ICU-Acquired Weakness

ICU acquired weakness is generalized, symmetric limb weakness that arises after the onset of critical illness and has no cause other than the illness or its treatment. It includes polyneuropathy, myopathy and a combination of both. This article concentrates on bedside diagnosis, outcomes, prevention and rehabilitation.

About 25% of patients ventilated for over 4 to 7 days develop it, rising to 40 to 60% with sepsis, acute respiratory distress syndrome or multiple organ failure. It prolongs ventilation by 4 to 7 days, lengthens hospital stay, and raises both hospital and 1-year mortality. At 1 year, 25 to 40% of survivors have persistent weakness, and many have reduced exercise capacity, fatigue, and difficulty returning to work. It forms part of post-intensive care syndrome, together with cognitive impairment, depression, anxiety and post-traumatic stress.

Risk factors: sepsis, multiple organ failure, hyperglycemia, immobility, prolonged deep sedation, corticosteroids, neuromuscular blocking drugs, older age, female sex, and pre-existing frailty. Complications: failure to wean, dysphagia and aspiration, falls, contractures, pressure injury and long-term disability.

• Failure to wean from mechanical ventilation, with no other cause found
• Symmetric flaccid limb weakness, reduced reflexes and muscle wasting
• Facial muscles relatively spared, with normal grimace to pain
• Reduced cough and diaphragm weakness
• Difficulty sitting, standing and swallowing after sedation is lifted
• Red flags: asymmetric weakness, a sensory level, cranial nerve palsies, ascending paralysis with areflexia and autonomic instability

1. Bedside strength testing in an awake, cooperative patient (able to follow at least five commands and CAM-ICU negative): MRC sum score of six muscle groups on each side (shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, ankle dorsiflexion), each graded 0 to 5. A total below 48 of 60 defines weakness, and below 36 severe weakness. Test daily once awake.
2. Handgrip dynamometry: below 11 kg in men and 7 kg in women confirms weakness.
3. Electrophysiology (nerve conduction studies and electromyography) to separate polyneuropathy, myopathy and mixed disease when it changes management.
4. Muscle and diaphragm ultrasound: quadriceps layer thickness, diaphragm excursion (below 10 mm) and thickening fraction (below 20%).
5. Exclusion of other causes: creatine kinase, electrolytes (potassium, magnesium, phosphate, calcium), thyroid function, cortisol, vitamin B12, thiamine, MRI of the spine for a cord lesion, cerebrospinal fluid analysis for Guillain-Barre syndrome and tests for myasthenia gravis.

Differentials: Guillain-Barre syndrome, myasthenia gravis, spinal cord lesion, electrolyte disorder, drug-induced weakness, prolonged neuromuscular blockade, rhabdomyolysis and motor neuron disease.

No drug treatment is proven, so prevention and rehabilitation are the core.

1. Prevention bundle for every ventilated patient:
   • Light sedation with a target Richmond Agitation Sedation Scale of 0 to -1, with daily interruption.
   • Early mobilization within 24 to 72 hours of cardiovascular and respiratory stability: passive then active range of motion, sitting at the bed edge, standing and walking, for 30 to 60 minutes daily.
   • Avoid neuromuscular blocking drugs unless essential, and use the shortest course.
   • Use corticosteroids only for clear indications, at the lowest dose and for the shortest duration.
   • Glycemic control with insulin infusion to 7.8 to 10 mmol/L, avoiding hypoglycemia.
2. Nutrition: enteral feeding within 24 to 48 hours at 20 to 25 kcal/kg a day, rising to 25 to 30 kcal/kg, with protein 1.3 to 2.0 g/kg a day.
3. Treat sepsis early, with source control.
4. Established weakness:
   • Structured physiotherapy and occupational therapy, daily, with graded resistance exercise and in-bed cycling.
   • Neuromuscular electrical stimulation for 30 to 60 minutes daily in patients unable to participate.
   • Respiratory muscle training and daily spontaneous breathing trials, with early tracheostomy when prolonged ventilation is expected.
   • Swallowing assessment before oral feeding, and speech therapy.
   • Correct vitamin D deficiency with cholecalciferol 50,000 units orally weekly for 8 weeks.
5. Neuropathic pain: gabapentin 300 mg orally at night, increased to 900 to 1800 mg a day in 3 divided doses (reduce in renal impairment).
6. Prevent secondary injury: pressure area care every 2 hours, splints for hands and feet, and padding over nerves.
7. Discharge planning: referral to a rehabilitation program, and an intensive care follow-up clinic at 1, 3, 6 and 12 months.

Screen survivors for depression, anxiety, post-traumatic stress and cognitive impairment, and give return-to-work counselling. Recovery is slow, so counsel the patient and family that gains may continue for 12 months.