Myasthenia Gravis and Thymoma Surgery: A Clinical Update for the Cardiothoracic Anesthesiologist

Myasthenia gravis (MG) is a rare neuromuscular disorder characterized by skeletal muscle weakness. Patients with MG who have thymoma and thymic hyperplasia have indications for thymectomy. The perioperative care of patients with MG scheduled for thymus resection should be focused on optimizing their neuromuscular function, identifying factors related to postoperative mechanical ventilation, and avoiding of triggers associated with myasthenic or cholinergic crisis. Minimally invasive surgical techniques, use of regional analgesia, and avoidance or judicious administration of neuromuscular blocking drugs (NMBs) is recommended during the perioperative period. If NMBs are used, sugammadex appears to be the drug of choice to restore adequately the neuromuscular transmission. In patients with postoperative myasthenic crisis, plasma exchange or intravenous immune globulin and mechanical support is recommended.

High-dose rocuronium for rapid-sequence induction and reversal with sugammadex in two myasthenic patients

The anesthetic management of patients affected by myasthenia gravis is usually challenging in elective surgery and even more so in emergency procedures. The difficulties involved are several-fold, ranging from the choice of an appropriate muscle relaxant (i.e. one that enables safe and rapid airway management) to neuromuscular monitoring and normal muscular recovery. Additionally, optimizing patient conditions - either pharmacologically or with plasmapheresis - before intervention is well beyond the realm of possibility. We discuss the anesthetic management of two myasthenic patients undergoing emergency surgery (for sigmoid perforation and upper gastrointestinal bleeding respectively). In both cases, we opted for rapid-sequence induction with high-dose rocuronium to prevent inhalation of gastric contents. We also report on the implication of neuromuscular monitoring. We found that the rocuronium-sugammadex combination was a useful and effective option in the emergency setting.

Coronary artery bypass grafting in a patient with myasthenia gravis

A 70-year-old male patient with myasthenia gravis required coronary artery bypass grafting due to triple-vessel disease. The anesthetic management was performed with general anesthesia using reduced doses of muscle relaxants. He was extubated four hours after surgery and the postoperative course was uneventful. Coronary artery bypass surgery in myasthenic patients can be challenging to anesthesiologists and cardiac surgeons. In this rare condition, a meticulous assessment of the patient's neurologic and cardiac status, and careful perioperative anesthetic management were needed in order to avoid life-threatening complications in both intraoperative and postoperative periods.

Rocuronium and sugammadex in patients with myasthenia gravis undergoing thymectomy

BACKGROUND

The use of neuromuscular blocking agents is still controversial in myasthenic patients but rocuronium could be useful after the introduction of sugammadex as a selective antagonist. The aim of the study was to evaluate the use of rocuronium-sugammadex in myasthenic patients undergoing thoracoscopic thymectomy.

METHODS

After ethical approval, 10 myasthenic patients undergoing videothoracoscopic-assisted thymectomy were enrolled in the study. Neuromuscular block was achieved with 0.3 mg/kg rocuronium and additional doses were given according to train-of-four (TOF) monitoring or movement of the diaphragm. Sugammadex 2 mg/kg was given after surgery. Recovery time (time to obtain a TOF value > 0.9) was recorded for all subjects.

RESULT

All patients were extubated in the operating room after administration of sugammadex. Mean rocuronium dose was 48 mg and the average operation time was 62 min. Recovery time after sugammadex administration was 111 s (min 35; max 240).

CONCLUSIONS

A rapid recovery of neuromuscular function was found in myasthenic patients receiving rocuronium when sugammadex was used for reversal. This combination could be a rational alternative for myasthenic patients for whom neuromuscular blockade is mandatory during surgery.

Anesthesia and myasthenia gravis

Myasthenia gravis (MG) is a disease affecting the nicotinic acetylcholine receptor of the post-synaptic membrane of the neuromuscular junction, causing muscle fatigue and weakness. The myasthenic patient can be a challenge to anesthesiologists, and the post-surgical risk of respiratory failure has always been a matter of concern. The incidence and prevalence of MG have been increasing for decades and the disease is underdiagnosed. This makes it important for the anesthesiologist to be aware of possible signs of the disease and to be properly updated on the optimal perioperative anesthesiological management of the myasthenic patient. The review is based on electronic searches on PubMed and a review of the references of the articles. The following keywords were used: myasthenia gravis AND neuromuscular blocking agents, myasthenia gravis AND sevoflurane, myasthenia gravis AND epidural, myasthenia gravis AND neuromuscular blockade reversal and myasthenia gravis AND pyridostigmine. The articles included were from reviews and clinical trials written in English. MG patients can easily be anesthetized without need for post-surgery mechanical ventilation whether it is general anesthesia or peripheral nerve block. Volatile anesthesia or the use of an epidural for the patient makes it possible to avoid the use of neuromuscular blocking agents, and when used, it should be in smaller doses and the patient should be carefully monitored. This review shows that with thorough pre-operative evaluation, continuing the daily pyridostigmine and careful monitoring the MG patient can be managed safely.

Neuromuscular pharmacodynamics of mivacurium in adults with major burns

BACKGROUND

Mivacurium is metabolized by plasma pseudocholinesterase (PChE) enzyme, which is decreased in burns. We tested whether the decreased metabolism of mivacurium due to decreased PChE activity can overcome the pharmacodynamic resistance to non-depolarizing relaxants previously seen in major burns.

METHODS

Thirty adults with 35 (13)% [mean (sd)] burn were studied at 5-91 post-burn days and 31 non-burns matched controls. Mivacurium 0.2 mg kg(-1) was administered as a single bolus. Neuromuscular block was monitored with single-twitch response using TOF-Watch™. Onset time (drug administration to maximal twitch suppression) and spontaneous recovery were measured.

RESULTS

Onset time was significantly prolonged in burns when compared with non-burns (115 vs 90 s; P<0.001). The PChE levels were lower in burns [1432 (916) vs 2866 (731) IU litre(-1); P<0.001] and the neuromuscular recovery to 50% of baseline twitch height was prolonged in burns (41 vs 26 min; P<0.001). There was a significant correlation between PChE and time to 50% recovery for the whole group together (r=-0.6; P<0.001). The dibucaine numbers were not different.

CONCLUSIONS

The prolonged onset time suggests resistance to neuromuscular effects, whereas the prolonged recovery suggests increased sensitivity. This divergent response can be explained by qualitative and quantitative changes in acetylcholine receptor expression causing resistance and decreased PChE activity causing sensitivity. Despite using a relatively large dose of mivacurium (0.2 mg kg(-1)) in the presence of decreased PChE levels, this did not overcome the resistance resulting from up-regulated receptors.