Barriers to Mobility in the ICU: Insights from Severe COVID-19 and Implications for Improving Patient Outcomes.

The COVID-19 pandemic has presented numerous unexpected challenges that have impacted society and health care systems worldwide. 1 , 2 Although vaccinations, improved treatments, and changes in the SARS-CoV-2 virus itself have ameliorated SARS-CoV-2 infection-related mortality rates, as of December 2023 the pandemic has still resulted in 772 million confirmed cases and nearly 7 million deaths globally. 3 , 4 A recent systematic review and meta-analysis including over 80,000 patients found that an average of 10.96% required hospitalization in an intensive care unit (ICU). 5 During the first wave of the pandemic in particular, there was a substantial increase in acute and critical care hospital admissions around the world. 2

The first major epicenter of the COVID-19 outbreak within the United States was in New York City where a total of over 203,000 cases were confirmed during the first wave of the pandemic (February 29, 2020 through June 1, 2020), with over 21,000 deaths attributed to COVID during this period. 6 , 7 , 8 Initial reporting focused on demographics, risk factors, and case fatality rates, but more recently scientific research has shifted its attention to other long-term outcomes including the prevalence of physical function and postintensive care syndrome (PICS). 9 , 10 , 11 , 12 , 13 Several commentaries regarding rehabilitation and early mobilization in the severe COVID-19 population have been published in the United States and abroad, 14 , 15 , 16 , 17 , 18 but to date no studies have addressed the prevalence of mobilization in the ICU in this at risk cohort in the United States.

Immobilization in the ICU setting leads to negative consequences in both the acute and chronic phases of recovery. Short-term effects include pressure ulcers, deep vein thrombosis, pneumonia, urinary tract infection, soft tissue contractures, atelectasis, and pulmonary embolism. 19 , 20 Long-term consequences can be debilitating, including rapid muscle wasting, ICU-acquired weakness (ICUAW), and PICS, 20 , 21 , 22 , 23 resulting in prolonged mechanical ventilation and hospitalization, higher mortality, persistent weakness and fatigue, and reduced function and quality of life. 24 , 25 , 26 , 27 , 28 , 29 , 30

Immobilization is the leading modifiable risk factor for development of ICUAW. 20 , 23 , 31 Early mobilization improves muscle strength, reduces oxidative stress and inflammation, is associated with increased ventilator-free days, enhances ambulation, and lowers ICUAW incidence at discharge. 32 , 33 , 34 , 35 Any immobilized person in the ICU is at risk for poor outcomes, with those suffering from severe COVID-19 infection being particularly vulnerable because of prolonged critical care, respiratory and multiorgan complications, isolation, and treatments that limit mobility. Despite this, there is a dearth of literature examining mobilization status and rates of utilization of mobilization protocols in patients with severe COVID-19 in the ICU and the implications for postrecovery outcomes.

The primary aim of this study is to characterize the mobility status of persons with severe COVID-19 on mechanical ventilation in the ICU and to compare mobility status with a matched sample of non-COVID-19 ICU patients. Secondary aims include evaluating length of stay, number of physical therapy (PT) visits, and mortality as well as identifying factors associated with lower mobility status. We hypothesize that immobilization will be greater in the severe COVID-19 sample, and that those with severe COVID-19 will have greater rates of adverse outcomes including muscular weakness, ICUAW, and PICS. This work is intended to better inform our understanding of the therapeutic benefit of early mobilization in patients with severe COVID-19 in the ICU setting, as well as identify potential barriers to this population receiving early mobilization so that strategies can be developed to address these obstacles.

Methods

Study design

This was a retrospective cohort study comparing a convenience sample of 2 groups of patients admitted to the ICU at a large tertiary care center at the epicenter of the COVID-19 pandemic: those found to be COVID-19 positive and those without COVID-19 infection. Approval for this study was provided by the Institutional Program for Protection of Human Subjects IRB STUDY-20-01192. Waiver of informed consent was granted.

Participants

Persons included in the analysis were adults ages 18 and older who were admitted to the ICU between April 14, 2019 and July 7, 2020. We selected April 2019 to July 2020 to include a representative prepandemic baseline and the initial pandemic surge, with July 2020 marking both the limit of available data at the time of collection and the lull prior to the subsequent second wave. Inclusion criteria for the COVID-19 sample included confirmed COVID-19 infection via polymerase chain reaction and/or antibody testing and admission to any ICU. We performed a complete case analysis, excluding patients with missing data on APACHE-III score, Richmond Agitation Sedation Scale (RASS) score, or on any of the study variables. Additionally, unsuccessful matching resulted in exclusion. Patients admitted to ad-hoc ICU’s that were opened to address the influx of patients from the COVID-19 surge were also excluded as the goal of this study was to understand how ICU mobilization protocols were followed in traditional ICUs.

Outcome measures

The primary outcome measure was maximum ICU mobility status at any time during the stay, categorized as ‘immobile,’ ‘nonambulatory,’ and ‘ambulatory.’ The patient’s highest level of mobility during the ICU stay was categorized according to the validated ICU Mobility Scale. 36 The classified mobility stages range from 0 (none, lying on the bed) to 10 (walking independently without gait aid). A score of 0 was categorized as Immobile, 1-7 as Nonambulatory, and 8-10 as Ambulatory. Highest level of mobility was determined by reviewing the mobility scores assigned daily by medical team including physical and occupational therapists, nursing and the attending physician. Secondary outcomes were clinical factors relevant to mobility status including age, sex, BMI (body mass index), acute physiology, Age and Chronic Health Evaluation III (APACHE-III) score, Richmond Agitation Sedation Scale (RASS), patient expired, tracheostomy status, percutaneous endoscopic gastrostomy (PEG) status, hospital length of stay (LOS), prone status, and PT status (received versus not).

Data collection

Chart review was performed using a pre-existing electronic medical record report that was refined to capture patient demographics, variables, and outcome data. Variables collected were age, sex, BMI, APACHE-III score, RASS score, tracheostomy status, PEG status, PT visits, and prone status. Severity of disease and in-hospital mortality risk was classified using the APACHE-III score. 37 This score provides an initial risk stratification for severely ill hospitalized patients as well as hospital mortality. A 5-point increase in APACHE-III score is independently associated with a statistically significant increase in the relative risk of hospital death. 37

The unit of analysis for the study was ICU visits, not the individual, given the proclivity of the electronic medical record report to use visit as the unit of analysis, and each visit was treated as an independent event. However, readmissions within 24 hours were merged into a single visit. Once the cohort was determined, coarsened exact matching (CEM) was used to create comparable groups by reducing imbalance between the COVID (COVID-19 positive) and non-COVID (COVID-19 negative) groups among important confounding factor(s). ICU visits were matched based on age and sex and were incorporated into all regression analyses.

Mobilization program

The large academic hospital at which the study was conducted have ICUs with a well-established mobility program with the goal of reducing hospital LOS while simultaneously improving functional outcomes and overall quality of life. 38 During the initial COVID-19 surge in 2020 there was no decrease in physical therapists or occupational therapists available to implement mobilization in the ICU. The mobility protocol is initiated upon admission to an ICU unless a contraindication exists. The goal is to initiate mobilization as early as possible and advance to the highest levels achievable. Absolute contraindications to progression in the mobilization program include but are not limited to patients who require intravenous antihypertensive for hypertensive emergency, prone positioning, RASS > +2, active management of intracranial hypertension with intracranial pressure not in desired range, uncontrolled seizures and active bleeding. 39

Statistical analysis

Descriptive statistics were used to summarize visit demographics for the overall cohort and stratified by COVID status. Continuous data are presented as mean (SD); categorical data are reported as n (%). Normality was assessed using visual methods (histograms and Q-Q plots).

We applied CEM to confounding when comparing ICU visits with and without COVID-19, matching on age and sex as covariates. CEM stratifies data by coarsening continuous and categorical covariates into bins, ensuring exact matches within strata. After matching, balance between groups was assessed using standardized mean differences (SMDs), with SMD<0.1 indicating acceptable balance.

Comparisons used t tests or Mann–Whitney U test for 2-group continuous data, analysis of variance or Kruskal–Wallis for multigroup data, and chi-square or Fisher exact for categorical data. Given the large sample size, where small differences can yield significant P values, we also calculated SMD for 2-group comparisons and average SMD for multigroup comparisons to quantify effect sizes. a,b

Multinomial regression examined the association between ICU factors and the highest ICU mobility category achieved (reference: “Immobile”). Covariates included APACHE-III score (analyzed continuously and by quartiles), mortality status at ICU discharge (“expired”), tracheostomy, PEG placement, sedation (average RASS), and hospital LOS. We evaluated multicollinearity with variance inflation factor, adjusting or removing predictors >10 to maintain model stability. a,c

Separate logistic regressions were performed to assess odds of receiving PT in the ICU (coded as any PT vs none) and proning status, with COVID-19 status as the main predictor. Both models were adjusted for APACHE-III score, age, sex, RASS score, expired status, tracheostomy, PEG placement, and hospital length of stay. To further explore severity, proning analyses were stratified by mechanical ventilation status and APACHE-III quartiles. Model diagnostics, including multicollinearity checks, residual analysis, and goodness-of-fit measures, were conducted for each regression. c

To address potential confounding by indication, we conducted a post-hoc sensitivity analysis excluding COVID-19 status from the multinomial regression model. We compared the Akaike information criterion between the primary and sensitivity models to evaluate any differences in fit and coefficient stability. c

Results

Of the 4332 available records, 3520 (81.25%) included APACHE-III scores ( fig 1 ). Before matching, 218 additional records (6.19%) were removed because of missing data required for regression analyses. After CEM, postmatching assessments showed excellent balance for sex (SMD=0.075) and age (SMD=0.01). Only 27 unmatched cases (0.81%), all from the non-COVID group were excluded, resulting in a cohort of 3275 ICU cases. Of the included cases, 99.57% (3261/3275) of visits indicated mechanical ventilation. The excluded visits (n=245, 6.96%) differed significantly from the analysis cohort. Excluded visits had higher BMI ( P =.004), higher APACHE-III scores ( P =.013), fewer PT visits in the ICU ( P <.001), were more likely to have expired ( P <.001), and were overwhelmingly classified as Immobile ( P <.001).

Descriptive characteristics

COVID visits were associated with higher BMI ( P <.001), a higher proportion of deaths ( P <.001), higher final APACHE-III scores ( P =.001), longer hospital LOS ( P <.001), increased sedation ( P <.001), fewer PT visits in the ICU ( P =.001), more frequent proning ( P <.001) and tracheostomy ( P <.001) ( table 1 ). COVID visits were most commonly categorized as Immobile ( P <.001), whereas Ambulatory was the most frequent category for non-COVID visits ( fig 2 ). Stratified by mobility category, significant differences were found for most demographic and visit characteristics, except for COPD status, obesity, and diabetes ( table 2 ).

Regression analyses

Multinomial regression demonstrated strong effects of COVID-19 status on ICU mobility ( table 3 ). Compared with non-COVID visits, COVID visits had a 60% decrease in the odds of being Nonambulatory versus Immobile and a 93% decrease in the odds of being Ambulatory versus immobile. Covariates such as illness severity (APACHE-III score, length of stay), sedation (RASS), mortality, and select procedures (tracheostomy, PEG) were also associated (all P <.05) with mobility, consistent with their clinical relevance; see table 3 for more information.

Figure 2 shows predicted probabilities of ICU mobility categories from the multinomial regression. COVID visits were most often Immobile (∼50%) or Nonambulatory (∼45%), with only ∼5% Ambulatory. In contrast, non-COVID visits showed the opposite pattern, with Ambulatory as the most frequent category.

Sensitivity analysis

To address potential imbalances, a post-hoc sensitivity analysis excluded COVID-19 status from the multinomial regression model. The sensitivity model produced a lower Akaike information criterion (4859.08) compared to the primary model (5196.42), indicating better fit. Estimated effects in the sensitivity model were consistent with those of the primary analysis ( supplemental table S1 , available online only at http://www.archives-pmr.org/ ).

Additional models

We ran 2 additional logistic regression models to examine secondary outcomes ( Table 4 , Table 5 ). COVID ICU visits had more than a 4-fold increased odds of not receiving PT compared with non-COVID visits and had more than an 11-fold increased odds of being proned. Other covariates such as illness severity (APACHE-III score, LOS), sedation level (RASS), mortality, and select procedures (PEG, tracheostomy) also showed associations ( P <.05) with PT receipt and proning, consistent with their role as indicators of critical illness.

To further characterize proning, we stratified by mechanical ventilation, and APACHE-III quartiles ( fig 3 ). Proning occurred only among mechanically ventilated patients. Of 3275 visits, 98 (3.0%) were both proned and ventilated, 3163 (96.6%) were ventilated without proning, and 14 (0.4%) were neither; no visits were proned without ventilation. When stratified by APACHE-III quartiles, the proportion of patients who were proned rose modestly with illness severity, from 2.6% in quartile 1 to 3.5% in quartile 4. This pattern suggests a weak association between higher APACHE-III scores and proning, and overall proning rates remained low across all severity levels.

Discussion

In this large retrospective, single center case–control study captured during the height of the COVID-19 pandemic, we identified a significant disparity in the mobility levels of mechanically ventilated patients with severe COVID-19 during their ICU stay compared to their non-COVID-19 critically ill counterparts. Patients with severe COVID-19 achieved significantly lower levels of mobility during their ICU stay. Furthermore, COVID-19 patients had fewer PT visits in the ICU, were more likely to be placed in prone position, were sedated more deeply, had longer lengths of stay, higher severity of illness (APACHE-III) and higher mortality compared to those patients without COVID-19.

Patients with severe COVID-19 were most likely to be classified as immobile, or bed bound (69.1% vs 22.3% in patients without COVID-19). They were 60% less likely to be classified as nonambulatory and 93% less likely to be classified as ambulatory. Despite our institution’s well- established early mobilization program and full therapist staffing, individuals with severe COVID-19 infection were 4.06 times less likely to receive PT during their ICU stay. This is attributable to a host of factors associated with mobility, and it should be noted that that severe COVID-19 infection requiring mechanical ventilation status itself seems to have a role in a person’s mobility and outcomes.

Both a RASS score of < −2 and prone positioning are contraindications to mobilization in the ICU, thus greatly impacting mobility. The COVID-19 cohort had significantly higher incidence of these contraindications than the non-COVID-19 cohort. Patients with COVID-19 had significantly worse RASS Scores compared to those without COVID-19 (−2.56 vs −0.77). This is consistent with the results of the COVID-D study which found that more than 80% of patients with severe COVID-19 underwent prolonged periods of deep sedation. 40 In addition, we found that patients with COVID-19 were a staggering 11.64 times more likely to be proned than non-COVID-19 patients.

Although it may seem intuitive to assume that patients with severe COVID-19 were simply sicker and therefore less mobile, our study design controlled for severity of illness through matching and adjustment using APACHE-III scores. Importantly, the APACHE-III scores were not clinically significantly different between groups postmatching, indicating that COVID-19 and non-COVID-19 patients had comparable baseline severity of illness. Despite this, COVID-19 patients experienced markedly more frequent proning and deeper sedation—both of which are clear contraindications to ICU mobilization.

The finding that all proned patients were mechanically ventilated aligns with standard critical care practices, but also underscores how closely linked these interventions are in the context of severe COVID-19. Although there was a slight upward trend in proning rates across increasing APACHE-III quartiles, the overall magnitude of the difference was small. This supports the conclusion that proning was not solely driven by baseline severity as captured by APACHE-III scores. Rather, the decision to prone likely reflects clinical trajectories and treatment paradigms specific to COVID-19, independent of illness severity per se. These data support our analytic decision to adjust for APACHE-III and highlight how proning is not simply a direct surrogate for severity as measured by global severity scales—particularly in pandemic contexts.

Ultimately, what we observed was that while global severity scores like APACHE-III suggest similar illness acuity, the clinical trajectories and management strategies for COVID-19 patients diverged in meaningful ways. This strongly suggests that there is something fundamentally different about how critical illness manifests and is treated in COVID-19 patients—not necessarily in terms of baseline severity, but rather in the clinical course that follows. These findings reinforce that the vastly reduced mobility in the COVID-19 group likely stems not from differences in initial severity, but from treatment-specific factors such as proning and heavy sedation. This distinction is critical, as it highlights the need for new mobilization approaches that acknowledge these unique clinical patterns, rather than relying solely on traditional severity indices which may not necessarily align with observed outcomes.

Understanding a person’s mobility status during severe illness and ICU stay is essential given that the development of ICUAW and PICS leads to increased mortality and many long-lasting deficits resulting in reduced quality of life. 25 , 26 , 27 , 28 , 29 , 30 , 31 Further underscoring this concern, the patients with severe COVID-19 infections requiring mechanical ventilation in our sample were at extreme risk of developing ICUAW and PICS. Studies have also demonstrated high rates of postacute sequelae of SARS-CoV-2 infection, or long-COVID, in survivors of severe COVID-19. 41 , 42 , 43 Long-COVID often manifests as a constellation of debilitating symptoms, including profound fatigue, musculoskeletal pain, and cognitive impairment, that exacerbate the deficits seen in ICU survivors. 44 , 45 , 46 These lingering consequences of long-COVID have had broad implications for health care systems, as they compound the pre-existing burden of post-ICU disabilities.

The findings of this study highlight the critical need for innovation in sedation protocols and strategies for mobilizing sedated or proned patients. As the health care system continues to grapple with evolving COVID-19 variants and treatments, the long-term impacts will place significant disability burdens on both health care and social structures. Developing advanced ICU mobilization strategies is essential not only for addressing current challenges but also for future pandemics involving critically ill patients requiring intensive care.

Study limitations

Despite the use of well-established mobility protocols in our study that had previously proven successful, 38 the pandemic’s impact on practice modifications cannot be overlooked. An international study showed that the implementation of a standardized multidisciplinary care bundle for critically ill patients was significantly lower compared to the pre-COVID era, 47 suggesting alterations in ICU care practices because of the overwhelming patient influx.

Our research, being a single-center cohort study, has limited generalizability because of the unique protocols, staffing, and resources of our institution. This design, however, reduces the variability that could arise from different mobility protocols and therapy staffing in other institutions. Additionally, our study’s sample size was confined to patients at our institution, further narrowed by excluding COVID-19 patients from makeshift ICUs to maintain consistency in the mobilization protocol. Despite its nonrandomized design, which limits the ability to draw causal conclusions, our study is a valuable contribution to critical care literature, demonstrating the feasibility and potential benefits of early mobilization for improving patients’ functional outcomes.

Conclusions

Our study highlights the significant impact of severe COVID-19 on mobility status among ICU patients and its potential implications for long-term outcomes. Patients with severe COVID-19 requiring mechanical ventilation faced substantial barriers to mobilization, primarily because of higher rates of mobilization contraindications in this cohort such as deep sedation and prone positioning. Our results underscore the need to develop innovative strategies to mobilize patients with severe mobility constraints, including those who are deeply sedated or proned, as this could significantly improve both immediate and long-term functional outcomes by reducing the risk of developing ICUAW and PICS. Understanding which factors contribute most significantly to post-ICU debility allows us to begin developing targeted interventions to mitigate these challenges and improve patient recovery in both daily ICU care and future pandemic scenarios.

Suppliers

Stata; StataCorp.

SPSS; IBM.

R, version 4.0; R Core Team.

Disclosure

The investigators have no financial or nonfinancial disclosures to make in relation to this project.

Footnotes

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.arrct.2025.100537 .

Supplementary materials

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Associated Data

Supplementary Materials