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. 2024 Mar;69(3):281–289. doi: 10.4187/respcare.11436

Home Oxygen After Hospitalization for COVID-19: Results From the Multi-Center OXFORD Study

Michael B Freedman 1,✉, Yoo Jin Kim 1, Ramandeep Kaur 1, Bijal V Jain 1, Ayodeji O Adegunsoye 1, Yu-Che Chung 1, Julie A DeLisa 1, Jessica M Gardner 1, Howard S Gordon 1, Jared A Greenberg 1, Malvika Kaul 1, Nader Khouzam 1, Stephanie L Labedz 1, Babak Mokhlesi 1, Jacob Rintz 1, Israel Rubinstein 1, Analisa Taylor 1, David L Vines 1, Lubna Ziauddin 1, Lynn B Gerald 1, Jerry A Krishnan 1
PMCID: PMC10984596  PMID: 38176902

Abstract

BACKGROUND:

In the first months of the pandemic, prior to the introduction of proven-effective treatments, 15–37% of patients hospitalized with COVID-19 were discharged on home oxygen. After proven-effective treatments for acute COVID-19 were established by evidence-based guidelines, little remains known about home oxygen requirements following hospitalization for COVID-19.

METHODS:

This was a retrospective, multi-center cohort study of subjects hospitalized for COVID-19 between October 2020–September 2021 at 3 academic health centers. Information was abstracted from electronic health records at the index hospitalization and for 60 d after discharge. The World Health Organization COVID-19 Clinical Progression Scale score was used to identify patients with severe COVID-19.

RESULTS:

Of 517 subjects (mean age 58 y, 47% female, 42% Black, 36% Hispanic, 22% with severe COVID-19), 81% were treated with systemic corticosteroids, 61% with remdesivir, and 2.5% with tocilizumab. About one quarter of subjects were discharged on home oxygen (26% [95% CI 22–29]). Older age (adjusted odds ratio [aOR] 1.02 per 5 y [95% CI 1.02–1.02]), higher body mass index (aOR 1.02 per kg/m2 [1.00–1.04]), diabetes (yes vs no, aOR 1.73 [1.46–2.02]), severe COVID-19 (vs moderate, aOR 3.19 [2.19–4.64]), and treatment with systemic corticosteroids (yes vs no, aOR 30.63 [4.51–208.17]) were associated with an increased odds of discharge on home oxygen. Comorbid hypertension (yes vs no, aOR 0.71 [0.66–0.77) was associated with a decreased odds of home oxygen. Within 60 d of hospital discharge, 50% had documentation of pulse oximetry; in this group, home oxygen was discontinued in 46%.

CONCLUSIONS:

About one in 41 subjects were prescribed home oxygen after hospitalization for COVID-19, even after guidelines established proven-effective treatments for acute illness. Evidence-based strategies to reduce the requirement for home oxygen in patients hospitalized for COVID-19 are needed.

Keywords: hypoxemia, Long COVID, SARS-CoV-2l, post-acute sequelae of SARS-CoV-2, durable medical equipment

Introduction

The consequences of COVID-19, caused by SARS-CoV-2, can vary from mild or asymptomatic disease to acute respiratory failure and death. Since the start of the COVID-19 pandemic in March 2020,1 there have been over 6.4 million hospitalizations and 1.1 million deaths due to COVID-19 in the United States alone (https://covid.cdc.gov/covid-data-tracker/#datatracker-home. Accessed November 1, 2023). Starting in late spring and early summer of 2020, the National Institutes of Health began recommending systemic corticosteroids and remdesivir for patients hospitalized with COVID-192 based on the results of clinical trials that demonstrated a reduction in the risk of death3 and time to recovery,4 respectively. Coincident with these developments, the ancestral SARS-CoV-2 virus was replaced with a series of variants, each with differences in transmissibility, morbidity, and mortality.5 Multiple factors, including the use of effective treatments and changes in the prevalent viral variants, likely contributed to a 40% reduction in the infection-fatality ratio during the first year of the pandemic.6

The pulmonary consequences of COVID-19 are not limited to the acute illness following infection with SARS-CoV-2. Patients may experience long-lasting pulmonary symptoms or develop new pulmonary conditions, including chronic hypoxemia.7 Studies in subjects hospitalized for COVID-19 from February–May 2020 reported that 15–37% required home supplemental oxygen therapy (home oxygen) after hospital discharge.8-11 Whether there has been a reduction in the need for home oxygen after the introduction of proven-effective treatments is unclear. Likewise, little is known about the risk factors for discharge on home oxygen in patients hospitalized with COVID-19 or the duration of home oxygen requirements after hospital discharge. Addressing these knowledge gaps would help to inform the need for developing evidence-based strategies to reduce the requirement for home oxygen in patients hospitalized for COVID-19.

The primary objective of this study was to estimate the proportion of subjects discharged on home oxygen among oxygen-naïve individuals hospitalized with COVID October 19, 2020–September 2021, a period in which the prevalent viral variants continued to evolve5 and proven-effective vaccines12-14 and medication for acute COVID-1915 were recommended by guidelines. The secondary objectives were to (1) assess changes over time in the proportion of subjects discharged on home oxygen during the study period, (2) identify subject characteristics and treatments associated with initiation of home oxygen on hospital discharge, and (3) determine if requirements for home oxygen persisted in the 60 d after hospital discharge.

QUICK LOOK.

Current knowledge

In the first few months of the pandemic, prior to the identification of proven-effective vaccines to prevent COVID-19 and treatments for acute COVID-19, various studies reported that 15–37% of subjects hospitalized for COVID-19 required home supplemental oxygen therapy at hospital discharge.

What this paper contributes to our knowledge

Despite changes in the prevalent viral variants and the introduction of evidence-based recommendations to prevent and treat acute COVID-19, the proportion of subjects prescribed home supplemental oxygen following COVID-19 hospitalizations remained stubbornly high (26%). Home oxygen prescription was associated with obesity, greater comorbidities, more severe illness and older age. Half of subjects discontinued home oxygen at 60 days post discharge.

Methods

Setting and Subject Population

The OXygen status Following hOspitalization with coRonavirus Disease 2019 (OXFORD) study was a retrospective multi-center cohort study at 3 university-affiliated hospitals in Chicago, Illinois (see expanded methods, e-Appendix 1; see related supplementary materials at http://www.rcjournal.com). The study protocol was determined to be exempt by the institutional review boards at each of the participating institutions (Rush: number 22011401-IRB01; UI Health: number STUDY2022-1101; JBVA: 1673353).

We employed a 3-stage sampling process to identify eligible patients. In stage 1, we queried the electronic health records (EHRs) to identify patients who were (1) 18 y or older on the date of hospitalization at a study hospital; (2) admitted to the hospital on a date between October 1, 2020–September 31, 2021; and (3) positive on a laboratory test for SARS-CoV-2. Because of limited availability of research staff across the 3 study hospitals, a random 25% or 50% sample of patients identified in stage 1 was selected for manual chart review and data abstraction (stage 2). In stage 2, patients were excluded from the study if the EHR indicated any of the following: (1) discharge to a location other than home (eg, a long-term acute care facility, skilled nursing facility, acute rehab, or outside acute care hospital), (2) discharge to home with hospice care, (3) death during the index hospitalization, or (4) positive laboratory SARS-CoV-2 test was incidental to the hospitalization based on provider documentation (ie, the primary discharge diagnosis was not associated with COVID-19 and the patient was not treated for COVID-19). In stage 3, patients who were already on home oxygen at the time of admission to the index hospitalization were excluded from the analysis.

Data Collection

The following information was abstracted from the EHR during the index hospitalization: demographics, smoking history, comorbid conditions, use of home oxygen prior to hospital admission, medical therapies recommended by National Institutes of Health (NIH) guidelines for acute COVID-19 during the study period (corticosteroids, remdesivir, tocilizumab, anticoagulation),15 level of respiratory support, and discharge on home oxygen (e-Appendix 2 for the case report form, see related supplementary materials at http://www.rcjournal.com). In the subset of subjects who were discharged on home oxygen, the EHR, including information available through the associated health information exchanges (expanded methods, e-Appendix 1), was also reviewed to abstract information about the 60-d period after the index hospitalization: attendance at an out-patient clinic visit, type of clinic (primary care, pulmonary, other specialty), measurement of pulse oximetry either at rest or with exertion, and discontinuation of home oxygen.

Research staff at the 3 study hospitals were trained in data collection procedures. To promote high levels of inter-rater reliability of data recorded by manual abstraction from the EHR, data were abstracted independently by a second trained member of the study team in a random 10% sample every 50 subjects. Differences between data independently collected by the 2 members of the study team were resolved by discussion and with the approval of the senior investigator (JAK). If the cumulative κ statistic for a particular variable was < 0.8 (moderate agreement or worse),16 a second member of the study team independently repeated the data collection for that item for all subjects, and discrepancies were resolved as described above.

Discharge on Home Oxygen

The primary outcome, discharge on home oxygen (yes, no, or unable to determine), was determined by review of the discharge summary including the hospital course and discharge orders.

Statistical Analysis

Descriptive statistics, including means (SD) and counts (percentages), were calculated. We examined changes in the proportion of subjects discharged on home oxygen in each of the 4 consecutive 3-month intervals using a chi-square test. To identify subject-level characteristics associated with initiation of home oxygen, candidate variables were selected a priori for inclusion in a logistic regression model. Subject characteristics identified in a previous report that were associated with long-term oxygen therapy after COVID-19 (older age, sex, chronic lung disease, and more severe COVID-19)17 and those for which there is biologic plausibility for developing hypoxemia or more severe COVID-19 (chronic kidney disease, heart disease, hypertension, obesity, obstructive sleep apnea) were included in our model. The highest World Health Organization COVID-19 Clinical Progression Scale (WHO-CPS)18 score during index hospitalization was used to categorize the severity of COVID-19 as either severe or moderate (e-Table 1, see related supplementary materials at http://www.rcjournal.com). We also included the use of systemic corticosteroids and remdesivir but not anticoagulation because the data were not collected in a way to differentiate between prophylactic and therapeutic dosing. We also did not include tocilizumab and sarilumab in the regression models because they were rarely (in < 5% of subjects) used during the study period. We modeled older age and obesity as continuous variables in increments of 5 y and 1 kg/m2 body mass index (BMI), respectively. We calculated adjusted odds ratios (aORs) with 95% CI using a multivariable logistic regression model that accounted for within-hospital correlation of outcomes. All analyses were conducted with R, version 4.1.3 (R Foundation for Statistical Computing, Vienna, Austria).

Table 1.

Characteristics of Subjects in the OXFORD Cohort

graphic file with name DE-RESC240010T001.jpg

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Results

Study Population

There were 517 subjects included in the analysis (Fig. 1). About half were female; mean age was 58 y, and nearly 80% were Black or Hispanic (Table 1). About one in 5 subjects were current or former smokers. The most common comorbid conditions were hypertension, obesity, and diabetes. About one in 5 subjects had chronic kidney disease, heart disease, or chronic lung disease. There was a decline in the number of subjects hospitalized for COVID-19 over the 12-month study period (Fig. 2).

Fig. 1.

Fig. 1.

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Flow chart. In stage 1, a random sample of patients who met inclusion criteria were sampled from each of the 3 study hospitals. In stage 2, manual review of electronic health records (EHRs) was used to identify patients who met exclusion criteria. In stage 3, patients on home oxygen at the time of hospital admission were excluded from the analysis. *The total number of patients who were determined to be ineligible by chart review (n = 293) is less than the sum of those ineligible for each listed reason (298) because some patients were ineligible for more than one reason.

Fig. 2.

Fig. 2.

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Proportion of subjects (with 95% CI) initiated on home oxygen after hospitalization for COVID-19 over 3-month periods from October 2020–September 2021. We did not observe differences in the proportion of subjects who were started on home oxygen when comparisons were made between subjects admitted during each 3-month period of the OXFORD study. The horizontal dashed line represents the percentage of subjects (26%) discharged on home oxygen over the entire study period, October 2020 – September 2021.

Most subjects (78%) were hospitalized with moderate COVID-19 (55% standard flow nasal canula, 23% no respiratory support). The remaining 22% of subjects had severe COVID-19 (16% high-flow nasal canula, 6% invasive or noninvasive mechanical ventilation). During the hospitalization, systemic corticosteroids (81%), remdesivir (61%), and anticoagulation (96%) were commonly administered. By contrast, tocilizumab (2.5%) was rarely used. The proportion of subjects receiving systemic corticosteroids, remdesivir, or anticoagulation did not change from October 2020–September 2021 (e-Table 2, see related supplementary materials at http://www.rcjournal.com). The use of tocilizumab increased over time to from 0% to 8% by September 2021.

Table 2.

Subject Characteristics and Treatments Associated With Initiation of Home Oxygen After Hospitalization for COVID-19 From October 2020–September 2021, a Multivariate Logistic Regression Model

graphic file with name DE-RESC240010T002.jpg

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Discharge on Home Oxygen

The inter-rater reliability among research staff abstracting information from the EHR about whether a subject was discharged on home oxygen demonstrated almost perfect agreement (κ ≥ 0.93) across the 3 hospitals. From October 2020–September 2021, 26% (132/517 [95% CI 22–29]) (Fig. 2) of subjects were started on home oxygen at hospital discharge. We did not observe a change in the proportion of subjects discharged on home oxygen during the 12-month study period (P = .50).

Subject Characteristics and Treatments Associated With Discharge on Home Oxygen

In a multivariable logistic regression model, older age, higher BMI, comorbid diabetes, and severe (vs moderate) COVID-19 were associated with an increased odds of discharge on home oxygen (Table 2; univariate analyses available in e-Table 3, see related supplementary materials at http://www.rcjournal.com). Comorbid hypertension was associated with a decreased odds of home oxygen initiation. Treatment with systemic corticosteroids, but not remdesivir, was associated with discharge on home oxygen.

Requirements for Home Oxygen Within 60 Days After Hospital Discharge

Just under three quarters (71%, Fig. 3) of subjects discharged on home oxygen attended an out-patient clinic visit within 60 d of discharge, most commonly in primary care (78%). Exactly half (50%, 66/132) of subjects discharged on home oxygen had pulse oximetry measurements documented in the EHR during the follow-up period. Among those subjects who had a documented pulse oximetry measurement, home oxygen was discontinued in nearly half.

Fig. 3.

Fig. 3.

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Sankey flow diagram of out-patient follow-up and management of home oxygen in the 60 d after hospital discharge.

Discussion

Approximately one in 4 subjects who were hospitalized for COVID-19 from October 2020–September 2021 were discharged on home oxygen, similar to findings published prior to the availability of evidence-based treatment recommendations for acute COVID-19. Older age, higher BMI, comorbid diabetes, hospitalization with severe COVID-19, and treatment with systemic corticosteroids were associated with initiation of home oxygen at hospital discharge. Hypertension was associated with reduced odds of home oxygen after hospital discharge. We were unable to determine the degree to which home oxygen requirements persisted in the 60 d after hospital discharge because of incomplete information about pulse oximetry. Among subjects with a documented pulse oximetry measurement at an out-patient visit, home oxygen was discontinued in about half.

The current report adds several findings to the existing literature. First, we found a similar proportion of subjects with COVID-19 were prescribed home oxygen as reported in previous studies, despite greater use of systemic corticosteroids (81%) and remdesivir (61%) in our report compared to previous studies (12–14%9-11 and 6–13%,8,10,13 respectively). The proportion of subjects with prescribed home oxygen after a COVID-19 hospitalization (26% in our report) appears to be higher than after hospitalization associated with other respiratory viruses (21% human metapneumovirus, 19% respiratory syncytial virus, and 13% influenza).19

Second, our study is the first to examine changes in the proportion of subjects discharged on home oxygen from the same hospitals over time. Over the 12-month study period, there was a 73% decline in the number of hospitalizations for COVID-19 and an increase in the use of tocilizumab (from 0% to 8%) across our 3 hospitals. Local surveillance data by the Chicago Department of Public Health indicated the emergence of alpha variants as the dominant circulating strain in April 2021 and subsequently delta variants in July 202120 and greater use of proven-effective vaccines (0% in December 2020, 68% in September 2021) (https://www.chicago.gov/city/en/sites/covid19-vaccine/home/covid-19-vaccine-coverage.html. Accessed November 2, 2023). However, we did not observe a corresponding reduction in the initiation of home oxygen (26, 24, 30, 20% across the 3-month intervals). Our findings suggest that interventions such as vaccines and medications that are effective in preventing hospitalizations or treating severe acute COVID-19 may be insufficient to prevent the need for home oxygen among individuals who are sufficiently ill to require hospitalization. Alternatively, potential changes in clinical practice regarding the prescribing of home oxygen or in the availability of home oxygen equipment could have contributed to the stable rates of home oxygen prescriptions. Additional studies are needed to distinguish between these potential explanations.

Third, our report adds to existing literature by identifying demographic, comorbidity, and treatment-related risk factors associated with initiating home oxygen immediately following a hospitalization with COVID-19. A study conducted in Sweden about the initiation of home oxygen at any point over a 20-month period following a positive SARS-CoV-2 test found that older age, female sex, severe (defined as hospitalized) or critical (defined as admission to ICU) COVID-19, and chronic lung disease were associated with long-term oxygen requirements.17 We similarly identified older age and more severe COVID-19 and additionally identified greater BMI, comorbid diabetes, hypertension, and use of systemic corticosteroids as associated with either increased or decreased odds of initiation of home oxygen.

The association of higher BMI and initiation of home oxygen after hospitalization for COVID-19 may be explained by ventilation/perfusion mismatch among obese individuals.21 The findings in the current report are consistent with previous studies suggesting a higher risk of respiratory failure among obese subjects with COVID-1922 and other pre-pandemic research linking obesity to reductions in oxygen saturation.21,23 Likewise, the increased odds of home oxygen in subjects with COVID-19 and comorbid diabetes in our study build on previous literature that demonstrates an increased risk of hypoxemia in subjects hospitalized with COVID-19 with comorbid diabetes24,25 and studies conducted prior to the COVID-19 pandemic that demonstrated a reduction in lung diffusion capacity among subjects with diabetes.26 The association between treatment with systemic corticosteroids and increased odds of discharge on home oxygen could represent residual confounding by indication (ie, subjects with severe COVID-19 were more frequently prescribed corticosteroids) or an adverse effect of therapy.

Our finding that hypertension was associated with a lower odds of home oxygen was unexpected. According to the United States Centers for Disease Control and Prevention, the relationship between hypertension and severity of COVID-19 is inconsistent (https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-care/underlyingconditions.html. Accessed November 1, 2023). Results of some studies suggest that a diagnosis of hypertension is associated with an increased risk of severe COVID-19 and death,27,28 while other studies do not.29 Still, other studies suggest that poor blood pressure control, rather than a diagnosis of hypertension, is associated with worse outcomes in subjects with COVID-19.30,31 In our study, we did not, however, collect data about blood pressure control prior to or during the index hospitalization.

We were unable to determine if home oxygen requirements persisted for 60 d after hospital discharge for COVID-19 because pulse oximetry measurements after hospital discharge were documented in less than half of subjects after hospital discharge. In a previously published single-center study, several coauthors in the current report found that only 29% of subjects hospitalized with COVID-19 from March 2020–February 2021 and discharged on home oxygen underwent a 6-min walk test within 6 months of hospital discharge.32 Taken together with findings in the current study, gaps in re-reassessment of home oxygen requirements after hospital discharge appear to be pervasive and similar to reports in studies conducted in COPD.33,34

Strengths and Limitations

Our study has several strengths including observations about home oxygen beyond the initial months of the COVID-19 pandemic, use of a multi-center design, analysis of data from over 500 subjects, and high levels of inter-rater reliability in abstracting data about home oxygen from the EHR. The interpretation of the study findings is, however, subject to limitations. We relied on information documented in the EHR and associated health information exchanges. Therefore, results may reflect the completeness and quality of documentation. The study was conducted in a modest sample of about 500 subjects at 3 academic health centers in one urban city, was enriched with subjects who were Black or Hispanic, and ended before the emergence of the omicron variant. Results, therefore, may not be generalizable to all hospitals, populations, or time periods. We also did not collect data quantifying the degree of hypoxemia on presentation (eg, the PaO2/FIO2) nor about subjects’ use of prescribed home oxygen after discharge.

Implications

The proportion discharged on home oxygen after COVID-19 (about one in 4 subjects) is higher (eg, double compared to influenza) than after a hospitalization for other respiratory viral infections. Home oxygen is costly,35 can lead to physical harm from burns36 and falls,37 as well as social stigmatization and isolation.38 However, few clinical trials exploring the use of noninvasive respiratory support in subjects hospitalized with COVID-19 pneumonia assessed the clinical recovery as defined by an improvement in oxygenation with the reduction of the need for high oxygen concentration as a major outcome.39,40 Additional studies specifically assessing the need for home oxygen as an end point in clinical trials involving subjects with hypoxemic respiratory failure are needed. Furthermore, additional research is needed to establish risk for and the trajectory of home oxygen requirements after discharge. Studies that rely exclusively on data routinely documented in EHRs are unlikely to be sufficient; prospective cohort studies that utilize remote monitoring technology to assess hypoxemia after discharge should be initiated.

Conclusions

Despite changes in the prevalent viral variants of SARS-CoV-2 and availability of evidence-based therapies for acute COVID-19, the requirement for home oxygen therapy after hospital discharge was common and largely unchanged compared to the first 3 months of the pandemic. Evidence-based strategies to reduce the requirement for home oxygen in patients hospitalized for COVID-19 are needed.

Supplementary Material

rc-11436-File001.docx
rc-11436-File001.docx (44.7KB, docx)

Footnotes

Dr Adegunsoye discloses relationships with the National Institute of Health, Genentech, Inogen, and Boehringer Ingelheim. Dr Gerald discloses relationships with the National Institute of Health, American Lung Association, UpToDate, American Lung Association of Arizona, and the Arizona Asthma Coalition. Dr Krishnan discloses relationships with the National Institutes of Health, COPD Foundation, Regeneron, Sergey Brin Family Foundation, Patient-Centered Outcomes Research Institute, American Lung Association, GSK, AstraZeneca, CereVu Medical, Propeller Health and ResMed, BData, University of Chicago, American Academy of Asthma, Allergy, and Immunology, Global Initiative for Asthma, American Thoracic Society, Central Society of Clinical and Translational Research, and the Respiratory Health Association. Dr Vines discloses relationships with the Rice Foundation, Teleflex Medical, Elsevier, Dräger, Mayo Clinic Didier Memorial Lecture, and the National Board for Respiratory Care. The remaining authors have disclosed no conflicts of interest.

Portions of this work were presented at the American Thoracic Society 2022 International Conference, held May 13–18, 2022, in San Francisco, California; and at the American Thoracic Society 2023 International Conference, held May 19–24, 2023, in Washington, District of Columbia.

Supplementary material related to this paper is available at http://www.rcjournal.com.

This work was funded by the National Heart, Lung, and Blood Institute grant number T32HL144909 (Dr Freedman) and the Clinical and Translational Science Award Program grant number UL1TR002003 (University of Illinois Chicago Center for Clinical and Translational Science). The funders of this work had no role in study design, data collection and analysis, preparation of the manuscript, or decision to publish.

See the Related Editorial on Page 379

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