Clinical aspects of bronchoscopy

The indications for bronchoscopy are outlined in Box 156-1. A complete history and physical examination are necessary for all patients undergoing bronchoscopy for whom an anesthesia provider has been asked to assist. Concurrent medical problems increase the risks associated with the procedure; for example, patients who have a history of lung disease have an increased incidence of bronchospasm during bronchoscopy. Similarly, patients with restrictive ventilatory defects (e.g., interstitial lung disease) with or without preexisting hypoxia may have significant hypoxia during the procedure. Patients with lung cancer undergoing bronchoscopy may have other comorbid conditions (e.g., central airway obstruction, superior vena cava obstruction, metastatic lesions [bone, brain, liver] and electrolyte imbalance [hyponatremia and hypercalcemia]). Patients with pulmonary hypertension, elevated blood urea nitrogen (>30 mg/dL), chronic renal disease, and aspirin ingestion have an increased risk of postoperative bleeding. Interestingly, patients with recent myocardial infarction, unstable angina, or refractory arrhythmias often undergo bronchoscopy without significant complications.

A preoperative chest radiograph is mandatory; other investigations (e.g., complete blood count, electrolyte panel, and coagulation studies) are performed as indicated. Resting pulse oximetry prior to the procedure is essential in providing baseline information. Pulmonary function testing establishes the presence and severity of restrictive versus obstructive disease and the degree of reversibility, if any, with treatment. If respiratory failure is suspected or if the patient is on domiciliary oxygen, a preoperative arterial blood gas analysis is indicated.

Aims of anesthesia for bronchoscopy

During bronchoscopy, it is important to suppress the patient’s cough reflex and the hemodynamic response associated with bronchoscopy. Anesthesia may vary from no sedation, to mild to deep sedation, to general anesthesia. The type of anesthesia depends on the type of bronchoscope used—(FOB or rigid). The use of a topical anesthetic agent with or without sedation is used in most flexible FOB procedures. General anesthesia is usually required for rigid bronchoscopy and often in patients undergoing relief of a central obstruction with a FOB: however, sedation and local anesthesia may also be successfully used in both of these scenarios.

Preoperative preparation

After anesthesia and risks are discussed with a fasting (>6 h) patient, an antisialagogue (either atropine, 0.4-0.8 mg, or glycopyrrolate, 0.1-0.2 mg) is administered intramuscularly or intravenously 40 min prior to the procedure. Aerosolized bronchodilators, β₂-adrenergic receptor agonists, and anticholinergic agents are administered to patients with reactive airway disease before they undergo bronchoscopy. Corticosteroids are indicated during an exacerbation of reactive airway disease. The American Heart Association recommends subacute bacterial endocarditis prophylaxis for rigid bronchoscopy but not for bronchoscopy using a FOB unless the patient has a prosthetic heart valve, a surgically corrected intracardiac defect, or a history of endocarditis. Depending on the situation, patients on intravenous heparin should have the heparin discontinued 4 to 6 h before the procedure, and platelets should be transfused to maintain platelet levels greater than 50,000/mL. For patients undergoing any type of anesthesia, the American Society of Anesthesiology guidelines for monitoring should be followed.

Sedation

Without sedation, bronchoscopy is associated with increased cough, increased sense of asphyxiation, less amnesia for the procedure, and a significant increase in heart rate and blood pressure. Conscious sedation is usually achieved with intravenously administered incremental doses of midazolam (0.5-1.0 mg) or diazepam (1-2 mg). Intravenously administered opioids act synergistically with benzodiazepines to provide sedation and suppress airway reflexes but at the expense of potentiating respiratory depression. Fentanyl, sufentanil, alfentanil, and remifentanil are suitable opioid choices. Propofol can be used as a sedative agent, titrated in 10-mg doses, to provide conscious sedation and suppression of cough reflexes; however, significant hypotension and even apnea may result from excess drug administration. Intravenously administered dexmedetomidine has also been used to provide sedation for flexible bronchoscopy with a FOB.

Topical anesthesia for bronchoscopy

The sensory innervation of the upper airway is described in Table 156-1. Topical anesthetic agents, administered topically or via peripheral nerve blocks, can be used to anesthetize the upper airway. Two percent lidocaine (liquid or gel) is commonly used for topical airway anesthesia due to its margin of safety, rapid onset, and short duration of action. The maximum safe dose of lidocaine is 4 mg/kg. Toxicity depends on the rate of absorption and the resulting blood levels. Two percent lidocaine sprayed into or 4% viscous lidocaine-soaked pledgets placed in the nares (along with phenylephrine or cocaine to vasoconstrict the mucosal surfaces) can be used to anesthetize the nasopharynx. Oropharyngeal anesthesia can be achieved by one of several means (Box 156-2). These techniques provide satisfactory anesthesia of the upper airway. If persistent gag reflex prevents bronchoscopy, then the use of bilateral glossopharyngeal nerve blocks is indicated. Using a tonsillar needle, 3 mL of 2% lidocaine is injected into the midpoint of both posterior tonsillar pillars to a depth of 1 cm. This will effectively block the submucosa pressor receptors at the posterior aspect of the tongue. These blocks should always be performed following superior laryngeal nerve blocks because, without them, significant pharyngeal muscle and tongue relaxation may result, obstructing the airway.

Treatment of hypoxemia for bronchoscopy with a fiberoptic bronchoscope under sedation and topical anesthesia

Hypoxemia during bronchoscopy may occur because of a decreased inspired fraction of O₂ (FIO₂), hypoventilation due to excess sedation or upper airway obstruction, ventilation-perfusion mismatch due to pneumothorax secondary to transbronchial biopsy or excessive bleeding or from pulmonary lavage. Pulse oximetry is essential for monitoring, with a goal of maintaining an O₂ saturation (SpO₂) of at least 90%. Administration of supplemental O₂ (4-6 L/min) via nasal prongs or mask may help achieve this goal. If hypoxia persists, a nasopharyngeal tube should be inserted and O₂ administered via this route. If the SpO₂ saturation remains below 90%, the next step is to administer O₂ via a catheter passed nasally that is placed either above the larynx or in the proximal trachea. If O₂ desaturation continues, the bronchoscope should be withdrawn, an arterial blood gas should be measured, the sedation reversed, and an anesthesia bag and mask used to ventilate the patient. In such circumstances, tracheal intubation and ventilation with a high FIO₂ may be necessary.

An awake intubation should be planned for an anticipated difficult airway. If awake intubation is not feasible, an inhalation induction technique is a safe alternative. An intravenous induction technique is used if no airway difficulty is anticipated. Anesthesia can be maintained with either an inhalation or intravenous technique.

Propofol is an ideal choice to maintain anesthesia if a total intravenous anesthetic technique is used because of its rapid onset and offset plus its suppression of airway reflexes. The administration of a potent opioid is often necessary because bronchoscopy can increase mean arterial pressure, heart rate, cardiac output, and pulmonary artery occlusion pressure to unacceptable levels. Fentanyl and sufentanil can be administered intermittently, or alfentanil and remifentanil can be given as a continuous infusion following a loading dose.

Neuromuscular blockade, which is often required, can be achieved with the use of a nondepolarizing agent with rapid onset and intermediate duration of action (e.g., rocuronium) or, alternatively, with a succinylcholine drip. Lambert-Eaton syndrome, a neuromuscular disorder associated with small cell lung neoplasms, increases the sensitivity of patients who have the syndrome to the effects of both depolarizing and nondepolarizing neuromuscular blocking agents.

If the duration of the procedure is short, apneic oxygenation with intermittent ventilation is both easy and effective. Following induction of anesthesia and neuromuscular blockade, the patient is denitrogenated with 100% O₂, and then O₂ at 6 L/min is insufflated through a catheter passed through the vocal cords to lie just above the main carina. Although it may be possible to maintain SaO₂, the PaCO₂ tension will increase approximately 4 to 6 mm Hg the first minute and 2 to 4 mm Hg per minute thereafter. Intermittent periods of ventilation may be necessary to attenuate the associated respiratory acidosis.

Sealing the open end of a rigid bronchoscope with the attached magnifying glass and attaching the breathing circuit from an anesthesia machine to the side arm of the rigid bronchoscope allows the anesthesia provider to better oxygenate and ventilate the patient, with the added benefit of permitting the provider to maintain anesthesia using an inhaled anesthetic agent. When this technique is used for prolonged procedures, hypoxemia and hypercapnia may develop during times that the proximal end of the bronchoscope is open for instrumentation of the airway.

The Sanders jet injector technique, with is now frequently employed, makes use of the Venturi principle, in which gas (FIO₂ ≥ 0.21) under high pressure (50 psi) flows through a long metal tube with a small orifice entraining air from the open outlet, maintaining ventilation. This technique works well except in patients with decreased lung compliance in whom ventilation and oxygenation may be difficult to maintain. Because the gas is injected under high pressure, care must be taken to avoid barotrauma.

Removal of a foreign body

The typical patient having a foreign body removed is a young, distressed, nonfasted child who has aspirated a peanut. Atropine is typically administered for its vagolytic and antisialagogue effects. Induction is aimed at reducing patient distress, which has the potential to disrupt the foreign body and cause asphyxia. Either systemic ketamine or a gradual inhalation technique with sevoflurane can be used. Following induction, the aim is to keep the patient spontaneously breathing to prevent further dislodgement of the foreign body. If neuromuscular blockade is necessary, then adequate expiratory time is important to prevent barotrauma from a ball-valve effect of the foreign body. The peanut usually lodges in the right main bronchus; adequate oxygenation and ventilation are maintained via the left lung; when the peanut is being removed, however, it may detach from the forceps and obstruct the lumen of the trachea. If the peanut is not readily retrieved and the patient becomes increasingly hypoxic, the solution is to push the peanut distally back into the bronchus to relieve the tracheal obstruction. When significant manipulation takes place, postprocedural obstruction due to mucosal edema may occur; therefore, corticosteroids are often administered prophylactically.

Management of massive hemoptysis

Massive hemoptysis (>600 mL of blood/24 h) is a rare but life-threatening crisis. The immediate therapy involves correcting the hypoxia by placing a tracheal tube (preferably a double-lumen tracheal tube if the bleeding is from either the right or left lung) and administering 100% O₂. Intravenous fluid resuscitation is indicated to correct hypovolemia, if present. If the bleeding is from the trachea or proximal main bronchi, the tracheal tube can be withdrawn and replaced with a rigid ventilating bronchoscope to locate the source of bleeding, aspirate blood and clots, instill iced saline and vasoconstrictors, and, if necessary, place a bronchial blocker into the bronchus from which the blood is emanating. A jet ventilation technique would be inappropriate in this situation because dry gas under pressure will cause the blood to solidify, thus exacerbating the obstruction and hypoxemia.

Bronchoscopy management of central airway obstruction

Until recently, central airway obstruction was usually caused by a foreign body or massive hemoptysis. Now, intrinsic processes (intraluminal malignancy and strictures related to lung transplantation or intubation) or extrinsic processes (external compression by tumors) are providing challenging cases for therapeutic bronchoscopy. For urgent obstruction relief, laser ablation, electrocautery, argon plasma coagulation, and placement of airway stents (metal, silicone, and hybrid) are used. Cryotherapy, brachytherapy, and photodynamic therapy provide delayed relief of central airway obstruction. A FOB or a rigid bronchoscope can be used, depending on the planned procedure and skill and experience of the bronchoscopist. With the use of a rigid bronchoscope for relief of an obstruction of the trachea or major bronchi, an inhalation induction technique should be attempted, with a trial of positive-pressure ventilation used once the patient has been adequately anesthetized. The rigid bronchoscope is then introduced, and the patient’s nose and mouth packed. Obstruction of the airway due to necrotic tissue and excessive bleeding during treatment of the obstruction, most often with laser therapy, can precipitate hypoxia, requiring cessation of the procedure, administration of 100% O₂, and vigorous suction. During laser therapy, it is important to decrease the FIO₂ to 0.3 or less to minimize the possibility of airway fires. The anesthesia provider must communicate with the bronchoscopist if unable to maintain an SpO₂ of at least 90% with an FIO₂ to 0.3 or less; in this situation, the bronchoscopist should stop using the laser until oxygenation is improved and the FIO₂ is again decreased to 0.3 or less.

Both lasers and argon plasma coagulation technology involve the use of gas flow, which has the potential to lead to gas embolism, exacerbating hypoxemia and, in some instances, causing cardiac arrest. A review of patients undergoing rigid bronchoscopy under general anesthesia for airway-stent placement found a complication incidence of 19.8% and a 30-day mortality rate of 7.8%, which was correlated with the patients’ underlying health status and the urgency of the procedure.

Complications associated with bronchoscopy

A mortality rate of less than 0.1%, a rate of major complications of less than 1.5%, and a rate of minor complications of less than 6.5% have been reported with the use of bronchoscopy (Box 156-3). Significantly, 50% of complications are due to the premedication, the general anesthetic, or the local anesthetic agent used for the procedure. Because rigid bronchoscopy is usually carried out under total intravenous anesthesia, awareness is a recognized complication.

Bronchoscopy-induced hemodynamic changes increase myocardial O₂ demand in patients at risk of developing myocardial ischemia. Hypoxemia predisposes the patients to developing cardiac arrhythmias and ST-segment changes, whereas coronary artery disease, per se, does not increase the risk for developing arrhythmias. Hypoxemia and hypercarbia contribute greatly to the cardiovascular complications associated with bronchoscopy. Severe hypoxemia and hypercarbia may also result in seizures, but these are usually associated with local anesthetic toxicity.

Summary

The anesthesia provider is challenged during a bronchoscopic procedure because she or he must share the airway with the bronchoscopist. During bronchoscopy, the airway is always at risk for obstruction so the provider must remember, “A FOB is never an airway, whereas a rigid bronchoscope may be.” Complications of bronchoscopy, such as hypoxemia and hypercarbia, are common and can result in cardiovascular complications, even cardiopulmonary arrest. Because the airway is shared, so too are the complications shared between the anesthesia provider and the bronchoscopist. Communication, cooperation, vigilance, and attention to detail—especially to O₂ saturation and minute ventilation—improve outcomes.