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.