2. Treatment includes administration of anticholinesterase drugs, thymectomy, corticosteroids, and immunosuppressants. Whereas underdosage with anticholinesterase drugs results in skeletal muscle weakness, overdosage leads to a “cholinergic crisis.” The role of thymectomy for the treatment of myasthenia is not clearly established.

3. Management of Anesthesia

a. The primary concern is the potential interaction among the disease, treatment of the disease, and neuromuscular blocking drugs. Patients with uncontrolled or poorly controlled myasthenia are exquisitely sensitive to even small (defasciculating) doses of nondepolarizing muscle relaxants.

b. The variability in response to different muscle relaxants warrants careful monitoring with a peripheral nerve stimulator and its correlation with clinical signs of recovery from neuromuscular blockade. Short- or intermediate-acting nondepolarizing muscle relaxants are usually recommended.

B. Myasthenic Syndrome (Lambert-Eaton Syndrome)

1. The myasthenic syndrome is a disorder of neuromuscular transmission associated with carcinomas, particularly small cell carcinoma of the lung. (This syndrome should be suspected in patients undergoing diagnostic procedures, such as diagnostic bronchoscopy, mediastinoscopy, or exploratory thoracotomy for possible cancer) (Table 23-5).

2. Management of Anesthesia

a. Patients with myasthenic syndrome are sensitive to the effects of both depolarizing and nondepolarizing muscle relaxants.

b. Administration of 3,4-diaminopyridine should be continued until the time of surgery.

V. GUILLAIN-BARRÉ SYNDROME (POLYRADICULONEURITIS). Guillain-Barré syndrome (polyradiculoneuritis) is the acute form of a group of disorders classified as inflammatory polyneuropathies (autoimmune disease caused by a bacterial or viral infection that triggers an immune response, producing antibodies that damage the myelin sheath and cause axonal degeneration).

A. This syndrome is characterized by the acute or subacute onset of skeletal muscle weakness or paralysis of the legs, which spreads cephalad and may result in difficulty swallowing and impaired ventilation from paralysis of the intercostal muscles.

1. The most serious immediate problem is hypoventilation. Vital capacity should be monitored frequently. If it decreases below 15 to 20 mL/kg, mechanical ventilation of the lungs is indicated.

2. Although 85% of patients with this syndrome achieve a good recovery, chronic recurrent neuropathy develops in 3% to 5% of patients.

3. Autonomic nervous system dysfunction with wide fluctuations in blood pressure (physical stimulation may precipitate hypertension), tachycardia, cardiac dysrhythmias, and cardiac arrest.

B. Management of Anesthesia

1. Compensatory cardiovascular responses may be absent (autonomic nervous system dysfunction), resulting in significant hypotension secondary to postural changes, blood loss, or positive airway pressure. Conversely, stimuli such as laryngoscopy and tracheal intubation may produce hypertension and tachycardia.

2. SCh is not recommended because drug-induced potassium release may result in hyperkalemia and cardiac arrest. The response to nondepolarizing muscle relaxants ranges from sensitivity to resistance.

3. It is likely that mechanical ventilation will be required during the immediate postoperative period.

VI. CENTRAL NERVOUS SYSTEM DISEASES

A. Multiple sclerosis is characterized by multiple sites of demyelination in the brain and spinal cord, leading to visual disturbances, limb weakness, and paresthesias.

1. Therapy for multiple sclerosis is directed at modulating the immunologic and inflammatory responses that damage the central nervous system (CNS) (corticosteroids, interferon, glatiramer, mitoxantrone [maybe cardiotoxic]).

2. Management of Anesthesia. The effect of anesthesia and surgery on the course of multiple sclerosis is controversial.

a. Regional and general anesthesia have been reported to exacerbate or have no effect on multiple sclerosis. Factors other than anesthesia, such as infection, emotional stress, and hyperpyrexia, may contribute to an increased risk of perioperative exacerbation.

b. A neurologic examination before anesthesia and surgery is helpful to document coexisting neurologic deficits.

c. Patients being treated with corticosteroids may require perioperative supplementation, and immunosuppressants may produce cardiotoxicity and subclinical cardiac dysfunction.

d. Autonomic dysfunction caused by multiple sclerosis may produce exaggerated hypotensive effects in response to volatile anesthetics.

e. Respiratory muscle weakness and dysfunction may increase the likelihood of the need for postoperative mechanical ventilation.

B. Epilepsy (Table 23-6)

1. The sudden onset of seizures in a young to middle-aged adult should arouse the suspicion of focal brain disease (tumor); onset after 60 years of age is usually secondary to cerebrovascular disease.

2. The availability of new antiseizure drugs has increased the therapeutic options for patients with epilepsy (Table 23-7). The newer antiseizure drugs target ion channels, γ-aminobutyric acid (GABA) receptors, amino acid receptors, and synaptic proteins.

3. Management of Anesthesia

a. Antiseizure medications should be maintained throughout the perioperative period.

b. An anesthetic technique that minimizes the risk of seizure activity should be used. Although most inhaled anesthetics, including nitrous oxide, have been reported to produce seizure activity, such activity during the administration of isoflurane and desflurane is extremely rare. (Sevoflurane may be epileptogenic, but the clinical significance is uncertain.) Ketamine may produce seizure activity in patients with known seizure disorders. Reported seizure activity after administration of opioids may reflect myoclonic activity.

C. Alzheimer disease is the major cause of dementia in the United States, and more than 5 million people in the United States have the disease. The incidence is 5% in persons older than age 65 years and 30% in those older than age 85 years.

1. Alzheimer disease is characterized by cognitive impairment, poor decision making, language deterioration, gait disturbances, seizures, agitation, and psychosis.

2. A positive diagnosis can, however, only be made at autopsy. Imaging studies show hippocampal atrophy (magnetic resonance imaging [MRI]) and glucose hypometabolism (positron emission tomography).

3. There is no specific therapy for Alzheimer disease, but the initial symptomatic therapy (nausea, bradycardia, syncope, fatigue) is with cholinesterase inhibitors and an N-methyl-d-aspartic acid (NMDA) receptor antagonist.

4. Animal studies have demonstrated that volatile, halogenated anesthetics produce neuronal changes that resemble the diseased neurons of patients with Alzheimer disease (thus, there is controversy about the use of halogenated anesthetics in neonates and elderly patients).

5. Postoperative cognitive dysfunction (POCD) is well known in elderly patients, but the causes remain elusive. Patients and their families should be advised that POCD can occur.

6. Sedative premedication should be used with caution, if at all, because mental confusion may worsen. If an anticholinergic is required, glycopyrrolate, which does not cross the blood–brain barrier, is preferable to atropine or scopolamine.

D. Parkinson disease is a degenerative disease of the CNS caused by the loss of dopaminergic fibers in the basal ganglia of the brain. It occurs in 1% of population older than age 60 years of age.

1. Typical clinical features are secondary to depletion of dopamine from the basal ganglia (Table 23-8).

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