Postoperative Respiratory Care After Transsternal Thymectomy in Myasthenia Gravis

Postoperative Respiratory Care After Transsternal Thymectomy in Myasthenia Gravis· A 3-Year Experience in 53 Patients Douglas R. Gracey, M.D., F.G.G.P.; Matthew B. Divertie, M.D., F.G.G.P.; Frank M. Howard, J1:, M.D.; and W Spencer Payne, M.D., EC.C.P.

During a three-year period, 53 patients with myasthenia gravis underwent transstemal thymectomy by a partial stemum-splitting technique at our institution. This procedure was carried out (1) because an x-ray &1m or a computed tomography scan had suggested the presence of a thymoma or (2) to manage symptoms of myasthenia gravis. In 41 patients the endotracheal tube was removed in the postanesthesia recovery room. The remaining 12 patients were extubated in the Respiratory Care Unit-in 6ve, after

patients with myasthenia gravis have an increased anesthetic and postoperative risk, and for them surgery is one of the common precipitating factors in the development of respiratory failure. We evaluated the postoperative care of our patients with myasthenia gravis who have undergone transsternal total thymectomy. We were particularly interested in the respiratory complications and in determining specific clinical features that might identify preoperatively those myasthenic patients in whom these complications are likely to develop. METHODS

We reviewed the records of 53 patients with myasthenia gravis who underwent transstemal thymectomy by a partial stemumsplitting approach at this institution between Jan 1, 1978, and Dec 31, 1980. In 12 cases an abnormal roentgenogram or computed tomography (CT) scan of the chest suggested the presence of thymoma; in the rest, the operation was carried out as part of the empiric management of myasthenia gravis. Patients were divided into groups according to the Osserman classification which depends particularly on bulbar involvement. 1 Group 1 myasthenia gravis is characterized by ocular involvement only. Group 2A is generalized muscular involvement but without respiratory impairment; group 2B has more bulbar manifestations than group 2A. Group 3 includes rapid onset and progression of bulbar and generalized disease with respiratory muscle weakness; the incidence of thymoma is high and there is significant mortality. In group 4, progressive myasthenia gravis symptoms develop at least *From the Division of Thoracic Diseases and Internal Medicine and Section of Critical Care Medicine (Drs. Gracey and Divertie), Department of Neurology (Dr. Howard), and Department of Surgery (Dr. Payne), Mayo Clinic and Mayo Foundation, Rochester, Minnesota. Manuscript received May 6; revision accepted December 14. Reprint requests: Section ofPublications, Mayo Clinic, Rochester, Minnesota 55901

prolonged mechanical ventilation. From our experience, the only factor ~fu1 for predicting the probable need for prolonged postoperative mechanical ventilation is the degree of bulbar involvement. Patients in Osserman classification groups 3 and 4 have an extremely high incidence of postoperative respiratory failure. Consideration should be given to the use of preoperative plasmapheresis in myasthenia gravis patients who have significant bulbar symptoms.

two years after the patient has previously been in group 1 or 2, there

is a high incidence of thymomas, the response to drug therapy is

poor, and the prognosis is very poor. For each patient, vital statistics, clinical, roentgenographic, physiologic, and pathologic data, dose of medication used, and postoperative course were reviewed. Particular attention was paid to the respiratory status and its relationship to the clinical severity of the disease. RESULTS

The group included 38 female and 15 male patients (mean age, 32 ± 16 years; females, 28 ± 13; males, 41 ± 19). The duration of symptoms averaged four years (range, one month to 20 years). Five patients (four female, one male) required prolonged mechanical ventilation; their average age was 29 ± 16 years (range, 1). to 49 years). The distribution by Osserman group is shown in Table 1. All three group 1 patients had CT scans suggesting thymoma: one was found to have a thymoma, and the scans were false-positive in two. Full pulmonary function tests were carried out preoperatively in 30 patients; only four of these reTable I-Patient Gmu". by Ouennaft Claaification and POBtopertJtive BapirtJtorfl Failure Group

Total No. of Patients

No. of Patients With Prolonged Mechanical Ventilation

1 2A

21

3

o o

2B

3 4 Total

23 3

1 3

53

5

3

1*

*One additional group 4 patient required prolonged endotracheal intubation. . CHEST / 86 / 1 / JULY, 1984

87

quired prolonged mechanical ventilation. Vital capacitywas 3.3 ± 1.1 L (range, 1.0 t06.3 L) in the 26 patients who did not require prolonged mechanical ventilation, and 2.6 ± 1.0 L (range, 1.5 to 3.5 L) in the four who did require such management. The large standard deviations make the difference between these vital capacity values not statistically significant. Maximum static inspiratory and expiratory pressures were measured postoperatively, four times daily at one-half to one hour before the next dose of anticholinesterase medication. At the time that mechanical ventilation was discontinued, maximum inspiratory pressure averaged - 38 ± 8 cm H 20 (range -27 to -45 cm H.O), and maximum expiratory pressure was + 35 ± 2 cm H.O (range, + 32 to + 36 cm H.O). In these patients, oxygenation was adequate while they were breathing 40 percent inspired oxygen via a T-piece, and there was no carbon dioxide retention when they were breathing spontaneously through this device. The 48 patients who did not require mechanical ventilation postoperatively had maximal static respiratory pressures of more than ± 40 cm H 20 and normal arterial blood gas tensions while receiving supplemental oxygen. Thymic Pathology In 45 patients, no thymic neoplastic process was

found, Of these, 31 patients showed only lymphoid

hyperplasia, and 13of them had well-defined germinal centers on pathologic examination. Twelve of the 45 patients showed thymic lymphoid depletion with fat replacement, and two patients additionally had benign thymic cysts. Eight patients were found to have a thymoma, and fOur of these tumors displayed malignant features with variable degrees of extension to extrathymic structures. No relationship could be established between thymic pathology and the need fOr prolonged mechanical ventilation. Ainooy Care Forty-three of the patients were extubated in the postanesthesia recovery room, and only two required subsequent reintubation for assisted mechanical ventilation (both were reintubated approximately 24 hours postoperatively). Ten patients were extubated in the respiratory ICU; they had been transferred there from the postanesthesia recovery room with an endotracheal tube in place. Five were extubated in the leu 24 to 48 hours postoperatively, and two of these required reintubation within another 24 hours-for the purpose of clearing retained secretions in one group 4 patient and for assisted mechanical ventilation in the other; In six instances, endotracheal or tracheostomy tubes were required for longer than 48 hours (mean, 8±4.0 18

days; range, 3 to 14 days). Only two of these patients had complications from the oral endotracheal tubes. Severe pharyngeal pain developed in one when an attempt was made to remove the tube four days postoperatively, and because of this, extubation was impossible. Consequently, a tracheostomy was performed with the retained endotracheal tube in place, and it was then easily 'removed under anesthesia. A later examination of the upper airway and vocal cords revealed no abnormalities. The second patient extubated himself within a few hours after operation and was reintubated without incident. In only one instance was tracheostomy required postoperatively. It was performed on the fifth postoperative day because of the tight endotracheal tube described above. In a second patient (group 3), a tracheostomy was necessary fiveweeks before thymectomy to permit prolonged mechanical ventilation. One additional group 4 patient required an endotracheal tube for five days postthymectomy to control his tracheobronchial secretions.

Mechanical Ventilation Five patients (three in group 3, one in group 2B, and one in group 4 preoperatively) required continuous prolonged mechanical ventilation for three to 12 days (mean, 7 ± 3.6 days) after operation (Iable 1). Their mean hospital stay was 16.7±10.1 days (range, 5 to 31 days) compared with a mean hospitalization for those not requiring prolonged mechanical ventilation of 5.9±2.6 days (range, 2 to 14 days). One of these five had had intermittent mechanical ventilation for several weeks before thymectomy and required continued support intermittently for a total of 26 days. This patient, in whom a thymoma had been detected on a chest roentgenogram, could not be weaned from mechanical ventilation despite optimal medication with prednisone and pyridostigmine bromide. This patient was seen before we had gained experience in plasmapheresis for myasthenia gravis; otherwise, preoperative plasmapheresis would have been used to attempt to wean her from assisted ventilation. All five patients had problems with respiratory muscle weakness and with retention of secretions that had been increased by anticholinesterase medications. All five were eventually weaned from mechanical ventilation and extubated. At the time of removal from ventilator support, each had a vital capacity of more than 1.0 L and maximum static respiratory pressures of more than ± 30 cm H.O. Complications

The incidence of early postoperative respiratory complications was directly related to the severity of the myasthenia gravis. However; the occurrence of previous respiratory difficulty had little prognostic value

with regard to the postoperative course. Three of the patients who did not require postoperative mechanical ventilation had required it in the past-two for respiratory failure due to pneumonia and one when succinylcholine was given before gynecologic surgery five years before thymectomy. Two others had pneumonia but had not required ventilator support. All five of these patients had an uneventful course after thymectomy. All 53 patients received chest physical therapy postoperatively, including incentive spirometry, chest clapping, intermittent positive-pressure breathing (IPPB), aerosols, and endotracheal suctioning. In spite of this, atelectasis developed in four of them. Two required fiberoptic bronchoscopy for treatment (one of them on two occasions). Two heavy cigarette smokers with previous physiologic evidence of chronic obstructive disease of the airways had postoperative exacerbation of preexisting bronchospasm which responded well to intravenous (IV) administration of aminophylline. In two other patients, a postoperative pneumothorax developed (in one case, ten days after thymectomy). Both conditions cleared completely after placement of pleural drainage tubes. Atrial flutter with variable block developed in one patient on the second postoperative day; it was controlled with digitalis and was successfully treated by cardioversion on the ninth postoperative day. Of the five patients who required prolonged mechanical ventilation, three experienced significant metabolic alkalosis because of nasogastric suction, and this slowed attempts to wean them from ventilator support. There were no postoperative deaths, and all patients left the hospital with an improved respiratory status. DISCUSSION

There is considerable evidence that thymectomy improves survival, rate of remission, and rapidity of improvement in patients with myasthenia gravis who do not have thymoma." The increased need for mechanical ventilation postoperatively in these patients has led to a desire to predict accurately who will require such support and who will not. In most cases, the decision to extubate the patient postoperatively is made in the postanesthesia recovery area ·by an anesthesiologist on the basis of maximum respiratory pressures, vital capacity, and the general strength and alertness of the patient. Early extubation, if possible, makes convalescence more rapid. In certain casessuch as one of ours in which the patient had required intermittent mechanical ventilation for five weeks preoperatively-it is obvious before operation that long-term postoperative ventilator management will be needed. Loach and associates' proposed the following four factors as indicating the likely need for mechanical

ventilation after thymectomy for myasthenia gravis: (1) preoperative vital capacity less than 2.0 L while the patient is receiving optimal anticholinesterase therapy, (2) the presence of thymoma, (3) bulbar symptoms, especially dysphagia, and (4) age greater than 50 years. The mean age for our mechanical ventilator patients was 29 ± 16 years, whereas for the total group undergoing thymectomy it was 32 ± 16 years. Consequently, we do not regard age as an important factor bearing on the likelihood of postoperative respiratory complications. The same authors' also stressed the need for tracheostomy in the postoperative care of persons requiring postthymectomy mechanical ventilation. Only one of our 53 patients required tracheostomy after the thymus was removed, and one other needed this procedure because of prolonged ventilator dependence before thymectomy. Leventhal and eo-workers" used discriminant analysis to evaluate their experience with 24 patients who had undergone thymectomy for the treatment of myasthenia gravis, and they found four risk factors that showed significant correlation with the need for postoperative ventilatory support: (1) duration of symptoms of myasthenia gravis for more than six years, (2) history of other chronic respiratory disease, (3) preoperative (48 hours) dosage of pyridostigmine more than 750 mg/day, and (4) preoperative vital capacity less than 2.9 L. Yet, fOur of our five patients who required support postoperatively had been symptomatic for six months or less. The remaining patient had had clinical evidence of myasthenia gravis for more than six years. One patient who required prolonged mechanical ventilation had long-standing chronic bronchitis, and one other was ventilator-dependent preoperatively because of muscle weakness due to his primary disease. None of our patients who needed mechanical ventilation after thymectomy was receiving pyridostigmine at more than 750 mg daily at any time before the operation. On the other hand, eight of the 48 patients in whom recovery was uneventful had a preoperative vital capacity of less than 2.9 L. Thymic pathology did not appear to be related to the need for postoperative mechanical ventilation, and only one of our five patients who required this type of support had a thymoma. Thus, the criteria suggested by Leventhal and eo-workers" are not substantiated by our study; the reasons for this are not clew: Significant improvement in respiratory care over the past 20 years has led to reduced postoperative mortality in patients with myasthenia gravis. This improvement is a result of a combination of advances, which include a better understanding of pulmonary physiology and anesthesia techniques, the use of arterial blood gas measurements, and the availability of ICUs staffed by highly trained nurses and respiratory therapists. CHEST I 88 I 1 I JULY, 1984

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Papatestas and associates" reported an operative mortality of 21 percent from 1941 to 1960 and 2.9 percent from 1960 to 1969 in III thymectomy patients. They attributed this impressive improvement to the use of tracheostomy and the availability of mechanical ventilators of improved design. Cohn and his colleagues' noted a similar decrease in deaths after transsternal thymectomy for myasthenia gravis between 1946 and 1974: before 1962, five of 18 patients died in the early postoperative period from pulmonary insufficiency; between 1962 and 1974, there were only two deaths in a series of 38 patients. None of the 53 patients reported here died. Temporary cessation of anticholinesterase medication and a resulting decrease in secretions postoperatively, good ventilatory support, meticulous care of the airway, and objective assessment of ventilatory function all contributed to this decrease in mortality. In keeping with this opinion, it has been our experience that patients with myasthenia gravis are almost always less weak for 12 to 48 hours after any surgical procedure when use of anticholinesterase medication is discontinued during this time. However, use of these drugs usually has to be reinstituted after this interval. The objective assessment of ventilatory function is of great value in the management of these patients. In this regard, measurements of maximal respiratory pressures'" and vital capacity before and after thymectomy are especially useful as simple methods of determining respiratory muscle strength. In a study of nine patients with myasthenia gravis, Ringqvist and Ringqvist'" found that the maximum expiratory pressure was relatively more abnormal than any other variable of lung function, including the maximum inspiratory pressure. This finding has great implication for the ability to cough and to clear secretions, especially when these are copious and viscid. One of our patients required prolonged intubation for management of retained secretions in the presence of good ventilatory function. We routinely measure respiratory pressures and vital capacity postoperatively four times daily, three hours after anticholinesterase medication has been given. In the group reported here, at the time mechanical ventilation was discontinued, the mean vital capacity was 1.1±0.2 L, maximum inspiratory pressure was - 38 ± 8 em H20 , and maximum expiratory pressure was + 35 ± 2 cm H20 . These measurements give much earlier warnings of respiratory muscle failure than do arterial blood gas values. In 1974 Mulder and his co-workers" reported on their experience with 100 consecutive thymectomies for myasthenia gravis, all performed through a median sternotomy incision. Concomitant tracheostomy was done in the presence of one or more of the following: oropharyngeal weakness (bulbar symptoms), prior res70

piratory complications, prior myasthenic crises, and a vital capacity less than 2.0 L preoperatively. In all other cases, a nasotracheal tube was left in place for 24 to 48 hours after the operation. Since that report, the availability of endotracheal tubes With high-volume, low-pressure balloon cuffs has made tracheostomy less necessary because a nasotracheal airway can be maintained in place for up to 14 days. Although there may be complications with this method, they tend to be less severe and less frequent than with tracheostomy. 12.13 Furthermore, if tracheostomy does become necessary, it can be performed later over an artificial airway that has already been placed. Our experience has led us to conclude that tracheostomy is rarely necessary and that prolonged nasotracheal intubation is a superior alternative if prolonged access is required. Of the 43 patients who were extubated in the postanesthesia recovery room, 41 required no further airway intervention (two required reintubation within 24 hours). Management of these patients has indicated to us that the most important preoperative observation signifying the need for postoperative mechanical ventilation is the severity of bulbar involvement (Osserman groups 3 and 4), usually indicated by significant dysarthria and dysphagia along with borderline respiratory function. We have been impressed with the effectiveness of plasmapheresis in the treatment of a small number of patients with refractory respiratory failure in myasthenia gravis and have reported our experience with it. 14 The high incidence of the need for mechanical ventilation or prolonged intubation (or both) in groups 3 and 4 in this three-year study suggests that plasmapheresis should be performed preoperatively in these high-risk groups, before transsternal thymectomy. If this step proves effective in preventing postoperative respiratory failure, it certainly seems to be indicated medically and economically. In our institution, the cost of three or four plasma exchanges is less than the cost of several days of mechanical ventilation in an leu. In addition, although the recorded experience is not extensive, the medical hazards attending plasmapheresis may be less than those attending tracheal intubation and mechanical venttlation.P'" Olanow and associates" used plasmapheresis to optimize the medical status of 21 myasthenia gravis patients undergoing sternum-splitting total thymectomy. We believe that this approach is especially indicated in patients with severe bulbar symptoms.

REFERENCES 1 Osserman ICE, Genkins G. Studies in myasthenia gravis: review of a twenty-year experience in over 1200 patients. Mt Sinai JMed (NY) 1971; 38:497-537 2 Buckingham JM, Howard FM Jr, Bematz PE, Payne WS, PoatoperaINe

care after Thymectomy In Myasthenia Gravis (Gracey et aI)

3 4

5 6

7 8 9

Harrison EC Jr; O'Brien PC, et al. The value of thymectomy in myasthenia gravis: a computer-assisted matched study. Ann Surg 1976; 184:453-7 Papatestas AE, Osserman KE, Kark AE. The effects of thymectomyon the prognosis in myasthenia gravis. Mt Sinai J Med (NY) 1971; 38:586-93 Loach AB, Young AC, Spalding JMK, Crampton Smith A. Postoperative management after thymectomy. Br Med J 1975; 1:309-12 Leventhal SR, Orkin FK, Hirsh RA. Prediction of the need for postoperative mechanical ventilation in myasthenia gravis. Anesthesiology 1980; 53:26-30 Papatestas AE, Alpert LI, Osserman KE, Osserman RS, Kark AE. Studies in myasthenia gravis: effects of thymectomy; results on 185 patients with nonthymomatous and thymomatous myasthenia gravis, 1941-1969. Am J Moo 1971; 50:465-74 Cohn HE, Solit RW, Schatz NJ, Schlezinger N. Surgical treatment in myasthenia gravis: a 27 year experience. J Thorac Cardiovasc Surg 1974; 68:876-83 Black LF, Hyatt RE. Maximal respiratory pressures: normal values and relationship to age and sex. Am Rev Respir Dis 1969; 99:696-702 Black LF, Hyatt RE. Maximal static respiratory pressures in

10 11 12

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generalized neuromuscular disease. Am Rev Respir Dis 1971; 103:641-50 Ringqvist I, Ringqvist '[ Respiratory mechanics in untreated myasthenia gravis with special reference to the respiratory forces. Acta Moo Scand 1971; 190:499-508 Mulder DC, Herrmann C, Buckberg CD. Effect of thymectomy in patients with myasthenia gravis: a sixteen year experience. Am J Surg 1974; 128:202-5 Stauffer JL, Olson DE, Petty TL. Complications and consequences of endotracheal intubation and tracheotomy: a prospective study of 150 critically ill adult patients. Am J Moo 1981; 70:65-76 Stauffer JL, Silvestri RC. Complications of endotracheal intubation, tracheostomy, and artificial airways. Respir Care 1982; 27:417-34 Gracey DR, Howard FM J~ Divertie MB. Plasma pheresis in the treatment of ventilator dependent myasthenia gravis patients: report of four cases. Chest 1984; 85:739-43 Bone RC. Complications of mechanical ventilation and positive end-expiratory pressure. Respir Care 1982; 27:402-7 Olanow C~ Wechsler AS, Roses AD. A prospective study of thymectomy and serum acetylcholine receptor antibodies in myasthenia gravis. Ann Surg 1982; 196:113-21

Recent Advances in Pulmonary and Critical Care Medicine The Department of Medicine, University of California , San Francisco, willpresent this course at the Hotel Meridien, San Francisco, September 20-22. For information, contact: CME Programs, Department of Medicine M979, University of California, San Francisco 94143 (415:666-5208).

Eastern Section, American Thoracic Society The Eastern Section of the American Thoracic Society will meet at the Holiday Inn, Portland, Maine, September 21-22. For further information, contact Michael A. Passero, M.D., Department of Medicine, Roger Williams General Hospital, 825 Chalkstone Avenue, Providence, Rhode Island 02908 (401:456-2060).

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