Neuromuscular Disease


Parameter

Normal value

Critical value

Forced vital capacity (FVC)

40–70 mL/kg

20 mL/kg

Maximal inspiratory pressure (MIP)

Men: >−100 cmH2O

−30 cmH2O

Women: >−70 cmH2O

Maximal expiratory pressure (MEP)

Men: >200 cmH2O

40 cmH2O

Women: >140 cmH2O


Table adapted from Wijdicks et al. [8]. By permission of Mayo Foundation for Medical Education and Research



It is important to identify if the patient requires ventilatory assistance, which can be provided in the form of non-invasive ventilation using the Bilevel Positive Airway Pressure (BiPAP), or via orotracheal intubation and conventional invasive mechanical ventilation. BiPAP may be particularly helpful in patients in myasthenic crisis and may prevent an intubation. Patients with Guillain-Barre syndrome experiencing respiratory distress secondary to neuromuscular failure should undergo prompt endotracheal intubation and mechanical ventilation as BiPAP is contraindicated. Patients may require long-term respiratory management and tracheostomy [6].

The role of the APC is essential for the prevention and timely recognition of secondary complications such as infection, gastric ulcer and deep vein thrombosis. Aggressive pulmonary toileting, early and frequent mobilization and volume management should also be priorities in the management of these patients.




16.4 Interventions and Management



16.4.1 Guillain-Barre Syndrome


Guillain-Barre Syndrome (GBS) is an autoimmune, inflammatory disease causing peripheral nerve damage to the myelin sheath portion of the nerve cell (Fig. 16.1). The inflammatory damage interferes with nerve conduction. GBS often presents after a bacterial or viral illness, thought to be the precipitating event for the development of auto-antibodies. The incidence is slightly higher in men than women, and increases with age. There are a few variants to this disease, although in this chapter we will discuss the most common, generalized and demyelinating form (acute inflammatory demyelinating polyradiculoneuropathy) [4].

A341029_1_En_16_Fig1_HTML.jpg


Fig. 16.1
Demyelination in nerve roots and peripheral nerves in Guillain-Barre Syndrome


16.4.1.1 Clinical Presentation


The most common clinical presentation consists of acute, symmetric, ascending weakness, sensory changes and decreased to complete absence of deep tendon reflexes. Initial symptoms often include paresthesias (or “pins and needles” sensation), especially in the feet and legs. Low back pain is also a frequent early complaint. Motor symptoms follow shortly after and subsequently predominate. As the disease progresses, the neuropathy can be mild, moderate, or severe.

Motor weakness is progressive, starting in the lower extremities and ascending to the hips and trunk followed by shoulders, arms and neck. Cranial nerves are frequently involved. Patients may develop ophthalmoparesis causing diplopia and bulbar muscle weakness (bilateral facial weakness, oropharyngeal muscle weakness) causing dysarthria and dysphagia. The degree of motor weakness may range from mild to complete (paralysis). The speed and severity of weakness are strong indicators of the risk of respiratory failure. Bulbar muscle weakness also predicts need for intubation and mechanical ventilation [4].

Respiratory failure requiring mechanical intubation occurs in one third of cases of GBS. Careful assessment and monitoring is needed to intervene when respiratory failure is imminent. Presence of paradoxical breathing pattern signifies diaphragmatic failure and should be considered a sign of impending neuromuscular respiratory failure. Bulbar muscle weakness may impair coughing and result in inability to manage secretions [7].

Autonomic dysfunction is another major manifestation of GBS. Patients may present with arrhythmias, dramatic swings in blood pressure (both hypotension and hypertension), ileus, bladder dysfunction and body temperature dysregulation.


16.4.1.2 Diagnosis


Initial evaluation consists of taking detailed history of present illness and conducting a thorough neurological examination. Patients may present anywhere on the symptom spectrum and may rapidly progress.

Nerve conduction studies (NCS) and electromyography (EMG) are helpful diagnostic tools that assess nerve conduction and degree of denervation. In the patient with the most typical form of GBS, acute inflammatory demyelinating polyradiculoneuropathy, NCS studies will show slowing of the motor nerve conduction velocity. The degree of slowing velocities in the motor nerves represents a good indicator of the severity of the demyelination. Some patients have more severe axonal form of GBS and those cases show decreased amplitude of the motor nerve action potentials. NCS/EMG is helpful in initial diagnosis and may be helpful to repeat later in the disease course to gauge the peak severity of the disease and monitor recovery [2].

Cerebrospinal fluid (CSF) should be obtained via lumbar puncture. Most often, CSF will have an elevated concentration of protein but normal cell count.

Baseline and serial pulmonary function tests (PFTs) should be obtained to monitor the degree of weakness of respiratory muscles. PFTs are a reliable measure of weakness progression in GBS, but only when patients are appropriately coached before the testing. APCs should become familiar with the technique of PFTs to assist respiratory therapists during their performance.


16.4.1.3 Treatment


Management of GBS includes supportive care and administration of immunomodulatory therapies. Prevention and early identification of secondary complications should always be a priority in the mind of the APC, in particular the recognition of early signs of respiratory failure. It is important for the APC to use critical thinking skills when monitoring for respiratory failure. Not all patients need mechanical ventilation. A general rule is that the GBS patient should be intubated if their forced vital capacity (FVC) falls below 15–20 ml/kg (Fig. 16.2). However, this rule does not apply to every patient and each case should be individually assessed considering all relevant factors (presence of bulbar weakness, dysautonomia, comorbid conditions, etc.) [4].

A341029_1_En_16_Fig2_HTML.gif


Fig. 16.2
Algorithm for respiratory management of Guillain-Barre Syndrome (Wiley-Blackwell, “The Practical Management of Guillain Barre Syndrome and myasthenic crisis” in Emergency Management in Neurocritical Care. Image used with permission from the Mayo Foundation for Medical Education and Research)

Patients should be closely monitored for breathing pattern and airway safety. It is worth emphasizing that pulse oximetry may show acceptable saturation values even in the setting of severe muscle weakness, especially when the patient is receiving supplemental oxygen. Once the patient develops signs of respiratory failure or airway compromise, orotracheal intubation is indicated without delay. Non-invasive ventilation is not safe in patients with severe GBS. Tracheostomy may be necessary for long-term respiratory management.

Only gold members can continue reading. Log In or Register to continue

Jan 31, 2018 | Posted by in NEUROSURGERY | Comments Off on Neuromuscular Disease
Premium Wordpress Themes by UFO Themes