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

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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

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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