Makindo Medical Notes

Related Subjects: |Respiratory Failure |Non-invasive ventilation (NIV) |Intubation and Mechanical Ventilation |Critical illness neuromuscular weaknesss |Haemodialysis |Dobutamine

Introduction

Critical illness neuromuscular weakness encompasses a range of acquired neuromuscular disorders that develop in critically ill patients, particularly those in the intensive care unit (ICU). The most common forms are Critical Illness Polyneuropathy (CIP) and Critical Illness Myopathy (CIM). These conditions contribute to prolonged mechanical ventilation, delayed weaning, increased ICU stay, and overall morbidity and mortality. Early recognition and appropriate management are essential to improve patient outcomes.

About

Critical illness neuromuscular weakness is characterized by diffuse, symmetric weakness of limb and respiratory muscles. It results from direct effects of critical illness on nerves and muscles, leading to impaired neuromuscular function. This weakness can delay recovery and rehabilitation, impacting the patient's quality of life post-ICU.

Risk Factors

• Prolonged Mechanical Ventilation: Extended periods of ventilation increase the risk due to immobility and exposure to sedatives and neuromuscular blockers.
• Sepsis and Systemic Inflammatory Response Syndrome (SIRS): Severe infections trigger inflammatory responses that contribute to muscle and nerve damage.
• Use of Corticosteroids: High doses or prolonged use can lead to muscle atrophy and weakness.
• Neuromuscular Blocking Agents: Prolonged administration, especially of non-depolarizing agents, can contribute to muscle weakness.
• Immobilization: Lack of movement and prolonged bed rest lead to muscle wasting (disuse atrophy) and weakness.
• Multiorgan Failure: Conditions like acute respiratory distress syndrome (ARDS), renal failure, and hepatic failure increase susceptibility.
• Hyperglycemia: Poor glycemic control is associated with increased risk due to metabolic disturbances affecting nerves and muscles.
• Critical Illness Severity: Higher severity scores (e.g., APACHE II) correlate with increased risk.

Types of Critical Illness Neuromuscular Weakness

• Critical Illness Polyneuropathy (CIP):
  • Pathophysiology: An axonal sensory-motor polyneuropathy affecting peripheral nerves, often associated with sepsis and SIRS.
  • Clinical Features: Symmetric limb weakness, decreased or absent deep tendon reflexes, distal sensory loss, and muscle atrophy. Primarily affects lower limbs but can involve upper limbs and respiratory muscles.
• Critical Illness Myopathy (CIM):
  • Pathophysiology: Primary myopathy characterized by muscle fiber atrophy, necrosis, and loss of myosin filaments. Often linked to corticosteroid use and neuromuscular blocking agents.
  • Clinical Features: Generalized weakness, more pronounced in proximal muscles, including the diaphragm and respiratory muscles. Reflexes may be preserved or reduced.
• Overlap Syndrome:
  • Some patients exhibit features of both CIP and CIM, indicating a combined neuropathic and myopathic process.

Causes of Weakness in the ICU

Differential diagnosis of neuromuscular weakness in critically ill patients includes various conditions:

Clinical Presentation

Patients with critical illness neuromuscular weakness often present with:

• Prolonged ICU Stay: Often following severe sepsis, ARDS, or multi-organ failure.
• Difficulty Weaning from Mechanical Ventilation: Due to weakness of respiratory muscles, leading to prolonged ventilator dependence.
• Generalized Muscle Weakness: Flaccid quadriparesis or quadriplegia affecting both proximal and distal muscles.
• Reduced or Absent Deep Tendon Reflexes: More common in CIP.
• Facial Weakness: Symmetric facial muscle involvement may occur.
• Sensory Findings: In CIP, decreased sensation to pain, temperature, and vibration; CIM typically lacks sensory deficits.
• Preserved Extraocular Movements: Eye movements are usually spared.
• Normal Mental Status: Patients are alert when sedation is minimized, helping differentiate from central causes.

Differential Diagnosis

• Guillain-Barré Syndrome (GBS):
  • Acute inflammatory demyelinating polyneuropathy presenting with ascending weakness and areflexia.
  • May have elevated protein in CSF with normal cell count (albuminocytologic dissociation).
• Rhabdomyolysis:
  • Muscle breakdown leading to elevated creatine kinase (CK) levels, often >10,000 U/L.
  • Associated with myoglobinuria and risk of acute kidney injury.
• Myasthenia Gravis:
  • Autoimmune disorder causing fluctuating muscle weakness and fatigue.
  • Often involves ocular and bulbar muscles; reflexes are preserved.
• Spinal Cord Injury:
  • May present with weakness and sensory deficits below the level of the lesion.
  • Often spasticity develops after initial flaccid phase.
• Electrolyte Imbalances:
  • Hypokalemia, hypophosphatemia can cause muscle weakness.
  • Reversible with correction of electrolyte disturbances.

Investigations

A comprehensive workup is necessary to confirm the diagnosis and rule out other causes:

• Laboratory Tests:
  • Full Blood Count (FBC), Urea & Electrolytes (U&E), Liver Function Tests (LFTs), Vitamin B12, Folate levels.
  • Creatine Kinase (CK) Levels: May be normal or mildly elevated in CIM; significantly elevated in rhabdomyolysis.
  • Blood Glucose Levels: To assess glycemic control.
  • Thyroid Function Tests: To exclude thyroid disorders.
• Nerve Conduction Studies (NCS):
  • In CIP: Reduced amplitude of compound muscle action potentials (CMAPs) and sensory nerve action potentials (SNAPs), indicating axonal degeneration.
  • In CIM: Normal sensory nerve studies; motor studies may show reduced CMAPs.
• Electromyography (EMG):
  • In CIP: Features of denervation such as fibrillation potentials.
  • In CIM: Early recruitment of low-amplitude, short-duration motor units; reduced muscle membrane excitability.
  • EMG helps differentiate between neuropathic and myopathic processes.
• Lumbar Puncture (LP):
  • Performed if Guillain-Barré syndrome is suspected; may show elevated protein with normal cell count.
• Muscle Biopsy:
  • May be considered when diagnosis is unclear.
  • In CIM: Shows muscle fiber atrophy, loss of thick filaments (myosin loss), necrosis.
  • In CIP: May show axonal degeneration of peripheral nerves.
• Imaging Studies:
  • MRI: Of the spine if spinal cord pathology is suspected; may show signal changes in cases of myelitis or infarction.

Management

Management focuses on prevention, supportive care, and rehabilitation:

• Optimizing ICU Care:
  • Minimize sedation and avoid unnecessary use of neuromuscular blocking agents.
  • Use corticosteroids judiciously, balancing benefits and risks.
  • Implement glycemic control protocols to maintain blood glucose within target ranges.
  • Avoid hyperglycemia, which may exacerbate nerve and muscle damage.
• Early Mobilization:
  • Initiate passive and active range-of-motion exercises as early as feasible.
  • Engage physical and occupational therapy teams to develop individualized rehabilitation plans.
• Weaning from Mechanical Ventilation:
  • Gradual reduction of ventilator support as respiratory muscles regain strength.
  • Use of weaning protocols and respiratory muscle training techniques.
• Nutrition Support:
  • Ensure adequate caloric and protein intake to support muscle repair and prevent further catabolism.
  • Consider enteral nutrition as preferred route unless contraindicated.
• Prevention of Complications:
  • Prevent pressure ulcers, deep vein thrombosis, and joint contractures through appropriate measures.
  • Regular skin assessments, use of pressure-relieving devices, and prophylactic anticoagulation as indicated.
• Multidisciplinary Approach:
  • Involve neurologists, physiatrists, respiratory therapists, and dietitians in the care plan.
  • Provide psychological support to patients and families, addressing anxiety and depression.
• Monitoring and Follow-Up:
  • Regular assessment of muscle strength and functional status.
  • Plan for ongoing rehabilitation post-ICU discharge to maximize recovery.

Prognosis

Recovery from critical illness neuromuscular weakness can be variable:

• Many patients experience significant improvement over weeks to months.
• Some may have persistent weakness and functional limitations requiring long-term rehabilitation.
• Early intervention and prevention strategies can improve outcomes.

Conclusion

Critical illness neuromuscular weakness is a significant contributor to morbidity in ICU patients. Recognition of risk factors, early diagnosis, and implementation of preventive measures are essential. A multidisciplinary approach focused on minimizing risk factors, providing supportive care, and facilitating rehabilitation can improve patient outcomes and quality of life post-critical illness.

References

• Bolton CF. Neuromuscular manifestations of critical illness. Muscle Nerve. 2005;32(2):140-163.
• Latronico N, Bolton CF. Critical illness polyneuropathy and myopathy: a major cause of muscle weakness and paralysis. Lancet Neurol. 2011;10(10):931-941.
• Hermans G, et al. Intensive care unit acquired muscle weakness: critical illness polyneuropathy and myopathy. Crit Care Med. 2008;36(8):2438-2444.
• Bednarík J, et al. Critical illness polyneuromyopathy: the electrophysiological components of a complex entity. Intensive Care Med. 2003;29(9):1505-1514.
• Stevens RD, et al. Neuromuscular dysfunction acquired in critical illness: a systematic review. Intensive Care Med. 2007;33(11):1876-1891.
• Schweickert WD, et al. Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet. 2009;373(9678):1874-1882.