ICU Acquired Weakness

Original Editor - Tolulope Adeniji.

Top Contributors - Tolulope Adeniji, Vidya Acharya, Kim Jackson and Natalie Patterson


Critically ill patients often develop neuromuscular disorders such as Critical Illness Polyneuropathy (CIP) and Critical Illness Myopathy (CIM) called Intensive Care Unit Acquired weakness (ICUAW).[1][2] One of ICUAW's implications is that it causes generalized muscle weakness with more affectation on the limbs and respiratory muscles, leading to delays in mobilization and prolongation of hospitalization.[2][3] There are several diseases that make people with illness worsen to the extent of the need for ICU use. One of these diseases is COVID-19, which affects the respiratory system and leaves a person with this condition using a ventilator or ICU.  Knowledge of ICUAW among clinicians such as physiotherapists will therefore enhance effective delivery of healthcare to ICU patients such as patients with COVID-19. This paper will therefore examine the literature on ICUAW including its management and physiotherapy role in ICUAW.


Overiew of ICU acquired weakness

Pathophysiology of ICU Acquired Weakness

There are several muscular changes in critically ill patients. Distortion of protein to DNA ratio, muscle protein synthesis, and catabolic proteolysis, which explains some of the generalized muscle weakness in the acute phase of a person who is critically ill[5]. Not only does bed rest contribute to muscle loss in critically ill patients, but ICUAW also leads to muscle protein synthesis, muscle mass reduction, and increases muscle catabolism[5]. This contributes to less strength generated by muscle fiber as well as muscle wastage. The three ways in which ICUAW occurs in critically ill patients are polyneuropathy, myopathy, and/or muscle atrophy[6]. The characteristics of a person with critical illness polyneuropathy (CIP) are symmetrical, distal sensory-motor axonal polyneuropathy, which manifests in the affection of limbs and respiratory muscles and may also affect sensory and autonomic nerves[6]. Those with critical illness myopathy (CIM) show limb and respiratory muscle weakness without affecting sensory function. These three manifestations (muscle atrophy, CIM, CIP) may overlap in occurrence and therefore the manifestation of ICUAW varies between different patients[6].

Clinical Presentation

Common clinical presentation of ICUAW is a generalized, usually symmetrical, limb weakness[3]. The proximal muscles are more affected than the distal muscles, however, less affected are the facial and ocular muscles. The reduction of tendon reflexes, facial grimacing to painful stimulation without withdrawal of limbs is another clinical presentation. With CIP type ICUAW, sensations such as pain, temperature and vibration may be impaired and patients with ICUAW may also have autonomic dysfunction.[3]

Diagnostic Procedures

Diagnosis of ICUAW may involve: [3]

  • Medical Research Council (MRC) sum score for muscle strength evaluation. The MRC sum score ranges between 0 and 60, and a score of <48 is suggesting ICUAW.
  • Electrophysiological like EMG, Nerve Conduction (NC) test to evaluates neuromuscular integrity
  • Handheld dynamometry and handgrip strength for evaluating some neuromuscular function
  • Maximal inspiratory pressure to assess inspiratory muscle strength,

Outcome Measures

Muscle strength (MRC) and Neuromuscular integrity evaluation (electrophysiological testing-EMG, NC)

Respiratory Muscles assessment (Incentive spirometer)

Functional Independence Measure (FIM)

An exploratory study investigating functional outcomes at hospital discharge and health-related quality of life after six months in critically ill patients with severe, moderate, or no ICUAW suggested that the participants without ICUAW had superior functional performance at hospital discharge and shorter length of hospital stays when compared to participants with ICUAW. The primary functional outcomes for this analysis were the Functional Independence Measure (FIM) and the 6-Minute Walk Test (6MWT) at hospital discharge. Additional secondary outcomes of interest were FIM at ICU discharge, Timed ‘Up & Go’ at hospital discharge, hospital length of stay and discharge destination, tracheostomy incidence, ICU readmissions, hospital, and 6-month mortality as well as participants’ health-related quality of life determined with the Short Form 36 (SF-36) six months after hospital discharge[7].

Physiotherapy Role in ICUAW

Respiratory Muscle Training

Respiratory muscle weakness is a common feature of ICUAW patients. One explanation for this is that the critically ill patient depends on the mechanical ventilator for a longer period of time, which makes the respiratory muscles weak. Inspiratory muscle training when the patient is on a mechanical ventilator and when weaned improves the strength of the respiratory muscle[5].

Inspiratory muscle training can be achieved by [8]

  • Spontaneous breathing by means of a nonlinear resistor that increases respiratory workload;
  • Insensitive trigger threshold can be used during assisted mechanical ventilation support;
  • A threshold device (a device that provides a known constant inspiration resistance through the use of a flow-independent one-way valve) can also be used.

Physical Training

Physical training involves joint mobilization and muscle training regimes that aim to increase muscle strength, minimize atrophy, improve muscle mass, and function. It can be divided into the ICU admission period when the patient is on a ventilator and post ICU rehabilitation when the patient is weaned. A review by Nobuto Nakanishi et al. shows there exists progressive muscle atrophy in critically ill patients, and physical therapy, electrical muscle stimulation, muscle protective ventilator settings, and glucose control can help prevent atrophy and preserve muscle mass[9]. A systematic review and meta-analysis suggest early rehabilitation in the ICU reduces the incidence of developing ICUAW[10].

Physical training for patients with ICUAW during admission includes:

  • Passive range of motion treatment sessions
  • Passive cycling
  • Electrical muscle stimulation (EMS)

The EMS can also be used in preventing ICUAW.[5]

Post-ICU Physical therapy rehabilitation of a patient with ICUAW is not limited to the following[5]:

  • Strength training program
  • Aerobic session such as walking, arm and leg cycling exercises,
  • Functional activities therapy regime
  • And the provision of self-help manuals and program


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  10. Anekwe DE, Biswas S, Bussières A, Spahija J. Early Rehabilitation Reduces the Likelihood of Developing Intensive Care Unit-Acquired Weakness: A Systematic Review and Meta-Analysis. Physiotherapy. 2019 Dec 19.