Therapeutic Bronchoscopy, Airway Stents, and Other Closed Thorax Procedures

Scott Shofer
Momen M. Wahidi
Ian J. Welsby

Case Vignette

Therapeutic bronchoscopy, previously practiced primarily by thoracic surgeons, is becoming more commonly performed by pulmonologists who receive specialized training in the performance of airway surgical techniques for the treatment of central airways obstruction. Performing these procedures involves the use of the rigid bronchoscope, which requires careful coordination of care between the anesthesia team and the proceduralist. Several issues around the use of rigid bronchoscopy can often lead the anesthesiologist into unfamiliar territory, including release of the airway into the hands of the proceduralist, turning the head of the patient away from the anesthesiologist during the procedure, and often ceding control of ventilation to the procedural team. Good communication regarding procedural planning, ventilatory strategy, and anesthesia management are critical to optimize patient safety and provide for a successful procedure.

Therapeutic bronchoscopy is most commonly employed to treat patients with central airways obstruction (CAO) due to benign or malignant etiology. While the incidence of CAO is unknown, it is a commonly encountered clinical problem present in 20% to 30% of patients with primary lung cancer¹ and 7% to 18% of patients post-lung transplantation.² Additional common causes of CAO include tracheal stenosis, either post-tracheostomy or idiopathic, tracheomalacia, and foreign body aspiration.¹ While many of the techniques that will be described in this section are amenable to use with the flexible bronchoscope, rigid bronchoscopy provides definitive control of the airway permitting the use of general anesthesia to maximize patient comfort (Table 11–1).³ In addition, the rigid bronchoscope becomes a conduit for use of a variety of tools and suction devices to perform minimally invasive airway surgery. The bronchoscope itself can become a therapeutic tool useful for dilation of airway stenoses, and “coring out” of airway tumor providing rapid relief of central airway obstruction.³

Table 11–1. Indications for Rigid Bronchoscopy

RIGID BRONCHOSCOPY

The rigid bronchoscope was the only method of bronchoscopy available from the advent of the bronchoscope in 1897 by Gustav Killian, until the introduction of the flexible fiberoptic scope in 1967 by Ikeda. After the introduction of flexible bronchoscopy, use of the rigid bronchoscope declined by pulmonologists in North America. Its distinct advantages in controlling the airway while facilitating the passage of a wide variety of tools for minimally invasive airway surgery in conjunction with the development of reliable stents to promote airway patency has led to a renewal in interest in the use of rigid bronchoscopy by the pulmonary community over the past 15 years.⁴

Indications

Rigid bronchoscopy can be used for any bronchoscopic indication, however, the additional requirements of general anesthesia generally result in most centers limiting its use to therapeutic indications such as relief of central airway obstruction, foreign body removal, and for investigation of massive hemoptysis.

Patient Selection

Rigid bronchoscopy is generally well-tolerated among most patients, even those with significant respiratory disabilities due to their underlying pulmonary disease. However, several medical conditions may occur which raise the risk for complications. Major conditions to consider include ischemic or arrhythmic heart disease, bleeding diathesis (coagulopathy, thrombocytopenia, uremia), neurologic disease or head trauma, and respiratory insufficiency. Although bronchoscopy can be performed in patients who fall short of the ideal, the risk of the procedure increases accordingly, and options for more invasive manipulations (biopsies, lengthy procedures, etc) can be limited.

Preoperative laboratory studies, including platelet count, coagulation studies, blood urea nitrogen, and creatinine level, are often obtained to assess for bleeding tendencies. However, multiple studies examining the utility of preoperative laboratory examinations have determined that this is not universally necessary, but should be tailored to patients with medical histories suggesting an abnormality. In a retrospective study of 305 bronchoscopies with biopsy, Kozak and Brath identified five clinical risk factors which should prompt further pre-operative evaluation including prior anticoagulant therapy, liver disease, family or personal history of bleeding tendencies, active bleeding or recent transfusion requirements, and presence of an unreliable historian.⁵

Absolute contraindications to bronchoscopy are few and include inability to provide informed consent, status asthmaticus, severe hypoxemia, and unstable cardiovascular conditions. Detailed below are some of the main factors to consider when selecting a patient for bronchoscopy.

ASTHMA/BRONCHOSPASM

Although bronchoscopy can be safely performed in asthmatic patients, it is associated with a significant drop in FEV₁ and PaO₂ post-procedure. This drop correlates inversely with the concentration of methacholine required to produce a 20% fall in FEV₁ at baseline but not with the usual measures of asthma severity such as albuterol use, symptom scoring, and peak flow variation.⁶ Therefore, bronchoscopy should be approached cautiously in the patient with asthma, and avoided entirely in the setting of status asthmaticus. Elective procedures should be deferred until bronchospasm is effectively controlled.

HEAD TRAUMA/ELEVATED INTRACRANIAL PRESSURE

Increased intracranial pressure (ICP) has been anecdotally cited as a relative contraindication to bronchoscopy because of concerns that the rise in intrathoracic pressure induced by bronchoscopy-associated cough could abruptly raise ICP and precipitate herniation. A retrospective study found no increase in neurologic complications in patients with space-occupying central nervous system lesions undergoing bronchoscopy, although pretreatment with steroids was recommended to decrease cerebral edema.⁷ More recently, a prospective study of 23 patients with intracranial drains in place revealed substantial, though transient, increases in ICP in patients undergoing bronchoscopy, despite adequate levels of sedation, analgesia, and paralysis.⁸ No acute deterioration in the patient’s clinical status was observed, but unfortunately, long-term complications or sequelae from these changes remain unknown.⁸ Therefore, although fiber-optic bronchoscopy is often necessary in the care of patients after neurologic events, it should be used with caution in this patient population.

HYPOXEMIA/HIGH OXYGEN REQUIREMENT

Bronchoscopy carries a higher risk in patients who are hypoxemic at baseline, although determining the cause of hypoxemia is a common indication for bronchoscopy. Unfortunately, hypoxemia is also a complication of bronchoscopy, resulting from sedation-related hypoventilation and ventilation-perfusion mismatch secondary to partial airway occlusion (from bronchoscope), atelectasis from frequent suctioning, airway bleeding, lavage fluid, and jet ventilation.⁹ While there is no absolute amount of supplemental oxygen that is a contraindication for bronchoscopy, caution should be used in patients with high oxygen requirements. Severe hypoxemia with PaO₂ greater than 65 to 70 mm Hg despite supplemental oxygen therapy is generally considered a contraindication.¹⁰

ANTICOAGULANT/ANTIPLATELET THERAPY

Use of anticoagulant and antiplatelet agents is common among patients referred for bronchoscopy. Therefore, it is important to carefully review all medications with the patient prior to bronchoscopy and make appropriate recommendations for continuing or holding medications prior to the procedure date.

Aspirin Aspirin was previously considered a contraindication to bronchoscopy due to its anti-platelet effects and prolongation of bleeding time. However, a large multicenter randomized trial found no difference in bleeding from transbronchial biopsies in the aspirin compared with the no aspirin group.¹¹ Therefore, it is generally accepted that patients can undergo bronchoscopy with transbronchial biopsy without holding aspirin therapy.

Clopidogrel In contrast to aspirin, clopidogrel significantly increases bleeding risks following transbronchial biopsy. When the effect of clopidogrel on the incidence of bleeding was studied during transbronchial biopsy, significant bleeding rates increased to 89% compared with 3.4% in the control group.¹² In a small number of patients receiving both aspirin and clopidogrel, the incidence of significant bleeding was 100% following transbronchial biopsy.¹² Given the relatively long half-life of clopidogrel, most practices require patients to discontinue clopidogrel a minimum of 5 days prior to undergoing bronchoscopy with transbronchial biopsy.

Thrombocytopenia There is little data regarding what threshold for platelets constitutes safe levels for bronchoscopy. Transfusion guidelines and expert statements have recommended minimum platelet counts of 20,000 to 50,000/mm³ for fiberoptic bronchoscopy and greater than 50,000/mm³ for transbronchial biopsy.¹³

Procedure Risks and Complications

The risks of bronchoscopy and anesthesia should be specifically reviewed with the patient. The risk of major complications from bronchoscopy, including pneumothorax, pulmonary hemorrhage, infection, and respiratory failure, is 0.6%. When transbronchial biopsy is performed, the risk of serious complications reaches 1% to 6%.¹⁴ Complications specifically related to rigid bronchoscopy include airway perforation, pneumomediastinum, and fatal hemorrhage due to injury of the great vessels, which are rare. Minor complications from bronchoscopy include fever, cough, bronchospasm, transient hypoxia, and hemoptysis. Additionally, cardiovascular complications can occur from the stress of the procedure itself, particularly in high risk patients. Cardiac events can include vasovagal reactions, arrhythmias, myocardial ischemia, angina, and cardiac arrest.¹⁵ The mortality rate from bronchoscopy is approximately 0.01%, and has decreased in recent years as monitoring capabilities and technology have improved.¹⁴

Equipment

The rigid bronchoscope is essentially a stainless steel tube with a beveled tip at the distal end, while the proximal end usually contains a series of ports for ventilation, passage of suction catheters, grasping tools, a telescope, or a flexible bronchoscope (Figure 11–1). Fenestrated caps may be placed over the ports to permit closed ventilation during the procedure. Adult bronchoscopes are generally 9 to 13 mm in diameter and 40 cm long, while tracheoscopes are of similar diameter but are only 25 cm in length. Fenestrations are present in the side-wall at the distal end of the bronchoscope to allow for continued ventilation of the opposite lung if the scope is passed down one of the mainstem bronchi during the procedure.

Figure 11–1. Rigid bronchoscope and telescope. Note head portion of bronchoscope with ports for passage of tools and attachment to the anesthesia circuit or jet ventilator adaptor.

Insertion

Prior to bronchoscope insertion, the patient must be adequately anesthetized. Many centers choose to administer a muscle relaxant as well, although this is not absolutely required. The patient’s neck is hyperextended, and with the fingers of the left hand, the upper lip and teeth are covered with the operators thumb, the index finger is inserted into the patient’s mouth to displace the tongue towards the left side of the mouth, and the middle finger is used to cover the lower lip and teeth to prevent injury of these structures. The bronchoscope is held in the right hand with the barrel of the scope resting between the thumb and first finger with the bevel of the distal end of the scope facing down. The tip of the scope is inserted into the patient’s mouth against the base of the tongue. The tongue is visualized via the telescope inserted through the bronchoscope, and the scope is advanced along the base of the tongue until the epiglottis is visualized. The bevel of the scope is advanced under the epiglottis, and the tip is rotated upward, using the thumb located over the patient’s upper mandible as a fulcrum to lift the epiglottis and bring the vocal cords into view. The scope is then rotated 90 degrees clockwise to allow the beveled tip to slide between the cords. Rotation is continued an additional 90 degrees as the bronchoscope enters the trachea to run the bevel against the posterior wall of the trachea to prevent injury to the membranous tracheal wall.³

ANESTHETIC MANAGEMENT FOR RIGID BRONCHOSCOPY

Due to the irritating nature of the rigid intubation, virtually all centers perform rigid bronchoscopy under general anesthesia. Standard American Society of Anesthesiologists’ recommended monitoring should be used for these cases. Additionally, a radial arterial line is generally useful for real-time hemodynamic monitoring and for providing access for arterial blood gas analysis as indicated.

The anesthesia plan can be based on a balanced technique with positive pressure ventilation or a spontaneously breathing technique. For spontaneous assisted ventilation,¹⁶ anesthesia is closely titrated to permit spontaneous ventilation. The rigid bronchoscope is capped and the mouth is packed with gauze to provide a seal around the barrel of the bronchoscope. Ventilation is provided by attaching the anesthesia circuit to the side port of the bronchoscope, resulting in a closed system that is suitable for delivery of oxygen and gas anesthetics to the patient if desired. Instruments are introduced into the airway through fenestrated caps on the rigid scope. The patient is lightly anesthetized for the majority of the procedure to permit continued spontaneous ventilation except during particularly noxious portions of the procedure when anesthetics are titrated up to prevent patient motion. At these times, ventilation may need to be supported with positive pressure ventilation, as the patient is likely to become apneic. While an effective technique, some operators find the need for capping the rigid bronchoscope cumbersome, because this limits the number of instruments that may be introduced into the bronchoscope. Also, in order to reduce entrainment of ambient air with subsequent dilution of inspired oxygen and anesthetic gas concentrations, high gas flows are required, which increases the consumption of inhaled anesthetics and pollutes the operating room environment.

Two basic approaches are currently practiced to provide positive pressure ventilation during rigid bronchoscopy. The most basic form uses intermittent apnea while the proceduralist performs the necessary procedures followed by capping of the rigid scope to allow intermittent positive pressure ventilation. This approach becomes quite cumbersome for longer or complex procedures and is not favored by most centers. Therefore, the majority of North American interventional pulmonologists use some form of jet ventilation during rigid bronchoscopy, either a Sander’s jet ventilator or an automated jet ventilator, which allows the anesthesiologist to be freed from managing the Sander’s jet during the procedure.^17,18

Limited data exist comparing outcomes between ventilation strategies, however there is some evidence to suggest that spontaneous assisted ventilation may reduce rates of reintubation following rigid bronchoscopy.¹⁶ This result may be partially explained by the need for muscle relaxants with jet ventilation, underscoring the importance of monitoring and avoidance of residual curarization while using this technique. Positive pressure techniques in a paralyzed patient are better suited to the more complex procedures such as airway tumor debulking and customized stent deployment. Therefore, details of the anesthetic technique discussed below focus on this.

Induction of anesthesia is typically intravenous, as this patient population is susceptible to paroxysms of coughing. Standard considerations for rapid sequence induction apply and the choice of induction agent is at the anesthesiologist’s discretion, although propofol or ketamine are better suited to patients with preexisting bronchospasm. Procedures generally have a duration of 20 to 60 minutes, and choice of neuromuscular blocker should reflect this. Residual curarization or recurarization in this population will be poorly tolerated,¹⁶ so pancuronium is rarely indicated. A balanced technique is not mandatory but avoids the cardiovascular effects of deep anesthesia that would otherwise be necessary, as bucking or coughing against the rigid bronchoscope can lead to serious tracheal injury. Depending on the circumstance, the trachea can be intubated prior to the bronchoscopic procedure, or more usually induction will occur once the pulmonologist is poised to pass the rigid bronchoscope. The rigid bronchoscope is not cuffed and may not protect against aspiration, but the airway is continuously visualized and endobronchial toilet can be immediately performed should soiling occur.

The passage of the rigid bronchoscope is very stimulating and blunting of the pressor response to intubation can be achieved with short acting opiates such as remifentanil or alfentanil, as postoperative pain is minimal and opiate induced respiratory depression will be dangerous. If the bronchoscope is capped appropriately necessitating intermittent use of the lumen for the procedure, interrupted inhalational anesthesia may be used for maintenance of anesthesia, however, a total intravenous anesthetic (TIVA) technique may better suited to rigid bronchoscopy to ensure continuous anesthesia delivery and avoid interruptions to the procedure. The TIVA should be started at the time of induction through a dedicated intravenous cannula that can easily be inspected to confirm intravenous delivery, especially if hemodynamic parameters or anesthesia depth monitors suggest inadequate anesthesia.

Assuming TIVA is used for maintenance of anesthesia, jet ventilation is used as described below, with either a jet ventilator or manually delivered using a Sanders injector. Adequate tidal volume is estimated by visually appreciating chest rise and is greatly facilitated by reverse Trendelenburg positioning. Arterial blood gas analysis or use of a percutaneous carbon dioxide monitor is advisable to avoid over or under ventilation. Prior to emergence, the patient is intubated with a cuffed endotracheal tube, reexpansion of previously collapsed lung segments is achieved with positive end expiratory pressure, and a final toilet bronchoscopy is performed with a flexible bronchoscope. Full reversal of neuromuscular blockade is confirmed prior to extubation.

This patient population is at high risk for respiratory distress after extubation and consideration should be given to nebulized bronchodilators or lidocaine for bronchospasm or excessive coughing respectively. The team should have a low threshold for awake bronchoscopy to diagnose and treat excessive secretions mobilized from newly expanded lung segments, de novo airway bleeding or stent migration.

Jet Ventilation

Jet ventilation employs a short burst of high-pressure gas delivered through a narrow (often 1-3 mm in diameter) catheter to provide ventilation through an open, uncuffed airway. Tidal volumes are usually low, often significantly less than dead space, with respiratory rates ranging from 60 to 150 breaths per minute. Given the low tidal volumes produced by the jet ventilator, mechanisms other than conventional bulk flow become important for effective gas exchange during jet ventilation.

Five mechanisms have been described to explain gas transport with jet ventilation: (1) Bulk flow or convective gas transport is responsible for gas delivery during conventional mechanical ventilation and likely plays a role in the large airways during jet ventilation as well. (2) Coaxial flow describes movement of gas in one direction down the center of an airway while movement in the opposite direction occurs along the airway periphery. This mechanism is very dependent on airway geometry and occurs more frequently at the site of bifurcations. (3) Taylor dispersion is a complex phenomenon that describes gas dispersion along the front of bulk gas flow. This probably plays the greatest role within the larger airways. (4) Molecular diffusion occurs at the alveolar level and plays a significant role in gas mixing within the alveoli in both jet and conventional ventilation. (5) Pendelluft describes the intra-alveolar mixing of gas due to impedance differences. This phenomenon may also involve airway gas as well and so result in alveolar ventilation.¹⁹

Other important considerations when using jet ventilation include the site of the injection catheter placement. We generally place the injection catheter at the proximal end of the bronchoscope (Figure 11–2). Others move it deeper into the airway to reduce dead space ventilation. This technique requires continuous airway pressure monitoring to prevent barotrauma, as airway obstruction related to the introduction of instrumentation through the bronchoscope may result in elevations in airway pressure.²⁰ In addition, caution must be used when central airways obstruction is present as placement of the catheter distal to an airway lesion may result in a ball valve mechanism leading to elevated alveolar pressures and pneumothorax.

Figure 11–2. Components needed for jet ventilation through the bronchoscope (Sanders injector). Wall connector for oxygen supply, reducing valve and pressure gauge, high-pressure tubing, toggle switch, and needle injector jet. (From: Eisenkraft JB, Neustein SM. Problems in Anesthesia. Vol 4. Philadelphia: JB Lippincott, 1990:223, with permission.)

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