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Anesthesia for the patient with myasthenia gravis
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Anesthesia for the patient with myasthenia gravis
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Literature review current through: Sep 2017. | This topic last updated: Mar 07, 2017.

INTRODUCTION — Myasthenia gravis (MG) is an autoimmune disorder characterized by fatigable weakness of skeletal muscles. Weakness results from an antibody-mediated immunological attack directed at acetylcholine receptors (or receptor-associated proteins) in the postsynaptic membrane of the neuromuscular junction.

Anesthetic concerns for patients with MG include the interactions among the disease, the disease treatment, and the medications used for anesthesia, particularly neuromuscular blocking agents (NMBAs). Patients with MG are unpredictably sensitive to nondepolarizing NMBAs and are resistant to succinylcholine, a depolarizing NMBA.

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder of the neuromuscular junction, with antibodies directed against the presynaptic voltage-gated calcium channels. It is often associated with an underlying malignancy, most commonly small cell lung cancer, though it is also associated with other autoimmune processes. Patients with LEMS are very sensitive to both depolarizing and nondepolarizing NMBAs.

This topic will discuss the anesthetic management of patients with MG and LEMS. Diagnosis, clinical manifestations, and management of MG and LEMS are discussed in detail separately. (See "Diagnosis of myasthenia gravis" and "Clinical manifestations of myasthenia gravis" and "Treatment of myasthenia gravis" and "Clinical features and diagnosis of Lambert-Eaton myasthenic syndrome" and "Treatment of Lambert-Eaton myasthenic syndrome".)

PREOPERATIVE EVALUATION — Preoperative preparation for elective surgery for patients with myasthenia gravis (MG) should be coordinated with the patient’s neurologist. Elective surgery should be performed during a stable phase of the disease, when the patient requires minimal immunomodulatory medication or glucocorticoids, to minimize the chance of postoperative myasthenic crisis. In addition to routine preoperative evaluation, assessment of patients with MG should focus on bulbar and respiratory symptoms, as well as prior history of exacerbations or myasthenic crisis. Surgery should be scheduled as early in the day as possible, when the patient is strongest [1].

History — Patients with MG should be evaluated preoperatively for the following:

Bulbar symptoms (eg, dysphagia, dysarthria, nasal speech, or low-intensity speech), which may predispose to aspiration

History of myasthenic crisis and need for endotracheal intubation

Respiratory muscle weakness, shortness of breath, and dyspnea

MG therapy

Associated diseases, including other autoimmune diseases (eg, thyroiditis, rheumatoid arthritis, systemic lupus erythematosus)

Patients having thymectomy for thymic mass may be at risk for airway compromise with induction of anesthesia. Imaging studies (eg, chest computed tomography) should be reviewed.

Prediction of postoperative myasthenic crisis

Risk factors — A number of authors have attempted to define risk factors for postoperative myasthenic crisis (MC). Retrospective studies including patients with MG who underwent transsternal thymectomy or videoscopic thymectomy using a variety of anesthetic strategies have reported associations between a number of preoperative factors and the need for postoperative ventilation. These include:

Vital capacity <2 to 2.9 L [2-4]

Duration of MG (greater than six years) [3]

Pyridostigmine dosage >750 mg/day [3]

History of chronic pulmonary disease [3]

Preoperative bulbar symptoms [5-8]

History of myasthenic crisis [5,8]

Intraoperative blood loss >1000 mL [5]

Serum antiacetylcholine receptor antibody >100 nmol/mL [5]

More pronounced decremental response (18 to 20 percent) on low frequency repetitive nerve stimulation [4].

Preoperative pulmonary evaluation — In consultation with the patient’s neurologist, pulmonary function testing (PFT) should be performed for patients with MG who will receive general anesthesia with the use of neuromuscular blocking agents (NMBAs) to assess optimization, to help establish a baseline for extubation, and to help plan for the level of postoperative care.

The available literature is insufficient to determine the level of preoperative pulmonary dysfunction that would predict the need for postoperative ventilation or the risk of MC for a specific surgical procedure. A retrospective review of patients who underwent video-assisted thoracoscopic thymectomy reported no difference in the need for intensive care unit (ICU) admission for patients with a preoperative vital capacity <2 L compared with those with vital capacity >2 L [8], although previous studies had found an association [2,3]. A retrospective review of patients who underwent videoscopic thymectomy found that patients who had MC had lower FVC than those who did not (2.1 versus 3.0 L) [4]  

Myasthenia gravis treatments — Patients with MG are treated with one or more of three medical therapies: symptomatic treatment (ie, anticholinesterase agents), chronic immunomodulating treatments (ie, glucocorticoids and other immunosuppressive medication), and rapid immunomodulating treatments (ie, plasmapheresis and intravenous immune globulin). (See "Treatment of myasthenia gravis".)

Anticholinesterase agents — We suggest continuing anticholinesterase agents (ie, pyridostigmine or neostigmine) up to and including the morning of surgery, recognizing that the response to both depolarizing and nondepolarizing NMBAs may be modified by these medications. In addition, the response to NMBA reversal agents may be unpredictable or insufficient. Patients with MG who are maintained on anticholinesterases can be quite sensitive to discontinuation of the medication, with development of respiratory and bulbar weakness if medication is withheld. (See 'Neuromuscular blocking agents (NMBAs)' below.)

A study of 14 patients with MG scheduled to undergo thymectomy randomly assigned patients to receive their usual dose of pyridostigmine on the morning of surgery or to discontinue the medication after the last dose the night prior to surgery. Three of seven (43 percent) patients who did not receive pyridostigmine on the morning of surgery complained of respiratory discomfort while waiting for surgery (including two who required rescue intravenous [IV] neostigmine preoperatively), compared with none of the patients who received their usual medication. The study reported resistance to and delayed onset of block with vecuronium administration in patients who took their morning dose of pyridostigmine, but full reversal of neuromuscular block was accomplished in all patients [9].

Pyridostigmine, the most commonly used anticholinesterase for MG, has a rapid onset of action (15 to 30 minutes), with peak action at about two hours, and its effects last for three to four hours, sometimes longer. The timing and dose of medication is individualized based on the patient’s symptoms. The starting dose is often 30 mg orally (PO), with the dose then titrated to effect. If IV dosing is necessary in the perioperative period, the IV dose is approximately one-thirtieth the oral dose (ie, 1 mg IV is equivalent to 30 mg PO).

Glucocorticoids — Patients whose treatment for MG includes glucocorticoids may be at risk for hypothalamic pituitary axis suppression and adrenal insufficiency in the perioperative period, and may require administration of stress-dose glucocorticoids, depending on the surgical procedure (table 1). (See "Major side effects of systemic glucocorticoids", section on 'Hypothalamic-pituitary-adrenal axis suppression' and "The management of the surgical patient taking glucocorticoids", section on 'Approach based upon HPA axis suppression'.)

Patients who have been taking glucocorticoids of any dose for less than three weeks, morning prednisone (<5 mg daily or its equivalent) for any duration, or less than 10 mg prednisone or its equivalent every other day are not at risk for hypothalamic–pituitary–adrenal (HPA) axis suppression. These patients should continue their glucocorticoid regimen perioperatively.

For patients who have been taking prednisone >20 mg/day for three weeks or more, and for patients with Cushingoid appearance, stress-dose glucocorticoids should be administered prior to induction of anesthesia (table 1).

Immunotherapy — Long-term immunotherapy for MG may include administration of azathioprine, cyclophosphamide, cyclosporine, methotrexate, mycophenolate mofetil, rituximab, and tacrolimus. There are no published data to guide management of these drugs around the time of surgery. Although parenteral substitution is possible for both cyclosporine and azathioprine, they likely can be held on the morning of surgery given the long duration of effect. The time course of immunomodulatory effects of these medications suggests that perioperative drug interruptions are not likely to cause significant symptomatic effect. (See "Chronic immunomodulating therapies for myasthenia gravis".)

Preoperative laboratory assessment including electrolytes, renal and hepatic function tests, and complete blood count should be performed for patients taking these medications. While azathioprine injected at supratherapeutic doses has been shown to reverse existing nondepolarizing neuromuscular block in animals, this is not likely a clinically relevant effect in humans [10-12]. Prior administration of azathioprine has been shown to have no effect on dose response curves of nondepolarizing neuromuscular blockade.

Rapid immunomodulating therapy — Plasmapheresis and IV immune globulin (IVIG) are rapid therapies that work quickly (over days), but the benefits are only short-term (weeks). They are used preoperatively before thymectomy or other surgery, as a bridge to slower-acting immunotherapies, during myasthenic crisis, and periodically to maintain remission for patients with MG that is not well controlled otherwise. (See "Treatment of myasthenia gravis", section on 'Rapid immunotherapies'.)

ANESTHESIA MANAGEMENT — Principles of the management of anesthesia for patients with myasthenia gravis (MG) include:

Avoidance of the use of neuromuscular blocking agents (NMBAs) whenever possible

Use of ultrashort- or short-acting sedatives, hypnotics, and anesthetic agents to minimize respiratory depression on emergence from anesthesia

Premedication — In many cases, premedication with sedatives can be avoided by reassurance and explanation of expected procedures. If premedication is necessary, the smallest effective dose should be administered incrementally (eg, midazolam 0.5 mg intravenously [IV]), with continuous monitoring for signs of bulbar weakness and respiratory compromise.

Choice of anesthetic technique — When possible, local or regional anesthesia should be used. Regional anesthesia should be considered for peripheral procedures that can be done with relatively low-level neuraxial anesthesia, either epidural or spinal, or with peripheral nerve blocks. If local anesthetics are used, amide local anesthetics (ropivacaine, mepivacaine, bupivacaine, lidocaine) should be chosen over esters [13]. Anticholinesterases, used for treatment for patients with MG, may theoretically impair the hydrolysis of ester local anesthetics and result in prolonged block.

Additional concerns specific to the patient with MG include:

Neuraxial anesthesia – Mid-thoracic or higher levels of neuraxial anesthesia can result in paralysis of accessory muscles of breathing. Patients with preoperative respiratory compromise or bulbar weakness may not tolerate such levels of motor block. (See "Overview of neuraxial anesthesia".)

Brachial plexus blocks – Supraclavicular and interscalene brachial plexus blocks for upper-extremity surgery paralyze the diaphragm by blocking the phrenic nerve, potentially for many hours, which may not be tolerated by patients with respiratory compromise. (See "Upper extremity nerve blocks: Techniques", section on 'Side effects and complications of interscalene block' and "Anesthesia for patients with chronic obstructive pulmonary disease", section on 'Peripheral nerve blocks'.)

Induction and maintenance of anesthesia — A variety of strategies have been used for induction and maintenance of anesthesia for patients with MG. The overarching goals are to prevent prolonged effects on respiratory and bulbar muscles, and to allow rapid recovery at the end of surgery. NMBAs should be avoided when possible.

Inhalational agents The potent inhaled anesthetics (isoflurane, sevoflurane, desflurane, halothane) provide dose-dependent neuromuscular relaxation in patients with MG [14-17]. These agents may provide adequate relaxation for endotracheal intubation and surgery, possibly equivalent to the level of relaxation achieved with NMBAs in normal patients. There are many reports of thymectomy performed with the use of potent inhalational agents, without the need for NMBAs [8,17,18]. Muscle strength recovers as the inhalational agent is eliminated, without the need for reversal agents.

Intravenous agents – Intravenous (IV) anesthetics have also been used for induction and maintenance of anesthesia for patients with MG, with or without small doses of NMBAs. Propofol is most commonly used for induction of anesthesia, as it provides rapid onset, short duration of action, and suppression of airway reflexes. Total intravenous anesthesia (TIVA) with infusions of propofol and remifentanil has been described for anesthesia without the use of NMBAs for patients with MG undergoing thymectomy [8,19,20].

Remifentanil, an ultrashort-acting opioid, is particularly useful for intubation while avoiding NMBAs. For a high-dose remifentanil intubation, the administration of propofol (2 mg/kg) plus remifentanil (4 to 5 mcg/kg) provides good to excellent intubating conditions at 2.5 minutes after induction [21]. We give ephedrine (10 mg IV) along with the propofol for this type of induction to avoid the profound bradycardia and hypotension that may result from this dose of remifentanil. This combination of medications can be used for rapid sequence induction.

Other IV agents may be used to reduce the reflexes in response to laryngoscopy and intubation while avoiding the administration of NMBAs. IV lidocaine (1 to 1.5 mg/kg IV), small doses of short-acting opioids (eg, fentanyl 50 to 100 mcg), and esmolol (10 to 50 mg) can be given with induction.

Neuromuscular blocking agents (NMBAs) — We avoid NMBAs in patients with MG unless absolutely necessary. Myasthenic patients, including those with only ocular MG and those in remission, have a variable, unpredictable response to administration of NMBAs compared with normal patients, as well as a variable response to NMBA reversal, including the possibility of cholinergic crisis [22,23]. They tend to be resistant to depolarizing NMBAs and very sensitive to nondepolarizing NMBAs. In addition, treatment with anticholinesterase medication affects the degree of relaxation and duration of action of NMBAs. If NMBAs are administered, the degree of neuromuscular blockade should be monitored using a quantitative train-of-four nerve stimulator.

For most surgical procedures, administration of NMBAs is not necessary for myasthenic patients. Adequate relaxation for surgery is often provided by the administration of the potent inhalational agents and, to a lesser extent, by the depth of anesthesia achieved with the use of IV agents. (See 'Induction and maintenance of anesthesia' above.)

Depolarizing NMBAs — Patients with MG are resistant to neuromuscular blockade with depolarizing NMBAs (eg, succinylcholine), possibly because they have a decreased number of acetylcholine receptors [24,25]. The 95 percent effective dose (ED95) of succinylcholine for patients with MG is 2.6 times that of normals (0.8 versus 0.3 mg/kg). Because succinylcholine is metabolized by plasma cholinesterase, treatment with anticholinesterase medication (eg, pyridostigmine) may prolong the effect of succinylcholine [26].

Myasthenic patients are also at higher risk of development of phase II neuromuscular block (prolonged, unpredictable block with features of nondepolarizing block), especially with repeated doses of succinylcholine [27]. (See "Clinical use of neuromuscular blocking agents in anesthesia".)

Nondepolarizing NMBAs — Patients with MG are extremely sensitive to nondepolarizing NMBAs (eg, rocuronium, vecuronium, cisatracurium). Very small doses and residual drug effect may result in respiratory distress or loss of airway protection after emergence from anesthesia. Nondepolarizing NMBAs should be administered in incremental, small doses of 0.1 to 0.2 times the ED95, titrated to effect and guided by the use of a train-of-four nerve stimulator. If the plan is to extubate the patient at the end of the anesthetic, the nondepolarizing NMBA should be reversed with anticholinesterase and anticholinergic medication. Reversal should be confirmed with a quantitative peripheral nerve stimulator or with formal, repetitive nerve conduction studies. (See 'Reversal of NMBAs' below.)

Mivacurium is a nondepolarizing NMBA that is metabolized by plasma cholinesterase. Pyridostigmine inhibits metabolism of mivacurium. Therefore, paralysis with mivacurium may be prolonged in patients who have taken pyridostigmine on the morning of surgery, though this effect is variable [28,29].

Reversal of NMBAs — Response to reversal of nondepolarizing NMBAs may be unpredictable, especially for those patients who are taking anticholinesterase medication [30]. If NMBAs are administered, reversal medication (eg, neostigmine) should be titrated to effect to avoid cholinergic crisis, and a quantitative train-of-four peripheral nerve stimulator (ie, using accelerometry or kinemyography) should be used to guide adequacy of reversal, or a ratio of fourth to first twitch of ≥0.9 [31-33] (See 'Cholinergic crisis' below.)

In contrast, clinical signs of reversal (eg, five-second head lift, vital capacity ≥15 mL/kg, negative inspiratory force ≥25 cmH2O, strength of hand grip) are unreliable measures of neuromuscular reversal. These metrics can be achieved despite residual neuromuscular blockade and a train-of-four ratio as low as 0.45. In addition, when a standard, non-quantitative train-of-four monitor is used, visual and manual detection of fade may not be possible, even with train-of-four ratios between 0.4 and 0.7 [34].

Sugammadex – Sugammadex is a cyclodextrin medication that can be used to reverse neuromuscular blockade of the steroidal NMBAs (eg, vecuronium and rocuronium) by encapsulation of the NMBA molecule, without the need for anticholinesterase medication. Sugammadex has been shown to be useful in reversing neuromuscular blockade from a steroidal NMBA in MG patients. Sugammadex 2 to 4 mg/kg IV has been reported to reverse moderate to deep vecuronium and rocuronium blockade in patients with MG within four minutes. Reversal with sugammadex is not affected by anticholinesterase medication [35].

Medications that may exacerbate myasthenia gravis — A number of other medications (table 2 and table 3) commonly administered in the operating room can affect neuromuscular transmission in some way. In normal patients, these effects are usually of no consequence, but in patients with MG, they can exacerbate muscle weakness, especially in the presence of residual anesthetic agents.

Several classes of antibiotics can affect neuromuscular transmission, including aminoglycosides (eg, gentamicin) and polymyxins. There are case reports of ampicillin (but not other penicillin-based antibiotics), macrolides (eg, erythromycin, azithromycin), tetracycline, and fluoroquinolones (eg, ciprofloxacin) causing weakness.

Glucocorticoids are known to cause weakness, even though they are often used to treat MG. Thus it would be prudent to avoid starting a glucocorticoid in the perioperative period to prevent this potential side effect.

Other medications with the potential to exacerbate weakness include certain local anesthetics, beta blockers, calcium channel blockers, antiepileptics (gabapentin and phenytoin), phenothiazines, diuretics, procainamide, magnesium, and opioids. When any of these medications is given in the operating room or the recovery room, the potential for respiratory or bulbar weakness should be considered.

Extubation — The anesthetic strategy for patients with MG should be designed to maximize the possibility of extubation at the end of surgery. Components of the plan include the use of short-acting anesthetics and multimodal analgesia to minimize opioid side effects, pulmonary toilet, and avoiding medications known to interfere with neuromuscular transmission (table 2 and table 3).

Criteria for extubation should be similar to those for any patient having surgery, with proof of adequate ventilation and oxygenation, strength, and the ability to protect the airway, once objective confirmation of reversal of NMBAs is obtained, if used. (See 'Reversal of NMBAs' above.)

POSTOPERATIVE CONSIDERATIONS FOR PATIENTS WITH MYASTHENIA GRAVIS — The need for postoperative monitoring and/or hospital admission for patients with myasthenia gravis (MG) should be individualized based on clinical features, the surgical procedure, the type of anesthetic, the intraoperative and immediate postoperative courses, and the need for postoperative care, including pain relief. Preoperative consultation with the patient’s neurologist should include planning for postoperative care, the possibility of intensive care, and postoperative management of anticholinesterase medication. Chronic immunotherapies can be resumed when the patient is taking oral medications.

Ambulatory surgery can be considered for patients who have had minor surgical procedures, with monitored anesthesia care using short-acting sedatives, regional anesthesia, or general anesthesia without neuromuscular blocking agents. Patients who develop any signs of bulbar or respiratory weakness in the recovery room should be admitted to the hospital for monitoring.

Myasthenic crisis — Myasthenic crisis is defined as respiratory muscle and/or bulbar muscle weakness severe enough to necessitate intubation or to delay extubation after surgery. It can occur spontaneously with the stress of surgery, or as a result of a number of precipitants, including infection, residual anesthetics, withholding or tapering of MG medications, or any of a number of medications known to exacerbate MG (table 2 and table 3).

Myasthenic crisis must be distinguished from cholinergic crisis, another possible cause of weakness in patients with MG, as the treatment of the two conditions is very different. Formal neurophysiologic studies may be necessary and may provide more information, as excess cholinergic activity can be assessed, as well as cholinergic deficit. (See 'Cholinergic crisis' below.)

Myasthenic crisis may include weakness of respiratory and bulbar muscles. In awake patients, signs of impending crisis can include dysphagia, change in phonation, obstruction, weak cough, and difficulty handling secretions. Since the MG patient has a normal respiratory drive, the first sign of impending crisis may be an increase in respiratory rate with shallower tidal volume breaths [36]. Use of accessory muscles or paradoxical movement of the abdomen might be seen, even in patients who are still intubated at the end of surgery. Blood gases may initially show hypocapnia in spontaneously breathing patients. An increase in partial pressure of carbon dioxide (pCO2) is a sign of impending respiratory failure.

Treatment of myasthenic crisis should be coordinated with a neurologist. If weakness at the end of surgery suggests myasthenic crisis, delay of extubation is required, as well as intensive care. Urgent rapid therapy with plasma exchange or intravenous (IV) immune globulin is often initiated, in addition to immunomodulating therapy. (See "Myasthenic crisis", section on 'Evaluation and management'.)

Risk factors for postoperative myasthenic crisis after thymectomy are discussed above. (See 'Prediction of postoperative myasthenic crisis' above.)

Cholinergic crisis — Patients who receive anticholinesterases are at risk for cholinergic crisis, which is manifested by paradoxical weakness along with other signs of cholinergic excess, such as those identified by the mnemonic "SLUDGE": salivation, lacrimation, urination, defecation, gastrointestinal distress, and emesis [1]. It happens rarely in patients outside the operating room but may occur after administration of an anticholinesterase for reversal of neuromuscular blockade in patients with MG [37,38]. In such cases, prolonged paralysis often results.

Neuromuscular blocking agents (NMBAs) should be administered during anesthesia only when absolutely necessary. Avoiding NMBAs avoids the need for reversal and therefore the risk of cholinergic crisis. (See 'Neuromuscular blocking agents (NMBAs)' above.)

If cholinergic crisis is suspected, atropine (0.4 to 2 mg IV) or glycopyrrolate (0.2 to 1 mg IV) should be administered, if not already given, to counteract muscarinic effects, and further anticholinesterase should be withheld. Repeated dosing of anticholinergic may be required.

OBSTETRIC ANESTHESIA — Pregnant patients with myasthenia gravis (MG) should have antepartum anesthesia consultation. The plans for labor analgesia and anesthesia for potential instrumented or operative delivery should be determined well before the patient presents in labor. Like other surgical patients, obstetric patients should be assessed for the degree of bulbar dysfunction and respiratory muscle weakness, and also for the predicted ability to tolerate midthoracic levels of regional anesthetic block. Anesthesia concerns specific to labor and delivery include the following:

Labor analgesia – Most patients require some degree of analgesia during labor. Neuraxial analgesia is the preferred method of pain control during labor for patients with MG because it reduces or eliminates the need for systemic opioid administration, thereby minimizing respiratory depression for patients with respiratory compromise. Excellent labor analgesia can be achieved with low levels of very dilute local anesthetic and opioid medications, which result in a minimal, if any, degree of motor block. (See "Neuraxial analgesia for labor and delivery (including instrumented delivery)", section on 'Neuraxial analgesia drug choice'.)

Instrumented delivery – The first stage of labor depends on uterine smooth muscle and is unaffected by MG. However, the second stage of labor requires the use of striated muscle, which may weaken, increasing the need for instrumented delivery. Neuraxial analgesia can be augmented to provide adequate lumbosacral levels of anesthesia for forceps- or vacuum-assisted delivery.

Cesarean section – While neuraxial anesthesia (ie, spinal and epidural) is used most commonly for cesarean section, patients with MG may not tolerate the high level of block required. Neuraxial anesthesia results in both sensory and motor block; for cesarean section, a midthoracic level of anesthesia is required, which often affects the accessory muscles of respiration. For patients with significant bulbar or respiratory compromise, general anesthesia should be performed for cesarean section.

Anticholinesterases, used for treatment for patients with MG, may theoretically impair the hydrolysis of ester local anesthetics and result in prolonged block. The amide class of local anesthetic should therefore be used for patients who take anticholinesterase medication.

LAMBERT-EATON MYASTHENIC SYNDROME — Lambert-Eaton myasthenic syndrome (LEMS) is a rare disorder of the neuromuscular junction, much less common than myasthenia gravis (MG). It is often associated with small cell lung cancer or other malignancies, but it can be associated with autoimmune processes as well. Patients with LEMS have muscle weakness caused by reduced acetylcholine release from presynaptic nerve terminals. Unlike MG, autonomic dysfunction is common with LEMS. Bulbar symptoms occur less commonly than with MG. Respiratory muscle weakness can rarely result in respiratory failure [39]. (See "Clinical features and diagnosis of Lambert-Eaton myasthenic syndrome".)

Anesthetic concerns for patients with LEMS include the following:

Patients with LEMS are very sensitive to both nondepolarizing and depolarizing neuromuscular blocking agents (NMBAs) [40], unlike patients with MG, who are resistant to depolarizing NMBAs and sensitive to nondepolarizing NMBAs. Patients with LEMS are more sensitive to nondepolarizing NMBAs than patients with MG, and reversal with neostigmine may be ineffective [41]. We avoid NMBAs for patients with LEMS unless absolutely necessary. Patients who do receive NMBAs should receive small, titrated doses, and should be monitored with an objective peripheral nerve stimulator. (See 'Neuromuscular blocking agents (NMBAs)' above.)

Patients with LEMS may be treated symptomatically with guanidine, aminopyridines (eg, 3,4 Diaminopyridine), and anticholinesterases (eg, pyridostigmine). Other treatments include immunologic therapy with intravenous (IV) immune globulin; oral immunosuppressive agents (eg, prednisone, azathioprine, mycophenolate, cyclosporine); and, least commonly, plasma exchange or rituximab. (See "Treatment of Lambert-Eaton myasthenic syndrome".).

Patients should continue these medications up to the time of surgery, as there are case reports of respiratory insufficiency when medications were held prior to surgery [42]. Patients who chronically take glucocorticoids may require stress doses at the time of induction of anesthesia. (See 'Myasthenia gravis treatments' above.)

Autonomic dysfunction with LEMS may result in exaggerated hypotension with anesthesia induction agents and other vasodilators. A retrospective review of 60 anesthetics for patients with LEMS reported that hypotension occurred no more commonly in patients with autonomic dysfunction than in those without it, and all episodes of hypotension were treated easily with boluses of phenylephrine or ephedrine [42].

Postoperative concerns for patients with LEMS are similar to those for patients with MG.

SUMMARY AND RECOMMENDATIONS

Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction that results in muscle weakness and often bulbar symptoms, with significant implications for anesthesia.

Patients with MG are unpredictably resistant to depolarizing neuromuscular blocking agents (NMBAs) (eg, succinylcholine) and unpredictably sensitive to nondepolarizing NMBAs (eg, rocuronium, vecuronium, cisatracurium). (See 'Neuromuscular blocking agents (NMBAs)' above.)

Treatment for MG often includes anticholinesterases, which can prolong the effect of succinylcholine and delay the onset of nondepolarizing NMBAs. (See 'Myasthenia gravis treatments' above.)

Principles for the management of anesthesia for patients with MG include (see 'Anesthesia management' above):

Continuation of MG medication up to the time of surgery

Use of ultrashort- or short-acting sedatives, hypnotics, and anesthetic agents

Avoidance of the use of NMBAs whenever possible

When the use of a NMBAs is required, small doses should be titrated to effect, guided by monitoring with a quantitative train-of-four peripheral nerve stimulator (ie, one that uses accelerometry or kinemyography to show the numeric ratio of the fourth to first twitch). Reversal medication (eg, neostigmine) should be titrated to effect, guided by the same monitor, aiming for a fourth to first twitch ratio of ≥0.9. Where available, sugammadex should be used for reversal of steroidal NMBAs. (See 'Neuromuscular blocking agents (NMBAs)' above and 'Reversal of NMBAs' above.)

The need for postoperative monitoring and/or hospital admission for patients with MG should be individualized based on the clinical features, the risk factors for myasthenic crisis, the surgical procedure, the type of anesthetic, the intraoperative and immediate postoperative course, and the need for postoperative care, including pain relief. (See 'Postoperative considerations for patients with myasthenia gravis' above.)

Myasthenic crisis can be precipitated by surgery, administration of NMBAs, or any of a number of medications and conditions. Myasthenic crisis requires endotracheal intubation and ventilation, intensive care, and often rapid immunomodulating therapy. It should be distinguished from cholinergic crisis, which is the result of excessive administration of anticholinesterase medication and may also require ventilatory support. (See 'Myasthenic crisis' above and 'Cholinergic crisis' above and "Myasthenic crisis".)

Pregnant patients with myasthenia gravis (MG) should have antepartum anesthesia consultation to plan for labor analgesia and for anesthesia for potential instrumented or operative delivery. The degree of bulbar and respiratory dysfunction should be assessed, as well as the ability to tolerate a midthoracic level of neuraxial anesthesia. (See 'Obstetric anesthesia' above.)

In contrast to MG, patients with Lambert-Eaton myasthenic syndrome (LEMS) are sensitive to both depolarizing and nondepolarizing NMBAs. Anesthesia concerns for patients with LEMS are otherwise similar to those for patients with MG. (See 'Lambert-Eaton myasthenic syndrome' above.)

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