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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.55 no.3 Campinas May/June 2005
Thoracic epidural anesthesia for mammaplasty in myasthenia gravis patient. Case report*
Anestesia peridural torácica para cirugía plástica de mama en paciente portadora de miastenia gravis. Relato de caso
Fabiano Timbó Barbosa, TSA, M.D.I; Marta Cristiane Bezerra Correia, M.D.II; Rafael Martins da Cunha, M.D.III; Ismar Lima Cavalcanti, TSA, M.D.IV
IAnestesiologista da Unidade de Emergência
Armando Lages, da Santa Casa de Misericórdia de São Miguel dos
Campos e Intensivista da Clínica Santa Juliana, Especialista em Docência
para o Ensino Superior
IIAnestesiologista da Unidade de Emergência Armando Lages e da Maternidade Santa Mônica
IIIProfessor de Farmacologia do Centro de Ensino Superior de Maceió, Professor Convidado de Farmacologia da Escola de Ciências Médicas de Maceió, Anestesiologista do Hospital UNIMED
IVDoutor em Medicina pela Escola Paulista de Medicina - UNIFESP, Responsável pelo CET/SBA do Hospital Geral de Nova Iguaçu, Diretor do Departamento Científico da SBA, Certificado na Área de Atuação em Dor pela AMB
BACKGROUND AND OBJECTIVES: Myasthenia
gravis is a chronic autoimmune disease characterized by skeletal muscles weakness
promoted by decreased acetylcholine receptors in the neuromuscular junction.
This report aimed at describing a case of myasthenia gravis patient submitted
to thoracic epidural anesthesia for cosmetic mammaplasty.
CASE REPORT: Female patient, 51 years old, with myasthenia gravis and submitted to thoracic epidural anesthesia with bupivacaine and fentanyl. There was no respiratory depression. Patient was discharged 36 hours later.
CONCLUSIONS: Our case suggests epidural anesthesia as a single technique for myasthenia gravis patients, without mandatory tracheal intubation.
Key words: ANESTHETIC TECHNIQUES, Regional: epidural; DISEASES: myasthenia gravis
JUSTIFICATIVA Y OBJETIVOS: La miastenia
gravis es una enfermedad crónica, auto-inmune, caracterizada por
la debilidad de la musculatura esquelética resultante de la disminución
de los receptores de acetilcolina en la unión neuromuscular. El objetivo
de este relato es mostrar el caso de una paciente con miastenia gravis
sometida a anestesia peridural torácica para una cirugía plástica
RELATO DEL CASO: Paciente del sexo femenino, 51 años, portadora de miastenia gravis fue sometida a anestesia peridural torácica con bupivacaína y fentanil. No hubo señales de depresión respiratoria. La paciente recibió alta hospitalaria después de 36 horas.
CONCLUSIONES: Este actual caso sugiere como conducta anestésica para el paciente portador de miastenia gravis la anestesia peridural como única técnica, sin la obligatoriedad de intubación orotraqueal.
Myasthenia gravis is a chronic autoimmune disease characterized by skeletal muscles weakness and fatigue due to decreased acetylcholine receptors in the neuromuscular junction 1. Its estimated prevalence is 50 to 125 per one million people 2.
The disease requires further care with drugs promoting muscle relaxation, especially neuromuscular blockers. The inadequate use of these drugs may require postoperative mechanical ventilation. Major perioperative complications are in general related to ventilatory parameters 3.
Diagnosis is confirmed by previous history, physical evaluation and supplemental exams such as: electroneuromyography, antibodies screening and anticholinesterase test 4.
This report aimed at presenting a case of myasthenia gravis patient submitted to cosmetic mammaplasty under thoracic epidural anesthesia.
Caucasian female patient, 51 years old, 60 kg with myasthenia gravis and thymectomy 3 years ago, under 120 mg/day pyridostigmine, admitted for cosmetic mammaplasty. Laboratory tests were normal and ECG showed sinus bradycardia. At preanesthetic consultation, the patient exhibited cardiologic and pneumologic approvals for surgery and informed being allergic to benzathine G penicillin. No respiratory effort or accessory respiratory muscles activity were observed during physical examination at rest and patient was classified as Osserman's clinical classification type I.
The preanesthesia preparation included 12-hour fasting, the maintenance of the morning dose of pyridostigmine and no sedatives.
Monitoring in the operating room consisted of cardioscopy, pulse oximetry and noninvasive blood pressure. Patient was given intramuscular ethylephrine (10 mg) and a venoclysis with a 18G catheter was established for the administration of lactated Ringer's solution. Epidural puncture was performed having the patient in the sitting position via median approach with a 18G Tuohy needle between 7th and 8th thoracic vertebrae. The epidural space was identified by loss of resistance to air and 25 mL of 0.5% bupivacaine (125 mg) with vasoconstrictor plus 2 mL fentanyl (0.1 mg) were injected. Sensory level was tested with ether. Upper level of the sensory block was between dermatomes T8 and C5 before the start of surgery. During the procedure, the patient was maintained under oxygen therapy through nasal catheter (5 L.min-1) and conscious sedation with intravenous boluses of midazolam (7.5 mg). The patient was operated in the supine position with 15 degrees elevation of the dorsum. Intravenous dipirone (2 g) and tramadol (100 mg) were administered 20 minutes before the end of the surgery.
Surgery lasted 210 minutes. After surgery, the patient remained in the operating room for 60 minutes under monitoring and oxygen therapy, and was transferred to the ward after reaching 10 points in the Aldrete-Kroulik scale.
There were no post-anesthetic complications and the patient was discharged 36 hours after the end of the surgery.
Myasthenia gravis is a chronic disease affecting skeletal muscles by destroying neuromuscular junction nicotinic receptors by immunoglobulin G 5,7. There is loss of post-synaptic membrane folds 6,8 and this aggression is related to complement activation 9.
The incidence is 1:20,000 9,10 being more frequent among females 2,6,9, in a 6:4 ratio 5. Females are in general affected in the third decade of life and males between the sixth and seventh decade 2,6.
This disease evolves with episodes of crises and remissions 2,8.
The reason is unknown, but it is believed that there might be an immunoregulation defect or genetic predisposition 10. Pre-synaptic receptors destruction has also been postulated, however acetylcholine release may be up to three times higher in those patients as compared to normal patients 10. In general, it is associated to thyme abnormalities 4,6,10. Thymic hyperplasia is present in 65% 6 being more common in young people 4,9,10 while thymoma is present in 10%, especially in the elderly 4,6,9,10.
Myasthenia gravis is often associated to other autoimmune diseases such as 5: Graves' disease, rheumatoid arthritis, idiopathic thrombocytopenic purpura, systemic lupus eritematosus, multiple sclerosis, lymphoma, Sjögren syndrome and scleroderma. These diseases should be investigated during preanesthetic evaluation 8 and medications should be adjusted for surgical procedure.
Some drugs may exacerbate myasthenic crises and should be avoided, such as 5; aminoglycosides, clindamycin, cholistine, polymixyn B, tetracyclin, propranolol, lidocaine, thyroid hormones, lithium, oxytocin, phentoin and chlorpromazine. In addition, some triggering factors should also be avoided, such as extreme heat 9, stress 6,9,11 and surgery 6,9.
Patients may present weakness of any muscle group 2,5 which improves with rest and worsens with exercise 2,6. Very often, the first affected group is extra-ocular muscles 2,5,6, which worsens late in the afternoon when most cholinergic receptors are already occupied 4.
Osserman's clinical classification divides patients according to the affected muscle group and the intensity of involvement in 2,4,5,9,10: type I for patients with ocular myasthenia, palpebral ptosis and diplopia; type II A for generalized myasthenia with mild evolution without respiratory crisis; type II B for generalized myasthenia with more severe muscle and bulbar involvement, however without respiratory crisis; type III for patients with fulminating myasthenia, with rapid evolution, respiratory crisis and poor response to drug therapy; and type IV which is the most severe form resulting from groups I and II with poor response to drug therapy.
Diagnosis may be confirmed by electroneuromyography, anticholinesterase test and antibody screening 4,9.
Pharmacological test is done with atropine and neostigmine 4 or edophronium 5,9 followed by assessment of palpebral opening and of diplopia. It should be preferably performed in late afternoon 4 and in adequate environment since worsening of symptoms and respiratory distress may occur.
Antibodies should be investigated, although up to 20% of patients do not present circulating immunoglobulins 6,8, which does not rule out the diagnosis.
The treatment includes 2,5,9 anticholinesterase drugs, immune suppressors, plasmapheresis and surgery.
Pyridostigmine is the most popular anti-cholinesterase agent and is indicated as a first-line medication 1. Daily doses may or may not be decreased after thymectomy. The major mechanism of action of this drug includes irreversible inhibition of acetylcholinesterase degrading enzymatic activity, which increases acetylcholine concentration in the neuromuscular junction. Doses should be tailored, since large amounts of acetylcholine in the synaptic cleft can decrease muscle strength. Each 30 mg orally administered are equivalent to intravenous (1 mg) 7.
Immune therapy is indicated when patients do not respond to pyridostigmine 2. The mostly used drugs include azathioprine 2,5,9, cyclosporine 2,5,9, cyclophosphamide 5,9 and steroids 2,5,9. Steroids are the most commonly used, with satisfactory effectiveness 2.
Plasmapheresis is a temporary treatment and should be used for severely ill patients in preparation to general anesthesia 2,5. There are two nicotinic receptors in the neuromuscular junction 8,10: stable and short-living. Stable receptors have half-lives of 12 days while short-living receptors have half-lives of approximately 24 hours 8,10. Short-living receptors are precursors of stable receptors 10. Plasmapheresis promotes immediate clinical improvement by removing antibodies to such receptors and allowing the increase of short-living receptor concentration 8.
Surgical treatment is thymectomy 1,2,5. It is currently performed in patients with or without thymoma 1. Up to 20% of patients have complete remission and 40% markedly improve with smaller doses of anticholinesterase drugs 5.
Some parameters may indicate the need for postoperative mechanical ventilation, such as 2: disease lasting more than 6 years, associated lung disease, pyridostigmine dose equal to or above 750 mg/day in the 48 hours preceding surgery, and vital capacity below 2.9 liters.
During the preanesthesia consultation, it is important to investigate other autoimmune and pulmonary diseases which may complicate the procedure. In our case, the patient did not present signal of respiratory distress or reported difficulty in swallowing. Difficult swallowing raises the possibility of aspiration of gastric contents so that Mendelson's syndrome prophylaxis is indicated with measures, such as awake or rapid sequence intubation; metoclopramide, H2-blockers and non-particulate antacids. In spite of the satisfactory results available in the literature with such drug regimens, confirmatory studies in this group of patients are still lacking 6.
Myasthenia gravis patients may present myocarditis with atrial fibrillation or some degree of cardiac block 2. It is recommended a very thorough pre-surgical evaluation of cardiac function.
Our service does not premedicate for sedation purposes because patients are admitted the day of the surgery. Maintaining patients for a longer time in contact with relatives and the preanesthetic evaluation may decrease the need for preoperative anxiolytic drugs. Some myasthenia gravis patients are very sensitive to respiratory depressants, such as opioids, benzodiazepines and similar substances, which should be avoided as preanesthetic medication 6.
It is possible to eliminate morning anticholinesterase drug dose in non-severe cases, when the objective is tracheal intubation without neuromuscular blockers, since muscles become weaker and intubation maneuvers, are easier 5. The timing for resuming anticholinesterase medication is still controversial. One suggested approach is to wait for normal gastrointestinal function recovery to restart oral medication 5.
Muscular ethylephrine before blockade was used to prevent hypotension.
Nondepolarizing neuromuscular blockers have their sensitivity increased in this group of patients 1,2. When indicated, intermediate or short action drugs should be preferred. Atracurium 1,9, rocuronium 9 and mivacurium 2,9 may be safely used. Atracurium is 1.7 to 1.9 times more potent in myasthenic as compared to normal patients 10. These patients have increased sensitivity to vecuronium 2.
Response to succinylcholine is unpredictable and there may be resistance, prolonged effect or unexpected responses 6. Phase II blockade occurs more easily 7. Probably plasma cholinesterase inhibition by anticholinesterase drugs justify this finding 10.
Inhalational anesthetics may promote some degree of muscle relaxation in myasthenia gravis patients 8. Isoflurane seems to be best indicated since it induces 30% to 50% neuromuscular block 7. Very high concentrations allow for surgical intervention without neuromuscular blockers, with possible delay in emergence and hemodynamic impairment. Nitrous oxide may also be used in myasthenic patients without worsening of the disease 13. Intravenous anesthesia, associated or not to neuraxial block, may be induced. Thiopental is counterindicated since it depresses peripheral synapses and neuromuscular junction 10.
Epidural anesthesia was chosen for our patient because it does not depress the ventilatory response to CO2 even in myasthenic patients 14, very often does not induce complete motor block 15, does not block diaphragm innervation and does not produce muscle fatigue 7.
Thoracic epidural anesthesia promotes some respiratory effects, such as 16: mild vital capacity decrease, mild decrease in forced respiratory volume in the first second and decreased total pulmonary capacity. These changes have minor clinical implications in healthy patients. However they may prevent cough effectiveness in patients with severe pulmonary impairment 16.
Epidural catheter would allow for more fractional local anesthetic doses, less hemodynamic repercussion and lower anesthetic doses. Global rate of technique-related complications is 46.3%, being 13.9% directly related to the catheter 17, mostly without clinical repercussions 7. Epidural catheters are unavailable in our service.
Bupivacaine was the drug of choice because it is an aminoamide local anesthetic independent of pseudocholinesterase function for its metabolism since this enzyme may be inhibited by pyridostigmine 10, does not precipitate myasthenic crises, and has action time of 180 to 240 minutes, which would allow completion of the surgical procedure and patient's referral to the ward without motor block. The high local anesthetic dose used in this case aimed at maximizing sensory block duration. Even in cervical epidural anesthesias, with 100 mg dose and 0.5% concentration, this anesthetic has mild repercussion on the phrenic nerve 18.
This case suggests epidural anesthesia as a single technique without mandatory tracheal intubation for myasthenia gravis patients.
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Dr. Fabiano Timbó Barbosa
Address: Rua Comendador Palmeira, 113/202 Farol
ZIP: 57051-150 City: Maceió, Brazil
Submitted for publication August 26, 2004
Accepted for publication January 17, 2005
* Received from Santa Casa de Misericórdia de São Miguel dos Campos, Maceió, AL