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. 2026 Jul 15;39(5):918–923. doi: 10.1080/08998280.2026.2691632

A pilot randomized controlled trial protocol of overground robotic exoskeleton–assisted early ambulation after cardiovascular and thoracic surgery in the acute care setting (REACT-CVTS)

Katelyn D Brown a,✉, Dannae Arnold a,b, Christi Stevens a,b, Molly Trammell b, Monica Bennett c, Neil Keshvani d, Seema Sikka a,b, Gary Schwartz e, Robert L Gottlieb f,g,h,i,j, Dan M Meyer i,k
PMCID: PMC13532010  PMID: 42454761

Abstract

Early ambulation following cardiovascular and thoracic surgery (CVTS) is associated with improved postoperative outcomes. However, barriers such as patient debility, high acuity, hemodynamic instability, cardiopulmonary complications, or resource limitations (e.g., intensive care unit setting, specialized equipment, or staff training) often prevent or delay early ambulation. Overground robotic exoskeletons (ORE) may facilitate earlier and higher-dose ambulation, yet their role in acute CVTS recovery remains uninvestigated. To evaluate the safety, feasibility, and preliminary outcomes of ORE-assisted early ambulation in postoperative CVTS patients in the intensive care unit setting, we will conduct a single-center pilot randomized controlled trial. Twenty participants will be randomized 2:1 to receive either ORE plus usual care or usual care alone. Primary outcomes include time from intensive care unit admission to first upright ambulation (hours) and ambulation dosage (upright time, walking time, and steps). Secondary outcomes assess safety (adverse events) and feasibility (staffing requirements). This randomized controlled trial is the first investigation of ORE for early ambulation in the CVTS population and will lay the groundwork for the integration of advanced ORE technology into cardiopulmonary rehabilitation.

Keywords: Early ambulation, exoskeleton device, intensive care units, thoracic surgery

More than 900,000 cardiovascular and thoracic surgeries (CVTS) are performed annually in the United States,1 with volumes projected to increase by over 60% by 2035 due to population aging, rising chronic disease prevalence, and advances in surgical care.2 Despite improvements in perioperative management, postoperative immobility remains a pervasive challenge, particularly during the critical first 24 to 72 hours following CVTS.3 Reduced mobility during this period is associated with increased complication rates,4 prolonged hospitalizations,5 and delayed functional recovery.6

Contemporary enhanced recovery after surgery (ERAS) guidelines strongly endorse early ambulation (EA) following CVTS,7 due to benefits including reduced postoperative complications and improved functional outcomes.8 Usual care EA (UC-EA) typically follows a graded progression from bed mobility and seated activities to standing, transfers, and ambulation as tolerated.9 However, effective implementation is frequently constrained by patient-specific factors (e.g., weakness, hemodynamic instability, medical complexity, need for extensive physical assistance) as well as logistical challenges, such as staffing demands, equipment availability, and time constraints.3 These barriers result in a gap between guideline recommendations and clinical practice, which can result in many high-risk patients being inadequately mobilized during the early postoperative recovery period.10

Overground robotic exoskeletons (ORE) are rehabilitation devices approved by the US Food and Drug Administration to facilitate upright mobility in individuals requiring substantial physical assistance.11 Although initially developed for neurological populations, growing evidence suggests that ORE use is safe,12 feasible,13 and well tolerated across inpatient rehabilitation and acute care settings14–16 and may enable earlier initiation of ambulation at higher dosages while reducing the physical demands on clinical staff.17 Preliminary case-based evidence also supports the feasibility of ORE use in medically complex cardiovascular populations, including patients supported with a left ventricular assist device.18 However, no prospective studies have systematically evaluated the use of ORE-assisted EA in postoperative CVTS patients. Consequently, the safety, feasibility, and potential impact of ORE-assisted mobility in this population is unknown.

To address this gap, we will conduct a pilot randomized trial comparing ORE-assisted EA (ORE-EA) plus usual care EA (UC-EA) to UC-EA alone in postoperative CVTS patients admitted to the intensive care unit (ICU). Building on prior work demonstrating successful ORE implementation across rehabilitation and in select acute care populations, this study will evaluate the safety and feasibility of ORE-EA while generating preliminary data on time to ambulation and ambulation dosage. These findings will inform the design of future multicenter and definitive trials and help determine the role of advanced rehabilitation technologies in postoperative CVTS rehabilitation.

The study has three aims:

  1. To assess the safety of ORE-EA in postoperative CVTS patients admitted to the ICU. Safety outcomes include the incidence of adverse events and adverse events of special interest occurring during or immediately following EA sessions. Hypothesis 1: ORE-EA will demonstrate a comparable safety profile (rate of adverse events and adverse events of special interest) compared to UC-EA.15

  2. To assess the feasibility of implementing ORE-EA in postoperative CVTS patients admitted to the ICU. Feasibility outcomes include the number and clinical roles of staff required to deliver ambulation sessions. Hypothesis 2: ORE-EA can be implemented within existing ICU rehabilitation workflows with staffing requirements comparable to UC-EA.15

  3. To compare time to ambulation and ambulation dosage between ORE-EA and UC-EA in postoperative CVTS patients admitted to the ICU. Time to ambulation is defined as the interval between ICU admission and first upright ambulation, and ambulation dosage is quantified using upright time, walking time, and step count. Hypothesis 3: ORE-EA will result in a comparable time to ambulation and ambulation dosage as UC-EA in postoperative CVTS patients.

METHODS

The design is a single-center, prospective, pilot randomized controlled trial. The study is approved by the local institutional review board (IRB) and registered on ClinicalTrials.gov (NCT07353892). Due to the nature of the intervention, which involves use of a visible and therapist-delivered ORE device, blinding of participants, treating clinicians, and study personnel is not feasible. The intervention design and timeline are outlined in Figure 1.

Figure 1.

Flowchart detailing patient admission, screening, and randomization for an ICU study into two groups: ORE-EA and UC-EA. The flowchart depicts the patient enrollment process for an ICU clinical study. It starts with "Admitted to ICU," followed by "Screen CVTS Patients" and "Consent Eligible Patients". Eligible patients are randomly assigned in a 2:1 ratio to two groups: ORE-EA (n~14) for up to 3 sessions during ICU admission, or UC-EA (n~6) for all sessions during ICU admission. The layout uses arrows to show the sequential flow and group sizes are noted.

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Study design.

Study setting

The study will take place in the cardiothoracic ICU at Baylor University Medical Center in Dallas, Texas. Baylor University Medical Center is part of Baylor Scott & White, the largest not-for-profit healthcare system in Texas, and is a high-volume CVTS center, performing more than 50 CVTS procedures per month.

Participants/recruitment

Participants will be recruited from the cardiothoracic ICU at Baylor University Medical Center using a collaborative approach between the research and clinical teams. Potential participants will be identified through electronic medical record screening and provider referral.

Potential participants will be approached postoperatively, as study eligibility cannot be fully determined before surgery and depends on postoperative clinical stability, mobility status, cognitive status, respiratory and hemodynamic parameters, and compatibility with ORE device requirements. Adult patients aged ≥18 years who have undergone CVTS, including but not limited to coronary artery bypass grafting, valve repair or replacement, aortic surgery, lung resection, heart or lung transplantation, ventricular assist device implantation, temporary mechanical circulatory support, or venovenous extracorporeal membrane oxygenation, will be considered eligible. Participants must be medically cleared for upright activity and ambulation by a physician or advanced practice provider, require at least 50% physical assistance to perform upright activity, be hemodynamically stable with a mean arterial pressure of at least 60 mm Hg, and be able to provide informed consent directly or via a legally authorized representative. Participants must also meet ORE manufacturer frame specifications: height ∼ 5′0” to 6’4”; weight ≤ 220 lb; standing hip width ≤ 18”; near normal range of motion in hips, knees, and ankles; no significant upper or lower leg length discrepancies.19

Exclusion criteria include cognitive or behavioral impairment interfering with safe participation (including active delirium), moderate or high vasopressor or inotrope requirements beyond predefined thresholds, sustained ventricular arrhythmias requiring intervention at the time of mobilization, active angiotensin II infusion, severe oxygenation impairment, femoral arterial access lines (with limited intraaortic balloon pump exceptions), skin integrity concerns at ORE frame contact sites, pregnancy, concurrent interventional trials that could confound outcomes, or any condition deemed by the clinical or research team to pose unacceptable risk.

Cognitive status will be assessed using the Orientation Log (O-Log), a cognitive assessment tool used to measure a person’s orientation to time, place, and situation,20 to determine capacity for informed consent. Individuals who score ≥24/30 will be deemed to have the comprehension necessary for study consent and will be cleared for independent consent. Individuals who score <24/30 will not be cleared to provide self-consent; per institutional guidelines, their legally authorized representative will be approached to provide consent on their behalf. Individuals requiring a legally authorized representative to consent will still need to provide assent before they can be enrolled in the study.

Participants meeting all inclusion criteria will be approached for informed consent by a study staff member who has been appropriately trained and authorized to obtain informed consent in accordance with IRB-approved procedures. The informed consent form will be reviewed by the study staff member with the participant, and all study-related questions will be answered prior to consent. All screening procedures are approved by the IRB.

Intervention

ORE-EA. Participants randomized to the intervention group will receive up to three ORE-EA sessions using a battery-powered ORE (EksoNR, Ekso Bionics, San Rafael, California) in addition to standard of care UC-EA. ORE-EA sessions will be delivered by an ORE-trained physical therapist, in collaboration with the patient’s treatment team. Each participant will complete one to three ORE-EA sessions on separate days during their admission, contingent on medical stability and safety. All ORE-EA activities will be delivered at the discretion of a licensed physical therapist based on the patient’s medical stability, functional status, and safety within the ICU environment. A maximum of three sessions was selected because the study is designed to evaluate safety, feasibility, and implementation during the immediate postoperative ICU recovery period, where patients are most vulnerable to immobility-related complications and typically have relatively short ICU lengths of stay. Additionally, ORE-EA sessions will occur no more than once daily to align with routine ICU rehabilitation practice, allow adequate recovery between mobility sessions, and minimize participant burden during acute recovery.

UC-EA. Participants randomized to the control group will receive UC-EA delivered by licensed physical therapists according to standard of care in the ICU setting. Interventions may include bed mobility, sitting at the edge of the bed, standing, transfers, and ambulation as tolerated, with progression determined by participant status and clinical judgment. All UC-EA activities will be delivered at the discretion of a licensed physical therapist based on the patient’s medical stability, functional status, and safety within the ICU environment.

Outcome measures

Baseline demographic and clinical characteristics (e.g., mobility scores) will be abstracted from the medical record following enrollment. Outcome data will be entered by trained study staff into REDCap,21,22 a secure web application that is compliant with the Health Insurance Portability and Accountability Act. Physical therapy sessions from postoperative day 1 through discharge will be documented for all participants.

Aim 1 outcome measures. Safety outcomes will include documentation of all adverse events and predefined adverse events of special interest, such as premature session termination due to medical deterioration, escalation of vasoactive support, hemodynamic or respiratory instability, pain limiting participation, or device-related complications.

Aim 2 outcome measures: Feasibility will be assessed by documenting the number and roles of staff required for session set up, delivery, and take down.

Aim 3 outcome measures: Time to ambulation will be recorded as hours from ICU admission to first ambulation. Ambulation dosage will be quantified during each session using upright time, walking time, and step count. Step counts will be obtained via the exoskeleton’s integrated system for ORE-EA participants and via manual tracking for UC-EA participants. Participants will not be compensated for their time, and no research-related costs will be incurred.

Sample size

This pilot study is not powered for hypothesis testing, as our primary objective is to assess safety, refine study procedures, and generate preliminary data and effect size estimates to inform a formal power analysis for future clinical trials. Consistent with a previous pilot study using ORE and acute care patients,15 and pilot study sample recommendations,23 we will enroll 20 postoperative CVTS patients, with approximately 14 allocated to the ORE-EA group and 6 to the UC-EA group.

Allocation

Patients meeting the eligibility criteria will be screened, consented, and enrolled into the study. After obtaining informed consent, participants will be randomized in a 2:1 ratio using a random number generator to either ORE-EA plus UC-EA (intervention group) or UC-EA alone (control group). This allocation will enhance feasibility and safety observations in the intervention group while maintaining a comparator group for preliminary analysis. To minimize variability in recovery trajectory, enrollment will occur within the first three treatment days after initiation of physical therapy treatment during the ICU stay. Participants will be informed that the study is voluntary and that they can withdraw at any time during the trial without impact on clinical care received.

Data management, quality assurance, and exclusion of bias

Outcome data will be entered by trained study staff into REDCap.21,22 After consent, participants will be given a unique subject ID (e.g., REACTXXX) for use in all databases and case report forms. Only authorized study personnel will have access to the decoding matrix, and the master list will be maintained on a secure server in a password-protected file. The principal investigator (PI) will maintain source documents for each participant, including a copy of the signed consent form and paper case report forms. Data management functions will occur on a quarterly basis and will include data quality checks and verification, as well as internal edits and logic checks (e.g., out-of-range values, internal inconsistencies).

Descriptive statistics will be calculated and included in quarterly reports to ensure the quality of data and progress of the study. Data will be backed up as part of the quarterly data management functions and stored in the biostatistician’s secure filing system on the secure server. Upon completion of the final study visit, a final study audit will be conducted, and all queries will be resolved. Once final analysis has occurred, the study data will be uploaded on a secure server and the study database will be locked. The PI will oversee all data entry and proper data monitoring and audit procedures.

All adverse events will be identified, graded for severity and assigned causality, reported to the IRB in accordance with institutional policy, and compiled for periodic review. The PI and participating physicians will evaluate all adverse events and determine whether they affect the risk/benefit ratio of the study and whether modifications to the protocol or informed consent form are required. The plan to monitor participant data and safety will include the following: (1) the PI and participating physicians will review all adverse events; (2) the IRB office will be contacted if there is an adverse event due to participation; and (3) the research protocol will be revised if it is determined that the protocol or intervention presents an unforeseen risk to participants.

Statistical analysis

Given the pilot nature of the study, analyses will emphasize descriptive statistics and exploratory comparisons rather than formal hypothesis testing. Continuous variables will be summarized using means and standard deviations or medians and interquartile ranges as appropriate, while categorical variables will be summarized using counts and percentages. Between-group comparisons will be explored using Fisher’s exact tests, t tests, or Mann-Whitney U tests, depending on data distribution. Analyses will be conducted using SAS version 9.4.

DISCUSSION

EA after CVTS is strongly recommended, yet consistent implementation in the ICU remains limited by patient acuity, hemodynamic instability, and high staffing demands. While ORE technology has demonstrated safety and feasibility across rehabilitation settings and select acute care populations, its application in postoperative CVTS patients has not been evaluated. This pilot study represents the next step from prior development-of-concept studies and future adequately powered efficacy trials. By generating safety, feasibility, and preliminary effect-size estimates in a postoperative CVTS population, the trial will provide essential information needed to design future multicenter studies evaluating the clinical effectiveness of ORE- EA.

To our knowledge, this is the first prospective randomized study to examine ORE-assisted mobility in the acute CVTS population. As a pilot investigation, the primary aims are to characterize safety and feasibility while generating preliminary estimates of time to ambulation and ambulation dosage. If shown to be safe and operationally feasible, ORE-EA may provide a structured approach to facilitate EA in highly dependent postoperative patients, potentially improving adherence to EA recommendations while supporting therapist safety and resource efficiency. Limitations include the single-center design, sample size, and lack of blinding of participants or therapists. Nonetheless, this study represents an important foundational step toward integrating advanced mobility technologies into CVTS critical care and informing future adequately powered trials.

Funding Statement

This work was supported by the Baylor Scott & White Cardiovascular Research Review Committee. Data will be made available upon reasonable request to the corresponding author.

Disclosure statement/Funding

The authors report no conflict of interest. This work was supported by the Baylor Scott & White Cardiovascular Research Review Committee. Data will be made available upon reasonable request to the corresponding author.

References

  • 1.MedSuite . Cardiac surgery market size, share, and trends analysis. United States | 2023-2029 | MedSuite . | Includes: Tissue Heart Valve Market, TAVI/TAVR Market, and 22 more. iData Research; 2025. https://idataresearch.com/product/cardiac-surgery-market-united-states/. Accessed March 1, 2025.
  • 2.Moffatt-Bruce S, Crestanello J, Way DP, Williams TE. Jr.. Providing cardiothoracic services in 2035: signs of trouble ahead. J Thorac Cardiovasc Surg. 2018;155(2):824–829. doi: 10.1016/j.jtcvs.2017.09.135. [DOI] [PubMed] [Google Scholar]
  • 3.Mayor MA, Khandhar SJ, Chandy J, Fernando HC.. Implementing a thoracic enhanced recovery with ambulation after surgery program: key aspects and challenges. J Thorac Dis. 2018;10(Suppl 32):S3809–s3814. doi: 10.21037/jtd.2018.10.106. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Stuart CM, Dyas AR, Mott NM, et al. Postoperative day of surgery ambulation improves outcomes following lung resection: a multicenter prospective cohort study. J Thorac Dis. 2024;16(11):7300–7309. doi: 10.21037/jtd-24-1183. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Schieren M, Stoelben E, Weber J, Wappler F, Defosse J, Working Group of the German Thorax Registry . Postoperative complications after thoracic surgery-an analysis from the German Thorax Registry. J Cardiothorac Vasc Anesth. 2025;39(9):2377–2383. doi: 10.1053/j.jvca.2025.05.034. [DOI] [PubMed] [Google Scholar]
  • 6.Damluji AA, Forman DE, van Diepen S, et al. Older adults in the cardiac intensive care unit: factoring geriatric syndromes in the management, prognosis, and process of care: a scientific statement from the American Heart Association. Circulation. 2020;141(2):e6–e32. doi: 10.1161/CIR.0000000000000741. [DOI] [PubMed] [Google Scholar]
  • 7.Grant MC, Crisafi C, Alvarez A, et al. Perioperative care in cardiac surgery: a joint consensus statement by the Enhanced Recovery After Surgery (ERAS) Cardiac Society, ERAS International Society, and The Society of Thoracic Surgeons (STS). Ann Thorac Surg. 2024;117(4):669–689. doi: 10.1016/j.athoracsur.2023.12.006. [DOI] [PubMed] [Google Scholar]
  • 8.Kanejima Y, Shimogai T, Kitamura M, Ishihara K, Izawa KP.. Effect of early mobilization on physical function in patients after cardiac surgery: a systematic review and meta-analysis. Int J Environ Res Public Health. 2020;17(19):7091. doi: 10.3390/ijerph17197091. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Borges MGB, Borges DL, Ribeiro MO, Lima LSS, Macedo KCM, Nina V.. Early mobilization prescription in patients undergoing cardiac surgery: systematic review. Braz J Cardiovasc Surg. 2022;37(2):227–238. doi: 10.21470/1678-9741-2021-0140. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Piler T, Schauer M, Larisch C, et al. Priorities and strategy for the implementation of enhanced recovery after surgery (ERAS) in thoracic surgery. J Thorac Dis. 2024;16(7):4165–4173. doi: 10.21037/jtd-23-1866. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Gorgey AS. Robotic exoskeletons: the current pros and cons. World J Orthop. 2018;9(9):112–119. doi: 10.5312/wjo.v9.i9.112. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Swank C, Galvan C, DiPasquale J, Callender L, Sikka S, Driver S.. Lessons learned from robotic gait training during rehabilitation: therapeutic and medical severity considerations over 3 years. Technol Disabil. 2020;32(2):103–110. doi: 10.3233/TAD-190248. [DOI] [Google Scholar]
  • 13.Swank C, Sikka S, Driver S, Bennett M, Callender L.. Feasibility of integrating robotic exoskeleton gait training in inpatient rehabilitation. Disabil Rehabil Assist Technol. 2020;15(4):409–417. doi: 10.1080/17483107.2019.1587014. [DOI] [PubMed] [Google Scholar]
  • 14.Gillespie J, Arnold D, Trammell M, et al. Utilization of overground exoskeleton gait training during inpatient rehabilitation: a descriptive analysis. J Neuroeng Rehabil. 2023;20(1):102. doi: 10.1186/s12984-023-01220-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Gillespie J, Wynne L, Ochoa C, et al. Overground robotic exoskeletons for early mobility in acute care therapy for patients with neurological injuries: a development-of-concept study. J Acute Care Phys Ther. 2025;16(3):79–87. doi: 10.1097/JAT.0000000000000256. [DOI] [Google Scholar]
  • 16.Arnold D, Gillespie J, Bennett M, et al. Clinical delivery of overground exoskeleton gait training in persons with spinal cord injury across the continuum of care: a retrospective analysis. Top Spinal Cord Inj Rehabil. 2024;30(1):74–86. doi: 10.46292/sci23-00001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Bosteder KD, Arnold D, Gillespie J, et al. Physiological and perceptual demand of gait training on inpatient physiotherapists. Clin Rehabil. 2025;39(7):976–988. doi: 10.1177/02692155251334286. [DOI] [PubMed] [Google Scholar]
  • 18.Ott P, Wilson A, Hamilton R, Callender L.. Safety and effectiveness of exoskeleton gait training in stroke survivors with a Left Ventricular Assist Device (LVAD). 2018.
  • 19.Ekso Bionics . EksoNR specifications. https://eksobionics.com/static/e81256e83cafb92c3c441ae07ae652b7/109173-EksoNR-Flyer.pdf. Accessed January 28, 2026.
  • 20.Jackson WT, Novack TA, Dowler RN.. Effective serial measurement of cognitive orientation in rehabilitation: the orientation log. Arch Phys Med Rehabil. 1998;79(6):718–720. doi: 10.1016/s0003-9993(98)90051-x. [DOI] [PubMed] [Google Scholar]
  • 21.Harris PA, Taylor R, Thielke R, Payne J, Gonzalez N, Conde JG.. Research electronic data capture (REDCap)—a metadata-driven methodology and workflow process for providing translational research informatics support. J Biomed Inform. 2009;42(2):377–381. doi: 10.1016/j.jbi.2008.08.010. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Harris PA, Taylor R, Minor BL, et al. The REDCap consortium: building an international community of software platform partners. J Biomed Inform. 2019;95:103208–103208. doi: 10.1016/j.jbi.2019.103208. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Whitehead AL, Julious SA, Cooper CL, Campbell MJ.. Estimating the sample size for a pilot randomised trial to minimise the overall trial sample size for the external pilot and main trial for a continuous outcome variable. Stat Methods Med Res. 2016;25(3):1057–1073. doi: 10.1177/0962280215588241. [DOI] [PMC free article] [PubMed] [Google Scholar]

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