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Cardiopulm Phys Ther J. 2012 March; 23(1): 5–13.
PMCID: PMC3286494

Early Mobilization in the Intensive Care Unit: A Systematic Review

Joseph Adler, PT, DPT, CCScorresponding author1 and Daniel Malone, PhD, MPT, CCS2

Abstract

Purpose

The purpose of this review is to evaluate the literature related to mobilization of the critically ill patient with an emphasis on functional outcomes and patient safety.

Methods

We searched the electronic databases of PubMed, CINAHL, Medline (Ovid), and The Cochrane Library for a period spanning 2000–2011. Articles used in this review included randomized and nonrandomized clinical trials, prospective and retrospective analyses, and case series in peer-reviewed journals. Sackett's Levels of Evidence were used to classify the current literature to evaluate the strength of the outcomes reported.

Results

Fifteen studies met inclusion criteria and were reviewed. According to Sackett's Levels of Evidence, 9 studies were level 4 evidence, one study was level 3, 4 studies were level 2, and one study was level one evidence. Ten studies pertained to patient safety/feasibility and 10 studies pertained to functional outcomes with 5 fitting into both categories.

Conclusion

A search of the scientific literature revealed a limited number of studies that examined the mobilization of critically ill patients in the intensive care unit. However, literature that does exist supports early mobilization and physical therapy as a safe and effective intervention that can have a significant impact on functional outcomes.

Key Words: mobilization, exercise, intensive care unit, critical illness, physical therapy

INTRODUCTION

The early mobilization of patients in the intensive care unit (ICU) has received considerable attention in clinical and scientific literature over the past several years.1,2,3 A wide range of published reports has attempted to study the effects of mobilization and physical therapy on multiple factors including patient safety, ambulation capacity, muscle strength, functional outcomes such as activities of daily living, duration of mechanical ventilation, ICU length of stay, hospital length of stay, and mortality.

There are inherent complications to mobilizing critically ill patients that appear straightforward but are not well established. These apparent complications include, but are not limited to: tenuous hemodynamic status, severe weakness, multiple central catheters and life supporting monitors, artificial airways and operational factors such as variable rehabilitation work practices.4,5,6,7

Studies have demonstrated that survivors of critical illness have impaired exercise capacity and persistent weakness, suboptimal quality of life, enduring neuropsychological impairments and high costs of health care utilization.8,9,10,11,12 It has been hypothesized that ICU-based interventions may play a role in reducing these ongoing physical and neuropsychological impairments in ICU survivors in both the short- and long-term, highlighting the importance of studying this population.12

When patients require admission or readmission to the ICU, a period of enforced bed rest generally ensues. Despite knowledge of the deleterious effects of bed rest on multiple body systems,13,14,15,16 the ICU is a complicated and difficult environment in which to mobilize the critically ill.1,17 Multiple life-sustaining catheters and monitors, sedative medication used to calm agitation or reduce energy expenditure, impaired levels of alertness from medications, sleep disturbances, electrolyte imbalances, and tenuous hemodynamic status all are contributing factors that limit mobilization.

As critical care medicine improves and overall mortality decreases, survivors of ICU admissions are realizing greater morbidity. Severe weakness, deficits in self-care and ambulation, poor quality of life, hospital readmission, and death have all been reported in patients up to 5 years after discharge from the ICU.12,18

Mobilizing patients in the intensive care environment is not without risk. Catheters and supportive equipment attached to patients can become dislodged and cause injury. Insertion and reinsertion of catheters can increase infection risk and cause unwanted stress and pain for patients and families already stressed by the medical acuity of the ICU. Critically ill patients with physiological derangements can have adverse hemodynamic responses to activity. Patients with limited aerobic capacity may respond to exertional stress with exaggerated heart rate and blood pressure responses or conversely may not have enough physiologic reserve to meet even the seemingly simple task of sitting on the edge of the bed.

Although the frequency of published reports related to mobilizing critically ill patients is increasing, the number of controlled, randomized trials is few. The purpose of this review was to examine the literature and characterize the clinical benefits of mobilizing critically ill patients found predominantly in the ICU, specifically related to safety and functional outcomes.

METHODS

Literature Search

The electronic databases of PubMed, CINAHL/Nursing, Medline (Ovid) and the Cochrane Library were searched as noted in Figure Figure1.1. The key search terms, “mobilization,” “exercise,” and “physical therapy” were combined with “intensive care unit” and “critical illness.” Reference lists of review articles and original publications were manually reviewed supplementing the electronic search to ensure that the database searches were comprehensive.

Figure 1
Search algorithm.

Study Selection Criteria

Articles included in this review were: prospective randomized trials, prospective cohort studies, retrospective analyses, and case series. We further limited our inclusion to articles that focused on adults that were published in English between January 1, 2000 and June 1, 2011 to capture the most recently published work. Studies were evaluated to determine fit to the inclusion criteria by review of the title, and the list of potential articles was further sorted by reviewing abstracts by the primary author (JA). Studies were excluded if they were review articles, only studied nonmobility interventions, and/or described programs or protocols designed to promote early mobilization. If relevancy was questioned, both authors then collaborated on the final decision for inclusion.

Levels of Evidence

Sackett's Levels of Evidence were used to rate the strength of the research19 process where research was ranked from strongest to weakest using a 5 point grading system as outlined in Table Table1.1. The authors (DM and JA) collaborated equally on scoring.

Table 1
Sackett's Levels of Evidence

RESULTS

Fifteen studies were included in this review and submitted to analysis. Many outcomes were reported in the mobilization of critically ill patients and included a wide range of data. The studies were categorized into two groups based on the outcome addressed: safety and functional outcomes. Functional outcomes were further subdivided into one of 3 areas: muscle strength; quality of life/patient symptoms, and mobility. Some studies overlapped multiple categories. Of the studies reviewed, 4 reported on muscle strength, two on quality of life, and 13 on functional mobility.

Studies included both prospective and retrospective design while randomization occurred in just 3 studies.20,21,22 The randomization in Chiang et al's study22 occurred in a postintensive care environment. Ten studies examined cohort populations or samples of convenience. Eleven of those were prospective.4,20,21,22,23,24,25,26,27,28,29 Four studies were retrospective analyses.18,30,31,32 Two of those studied patients in a postacute environment.30,31

Safety/Adverse Events

Of all studies reviewed, 10 papers reported data concerning untoward events (eg, line removal, extubation), physiological responses [eg, heart rate (HR), blood pressure (BP), pulse oximetry] and/or need for alteration in medical plan of care (eg, sedative or vasopressor administration). The authors (JA and DM) defined these events as pertaining to patient safety. As noted in Table Table22 untoward events occurred in ≤ 4% of total patient interactions. The reviewed studies used specific physiologic responses and patient complaints (see Table Table3)3) to initiate and terminate exercise or activity sessions. Bailey et al23 consecutively enrolled patients with respiratory failure who required mechanical ventilation for >4 days. There were 14 activity-associated untoward events during 1,449 activity sessions, none of which were deemed serious. In the study by Pohlman and colleagues32 a descriptive analysis of the intervention arm of the study by Schweickert et al,20 activity associated adverse events occurred in 16% (80 of 498) of therapy sessions with patients on mechanical ventilation. The authors describe many of the events as “expected physiological changes with exercise.” Examples include a HR increase greater than 20% of baseline (21 of 498 or 4.2 %), and a respiratory rate (RR) greater than 40 breaths per minute (20 of 498 interactions or 4.0%). Activity sessions were halted due to exceeding the predetermined criteria (see Table Table33).

Table 2
Safety and ICU Mobilization
Table 3
Criteria for Terminating a PT/OT Mobilization Session as Summarized from the Literature

Overall, the most commonly cited adverse event was oxygen desaturation. These episodes were of short duration lasting less than 3 minutes. In studies that reported on adverse events, accidental removal of patient support equipment happened rarely (<1%) further highlighting the safety of patient mobilization. Burtin et al21 reported one Achilles tendon rupture in their intervention group that used in-bed cycle ergometry. There were no serious adverse events that required life saving measures or alterations in the patient's medical care.

FUNCTIONAL OUTCOMES

Muscle Strength

Extremity muscle strength was measured by hand-held dynamometry or manual muscle testing [eg, Medical Research Council (MRC) scoring] in 4 studies as noted in Table Table44 and defined in Table Table5.5. Medical Research Council scores, handgrip, and extremity strength did not differ at time of discharge from the ICU20,21 but Burtin et al21 showed increased quadriceps muscle force at time of hospital discharge. In postacute settings where patients were mechanically ventilated for a minimum of 14 days prior to transfer, strength gains were observed. In one study,30 subjects were mechanically ventilated for a median duration of 46 to 52 days (22.8 ± 80.8 days) and demonstrated upper extremity/lower extremity (UE/LE) strength gains measured by dynamometry. In another study30 patients were mechanically ventilated for 18.1 ± 7 days and also demonstrated UE/LE strength gains by manual muscle testing (MMT). Both studies found increases in respiratory muscle strength.

Table 4
Outcomes of ICU Mobilization
Table 5
Medical Research Council (MRC) Scoring System for Muscle Strength*

Functional Mobility: The most frequently described functional outcomes assessed were: time to mobility milestones [eg, time to first out of bed (OOB), standing]; ambulation distance,24 the Barthel Index,33 the Functional Independence Measure (FIM)34 or select parts of the FIM [Functional Status Score in the ICU (FSS-ICU)].4 The FSS-ICU, similar to the FIM, rates functional activities between 1 (total assist) and 7 (complete independence). A score of 0 is assigned if a patient is unable to perform a task. Only 5 of the items from the FIM are included: (1) rolling, (2) transfer from supine to sit, (3) sitting at the edge of bed, (4) transfer from sit to stand, and (5) ambulation are combined in the cumulative FSS-ICU score.4

Mobility milestones were accomplished earlier in the intervention groups than the comparison groups in 4 studies.20,24,25,26 Compared to controls, ambulation frequency was greater in the study by Thomsen et al24 and ambulation distance was greater at time of hospital discharge in the studies by Schweickert et al20 and Burtin et al.21

Objective measures such as the FIM & Barthel Index improved in the intervention groups at time of hospital discharge but without significant differences at time of ICU discharge in the study by Schweickert et al.20 In the postacute care setting, bed mobility and transfers were improved in 3 studies22,30,31 but ambulation/locomotion were only improved in the studies by Chiang et al22 and Montagnani et al.31

Quality of Life & Patient Symptoms: Burtin et al21 noted improvements in the physical functioning (PF) subscore of the SF-36 at time of hospital discharge but quality of life (QOL) was not reported for the transition from ICU to ward. Dyspnea was measured in the postacute care setting in the study by Montagnani et al.31 These patients were hospitalized for approximately 40 days prior to postacute admission, had tracheostomies, and required prolonged mechanical ventilation. The symptom of dyspnea was reduced following the rehabilitation period.

DISCUSSION

The focus of critical care medicine in the ICU is restoration of physiological or hemodynamic stability and prevention of death. The historical approach to achieve these goals has included long periods of immobility and bedrest. The impact of life-sustaining ICU technology on patients that have required sedation, long-term mechanical ventilation, and bedrest has been profound with respect to severe muscle weakness, functional impairments, and loss of quality of life.15 By understanding the negative sequella of ICU-induced bed rest, investigators are attempting to correct these derangements by reducing the dosage and frequency of sedative medication and mobilizing critically ill patients once hemodynamic stability has been achieved. We have reviewed published reports that have studied this clinical approach.

Safety: Studies included in this review persuasively conclude that the mobilization of critically ill but stable patients in the ICU and immediate postacute environment, who have required a period of mechanical ventilation, can be done safely with minimal risk to the patient. Although most studies included patients receiving 4 or more days of mechanical ventilation, Pohlman et al20 demonstrated the safety of physical therapy intervention occurring within two days of intubation. The most common untoward event was transient oxygen desaturation that was attenuated by rest and increasing the FiO2 delivered to the patient. Line dislodgment and/or accidental extubation, frequently mentioned dangers of mobilization, happened rarely, further highlighting the safety profile of patient mobilization.

In all studies, hemodynamic, respiratory, and cognitive criteria were established a priori to ensure patient safety (Table (Table3).3). These criteria guided the clinicians to determine patient eligibility for mobilization and, it is presumed, limited untoward events by providing the treating physical therapist and/or occupational therapist parameters to guide the intensity of the mobilization sessions. Mobilization was loosely described in most studies citing therapist discretion for advancing activities based on patient tolerance and stability. However, Stiller et al27 provided an algorithm for initiating and terminating therapy sessions based on physiologic and laboratory data while Morris et al25 provided an algorithm for mobility progression based on patient's physical capabilities.

Overall activity-induced increases in HR, BP, respiratory rate (RR), tidal volume, and minute ventilation were within acceptable ranges, challenging the perception that patients in the ICU are “too sick” to participate in mobilization activities.4,27,28 As noted multiple studies have reported on safety and feasibility but the lack of reported negative events could reflect a bias of nonreporting of adverse incidents.

Muscle Strength: Although it is generally accepted that patients in critical care settings for prolonged periods of time are often “bed ridden,” deconditioned, and weak, muscle strength was infrequently reported as an outcome measure in the reviewed studies. In studies that did address muscle force production, strength was not significantly improved in the ICU20,21 but did improve by the time of discharge from the hospital.21 Interestingly, strength was consistently improved in the postacute care setting.22,30

Functional Mobility: The literature reviewed supports improvements in functional mobility following early and progressive physical therapy/occupational therapy (PT/ OT) in the ICU but the measurement of this outcome was not uniform across the literature. For example, as mentioned in the results section, variability of outcome measurements included acquisition of mobility milestones,18,20,21,23,24,26

FIM,20,22,30,31 FSS-ICU,4 and the Barthel Index.33 Time to mobility milestones was reduced and patient participation in advanced mobilization activities occurred more frequently in ICUs where mobilization and PT/ OT were emphasized.20,24,25,26 Within the ICU setting, objective measures such as the FIM & Barthel Index were used infrequently although two of the cited studies used these tools.4,20

The FIM and Barthel Index scores improved in the intervention group in the study by Schweickert et al20 with over 59% of patients achieving functional independence (FIM ≥ 5) compared to 35% of the control group at time of hospital discharge. The FIM scores also improved following rehabilitation in the postacute setting.22,30,31 Use of the FIM, or the related FSS-ICU4 to measure patient disability and to compare functional outcomes is attractive since the tool is well known to rehabilitation professionals. However, the validity and reliability of this tool has not been established in the ICU setting.

Quality of Life & Patient Symptoms: Quality of life and patient symptoms were seldom measured within the ICU. One study21 measured QOL and one study measured patient's symptoms.31 Burtin et al21 demonstrated improvements in the physical functioning domain of the SF-36 at hospital discharge while Montagnani et al31 reported reduced patient dyspnea. As noted in the introduction, quality of life and neuropsychological impairments such as depression, anxiety, and posttraumatic stress disorder are negatively impacted by prolonged mechanical ventilation and ICU duration. Rehabilitation in the ICU and its influence on these factors should be an area of future research.

The physiology and complications of bed rest are well understood. Intensive care unit-acquired weakness and functional dependency are recognized as unfortunate consequences of prolonged duration in ICUs and mechanical ventilation. Although sedative medications are used to reduce metabolic energy demand for patients in respiratory failure they inhibit participation in exercise and functional activity and often cause disturbances in levels of arousal. Despite the inherently complex environment and challenges that face critical care teams, including the human resources required to safely mobilize patients, feasibility and safety has been demonstrated as noted in Table Table2.2. Critically ill patients can exercise, sit up, transfer to bedside chairs, and ambulate in the hallways; however, few published papers have randomized and controlled this intervention. The work of Schweickert et al,20 Burtin et al,21 and Chiang et al22 have found that participation in monitored programs of physical activity can lead to statistically significant improvements in ambulation independence, reduced duration of mechanical ventilation, better ability to perform self care activities, and improved respiratory function.

CONCLUSION/IMPLICATIONS FOR FUTURE RESEARCH

In summary, the body of evidence that has studied the mobilization of critically ill patients is small. The few randomized controlled trials include a total of only 171 patients limiting the strength of evidence. Based on the studies reviewed, early physical therapy and ICU mobilization is feasible and safe. Acquisition of mobility milestones is enhanced in ICUs that promote early rehabilitation. Improvements in quality of life and muscle strength cannot be determined at this time.

In reviewing the literature, there are several questions that must be addressed. These questions include, but are not limited to: (1) How do published papers reflect current practice as mobilization has been reported in a small percentage of ICUs? (2) What is the appropriate level of clinical expertise or experience required to safely work in a critical care environment? (3) What intensity, frequency, and dose of physical activity will lead to optimal patient outcomes? (4) What generalization to other patient populations can be made since the majority of patients studied are found in medical ICUs? (5) Should all patients who require mechanical ventilation or ICU admission be referred to physical therapy? And (6) Are there optimal patient populations who would benefit most from early mobilization, as well as populations for whom physical therapy is clearly contraindicated? The answer to these questions will provide an evidence-based approach to optimize patient outcomes for the critically ill patient.

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Articles from Cardiopulmonary Physical Therapy Journal are provided here courtesy of Cardiopulmonary Physical Therapy Section of the American Physical Therapy Association