Mivacurium in the myasthenic patient

Anesthetic Management of Total Aortic Arch Replacement in a Myasthenia Gravis Patient under Deep Hypothermic Circulatory Arrest

The anesthetic management of myasthenia gravis patients undergoing cardiac or aortic surgery under cardiopulmonary bypass, especially with deep hypothermic circulatory arrest, is challenging. We describe a case of successful anesthetic management of a myasthenia gravis patient undergoing total arch replacement with deep hypothermic circulatory arrest under neuromuscular monitoring and complete reversal of the action of neuromuscular blocking drugs by sugammadex. The present case suggests that patients with well-controlled myasthenia gravis might be safely managed in cardiac or aortic surgery under cardiopulmonary bypass with deep hypothermic circulatory arrest.

Clinical Practice Guidelines for Sustained Neuromuscular Blockade in the Adult Critically Ill Patient

OBJECTIVE

To update the 2002 version of "Clinical practice guidelines for sustained neuromuscular blockade in the adult critically ill patient."

DESIGN

A Task Force comprising 17 members of the Society of Critical Medicine with particular expertise in the use of neuromuscular-blocking agents; a Grading of Recommendations Assessment, Development, and Evaluation expert; and a medical writer met via teleconference and three face-to-face meetings and communicated via e-mail to examine the evidence and develop these practice guidelines. Annually, all members completed conflict of interest statements; no conflicts were identified. This activity was funded by the Society for Critical Care Medicine, and no industry support was provided.

METHODS

Using the Grading of Recommendations Assessment, Development, and Evaluation system, the Grading of Recommendations Assessment, Development, and Evaluation expert on the Task Force created profiles for the evidence related to six of the 21 questions and assigned quality-of-evidence scores to these and the additional 15 questions for which insufficient evidence was available to create a profile. Task Force members reviewed this material and all available evidence and provided recommendations, suggestions, or good practice statements for these 21 questions.

RESULTS

The Task Force developed a single strong recommendation: we recommend scheduled eye care that includes lubricating drops or gel and eyelid closure for patients receiving continuous infusions of neuromuscular-blocking agents. The Task Force developed 10 weak recommendations. 1) We suggest that a neuromuscular-blocking agent be administered by continuous intravenous infusion early in the course of acute respiratory distress syndrome for patients with a PaO2/FIO2 less than 150. 2) We suggest against the routine administration of an neuromuscular-blocking agents to mechanically ventilated patients with status asthmaticus. 3) We suggest a trial of a neuromuscular-blocking agents in life-threatening situations associated with profound hypoxemia, respiratory acidosis, or hemodynamic compromise. 4) We suggest that neuromuscular-blocking agents may be used to manage overt shivering in therapeutic hypothermia. 5) We suggest that peripheral nerve stimulation with train-of-four monitoring may be a useful tool for monitoring the depth of neuromuscular blockade but only if it is incorporated into a more inclusive assessment of the patient that includes clinical assessment. 6) We suggest against the use of peripheral nerve stimulation with train of four alone for monitoring the depth of neuromuscular blockade in patients receiving continuous infusion of neuromuscular-blocking agents. 7) We suggest that patients receiving a continuous infusion of neuromuscular-blocking agent receive a structured physiotherapy regimen. 8) We suggest that clinicians target a blood glucose level of less than 180 mg/dL in patients receiving neuromuscular-blocking agents. 9) We suggest that clinicians not use actual body weight and instead use a consistent weight (ideal body weight or adjusted body weight) when calculating neuromuscular-blocking agents doses for obese patients. 10) We suggest that neuromuscular-blocking agents be discontinued at the end of life or when life support is withdrawn. In situations in which evidence was lacking or insufficient and the study results were equivocal or optimal clinical practice varies, the Task Force made no recommendations for nine of the topics. 1) We make no recommendation as to whether neuromuscular blockade is beneficial or harmful when used in patients with acute brain injury and raised intracranial pressure. 2) We make no recommendation on the routine use of neuromuscular-blocking agents for patients undergoing therapeutic hypothermia following cardiac arrest. 3) We make no recommendation on the use of peripheral nerve stimulation to monitor degree of block in patients undergoing therapeutic hypothermia. 4) We make no recommendation on the use of neuromuscular blockade to improve the accuracy of intravascular-volume assessment in mechanically ventilated patients. 5) We make no recommendation concerning the use of electroencephalogram-derived parameters as a measure of sedation during continuous administration of neuromuscular-blocking agents. 6) We make no recommendation regarding nutritional requirements specific to patients receiving infusions of neuromuscular-blocking agents. 7) We make no recommendation concerning the use of one measure of consistent weight over another when calculating neuromuscular-blocking agent doses in obese patients. 8) We make no recommendation on the use of neuromuscular-blocking agents in pregnant patients. 9) We make no recommendation on which muscle group should be monitored in patients with myasthenia gravis receiving neuromuscular-blocking agents. Finally, in situations in which evidence was lacking or insufficient but expert consensus was unanimous, the Task Force developed six good practice statements. 1) If peripheral nerve stimulation is used, optimal clinical practice suggests that it should be done in conjunction with assessment of other clinical findings (e.g., triggering of the ventilator and degree of shivering) to assess the degree of neuromuscular blockade in patients undergoing therapeutic hypothermia. 2) Optimal clinical practice suggests that a protocol should include guidance on neuromuscular-blocking agent administration in patients undergoing therapeutic hypothermia. 3) Optimal clinical practice suggests that analgesic and sedative drugs should be used prior to and during neuromuscular blockade, with the goal of achieving deep sedation. 4) Optimal clinical practice suggests that clinicians at the bedside implement measure to attenuate the risk of unintended extubation in patients receiving neuromuscular-blocking agents. 5) Optimal clinical practice suggests that a reduced dose of an neuromuscular-blocking agent be used for patients with myasthenia gravis and that the dose should be based on peripheral nerve stimulation with train-of-four monitoring. 6) Optimal clinical practice suggests that neuromuscular-blocking agents be discontinued prior to the clinical determination of brain death.

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.

Thymoma removal in a cat with acquired myasthenia gravis: a case report and literature review of anesthetic techniques

HISTORY AND PRESENTATION: A 12 year old, 4.2 kg, domestic long hair, castrated male cat was presented with regurgitation, inability to retract the claws, general weakness, cervical ventroflexion and weight loss. A thymic mass was evident on radiographs. Acetylcholine receptor antibody titer was positive for acquired myasthenia gravis (MG). Thymectomy via midline sternotomy was scheduled. ANESTHETIC MANAGEMENT:  Oxymorphone and atropine were administered subcutaneously as premedication, and anesthesia was induced with etomidate and diazepam given intravenously to effect. The cat's trachea was intubated and anesthesia was maintained with isoflurane in oxygen, and continuous infusions of remifentanil and ketamine. Epidural analgesia with preservative-free morphine was administered prior to surgery. Postoperative analgesia was provided by oxymorphone subcutaneously, interpleural bupivacaine, and fentanyl infusion. Postoperative complications included airway obstruction, hypoxemia and hypercapnia.

FOLLOW-UP

The cat was discharged 3 days after surgery. Discharge medications included pyridostigmine and prednisone. Nine days after surgery, the cat had a significant increase in its activity level, and medications were discontinued. Histopathologically, the mass was consistent with a thymoma. Approximately 6 weeks later the cat became weak again and pyridostigmine and prednisone administration was resumed.

CONCLUSION

The perioperative management of patients with MG for transsternal thymectomy is a complex task. The increased potential for respiratory compromise requires the anesthesiologist to be familiar with the underlying disease state, and the interaction of anesthetic and non-anesthetic drugs with MG. Careful monitoring of ventilation and oxygenation is indicated postoperatively.

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.

Anaesthetic considerations in paediatric myasthenia gravis

Myasthenia gravis is of particular interest to anaesthetists because of the muscle groups affected, the pharmacology of the neuromuscular junction, and interaction of both the disease and treatment with many anaesthetic drugs. Anaesthetists may encounter children with myasthenia either to facilitate treatment options or to institute mechanical ventilation in the face of a crisis. This paper reviews the literature pertaining to the pathophysiology and applied pharmacology of the disease and explores the relationship between these and the anaesthetic management. In addition to illustrating the tried-and-tested techniques, some newer management options are explored.

Neuromuscular junction in health and disease

A number of illnesses and other factors can affect the function of the neuromuscular junction (NMJ). These may have an affect at pre- or post-junctional sites. This review outlines the anatomy and the physiology of the NMJ. It also describes the mechanisms and physiological basis of many of the disorders of the NMJ. Finally, the importance of these disorders in anaesthetic practice is discussed.

Decreased number of acetylcholine receptors is the mechanism that alters the time course of muscle relaxants in myasthenia gravis

BACKGROUND

In myasthenic patients, the time course of action of non-depolarizing neuromuscular blocking agents is prolonged and the sensitivity is increased. We used our antegrade perfused rat peroneal nerve anterior tibialis muscle model to investigate if this altered time course of effect and sensitivity can be explained by the decreased acetylcholine receptor concentration that is caused by the disease.

METHODS

Functional acetylcholine receptors were reduced by administration of alpha-bungarotoxin or by injecting monoclonal antibodies against rat acetylcholine receptors (experimental autoimmune myasthenia gravis). After induction of anaesthesia, the model was set up and perfusion of the tibialis anterior muscle with blood was started. After stabilization of the twitch, rocuronium or pancuronium were infused until 90% block was obtained. Twitch data and infusion data were recorded and used to calculate the time course of effect and potency.

RESULTS

The potency of neuromuscular blocking agents was increased and the offset of the neuromuscular block was prolonged in both the alpha-bungarotoxin groups and the experimental autoimmune myasthenia gravis groups compared to controls.

CONCLUSION

This study shows that the increased sensitivity to neuromuscular-blocking agents in myasthenia gravis can be accounted for by a decreased number of acetylcholine receptors. It also shows that the antegrade perfused rat peroneal nerve anterior tibialis muscle model is a suitable model to study the effects of myasthenia gravis on the time course of effect of neuromuscular blocking agents.

Pharmacokinetic/pharmacodynamic modeling of rocuronium in myasthenic patients is improved by taking into account the number of unbound acetylcholine receptors

Patients with myasthenia gravis are more sensitive than healthy patients to nondepolarizing neuromuscular blocking drugs. We performed a pharmacokinetic/pharmacodynamic modeling study of rocuronium in eight myasthenic patients and eight matched control patients. Patients were anesthetized with propofol and sufentanil and a mixture of nitrous oxide/oxygen. Mechanomyographical monitoring of the adductor pollicis was applied. Rocuronium was infused at a rate of 25 micro g. kg(-1). min(-1) in myasthenic patients and 116.7 micro g. kg(-1). min(-1) in control patients and was terminated at 70% neuromuscular block. Arterial blood samples were drawn during onset and offset of the block and for 4 h after the administration of rocuronium. Plasma concentrations were determined by high-performance liquid chromatography. Pharmacokinetic/pharmacodynamic modeling was performed by using the Sheiner model and the unbound receptor model (URM), which takes into account the number of unbound acetylcholine receptors. The effective concentration at 50% effect and the steepness of the concentration-effect relationship were significantly decreased in myasthenic patients. Both the URM and the Sheiner model provided an adequate fit in myasthenic patients. The acetylcholine receptor concentration was significantly decreased in myasthenic patients. The URM explains the observed differences in time course and potency, whereas the Sheiner model does not.

IMPLICATIONS

We performed a pharmacokinetic/pharmacodynamic modeling study in myasthenic patients and control patients. The unbound receptor model, which takes into account the number of unbound acetylcholine receptors in the biophase, was introduced and compared with the model proposed by Sheiner.

Paradigm shift in surgical approaches to thymectomy

BACKGROUND

Thymectomy is an established therapy in the management of myasthenia gravis (MG) used in conjunction with medical treatment. The optimal surgical approach to thymectomy, however, has remained controversial.

METHOD

The present review discusses the author's experiences of and the literature regarding the management of MG using the video-assisted thoracic surgery (VATS) approach.

RESULTS

This approach was shown to be technically safe in experienced hands and associated with less postoperative pain, better preservation of lung function in the early postoperative period and better cosmetic results than alternative techniques. The intermediate term results of VATS are comparable to those of more radical approaches. It is hoped that this patient-friendly approach will lead to greater support by patients and their neurologists, for earlier surgery.

CONCLUSION

VATS is an attractive, alternative approach to thymectomy.

Video-assisted thoracoscopic thymectomy for myasthenia gravis

Thymectomy is an established therapy in the management of generalized myasthenia gravis, in addition to medical treatment. However, the optimal surgical approach to thymectomy has remained controversial. There are advocates for transternal, transcervical approaches or "maximal" thymectomy. Video-assisted thoracic surgery (VATS) presents a new approach to thymectomy and forms the basis of this article, in which we discuss patient selection, technique, and results. We believe complete thymectomy, comparable with the transternal approach, could be achieved by VATS. Our intermediate-term results compare well with other surgical techniques. By minimizing chest wall trauma, VATS not only causes less postoperative pain, shortens hospital stay, gives better cosmetic results but also leads to wider acceptance by patients (and their neurologists) for earlier surgery. However, the true role of this approach in thoracic surgery awaits long-term results.

Remifentanil and propofol total intravenous anaesthesia for thymectomy in myasthenia gravis

We report a case of trans-sternal thymectomy for myasthenia gravis using a non relaxant, total intravenous technique with propofol and remifentanil. This afforded excellent control of heart rate and pressor responses during surgery while allowing early return of spontaneous ventilation and extubation within nine minutes of termination of anaesthesia. Advantages and disadvantages of this approach versus relaxant and volatile techniques are discussed with particular reference to preservation of neuromuscular function.

Multivariate determinants of the need for postoperative ventilation in myasthenia gravis

PURPOSE

Following transsternal thymectomy, up to 50% of patients may require postoperative ventilation. The aim of this study was to identify the variables most useful in predicting the myasthenic patient who needs postoperative mechanical ventilation.

METHODS

We applied multivariate discriminant analysis to preoperative physical, historical, laboratory and intraoperative data of 51 myasthenic patients who underwent transcervical-transsternal thymectomy to select those variables most useful in predicting the postoperative need for mechanical ventilation. The receiver operating characteristic (ROC) curve was also used to describe the discrimination abilities and to explore the trade-offs between sensitivity and specificity of the model.

RESULTS

Discriminant analysis identified seven risk factors that correlated with the need for postoperative ventilation: FVC, FEF25-75%, MEF50% and their percentages of the predicted values, as well as, sex. The model correctly predicted the actual ventilatory outcome in 88.2% of patients. The area under the ROC curve verified that our model correctly predicted the actual ventilatory outcome with a probability of 88.2%.

CONCLUSIONS

This model can be used for predicting the need for postoperative mechanical ventilation in myasthenia gravis patients.