Degenerative neurological diseases and neuropathies

1

What is amyotrophic lateral sclerosis and its anesthetic considerations?

Also known as Lou Gehrig disease , amyotrophic lateral sclerosis (ALS) is a disease of both upper and lower motor neurons resulting from degeneration of alpha motor neurons in the brainstem and spinal cord. It usually affects men in the sixth through eighth decade of life. Patients with ALS develop progressive weakness, muscle atrophy, spasticity, and hyperreflexia, and eventually die (from pneumonia and pulmonary failure), often in a 3- to 5-year period. Bulbar muscles become affected, increasing the risk of aspiration. The pathogenesis is poorly understood and treatment options are limited. Tracheostomy, gastrostomy, mechanical ventilation, and other supportive treatments are common. There is no evidence that either regional or general anesthesia exacerbates the disease. Succinylcholine-induced hyperkalemia and subsequent cardiac arrest have been reported. Nondepolarizing muscle relaxants have a prolonged duration of action. One should anticipate varying degrees of autonomic dysfunction. Patients will likely need postoperative ventilatory support. Medications with respiratory depressant effects should be used with caution because of increased sensitivity.

2

Review the clinical manifestations of Guillain-Barré syndrome.

Guillain-Barré syndrome (also known as acute inflammatory demyelinating polyradiculopathy ) usually presents with sudden onset of weakness or paralysis, typically in the legs, that ascends to the trunk, arms, and bulbar muscles over several days. Bulbar involvement may be suggested by facial muscle weakness. Areflexia is also a feature. Respiratory failure requiring mechanical ventilation occurs in 20% to 30% of cases. About half of all cases are preceded by a respiratory or gastrointestinal infection. The pathogenesis is thought to be autoimmune, and recovery may occur within weeks. Mortality results from sepsis, adult respiratory distress syndrome, pulmonary embolism, or cardiac arrest.

3

How is the autonomic nervous system affected in Guillain-Barré syndrome?

Autonomic dysfunction is a common finding. Patients may experience wide fluctuations in blood pressure, profuse diaphoresis, peripheral vasoconstriction, tachyarrhythmias and bradyarrhythmias, cardiac conduction abnormalities, and orthostatic hypotension. Sudden death has been described.

4

What are the major anesthetic considerations for patients with Guillain-Barré syndrome?

Patients may not handle oral secretions well because of pharyngeal muscle weakness and have respiratory insufficiency secondary to intercostal muscle paralysis. Aspiration is a risk. Compensatory cardiovascular responses may be absent, and patients may become hypotensive, with mild blood loss or positive-pressure ventilation. Laryngoscopy may produce exaggerated increases in blood pressure. Responses to indirect-acting vasoactive drugs may also be exaggerated. Intraarterial blood pressure monitoring is recommended.

Succinylcholine is contraindicated because of the potential for exaggerated potassium release, and this state may persist even after symptoms resolve. Nondepolarizing neuromuscular blockers may cause prolonged weakness. Postoperative ventilation may be necessary.

5

Review the pathophysiological features of Parkinson disease.

Parkinson disease, an adult-onset degenerative disease of the extrapyramidal system, is characterized by the loss of dopaminergic neurons in the basal ganglia. With the loss of dopamine, there is diminished inhibition of the extrapyramidal motor system and unopposed action of acetylcholine.

6

Describe the clinical manifestations of Parkinson disease.

Patients with Parkinson disease display increased rigidity of the extremities, facial immobility, akinesia, shuffling gait, rhythmic resting tremor, dementia, depression, diaphragmatic spasms, and oculogyric crises (a dystonia in which the eyes are deviated in a fixed position).

7

What are the effects of levodopa therapy, particularly on intravascular volume status?

Levodopa, the immediate precursor to dopamine, crosses the blood-brain barrier, where it is converted to dopamine by a decarboxylase enzyme. Treatment with levodopa increases dopamine both in the central nervous system and peripherally. Increased levels of dopamine may increase myocardial contractility and heart rate. Renal blood flow increases, as do glomerular filtration rate and sodium excretion. Intravascular fluid volume decreases, the renin-angiotensin-aldosterone system is depressed, and orthostatic hypotension is a common finding. High concentrations of dopamine may cause negative feedback for norepinephrine production, which also causes orthostatic hypotension.