Early Mobilization for Critically Ill Patients

Abstract

Advances in the field of critical care medicine have helped improve the survival rate of these ill patients. Several studies have demonstrated the potential benefits of early mobilization as an important component of critical care rehabilitation. However, there have been some inconsistent results. Moreover, the lack of standardized mobilization protocols and the associated safety concerns are a barrier to the implementation of early mobilization in critically ill patients. Therefore, determining the appropriate modalities of implementation of early mobilization is a key imperative to leverage its potential in these patients. In this paper, we review the contemporary literature to summarize the strategies for early mobilization of critically ill patients, assess the implementation and validity based on the International Classification of Functioning, Disability and Health, as well as discuss the safety aspects of early mobilization.

Introduction

Advances in the field of critical care medicine have helped improve the survival rate of critically ill patients. However, for most patients, increased survival does not translate into improved functional status, secondary to dysfunction due to immobility. This leads to difficult weaning from mechanical ventilation, prolonged length of stay in the ICU, ICU-acquired weakness, and poor quality of life after discharge.¹ The strategy of early mobilization in the ICU environment has generated a lot of interest as a potential intervention to prevent or minimize dysfunction in critically ill patients.^2,3 However, there is a lack of standardized mobilization protocols for these patients, and the details of the implementation strategy are not clear.

We reviewed studies related to the early mobilization of critically ill subjects. For a comprehensive and in-depth description, we used a function-centered International Classification of Functioning, Disability and Health (ICF) theoretical framework to systematically describe the practical guidance and validity of mobilization from a functional perspective. We also discuss the mobilization strategies and the associated doses, the indications, contraindications, as well as the safety aspects of implementation. Our work may provide a reference for the implementation of critical care rehabilitation in the ICU.

Early Mobilization Strategies

Early mobilization of critically ill patients refers to a series of clinical intervention protocols (such as passive movement or active exercises) that confers physical benefits and is initiated and provided to patients at an early period in the ICU in collaboration with a multidisciplinary team (intensive care physicians, rehabilitation physicians, physical therapists, occupational therapists, respiratory therapists, and nurses). The aim of these interventions is to improve the mobility and functional status of critically ill patients.^4-7 Owing to the wide range of intervention strategies, we classified them into passive/active intervention strategies and progressive mobilization strategies according to the state of consciousness of the patient. The practical early mobilization strategies for critically ill patients are summarized in Table 1.

Table 1.

Practical Early Mobilization Strategies for Critically Ill Patients

Passive Mobilization

The instability of the physiological state of critically ill patients in the early stage and their poor ability to cooperate are major barriers to the implementation of early mobilization interventions. However, studies have demonstrated the safety and feasibility of implementation of passive strategies in critically ill patients in the early phases of the disease. Therefore, for sedated or unconscious patients, and those who are unable to cooperate (Richmond Agitation-Sedation Scale [RASS] score ≤ 2), passive intervention strategies (such as manual passive joint movement, device-dependent exercises, and neuromuscular electrical stimulation [NMES]) can be used to prevent complications of bed rest and to develop a foundation for subsequent functional status improvement.

Manual passive joint movement.

Critically ill patients in the ICU are at significantly increased risk of muscle atrophy, deep vein thrombosis, and limited joint mobility due to multiple factors. As early as 1995, Griffiths et al⁸ applied passive movement to critically ill subjects to reduce structural changes in muscle fibers. Thelandersson et al⁹ also showed the safety of passive joint movement in critically ill subjects. Subsequently, there was wider implementation of early passive joint movements in ICU.^10,11 Kim et al¹² applied upper-extremity passive movements in subjects with acute stroke in ICU at a dose of 15 min twice daily with 10 repetitions of each joint movement. Their results demonstrated the efficacy of passive movements in improving upper-extremity function and the ability to perform activities of daily living. In the same year, Genc et al¹³ further demonstrated the effectiveness of passive movement implemented in critically ill subjects with the same exercise dose of 10 repetitions of each joint movement. For critically ill subjects with decreased bowel dynamics, Morisawa et al¹⁴ demonstrated the efficacy of passive movements of the lower extremities and trunk with 10 repetitions of joint movements along with an additional 10 min of trunk rotation movement. However, other studies have yielded inconsistent results. Medrinal et al¹⁵ found no beneficial effect of passive joint movements on cardiac output in mechanically ventilated subjects in ICU.

Nonetheless, studies have demonstrated the efficacy of passive joint movements as a common intervention strategy for subjects with severe diseases requiring sedation and analgesia or those who are unconscious. It has been shown to be helpful in maintaining joint motion while providing some sensory input to the patient. However, the effects of mobility on other physiologic parameters, such as cardiac output, may depend on the adequate dose. Passive movement training lasting > 10 min or at least 10 repetitions of each movement at least once a day may be more beneficial. These include upper-limb movement (shoulder flexion and extension, adduction and abduction, internal and external rotation; elbow joint flexion and extension; forearm rotation; wrist flexion and extension; ulnar radial deviation; metacarpophalangeal and interphalangeal joint flexion and extension), lower-limb movement (hip flexion and extension, adduction and abduction, internal and external rotation; knee flexion and extension; ankle plantarflexion and dorsiflexion, internal and external rotation), and trunk rotation.

Continuous passive motion.

Continuous passive motion (CPM) refers to passive interventions to maintain joint range of motion (ROM) by means of an instrument. It is typically used on lower limbs and has good efficacy in improving ROM but is less frequently used in critically ill patients. Amidei and Sole¹⁶ applied CPM to mechanically ventilated critically ill subjects to assess their tolerance. They found that the application of CPM for 20 min per session reduced the level of inflammatory cytokines and improved subject comfort during and after the intervention. They further suggested that prolonged CPM might be more beneficial to patients. The above conjecture was confirmed by Sommers et al,¹⁷ who found that CPM administered 3 times a day for 3 h prevented joint contractures and helped maintain ROM in unconscious subjects. However, more studies are required to further determine the optimal therapeutic dose.

Passive cycling.

For critically ill patients who are unable to cooperate, passive cycling, which enables patients to move their limbs alternately in the supine position, is one of the more popular components of early passive mobilization strategies for critically ill patients. The safety of passive cycling (30 revolutions per minute [rpm] for 20 min/session) was confirmed by Camargo Pires-Neto et al¹⁸ in 2013. Subsequently, in a randomized controlled trial by Machado et al,¹⁹ passive cycling was found to significantly increase peripheral muscle strength in critically ill subjects; however, it had no effect on duration of mechanical ventilation or stay (parameters set at 20 rpm, 20 min/session). In the same year, Nickels et al²⁰ demonstrated the potential effect of passive cycling on the physical function and cognitive status of critically ill subjects. They also proposed a cycling protocol for sedated/unconscious patients or those who are unable to cooperate: 20 rpm, 30 min/session. In conclusion, some studies have demonstrated the advantages of passive cycling as an adjunctive therapy for preventing muscle atrophy; however, the underlying physiological mechanisms are not well characterized. Moreover, further research is required to explore the effects on other physical functions in critically ill patients or on respiratory function in mechanically ventilated patients.

Tilt table.

The tilt table has also been used with critically ill patients, as shown in Figure 1. In critically ill patients on mechanical ventilation, use of the tilt table can passively assist the patient to stand, facilitate the implementation of early mobilization interventions, briefly increase the patient’s minute ventilation, improve respiratory function, shorten the duration of mechanical ventilation, and promote recovery.^4,21-24 In a prospective study, Toccolini et al²⁵ showed the safety of the tilt table in critically ill subjects and pointed out the advantages conferred by improvements in patient level of consciousness and maximum inspiratory pressures. In unconscious subjects, studies by Bohannon and Green²⁶ and Ng et al²⁷ demonstrated the potential benefits of passive standing on a tilt table in improving level of consciousness and ankle mobility. However, there is a paucity of high-quality research to support these claims. Considering the potential impairment of sympathetic modulation during postural adaptation in critically ill patients (especially in neurocritical patients), the effects of different tilt table angles and durations of use should be further explored based on patient condition and tolerance.

Fig. 1.

Tilt table in ICU.

Neuromuscular electrical stimulation.

Muscle dysfunction is common in ICU patients, with muscle wasting occurring rapidly within days after admission in critically ill patients, which may also cause functional impairment and even ICU-acquired weakness. All of these issues may result in poor clinical outcomes in critically ill patients. Electrical stimulation has been used to improve muscle function by promoting muscle contraction and simulating the motor state in patients lacking voluntary muscle movement. Patients often do not cooperate well at the time of admission to ICU due to sedation or excessive anxiety, which can lead to delays in active exercises.²⁸ Therefore, electrical stimulation, which requires less patient cooperation, has been attracting attention.

In 1987, Bouletreau et al²⁹ described the beneficial effects of intermittent electrical stimulation on muscle metabolism in critically ill subjects. Subsequently, electrical stimulation in critically ill patients was widely used to maintain muscle mass and reduce the occurrence of severe polymyopathy in patients. In 2010, Routsi et al³⁰ applied NMES to the medial femoral, lateral femoral, and peroneus longus muscles of both lower limbs in critically ill subjects. They found that NMES was able to prevent muscle weakness and shorten the duration of mechanical ventilation in these subjects. In 2017, Dall’ Acqua et al³¹ also applied NMES in critically ill subjects and found that the muscle thickness in the intervention group was maintained, whereas muscle thickness in the control group was significantly reduced; in addition, the use of NMES also significantly shortened the hospital length of stay. This has led to much focus on the practical significance of NMES techniques on the muscle of critically ill patients.

A randomized controlled study by Fossat et al³² found that the application of NMES in the ICU did not improve the global muscle strength of critically ill subjects at discharge. In addition to the lack of strong evidence to support the effectiveness of this strategy, and considering the feasibility of electrical stimulation equipment, the Japanese Society of Intensive Care Medicine and the Japanese Association for Acute Medicine³³ do not recommend electrical stimulation as an ICU-acquired weakness preventive measure for critically ill patients. A meta-analysis by Zayed et al³⁴ in 2019 also supported the above assertion; they found no difference in global muscle strength, ICU mortality, duration of mechanical ventilation, or ICU length of stay in critically ill subjects treated with NMES compared to conventional treatment. In addition, a retrospective study of critically ill pediatric subjects by Magalhaes et al³⁵ similarly suggested a need for further research to demonstrate the efficacy of NMES in this population, although they found no adverse events related to the use of NMES.

Regarding differences in efficacy, a systematic review by Wageck et al³⁶ found much variability with respect to the modulation parameters used in the application of NMES in critically ill subjects. Whereas in most studies the frequency of electrical stimulation used was 30 Hz, the pulse duration settings varied from 300–400 µs. As high pulse duration is liable to lead to earlier onset of muscle fatigue, this may be a major reason for the negative results. Subsequently, Sommers et al¹⁷ recommended the intervention parameters (45 Hz, 60 min/time, 1 time/d) for physiotherapy in the ICU for unconscious critically ill subjects; however, they did not indicate the pulse duration. The physiological mechanisms of NMES in critically ill patients are still unclear, and more high-quality studies are required to further define the treatment parameters for different types of critically ill patients in order to optimize patient benefit.

Active Mobilization

For critically ill patients who are partially or fully cooperative (RASS score ≥ −2), we suggest active interventions that can help improve physical function as well as psychological state by alleviating patients’ fear and anxiety in the ICU through active participation. These include active exercises, functional electrical stimulation (FES), active cycling, and FES-assisted cycle ergometry (CE) (FES-CE).

Active exercises.

Active exercises refer to training in which patients participate actively or with the assistance of others. Active exercises can better promote energy metabolism in critically ill patients compared with passive intervention³⁷ and are gradually being used in the early mobilization of critically ill patients based on the level of cooperation of patients in the ICU. These broadly include bed exercises (active-assisted exercises, active resistance exercises, turning, bridge), out-of-bed exercises (transferring, balance training, and ambulation), and activities of daily living.³⁸ Many studies have confirmed their importance for critically ill patients. Active exercise was shown to improve physical function, shorten the stay, improve the mood, and reduce complications in the ICU.^39,40 A literature review by Reid et al⁴¹ published in 2018 agreed with these views. However, as critically ill patients are not physiologically stable, there is a need to clearly define the appropriate dose of exercise especially in the early stage. Only a few studies have clearly described the dose of exercise. Sommers et al¹⁷ found that the intensity at a Borg score of 11–13 and frequency of 1–2 sessions/d, 1–3 sets/time, 8–10/group was more suitable in critically ill subjects. In summary, although several studies have demonstrated the benefits of active exercises, the exercise doses used in the studies varied widely, and the evaluation criteria were not consistent. Thus, further high-quality studies are required to further clarify the exercise doses.

Functional electrical stimulation.

FES is a physiotherapeutic intervention that can induce more definite and effective functional muscle contractions through different modality settings and has shown many benefits in rehabilitation therapy. In recent years, FES has been gradually applied in the rehabilitation of respiratory function and early mobilization of critically ill patients. It has been shown to improve respiratory function and assist in the early weaning of critically ill patients from mechanical ventilation. A systematic review by Vorona et al⁴² suggested the importance of FES in improving clinical outcomes of difficult-to-wean subjects. This was subsequently supported by a similar study conducted by McCaughey et al;⁴³ they demonstrated the feasibility of FES in critically ill mechanically ventilated subjects and further showed the benefits of FES in reducing the duration of mechanical ventilation and ICU length of stay. In general, the benefits of FES in critically ill patients (especially respiratory function) deserve recognition, but further studies are required to determine the parameters of effective treatment.

Active cycling.

Several studies have also demonstrated the efficacy of active cycling (application of active-assisted, active modalities of CE to actively engage critically ill patients in cycling) in reducing muscle atrophy and improving physical function. Kho et al⁴⁴ demonstrated the safety and feasibility of cycling intervention in the ICU and showed its role in improving the function and prognosis of critically ill subjects. Subsequently, Kimawi et al⁴⁵ supported these views and further demonstrated the effective role of active participation in progressive cycling in improving the functional performance of critically ill subjects. In terms of exercise dose, most studies focused on 30 min of training time; however, there was much variability among studies with respect to the resistance settings, with some studies adjusting resistance parameters according to subject experience and others suggesting a gradual increase from low resistance.⁴⁶ Overall, active cycling is a worthwhile mobilization intervention to consider for critically ill patients who are able to cooperate.

Functional electrical stimulation–assisted cycle ergometry.

A combination of CE and FES has been used to optimize the rehabilitation of patients and to produce more effective and coordinated training programs, with good results in both healthy individuals and patients with spinal cord injuries.^47,48 Some studies conducted in the ICU environment have also shown the important role of FES-CE in critically ill subjects. A study by Parry et al⁴⁹ applied FES-CE in critically ill patients and demonstrated not only the safety and feasibility of FES-CE but also its positive effect on physical function. A study by Medrinal et al¹⁵ elucidated the effect of FES-CE in increasing cardiac output, muscle oxygen consumption, and metabolism in critically ill subjects. However, there are still relatively few studies in this category. More research is required to obtain more definitive evidence and to elucidate the mechanisms of therapeutic effect.

Progressive Mobilization

Progressive mobilization strategy for critically ill patients has been demonstrated to be safe and feasible, and it can provide interventions at a level that is appropriate according to the patient’s condition and make progressive dynamic adjustments based on the patient’s performance. This strategy has been shown to play an important role in reducing mortality in patients with respiratory failure, decreasing the days of delirium in critically ill patients, shortening the ICU length of stay, and improving functional state.^50,51 The progressive mobilization program was proposed by Morris et al⁵² in 2008, who established a 4-level progressive mobilization protocol with increasing difficulty based mainly on the patient’s state of consciousness and muscle strength. The fourth level of out-of-bed training included functional activities such as active bed-chair transferring, balance training, standing weight shifting, marching, and walking. The results showed that progressive mobilization shortened the length of stay of critically ill patients without increasing the cost of treatment. A randomized controlled trial by Schweickert et al⁵³ further demonstrated the important role of progressive mobilization in reducing the duration of mechanical ventilation and delirium and in improving functional performance at discharge in critically ill patients. Dantas et al⁵⁴ modified Morris’ mobilization strategy by adding a fifth phase of progressive mobilization, which not only emphasized limb stretching but also added cycling to the third to fifth phases of the protocol. The results demonstrated a better effect of the modified protocol on respiratory muscle and peripheral muscle strength in critically ill patients. Sigler et al⁵⁵ developed an 8-step progressive mobilization protocol for critically ill patients based on a combination of various intervention strategies, and the results likewise supported the aforementioned view and further pointed to the impact of sedation and analgesia on early activity in critically ill patients, which is consistent with Brock et al.⁵⁶

However, despite the observed safety and feasibility of progressive mobilization in critically ill patients, the implementation rate in the ICU has not increased significantly. This is mainly attributed to various factors such as insufficient space to implement mobilization in the ICU, the influence of sedation and analgesia, inadequate communication among the multidisciplinary team members, different conception of mobilization, lack of implementers, and unstable condition of the patients.^57,58 Therefore, we suggest that the clinical application of progressive mobilization strategies should be based on multidisciplinary teamwork, with strict contraindications, reasonable adjustment of sedation measures, and close monitoring of patients’ hemodynamics and other adverse events to promote its effective application in the ICU.

Implementation of Early Mobilization

For better implementation of early mobilization in intensive care settings, there is a need for comprehensive assessment of the patient’s status in order to select the best mobilization protocol. For the collection of health information, the World Health Organization (WHO) proposed the ICF framework, which covers the body functions and structures, activities and participation, environmental factors, and personal factors.⁵⁹ As a core component of the WHO Family of International Classifications, the ICF provides a comprehensive and practical description of a persons’ health status at the functional level and establishes a theoretical system based on the “bio-psycho-social” functional model, which is the core theoretical framework in the field of rehabilitation and can systematically and comprehensively guide the implementation of early mobilization in the ICU.⁶⁰ In this section, we provide practical guidance on early mobilization based on ICF and further discuss the relationship between the level of consciousness of critically ill patients and the timing of initiation of mobilization to facilitate the implementation of early mobilization.

Practical Guidance Based on ICF

For critically ill patients, a comprehensive and specific assessment before early mobilization is the key to implementation.⁶¹ We summarized the early mobilization practice procedure based on the ICF and some related studies.^60,62 As shown in Figure 2, the early mobilization practice procedure includes 5 stages: functional diagnoses of critically ill patients, selection of the mobilization strategies, implementation of mobilization with multidisciplinary teamwork, functional reassessment, and functional outcome assessment. The functional diagnosis, assessment, and outcome assessment of critically ill patients should be based on the ICF framework.

Fig. 2.

Early mobilization practice procedure based on the International Classification of Functioning, Disability and Health.

For example, the early mobilization implementation process for critically ill patients with decreased muscle strength is illustrated in Figure 2. Critically ill patients with decreased muscle strength may have muscle atrophy and impaired joint movement at the physical level and limited mobility, such as inability to turn over and walk, at the individual level. According to the availability of mobilization-related assistive devices (eg, hoists) in the ICU environment and based on the patient’s needs and attitudes, safety-oriented mobilization for critically ill patients should be implemented by a multidisciplinary team. The optimal mobilization strategy for individual patients should be selected, and repeat assessments of patients’ functioning should be performed during the mobilization period. Further, the mobilization protocol should be adjusted based on feedback from the reassessment results. In addition, after the discharge of the patients from the hospital, their functioning level should be assessed to better describe the health outcomes and help optimize the implementation of early mobilization.

Of note, the patients’ functional diagnoses and assessments should be made under the ICF framework. In addition to the environmental and personal factors, the functional diagnosis and assessment before and during mobilization should focus on body functions (b1–b8), body structures (s1–s8), and basic activities (d1–d5), whereas the outcome assessment after discharge should focus on the activities of daily living and participation in social life (d6–d9).

Timing of Initiation of Mobilization

Early mobilization of critically ill patients in the ICU can be implemented for patients who qualify the indications for the same; however, due to the variable condition of critically ill patients, the timing of initiation of early mobilization may affect the efficacy.⁶³ Nevertheless, there is a wide variability in the timing of initiation of early mobilization, which may be attributable to the differences in ICU management and culture.^64,65 Most importantly, the selection and implementation of mobilization strategies are often limited by the level of consciousness of critically ill patients.⁶⁶ The timing of initiation of mobilization is not consistent for each treatment unit for patients with different levels of consciousness, which may be a major factor in the current lack of consistency in the implementation of early mobilization.

Most studies have shown the benefits of early mobilization for subjects who are able to cooperate well. However, in critically ill patients with impaired consciousness or those requiring sedation and analgesia, the inability to cooperate during early mobilization has led to a divergence of attitudes among clinicians regarding the implementation of early mobilization. There are often delays or inconsistencies in mobilizing critically ill patients with impaired consciousness, ultimately leading to muscle atrophy and varying outcomes post implementation. With regard to the relation between the timing of initiation and the validity of early mobilization, Hodgson et al⁶⁷ suggested that the first few days may be a critical period for observing the effectiveness of early mobilization in critically ill patients on mechanical ventilation. Impaired consciousness secondary to a primary neurological injury is often prolonged, and thus failure to mobilize early can result in various complications affecting multiple dimensions that impact patient health.⁶⁸ Owing to the influence of the level of consciousness on early mobilization, Schaller et al⁶⁹ enrolled subjects with impaired consciousness and initiated early mobilization within 72 h of ICU admission. The results showed the safety of early mobilization for critically ill subjects with impaired consciousness and improved functional independence and functional performance at discharge. Similarly, Tsuboi et al⁷⁰ showed that early mobilization was safe for subjects who were unable to cooperate, and it helped improve level of consciousness. Considering the specific condition of patients with impaired consciousness, there is a need for the rational application of passive and active strategies at different conscious stages⁷¹ to reduce delays in initiating early mobilization.

Some authors believe that mobilization should be implemented as soon as possible in critically ill patients (within 24–72 h of ICU admission) to prevent muscle atrophy and other serious complications such as ICU-acquired weakness and post–intensive care syndrome.^52,72-74 This strategy has been shown to be safe and well tolerated by most critically ill patients. However, others have delayed the initiation of early mobilization until 7–14 d after ICU admission; and although there were no significant differences, all critically ill subjects who participated in early mobilization showed improvement compared to their pre-mobilization status.⁷⁵ In summary, the difference in the timing of initiation leads to inconsistency in the definition of early mobilization in critically ill patients. Considering the complexity of the condition of critically ill patients and the fact that the implementation of early mobilization is influenced by illness acuity, especially the impact of the consciousness, more studies are required to explore the optimal timing of early mobilization intervention for various types and consciousness level for critically ill patients.

Validity of Early Mobilization Based on ICF

As early as the late 19th century, Ries⁷⁶ noted the adverse effects of bed rest on critically ill patients and suggested that reducing the duration of bed rest may improve the physical function. Subsequently, numerous studies have demonstrated the benefits of implementing early mobilization in critically ill subjects, including prevention of complications such as muscle atrophy, post–intensive care syndrome, and ICU-acquired weakness in critically ill patients.^33,77 Overall, the efficacy of early mobilization of critically ill patients has been assessed by different studies using different functional assessments. In the following, we discuss the validity of the early mobilization of critically ill patients based on the ICF framework from 3 perspectives: body functions, activities and participation, and interaction with the environment.

Body Functions

Most studies of early mobilization have shown it to be an effective strategy for improving body function in critically ill patients. Early mobilization can help maintain joint mobility and improve joint range of motion. In terms of muscle function, early mobilization using NMES can prevent muscle atrophy and ICU-acquired weakness in critically ill patients by improving glucose metabolism in the muscle tissue; moreover, active intervention strategies and cycling can help maintain muscle volume and even enhance muscle strength.⁷⁸ In terms of respiratory function, early mobilization can increase lung aeration and ventilator-free days.^53,79 However, there is a need to further explore the effect of mobilization on respiratory dynamics of critically ill patients. In addition, early mobilization was shown to reduce the number of days of delirium in critically ill patients and improve their cognitive status with optimal sedation and analgesia,⁵⁴ which indicates the importance of early mobilization for body function in critically ill patients.

Activities and Participation

Early mobilization was mainly used to improve patients’ activity and participation through active intervention strategies such as out-of-bed exercises, balance training, transferring, walking, and daily living exercises. Physical Function ICU Test, length of stay (LOS) in ICU, Functional Status Score in Intensive Care, Short Form 36 (SF-36), Barthel Index, 6-min walk test, de Morton Mobility Index, and Functional Independence Measure can be used to evaluate activity and participation of critically ill patients, among which LOS, 6-min walk test, de Morton Mobility Index, Barthel Index, and SF-36 are more commonly used. However, only a few studies have shown the effect of early mobilization on the quality of life of critically ill subjects.^75,80,81 A meta-analysis by Okada et al⁸² in 2019 disputed the validity of early mobilization and stated that early mobilization implementation failed to improve health-related quality of life in critically ill subjects. This disagreement was attributed to differences in the condition of critically ill subjects. It was further noted that critically ill subjects with immobility or preserved neuromuscular excitability were more likely to have positive treatment outcomes.⁸³ This discrepancy may explain the disagreement on the effectiveness of early mobilization. In conclusion, there is a lack of sufficient evidence of the beneficial effects of early mobilization on the ability of critically ill patients to participate in daily life at discharge, but some studies have demonstrated the beneficial effects of early mobilization in reducing the ICU length of stay, and some studies have shown that early mobilization significantly improves the unassisted ambulation of critically ill subjects at discharge.⁸⁴ Both these studies indicate the potential effects of early mobilization in terms of activity and participation in critically ill patients.

Environmental Factors

As a part of the ABCDEF bundle for critically ill patients,⁸⁵ implementation requires the cooperation of a multidisciplinary team; and in terms of the ICU environment, the cultural environment (for the staff) and the hardware environment (monitoring equipment and mobilization devices) affect the implementation of early mobilization in critically ill patients.⁸⁶ Early mobilization strategies for critically ill patients are increasingly being adopted in ICU settings, but there are still several barriers. In terms of the ICU cultural environment, positive attitudes of team members and increased recognition of early mobilization have been shown to foster its implementation;⁸⁷ daily postural changes (eg, elevating the head of the bed, rolling and knocking, etc) with the cooperation of the nursing team can better improve oxygenation levels and ventilation in critically ill patients. In addition, postural transfers or walking assistive devices (eg, ambulation walkers) can promote the implementation of early mobilization in critically ill patients.⁸⁸ With respect to the psychological state of patients, various alarms and lighting in the ICU tend to affect patients’ psychological perceptions or induce anxiety and fear of early mobilization; these factors may also pose a barrier for the implementation.⁸⁹

Safety of Early Mobilization

Concerns about the safety of early mobilization of critically ill patients are a key barrier to its implementation.^90,91 Better awareness of the indications and contraindications for early mobilization, the impact of intensity, and close monitoring of patients for adverse events can help overcome these barriers and enhance the feasibility of implementation of early mobilization.

Indications and Contraindications

Critically ill patients often have complex comorbid conditions involving multiple systems. Before implementing early mobilization, it is essential to understand the indications and contraindications (or criteria for stopping) of early mobilization in critically ill patients. A summary of the relative indications and contraindications^17,92-95 for the implementation of early mobilization is presented in Table 2.

Table 2.

Indications and Contraindications for Early Mobilization

Although most of the studies had similar criteria in terms of indications and contraindications for early mobilization, there were still differences, especially in the few studies that carried out early mobilization interventions in neurocritical patients. Some studies used neurological impairment as an exclusion criterion for early mobilization interventions in critically ill patients, with fewer indications and contraindications related to the neurological manifestations in critically ill patients. Therefore, all systemic manifestations should be considered to ensure the safe implementation of early mobilization in critically ill patients.

Intensity of Mobilization

The intensity of mobilization may influence its safety and efficacy for critically ill patients. In an observational study, half of all critically ill subjects developed ICU-acquired weakness despite the implementation of early mobilization; comparative analysis indicated that this may be related to the use of low-intensity bed exercises in early mobilization.⁶⁷ High-intensity early mobilization has also been used in subjects within 24 h after stroke, and the results did not support any significant effect of high-intensity early mobilization.⁹⁶ This further suggests that appropriate intensity and effective assessment are essential for early mobilization. In this regard, Trinity et al⁹⁷ included hemodynamic factors in the study of exercise intensity and found that an increase in cardiac output was associated with elevated intensity of exercise. This is consistent with several previous studies in which increased exercise intensity was found to cause an increase in muscle oxygen consumption with a consequent increase in both cardiac output and maximal oxygen uptake.^98,99 Although such changes have been shown to persist in critically ill patients, there is a paucity of studies conducted in critically ill patients. Medrinal et al¹⁵ compared 4 modalities of early mobilization strategies using cardiac output as a measure of exercise intensity. They demonstrated the important role of exercise intensity in critically ill patients, while noting that FES-CE training with high levels of patient participation significantly improved patients’ metabolic levels. However, they noted the need for further studies to explore the dose and intensity settings. Interestingly, although in the study by Scheffenbichler et al¹⁰⁰ high doses (exercise intensity and duration) of exercise were associated with poor prognosis, critically ill subjects did not experience more adverse events with increases in exercise dose. In addition to the intensity of exercise, the duration of exercise is another key determinant. The Borg scale, as a subjective fatigue score, can indirectly reflect patient tolerance of exercise intensity, but it has certain requirements regarding mental status and cognition. Therefore, further studies are required to explore the impact and application of exercise intensity and its evaluation in critically ill patients.

Adverse Events

Many studies have demonstrated the safety of early mobilization. However, the definition of safety events in early mobilization has not been consistent.^101,102 Nydahl et al¹⁰³ defined safety events as worsening clinical status including cardiac arrest, falls, line dislodgement, changes in hemodynamic, and other physiologic parameters based on results from meta-analysis of early mobilization studies in the ICU (n = 22,000). The results showed a potential safety event rate of 2.6% for early mobilization in critically ill subjects, whereas the occurrence of serious problems was much less common, which further confirmed safety of the technique. In the same year, a study by Conceicao et al⁹² supported the above findings; but the authors concluded that the criteria used for defining safety events are not yet consistent, particularly for neurologic incidences. In addition, in critically ill patients on mechanical ventilation, there is heightened risk of cardiovascular events during changes in position (sitting on the edge of bed, standing, or ambulating) during early mobilization.¹⁰⁴ Therefore, the risk of adverse events should be carefully considered in the implementation of early mobilization in critically ill patients; and adverse events or potential adverse events should be defined and followed by real-time monitoring under the guidance of a multidisciplinary team, with particular attention to line dislodgement, falls, profuse sweating, abnormal facial color, pain, and fatigue during mobilization.

Summary

Early mobilization is an important component of critical care rehabilitation that is feasible in the ICU. Mobilization strategies can be broadly classified into active, passive, and progressive mobilization strategies. We provided practical recommendations for implementing early mobilization and discussed the relationship between the timing of initiation of mobilization and the level of consciousness from an implementation perspective. We have also summarized the validity of early mobilization and functional assessment of critically ill patients based on the ICF framework, showing the advantages of early mobilization in improving physical function and increasing activity level. However, clinicians need to consider the safety of mobilization and the effects of different intensities and timings for mobilization on critically ill patients. More robust prospective studies are required to further optimize early mobilization strategies for critically ill patients in the ICU, taking cognizance of the disease conditions and the level of consciousness.