Anatomy

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  Upper airway

  
  
  
  
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    Nose, nasopharynx, and oropharynx

    
    
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    Function: warm and humidify inspired gases; ciliary clearance of airway irritants and secretions.

  
  
  
  

  Note: loss of this normal function needs to be remedied during anesthesia .

  
  
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  Bronchopulmonary tree

  
  
  
  
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    Each lobe subdivides into segments.

    
    
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    Each segment gives off between 10 and 25 branches.

    
    
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    Lung reflex innervation is mediated via branches of the vagus nerve.

    
    
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    Airway smooth muscle tone is mediated by the parasympathetic nervous system. Cholinergic nervous stimulation results in airway smooth muscle spasm, mucus secretion, and bronchial vasodilatation. Airway smooth muscle relaxation is mediated by inhibitory nonadrenergic non cholinergic (NANC) nerves. Exitatory NANC nerves may contribute to bronchoconstriction. Sympathetic adrenergic nerves have little or no role in regulating airway smooth muscle tone. However, note that human airway smooth muscle richly expresses beta-adrenergic receptors, the stimulation of which produces bronchodilation.

    
    
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    Tracheobronchial blood vessels are innervated by adrenergic nerves

  
  

Physiology

During the perioperative period, significant events can occur in

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  Lung mechanics

  
  
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  Thoracic cage mechanics

  
  
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  Respiratory muscle function

  
  
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  Alveolar gas exchange

  
  
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  Baseline parameters for the above-quantified by preoperative pulmonary function studies and measurement of arterial blood gases.

Endotracheal Tubes

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  Bypass the function of the upper airway resulting in the passage of dry, cold gases and buildup of secretions and irritants.

  
  
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  Reduce the size of the trachea (usually by 30-50%) which in turn increases airway resistance

Vapors

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  Smooth muscle relaxants

  
  
  
  
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    Cause collapse and occasionally occlusion of the soft palate of the upper airway.

    
    
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    Decrease the centrally mediated respiratory response to hypercapnia and hypoxia.

  
  
  
  
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  Potent bronchodilators—can be used in the management of status asthmaticus.

  
  
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  Attenuate the hypoxic pulmonary vasoconstriction (HPV) response.

Neuromuscular Blockade

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  Loss of muscle tone allows for cephalad movement of the diaphragm.

  
  
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  In most cases, neuromuscular blockade is reversed with antagonists at the termination of surgery.

Opiates

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  Centrally acting respiratory depressants

  
  
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  Decrease responsiveness to CO ₂

  
  
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  Mu receptor agonists

Positioning

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  Supine position :

  
  
  
  
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    Used during induction and emergence of anesthesia.

    
    
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    Supine position while awake decreases functional residual capacity (FRC).

    
    
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    Supine position while under anesthesia decreases FRC by another 15% to 20% due to the cephalad movement of the diaphragm

  
  
  
  
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  Lateral decubitus position:

  
  
  
  
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    Used for the majority of thoracic surgical procedures.

    
    
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    In adults, there is a moderate decrease in the FRC of the dependent lung owing to compression from the mediastinum and abdominal contents.

    
    
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    In infants and young children, there is a larger decrease in FRC because there is also compression of the dependent lung from the rib cage.

  
  

Lung Volumes

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  Decreased FRC

  
  
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  Closing capacity approaches, or surpasses, FRC, which leads to alveolar collapse.

Positive Pressure Ventilation

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  Increases intrathoracic pressure, which, in turn, reduces venous return to the heart.

  
  
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  Decreased right-sided heart output impairs blood flow through the pulmonary vessels.

  
  
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  Decreased left-sided heart output impairs oxygen delivery to the tissues.

Obstructive Lung Disease

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  Pathophysiology

  
  
  
  
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    “Irreversible”—emphysema and chronic bronchitis

    
    
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    “Reversible”—asthma

    
    
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    Have pre-existing reduced FEV ₁

    
    
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    Have pre-existing V/Q mismatch

  
  
  
  
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  Often require medications to assist pulmonary function.

  
  
  
  
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    Oral or inhaled steroids

    
    
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    Home oxygen

    
    
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    Nebulizers or metered-dose inhalers

  
  
  
  
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  Patients are often former smokers or are still smoking at the time of surgery. Effects of smoking on general anesthesia include :

  
  
  
  
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    Hypersecretions and impairment of mucociliary transport activity. It takes 4 to 8 weeks to return to normal after smoking cessation.

    
    
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    Increased plasma levels of carboxyhemoglobin shifts the oxyhemoglobin dissociation curve. It takes 4 to 6 hours to return to normal after smoking cessation.

  
  

General Anesthesia and Obstructive Lung Disease

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  Instrumentation of the airway, as in laryngoscopy, bronchoscopy and intubation may precipitate bronchospasm.

  
  
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  Vapors and local anesthetics may attenuate this response.

  
  
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  Humidified circuits should be used to warm and humidify the inspired gases.

  
  
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  Anticholinergics may be required to treat excess airway secretions.

  
  
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  Anesthetic vapors are potent bronchodilators but will impair the HPV response, resulting in further V/Q mismatch.

  
  
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  Nitrous oxide expands gas-enclosed spaces and should be avoided in patients with bullae because it can expand or rupture the bullae, resulting in a pneumothorax or tension pneumothorax.

  
  
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  PEEP will minimize the atelectasis but at the expense of decreased cardiac output and risk of barotraumas.

  
  
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  Beta-2 agonists used to treat bronchospasm can produce tachyarrythmias.

Restrictive Lung Disease

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  Pathophysiology

  
  
  
  
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    Intrinsic restrictive lung disease (RLD)—example: interstitial lung disease

    
    
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    Thoracic restrictive disorders:

    
    
    
    
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      Morbid obesity

      
      
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      Pleural disorders, for example, fibrothorax

      
      
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      Neuromuscular respiratory disorders

      
      
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      If it is large, anterior mediastinal mass can contribute to restrictive physiology

    
    

  
  
  
  
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  Have pre-existing decreased total lung capacity (TLC) +/- diffusing capacity

  
  
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  Can have associated pulmonary hypertension

General Anesthesia and Restrictive Lung Disease

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  Similar precautions for patients with obstructive lung disease should be used for patients with RLD

  
  
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  Increased risk for biventricular cardiac failure due to cardiac depressant effects of anesthetic vapors in patients with pre-existing pulmonary hypertension and cor pulmonale.

  
  
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  Special consideration for patients with anterior mediastinal mass :

  
  
  
  
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    Often symptoms are not manifested until after the patient is anesthetized.

    
    
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    Loss of muscle tone from anesthesia paralysis can result in complete airway or vascular obstruction.

    
    
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    Emergency airway equipment and ability to perform cardiac bypass should be available for large anterior mediastinal masses

  
  

More and More Neoadjuvant Therapy is Received Prior to Surgery for Patients Who Presented with Metastatic Lung Cancer

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  Multiple chemotherapy drugs (e.g., bleomycin, paclitaxel [Taxol], and so on) have been associated with postoperative adult respiratory distress syndrome (ARDS).

  
  
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  Greater risk for intraoperative bleeding if radiation therapy was given.

  
  
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  Inspiratory oxygen levels must be decreased during surgery (preferably below 40%).

  
  
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  Fluids are minimized.

Surgery is Often Diagnostic, not Curative

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  Examples include lung and lymph node biopsies.

  
  
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  No improvement in respiratory symptoms postoperatively.

Endotracheal Tubes that Provide One-Lung Ventilation

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  One-lung ventilation (OLV) is almost essential in thoracoscopic surgery.

  
  
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  A review by Weiskopf and Campos demonstrates many ways to achieve OLV in adults.

  
  
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  We provide lung separation using a double-lumen tube (DLT; Mallinckrodt Medical, Inc, St. Louis, MO).

  
  
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  DLTs provide excellent lung separation and allow suctioning of the nonventilated lung during the surgery.

  
  
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  Most of the time, we place a R-DLT for all left-sided surgeries and an L-DLT for all right sided surgeries. The exception to this is when the right upper lobe takeoff lies proximal to the tracheal carina (incidence of 0.4%). In this case, an L-DLT would be used for a left-sided surgery.

  
  
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  Most institutions only place L-DLT, citing a greater ease of use and a greater safety margin during positioning.

  
  
  
  
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    Proponents of the left-sided policy state that R-DLTs are harder to place because if the Murphy eye for the right upper lobe moves a tiny amount, the right upper lobe is not ventilated and the patient becomes hypoxic.

    
    
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    We find that the L-DLTs move as much as R-DLTs.

    
    
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    Right-sided tubes are needed for left sided sleeve resections and are easier to use for left pneumectomies. A L-DLT for a left pneumonectomy would require pulling back to the DLT and adjusting its position before stapling the bronchus.

  
  

Double-Lumen Tube Size

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  There is no exact science to determine which size DLT should be placed.

  
  
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  Brodsky and colleagues measured tracheal widths on preoperative chest x-ray studies to help determine the size of L-DLTs. This technique provided tubes too large for a mostly Asian population.

  
  
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  Because we select a DLT opposite to the side of the surgery, we always ventilate through the bronchial lumen. The method of ventilating through the bronchial lumen makes tube size very important:

  
  
  
  
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    A tube that is too small will usually result in a leak around the bronchial cuff.

    
    
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    To compensate for a bronchial leak, one often puts an excessive volume of air into the bronchial balloon, which can (1) cause airway trauma, (2) make it easier for the bronchial cuff to herniate out of the main stem bronchus, resulting in tube misalignment, and (3) rarely, rupture the main stem bronchus.

    
    
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    A tube that is too large can (1) be difficult to place and (2) result in airway trauma.

  
  
  
  
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  We have found good results using (for both right and left sided DLTs) 39F DLTs for men and 37F DLTs for women.

Fiberoptic Bronchoscopy

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  Although some anesthesiologists position the DLT with an x-ray, that is a time consuming process.

  
  
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  Our policy is to position every DLT with a fiberoptic bronchoscope.

  
  
  
  
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    This allows us to line up the ventilating slots with the appropriate bronchi and to check for any unforeseen pathology, such as intrabronchial tumors.

    
    
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    Intraoperative hypoxia is usually due to misalignment of the DLT. Left-sided tubes can be too deep, so that the left upper lobe is not being ventilated. Right-sided tubes can move so that the right upper lobe is not being ventilated.

  
  
  
  
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  Occasionally when direct laryngoscopy proves to be difficult, a fiberoptic bronchoscope is very helpful for intubation:

  
  
  
  
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    Fiberoptic intubations are best performed with the patient’s neck hyperextended and his or her tongue pulled out of the mouth.

    
    
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    The fiberoptic bronchoscope is placed through the bronchial lumen of the DLT.

    
    
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    The bronchoscope is passed along the midline of the tongue and then under the epiglottis to visualize the vocal cords.

    
    
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    Once the bronchoscope is in the correct main stem bronchus, the DLT slides over the bronchoscope and into the main stem bronchus.

  
  

Checking for Complete One-Lung Ventilation

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  Lung surgery and especially VATS procedures depend on good isolation of the lung.

  
  
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  If the operated lung stays expanded or is ventilated during the operation, the ability of the surgeon to perform the procedure is compromised and much time is wasted in repositioning the tube.

  
  
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  Proper function of the DLT should be done as soon as it is placed.

  
  
  
  
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    Our policy is to position the DLT with the fiberoptic bronchoscope.

    
    
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    Because we always place our DLT opposite to the side of the surgery, we clamp off the tracheal portion of the DLT so that the surgical side is not ventilated and ventilation only occurs through the bronchial tube.

    
    
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    Distal to the clamp, the tubing to the tracheal side is opened to allow the air from the surgical lung to escape, resulting in collapse of that lung.

    
    
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    If there is evidence of ventilation in the surgical lung, the DLT may need to be adjusted or a larger tube may need to be placed for a better seal.

  
  

Difficult Airway

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  When a difficult airway is recognized in the operating room, be even more cautious regarding extubation at the end of the procedure

  
  
  
  
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    Make sure that the patient has minimal chances of postoperative respiratory distress.

    
    
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    Consider watching the patient for a longer period of time in the recovery room.

  
  
  
  
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  For the remainder of the patient’s hospitalization, a sign over the patient’s hospital bed should state that the patient has a difficult airway. This lowers the threshold for health-care providers to electively intubate the patient if respiratory distress develops.

Ventilators that Provide Both Volume Control and Pressure Control

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  Flexibility in ventilatory modes (volume cycled; pressure pre-set modes) required for optimizing ventilation in different patient disease populations.

Measurement of Both Inspiratory and Expiratory Tidal Volumes to Assess Air Leaks

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  Used to assess air leak (for example, for bilateral lung volume reduction surgery).

  
  
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  The inspiratory and expiratory volumes are measured before the operation and after the resection. If the difference is greater than 50 mL, then the lung is inspected for leaks.

Invasive Monitors

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  Arterial lines are usually placed.

  
  
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  Central venous lines are not routinely used, but they are placed when the operation is expected to be bloody, when a pneumonectomy is performed, or when central venous pressures will be monitored postoperatively.

  
  
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  A pulmonary artery catheter is required for patients with pulmonary hypertension or cor pulmonale, or for any patient with postoperative hypotension that is unresponsive to fluid boluses.

Patient-Controlled Anesthesia versus Epidurals for Postoperative Pain Management

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  Our standard practice is to place a thoracic epidural for all thoracotomies, bilateral video-assisted thoracic surgeries (VATS), patients with low pain thresholds, and patients with a marginal performance status.

  
  
  
  
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    This avoids the respiratory depressant effects of parental opiates.

    
    
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    All epidurals are placed with the patient awake, either at the start of the surgery or after surgery (for unexpected VATS converted to a thoracotomy).

    
    
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    Postoperatively patients with an epidural receive a continuous infusion of fentanyl 5 μg/mL plus bupivacaine 1/16.

  
  
  
  
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  Sympathetic blockade from local anesthetics produces a small decrease in FEV ₁ and VC, but the decrease is negligible compared with those patients who had thoracic surgery and did not receive an epidural.

  
  
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  There is no evidence to suggest the sympathetic blockade effects bronchial tone.

  
  
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  For all other thoracic surgical patients, the surgeons perform intercostal nerve blocks and, when necessary, the patients receive patient-controlled anesthesia (PCA). More than 90% of lobectomies are performed by VATS, and epidural catheters are not used for those cases.