Pulse Oximetry for Monitoring Patients with COVID-19 at Home. Potential Pitfalls and Practical Guidance

Home-Based Physiological Monitoring of Patients with COVID-19

The COVID-19 pandemic has necessitated the rise of telehealth modalities to relieve the incredible stress the pandemic has placed on the healthcare system. This rise has seen the emergence of new software, applications, and hardware for home-based physiological monitoring, leading to the promise of innovative predictive and therapeutic practices. This article is a literature-based review of the most promising technologies and advances regarding home-based physiological monitoring of patients with COVID-19. We conclude that the applications currently on the market, while helping stem the flow of patients to the hospital during the pandemic, require additional evidence related to improvement in patient outcomes. However, new devices and technology are a promising and successful venture into home-based monitoring with clinical implications reaching far into the future.

Impact of prone position on outcomes of COVID-19 patients with spontaneous breathing

Background

In this study, we explored whether early application of the prone position (PP) can improve severe hypoxemia and respiratory failure in coronavirus disease 2019 (COVID-19) patients with spontaneous breathing.

Methods

This is a prospective observational study of severe, critically ill adult COVID-19 patients admitted to the intensive care unit. All vital parameters were recorded in real time for all patients. Moreover, the results of chest computed tomography (CT), when available, were analyzed.

Results

PP was applied in 21 patients who were breathing spontaneously. The application of PP was associated with a significant increase in oxygen saturation measured by pulse oximetry (SpO₂) from 82%±12% to 96%±3% (P<0.001) 1 hour later. Moreover, PP was associated with a significant reduction in respiratory rate from 31±10 to 21±4 breaths/min (P<0.001). Furthermore, the number of patients who exhibited signs of respiratory distress after PP was reduced from 10 (47%) to 3 (14%) (P=0.04). Early PP application also led to a clear improvement on CT imaging. It was not, however, associated with a reduction in mortality rate or in the use of invasive mechanical ventilation (P>0.05 for both).

Conclusions

Our study confirmed that the early application of PP can improve hypoxemia and tachypnea in COVID-19 patients with spontaneous breathing. Randomized controlled trials are needed to confirm the beneficial effects of PP in COVID-19 patients with spontaneous breathing.

Placement of finger oximeter on the ear: comparison with oxygen saturation values taken from the finger

Pulse oximetry is widely used to assess oxygen saturation (SpO₂) in order to guide patient care and monitor the response to treatment. However, inappropriate oximeter probe placement has been shown to affect the measured oximetry values in healthy and normoxic outpatients. This study evaluated how treatment decisions might be impacted by SpO₂ values obtained using a finger probe placed on the pinna of the ear in a cohort of 46 patients receiving non-invasive ventilation compared with values obtained from a probe on the finger and the results of arterial blood gas (ABG) (SaO₂) analysis. Bland-Altman analysis was performed to evaluate agreement between the methods. Finger probe saturation was not statistically different from SaO₂, with a mean difference of -0.66% (P>0.05). Saturation from the ear was significantly different (-4.29%; P<0.001). Subgroup analysis in hypoxic patients (SaO₂<90%) showed a significant difference between ABG SaO₂, and finger and ear SpO₂. The study provides evidence that placement of a finger probe on the ear is unsafe clinical practice, potentially leading to patient mismanagement.

Developing a pulse oximetry home monitoring protocol for patients suspected with COVID-19 after emergency department discharge

Objectives

Patients with COVID-19 can present to the emergency department (ED) without immediate indication for admission, but with concern for decompensation. Clinical experience has demonstrated that critical illness may present later in the disease course and hypoxia is often the first indication of disease progression. The objectives of this study are to (a) assess feasibility and describe a protocol for ED-based outpatient pulse-oximetry monitoring with structured follow-up and (b) determine rates of ED return, hospitalisation and hypoxia among participants.

Methods

Prospective observational study of patients presenting to a single academic ED in Boston with suspected COVID-19. Eligible patients were adults being discharged from the ED with presumed COVID-19. Exclusion criteria included resting oxygen saturation <92%, ambulatory oxygen saturation <90%, heart rate >110 beats per minute or inability to use the device. Study personnel made scripted phone calls on postdischarge days 1, 3 and 7 to review the pulse-oximetry readings and to evaluate for decompensation. Return visit and admission information were collected via medical record and 28-day follow-up calls.

Results

81 patients were enrolled of which 10 (12%) developed hypoxia after their initial discharge from the ED. Overall, 23 (28%) of the 81 patients returned to the ED at least once and 10 of those who returned (43%) were admitted. We successfully contacted 76/81 (94%) of subjects via phone at least once for follow-up assessment.

Discussion

Patients are eager and willing to participate in home monitoring systems and are comfortable with using technology, which will allow providers and health systems to extend our hospitals capabilities for tracking patient populations in times of crisis.

Conclusions

It is feasible to implement an outpatient pulse-oximetry monitoring protocol to monitor patients discharged from the ED with confirmed or suspected COVID-19.

Remote home monitoring (virtual wards) for confirmed or suspected COVID-19 patients: a rapid systematic review

BACKGROUND

the aim of this review was to analyze the implementation and impact of remote home monitoring models (virtual wards) for confirmed or suspected COVID-19 patients, identifying their main components, processes of implementation, target patient populations, impact on outcomes, costs and lessons learnt.

METHODS

we carried out a rapid systematic review on models led by primary and secondary care across seven countries (US, Australia, Canada, The Netherlands, Ireland, China, UK). The main outcomes included in the review were: impact of remote home monitoring on virtual length of stay, escalation, emergency department attendance/reattendance, admission/readmission and mortality. The search was updated on February 2021. We used the PRISMA statement and the review was registered on PROSPERO (CRD: 42020202888).

FINDINGS

the review included 27 articles. The aim of the models was to maintain patients safe in the appropriate setting. Most models were led by secondary care and confirmation of COVID-19 was not required (in most cases). Monitoring was carried via online platforms, paper-based systems with telephone calls or (less frequently) through wearable sensors. Models based on phone calls were considered more inclusive. Patient/career training was identified as a determining factor of success. We could not reach substantive conclusions regarding patient safety and the identification of early deterioration due to lack of standardized reporting and missing data. Economic analysis was not reported for most of the models and did not go beyond reporting resources used and the amount spent per patient monitored.

INTERPRETATION

future research should focus on staff and patient experiences of care and inequalities in patients' access to care. Attention needs to be paid to the cost-effectiveness of the models and their sustainability, evaluation of their impact on patient outcomes by using comparators, and the use of risk-stratification tools.

Screening, Diagnostic and Prognostic Tests for COVID-19: A Comprehensive Review

While molecular testing with real-time polymerase chain reaction (RT-PCR) remains the gold-standard test for COVID-19 diagnosis and screening, more rapid or affordable molecular and antigen testing options have been developed. More affordable, point-of-care antigen testing, despite being less sensitive compared to molecular assays, might be preferable for wider screening initiatives. Simple laboratory, imaging and clinical parameters could facilitate prognostication and triage. This comprehensive review summarises current evidence on the diagnostic, screening and prognostic tests for COVID-19.

Screening, Diagnostic and Prognostic Tests for COVID-19: A Comprehensive Review

While molecular testing with real-time polymerase chain reaction (RT-PCR) remains the gold-standard test for COVID-19 diagnosis and screening, more rapid or affordable molecular and antigen testing options have been developed. More affordable, point-of-care antigen testing, despite being less sensitive compared to molecular assays, might be preferable for wider screening initiatives. Simple laboratory, imaging and clinical parameters could facilitate prognostication and triage. This comprehensive review summarises current evidence on the diagnostic, screening and prognostic tests for COVID-19.

Admission respiratory status predicts mortality in COVID-19

COVID-19 has significant case fatality. Glucocorticoids are the only treatment shown to improve survival, but only among patients requiring supplemental oxygen. WHO advises patients to seek medical care for "trouble breathing," but hypoxemic patients frequently have no respiratory symptoms. Our cohort study of hospitalized COVID-19 patients shows that respiratory symptoms are uncommon and not associated with mortality. By contrast, objective signs of respiratory compromise-oxygen saturation and respiratory rate-are associated with markedly elevated mortality. Our findings support expanding guidelines to include at-home assessment of oxygen saturation and respiratory rate in order to expedite life-saving treatments patients to high-risk COVID-19 patients.

Validation of the Withings ScanWatch as a Wrist-Worn Reflective Pulse Oximeter: Prospective Interventional Clinical Study

BACKGROUND

A decrease in the level of pulse oxygen saturation as measured by pulse oximetry (SpO2) is an indicator of hypoxemia that may occur in various respiratory diseases, such as chronic obstructive pulmonary disease (COPD), sleep apnea syndrome, and COVID-19. Currently, no mass-market wrist-worn SpO2 monitor meets the medical standards for pulse oximeters.

OBJECTIVE

The main objective of this monocentric and prospective clinical study with single-blind analysis was to test and validate the accuracy of the reflective pulse oximeter function of the Withings ScanWatch to measure SpO2 levels at different stages of hypoxia. The secondary objective was to confirm the safety of this device when used as intended.

METHODS

To achieve these objectives, we included 14 healthy participants aged 23-39 years in the study, and we induced several stable plateaus of arterial oxygen saturation (SaO2) ranging from 100%-70% to mimic nonhypoxic conditions and then mild, moderate, and severe hypoxic conditions. We measured the SpO2 level with a Withings ScanWatch on each participant's wrist and the SaO2 from blood samples with a co-oximeter, the ABL90 hemoximeter (Radiometer Medical ApS).

RESULTS

After removal of the inconclusive measurements, we obtained 275 and 244 conclusive measurements with the two ScanWatches on the participants' right and left wrists, respectively, evenly distributed among the 3 predetermined SpO2 groups: SpO2≤80%, 80%

CONCLUSIONS

In conclusion, the Withings ScanWatch is able to measure SpO2 levels with adequate accuracy at a clinical grade. No undesirable effects or adverse events were reported during the study.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04380389; http://clinicaltrials.gov/ct2/show/NCT04380389.

Collapse

Key Words

• COPD
• COVID-19
• SpO2
• Withings ScanWatch
• accuracy
• connected watch
• neural network
• oximeter
• oxygen
• pulse oxygen saturation
• reflective pulse oximeter
• respiratory
• respiratory disease
• safety
• sleep apnea syndrome
• validation
• wearable

Collapse

MESH Headings

• Adult
• Female
• Humans
• Male
• Young Adult
• COVID-19/blood
• COVID-19/complications
• Healthy Volunteers
• Hypoxia/blood
• Hypoxia/complications
• Lung Diseases/blood
• Lung Diseases/complications
• Monitoring, Physiologic
• Oximetry/adverse effects
• Oximetry/standards
• Oxygen/blood
• Prospective Studies
• Single-Blind Method
• Wrist

Collapse

Grants Collapse

Affiliation(s)

Romain Kirszenblat Withings, Issy-Les-Moulineaux, France
Paul Edouard Withings, Issy-Les-Moulineaux, France

Collapse

Silent hypoxia in COVID-19: pathomechanism and possible management strategy

The novel coronavirus disease 2019 (COVID-19) has become a severe health issue, especially to the patients who develop silent hypoxia condition after SARS-CoV-2 infection. Due to the lack of dyspnoea and extremely low oxygen saturation level, these patients are at exceptionally higher risk. Although the prevalence of silent hypoxia in COVID-19 patients has been evident in several cases, the underlying pathomechanism behind this condition is still unclear. Silent hypoxia in SARS-CoV-2 infected patients can be diagnosed with the help of a pulse oximeter, blood gas levels, and a 6-min walking test. While the clinicians and researchers figure out the exact reason for this phenomenon, the patients must be under strict day-to-day monitoring. In this article, we aim to provide comprehensive insights into the underlying symptoms, mechanism, and possible factors behind the occurrence of silent hypoxia among COVID-19 patients.

[Pulse oximetry: Role in the COVID-19 patient at home]

La COVID-19 se comporta como una enfermedad heterogénea. Algunos pacientes pueden presentar hipoxemia sin disnea durante su evolución (hipoxemia silente). La pulsioximetría juega un papel crucial en la detección de la hipoxemia en estos pacientes, especialmente cuando permanecen en su domicilio. Pacientes con niveles de SpO₂ ≤ 92% o desaturaciónes ≥ 3% tras el ejercicio precisan de ingreso hospitalario. Los descensos progresivos de la saturación que alcancen niveles SpO₂ < 96% precisan de valoración clínica estricta (estudio radiológico, analítica sanguínea) para lo que será enviado a un centro sanitario.

Post-acute COVID-19 syndrome

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the pathogen responsible for the coronavirus disease 2019 (COVID-19) pandemic, which has resulted in global healthcare crises and strained health resources. As the population of patients recovering from COVID-19 grows, it is paramount to establish an understanding of the healthcare issues surrounding them. COVID-19 is now recognized as a multi-organ disease with a broad spectrum of manifestations. Similarly to post-acute viral syndromes described in survivors of other virulent coronavirus epidemics, there are increasing reports of persistent and prolonged effects after acute COVID-19. Patient advocacy groups, many members of which identify themselves as long haulers, have helped contribute to the recognition of post-acute COVID-19, a syndrome characterized by persistent symptoms and/or delayed or long-term complications beyond 4 weeks from the onset of symptoms. Here, we provide a comprehensive review of the current literature on post-acute COVID-19, its pathophysiology and its organ-specific sequelae. Finally, we discuss relevant considerations for the multidisciplinary care of COVID-19 survivors and propose a framework for the identification of those at high risk for post-acute COVID-19 and their coordinated management through dedicated COVID-19 clinics.

Prehospital hypoxemia, measured by pulse oximetry, predicts hospital outcomes during the New York City COVID-19 pandemic

OBJECTIVE

To determine if oxygen saturation (out-of-hospital SpO2), measured by New York City (NYC) 9-1-1 Emergency Medical Services (EMS), was an independent predictor of coronavirus disease 2019 (COVID-19) in-hospital mortality and length of stay, after controlling for the competing risk of death. If so, out-of-hospital SpO2 could be useful for initial triage.

METHODS

A population-based longitudinal study of adult patients transported by EMS to emergency departments (ED) between March 5 and April 30, 2020 (the NYC COVID-19 peak period). Inclusion required EMS prehospital SpO2 measurement while breathing room air, transport to emergency department, and a positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reverse transcription polymerase chain reaction test. Multivariable logistic regression modeled mortality as a function of prehospital SpO2, controlling for covariates (age, sex, race/ethnicity, and comorbidities). A competing risk model also was performed to estimate the absolute risks of out-of-hospital SpO2 on the cumulative incidence of being discharged from the hospital alive.

RESULTS

In 1673 patients, out-of-hospital SpO2 and age were independent predictors of in-hospital mortality and length of stay, after controlling for the competing risk of death. Among patients ≥66 years old, the probability of death was 26% with an out-of-hospital SpO2 >90% versus 54% with an out-of-hospital SpO2 ≤90%. Among patients <66 years old, the probability of death was 11.5% with an out-of-hospital SpO2 >90% versus 31% with an out-of-hospital SpO2 ≤ 90%. An out-of-hospital SpO2 level ≤90% was associated with over 50% decreased likelihood of being discharged alive, regardless of age.

CONCLUSIONS

Out-of-hospital SpO2 and age predicted in-hospital mortality and length of stay: An out-of-hospital SpO2 ≤90% strongly supports a triage decision for immediate hospital admission. For out-of-hospital SpO2 >90%, the decision to admit depends on multiple factors, including age, resource availability (outpatient vs inpatient), and the potential impact of new treatments.

How to Treat COVID-19 Patients at Home in the Italian Context: An Expert Opinion

The impact of the coronavirus disease (COVID-19), caused by the novel coronavirus SARS-CoV-2, continues to be widespread, with more than 100 million cases diagnosed in more than 220 countries since the virus was first identified in January 2020. Although patients with mild to moderate forms of COVID-19 could be efficiently managed at home, thus reducing the pressure on the healthcare system and minimizing socio-psychological impact on patients, no trial has been proposed, conducted, or even published on COVID-19 home therapy to date. These expert opinions provide indications on the therapeutical at home management of COVID-19 patients, based on the evidence from the literature and on current guidelines.

Clinical prediction rule for SARS-CoV-2 infection from 116 U.S. emergency departments 2-22-2021

Objectives

Accurate and reliable criteria to rapidly estimate the probability of infection with the novel coronavirus-2 that causes the severe acute respiratory syndrome (SARS-CoV-2) and associated disease (COVID-19) remain an urgent unmet need, especially in emergency care. The objective was to derive and validate a clinical prediction score for SARS-CoV-2 infection that uses simple criteria widely available at the point of care.

Methods

Data came from the registry data from the national REgistry of suspected COVID-19 in EmeRgency care (RECOVER network) comprising 116 hospitals from 25 states in the US. Clinical variables and 30-day outcomes were abstracted from medical records of 19,850 emergency department (ED) patients tested for SARS-CoV-2. The criterion standard for diagnosis of SARS-CoV-2 required a positive molecular test from a swabbed sample or positive antibody testing within 30 days. The prediction score was derived from a 50% random sample (n = 9,925) using unadjusted analysis of 107 candidate variables as a screening step, followed by stepwise forward logistic regression on 72 variables.

Results

Multivariable regression yielded a 13-variable score, which was simplified to a 13-point score: +1 point each for age>50 years, measured temperature>37.5°C, oxygen saturation<95%, Black race, Hispanic or Latino ethnicity, household contact with known or suspected COVID-19, patient reported history of dry cough, anosmia/dysgeusia, myalgias or fever; and -1 point each for White race, no direct contact with infected person, or smoking. In the validation sample (n = 9,975), the probability from logistic regression score produced an area under the receiver operating characteristic curve of 0.80 (95% CI: 0.79–0.81), and this level of accuracy was retained across patients enrolled from the early spring to summer of 2020. In the simplified score, a score of zero produced a sensitivity of 95.6% (94.8–96.3%), specificity of 20.0% (19.0–21.0%), negative likelihood ratio of 0.22 (0.19–0.26). Increasing points on the simplified score predicted higher probability of infection (e.g., >75% probability with +5 or more points).

Conclusion

Criteria that are available at the point of care can accurately predict the probability of SARS-CoV-2 infection. These criteria could assist with decisions about isolation and testing at high throughput checkpoints.

Diagnostic accuracy of subjective dyspnoea in detecting hypoxaemia among outpatients with COVID-19: a retrospective cohort study

OBJECTIVES

The majority of patients with mild-to-moderate COVID-19 can be managed using virtual care. Dyspnoea is challenging to assess remotely, and the accuracy of subjective dyspnoea measures in capturing hypoxaemia have not been formally evaluated for COVID-19. We explored the accuracy of subjective dyspnoea in diagnosing hypoxaemia in COVID-19 patients.

METHODS

This is a retrospective cohort study of consecutive outpatients with COVID-19 who met criteria for home oxygen saturation monitoring at a university-affiliated acute care hospital in Toronto, Canada from 3 April 2020 to 13 September 2020. Dyspnoea measures were treated as diagnostic tests, and we determined their sensitivity (SN), specificity (SP), negative/positive predictive value (NPV/PPV) and positive/negative likelihood ratios (+LR/-LR) for detecting hypoxaemia. In the primary analysis, hypoxaemia was defined by oxygen saturation <95%; the diagnostic accuracy of subjective dyspnoea was also assessed across a range of oxygen saturation cutoffs from 92% to 97%.

RESULTS

During the study period, 89/501 (17.8%) of patients met criteria for home oxygen saturation monitoring, and of these 17/89 (19.1%) were diagnosed with hypoxaemia. The presence/absence of dyspnoea had limited accuracy for diagnosing hypoxaemia, with SN 47% (95% CI 24% to 72%), SP 80% (95% CI 68% to 88%), NPV 86% (95% CI 75% to 93%), PPV 36% (95% CI 18% to 59%), +LR 2.4 (95% CI 1.2 to 4.7) and -LR 0.7 (95% CI 0.4 to 1.1). The SN of dyspnoea was 50% (95% CI 19% to 81%) when a cut-off of <92% was used to define hypoxaemia. A modified Medical Research Council dyspnoea score >1 (SP 98%, 95% CI 88% to 100%), Roth maximal count <12 (SP 100%, 95% CI 75% to 100%) and Roth counting time <8 s (SP 93%, 95% CI 66% to 100%) had high SP that could be used to rule in hypoxaemia, but displayed low SN (≤50%).

CONCLUSIONS

Subjective dyspnoea measures have inadequate accuracy for ruling out hypoxaemia in high-risk patients with COVID-19. Safe home management of patients with COVID-19 should incorporate home oxygenation saturation monitoring.

Reliability of Smartphone Pulse Oximetry in Subjects at Risk for Hypoxemia

BACKGROUND

Pulse oximeters are used to measure [Formula: see text] and pulse rate. These devices are either standalone machines or integrated into physiologic monitoring systems. Some smartphones now have pulse oximetry capabilities. Because it is possible that some patients might utilize this technology, we sought to assess the accuracy and usability of smartphone pulse oximeters.

METHODS

This was a prospective, observational study that involved noninvasive measurements of [Formula: see text] and heart rate with 3 devices: Masimo Radical-7, Kenek Edge with the Apple iPhone 6S, and the Samsung S8 smartphone. Ambulatory adult patients visiting our institution's pulmonary function lab for a 6-min walk test were eligible to participate in the study. Pretest and posttest results for each subject were obtained simultaneously using all 3 devices. All results were analyzed with the Spearman rho correlation test, and Bland-Altman plots were used to assess the agreement of measures between the devices.

RESULTS

Forty-seven subjects were enrolled in the study, with pulmonary hypertension (30%) and COPD (23%) being the 2 major diagnoses. The mean ± SD difference between the Masimo and Apple devices for pretest [Formula: see text] was 2.3 ± 2.4%, and the difference for posttest [Formula: see text] was 2.1 ± 3.9%. The mean difference between the Masimo and Samsung devices for pretest [Formula: see text] was 3.2 ± 2.8%, and the difference for posttest [Formula: see text] was 2.4 ± 3.5%. The number of subjects who were unable to obtain [Formula: see text] was higher with the Samsung device than with the Apple device in both pretest (14 of 47 vs 3 of 47) and posttest (17 of 47 vs 5 of 47). In contrast, the Masimo device was able to measure [Formula: see text] in all subjects.

CONCLUSIONS

Smartphone pulse oximeters were unreliable compared to a hospital pulse oximeter. Further research is needed with evolving technology to better understand smartphone pulse oximetry. (ClinicalTrials.gov registration NCT03534271.).

ESC working group on e-cardiology position paper: use of commercially available wearable technology for heart rate and activity tracking in primary and secondary cardiovascular prevention-in collaboration with the European Heart Rhythm Association, European Association of Preventive Cardiology, Association of Cardiovascular Nursing and Allied Professionals, Patient Forum, and the Digital Health Committee

Commercially available health technologies such as smartphones and smartwatches, activity trackers and eHealth applications, commonly referred to as wearables, are increasingly available and used both in the leisure and healthcare sector for pulse and fitness/activity tracking. The aim of the Position Paper is to identify specific barriers and knowledge gaps for the use of wearables, in particular for heart rate (HR) and activity tracking, in clinical cardiovascular healthcare to support their implementation into clinical care. The widespread use of HR and fitness tracking technologies provides unparalleled opportunities for capturing physiological information from large populations in the community, which has previously only been available in patient populations in the setting of healthcare provision. The availability of low-cost and high-volume physiological data from the community also provides unique challenges. While the number of patients meeting healthcare providers with data from wearables is rapidly growing, there are at present no clinical guidelines on how and when to use data from wearables in primary and secondary prevention. Technical aspects of HR tracking especially during activity need to be further validated. How to analyse, translate, and interpret large datasets of information into clinically applicable recommendations needs further consideration. While the current users of wearable technologies tend to be young, healthy and in the higher sociodemographic strata, wearables could potentially have a greater utility in the elderly and higher-risk population. Wearables may also provide a benefit through increased health awareness, democratization of health data and patient engagement. Use of continuous monitoring may provide opportunities for detection of risk factors and disease development earlier in the causal pathway, which may provide novel applications in both prevention and clinical research. However, wearables may also have potential adverse consequences due to unintended modification of behaviour, uncertain use and interpretation of large physiological data, a possible increase in social inequality due to differential access and technological literacy, challenges with regulatory bodies and privacy issues. In the present position paper, current applications as well as specific barriers and gaps in knowledge are identified and discussed in order to support the implementation of wearable technologies from gadget-ology into clinical cardiology.

Accuracy of Samsung Smartphone Integrated Pulse Oximetry Meets Full FDA Clearance Standards for Clinical Use

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.1,2,3,4 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 Africa5. 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 (SaO2) 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 SaO2 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 (SpO2) 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 SpO2 measurements to support at home assessment of COVID-19 patients.

The Use of Pulse Oximetry in the Assessment of Acclimatization to High Altitude

Background: Finger pulse oximeters are widely used to monitor physiological responses to high-altitude exposure, the progress of acclimatization, and/or the potential development of high-altitude related diseases. Although there is increasing evidence for its invaluable support at high altitude, some controversy remains, largely due to differences in individual preconditions, evaluation purposes, measurement methods, the use of different devices, and the lacking ability to interpret data correctly. Therefore, this review is aimed at providing information on the functioning of pulse oximeters, appropriate measurement methods and published time courses of pulse oximetry data (peripheral oxygen saturation, (SpO₂) and heart rate (HR), recorded at rest and submaximal exercise during exposure to various altitudes. Results: The presented findings from the literature review confirm rather large variations of pulse oximetry measures (SpO₂ and HR) during acute exposure and acclimatization to high altitude, related to the varying conditions between studies mentioned above. It turned out that particularly SpO₂ levels decrease with acute altitude/hypoxia exposure and partly recover during acclimatization, with an opposite trend of HR. Moreover, the development of acute mountain sickness (AMS) was consistently associated with lower SpO₂ values compared to individuals free from AMS. Conclusions: The use of finger pulse oximetry at high altitude is considered as a valuable tool in the evaluation of individual acclimatization to high altitude but also to monitor AMS progression and treatment efficacy.

Silent hypoxaemia in COVID-19 patients

The clinical presentation of COVID-19 due to infection with SARS-CoV-2 is highly variable with the majority of patients having mild symptoms while others develop severe respiratory failure. The reason for this variability is unclear but is in critical need of investigation. Some COVID-19 patients have been labelled with 'happy hypoxia', in which patient complaints of dyspnoea and observable signs of respiratory distress are reported to be absent. Based on ongoing debate, we highlight key respiratory and neurological components that could underlie variation in the presentation of silent hypoxaemia and define priorities for subsequent investigation.

Silent hypoxaemia in COVID-19 patients

The clinical presentation of COVID-19 due to infection with SARS-CoV-2 is highly variable with the majority of patients having mild symptoms while others develop severe respiratory failure. The reason for this variability is unclear but is in critical need of investigation. Some COVID-19 patients have been labelled with 'happy hypoxia', in which patient complaints of dyspnoea and observable signs of respiratory distress are reported to be absent. Based on ongoing debate, we highlight key respiratory and neurological components that could underlie variation in the presentation of silent hypoxaemia and define priorities for subsequent investigation.

An Evolving Clinical Need: Discordant Oxygenation Measurements of Intubated COVID-19 Patients

Since the first appearance of the severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) earlier this year, clinicians and researchers alike have been faced with dynamic, daily challenges of recognizing, understanding, and treating the coronavirus disease 2019 (COVID-19) due to SARS-CoV-2. Those who are moderately to severely ill with COVID-19 are likely to develop acute hypoxemic respiratory failure and require administration of supplemental oxygen. Assessing the need to initiate or titrate oxygen therapy is largely dependent on evaluating the patient’s existing blood oxygenation status, either by direct arterial blood sampling or by transcutaneous arterial oxygen saturation monitoring, also referred to as pulse oximetry. While the sampling of arterial blood for measurement of dissolved gases provides a direct measurement, it is technically challenging to obtain, is painful to the patient, and can be time and resource intensive. Pulse oximetry allows for non-invasive, real-time, continuous monitoring of the percent of hemoglobin molecules that are saturated with oxygen, and usually closely predicts the arterial oxygen content. As such, it was particularly concerning when patients with severe COVID-19 requiring endotracheal intubation and mechanical ventilation within one of our intensive care units were observed to have significant discordance between their predicted arterial oxygen content via pulse oximetry and their actual measured oxygen content. We offer these preliminary observations along with our speculative causes as a timely, urgent clinical need. In the setting of a COVID-19 intensive care unit, entering a patient room to obtain a fresh arterial blood gas sample not only takes exponentially longer to do given the time required for donning and doffing of personal protective equipment (PPE), it involves the consumption of already sparce PPE, and it increases the risk of viral exposure to the nurse, physician, or respiratory therapist entering the room to obtain the sample. As such, technology similar to pulse oximetry which can be applied to a patients finger, and then continuously monitored from outside the room is essential in preventing a particularly dangerous situation of unrealized hypoxia in this critically-ill patient population. Additionally, it would appear that conventional two-wavelength pulse oximetry may not accurately predict the arterial oxygen content of blood in these patients. This discordance of oxygenation measurements poses a critical concern in the evaluation and management of the acute hypoxemic respiratory failure seen in patients with COVID-19.

Working accuracy of pulse oximetry in COVID-19 patients stepping down from intensive care: a clinical evaluation

Introduction

UK guidelines suggest that pulse oximetry, rather than blood gas sampling, is adequate for monitoring of patients with COVID-19 if CO₂ retention is not suspected. However, pulse oximetry has impaired accuracy in certain patient groups, and data are lacking on its accuracy in patients with COVID-19 stepping down from intensive care unit (ICU) to non-ICU settings or being transferred to another ICU.

Methods

We assessed the bias, precision and limits of agreement using 90 paired SpO₂ and SaO₂ from 30 patients (3 paired samples per patient). To assess the agreement between pulse oximetry (SpO₂) and arterial blood gas analysis (SaO₂) in patients with COVID-19, deemed clinically stable to step down from an ICU to a non-ICU ward, or be transferred to another ICU. This was done to evaluate whether the guidelines were appropriate for our setting.

Results

Mean difference between SaO₂ and SpO₂ (bias) was 0.4%, with an SD of 2.4 (precision). The limits of agreement between SpO₂ and SaO₂ were as follows: upper limit of 5.2% (95% CI 6.5% to 4.2%) and lower limit of −4.3% (95% CI −3.4% to −5.7%).

Conclusions

In our setting, pulse oximetry showed a level of agreement with SaO₂ measurement that was slightly suboptimal, although within acceptable levels for Food and Drug Authority approval, in people with COVID-19 judged clinically ready to step down from ICU to a non-ICU ward, or who were being transferred to another hospital’s ICU. In such patients, SpO₂ should be interpreted with caution. Arterial blood gas assessment of SaO₂ may still be clinically indicated.