ANESTHESIA FOR THORACIC SURGERY Physiological Considerations during Thoracic Surgery: -lateral decubitus position -open pneumothorax -one lung ventilation lateral decubitus position Lateral decubitus position allows for optimal access for: -lungs -pleura -esophagus -great vessels -mediastinal structures -vertebrae Lateral decubitus position alters the V/Q relationship by: V/Q mismatch already altered by: induction of anesthesia ventilation: favors the less perfused upper lung mechanical ventilation perfusion: favors the less ventilated lower lung muscle paralysis increased V/Q mismatch increases the risk of hypoxemia opening of the chest cavity surgical retraction ______________________________________________________________________________________ Awake State : Lateral Decubitus Position : Spontaneous Ventilation: preserves V/Q matching nondependent lung: -decreased ventilation: due to less efficient contraction of the diaphragm, ∴less favorable position on the compliance curve -decreased perfusion : due to gravity dependent lung -increased ventilation: due to more efficient contraction of the diaphragm ∴more favorable position on the compliance curve -increased perfusion: due to gravity Lateraldecubitus Position: Induction of Anesthesia: decreases FRC -nondependent lung: becomes more compliant ↑V ↓Q ∴ V/Q ratio = ∞ dead space -dependant lung becomes less compliant ↓V ↑Q ∴ V/Q ratio = 0 shunting ______________________________________________________________________________________ Lateral Decubitus Position with Positive Pressure Ventilation increases V/Q mistmatching -nondependent lung favors PPV due to increased compliance than dependant lung increased compliance in open pneumothorax of the upper dependant lung -dependant lung less compliant lower dependant lung less tolerating to PPV muscle relaxants further decreases compliance of the lower dependant lung due to: -abdominal contents rising up upon the hemidiaphragm -impedance to dependant lung ventilation due to higher rising diaphragm stabilizing bean bag: further restricts the lower dependant lung ventilation OPEN PNEUMOTHORAX negative intrathoracic pressure: -normally keeps lungs open and not collapsed open pneumothorax: -losses the normal negative intrathoracic pressure -lungs tend to collapse on the affected side -collapse due to elastic recoil of the lung spontaneous ventilation in lateral decubitus position with open pneumothorax -paradoxical respirations -mediastinal shift -leads to progressive hypoxemia and hypercapnia -effects of hypoxemia and hypercapnia may be overcome by PPV -more negative parietal pleural pressure on the dependant side but not on the side of the pneumothorax Therefore: inspiration: creates a downward shift of the mediastinum expiration: creates an upward shift of the mediastinum major effect of the mediastinal shift: -dependant lung decreases contribution to the tidal volume -less contribution from dependant lung due to decreased expansion upon inspiration ONE LUNG VENTILATION -intentional collapse of the lung on the operative site -collapsed nondependent lung still receives perfusion which leads to right to left intrapulmonary shunt ( 20-30%) intrapulmonary shunt leads to: -increased (A –a) gradient -resultant hypoxemia Hypoxic Pulmonary Vasoconstriction (HPV) -compensatory mechanism of decreasing blood flow to nonventilated lung units factors which may inhibit HPV include: -both very high and very low pulmonary artery pressures -both very high and very low mixed venous oxygen saturation -hypocapnia -vasodilation (ex. NTP, NTG, β agonist, CCB, ) -pulmonary infections -inhalational anesthetics factors which counter the compensatory effects of HPV (∴ increases blood flow to the collapsed nonventilated lung) -high mean airway pressures in the ventilated lung -low FIO2 -vasoconstriction -intrinsic (auto) PEEP (ex. from inadequate expiratory time) factors which may increase airway pressure: -PEEP -hyperventilation -high peak inspiratory pressure TECHNIQUES FOR ONE LUNG VENTILATION patient related indications for one lung ventilation: -confine infection to one lung -confine bleeding to one lung -severe hypoxemia -separate ventilation to each lung: ex. bronchopleural fistula tracheobronchial disruption large lung cyst or bulla procedure related indications for one lung ventilation: -repair of thoracic aorta aneurysm -lung resection (ex. pneumonectomy, lobectomy, segmental resection) -thoracoscopy -esophageal surgery -single lung transplant -anterior approach to the thoracic spine -broncheoalveolar lavage technique for one lung ventilation: -double lumen endobronchial tube -single lumen endotracheal tube with bronchial blocker -single lumen endobronchial tube Double Lumen Endobronchial Tube (DLT) -most commonly used technique for one lung ventilation advantages of DLT include: -relative ease of positioning -ability of ventilating both lungs or a single lung in isolation -ability to suction either lungs endobronchial tubes contain: -larger bronchial lumen: enter either the right or left mainstem bronchus -smaller tracheal lumen: positioned in the lower trachea -preformed curvature: allows for selective entry into the desired bronchus -bronchial cuff: helps isolate one lung from another -tracheal cuff: helps isolate one lung from another one lung ventilation accomplished by either: -clamping the bronchial lumen and ventilate through the tracheal lumen -clamping the tracheal lumen and ventilate throught the bronchial lumen -collapse of the ipsilateral lung by opening the port to the appropriate connector Robert-Shaw type Double Lumen Endobronchial tube: most commonly used DLT sizes ranges from: 35F correlates with I.D ≅ 5.0 mm 37F correlates with I.D ≅ 5.5 mm 39F correlates with I.D ≅ 6.0 mm 41F correlates with I.D ≅ 6.5 mm women: 37F most commonly used men: 39F most commonly used right sided endobronchial tubes: were designed for left tracheostomies left -sided endobronchial tubes: were designed for right tracheostomies generally used for both left and right thoracotomies Anatomical Considerations: -length of the trachea is approximately 11 – 13 cm long -trachea begins at the level of the cricoid cartilage ≅ C6 -bifurcation of the trachea occurs approximately at the level of T6 -right bronchus lumen is more wide and diverges from the trachea at approximately 25° -left bronchus diverges from the trachea at approximately 45 ° -right bronchus divides into three lobe branches: upper lobe, middle lobe, and lower lobe branches -left bronchus divides into two lobe branches: upper lobe branch and lower lobe branch ANESTHESIA FOR LUNG RESECTION Tumors Bronchiectasis Infections TUMORS -benign -malignant Benign tumors -90% of benign tumors are: hemartomas, peripheral lesions -rarely metastisize -peripheral lesions often obstruct the bronchial lumen which causes recurrent pneumonias distal to the obstruction -pulmonary carcinoids are derived from APUD cells which secrete multiple hormones (ex. ACTH, arginine vasopressin) ex. pulmonary carcinoids, cylindromas, mucoepidermoid adenomas Malignant tumors -small cell (oat cell) carcinoma -nonsmall cell carcinoma (ex. squamous cell tumor, adenocarcinoma, large cell carcinoma ) clinical manifestations: symptoms may involve: -cough -hemoptysis -dyspnea -wheezing -weight loss -fever -productive sputum postobstructive pneumonia involves: -fever -productive sputum mediastinal involvement may include: -RLN compression: hoarsness of voice -Horners syndrome: ptosis, anhidrosis, miosis -Phrenic nerve compression: elevated diaphragm -Compression of esophagus: dysphagia -SVC Syndrome: cardiac involvement may involve: -pericardial effusion -cardiomegaly apical tumor extension may involve: -interference with the brachial roots (C7 – T2) -resultant shoulder pain -resultant arm pain ex. pancoast tumor metastasis of a primary tumor may travel to: -brain -bone -liver -adrenal glands Treatment nonsmall cell carcinoma: surgical resection is treatment of choice if the following are absent: -advanced LN involvement -direct extension into mediastinal structures -distant metastasis small cell carcinoma often treated with: -chemotherapy -chemotherapy with radiation -often tumor metastasis prior to diagnosis therefore surgical resection is not plausible Resectability -determined by the anatomical stage of the tumor staging includes: -chest xray -CT scan -bronchoscopy -mediastinoscopy resectable tumors include: -ipsilateral peribronchial LN metastasis -ipsilateral hilar lymph LN metastasis controversial resectable tumors include: -ipsilateral mediastinal LN metastasis -subcarinal LN metastasis nonresectable tumors include: -scalene LN metastasis -supraclavicular LN metastasis -contralateral mediastinal LN metastasis -contralateral hilar LN metastasis surgical goal: -maximize chances of cure -allows for adequate postoperative pulmonary function Lobectomy -often the procedure of choice for most lesions -posterior thoracotomy -through the 5th or 6th intercostal space Segmental (wedge) resection -for small peripheral lesion -patients with poor pulmonary reserve Pneumonectomy -lesions involving the left or right main bronchus -tumor extends to the hilum Sleeve Pneumonectomy -tumors involving the trachea OPERATIVE CRITEREA FOR PNEUMONECTOMY ABG: -PaC02 > 45 mmHg on room air -Pa02 < 50 mmHg PFT: -FEV1: < 2L -predicted postoperative FEV1 < 0.8L = < 40% predicted -FEV1/FVC < 50% of predicted -maximum breathing capacity < 50% of predicted -max V02 < 10 ml/kg/min Most commonly used criteria for operablilty: -predicted postoperative FEV1 > 800 ml If predicted postoperative FEV1 < 800 ml and resection is still being considered: -test the ability of the remaining pulmonary artery to tolerate the total blood flow -occlude the main pulmonary artery in diseased site with a balloon catheter not a candidate for pneumonectomy if: -mean pulmonary artery pressure > 40 mmHg -Pa02 < 45 mmHg removal of diseased lung may improve oxygenation without adversely affecting the pulmonary function ex. removing the source of intrapulmonary shunting Two main systems at greatest risk after lung resection include: -pulmonary system -cardiac system pulmonary system: V02: -if V02 > 20ml/kg: usually have low complication rates -if V02 < 10ml/kg: usually have unacceptable high morbidity and mortality rates cardiac system evaluate cardiac reserve -able to climb 2 –3 flights of stairs without shortness of breathe: often tolerate the procedure well -usually do not require further testing ANESTHETIC CONSIDERATION PREOPERATIVE MANAGEMENT baseline assessment of heart and lungs is needed due to frequent association of underlying risk factors for: -COPD/ Asthma, coronary artery disease, smoking, etc investigative studies may include: Echocardiography -allows for baseline cardiac function -may help in evaluating for presence of corpulmonale (ex. RVH) Dobutamine Stress Echocardiography -help assess for occult coronary artery disease Chest Xray, Chest CT, Chest MRI: -tracheal deviation: may complicate ETT intubation -bronchial deviation: may complicate EBT intubation -airway compression: may complicate ventilation especially after induction of anesthesia -pulmonary consolidation: may predispose to hypoxemia -atelectasis may predispose to hypoxemia -large pleural effusion: may predispose to hypoxemia Perioperative arrhythmias during thoracotomy may occur from: -surgical manipulation of the right atrium -distention of the right atrium due to reduction of the pulmonary vascular bed -increase in age -increased amount of pulmonary resection INTRAOPERATIVE MANAGEMENT -preparation -venous access -monitoring -induction of anesthesia -positioning -maintenance of anesthesia -management of one lung ventilation -alternative to one lung ventilation Preparation: particular patient population are prone to rapid onset of hypoxemia due to: -poor pulmonary reserve -anatomic abnormalities -compromise of the airway -need for one lung ventilation specialized equipment that should be available includes: -different sizes of SLT -different sizes of DLT -flexible fiberoptic bronchoscope -small diameter tube exchanger -CPAP delivery system -circuit adapter for delivering bronchodilators venous access may involve: -large bore intravenous access ( 14 or 16G) if extensive blood loss is expected: -central venous catheter preferred on same the site as the thoracotomy -blood warmer -rapid infusion device Monitoring Arterial line for: -one lung ventilation -large tumor resection -patients with limited pulmonary reserve -patients with significant cardiovascular disease Central Venous Pressure for: -pneumonectomies -large tumor resection helps assess: -overall venous capacitance -blood volume -right ventricular function Pulmonary Artery Pressure patients with: -pulmonary hypertension -corpulmonale -left ventricular dysfunction if the pulmonary artery catheter is: -in the nondependent lung -in the collapsed lung then during one lung ventilation cardiac output will be falsely decreased mixed venous oxygen saturation is falsely decreased MAINTENANCE OF ANESTHESIA generally preferred technique: potent halogenated anesthetic + opiod advantages of halogenated anesthetics: -dose related bronchodilation -blunting of airway reflexes -capability of high FI02 -ability to rapidly titrate anesthetic levels -minimal effect on HPV with values < 1MAC advantages of opiods: -hemodynamic stability -blunting of airway reflexes -postoperative analgesia nitrous oxide avoided due to: obligatory decrease of FI02 in setting of N20 administration -inhibition of HPV (similar to volatile anesthetics) -may exacerbate pulmonary hypertension muscle relaxants: -facilitate rib spreading -facilitates anesthetic maintenance fluid maintenance -generally restricted in patients undergoing pulmonary resections -basic maintenance requirements + blood loss requirements should be administered -blood loss often replaced with colloid or blood infusion -“lower lung syndrome” may occur with excessive fluid administration in the lateral decubitus position -“lower lung syndrome” gravity dependent transudation of fluid into the dependant lung intravenous fluids may contribute to intrapulmonary shunting in the lateral decubitus position by: -“lower lung syndrome” creating transudation to the lower dependant ventilated lung -the collapsed lung may be prone to edema following re-expansion secondary to surgical retraction Therefore: one lung ventilation is prone hypoxemia in the lateral decubitus positioning testing the bronchial stump for air leaks by: -transiently sustaining 30 cm H20 positive pressure of the airways Management of One Lung Ventilation greatest risk of one lung ventilation: -hypoxemia reducing the risk of hypoxemia during one lung ventilation: -reducing the period of one lung ventilation to a minimal -100% FI02 if peak airway pressure > 30 cm Hg: -may reduce the tidal volume ≅ 6 – 8 ml/kg -increase the respiratory rate -goal: maintain the same minute ventilation ( ↓TV ↑RR) with a resultant decrease in PAP interventions for hypoxemia during one lung ventilation under general anesthesia include: factors which are generally more effective include: -periodic inflation of oxygen into the collapsed lung -during pneumonectomy perform early ligation of the ipsilateral pulmonary artery -CPAP to the collapsed lung 5 – 10 cmH20 factors which are generally not as effective include: -ventilated lung: PEEP 5 – 10 cmH20 -collapsed lung: continuous insufflation of oxygen -alter minute ventilation by adjusting tidal volume and respiratory rate persistent hypoxia requires: -immediate expansion of collapsed lung -repeat fiberoptic flexible bronchoscope to confirm placement of the endobronchial tube -suction both tracheal and bronchial lumen of excessive secretions -rule out pneumothorax on the ventilated lung Alternative to One Lung Ventilation -apneic oxygenation -high frequency positive pressure ventilation -high frequency jet ventilation apneic oxygenation -100% oxygen insufflated at a rate greater than the oxygen consumption while ventilation has been discontinued -limited use of this technique to about 10 – 20 minutes due to progressive increase in PaC02 -↑PaC02 6 mmHg for the 1st minute then ↑PaC02 3 mmHg every minute thereafter POSTOPERATIVE MANAGEMENT early extubation help decrease the risk of: -pulmonary barotraumas -pulmonary infection patients with decreased or marginal pulmonary reserve: -often are left intubated until weaning parameters and extubation criteria are met -if left intubated , single lumen tube should be placed instead of the already placed double lumen tube patients status post throracotomy should be observed in: -PACU -SICU postoperative hypoxemia may occur due to: -atelectasis from surgical compression of the lungs -shallow breathing / splinting secondary to incisional pain -gravity-dependant transudation of fluid into the dependant lung -re-expansion edema of the collapsed nondependent lung signs of postoperative hemorrhage include: -increased chest tube drainage (> 200 ml/hr) -hypotension -tachycardia -falling hematocrit routine postoperative care for thoracotomy involves: -semi-upright position > 30° -supplemental oxygen 40-50% -incentive spirometry -close monitoring of ECG and hemodynamics -postoperative radiographs -adequate analgesia Postoperative Analgesia Goal: maximize patient comfort without compromising pulmonary function -caution since thoracotomy patients have a pre-existing marginal pulmonary function -PCA -Nerve Block -Epidural Opiod -Intrapleural Analgesia PCA -provides small intravenous doses of opiods which is beneficial over a larger intramuscular dose Nerve Block -intercostal nerve block provides excellent pain relief ex. ropivicaine 0.5% 4-5 ml in 2 levels above and below the incisional site may improve: -ABG -PFT -reduce length of hospital stay Epidural Opiod +/- Local Anesthesia -provides from 6 – 24 hours of analgesia devoid of: -autonomic blockade -sensory blockade -motor blockade ex. morphine 5 –7 mg in 10 – 15 ml in saline applications: -thoracic epidural -lumbar epidural Postoperative Complications -atelectasis -air leaks -bronchopleural fistula -torsion of a lobe/ segment -hemoptysis -pulmonary infarction -acute herniation of heart -extensive mediastinal dissection