What is myasthenia gravis? How is anesthesia managed during surgery?

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Anesthesia in patients with myasthenia gravis

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No.
1 Myasthenia gravis

What is myasthenia gravis?

Myasthenia gravis (MG) is a disorder that manifests as a disorder
of neuro-muscle transmission that affects the contractile function of skeletal muscles.
The incidence ranges from 5 to 12.
5 per 100,000 population
.
The exact cause of myasthenia gravis is unknown
.

At present, it is believed that the causes of myasthenia gravis are divided into two categories, one is congenital hereditary, very rare, and has nothing to do with autoimmunity; The second category is autoimmune diseases, the most common, whose antigen is acetylcholine receptor (AchR), the pathogenic antibody is acetylcholine receptor antibody (AchR-Ab), and the target organ is acetylcholine receptor
on the postsynaptic membrane of the neuromuscular junction.

diagnosis

Antibodies
are detectable in 80% of patients with generalized muscle weakness and 50% of patients with ocular symptoms alone.
The initial diagnosis of MG is often based on history and clinical examination, and then confirmed
by a series of diagnostic tests.
Clinical testing of stress tolerance includes upward gaze time, hand abduction extension time, and spirometry
.
Other tests to confirm MG include the following:

• Electrophysiological tests • Pharmacological tests • Serological tests

symptom

A large number of clinical data prove that AchR-Ab has a certain relationship
with the thymus.
Nearly 90% of patients with MG have thymoma or thymic hyperplasia, and thymectomy can achieve good results
in MG.
It is currently believed that the thymus gland is the site
where AchR-Ab is produced.

The onset of the disease is slow, and the symptoms are fluctuating; Breakfast is lighter, aggravated after work and in the evening, and better after rest; Muscle paralysis does not start from the distal end of the limb, but from the involvement of the extraocular muscles, manifested as limited eye movement, ptosis, strabismus, diplopia, etc.
, followed by cranial nerve innervation muscle groups such as facial muscles, masticatory muscles and throat muscles, neck muscles, scapular girdle muscles and flexor muscles of the hip, and in severe cases, ventilators; Tendon reflexes are mostly present
in MG patients.
treat

At present, there are 5 main categories of treatment, including: anticholinesterase drugs, adrenal corticosteroids, plasma exchange, thymectomy and other immunotherapies
.
Patients with myasthenia gravis often have thymic hypertrophy, of which 10% to 20% have thymic tumors
.
Most patients require thymectomy
.
Even if only thymus tissue is removed without a thymic tumor, satisfactory treatment results
can be obtained.

No.
2 Pre-anesthesia preparation

Adequate preoperative preparation is an important part of reducing postoperative complications and mortality in MG patients:

1
.
Understand the degree of muscle weakness and the response to drug treatment, rationally adjust the dose of anticholinesterase drugs, and maintain adequate ventilation and cough and swallowing ability with the minimum effective amount of anticholinesterase drugs.

2.
Complete preoperative examination, chest CT or MRI, mediastinal gas angiography can determine whether there is thymic tumor, its scope and nature; ECG and MCG can understand heart function and muscle strength; Pulmonary function tests help to understand lung function, and patients with significantly low lung function, cough, and poor swallowing function should delay surgery
.

3.
Supportive treatment, MG patients should rest adequately and strengthen nutrition
.

Pre-anesthesia medication is based on the principle
of small doses, which can be sedative without suppressing breathing.

Pay attention to myasthenia gravis!

No.
3

Anesthesia selection management

The choice of anesthesia should be based on the principle
that neuromuscular conduction and respiratory function are not affected as much as possible.
For non-open surgery, local anesthesia or neuraxial anesthesia
may be used.
In order to ensure safety, tracheal intubation should be selected for general anesthesia, and endotracheal intubation should be done with retained spontaneous breathing endotracheal intubation as much as possible, which can be done
under low-dose analgesia and sedation with anesthesia.

MG patients are usually sensitive to non-depolarizing muscle relaxants, which have been reported to be 20 times higher than normal people, and generally require 20%-25% of the conventional dose to meet muscle relaxation requirements, and short-acting drugs are safe
.
MG presents with resistance to depolarizing muscle relaxants or early phase II block
.
If succinylcholine is choline, attention should be paid to delayed respiratory depression
caused by desensitization block.
Therefore, it was once best not to use muscle relaxants in MG patients when performing anesthesia, but with the clinical application of sulgamose, clinical experience has shown that rocuronium bromide combined with sulgamose can be safely and effectively applied to MG patients
.

Some antibiotics can impede the release of acetylcholine, have the effect of blocking the neuromuscular junction, and can worsen muscle weakness
.
Some antiarrhythmic drugs (eg, quinidine, procainamide, etc.
) inhibit excitatory conduction of muscle fibers and reduce the release of acetylcholine
from postganglionic nerve endings.
The diuretic furosemide lowers serum potassium and can worsen muscle weakness
.
In addition, low sodium, low calcium, and high magnesium can interfere with acetylcholine release
.

During thymectomy, respiratory management is critical and adequate ventilation should be ensured, but hyperventilation
should be avoided.

Post-thymectomy complications include respiratory dysfunction, bleeding, and pneumothorax
.
Intubation of the endotrachea must achieve normal spontaneous breathing, complete consciousness, and normal
cough and swallowing reflexes.

In view of the need to continue anticholinesterase therapy after surgery, there may be increased respiratory secretions, and for patients with a long history of MG and preoperative pulmonary insufficiency, endotracheal intubation
should be retained after surgery.

Pay attention to myasthenia gravis!