Neuromuscular disorders (NMDs) in critical care may be divided into those that precipitate admission to the ICU and those that arise during ICU management.
Many patients who present to the ICU as a result of an underlying neuromuscular disorder will have a previously defined diagnosis. However, when a patient presents with recent onset of acute or subacute bilateral muscle weakness, a broad differential diagnosis must be considered.
A rapidly progressive spinal cord lesion is the most important diagnosis to consider and immediately exclude in patients presenting with ascending or flaccid paralysis.
The maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), vital capacity (VC), and qualitative judgment of oropharyngeal function are the most important parameters to follow in patients with NMDs.
An effective cough is unlikely with a MEP <40 cm H2O and risk of hypercapnia increases when MIP is less negative than −30 cm H2O. A VC <30 mL/kg impairs secretion clearance and respiratory failure is common at values <15 to 20 mL/kg.
Sleep-related deterioration in alveolar ventilation resulting in hypercapnia and hypoxia is common in patients with respiratory muscle impairment.
Most patients with Guillain-Barré syndrome or myasthenia gravis of sufficient severity to precipitate ICU admission will benefit from treatment with plasma exchange or intravenous immunoglobulin.
Muscle biopsy is useful in the diagnosis of polymyositis, mitochondrial disease, and other myopathies, and should be considered when electrophysiologic and other testing does not offer a clear diagnosis of peripheral neuropathy or myoneural junction diseases.
NEUROMUSCULAR DISORDERS IN CRITICAL CARE: GENERAL ASSESSMENT AND MANAGEMENT
Neuromuscular weakness may result from disorders involving the peripheral nerves, neuromuscular transmission, or skeletal muscles. Neuromuscular disorders encountered in the critical care setting may be divided into those that result in ICU admission and those that are acquired during treatment of critical illness. Most patients who present to the ICU as a result of an underlying neuromuscular disorder will have a previously defined diagnosis. However, when a patient presents with recent onset of acute or subacute bilateral muscle weakness, a broad differential diagnosis must be considered (Table 87-1). The initial approach to differential diagnosis attempts to define the principal level of abnormality based on the patient's history and findings on neurologic examination (Table 87-2). Additional diagnostic tests such as neuroimaging, nerve conduction, and electromyogram (EMG) studies are often needed to establish the underlying disorder more reliably. An easy to remember mnemonic, MUSCLES, may be helpful in remembering some of the most common causes of generalized weakness in the ICU1 (Table 87-3).
Causes of Acute and Subacute Bilateral Weakness
|Favorite Table|Download (.pdf) TABLE 87-1
Causes of Acute and Subacute Bilateral Weakness
|Syndrome/Level of Abnormality ||Representative Disorders |
|Basilar artery occlusion ||Embolic, thrombotic, vasculitic |
|Myelopathy ||Cord compression (eg, abscess, neoplasm, |
|disc herniation, trauma) |
|Transverse myelitis |
|Central nervous system infections ||Poliomyelitis |
|West Nile virus |
|Central nervous system toxins ||Neurotoxic fish poisoning |
|Peripheral nerve disorders ||Guillain-Barre syndrome |
|Phrenic nerve injury (eg, trauma, surgery ...|
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