Anesthetic consideration for anterior mediastinal mass resection

Anesthetic consideration for anterior mediastinal mass resection

Mediastinal anatomy

The mediastinum is the space in the center of the chest bounded by the plurae on either side, the sternum anteriorly and the thoracic vertebral column posteriorly. The upper boundary is the thoracic inlet, and the lower boundary is the diaphragm. It is divided into superior and inferior portions by a line joining the sternal angle to the fourth thoracic vertebra. The inferior portion is further divided into anterior, middle and posterior parts

Table 10.1 Contents of the mediastinum.

Superior                                                           Inferior

Aortic arch and branches                                      Anterior

Innominate vein                                               Lymph nodes

Superior vena cava                                                Middle

Trachea                                                           Heart

Esophagus                                                      Ascending aorta

Thoracic duct                                                   Pulmonary vessels

Thymus                                                           Superior vena cava

Recurrent laryngeal nerves                             Phrenic and vagus nerves

Lymph nodes                                                   Lymph nodes

                                                                            Posterior

Retrosternal extension ofthe thyroid

                                                                          Main bronchi

                                                                          Esophagus

                                                                          Descending aorta

                                                                          Azygos veins

                                                                          Thoracic duct

                                                                          Lymph nodes

The signs and symptoms of mediastinal pathology range from trivial to life-threatening, and include airway compression, superior vena cava syndrome, compression of the right heart and pulmonary arteries, and dysphagia from esophageal compression. Venous obstruction is a particular problem, because the smaller veins expand to allow collateral flow, increasing the risk of bleeding during anesthetic or surgical instrumentation. Neural compression is also common, and may produce severe pain, vocal cord palsy (recurrent laryngeal nerve) or Horner’s syndrome.

Anesthesia for resection of anterior mediastinal tumors

Evaluation of risk factors

Patients who have marked symptoms of airway compromise such as

dyspnea at rest, postural dyspnea, orthopnea, or even stridor are at high risk of intraoperative airway problems. Compression of the heart, SVC, and pulmonary arteries also can cause syncope, arrhythmias, head and neck edema, and even a degree of cyanosis, particularly in children.

Lung function tests, including arterial blood gas analysis, usually are performed as a baseline.

Careful evaluation of the airway is necessary during pre-operative assessment for surgery within the mediastinum. Chest X-ray, including thoracic inlet views when necessary, and thoracic computerized tomographs should be studied for evidence of airway compression or displacement. erect and supine spirometry may be helpful.l

The patient presenting for mediastinal surgery may also have systemic disease as a result of chemotherapy.

Systemic effects of the tumor

Patients who have an intrathoracic goiter may have abnormalities of thyroid function that require monitoring and treatment before surgery. Up to 30% of patients who have a thymoma have symptomatic myasthenia gravis, which obviously has significant anesthetic implications.

Management of airway obstruction

Treatment modalities that can (or have been) used to minimize risk are:

Posture

Ø _ Induce in sitting position

Ø _ Change supine position to lateral or prone position (access ?)

Maintain spontaneous respiration

Ø _ Awake fiberoptic intubation

Ø _ Inhalational induction

Ø _ Intravenous induction (ketamine?)

Airway stenting: conventional intravenous induction

Ø _ Long endotracheal tube

Ø _ Double-lumen endobronchial tube

Ø _ Rigid bronchoscope

Ø _ Insertion of tracheobronchial stents

Cardiopulmonary bypass

Ø _ Commenced under local anesthesia before induction

Ø _ Vessels prepared under local anesthesia, then general anesthesia

Airway stenting /conventional intravenous induction

a rigid bronchoscope can be advanced to stent the airway. After initial assessment of the anatomy/pathology, it may be possible to stent the airway for resection surgery with an endotracheal tube or a double-lumen endobronchial tube placed under direct vision into the most patent main bronchus. If this technique is not possible, ventilation can be maintained down the rigid bronchoscope via a Venturi injector, in the usual way, and anesthesia can be maintained intravenously.

Cardiopulmonary bypass

The use of cardiopulmonary bypass to overcome the problems of intraoperative gas exchange in patients who have severe airway narrowing and pulmonary artery involvement is used in some centers.

Vascular involvement/intraoperative bleeding

mediastinal tumors may invade or compress many of the intrathoracic vascular structures. SVC obstruction is a common presenting sign of large anterior mediastinal tumors, and bleeding from the SVC is a relatively common problem intraoperatively.

Effects of chemotherapy

Patients presenting for surgery and anesthesia may have undergone chemotherapy previously.

The pulmonary toxicity of bleomycin has been well documented, and it is important to have baseline pulmonary function tests in these patients.

Nerve section

Anterior mediastinal tumors may advance to surround or invade the

phrenic and/or recurrent laryngeal nerves. Surgical division of these nerves

may affect the postoperative course and in the case of the phrenic nerve is an

indication for postoperative ventilation.

Anesthesia for thymectomy in myasthenia

Thymectomy is a major undertaking in a myasthenic patient, and comprehensive pre-operative preparation of the patient, together with communication between surgeon and anesthetist, are important

to success. Surgery is best performed while the disease is in remission, but early thymectomy is usually the treatment of choice and excessive delaymay

result in worsening of myasthenic symptoms. Optimization of anticholinesterase therapy improves muscle function, and plasmapheresis to reduce the concentration of circulating auto-antibodies may be useful in some cases, producing improvement in post-operative respiratory function. Psychological preparation of the patient is important, firstly because stress may precipitate a myasthenic crisis and secondly because the improvement in symptoms following thymectomy is not always immediate, and patients may be disappointed with the result in the early post-operative period.

Pre-operative assessment should include baseline respiratory function tests, and appropriate thoracic imaging as described above for mediastinoscopy.

Patients with bulbar muscle involvement may have an impaired cough reflex, leading to tracheobronchial soiling which predisposes to chest infection. Thyroid function should be checked, as there may occasionally be associated thyroid abnormalities. There may also be some myocardial degenerative change associated with myasthenia, and consideration should be given to pre-operative echocardiography.Opinions vary as to the best way to manage anticholinesterase therapy, but on balance it is probably best to continue it on the day of surgery. Patients will be reluctant to omit their pyridostigmine

altogether, and post-operative respiratory function will probably be better if it is continued.

However, omitting the anticholinesterase may allow avoidance of neuromuscular blocking drugs during surgery.

Thymectomy is usually performed via a median sternotomy, although a limited upper hemisternotomy or a trans-cervical approach (similar to the incision for mediastinoscopy) may also be used. There is little difference in functional outcome between these approaches, although there is less disruption of chest mechanics with the transcervical approach, which may make it easier to

avoid prolonged post-operative mechanical ventilation.

Median sternotomy is easier for the surgeon and allows for more radical surgery, which is better for large masses or suspected thymoma.

An endobronchial tube is rarely required with any surgical approach for thymectomy. There is little to choose between anesthetic agents, provided

the problems associated with myasthenic patients are appreciated. Following induction of anesthesia immediate assisted ventilation may be required, even before neuromuscular blocking drugs are given. In severe myasthenia neuromuscular blocking drugs may be avoided completely, as the muscle-relaxing effect of volatile anesthetics is enhanced. Competitive neuromuscular blocking drugs are not contraindicated in myasthenic patients if used in small doses with adequate monitoring.

Suxamethonium is best avoided, though it rarely causes problems, as myasthenic patients are resistant to it and a prolonged phase II block

may develop (myasthenic patients do not fasciculate following depolarizing neuromuscular blocking drugs).

Median sternotomy is the least painful approach to major thoracic surgery, but adequate analgesia is vital for effective chest physiotherapy postoperatively.

A thoracic epidural is effective in the early post-operative period, but concerns about respiratory depression from opioid analgesia in the presence of neuromuscular disease should not prevent adequate post-operative analgesia. Tracheostomy was routine when thymectomy was first

introduced, but in modern practice extubation at the end of the procedure should be the aim.

However, this is not always possible and around 50% of patients who have a trans-sternal thymectomy require prolonged mechanical ventilation.

Scoring systems have been devised to predict the need for post-operative ventilation, but there is debate about the reliability of these and patients

should be considered individually. Severity of disease (Osserman groups III and IV), low forced vital capacity (<15 ml/kg), surgery viamedian sternotomy,

a history of respiratory failure secondary to myasthenia, and pre-operative steroid therapy are all associated with prolonged post-operative ventilation.

Osserman classification:

ossooogravis.

Group I Ocular symptoms only

Group IIA Mild generalized weakness

Group IIB Moderate bulbar and skeletal symptoms

Group III Acute severe disease (with respiratory compromise)

Group IV Chronic severe diseas

ANESTHESIA FOR LUNG RESECTION

ANESTHESIA FOR LUNG RESECTION
Pre-operative considerations
Lung resections are usually carried out for the diagnosis and treatment of pulmonary tumours and less commonly for complications of infection and bronchiectasis.
Tumours
Pulmonary tumours may be either benign or malignant or can have an intermediate nature hematomas account for 90% of benign pulmonary tumours. They are usually peripheral pulmonary lesions and represent disorganized normal pulmonary tissue.
Bronchial edema are usually but occasionally locally invasive.
Malignant pulmonary tumors are divided into small cell and non small cell carcinomas
• squamous cell
• Adenocarcinoma
• Large cell
Small cell carcinoma usually presents as central masses with endobronchial lesions. Adenocarcinoma and large cell carcinoma are more typically peripheral lesions that often involve the pleural.
Clinical manifestation
Symproms may include cough, hemoptesis, dyspnea, wheezing, weight loss, fever or productive sputum.
Pleuritic chest pain or pleural effusion suggests pleural extension.

Involvement of mediastinal structure is suggested by
• hoarseness that result from compression of recurrent laryngeal nerve.
• Horner’s synd caused by involvement of the symp chain
• An elevated hemidiaphragm due to compression of phrenic nerve
• Dysphagia from compression of the esophagus
• Or supra vena cava synd.
Distant metastasis most commonly involve the brain, liver, bone and adrenal glands. Lung carcinoma can produce paraneoplastic syndrome due to ectopic hormone production and immunologic cross reactively between the tumor and normal tissues such as cushing’s syndrome, Lambert Eatsn syndrome.

Treatment
Surgery is the treatment of choice for the curative treatment of lung cancer
Resectability and operability.
Resectability is determined by the anatomic stage of the tumor, anatomic staging include: chest radiography, CT, bronchoscopy, mediastinoscopy.


Types of surgery:
Labectomy via a post thoracotomy through the fifith or sixth intercostals space is the procedure of choice for nmost lesions.
Segmental or wedge resections may be performed in patient with small peripheral lesions and poor pulmonary reserve.
Pneumonectomy is necessary for curative treatment for lesions involving the left or right main bronchus.

Operability is dependent on the extent of the procedure and physiologic status of the patient.
Pulmonary function test offer useful preliminary guidelines.

Preoperative laboratory criteria for pneumonectomy

ABG paCO2 ˃ 45 high risk patient
paO2 ˂ 50
FEV1 ˂ 2L
Predicted postop FEV1 ˂ 300ml or 40% of predicted
FEV1/FVC ˂ 50% of predicted
Maximum breathing capacity ˂ 50% of predicted
Maximum Vo2 ˂ 10ml/kg/m

The most commonly used criteria for operability is a predicted postop FEV1 greater than 800ml
Postop FEV1 = % blood flow to remaining lung X total FEV1

Anesthetic Consideration
1. Preoperative management
The majority of patient undergoing pulmonary resection have underlying lung disease. Preoperative assessment of such patient include careful history and examination, lung function tests, arterial blood gases, radiological studies. It should be emphasized that smoking is a risk factor for both COPD and CAD. Evaluation of cardiac function may include CHO, dobutamine stress echo.
Ppremedication
Patient with moderate to severe respiratory compromise should receive little or no sedative premedication.
Anticholinergics are very useful in reducing copious secretions and improve visualization during laryngoscopy and facilitate the use of fiberoptic bronchoscope.
2. Intraoperative management
Venous access
At least one large bore IV line (14-16g) is mandatory for all thoracic surgeries.
Central venous access, a blood warmer and rapid infusion device are desirable if extensive blood loss is anticipated.
Monitoring
Direct art pr monitoring is indicated for one lung anesthesia, resection of large tumours, patient with limited pulmonary reserve or cardiac dysfunction.
Pulmonary artery is indicated in patient with pulmonary hypertension or cor pulmonale.
Induction of anesthesia
After adequate pre-oxygenation, an IV anesthetic is used for induction in most patient. The selection of an induction agent should be based on the patient’s preoperative status.
Direct laryngoscopy should be performed only after deep anesthesia to prevent bronchospasm and to blunt the cardiovascular pressor response.
Endotracheal intubation is facilitated with succinylcholine or non-depolarizing agent.
Most thoracotomies can be performed with an ordinary ETT but one lung anesthesia may require the insertion of double lumen ETT.

Positioning
Most lung resections are performed with the patient in lateral decubitus position.

Maintenance of anesthesia

All anesthetic techniques have been successfully used for thoracic surgeries, but the combination of potent halogenated agent with an opioid is prefereed.

Advantages of halogenated agents
1. Dose dependent bronchodilatation
2. Depression of airway reflexes
3. The ability to use high FiO2
4. Rapid adjustment in anesthetic depth
5. Minimal effect on HPV
Advantage of opioids
1. Minimal hemodynamic effect
2. Depression of airway reflexes
3. Residual postop analgesia

Maintenance of muscle paralysis with muscle relaxant facilitate reb spreading as well as anesthesia management.

Fluid management only consists of basic maintenance requirements and replacement of blood loss with blood or colloid.
Excessive fluid administration in the lateral decubitus position may promote lower lung yndrome (gravity dependent transudation of fluid into the dependent lung) which increase intrapulmonary shunting and promotes hypoxemia specially during one lung ventilation.

Management of one lung ventilation
The greatest risk of one lung ventilation is hypoxemia. To reduce this risk the period of one lung ventilation should be kept to minimum, 100% O2 should be used.
Adjustment of vent parameters of peak airway pr rise progressively ˃ 30cmH2O tidal volume may be reduced to 6 – 10ml/kg and vent rate increased to maintain minute ventilation.

Hypoxemia during one lung anesthesia require one or more of the following intervention
Consistently effective measures
1. Periodic inflation of the collapsed lung with O2
2. Early ligation or clamping of the ipsilateral pulmonary artery
3. 5 – 10 cmH20 of CPAP to the collapsed lung
Marginally effective measures
1. Continuous insufflations of O2 into the collapsed lung
2. Changing the tidal volume and respiratory rate
3. 5 – 10 cmH2O of PEEP to the ventilated lung

Causes of persistent hypoxemia
Surgical manipulation or traction can displace endobronchial tube or the bronchial blocker causing obstruction, excessive secretion of blood clots in the airway or pneumothorax on the dependent ventilated side.

Alternative to one lung ventilation
1. Apneic oxygenation
Vent can be stopped for short period if 100% O2 is insufflated at a rate greater than O2 consumption.
Progressive respiratory acidosis limits the use of this technique to 10-20 min in most patient
2. High frequency positive pressure ventilation and high frequency set vent
A standard entrocheal tube may be used with either techniques allowing ventilation of both lungs.
Mediastinal bounce (to and pro movement) may interfere with surgery.
3. Postoperative management
General Care
Most patient are extubated early to decrease the risk of pulmonary barotraumas and infection patient with marginal pulmonary reserve should be left intubated until standard extubation criteria are met. Double lumen tube should be replaced with regular single lumen ETT.
Routine postope care should include maintenance of semiupright position, supplemental O2, incentive spirometry, close ECG and hemodynamic monitoring, postop radiograph and aggressive pain relief.

Postop analgesia
Techniques for postop pain relief may include
1. Parental opioids through patient controlled analgesia device
2. Intercostals blocks with long acting agent such as 0-5% ropivacaine may be done intraoperative under direct vision or postoperative via standard techniques
3. Thoracic lumbar epidural analgesia by opioids with or without local anesthetics can provide excellent analgesia
4. Intrapleural analgesia

Postoperative complications
Minor postop complications
1. Blood clots and thick secretion obstruction of the airways and result in atelectasis
Therapeutic bronchoscopy should be considered for persistent atelectasis
2. Air leaks from the operative hemithorax most air leaks stop after few days.
3. Bronchopleural fistular presents as sudden large leak from the chest tube that may be associated with an increasing pneumothorax and partial lung collapse.

More serious postop complication
1. Postop bleeding
Signs of hemorrhage include increased chest tube drainage ˃ 200ml/h, hypotension tachycardia and falling hematocrit.
2. Tortion of lobe or segment can occur as the remaining lung on the operative side expand tpo occupy the hemithorax.
3. Acute herniation of the heart into the operative hemithorax can occur through a pericardial defect.
Herniation into the right hemothorax results in sudden severe hypotension with elevated CVP.
Herniation into the left hemithorax results in sudden compression of the heart a AV groove resulting in hypotension, ischemia and infarction.
4. Injury to the phrenic nerve, vagus, left recurrent laryngeal.
5. Paraplegia can rarely follow thoracotomy due to spinal cord ischemia due to injury to left lower intercostals arteries.

Double Lumen Endotracheal Tube Placement

VIDEO ASSISTED THORACOSCOPIC SURGERY

VIDEO ASSISTED THORACOSCOPIC SURGERY

Principles of thoracoscopic surgery

The minimal requirement for VAT are: rigid telescope, a light source with cable, a camera and an image processor.

The optimal devices are: slave monitor, semiflexible telescope and a video recorder.

• VATS require high light output power as blood is in the operative field absorb 50% of the light.
• The access site must be placed at sufficient distance from the target pathology to allow for adequate room.
• The thoracic is rigid and the access sites are limited to the intercostals space.
• Single lung anesthesia is necessary to deflate the lung’
• All movement should be under direct vision to prevent damage to surrounding tissue.
• The surgeon should be able to handle complication and converting to open procedures.
• Specific instruments include stapling device, laser, dissectors and retractors.

Indications

The common indications are:

1.       Cancer staging

2.       Diagnosis of pleural disease

3.       Management of persistent pneumothorax, retained hemothorax, infected pleural space    including empyema

4.       Pericardial drainage

5.       Thoracic sympathectomy
 with surgical advances other indications have been added to the list:

·         Thoracic duct ligation

·         Removal of thoracic cyst

·         Vagotomy

·         Lobar resection

·         Esophageal surgery

Contraindications

1.       Pleural symphysis caused by previous thoracic surgery or pleurodesis

2.       Bleeding disorders

3.       End stage pulmonary fibrosis

4.       Respiratory insufficiency and hempdynamic instability

Advantages

1.       Shorter length of hospital stay

2.       Less postoperative pain

3.       Preserved pulmonary function

4.       Superior cosmotic result

5.       Shorter recovery time

Anesthetic management of VATS
Preoperative evaluation

A thorough history and physical exam with special attention to the cardiorespiratory status is necessary for all patients. Routine lab investigation include full blood count, electrolyte levels, ECG, chest radiograph and CT scan help to make diagnosis and identify potential problems. Spirometry tests include FVC

                                                                                                FEV₁

                                                                                                FEV₁ // FVC

Preoperative optimization of respiratory function is achieved by bronchodilator, cessation of smoking, incentive spirometry and physiotherapy.

Intraoperative management

The goals of anesthesia include maintaining stable cardiovascular function, optimizing oxygenation and ventilation, minimizing airway reactivity and  preventing respiratory depression in the postoperative period.

Monitoring

In addition to standard monitoring techniques, invasive arterial pressure and central venous pressure monitoring may be needed in patient with limited cardio-respiratory reserve.

Anesthetic techniques

Thoracoscopic surgery has been performed under local, regional or general anesthesia

-          General anesthesia is usually induces with an IV agent such as propofol or thiopentone and maintained with inahalational agent in air/O2 misture

N2O is preferably avoided because of the risk of expansion of air filled spaces.

Advantage of inhalation agents to be mentioned

Narcotic analgesia attenuate stress response, reduce requirement of inhalational agent  and produce analgesia

-          Most VAT require patient to be placed in lateral decubitus position.

-          One lung anesthesia is required

-          Postoperative analgesia strategies include oral opioids, PCA, local anesthetic infiltration, intercostals block, paravertebral block and epidural analgesia.

-          Post op care

-          Carbon dioxide insufflations

It may be used to accelerate lung deflation.

Rapid or excessive insufflations of the gas may cause mediastinal shift resulting in hemodynamic instability, bradycardia, hypertension, hypoxia and surgical emphysema.

Gas flow is restricted to 2L/m with the pressure limited to 10mmHG

Complications

o   hypoxemia  caused by v/p mismatch

o   Chest pain caused by thermal damage to the parietal pleura and the periosteum over the ribs.

o   Respiratory complication: sputum retention, atelectasis

o   bleeding due  to injury to blood vessels or lung perforation.