Thymectomy

What the Anesthesiologist Should Know before the Operative Procedure

Thymectomy may be performed for tumors of the thymus or as a treatment modality for myasthenia gravis, with or without thymoma. The thymus has a complex anatomy, with tissue residing in the anterior mediastinum as well as the neck. Completeness of resection is essential for early and late prognosis in both myasthenic and non-myasthenic patients.

The size of the tumor and extent of tumor invasion will influence both surgical approach and anesthetic management. It is essential to evaluate the patient for symptoms related to tumor involvement of local structures as well as symptoms of myasthenia gravis. Patients may present with significant dyspnea, cough, chest pain, and weakness. The tumor can cause obstruction of major airways, main pulmonary arteries, superior vena cava, and cardiac chambers, leading to respiratory or cardiovascular collapse.

It is important to note that life-threatening complications may occur in the absence of symptoms in children.

Other rare systemic diseases associated with thymoma include red cell aplasia and hypogammaglobulinemia.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Thymomas are slow growing, malignant tumors. Spread is by local extension, and metastases are usually limited to the pleura, pericardium, or diaphragm. Extrathoracic metastases rarely occur.

Thymectomy is typically elective. In patients with severe myasthenic symptoms, such as severe bulbar and skeletal muscle weakness, including respiratory failure, surgery may be delayed for medical optimization. Increased doses of anticholinesterases and the addition of immunosuppressive drugs and plasmapheresis may help to decrease symptoms preoperatively and potentially decrease postoperative respiratory failure.

Thymectomy associated with tumors compressing major airways or vasculature may become urgent or emergent depending on the patient’s symptomatology. Physical exam often provides clues to the extent of airway and vascular compromise. Symptoms of dyspnea in the upright or supine positions, stridor, or cough may signify tracheal or bronchial compression. Signs of presyncope when supine may indicate cardiovascular compression. The patient should be evaluated for signs of SVC syndrome, including plethora and venous engorgement of the face and upper extremities.

Preoperative CT scan and echocardiography are invaluable in delineating the extent of airway and cardiovascular compromise, helping to guide anesthetic and airway management.

Emergent: Rarely emergent.

Urgent: Rarely urgent. Patient presenting with respiratory or cardiovascular compromise resulting from tumor compression of major airways, vasculature, and cardiac structures.

Elective: Usually elective. Patients may have life threatening respiratory compromise from tumor compression of trachea or bronchi and cardiovascular collapse on induction of anesthesia despite elective nature. History, physical exam, and imaging provide clues to extent of disease.

2. Preoperative evaluation

Evaluation of Myasthenia Gravis

Characterize the extent of disease with a detailed history and physical exam. Symptoms of bulbar and skeletal muscle weakness include respiratory failure, history of aspiration, and fatigability. History of preoperative bulbar symptoms, myasthenic crisis, infection, and large preoperative doses of pyridostigmine are independent risk factors for postoperative myasthenic crisis. Patient’s activity level, duration of the disease > 2 years, need for lung resection, and high preoperative pyridostigmine requirements increase the risk of postoperative respiratory failure and the need for mechanical ventilation. Preoperative pulmonary function tests will establish baseline respiratory function and help guide the need for postoperative mechanical ventilation.

Evaluation of anterior mediastinal mass

History and physical exam should evaluate for airway compromise, cardiovascular compression, and SVC syndrome.

Dyspnea in the upright or supine positions, stridor, or cough may signify tracheal or bronchial compression. Signs of presyncope, syncope, or chest pain, especially when supine, may indicate cardiovascular compression.

The patient should be evaluated for signs of SVC syndrome, including plethora and venous engorgement of the face and upper extremities. Note changes in symptomatology related to positioning, specifically upright, supine, lateral, and prone positioning.

Preoperative CT scans or MRI are invaluable in evaluating airway and cardiovascular compromise. Echocardiogram may be used to evaluate dynamic compression of cardiac chambers and/or pulmonary arteries. Rarely angiography is used to evaluate the superior vena cava or pulmonary arteries. PFTs may help to distinguish between cardiovascular and respiratory involvement.

Medically unstable conditions warranting further evaluation include: Myasthenia gravis with rapidly progressive weakness or respiratory failure. Acute dyspnea. SVC syndrome, including upper extremity edema and plethora. Stridor. Syncope. Chest pain. Cough.

Delaying surgery may be indicated for: Medical optimization of myasthenic symptoms. Increasing anticholinesterases, IVIG, initiating plasmapheresis, and/or immunosuppressive drugs, including steroids. Obtaining imaging studies. Pulmonary function testing.

3. What are the implications of co-existing disease on perioperative care?

Evaluation of Myasthenia Gravis

Characterize the extent of disease with a detailed history and physical exam. Symptoms of bulbar and skeletal muscle weakness including respiratory failure, history of aspiration, and fatigability. History of preoperative bulbar symptoms, myasthenic crisis, infection, and large preoperative dose of pyridostigmine are independent risk factors for postoperative myasthenic crisis. Patient’s activity level, duration of the disease > 2 years, need for lung resection, and high preoperative pyridostigmine requirements increase the risk of postoperative respiratory failure and the need for mechanical ventilation.

Evaluation of anterior mediastinal mass

History and physical exam should evaluate for airway compromise, cardiovascular compression, and SVC syndrome. Dyspnea in the upright or supine positions, stridor, or cough may signify tracheal or bronchial compression. Signs of presyncope, syncope, or chest pain, especially when supine, may indicate cardiovascular compression. The patient should be evaluated for signs of SVC syndrome, including plethora and venous engorgement of the face and upper extremities.

Note changes in symptomatology related to positioning, specifically upright, supine, lateral, and prone positions. Preoperative CT scans or MRI are invaluable in evaluating airway and cardiovascular compromise. Echocardiogram can evaluate dynamic compression of cardiac chambers and/or pulmonary arteries. Rarely angiography is used to evaluate the superior vena cava or pulmonary arteries. PFTs may help to distinguish between cardiovascular and respiratory involvement.

Perioperative evaluation:

Neurology consultation is essential in myasthenic patients. Complete history and physical exam, along with imaging studies, play an important role in all patients for thymectomy, specifically patients with anterior mediastinal masses. CT scan, MRI, echocardiography, venography, and PFTs provide specific information about cardiopulmonary compromise.

Perioperative risk reduction strategies:

For myasthenic patients, optimization of pyridostigmine, steroids, immunosuppressive agents and plasmapheresis may help to decrease postoperative respiratory failure. Continuation of pyridostigmine and immunosuppressants through the perioperative period may facilitate early extubation. Parenteral Pyridostigmine 2 to 5 mg IM or slow IV every 2-3 hours or one-thirtieth of the oral dose (e.g., 2 mg IV for 60 mg oral) may be given. Neurology consultation is helpful in the management of these medications. Minimizing use of muscle relaxants and long-acting opiates may facilitate extubation. Remifentanil is often used for its short and predictable half-life. Epidural analgesia will decrease intraoperative and postoperative pain, decreasing the need for opiates and muscle relaxants. Minimally invasive surgery, such as VATS or robotically-assisted surgery, may facilitate early extubation, decrease blood loss, decrease ICU stay, and decrease hospital stay.

b. Cardiovascular system:

Cardiovascular disease, including cardiomyopathies and valvular and coronary artery disease may exacerbate and contribute to acute cardiopulmonary compromise in cases of large compressive thymic tumors. The primary goal of intraoperative management is to maintain adequate intravascular volume. Large bore IV access is essential. Maintain preload with avoidance of large tidal volume, positive pressure ventilation, and excessive PEEP. This may also be achieved with spontaneous ventilation and upright positioning.

Pressure support ventilation promoting lower peak airway pressures is another strategy. Crossmatched blood should be readily available.

Acute/unstable conditions:

Cardiovascular collapse on induction of anesthesia in patients with large or invasive thymic tumors. Further exacerbated by preexisting cardiac conditions. Consider lower extremity IV access in certain cases.

Baseline coronary artery disease or cardiac dysfunction – Goals of management:

Maintain preload through spontaneous ventilation, positioning, and fluid administration. Monitor arterial pressure. Maintain coronary perfusion pressure. Maintain oxygenation. Preoperative femoral-femoral bypass has been reported to be effective in severe cases.

c. Pulmonary:

Acute pulmonary compromise resulting from tracheal or bronchial compression with induction of anesthesia may be avoided by maintenance of spontaneous ventilation and upright positioning. Symptom changes with positioning should be determined preoperatively. Lateral or prone positioning may be helpful.

Despite these maneuvers, obstruction may still occur, necessitating rigid bronchoscopy or intubation beyond the level of obstruction with a reinforced endotracheal tube. This may allow for active or passive oxygenation with or without ventilation. In severe cases, femoral-femoral bypass may be instituted. It is important to monitor the patient for airway compromise postoperatively.

Patients with severe myasthenia gravis may have difficulty coughing and clearing secretions. Patients may develop pneumonia and atelectasis. Paradoxical breathing may be present from diaphragmatic weakness, which may be worsened by phrenic nerve injury or involvement of the tumor. Aggressive suctioning and ventilatory support are necessary.

COPD:

Continue inhalers and/or steroids preoperatively and intraoperatively. Phrenic nerve injury may exacerbate respiratory failure. Optimize pain control, specifically epidural analgesia, to facilitate extubation and early ambulation. Aggressive pulmonary toilet. Chest physiotherapy, incentive spirometry, and early ambulation to decrease pulmonary complications.

Reactive airway disease (Asthma):

Similar to COPD. Continue inhalers and steroids. Exacerbated in the setting of cholinergic crisis. Be cautious with histamine-releasing medications, such as morphine.

d. Renal-GI:

Patients with myasthenia gravis are at an increased risk of aspiration secondary to diminished gag reflex and loss of pharyngeal tone. During induction, this risk must be balanced with the risk of cardiovascular collapse in the presence of a large thymic tumor. GI prophylaxis, including a nonparticulate antacid such as sodium citrate, H2 blockers and metoclopramide may be used.

e. Neurologic:

Current evidence suggests that in nonthymomatous myasthenia gravis, all thymic tissue (capsular and extracapsular) should be removed with thymectomy. The transsternal approach may lead to recurrent laryngeal nerve damage. Thymomas or thymic tumors may encase or involve the phrenic nerves. In the uncommon case where bilateral phrenic nerves are involved, only one side should be surgically resected. Division of the phrenic nerve may necessitate postoperative mechanical ventilation. Acute issues: Postoperative respiratory failure. Division of the phrenic or recurrent laryngeal nerves. Compounded by baseline respiratory weakness in myasthenic patients.

f. Endocrine:

Monitor glucose intraoperatively. Hyperglycemia secondary to chronic or high-dose steroid administration may necessitate insulin infusion.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (e.g., musculoskeletal in orthopedic procedures, hematologic in a cancer patient):

Myasthenia gravis is a disease characterized by an antibody-mediated destruction of acetylcholine receptors at the motor end plate. Weakness is provoked by sustained or repeated use of the muscle. This disease usually begins with ocular and facial muscle weakness, but may spread to involve the pharynx, diaphragm, and generalized limb weakness. It is important to minimize the risk of aspiration and respiratory failure with appropriate anesthetic technique and agents.

4. What are the patient’s medications and how should they be managed in the perioperative period?

Patients with myasthenia gravis should continue their anticholinesterase and immunosuppressive medications perioperatively. Parenteral Pyridostigmine 2 to 5 mg IM or slow IV every 2-3 hours or one-thirtieth of the oral dose (e.g., 2 mg IV for 60 mg oral) may be given. This will help to decrease the need for postoperative mechanical ventilation and facilitate early extubation.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Several drug classes may contribute to muscle weakness in myasthenic patients, specifically nondepolarizing muscle relaxants, inhalational agents, antibiotics (including aminoglycosides, macrolides, tetracycline, fluoroquinolones, clindamycin), calcium-channel blockers, beta-blockers, magnesium, procainamide, lithium, phenytoin, and paradoxically steroids.

i. What should be recommended with regard to continuation of medications taken chronically?

Anticoagulation medications should be reviewed and discontinued prior to epidural placement.

• Cardiac: Diuretics may be discontinued the night before. Other cardiac medications should be continued, specifically beta-blockers and statins. Some of these medications may contribute to muscle weakness in myasthenic patients.
• Pulmonary: Continue medications. Take inhalers the day of surgery.
• Renal: Continue medications.
• Neurologic: Continue medications.
• Anti-platelet medications: Risks and benefits of continuation of anti-platelet medications, such as clopidogrel, should be discussed with the surgeon and patient. Continuation may increase risk of intraoperative bleeding and is a contraindication to epidural placement.
• Psychiatric: Continue medications. Certain medications, such as phenytoin and lithium, may contribute to muscle weakness in the myasthenic patient, however discontinuation may be more detrimental.

j. How to modify care for patients with known allergies –

All allergies should be documented and communicated among operating room staff prior to the start of the procedure.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

Latex allergy should be documented and communicated among operating room staff prior to the start of the procedure.

l. Does the patient have any antibiotic allergies? Common antibiotic allergies and alternative antibiotics:

Penicillins and cephalosporins may be given safely without exacerbating neuromuscular weakness in myasthenics. Take precaution when administering other antibiotics, such as clindamycin or gentamicin, in penicillin allergic patients. These drugs are additive and will increase the effect of any other neuromuscular blocking agent. Vancomycin should be administered slowly.

m. Does the patient have a history of allergy to anesthesia?

Myasthenic patients do not have a true allergy to anesthesia: however, it is important to be aware of the sensitivity to inhalational anesthetics and muscle relaxants. Nondepolarizing muscle relaxants may be avoided altogether with the combination of potent inhalational agents, remifentanil, and ketamine.

Patients with myasthenia gravis will be sensitive to the effects of nondepolarizing muscle relaxants. There may be a varied effect, and possible resistance to depolarizing muscle relaxants, (e.g., succinylcholine).

5. What laboratory tests should be obtained? Has everything been reviewed?

Lab tests include a complete blood count, electrolytes, and renal function studies (BUN, creatinine). Patients may be at risk for infections such as pneumonia. Platelet counts are necessary prior to epidural placement. Baseline coagulation studies may be helpful, including PT/INR and PTT, depending on the patient’s comorbidities and possibility of intraoperative and postoperative bleeding. However, there is little evidence to support routine coagulation panels in patients with no clinical evidence of coagulopathy.

The patient should have a type and screen with blood products available.

Anti-acetylcholine receptor antibody levels have not been shown to correlate with disease severity. Na, Cl, bicarbonate, potassium, BUN, creatinine, platelet count, hemoglobin, and WBC count should be reviewed. Common laboratory normal values will be same for all procedures, with a difference by age and gender.

• Hemoglobin levels: Obtain baseline levels, monitor perioperatively.
• Electrolytes: May have mild disturbances related to current medications, however should be relatively normal.
• Coagulation panel: Review prior to epidural placement.
• Imaging: Chest X-Ray and CT chest to detect and evaluate thymoma. Possible echocardiography to evaluate cardiac compromise and function when indicated. MRI chest to evaluate thymoma when indicated. Angiography of SVC and pulmonary arteries when indicated.
• Other tests: Pulmonary function tests in patients with respiratory symptoms. Baseline pulse oximetry and arterial blood gas in select cases.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

General anesthesia with endotracheal intubation is the mainstay for thymectomy. Preinduction monitors are directed by preoperative thymoma involvement of the airways and cardiovascular structures. There should be consideration for femoral central venous access, arterial line, as well as femoral-femoral cardiopulmonary bypass.

Induction should be in the upright position in patients with respiratory compromise. Assess symptoms with regards to change in position when patient is upright, supine, lateral, and prone prior to induction of anesthesia.

Maintain spontaneous ventilation with inhalational induction or carefully titrated intravenous agents such as ketamine. Awake intubation with airway topicalization is possible in select cases.

Emergency airway equipment should be readily available in the operating room, specifically, a rigid bronchoscope with experienced personnel.

Maintenance of anesthesia may be carried out by a variety of approaches, depending on the patient. Avoidance of muscle relaxants in patients with myasthenia gravis is prudent when possible. Patients with compressive thymomas benefit from spontaneous ventilation even after intubation. Pressure support ventilation with low positive pressure assistance is useful in spontaneously breathing patients.

Depending on the surgical approach, such as VATS, placement of thoracic epidural and double lumen tube may be desirable.

Regional Anesthesia

Thoracic epidural analgesia, adjunct to general anesthesia.

Neuraxial

• Benefits. Superior pain control with decreased need for intraoperative and postoperative opiates. Facilitates early extubation and improved pulmonary mechanics postoperatively. Ideal for thoracotomy or VATS approach, but may be beneficial in sternotomy with severe preoperative pulmonary dysfunction.
• Drawbacks. May not completely alleviate pain, specifically shoulder pain from diaphragmatic irritation or apical chest tube placement. Possible respiratory depression from epidural opiates. Hemodynamic instability may result from epidural local anesthetics, more likely with high concentration local anesthetics or bolus techniques. Accidental dural puncture with resulting headache. Rare catastrophic epidural hematoma or abscess.

Issues

Contraindications include patient refusal, patients with coagulopathy or on anticoagulants, sepsis, local skin infections over site placement, and acute hemodynamic instability or hypovolemia.

General Anesthesia

The thymus is a geometrically complex organ primarily located in the anterior mediastinum with accessory cervical lobes. The dissection can be complex and tedious in cases of invasive carcinoma. Completeness of resection of the thymus along with all accompanying fat is critical in nonthymomatous myasthenia gravis. General anesthesia with endotracheal intubation not only provides optimal surgical conditions and patient comfort but allow for a controlled airway in case of emergency.

• Benefits. Provides optimal surgical conditions and patient comfort. Controlled airway in emergency settings.
• Drawbacks. Risk of cardiovascular or respiratory collapse on induction of general anesthesia. Possible ventilatory depression from anesthetic agents, necessitating postoperative mechanical ventilation.
• Other issues. Induction of general anesthesia in a patient with a large or invasive thymic tumor may lead to cardiovascular collapse secondary to obstruction of major vascular structures, such as the SVC, pulmonary arteries, or cardiac chambers.
• Airway concerns. Large thymic tumors may lead to tracheal or bronchial compression with inability to ventilate on induction of general anesthesia. Myasthenic patients may be at risk for aspiration. Preoperative history, physical exam, CT scan, and PFT’s may help delineate this risk. Given the risk of airway collapse versus aspiration, an awake fiberoptic intubation may be necessary. Emergency airway equipment, specifically a rigid bronchoscope, and experienced personnel should be present. Postoperative respiratory failure secondary to tracheal malacia or weakness may necessitate mechanical ventilation.

Monitored Anesthesia Care

Not currently recommended.

6. What is the author’s preferred method of anesthesia technique and why?

What prophylactic antibiotics should be administered?

Cefazolin (1 gram for patients <80kg, 2 grams for patients >80kg or diabetics) or Cefuroxime approved for primary prophylaxis. Vancomycin or clindamycin may be used in case of beta lactam allergy. SCIP 2007

What do I need to know about the surgical technique to optimize my anesthetic care?

Completeness of resection is the most commonly cited significant prognostic factor in thymoma surgery. Currently, median sternotomy is the most common surgical approach, however VATS is quickly becoming more common. Other approaches include mini sternotomy, transcervical thymectomy, infrasternal thymectomy, unilateral or bilateral VATS thymectomy, and VATS with robotic assistance.

A combination of the above procedures may improve visualization and completeness of resection. In locally invading disease (stage III), thymectomy in combination with partial pleurectomy, pericardial resection, resection of lung tissue, superior vena cava resection, innominate vein resection, and single phrenic nerve resection may improve survival. Surgical approach will determine need for placement double lumen tube and thoracic epidural.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Lung isolation with single-lung ventilation facilitates visualization in endoscopic surgery, such as VATS and robotic surgery. Patients may be positioned supine with a roll or bump under the operating side. Given the relatively supine patient position, singe-lung ventilation may prove difficult, specifically in patients with a high BMI or when paralytic agents are not being used.

The table may be turned towards the surgeon or positioned farther away from the anesthesiologist to facilitate robotic equipment. It is critical to have access to the head of the bed to perform lung maneuvers and manage ventilation issues. Small tidal volume and pressure control ventilation with low inspired oxygen concentrations as tolerated are employed as lung protective strategies.

What are the most common intraoperative complications and how can they be avoided/treated?

Cardiovascular or respiratory collapse on induction of anesthesia or supine positioning in patients with anterior mediastinal masses. Assess the patient preoperatively, including a detailed history, physical exam, and review of studies, such as CT scan, echocardiography, MRI, and PFTs. Large bore IV access. Lower extremity IV access, arterial line, femoral vein and femoral arterial access for femoral-femoral bypass prior to induction if concern for cardiovascular collapse.

Sternal saw and emergency airway equipment should be readily available, including rigid bronchoscope with trained personnel. Induction should be with maintenance of upright positioning and maintenance of spontaneous ventilation, with inhalational induction with glycopyrrolate and ketamine as adjunct.

Patient may require awake fiberoptic intubation. Test ability to ventilate. Avoid muscle relaxants, depending thymoma extension and surgical approach. Change patient position to upright, lateral, or prone for treatment of compete cardiopulmonary collapse.

Other major complications include bleeding from the innominate artery/vein, pulmonary arteries, cardiac chambers, sternum etc. Blood should be crossmatched and readily available. Laryngeal injury. Careful placement of double lumen endotracheal tube. Avoid excessive cuff pressure or oversized tube.

Surgical Approaches

Transsternal thymectomy

This is the most common approach to thymectomy. All mediastinal thymic tissue and fat is removed through a median sternotomy incision. Cervical thymic tissue may be removed from below without a formal neck dissection. Residual cervical thymic tissue and fat has been found on reoperation.

VATS/thoracotomy thymectomy

Minimally invasive techniques are becoming more routine. May be performed unilaterally or bilaterally. Bilateral VATS offers visualization of both sides of the mediastinum, and especially both phrenic nerves. The thymus and fat are usually removed en bloc but may be removed separately. Cervical extensions of the thymus may be removed from below, however accessory cervical thymic lobes are missed. A cervical incision may be added to excise the cervical thymic lobes and cervical fat with dissection of the recurrent laryngeal nerve. Mediastinal pleural sheets are not removed.

The VATS approach produces smaller scars. This option is appealing to young women and young professionals desiring less scar formation and the ability to return to work more quickly.

Transcervical thymectomy

May be performed alone or in combination with a partial median sternotomy, a subxiphoid approach, a manubrial retractor for improved mediastinal exposure, or with VATS. Extent of thymic resection will depend on the specific approach. Transcervical thymectomy alone may not provide as extensive a resection as other approaches.

Transcervical-transsternal thymectomy

This technique provides a wide exposure through a cervical incision and median sternotomy. This technique also allows complete resection of cervical and mediastinal thymic tissue and fat. The procedure may include resection of both sheets of mediastinal pleura, with dissection along the pericardium. Care is taken to protect the recurrent laryngeal, left vagus, and phrenic nerves.

Robotically-assisted VATS

Three-dimensional binocular vision, magnification, and multiarticulated instruments help to overcome some of the technical limitations of VATS while maintaining a minimally-invasive approach. A bilateral approach may improve visualization of thymic tissue and completeness of resection. An experienced surgeon is essential to success when performing minimally-invasive surgery.

• Cardiac complications: Cardiovascular collapse on induction of general anesthesia in patients with large compressive tumors. Bleeding. Major vascular injury, including innominate vein, aorta, pulmonary arteries, and SVC. Direct cardiac injury. Sternal bleeding. Arrhythmias. Pericarditis.
• Pulmonary: Respiratory failure on induction of general anesthesia in patients with compressive tumors. Aspiration in myasthenic patients. Weakness of respiratory muscles, including diaphragm, and inability to cough in myasthenics. Atelectasis. Pneumonia. Pneumothorax. Persistent air leak. Direct lung injury from surgical dissection or VATS approach. Tracheal or bronchial malacia/stenosis from long-standing compressive or invasive tumors. Stridor.
• Neurologic: Phrenic nerve injury, recurrent laryngeal nerve injury, intercostal neuralgia.

a. Neurologic:

Phrenic nerve injury related to surgical dissection. May compound respiratory weakness in patients with preexisting respiratory conditions or myasthenia gravis. Recurrent laryngeal nerve injury, more common in transsternal thymectomy. Intercostal neuralgia related to VATS.

b. If the patient is intubated, are there any special criteria for extubation?

Patients with myasthenia gravis are exquisitely sensitive to nondepolarizing muscle relaxants, and doses should be substantially reduced or avoided altogether. Perioperative continuation of anticholinesterase may antagonize nondepolarizing muscle relaxants, inhibit pseudocholinesterase, and lead to unpredictable results. If muscle relaxants are used, a twitch monitor should be applied to assess effect and the muscle relaxant should be fully reversed at the end of the procedure.

There is the potential for decreased need for postoperative ventilation and decreased hospital stay in minimally invasive approaches, such as VATS.

General extubation criteria apply. The patient should be awake, alert, strong, and demonstrate adequate pulmonary mechanics. Comparison of baseline and preextubation arterial blood gas in patients with preexisting respiratory compromise may guide extubation. A significant hypercarbia or hypoxia from baseline warrants continued ventilation. Patients with longstanding, large thymic masses may be at risk for tracheal or bronchial malacia/stenosis. Postoperatively, the patient should be monitored closely for signs of respiratory failure or airway obstruction.

c. Postoperative management:

What analgesic modalities can I implement?

Patient-controlled epidural analgesia

PCEA, provides excellent pain control while avoiding the sedation and hypoventilation associated with systemic opioids. Epidural analgesia is highly effective for VATS or the thoracotomy approach. Epidural analgesia may be less effective for a sternotomy approach but may still be beneficial in patients with baseline respiratory compromise or patients with chronic pain.

Benefits: Superior pain control with decreased need for intraoperative and postoperative opiates. Facilitates early extubation and improved pulmonary mechanics postoperatively.

Drawbacks: May not completely alleviate pain, specifically shoulder pain from diaphragmatic irritation or apical chest tube placement. Possible respiratory depression from epidural opiates. Hemodynamic instability from epidural local anesthetics, more likely with high concentration local anesthetics or bolus techniques. Accidental dural puncture with resulting headache. Rare catastrophic epidural hematoma or abscess.

Issues: Contraindications include patient refusal, patients with coagulopathy or on anticoagulants, sepsis, local skin infections over site placement, and acute hemodynamic instability or hypovolemia.

Systemic opioids

These are used in situations where neuraxial or regional nerve blocks are ineffective or contraindicated. Patient-controlled analgesia, PCA, may help to provide steady plasma levels and avoid large swings associated with pure bolus techniques. Systemic opioid side effects include sedation and respiratory depression and should be used cautiously in patients with myasthenia gravis, poor respiratory function, and obstructive sleep apnea.

NSAIDs and acetaminophen

These have both analgesic and anti-inflammatory properties. Used effectively for breakthrough pain, shoulder pain, and chest tube pain. May decrease opioid consumption without the risk of hypoventilation and sedation. Untoward effects of NSAIDs specifically include decreased platelet function, increased bronchial reactivity, decreased renal function, and gastrointestinal bleeding.

Ketamine

Low dose intravenous ketamine infusion may be used in opioid tolerant patients or patients with chronic pain.

Intercostal nerve and paravertebral blocks

These may be beneficial in VATS or thoracotomy approaches.

Benefits: ease of administration, fast-acting pain control with little systemic side effects, fewer failed blocks, decreased risk of neuraxial hematoma or abscess. Paravertebral blocks have comparable analgesia, less hypotension, nausea, and urinary retention.

Drawbacks: short acting, intercostals have rapid absorption, require multiple levels and multiple injections.

Issues: monitor dosing, awareness of potential for systemic local anesthetic toxicity, pneumothorax in patients without an ipsilateral chest tube, hematomas, muscle injury, nerve injury, total spinal and infection.

What level bed acuity is appropriate?

Minimally invasive techniques such as VATS and robotically-assisted thymectomy have been shown to decrease hospital stay and reduce postoperative pain. In general, a monitored bed should be made available for the immediate postoperative period. Length of stay in a monitored setting will vary and depend on the patient’s baseline medical condition and any intraoperative complications. Healthier patients may be extubated in the operating room, monitored for a shorter period of time, and be moved to a standard floor. Conversely, myasthenic patients with severe respiratory compromise preoperatively may remain intubated and monitored in the ICU.

What are common postoperative complications, and ways to prevent and treat them?

The most common postoperative complications include bleeding, respiratory failure requiring reintubation, pleural effusion, wound infection, myasthenic crisis, pneumonia, DVT, and arrhythmias. VATS technique has been shown to decrease hospital stay and postoperative pain scores. Studies comparing open versus minimally-invasive techniques in regards to outcome are still being debated. However, experts agree that completeness of thymus tissue resection is important for improvement of symptoms in myasthenic patients. Effective analgesia, specifically epidural analgesia, may facilitate extubation and early ambulation.

What’s the Evidence?

POSTOPERATIVE COMPLICATIONS

Bachmann, K, Burkhardt, D, Schreiter, I, Kaifi, J, Busch, C, Thayssen, G, Izbicki, JR, Strate, T. “Long-term outcome and quality of life after open and thorascopic thymectomy for myasthenia gravis: Analysis of 131 patients”. Surg Endosc. vol. 22. 2008. pp. 2470-77.

Leuzzi, G, Meacci, E, Cusumano, G, Cesario, A. “Thymectomy in myasthenia gravis: Proposal for a predictive score of postoperative myasthenic crisis”. Eur J Cardiothoracic Surg . vol. 45. 2014 April. pp. 76-88.

Liu, CW, Luo, M, Mei, JD, Zhu, YK. “Perioperative and long-term outcome of thymectomy for myasthenia gravis: Comparison of surgical approaches and prognostic analysis”. Chin Med J (Engl). vol. 126. 2013 Jan. pp. 34-40.

ROLE OF SURGERY IN THE THYMECTOMY

Davenport, E, Malthaner, RA. “The role of surgery in the management of thymoma: A systematic review”. Ann Thorac Surg. vol. 86. 2008. pp. 673-84.

Jurardo, J, Javidfar, J, Newmark, A, Lavelle, M. “Minimally invasive thymectomy and open thymectomy: Outcome analysis of 263 patients”. Ann Thoracic Surg. vol. 94. 2012 Sep. pp. 974-81.

ROBOTIC THYMECTOMY

Goldstein, SD, Yang, SC. “Assessment of robotic thymectomy using the Myasthenia Gravis Foundation of America guidelines”. Ann Thorac Surg. vol. 89. 2010. pp. 1080-6.

Marulli, G, Schiavon, M, Perissinotto, E, Bugana, A. “Surgical and neurologic outcomes after robotic thymectomy in 100 consecutive patients with myasthenia gravis”. J Thoracic Cardiovasc Surg. vol. 145. 2013 March. pp. 730-35.

PREOPERATIVE AND INTRAOPERATIVE MANAGEMENT OF ANTERIOR MEDIASTINAL MASSES

Gothard, J. “Anesthetic considerations for patients with anterior mediastinal masses”. Anesthesiology Clin. vol. 26. 2008. pp. 305-14.

TRANSSTERNAL AND MINIMALLY INVASIVE THYMECTOMY

Meyer, DM, Herbert, MA, Sobhani, NC, Tavakolian, P, Duncan, A, Bruns, M, Korngut, K, Williams, J, Prince, SL, Huber, L, Wolfe, GI, Mack, MJ. “Comparative clinical outcomes of thymectomy for myasthenia gravis performed by extended transsternal and minimally invasive approaches”. Ann Thorac Surg. vol. 87. 2009. pp. 385-91.

ANATOMY OF THYMUS AND VARIOUS SURGICAL APPROACHES TO THYMECTOMY

Sonett, JR, Jaretzki, A. “Thymectomy for nonthymomatous myasthenia gravis: A critical analysis”. Ann. N.Y. Acad. Sci.. vol. 1132. 2008. pp. 315-328.

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