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Neurology India, Vol. 50, No. 3, Sept, 2002, pp. 348-351 Case Report Intensive Respiratory Care in Patients with Myasthenic Crisis A.N. Aggarwal, D. Gupta, D. Behera, S. Prabhakar,* S.K. Jindal Departments of Pulmonary Medicine and Neurology*, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012, India, Correspondence to : Dr. S.K. Jindal, Department of Pulmonary Medicine, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012, India. Accepted for publication : 24th January, 2001. Code Number: ni02098 Summary Six patients received mechanical ventilation for 8 episodes of myasthenic crisis in a two year period. Median duration of ventilation was 8 days. Only one patient required ventilation for more than three weeks and underwent tracheostomy. Atelectasis and pneumonia were the common ventilator associated complications observed, and these responded to therapy. Two patients underwent thymectomy after initial stabilization and while being ventilated. All patients recovered completely. Key words : Myasthenia gravis, Respiratory failure, Mechanical ventilation, Thymectomy, Atelectasis. Introduction Myasthenia gravis is an autoimmune disorder caused by antibodies directed against the acetylcholine receptor of the postsynaptic portion of neuromuscular junction. About 15-20% patients develop an exacerbation during the course of their illness, producing respiratory and oropharyngeal muscle weakness requiring mechanical ventilation; these patients are considered to be in myasthenic crisis.1,2 Although a common neurologic emergency, myasthenic crisis in today's era is rarely fatal, largely because of improved ventilatory management of respiratory failure in these patients. We present our experience in the intensive respiratory care of patients in myasthenic crisis. Material and Methods Patients with myasthenic crisis, admitted to the respiratory intensive care unit (RICU) of this institute over a two-year period, were managed as per protocol described herein. Diagnosis of myasthenia gravis was established clinically, and supplemented by data from pharmacological, laboratory and electrophysiologic tests wherever available. For purpose of analysis, myasthenic crisis was defined as an episode of respiratory failure requiring treatment with mechanical ventilation.3,4 Age, gender, duration of illness, baseline symptoms and comorbid conditions were recorded for all patients. The ultimate outcome measure studied was hospital survival. Duration of mechanical ventilation and ventilator associated complications (if any) were also recorded. All patients were ventilated using Puritan Bennett 7200ae ventilators. The need for tracheal intubation and mechanical ventilation was assessed by clinical examination (level of overall patient comfort, frequency and depth of breathing, presence of paradoxical respiration, single breath count, and gag reflex) and arterial blood gas (ABG) analysis.3 Initially, control mode ventilation (CMV) with tidal volumes of around 10 ml/kg was used. Patients were gradually switched to synchronized intermittent mandatory ventilation (SIMV) with pressure support after stabilization. An effort was made to maintain oxygen fraction in inspired air (FiO2) at <0.5, while maintaining adequate oxygenation (pO2 >60 mm Hg). Adequate care was taken for asepsis, nutrition, humidification of inspired air, and regular endotracheal toiletting. Continuous monitoring of hemodynamic and respiratory (including ABG and respiratory mechanics) variables was done. Weaning was accomplished by gradual reduction in the SIMV rate and the level of pressure support. A T-piece trial was given and patients were extubated if they had normal bulbar reflexes and did not show any worsening (as manifested by respiratory muscle fatigue on clinical examination and/or CO2 retention on ABG analysis) during this period. Anticholinesterase drugs were discontinued after initiation of mechanical ventilation, and reintroduced in escalating doses only when weaning was contemplated.3 Propantheline bromide was routinely administered during this phase to counter excessive airway secretions. Possible precipitating factors were explored and treated. Immunotherapy with intravenous immunoglobulin (IVIG) was administered wherever feasible.5 Tracheostomy was performed for patients requiring prolonged mechanical ventilation. Results Six patients (3 males and 3 females) with myasthenic crisis underwent 8 episodes of mechanical ventilation during the study period. Two patients had required respiratory support on two separate occasions. All patients had generalized disease of two years' duration or less (Table I). Thoracic CT scan was normal in three, showed diffuse hyperplasia in one, and thymoma in two patients. Myasthenic crisis was precipitated by introduction of corticosteroid therapy in 3 of 8 episodes, and by aspiration pneumonitis in one; no definite trigger could be identified in other instances. The median duration of mechanical ventilation was 8 days. All except one patient, who had underlying bronchial asthma and psychological ventilator dependence, required assisted ventilation for less than 3 weeks. Two patients developed ventilator associated pneumonia, which responded to parenteral antibiotics (Table I). Three patients developed atelectasis related to excessive airway secretions during introduction of anticholinesterase drugs (Table I), all improved after airway toiletting under vision through a fibreoptic bronchoscope. All patients had made complete clinical and neurological recovery at the time of discharge from RICU. IVIG was administered to 2 patients. Only one patient (patient 3) required tracheostomy as she was ventilated for 7 weeks. Thymectomy was performed after initial stabilization in two patients, while they were still being ventilated, in the second (patient 4) and third (patient 3) week (Table I). Neither patient had any significant surgical complications or exacerbation of myasthenic weakness during postoperative period. Discussion Respiratory failure due to myasthenic crisis is an important indication for mechanical ventilation.6 Two possible mechanisms can result in life threatening respiratory compromise in myasthenic patients.3 Respiratory muscles weakness can lead to impaired lung expansion, hypoventilation and weak cough. Secondly, oropharyngeal weakness can result in inability to clear airways and aspiration of secretions can occur. Patients often deteriorate rapidly. Close monitoring and early intervention (tracheal intubation and mechanical ventilation) are therefore necessary for a favourable outcome. All patients studied in this report had disease of a relatively short duration . It is well recognized that most crises occur within the first two years of onset of disease.2 Common precipitating factors include respiratory infections, aspiration pneumonia and medication change (such as withdrawal or initiation of corticosteroids, withdrawal of cholinesterase drugs, aminoglycoside administration); in about a third of patients no precipitating cause can be identified.3,4 These triggers were identified in some of our patients. As most patients in myasthenic crisis do not have significant pulmonary disease (and therefore normal lung mechanics), mechanical ventilation is relatively easy. These patients have low oxygen requirements and tolerate large tidal volumes well without complications. None of the patients studied herein had barotrauma related to mechanical ventilation. The only significant problem may arise when anticholinesterase medication is reintroduced, as these drugs tend to increase airway secretions and thereby increase risk of atelectasis through formation of mucus plugs in the airways.7 Although we ensured adequate airway toiletting and routinely administered propantheline during this period, three episodes of lobar or lung collapse were recorded. Fibreoptic bronchoscopy is useful in such circumstances and airway patency can be restored under vision by sitedirected suctioning.8 Bronchoscopy was successful in treating atelectasis in all these patients. Two patients, who had developed ventilatorassociated pneumonia, responded to antibiotic therapy. One of these patients had required prolonged mechanical ventilation. It is well known that the risk of ventilator associated pneumonia increases progressively with duration of mechanical ventilation.9 Both pneumonia and atelectasis are among the common medical complications encountered in these patients.2 All patients were successfully ventilated and no death was recorded during hospital stay. Mortality during crises is largely determined by presence of severe comorbid illness and not by the basic disease per se.2 Most patients in myasthenic crisis require ventilation for a brief duration (less than two weeks).2,7 Only one of our patient required prolonged respiratory support and tracheostomy. She was suffering from bronchial asthma and had also developed ventilator-associated pneumonia. Even after adequate control of both these disorders, she was uncomfortable during weaning trials. She had developed psychological dependence on assisted ventilation and could be weaned successfully only after regular counseling. Two patients underwent thymectomy after initial stabilization while they were still being ventilated. This was tried to save time spent in the hospital and on ventilator. It is recommended that thymectomy should not be performed during crisis.10 However, both these patients were already stabilized and were on immunosuppressive therapy. Both of them tolerated the procedure well and developed no complications. This approach is useful in settings where demand for surgical and ventilatory resources far exceeds available resources. It saves an additional episode of hospitalization and possible postoperative mechanical ventilation. Since there is no well documented information regarding such an approach, more data with larger number of patients is needed. In conclusion, patients in myasthenic crisis have an excellent outcome if respiratory support can be provided adequately and in time. Mechanical ventilation, usually needed for a short duration, is safe and well tolerated by most of these patients. References
Copyright 2002 - Neurology India. Also available online at http://www.neurologyindia.com The following images related to this document are available:Photo images[ni02098t1.jpg] |
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