Effect of skin pigmentation on pulse oximetry accuracy in the emergency department

Effect of Skin Pigmentation and Finger Choice on Accuracy of Oxygen Saturation Measurement in an IoT-Based Pulse Oximeter

Pulse oximeters are widely used in hospitals and homes for measurement of blood oxygen saturation level (SpO2) and heart rate (HR). Concern has been raised regarding a possible bias in obtaining pulse oximeter measurements from different fingertips and the potential effect of skin pigmentation (white, brown, and dark). In this study, we obtained 600 SpO2 measurements from 20 volunteers using three UK NHS-approved commercial pulse oximeters alongside our custom-developed sensor, and used the Munsell colour system (5YR and 7.5YR cards) to classify the participants' skin pigmentation into three distinct categories (white, brown, and dark). The statistical analysis using ANOVA post hoc tests (Bonferroni correction), a Bland-Altman plot, and a correlation test were then carried out to determine if there was clinical significance in measuring the SpO2 from different fingertips and to highlight if skin pigmentation affects the accuracy of SpO2 measurement. The results indicate that although the three commercial pulse oximeters had different means and standard deviations, these differences had no clinical significance.

Effect of skin tone on the accuracy of the estimation of arterial oxygen saturation by pulse oximetry: a systematic review

BACKGROUND

Pulse oximetry-derived oxygen saturation (SpO2) is an estimate of true arterial oxygen saturation (SaO2). The aim of this review was to evaluate available evidence determining the effect of skin tone on the ability of pulse oximeters to accurately estimate SaO2.

METHODS

Published literature was screened to identify clinical and non-clinical studies enrolling adults and children when SpO2 was compared with a paired co-oximetry SaO2 value. We searched literature databases from their inception to March 20, 2023. Risk of bias (RoB) was assessed using the QUADAS-2 tool. Certainty of assessment was evaluated using the GRADE tool.

RESULTS

Forty-four studies were selected reporting on at least 222 644 participants (6121 of whom were children) and 733 722 paired SpO2-SaO2 measurements. Methodologies included laboratory studies, prospective clinical, and retrospective clinical studies. A high RoB was detected in 64% of studies and there was considerable heterogeneity in study design, data analysis, and reporting metrics. Only 11 (25%) studies measured skin tone in 2353 (1.1%) participants; the remainder reported participant ethnicity: 68 930 (31.0%) participants were of non-White ethnicity or had non-light skin tones. The majority of studies reported overestimation of SaO2 by pulse oximetry in participants with darker skin tones or from ethnicities assumed to have darker skin tones. Several studies reported no inaccuracy related to skin tone. Meta-analysis of the data was not possible.

CONCLUSIONS

Pulse oximetry can overestimate true SaO2 in people with darker skin tones. The clinical relevance of this bias remains unclear, but its magnitude is likely to be greater when SaO2 is lower.

SYSTEMATIC REVIEW PROTOCOL

International Prospective Register of Systematic Reviews (PROSPERO): CRD42023390723.

Discrepancy between arterial oxygen saturation and pulse oximetry measurement in a Chinese pediatric patient cohort

Background

Increasing evidence suggest a racial bias in pulse oximetry measurement, but this was under investigated in Asian pediatric populations.

Methods

Via the Pediatric Intensive Care database, this retrospective study included pediatric patient records of arterial oxygen saturation (SaO2) and oxygen saturation on pulse oximetry (SpO2) measured within 10 min. Discrepancy was examined, and potential predictors of occult hypoxemia (defined as SaO2 <88% with the paired SpO2 ≥92%) as well as its association with outcomes were explored by logistic regression.

Results

A total of 390 patients were included with 454 pairs of SaO2-SpO2 readings. The study population consisted of Han Chinese (99.0%) and 43.6% were female. Occult hypoxemia was observed in 20.0% of the patients, with a mean SaO2 of 71.4 ± 15.8%. Potential predictors of occult hypoxemia included female, being first admitted to cardiac ICU, congenital heart disease, increased heart rate, while patients with prior surgery records were less likely to experience occult hypoxemia. Patients with occult hypoxemia had numerically higher in-ICU mortality (16.7% versus 10.9%) and in-hospital mortality (17.9% versus 10.9%), but the associations were not statistically significant.

Conclusions

There was a substantial proportion of hypoxemia that was not detected by pulse oximetry in the Chinese pediatric patients, which might be predicted by several characteristics and seemed to associate with mortality.

The performance of 11 fingertip pulse oximeters during hypoxemia in healthy human participants with varied, quantified 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.

Inaccuracy of pulse oximetry with dark skin pigmentation: clinical implications and need for improvement

Recent reports highlight potential inaccuracies of pulse oximetry in patients with various degrees of skin pigmentation. We summarise the literature, provide an overview of potential clinical implications, and provide insights into how pulse oximetry could be improved to mitigate against such potential shortcomings.

Racial Disparity in Oxygen Saturation Measurements by Pulse Oximetry: Evidence and Implications

The pulse oximeter is a ubiquitous clinical tool used to estimate blood oxygen concentrations. However, decreased accuracy of pulse oximetry in patients with dark skin tones has been demonstrated since as early as 1985. Most commonly, pulse oximeters may overestimate the true oxygen saturation in individuals with dark skin tones, leading to higher rates of occult hypoxemia (i.e., clinically unrecognized low blood oxygen saturation). Overestimation of oxygen saturation in patients with dark skin tones has serious clinical implications, as these patients may receive insufficiently rigorous medical care when pulse oximeter measurements suggest that their oxygen saturation is higher than the true value. Recent studies have linked pulse oximeter inaccuracy to worse clinical outcomes, suggesting that pulse oximeter inaccuracy contributes to known racial health disparities. The magnitude of device inaccuracy varies by pulse oximeter manufacturer, sensor type, and arterial oxygen saturation. The underlying reasons for decreased pulse oximeter accuracy for individuals with dark skin tones may be related to failure to control for increased absorption of red light by melanin during device development and insufficient inclusion of individuals with dark skin tones during device calibration. Inadequate regulatory standards for device approval may also play a role in decreased accuracy. Awareness of potential pulse oximeter limitations is an important step for providers and may encourage the consideration of additional clinical information for management decisions. Ultimately, stricter regulatory requirements for oximeter approval and increased manufacturer transparency regarding device performance are required to mitigate this racial bias.

The accuracy of pulse oximetry in measuring oxygen saturation by levels of skin pigmentation: a systematic review and meta-analysis

BACKGROUND

During the COVID-19 pandemic, there have been concerns regarding potential bias in pulse oximetry measurements for people with high levels of skin pigmentation. We systematically reviewed the effects of skin pigmentation on the accuracy of oxygen saturation measurement by pulse oximetry (SpO2) compared with the gold standard SaO2 measured by CO-oximetry.

METHODS

We searched Ovid MEDLINE, Ovid Embase, EBSCO CINAHL, ClinicalTrials.gov, and WHO International Clinical Trials Registry Platform (up to December 2021) for studies with SpO2-SaO2 comparisons and measuring the impact of skin pigmentation or ethnicity on pulse oximetry accuracy. We performed meta-analyses for mean bias (the primary outcome in this review) and its standard deviations (SDs) across studies included for each subgroup of skin pigmentation and ethnicity and used these pooled mean biases and SDs to calculate accuracy root-mean-square (Arms) and 95% limits of agreement. The review was registered with the Open Science Framework ( https://osf.io/gm7ty ).

RESULTS

We included 32 studies (6505 participants): 15 measured skin pigmentation and 22 referred to ethnicity. Compared with standard SaO2 measurement, pulse oximetry probably overestimates oxygen saturation in people with the high level of skin pigmentation (pooled mean bias 1.11%; 95% confidence interval 0.29 to 1.93%) and people described as Black/African American (1.52%; 0.95 to 2.09%) (moderate- and low-certainty evidence). The bias of pulse oximetry measurements for people with other levels of skin pigmentation or those from other ethnic groups is either more uncertain or suggests no overestimation. Whilst the extent of mean bias is small or negligible for all subgroups evaluated, the associated imprecision is unacceptably large (pooled SDs > 1%). When the extent of measurement bias and precision is considered jointly, pulse oximetry measurements for all the subgroups appear acceptably accurate (with Arms < 4%).

CONCLUSIONS

Pulse oximetry may overestimate oxygen saturation in people with high levels of skin pigmentation and people whose ethnicity is reported as Black/African American, compared with SaO2. The extent of overestimation may be small in hospital settings but unknown in community settings. REVIEW PROTOCOL REGISTRATION: https://osf.io/gm7ty.

Influence of Sex, BMI, and Skin Color on the Accuracy of Non-Invasive Cuffless Photoplethysmography-Based Blood Pressure Measurements

Vital signs obtained by photoplethysmography-based devices might be influenced by subcutaneous fat and skin color. This observational comparison study aimed to test the accuracy of blood pressure (BP) measurements between a photoplethysmography-based device and cuff-based BP device in ambulatory individuals, coming for a routine BP checkup. Systolic BP (SBP) and diastolic BP (DBP) measurements were stratified based on sex, BMI (<25; 25 ≤BMI<30; 30 ≤kg/m²), and skin color (types 1–3 and 4–6 by the Fitzpatrick scale). A total of 1548 measurements were analyzed. Correlations of SBP and DBP between the devices among males/females were between 0.914–0.987 (p < 0.001), and Bland-Altman analysis showed a bias of less than 0.5 mmHg for both sexes. Correlations of SBP and DBP between the devices among BMI groups were between 0.931–0.991 (p < 0.001), and Bland-Altman analysis showed a bias of less than 1 mmHg for all. Correlations of SBP and DBP between the devices among the skin color groups were between 0.936–0.983 (p < 0.001), and Bland-Altman analysis showed a bias of less than 1 mmHg for all. This study shows similar and high agreements between BP measurements obtained using a PPG-based non-invasive cuffless BP device and a cuff-based BP device across sex, BMI, and skin color groups.

Impact of ethnicity on the accuracy of measurements of oxygen saturations: A retrospective observational cohort study

Background

Pulse oximeters are routinely used in community and hospital settings worldwide as a rapid, non-invasive, and readily available bedside tool to approximate blood oxygenation. Potential racial biases in peripheral oxygen saturation (SpO2) measurements may influence the accuracy of pulse oximetry readings and impact clinical decision making. We aimed to assess whether the accuracy of oxygen saturation measured by SpO2, relative to arterial blood gas (SaO2), varies by ethnicity.

Methods

In this large retrospective observational cohort study covering four NHS Hospitals serving a large urban population in Birmingham, United Kingdom, consecutive pairs of SpO2 and SaO2 measurements taken on the same patient within an interval of less than 20 min were identified from electronic patient records. Where multiple pairs of measurements were recorded in a spell, only the first was included in the analysis. The differences between SpO2 and SaO2 measurements were compared across groups of self-identified ethnicity. These differences were subsequently adjusted for age, sex, bilirubin, systolic blood pressure, carboxyhaemaglobin saturations and the time interval between SpO2 and SaO2 measurements.

Findings

Paired O2 saturation measurements from 16,818 inpatient spells between 1st January 2017 and 18th February 2021 were analysed. The cohort self-identified as being of White (81.2%), Asian (11.7%), Black (4.0%), or Other (3.2%) ethnicities. Across the cohort, SpO2 was statistically significantly higher than SaO2 (p < 0.0001), with medians of 98% (interquartile range [IQR]: 95-100%) vs. 97% (IQR: 96-99%), and a median difference of 0.5% points (pps; 95% confidence interval [CI]: 0.5-0.6). However, the size of this difference varied considerably with the magnitude of SaO2, with SpO2 overestimating by a median by 3.8pp (IQR: 0.4, 8.8) for SaO2 values <90% but underestimating by a median of 0.4pp (IQR: -2.0, 1.4) for an SaO2 of 95%. The differences between SpO2 and SaO2 were also found to vary by ethnicity, with this difference being 0.8pp (95% CI: 0.6-1.0, p < 0.0001) greater in those of Black vs. White ethnicity. These differences resulted in 8.7% vs. 6.1% of Black vs. White patients who were classified as normoxic on SpO2 actually being hypoxic on the gold standard SaO2 (odds ratio: 1.47, 95% CI: 1.09-1.98, p = 0.012).

Interpretation

Pulse oximetry may overestimate O2 saturation, and this is possibly more pronounced in patients of Black ethnicity. Prospective studies are urgently warranted to assess the impact of ethnicity on the accuracy of pulse oximetry, to ensure care is optimised for all.

Funding

PIONEER, the Health Data Research UK (HDR-UK) Health Data Research Hub in acute care.

Skin Pigmentation Influence on Pulse Oximetry Accuracy: A Systematic Review and Bibliometric Analysis

Nowadays, pulse oximetry has become the standard in primary and intensive care units, especially as a triage tool during the current COVID-19 pandemic. Hence, a deeper understanding of the measurement errors that can affect precise readings is a key element in clinical decision-making. Several factors may influence the accuracy of pulse oximetry, such as skin color, body temperature, altitude, or patient movement. The skin pigmentation effect on pulse oximetry accuracy has long been studied reporting some contradictory conclusions. Recent studies have shown a positive bias in oxygen saturation measurements in patients with darkly pigmented skin, particularly under low saturation conditions. This review aims to study the literature that assesses the influence of skin pigmentation on the accuracy of these devices. We employed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement to conduct a systematic review retrospectively since February 2022 using WOS, PubMed, and Scopus databases. We found 99 unique references, of which only 41 satisfied the established inclusion criteria. A bibliometric and scientometrics approach was performed to examine the outcomes of an exhaustive survey of the thematic content and trending topics.

Wearable Photoplethysmography for Cardiovascular Monitoring

Smart wearables provide an opportunity to monitor health in daily life and are emerging as potential tools for detecting cardiovascular disease (CVD). Wearables such as fitness bands and smartwatches routinely monitor the photoplethysmogram signal, an optical measure of the arterial pulse wave that is strongly influenced by the heart and blood vessels. In this survey, we summarize the fundamentals of wearable photoplethysmography and its analysis, identify its potential clinical applications, and outline pressing directions for future research in order to realize its full potential for tackling CVD.

Photoplethysmogram Analysis and Applications: An Integrative Review

Beyond its use in a clinical environment, photoplethysmogram (PPG) is increasingly used for measuring the physiological state of an individual in daily life. This review aims to examine existing research on photoplethysmogram concerning its generation mechanisms, measurement principles, clinical applications, noise definition, pre-processing techniques, feature detection techniques, and post-processing techniques for photoplethysmogram processing, especially from an engineering point of view. We performed an extensive search with the PubMed, Google Scholar, Institute of Electrical and Electronics Engineers (IEEE), ScienceDirect, and Web of Science databases. Exclusion conditions did not include the year of publication, but articles not published in English were excluded. Based on 118 articles, we identified four main topics of enabling PPG: (A) PPG waveform, (B) PPG features and clinical applications including basic features based on the original PPG waveform, combined features of PPG, and derivative features of PPG, (C) PPG noise including motion artifact baseline wandering and hypoperfusion, and (D) PPG signal processing including PPG preprocessing, PPG peak detection, and signal quality index. The application field of photoplethysmogram has been extending from the clinical to the mobile environment. Although there is no standardized pre-processing pipeline for PPG signal processing, as PPG data are acquired and accumulated in various ways, the recently proposed machine learning-based method is expected to offer a promising solution.

Self-reported Race/Ethnicity and Intraoperative Occult Hypoxemia: A Retrospective Cohort Study

BACKGROUND

Pulse oximetry is ubiquitous in anesthesia and is generally a reliable noninvasive measure of arterial oxygen saturation. Concerns regarding the impact of skin pigmentation and race/ethnicity on the accuracy of pulse oximeter accuracy exist. The authors hypothesized a greater prevalence of occult hypoxemia (arterial oxygen saturation [Sao2] less than 88% despite oxygen saturation measured by pulse oximetry [Spo2] greater than 92%) in patients undergoing anesthesia who self-reported a race/ethnicity other than White.

METHODS

Demographic and physiologic data, including self-reported race/ethnicity, were extracted from a departmental data warehouse for patients receiving an anesthetic that included at least one arterial blood gas between January 2008 and December 2019. Calculated Sao2 values were paired with concurrent Spo2 values for each patient. Analysis to determine whether Black, Hispanic, Asian, or Other race/ethnicities were associated with occult hypoxemia relative to White race/ethnicity within the Spo2 range of 92 to 100% was completed.

RESULTS

In total, 151,070 paired Sao2-Spo2 readings (70,722 White; 16,011 Black; 21,223 Hispanic; 8,121 Asian; 34,993 Other) from 46,253 unique patients were analyzed. The prevalence of occult hypoxemia was significantly higher in Black (339 of 16,011 [2.1%]) and Hispanic (383 of 21,223 [1.8%]) versus White (791 of 70,722 [1.1%]) paired Sao2-Spo2 readings (P < 0.001 for both). In the multivariable analysis, Black (odds ratio, 1.44 [95% CI, 1.11 to 1.87]; P = 0.006) and Hispanic (odds ratio, 1.31 [95% CI, 1.03 to 1.68]; P = 0.031) race/ethnicity were associated with occult hypoxemia. Asian and Other race/ethnicity were not associated with occult hypoxemia.

CONCLUSIONS

Self-reported Black and Hispanic race/ethnicity are associated with a greater prevalence of intraoperative occult hypoxemia in the Spo2 range of 92 to 100% when compared with self-reported White race/ethnicity.

EDITOR’S PERSPECTIVE

Exploring the impact of pulse oximeter selection within the COVID-19 home-use pulse oximetry pathways

Background

During the COVID-19 pandemic, portable pulse oximeters were issued to some patients to permit home monitoring and alleviate pressure on inpatient wards. Concerns were raised about the accuracy of these devices in some patient groups. This study was conducted in response to these concerns.

Objectives

To evaluate the performance characteristics of five portable pulse oximeters and their suitability for deployment on home-use pulse oximetry pathways created during the COVID-19 pandemic. This study considered the effects of different device models and patient characteristics on pulse oximeter accuracy, false negative and false positive rate.

Methods

A total of 915 oxygen saturation (s_pO₂) measurements, paired with measurements from a hospital-standard pulse oximeter, were taken from 50 patients recruited from respiratory wards and the intensive care unit at an acute hospital in London. The effects of device model and several patient characteristics on bias, false negative and false positive likelihood were evaluated using multiple regression analyses.

Results and conclusions

All five portable pulse oximeters appeared to outperform the standard to which they were manufactured. Device model, patient s_pO₂ and patient skin colour were significant predictors of measurement bias, false positive and false negative rate, with some variation between models. The false positive and false negative rates were 11.2% and 24.5%, respectively, with substantial variation between models.

Pulse Oximetry: The Working Principle, Signal Formation, and Applications

Pulse oximeters are routinely used in various medical-grade and consumer-grade applications. They can be used to estimate, for example, blood oxygen saturation, autonomic nervous system activity and cardiac function, blood pressure, sleep quality, and recovery through the recording of photoplethysmography signal. Medical-grade devices often record red and infra-red light-based photoplethysmography signals while smartwatches and other consumer-grade devices usually rely on a green light. At its simplest, a pulse oximeter can consist of one or two photodiodes and a photodetector attached, for example, a fingertip or earlobe. These sensors are used to record light absorption in a medium as a function of time. This time-varying absorption information is used to form a photoplethysmography signal. In this chapter, we discuss the working principles of pulse oximeters and the formation of the photoplethysmography signal. We will further discuss the advantages and disadvantages of pulse oximeters, which kind of applications exist in the medical field, and how pulse oximeters are utilized in daily health monitoring.

Racial discrepancy in pulse oximeter accuracy in preterm infants

OBJECTIVE

Pulse oximetry is commonly used in Neonatology, however recent adult data suggest racial disparity in accuracy, with overestimation of oxygen saturation for Black patients.

STUDY DESIGN

Black and White infants <32 weeks gestation underwent simultaneous arterial blood gas and pulse oximetry measurement. Error by race was examined using mean bias, Arms, Bland-Altman, and linear/non-linear analysis.

RESULTS

A total of 294 infants (124 Black, 170 White) were identified with mean GA of 25.8 ± 2.1 weeks and mean BW of 845 ± 265 grams, yielding 4387 SaO2-SpO2 datapoints. SpO2 overestimation, measured by mean bias, was 2.4-fold greater for Black infants and resulted in greater occult hypoxemia (SpO2 > 90% when SaO2 < 85%; 9.2% vs. 7.7% of samples). Sensitivity and specificity for detection of true hypoxemia were similar between groups (39 vs. 38%; 81 vs. 78%).

CONCLUSION

There is a modest but consistent difference in SpO2 error between Black and White infants, with increased incidence of occult hypoxemia in Black infants.

Evaluation of the performance of two new generation pulse oximeters in cats at different probe positions and under the influence of vasoconstriction

Objectives

The aim of this study was to compare the failure rate of two new generation pulse oximeters at different probe positions, and with and without vasoconstriction, in anaesthetised cats.

Methods

This prospective clinical study included 103 cats in which the new generation pulse oximeters, the Rad-5 (Masimo) and EDAN H100N (EDAN), were evaluated. Premedication consisted of the vasoconstrictive drug combination butorphanol (0.2 mg/kg IV) and dexmedetomidine (5 µg/kg IV), or butorphanol only (0.2 mg/kg IV). Pulse oximeter failure rate at the tongue was compared between both groups. Pulse oximeter failure rate was also analysed at the alternative probe positions of the lip, pinna, knee fold and toe in the butorphanol group. Student’s t-test, Wilcoxon matched pairs signed rank test, Mann−Whitney U-test, Friedman test and χ² test were performed. A P value <0.05 was considered to be statistically significant.

Results

Overall failure to achieve an adequate signal was 37.6% with the Masimo and 48.0% with the EDAN pulse oximeter (P <0.0001). At the standard probe position on the tongue, the Masimo failed in 4.5%, while the EDAN failed in 35.3% (P <0.0001). Vasoactive premedication increased the failure rate for the Masimo from 3.8% to 5.2% (P = 0.3414) and for the EDAN from 22.4% to 49.0% (P <0.0001). At the alternative probe positions of the lip and knee fold, failure rates for the Masimo were lower (39.7% and 81.4%) than with the EDAN (52.6% and 94.4%; P = 0.0231 and P = 0.0005, respectively), while the Masimo failed more often at the pinna (63.5%) than the EDAN (47.4%; P = 0.0044). At the alternative probe position of the toe, the failure rate for the Masimo (32.7%) was not different from the EDAN (38.5%; P = 0.7547).

Conclusions and relevance

The Masimo pulse oximeter had lower signal failure rates at the standard probe position on the tongue and at 2/4 alternative probe positions. The standard probe position on the tongue had the lowest failure rate for both devices. Dexmedetomidine-induced vasoconstriction increased the failure rate for the EDAN but not for the Masimo pulse oximeter.

The effect of patient ethnicity on the accuracy of peripheral pulse oximetry in patients with COVID-19 pneumonitis: a single-centre, retrospective analysis

Pulse oximetry is used widely to titrate oxygen therapy and for triage in patients who are critically ill. However, there are concerns regarding the accuracy of pulse oximetry in patients with COVID‐19 pneumonitis and in patients who have a greater degree of skin pigmentation. We aimed to determine the impact of patient ethnicity on the accuracy of peripheral pulse oximetry in patients who were critically ill with COVID‐19 pneumonitis by conducting a retrospective observational study comparing paired measurements of arterial oxygen saturation measured by co‐oximetry on arterial blood gas analysis (SaO₂) and the corresponding peripheral oxygenation saturation measured by pulse oximetry (S_pO₂). Bias was calculated as the mean difference between SaO₂ and S_pO₂ measurements and limits of agreement were calculated as bias ±1.96 SD. Data from 194 patients (135 White ethnic origin, 34 Asian ethnic origin, 19 Black ethnic origin and 6 other ethnic origin) were analysed consisting of 6216 paired SaO₂ and S_pO₂ measurements. Bias (limits of agreement) between SaO₂ and S_pO₂ measurements was 0.05% (−2.21–2.30). Patient ethnicity did not alter this to a clinically significant degree: 0.28% (1.79–2.35), −0.33% (−2.47–2.35) and −0.75% (−3.47–1.97) for patients of White, Asian and Black ethnic origin, respectively. In patients with COVID‐19 pneumonitis, S_pO₂ measurements showed a level of agreement with SaO₂ values that was in line with previous work, and this was not affected by patient ethnicity.

Performance of popular pulse oximeters compared with simultaneous arterial oxygen saturation or clinical-grade pulse oximetry: a cross-sectional validation study in intensive care patients

Objectives

To evaluate the performance of direct-to-consumer pulse oximeters under clinical conditions, with arterial blood gas measurement (SaO₂) as reference standard.

Design

Cross-sectional, validation study.

Setting

Intensive care.

Participants

Adult patients requiring SaO₂-monitoring.

Interventions

The studied oximeters are top-selling in Europe/USA (AFAC FS10D, AGPTEK FS10C, ANAPULSE ANP 100, Cocobear, Contec CMS50D1, HYLOGY MD-H37, Mommed YM101, PRCMISEMED F4PRO, PULOX PO-200 and Zacurate Pro Series 500 DL). Directly after collection of a SaO₂ blood sample, we obtained pulse oximeter readings (SpO₂). SpO₂-readings were performed in rotating order, blinded for SaO₂ and completed <10 min after blood sample collection.

Outcome measures

Bias (SpO₂–SaO₂) mean, root mean square difference (A_RMS), mean absolute error (MAE) and accuracy in identifying hypoxaemia (SaO₂ ≤90%). As a clinical index test, we included a hospital-grade SpO₂-monitor (Philips).

Results

In 35 consecutive patients, we obtained 2258 SpO₂-readings and 234 SaO₂-samples. Mean bias ranged from −0.6 to −4.8. None of the pulse oximeters met A_RMS ≤3%, the requirement set by International Organisation for Standardisation (ISO)-standards and required for Food and Drug Administration (FDA) 501(k)-clearance. The MAE ranged from 2.3 to 5.1, and five out of ten pulse oximeters met the requirement of ≤3%. For hypoxaemia, negative predictive values were 98%–99%. Positive predictive values ranged from 11% to 30%. Highest accuracy (95% CI) was found for Contec CMS50D1; 91% (86–94) and Zacurate Pro Series 500 DL; 90% (85–94). The hospital-grade SpO₂-monitor had an A_RMS of 3.0% and MAE of 1.9, and an accuracy of 95% (91%–97%).

Conclusion

Top-selling, direct-to-consumer pulse oximeters can accurately rule out hypoxaemia, but do not meet ISO-standards required for FDA-clearance

Repeatability and accuracy of fingertip pulse oximeters for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate in anesthetized dogs breathing 100% oxygen

OBJECTIVE

To evaluate the repeatability and accuracy of fingertip pulse oximeters (FPO) for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate (PR) in anesthetized dogs breathing 100% O₂.

ANIMALS

29 healthy client-owned anesthetized dogs undergoing various surgical procedures.

PROCEDURES

In randomized order, each of 7 FPOs or a reference pulse oximeter (PO) was applied to the tongue of each intubated anesthetized dog breathing 100% O₂. Duplicate measurements of oxygen saturation (Spo₂) and PR were obtained within 60 seconds of applying an FPO or PO. A nonparametric version of Bland-Altman analysis was used. Coefficient of repeatability was the interval between the 5th and 95th percentiles of the differences between duplicate measurements. Bias was the median difference, and the limits of agreement were the 5th and 95th percentiles of the differences between each FPO and the PO. Acceptable values for the coefficient of repeatability of Spo₂ were ≤ 6%. Agreements were accepted if the limits of agreement had an absolute difference of ≤ ± 3% in Spo₂ and relative difference of ≤ ± 10% in PR.

RESULTS

Coefficient of repeatability for Spo₂ was acceptable for 5 FPOs, but the limits of agreement for Spo₂ were unacceptable for all FPOs. The limits of agreement for PR were acceptable for 2 FPOs.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that some FPOs may be suitable for accurately monitoring PRs of healthy anesthetized dogs breathing 100% O₂, but mild underestimation of Spo₂ was common.

Effect of newborn screening for critical CHD on healthcare utilisation

OBJECTIVE

To evaluate the impact of state-mandated policies for pulse oximetry screening on healthcare utilisation, with a focus on use of echocardiograms.

DATA SOURCES/STUDY SETTING

Healthcare Cost and Utilisation Project, Statewide Inpatient Databases from 2008 to 2014 from six states.

METHODS

We defined pre- and post-mandate cohorts based on dates when pulse oximetry became mandated in each state. Linear segmented regression models for interrupted time series assessed associations between implementation of the screening and changes in rate of newborns with Critical CHD-negative echocardiogram results. We also evaluated the changes in rate of newborns who underwent echocardiogram but were not diagnosed with any health issues that could cause hypoxemia.

RESULTS

We identified 5967 critical CHD-negative echocardiograms (2847 and 3120 in the pre- and post-mandate periods, respectively). Our models detected a statistically significant increasing trend in rate of critical CHD-negative echocardiograms in the pre-mandate period (Incidence Rate Ratio: 1.08, p = 0.02), but did not detect any statistical differences in changes between pre- and post-mandate periods (Incidence Rate Ratio: 0.93, p = 0.14). Among non-Whites, an increasing trend of Critical CHD-negative echocardiogram during the pre-mandate period was detected (Incidence Rate Ratio 1.12, p < 0.01) and was attenuated during the post-mandate period (Incidence Rate Ratio 0.89, p = 0.02). Similar results were observed in the sensitivity analyses among both Whites and non-Whites.

CONCLUSIONS

Results suggest that mandatory state screening policies are associated with reductions in false-positive screening rates for hypoxemic conditions, with reductions primarily attributed to trends among non-Whites.

The Sensing Endotracheal Tube

Current pulse oximetry sensors are not very well suited to use in anaesthetised patients as it has been shown that during episodes of reduced peripheral circulation they do not function correctly or fail all together [1], [2]. To address this problem a new design for a photoplethysmography (PPG) endotracheal (ET) sensor to monitor pulse rate and oxygen saturation (SpO₂) internally is presented. Flexible printed circuit board (PCB) technology and miniature optoelectronic components have been implemented and integrated with a custom instrumentation system [3]. The sensor adheres and conforms to the curvature of standard french-gauge 7 and 8 ET tubes at the point just above the inflatable cuff within the laryngeal positioning markings. A 3D-modelled, optically clear, soft silicon encapsulation electronically and thermally isolates the electronic components whilst providing a smooth surface to aid the insertion on the ET tube during standard intubation procedures. A pilot study with 5 patients (3 Female, 2 Male), undergoing abdominal and limb laproscopic procedures has demonstrated the operation of the sensing ET tube, showing good quality red and infra-red PPG signals. Preliminary signal analysis reveals heart rate can be measured via PPG successfully, with saturation (SpO₂) readings in close agreement with the commercial monitors of 97.9 % (STD 0.2 %) and 98.6 % (STD 0.8 %) respectively.

Observational study on the influence of averaging time on oximetry results in infants and children

AIM

Oximetry values are influenced by the averaging time (AT) used. We aimed to evaluate the effect of different ATs on number, duration, mean single event and total integral of desaturations in preterm infants and children to convert between parameters obtained with different ATs.

METHODS

In a prospective observational study, 49 children underwent sleep laboratory-based polysomnography and 15 preterm infants were studied in the intensive care unit. Their raw red-to-infrared-saturation-data were reprocessed using seven different ATs (3-16 seconds). Desaturation thresholds were <80% (infants) and <90% (children), conversion formulas and their median percentage errors were calculated.

RESULTS

We found a linear relationship between the logarithms of the ATs and those of the desaturation parameters, leading to a conversion formula with different exponents. Based on this relationship, the number of desaturations decreased from AT = 3s to AT = 16s by factor 0.28 (children) and 0.18 (infants); total oxygen saturation integral decreased by factor 0.72 (children) and 0.48 (infants). The desaturation duration increased by factor 1.89 (children) and 3.34 (infants).

CONCLUSION

The number and total integral decreased, but the duration and mean single event integral increased with increasing AT. These changes were stronger in infants. Conversion formulas may facilitate comparisons between studies using different averaging times.

A Novel Photoplethysmography Sensor for Vital Signs Monitoring from the Human Trachea

Current pulse oximeter sensors can be challenged in working accurately and continuously in situations of reduced periphery perfusion, especially among anaesthetised patients. A novel tracheal photoplethysmography (PPG) sensor has been developed in an effort to address the limitations of current pulse oximeters. The sensor has been designed to estimate oxygen saturation (SpO2) and pulse rate, and has been manufactured on a flexible printed circuit board (PCB) that can adhere to a standard endotracheal (ET) tube. A pilot clinical trial was carried out as a feasibility study on 10 anaesthetised patients. Good quality PPGs from the trachea were acquired at red and infrared wavelengths in all patients. The mean SpO2 reading for the ET tube was 97.1% (SD 1.0%) vs. the clinical monitor at 98.7% (SD 0.7%). The mean pulse rate for the ET sensor was 65.4 bpm (SD 10.0 bpm) vs. the clinical monitor at 64.7 bpm (SD 9.9 bpm). This study supports the hypothesis that the human trachea could be a suitable monitoring site of SpO2 and other physiological parameters, at times where the periphery circulation might be compromised.

Pulse Oximeter for Low SpO2 Level Detection Using Discrete Time Signal Processing Algorithm

Oximeter is an important clinical device used for measuring peripheral capillary oxygen saturation (SpO2) in blood and hence accurate results are needed in order to help physicians predict clinical problems in the initial stage(s) of liver or kidney diagnosis. Different issues associated with the accuracy of SpO2 and heart rate measurement accuracy are studied in this work. With the understanding of these issues, a new SpO2 monitoring system is proposed that comprises of a better detection method, novel discrete time signal processing (DTSP) algorithm, and a custom-made oximeter probe head. The proposed SpO2 measurement system is capable of determining low levels of SpO2 present in human blood and produce the results in a short time that enable real-time monitoring of a patient SpO2. It can also distinguish low level of SpO2 against background noise.

Pulse Oximetry: A Survey of Knowledge among Staff of an Emergency Department

Introduction

Pulse oximetry measures arterial oxygen saturation and was introduced into the clinical field since the 1980s. It provides a simple, portable, non-invasive and inexpensive way for monitoring blood oxygen saturation. Previous studies demonstrated that most hospital staff had limited knowledge on the correct use of pulse oximetry and what might affect the readings. This study aimed at evaluating the extent of knowledge in pulse oximetry among the clinical staff of an emergency department.

Method

A 25-item multiple-choice type questionnaire was given to the medical and nursing staff of the Accident and Emergency Department (AED) of the Alice Ho Miu Ling Nethersole Hospital. In addition to demographic information, respondents were required to answer questions relating to the basic principles of pulse oximetry, recognition of physiological factors limiting its accuracy and management regarding hypothetical scenarios. The scores were expressed and analysed on a scale of 0–100.

Results

A total of 44 questionnaires were completed by 27 nurses and 17 doctors with their test scores ranging from 20 to 72 (median=46). Doctors (median=56) did better than nurses (median=44) in general (P=0.036) but this advantage, however, did not apply to questions on hypothetical scenarios where nurses performed better on the contrary. Correlation analysis proved that there was no linear relationship between respondents' test scores and their years of clinical experience (r=0.051, Spearman). This absence of linear relationship also applied to individual doctors (r=0.244, Spearman) and nurses groups (r=0.162, Spearman).

Conclusion

There was insufficient knowledge on the use of pulse oximetry among staff of the AED. The level of understanding did not correlate with their clinical experience. Training programs targeting both the fresh and the experienced staff are recommended.

The Accuracy of 6 Inexpensive Pulse Oximeters Not Cleared by the Food and Drug Administration: The Possible Global Public Health Implications

BACKGROUND

Universal access to pulse oximetry worldwide is often limited by cost and has substantial public health consequences. Low-cost pulse oximeters have become increasingly available with limited regulatory agency oversight. The accuracy of these devices often has not been validated, raising questions about performance.

METHODS

The accuracy of 6 low-cost finger pulse oximeters during stable arterial oxygen saturations (SaO2) between 70% and 100% was evaluated in 22 healthy subjects. Oximeters tested were the Contec CMS50DL, Beijing Choice C20, Beijing Choice MD300C23, Starhealth SH-A3, Jumper FPD-500A, and Atlantean SB100 II. Inspired oxygen, nitrogen, and carbon dioxide partial pressures were monitored and adjusted via a partial rebreathing circuit to achieve 10 to 12 stable target SaO2 plateaus between 70% and 100% and PaCO2 values of 35 to 45 mm Hg. Comparisons of pulse oximeter readings (SpO2) with arterial SaO2 (by Radiometer ABL90 and OSM3) were used to calculate bias (SpO2 - SaO2) mean, precision (SD of the bias), and root mean square error (ARMS).

RESULTS

Pulse oximeter readings corresponding to 536 blood samples were analyzed. Four of the 6 oximeters tested showed large errors (up to -6.30% mean bias, precision 4.30%, 7.53 ARMS) in estimating saturation when SaO2 was reduced <80%, and half of the oximeters demonstrated large errors when estimating saturations between 80% and 90%. Two of the pulse oximeters tested (Contec CMS50DL and Beijing Choice C20) demonstrated ARMS of <3% at SaO2 between 70% and 100%, thereby meeting International Organization for Standardization (ISO) criteria for accuracy.

CONCLUSIONS

Many low-cost pulse oximeters sold to consumers demonstrate highly inaccurate readings. Unexpectedly, the accuracy of some low-cost pulse oximeters tested here performed similarly to more expensive, ISO-cleared units when measuring hypoxia in healthy subjects. None of those tested here met World Federation of Societies of Anaesthesiologists standards, and the ideal testing conditions do not necessarily translate these findings to the clinical setting. Nonetheless, further development of accurate, low-cost oximeters for use in clinical practice is feasible and, if pursued, could improve access to safe care, especially in low-income countries.

The Effect of Skin Pigmentation on the Accuracy of Pulse Oximetry in Infants with Hypoxemia

To compare pulse oximetry measurement bias between infants with hypoxemia with either dark skin or light skin with Masimo Radical 7 and Nellcor Oximax. There was no significant difference in systematic bias based on skin pigment for either oximeter.

Assessing the tongue colour of newly born infants may help to predict the need for supplemental oxygen in the delivery room

AIM

It takes several minutes for infants to become pink after birth. Preductal oxygen saturation (SpO2) measurements are used to guide the delivery of supplemental oxygen to newly born infants, but pulse oximetry is not available in many parts of the world. We explored whether the pinkness of an infant's tongue provided a useful indication that supplemental oxygen was required.

METHODS

This was a prospective observational study of infants delivered by Caesarean section. Simultaneous recording of SpO2 and visual assessment of whether the tongue was pink or not was made at 1-7 and 10 min after birth.

RESULTS

The 38 midwives and seven paediatric trainees carried out 271 paired assessments on 68 infants with a mean (SD) birthweight of 3214 (545) grams and gestational age of 38 (2) weeks. When the infant did not have a pink tongue, this predicted SpO2 of <70% with a sensitivity of 26% and a specificity of 96%.

CONCLUSION

Tongue colour was a specific but insensitive sign that indicated when SpO2 was <70%. When the tongue is pink, it is likely that an infant has an SpO2 of more than 70% and does not require supplemental oxygen.

A conversion formula for comparing pulse oximeter desaturation rates obtained with different averaging times

Objective

The number of desaturations determined in recordings of pulse oximeter saturation (SpO₂) primarily depends on the time over which values are averaged. As the averaging time in pulse oximeters is not standardized, it varies considerably between centers. To make SpO₂ data comparable, it is thus desirable to have a formula that allows conversion between desaturation rates obtained using different averaging times for various desaturation levels and minimal durations.

Methods

Oxygen saturation was measured for 170 hours in 12 preterm infants with a mean number of 65 desaturations <90% per hour of arbitrary duration by using a pulse oximeter in a 2–4 s averaging mode. Using 7 different averaging times between 3 and 16 seconds, the raw red-to-infrared data were reprocessed to determine the number of desaturations (D). The whole procedure was carried out for 7 different minimal desaturation durations (≥1, ≥5, ≥10, ≥15, ≥20, ≥25, ≥30 s) below SpO₂ threshold values of 80%, 85% or 90% to finally reach a conversion formula. The formula was validated by splitting the infants into two groups of six children each and using one group each as a training set and the other one as a test set.

Results

Based on the linear relationship found between the logarithm of the desaturation rate and the logarithm of the averaging time, the conversion formula is: D₂ = D₁ (T₂/T₁)^c, where D₂ is the desaturation rate for the desired averaging time T₂, and D₁ is the desaturation rate for the original averaging time T₁, with the exponent c depending on the desaturation threshold and the minimal desaturation duration. The median error when applying this formula was 2.6%.

Conclusion

This formula enables the conversion of desaturation rates between different averaging times for various desaturation thresholds and minimal desaturation durations.

Clinical use of pulse oximetry: official guidelines from the Thoracic Society of Australia and New Zealand

Pulse oximetry provides a simple, non-invasive approximation of arterial oxygenation in a wide variety of clinical settings including emergency and critical-care medicine, hospital-based and ambulatory care, perioperative monitoring, inpatient and outpatient settings, and for specific diagnostic applications. Pulse oximetry is of utility in perinatal, paediatric, adult and geriatric populations but may require use of age-specific sensors in these groups. It plays a role in the monitoring and treatment of respiratory dysfunction by detecting hypoxaemia and is effective in guiding oxygen therapy in both adult and paediatric populations. Pulse oximetry does not provide information about the adequacy of ventilation or about precise arterial oxygenation, particularly when arterial oxygen levels are very high or very low. Arterial blood gas analysis is the gold standard in these settings. Pulse oximetry may be inaccurate as a marker of oxygenation in the presence of dyshaemoglobinaemias such as carbon monoxide poisoning or methaemoglobinaemia where arterial oxygen saturation values will be overestimated. Technical considerations such as sensor position, signal averaging time and data sampling rates may influence clinical interpretation of pulse oximetry readings.

Pulse oximetry in adults

Pulse oximetry, a straightforward method for estimating arterial oxygen saturation, can detect hypoxemia early; it's used often and in a variety of settings. But what's not always clear is how frequently-or even whether-patients should be monitored, and unless guidelines are understood and followed, pulse oximetry can be misused or overused. This article reviews the technology and its limitations and discusses current guidelines and their implications for nurses.

Diagnostic room-air pulse oximetry: effects of smoking, race, and sex

OBJECTIVE

We sought to determine the distribution of oximetry (SpO2) values in awake, asymptomatic adults and the effect of personal characteristics on these values.

METHODS

Using a cross-sectional design, we sampled oximetry readings in awake, asymptomatic adults in an emergency department setting. Personal characteristics were analyzed using logistic regression, with lower oximetry readings, defined by the 20th percentile, as the dependent variable.

RESULTS

Of 871 eligible subjects, 50 (5.7%) had an SpO2 value less than 97%, and 13 (1.5%) had an SpO2 value less than 96%. Lower readings were associated with the following characteristics (odds ratio with 95% confidence interval): male sex, 3.8 (2.5-5.6); age > or = 60 years, 2.4 (1.3-4.5); white race, 5.3 (3.6-7.8); obesity, 3.2 (2.1-4.8); history of asthma, 3.2 (1.6-6.2). Smoking was not associated with lower SpO2 values.

CONCLUSION

Room-air SpO2 values less than 97% are rare in asymptomatic, awake adults. White race and male sex are associated with lower SpO2 readings.

Transcutaneous Pco2 monitoring in critically ill adults: Clinical evaluation of a new sensor*

OBJECTIVE

In critically ill patients, arterial blood gas analysis is the gold standard for evaluating systemic oxygenation and carbon dioxide partial pressure. A new miniaturized carbon dioxide tension Pco2-Spo2 single sensor (TOSCA, Linde Medical Sensors AG, Basel, Switzerland) continuously and noninvasively (transcutaneously) monitors both Paco2 and oxygen saturation by pulse oximetry (Spo2). The present study was designed to investigate the usability and the accuracy of this device in critically ill patients.

DESIGN

Prospective clinical investigation.

SETTING

A 20-bed, university-affiliated, surgical intensive care unit.

PATIENTS

Patients admitted after major surgery, multiple trauma, or septic shock equipped with an arterial catheter.

INTERVENTIONS

The heated (42 degrees C) sensor was fixed at the earlobe using an attachment clip. Transcutaneous Pco2 (TcPco2) measurements were correlated with Paco2 values (measured using a blood gas analyzer). In addition, the differences between Paco2 and TcPco2 values were evaluated using the method of Bland-Altman.

MEASUREMENTS AND MAIN RESULTS

We studied 55 patients, aged 18-80 (mean 57 +/- 15) yrs. A total of 417 paired measurements were compared. Correlation between TcPco2 and Paco2 was r = .86 (p < .01) in the Paco2 range of 24-101 mm Hg. Mean bias (+/-sd) between the two methods of measurement (Bland-Altman analysis) was 1.2 +/- 6.0 mm Hg with TcPco2 slightly overestimating arterial carbon dioxide tension. Nineteen percent of the measured values were outside of the acceptable clinical range of agreement of +/-7.5 mm Hg.

CONCLUSIONS

The present study suggests that Paco2 can be acceptably assessed by measuring TcPco2 using the TOSCA Pco2-Spo2 sensor.

Racial variations in processes of care for patients with community-acquired pneumonia

BACKGROUND

Patients hospitalized with community acquired pneumonia (CAP) have a substantial risk of death, but there is evidence that adherence to certain processes of care, including antibiotic administration within 8 hours, can decrease this risk. Although national mortality data shows blacks have a substantially increased odds of death due to pneumonia as compared to whites previous studies of short-term mortality have found decreased mortality for blacks. Therefore we examined pneumonia-related processes of care and short-term mortality in a population of patients hospitalized with CAP.

METHODS

We reviewed the records of all identified Medicare beneficiaries hospitalized for pneumonia between 10/1/1998 and 9/30/1999 at one of 101 Pennsylvania hospitals, and randomly selected 60 patients at each hospital for inclusion. We reviewed the medical records to gather process measures of quality, pneumonia severity and demographics. We used Medicare administrative data to identify 30-day mortality. Because only a small proportion of the study population was black, we included all 240 black patients and randomly selected 720 white patients matched on age and gender. We performed a resampling of the white patients 10 times.

RESULTS

Males were 43% of the cohort, and the median age was 76 years. After controlling for potential confounders, blacks were less likely to receive antibiotics within 8 hours (odds ratio with 95% confidence interval 0.6, 0.4-0.97), but were as likely as whites to have blood cultures obtained prior to receiving antibiotics (0.7, 0.3-1.5), to have oxygenation assessed within 24 hours of presentation (1.6, 0.9-3.0), and to receive guideline concordant antibiotics (OR 0.9, 0.6-1.7). Black patients had a trend towards decreased 30-day mortality (0.4, 0.2 to 1.0).

CONCLUSION

Although blacks were less likely to receive optimal care, our findings are consistent with other studies that suggest better risk-adjusted survival among blacks than among whites. Further study is needed to determine why this is the case.

Interferência da coloração de esmaltes de unha e do tempo na oximetria de pulso em voluntários sadios

INTRODUÇÃO: A oximetria de pulso é um método não invasivo de mensuração da saturação periférica da oxiemoglobina (SpO2). É freqüentemente utilizado em unidades de emergência, de terapia intensiva e em centro cirúrgico. A leitura da oximetria de pulso tem acurácia limitada na presença de metaemoglobina, carboxiemoglobina, anemia, vasoconstrição periférica, esmalte de unha, luz fluorescente e movimentação. OBJETIVO: Avaliar a interferência da coloração de esmalte de unha e do tempo sobre a SpO2 em indivíduos sadios. MÉTODO: Participaram do estudo 61 voluntárias sadias, com idades entre 18 e 32 anos. Foi avaliada SpO2 nas seguintes colorações de esmaltes: base (dedo mínimo), rosa claro (dedo anular), rosa claro com cintilante (dedo médio) e vermelha (polegar). O indicador não recebeu esmalte. Foi analisado o tempo para cada coloração de esmalte, a cada minuto até completar cinco minutos. RESULTADOS: Quando comparadas as medidas da SpO2 com o controle, as colorações base (p = 0,56), rosa claro (p = 0,56) e rosa claro com cintilante (p = 0,37) não apresentaram diferença estatisticamente significante. A SpO2 apresentou variação significante na cor vermelha (p < 0,001), porém manteve-se dentro dos parâmetros de normalidade. Não houve variação significativa da SpO2 ao longo do tempo. CONCLUSÃO: Apesar da diferença encontrada com o uso de esmalte vermelho, todas as medidas da SpO2 obtidas encontraram-se dentro do intervalo de normalidade, para indivíduos normais. A análise de cada cor de esmalte de unha em relação ao tempo mostrou que não houve variação na leitura da SpO2 .

An Ethiopian pattern of human adaptation to high-altitude hypoxia

We describe, in Ethiopia, a third successful pattern of human adaptation to high-altitude hypoxia that contrasts with both the Andean "classic" (erythrocytosis with arterial hypoxemia) and the more recently identified Tibetan (normal venous hemoglobin concentration with arterial hypoxemia) patterns. A field survey of 236 Ethiopian native residents at 3,530 m (11,650 feet), 14-86 years of age, without evidence of iron deficiency, hemoglobinopathy, or chronic inflammation, found an average hemoglobin concentration of 15.9 and 15.0 gdl for males and females, respectively, and an average oxygen saturation of hemoglobin of 95.3%. Thus, Ethiopian highlanders maintain venous hemoglobin concentrations and arterial oxygen saturation within the ranges of sea level populations, despite the unavoidable, universal decrease in the ambient oxygen tension at high altitude.

Cardiopulmonary responses to exercise in women with sickle cell anemia

Multiple factors contribute to exercise intolerance in patients with sickle cell anemia, but little information exists regarding the safety of maximal cardiopulmonary exercise testing (CPET) or the mechanisms of exercise limitation in these patients. The purpose of the present study was to examine these issues. Seventeen adult women with sickle cell anemia underwent symptom-limited maximal CPET using cycle ergometry and ramp protocols; blood gases and lactate concentrations were measured every 2 minutes. All patients completed CPET without complications. No patient demonstrated a mechanical ventilatory limitation to exercise or had evidence of myocardial ischemia. However, we observed three pathophysiologic patterns of response to exercise in these patients. Eleven patients had low peak VO2, low anaerobic threshold (AT), gas exchange abnormalities, and high ventilatory reserve; this pattern is consistent with exercise limitation due to pulmonary vascular disease in this patient subgroup. Three patients had low peak VO2, low AT, no gas exchange abnormalities, and a high heart rate reserve, a pattern consistent with peripheral vascular disease and/or a myopathy. The remaining three patients had low peak VO2, low AT, no gas exchange abnormalities, and a low heart rate reserve; this pattern of exercise limitation is best explained by anemia.