Anesthesia and Myasthenia Gravis

Introduction

Neuromuscular diseases (NMDs) are a leading cause of mortality and morbidity. One such disease is myasthenia gravis (MG), which is distinguished by weakness and fatigue of the skeletal muscles. MG is an autoimmune disorder characterized by antibodies acting against the postsynaptic muscarinic, nicotinic, and acetylcholine (ACh) receptors at the neuromuscular junction, reducing the ability of the neuromuscular endplate to transmit nerve signals resulting in muscle weakness and fatigue.

Patients typically exhibit enhanced weakness at the end of the day, or after exercise or exertion, with symptoms resolving after rest. Autonomic dysfunction is uncommon, and deep tendon reflexes are normal. However, respiratory muscles frequently become a significant concern as the disease advances. The disease affects young women and the elderly, who are underdiagnosed. Medical and surgical treatment of the illness has improved over time, allowing patients with MG to live longer. However, the disease's significant impact on the body and the medications commonly used to treat it pose unique challenges to the anesthesia provider.

How Is Myasthenia Gravis Diagnosed?

Strengthening after intravenous administration of the Edrophonium supports the diagnosis, and the presence of anti-nAChR antibodies or muscle-specific tyrosine kinase (MuSK) antibodies, along with clinical manifestations, confirms the diagnosis of myasthenia gravis. Anti-nAChR antibodies are found in 80 to 85 percent of MG patients. The thymus is affected in most nAChR-positive individuals, resulting in a thymoma or abnormal thymus formation.

What Are the Two Types of Crisis That Occurs in Myasthenia Patients?

Myasthenic patients are vulnerable to two crises: myasthenic and cholinergic.

• Myasthenia Crisis:

  • A myasthenic crisis is an aggravation of the condition caused by various factors, such as respiratory system infection, emotional stress, and surgery.

  • As a result, the patient's symptoms worsen, with increased weakness of the muscles and respiratory deficiency. These crises usually occur during the initial two years of the disease.

  • The patient's age, time is taken for crisis recognition, and need for endotracheal intubation are all significant predictors of death in these patients.

  • Therefore, additional cholinesterase inhibitor dosages are required in this kind of crisis, and if the patient does not improve, intravenous immunoglobulins, plasmapheresis, or endotracheal intubation are required.

• Cholinesterase Crisis:

  • Patients who overdose on cholinesterase inhibitors may develop symptoms such as increased salivation, sweating, abdominal pain, urinary urgency, bradycardia, muscle fasciculations, or muscle weakness.

  • Endotracheal intubation, Atropine, and discontinuation of cholinesterase inhibitors are among the treatments used till the crisis is resolved.

What Is Neuromuscular Blocking Agent’s Role in Myasthenia Gravis?

• Due to the low number of normal nAChRs, MG patients have an abnormal response to neuromuscular depolarizing agents. Once the individuals are given cholinesterase inhibitors, their plasma cholinesterase is also suppressed, indicating that inactivation of the succinylcholine takes much longer. The individuals are at risk of a prolonged blockade.

• Individuals who did not receive cholinesterase inhibitors have a low susceptibility to succinylcholine because there are no sufficient normal nAChRs to cause depolarization. On the other hand, the relatively low number of receptors increases sensitivity to nondepolarizing NMBA (neuromuscular blocking agents).

How Is a Myasthenia Gravis Patient Managed Pre-operatively?

• It is essential to explain to the patient and family members before the procedure that stress in the form of surgery can aggravate symptoms but that the illness will usually come back to baseline.

• If the patient has elective procedures, the best time to perform them is during a stable phase when the patient is only receiving minimal medications. The patient's neurologist should be consulted regarding the continuation of immunosuppressive drugs, as this depends on the extent to which the patient is dependent on the medication.

• Except for Azathioprine, which prolongs the effect of Succinylcholine and surpasses nondepolarizing blocking agents, most immunosuppressives do not interact with anesthesia.

• If urgent surgery is required and the patient is experiencing a myasthenic crisis. Due to the depressive effect on respiration, regular premedication with sedatives or opioids should be prevented.

• Some physicians discovered that a high preoperative cholinesterase inhibitor dosage, severe bulbar symptoms, and severe myasthenia gravis with a history of respiratory crisis and cardiorespiratory disease are major risk factors for postoperative mechanical ventilation.

• To conclude, previous respiratory issues and bulbar symptoms are major risk factors, but the effect of the usual pyridostigmine dose on the requirement for mechanical ventilation is controversial.

How Is Myasthenia Gravis Patient Managed Perioperatively?

• The care of MG patients who undergo surgery is a collaborative effort. Therefore, team members should understand the patient's overall health and disease condition completely.

• Before undergoing any procedure, the patient's disease management should be optimized, which starts with the patient's primary care physician or neurologist.

• Staff in the postanesthesia care unit are critical in monitoring for signs and symptoms of cholinergic or myasthenic crisis after surgery. Furthermore, active management of airway secretions is crucial for reducing postoperative aspiration events.

What Is the Role of Volatile Anesthetics Usage in Myasthenia Gravis?

• Volatile anesthetics are known to diminish neuromuscular transmission primarily through various pathways, one of which is the inhibition of the postsynaptic nAChR.

• Numerous studies have shown that using inhalational anesthesia with Sevoflurane for MG patients allows them to avoid neuromuscular blocking agents (NMBA) - even during induction and intubation.

• MG patient's administration of SevofluraneIn resulted in a decrease in TOF and an increase in train-of-four (TOF) when the administration was discontinued.

What Is the Role of Epidural Anesthesia for MG Patients?

• In abdominal surgery, regional analgesia may decrease or eliminate the need for muscle relaxants. Epidural analgesia also provides postoperative control of pain with little or no opioid use.

• Epidural analgesia was utilized successfully during labor for MG patients. However, administering high epidural analgesia has already been considered to compromise the patient's respiratory function, increasing the probability of postoperative demand for better mechanical ventilation.

• Epidural anesthesia improves postoperative pain control and respiratory function while reducing the need for neuromuscular blocking agents (NMBA) during surgery.

How Is Myasthenia Gravis Patient Managed Postoperatively?

• MG patients need to have enough spontaneous breathing before extubation. Therefore, separate specific guidelines for myasthenic patient extubation have been suggested, such as average level of consciousness, tidal volume of five ml (milliliters) x body weight (kg) or more, spontaneous ventilation with a partial pressure of carbon dioxide (PaCO2) of 50 mmHg or less and respiratory rate of 30 breaths per minute or less.

• The most important thing is to ensure no residual curarization before extubation, either with a TOF monitor in the unconscious patient or with a head lift of more than five seconds in the conscious patient.

Conclusion

The care of MG patients who undergo surgery is a collaborative effort. Team members should completely understand the patient's overall health and disease condition. Before undergoing any procedure, the patient's disease management should be optimized, which starts with the patient's primary care physician or neurologist. Staff in the postanesthesia care unit are critical in monitoring for signs and symptoms of cholinergic or myasthenic crisis after surgery. Furthermore, active management of airway secretions is crucial for reducing postoperative aspiration events.