cover slip applied and scanned with the SCiO spectrometer. The spectrograms were used to create simple linear models predicting [COHb] or [MetHb] based on spectrogram maxima, minima and isobestic wavelengths. Our model predicted clinically significant carbon monoxide poisoning (COHb ≥15%) with a sensitivity of 93% and specificity of 88% (regression r2 = 0.63, slope P<0.0001), with a mean bias of 0.11% and an RMS error of 21%. Methemoglobinemia severe enough to cause symptoms (>20% MetHb) was detected with a sensitivity of 100% and specificity of 71% (regression r2 = 0.92, slope P<0.001) mean bias 2.7% and RMS error 21%. Although not as precise as a laboratory CO-oximeter, an inexpensive pocket-sized infrared scanner/smartphone detects >15% COHb or >20% MetHb on a single drop of blood with enough accuracy to be useful as an initial clinical screening. The SCiO and similar relatively low cost spectrometers could be developed as inexpensive diagnostic tools for developing countries.

Background

Pulse oximeter performance is degraded by motion artifacts and low perfusion. Manufacturers developed algorithms to improve instrument performance during these challenges. There have been no independent comparisons of these devices.

Methods

We evaluated the performance of four pulse oximeters (Masimo Radical-7, USA; Nihon Kohden OxyPal Neo, Japan; Nellcor N-600, USA; and Philips Intellivue MP5, USA) in 10 healthy adult volunteers. Three motions were evaluated: tapping, pseudorandom, and volunteer-generated rubbing, adjusted to produce photoplethsmogram disturbance similar to arterial pulsation amplitude. During motion, inspired gases were adjusted to achieve stable target plateaus of arterial oxygen saturation (SaO2) at 75%, 88%, and 100%. Pulse oximeter readings were compared with simultaneous arterial blood samples to calculate bias (oxygen saturation measured by pulse oximetry [SpO2] – SaO2), mean, SD, 95% limits of agreement, and root mean square error. Receiver operating characteristic curves were determined to detect mild (SaO2 < 90%) and severe (SaO2 < 80%) hypoxemia.

Results

Pulse oximeter readings corresponding to 190 blood samples were analyzed. All oximeters detected hypoxia but motion and low perfusion degraded performance. Three of four oximeters (Masimo, Nellcor, and Philips) had root mean square error greater than 3% for SaO2 70 to 100% during any motion, compared to a root mean square error of 1.8% for the stationary control. A low perfusion index increased error.

Conclusions

All oximeters detected hypoxemia during motion and low-perfusion conditions, but motion impaired performance at all ranges, with less accuracy at lower SaO2. Lower perfusion degraded performance in all but the Nihon Kohden instrument. We conclude that different types of pulse oximeters can be similarly effective in preserving sensitivity to clinically relevant hypoxia.