Myasthenia gravis is the prototype of adult autoimmune neuromuscular diseases, characterized by fatigability and weakness of the lean muscles due to down - regulation of the acetylcholine receptors in the postsynaptic membrane (either by destruction or by failure) (1, 2). Included among the postjunctional anomalies, MG associates histocompathibility antigens (HLA A1, B8 and DR3), mainly to women under their forties (3, 4).
The clinical diagnosis is based on signs and symptoms of muscular asthenia, weakness and motor failure of the muscles involved. The most vulnerable are the skeleton muscles innervated by the cranial nerves (bulbar): ocular, pharyngeal, laryngeal.
MG is classified according to clinical criteria of gravity into four classes, and the severity of disease is evaluated by a MDS (mean disability score) (5).
Laboratory diagnosis consists in:
· the EMG test (electromyography) - fading of the muscular contraction to repetitive electrical stimulation;
· edrophonium - 2-10mg intravenously with EMG monitoring;
· regional curare test;
· Anti-nicotine receptor antibodies knowing that the test is in 10-15% cases negative (6).
The differential diagnosis implies ruling out the following: congenital myasthenic syndromes, drug induced MG, the Eaton-Lambert syndrome, hyperthyroidism, botulism, external progressive ophtalomplegia, intracranial mass syndrome.
The treatment consists in: anticholinesterase drugs, thymectomy, immunosuppressive therapy (steroids, cyclosporine and azathioprine in cases of failure to control the disease by anticholinesterase drugs). Short immuno-therapy includes: plasmapheresis (removing the antiacetilcholine receptors, the effects lasting but a few weeks,
extracorporeal immunoadsorbtion (eliminating mainly the specific antibodies, but sparing the irrelevant immuno-globulin and other plasma proteins) and immunoglobulin (as efficient as plasmapheresis, but costly).
Thymectomy is indicated in: all thymomas, potential sources of antibodies and all the patients aged under 50 years (or 60 according to the American Academy of Neurology) to whom anticholinesteraze therapy is inefficient (7).
We prospectively screened all the patients submitted to thymectomy for MG in the Clinic of Surgery number I in Tg. Mures, Romania. The patients were initially prepared by the neurologist, examined by the anesthetist, and admitted in the Clinic of Anesthesia and Intensive Care I in Tg. Mures postoperatively. The first five years the thymus was removed by extended sternotomy (1994-1998). We then preferred VATS by left approach. The patients were prospectively included in the aim well defined in the very beginning of our team approach of identifying the best surgical and anesthesiological management for the myasthenic patients. We included a number of 103 patients who underwent thymectomy, 51 by VATS. (fig. 1, 2, 3, 4)
The preanesthetic examination evaluated the severity of the disease. The main concern was bulbar involvement with respiratory failure. Roughly one third of the cases in the beginning of our activity were postponed for a better preparation and treatment of co morbidities: thyroid storm and rheumatoid arthritis. Literature points out also to
lymphomas, magaloblastic anemia and systemic lupus (8). We also postponed and treated all the patients with sepsis, knowing that sepsis is a precipitating factor for myasthenia crises. We did not prescribe antibiotics to the viral infections in order to avoid colitis due to Clostridium difficile, reputed for its devastating effects (9).
Preoperative assessment of the respiratory performance by spirometry was not evocative, since normal values do not guarantee a complication-free evolution. In one case operated as a last resort (drug therapy absolutely inefficient), the patient was prepared by plasmapheresis (performed 3 times for four hours each). Plasmapheresis is often considered an underutilized procedure (10, 11). The operation was in this case uneventful, but the postoperative evolution was difficult. The patient needed prolonged ventilatory support (one week) but succeeded to survive ventilation associated pneumonia. (The patient already had a history of thymectomy at the age of 17 and thus we only removed the remaining thymic tissue by
sternotomy. However, it is emphasized that in order to have a good clearance of the airways, forced vital capacity has to be 3 times the tidal volume. A forced vital capacity reduced by more then half of the expected value is considered to be an indicator of a high risk of postoperative dependency on mechanical ventilation (Gas cit by 12). The patient has to be fully informed on the optimal moment of surgery but also on the expected postoperative evolution, on the need of
mechanical ventilation or other support therapies. This is the only way one could expect an unconditioned cooperation.
Choosing the optimal moment for surgery was at the beginning extremely cautious, but then it became routine. Initially all the patients were prepared by the neurologist. We then took the advice of the anesthesiologist who took care of the critically ill patients with MG preoperatively. It is essential to reach to an agreement between the surgeon, the neurologist and the anesthetist.
Immunosuppression is not to be interrupted. If one has to administer immunoglobulin, the dose is 400 mg/kgc/day for five days (9, 13). Steroids were also administered according to the usual dosage (alternate day therapy). We had no patients on azathioprine or cyclosporine. Immunoglobulin is
considered to be as efficient as plasmapheresis, although expensive (9).
Premedication is not necessary in our opinion, a correct interview being an acceptable surrogate (for some, the best sedative). Despite reservations on benzodiazepines, the most efficient seemed to be midazolam (to the young)
associated to atropine administered intramuscularly 30 min before the incision.
Anticholinesteraze therapy was given in the morning of surgery 1-2 hours preoperatively. It is important to schedule thymectomy as the first operation in the morning in order to avoid unnecessary exhaustion of the patient (stress is not to be favored) and to speculate on the maximal effect of anticholinesteraze drugs at the arousal from anesthesia. With a mean duration of thymectomy of 90 minutes (be it classical or by VATS), one can anticipate a fair awakening with no need to antagonize the neuromuscular block at the end of surgery (14).
The majority of our patients were classified in ASA I group, 44 in ASA II, 10 ASA III (2 cases ASA III E) and ASA IV (I case).
All the patients were delivered general anesthesia with monitoring of the muscle relaxation by TOF (train of four) guard in 51 cases. For VATS it is essential for the surgeon to have the patient in stand still in order to avoid lacerations.
We used balanced anesthesia, but also TIVA (total intravenous anesthesia) with propofol and fentanyl. Despite the different opinions, we could manipulate even sevoflurane, reputed to potentiate the neuromuscular block due to atracurium to the aged (15). We avoided mask induction with sevoflurane fearing the risk of aspiration, although it is recommended to the children for its smooth induction, rapid awakening caring no risk of hemodynamic instability or residual asthenia (16). Succinylcholine was avoided and we easily intubated all the patients on the induction dose (usually two thirds of the calculated dose on the basis of actual weight). We failed to appreciate awake intubation praised by others.
Positioning on the surgery table is decubitus for
sternotomy. We positioned for VATS initially the patients in right lateral position at approximately 45 degrees (which caused a compression of the upper arm in one case with pain postoperatively). Thus the right lung became dependant. This resulted also in reflux of the blood from the peripheral cannulated veins. However we used two large bore catheters to start with and needed but twice invasive arterial lines (for selected patients ASA IV and III). There was never need for extra venous lines during surgery.
During surgery we ventilated the patients initially in the IPPV (intermittent positive pressure ventilation), since 2000 only in PCV (pressure controlled ventilation), a mode we consider to be closer to physiology and less prone to hyperventilation.
There are some moments during surgery that require full attention: disconnection of ventilation during sternotomy and insufflating the gas (in our clinic CO2) during induced pneumothorax for VATS.
We separated the lungs for VATS using left DLTs (double lumen tubes) because we could not verify the position of the tubes in all the cases. Left selective cannulation is less prone to inadvertent positioning when verified at auscultation
compared to right bronchial cannulation. We did not need to reposition the bronchial cannula during surgery. We tested the patients before inducing pneumothorax by administering O2 in FiO2 0, 3 (inspiratory fraction) concentration, ventilating with a tidal volume of 5ml/kg body weight and a frequency of 14/min for 10 minutes. This was considered to be a test of
tolerance for one-lung ventilation and for a good positioning of the bronchial tube.
We experienced few hypoxic episodes during surgery. In a case where we selectively intubated the right bronchus, hypoxia emerged twice despite apparently well positioning of the DLT. It was rapidly reversed by manual ventilation with pure oxygen and subsequent PEEP of 5 cm H2O (to diminish the intrapulmonary shunt due to the collapse of the upper lung). We suspected obstruction of the upper right lobe (possible by the cuff of the bronchial balloon). In one another case we used too small a DLT compared to the actual diameter of the bronchi. Bronchial aspiration during surgery was needed in one case (a neglected MG).
Sometimes during VATS the surgeons elicit premature ventricular contractions or bradicardia when reaching the pericardium, bur they are spontaneously disappearing when the maneuver stops.
Complications during surgery are rarely attributed to anesthesia (we could not blame on anesthesia any complications, but eventually incidents). We experienced one pericardial and one myocardial lesions leading to sternotomy. Fortunately the blood loss was minimal and the recovery uneventful. There was no need for blood transfusion. We did not encounter any adverse hemodynamic events when insufflating CO2. Therefore we believe that a good and monitored technique to insufflate the gas in the thoracic cavity is paramount to avoid hemodynamic complications and gas embolic events. Plummer recommended maximum 2l of CO2 with low
velocity (12). Induced pneumothorax enhances visibility and speeds lung collapse. CO2 embolism is supposed to be
detected by concomitant capnography and pulsoximetry:
fading to zero of the CO2 line and hemoglobin desaturation. No such case occurred. There were no bronchopleural
We did not reverse the neuromuscular blocking agents at the end of surgery. We extubate the patients as a rule at the end of surgery in the operating room. If we anticipate the need for mechanical ventilation, we change the
tracheal tube for a single lumen one. We advocate for early weaning from mechanical ventilation in order to avoid
septic complications and an ulterior difficult weaning. A nazogastric tube was placed in order to allow for enteral drug administration, but we now insert it only in selected cases. Two hours following surgery the VATS patients are able to ingest liquids.
We administered either two thirds of the preoperative anticholinesterase drugs postoperatively (to the young) or the preoperative doses starting in the afternoon of surgery. Steroids were continued as prescribed. Tracheostomy was rarely needed (only when contemplating mechanical ventilation for more then two weeks - 5 patients).
Myasthenia crises were rare, mainly to the ASA III and IV patients. All the patients we lost (6 patients) were submitted to sternotomy and subject of co-morbidities. In one case submitted to plasmapheresis and mechanically ventilated, we stopped anticholinesterase therapy and waited for the patient to resume ventilation. The evolution was uneventful, but he was readmitted one month later for bilateral pneumonia and deceased in multiple system organ failure.
One patient was later operated for a granuloma of the vocal cords. The factors influencing the outcome of trans
sternal thymectomy for MG were extensively reviewed and analyzed by others (17, 18). Naguib identified 7 risk factors for the need of postoperative ventilation: 3 measured respiratory parameters and their % of the predicted value and sex. The precision of his model is of 88.2% (19).
We believe that intraoperative clinical status and the need for muscular relaxation as appreciated by monitoring are evocative for the respiratory reserve of the patient (20).
Postoperative long term follow up is done by the
neurologist. Immediate postoperative remission occurred in 89 (out of 103) of the patients.
The remission rate on the long run was evaluated by the neurologist but was not one of the targets of this study; therefore it is not to be mentioned here.
VATS is appropriate for almost all thymectomies, but the outcome is heavily dependant on a team approach: neurologist, surgeon and anesthetist, the later being in our country also an intensivist. Following the strategy of a good preoperative
evaluation and preparing of the patient, early weaning,
shortening the mechanical ventilation and the ICU stay and using any of the general anesthesia models in the interest of the patient and in agreement with his medication lead to a good outcome of thymectomy. For now, VATS is our favored procedure in the best interest of the patient.
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