Endobronchial Ultrasound

Endobronchial ultrasound (EBUS) is a technique that uses ultrasound along with bronchoscopy to visualize the airway wall and structures adjacent to it. The clinical application and diagnostic benefit of EBUS have been established in many studies. EBUS has been incorporated into routine practice in many centers because of its high diagnostic value and low risk. It allows real-time guidance of transbronchial needle aspiration (TBNA) of mediastinal and hilar structures and parabronchial lung masses. As use of EBUS and EBUS-TBNA continues to grow, ongoing education in advanced bronchoscopic procedures is necessary to guarantee competency and successful patient outcomes. ^{[1, 2, 3, 4, 5, 6, 7]}

Two types of EBUS exist: radial probe EBUS (RP-EBUS) and convex probe EBUS (CP-EBUS). Physicians should have knowledge of mediastinal lymph node stations and sonographic anatomy of the airway wall. The endobronchial ultrasound image visualizes distinct layers of the bronchial wall with mucosa, submucosa, endochondrium, cartilage, perichondrium, connective tissue, and adventitia. The mucosa, endochondrium, perichondrial layer, and adventitia are hyperechoic, while the submucosa, cartilage, and connective tissue appear hypoechoic.

Patients should not eat or drink at least 6 hrs before the procedure, and the patient may need to discontinue blood thinning medications several days before the procedure. 

Indications

Staging of non-small cell lung cancer (NSCLC)

EBUS-guided transbronchial needle aspiration (TBNA) has higher diagnostic yield than conventional TBNA in all lymph node stations except subcarinal lymph nodes in determining the lymph node involvement in NSCLC. ^[8] Its ability to precisely visualize the airway wall invasion helps to categorize the tumor (T) component of staging and surgical resection planning. ^[9] It can be combined with endoscopic ultrasound-guided fine-needle aspiration to near complete sampling of mediastinum using a single endobronchial ultrasound bronchoscope. ^[10] It can also be used to restage lung cancer in the mediastinum. ^[11]  A 22- or 21-gauge EBUS needle is recommended for lung cancer diagnosis and staging. ^[12]  In cases in which additional sample tissue is needed, a 19-gauge needle may provide an increased diagnostic yield. ^{[13, 14]}

In a study of 209 patients who underwent sampling of hilar/mediastinal lymph nodes for the diagnosis/staging of lung cancer (99 EBUS-TBNA vs 110 c-TBNA), EBUS-TBNA was found to have significantly better results than conventional TBNA in terms of diagnostic accuracy (94.2% vs 89.7%), sample adequacy (70.3% vs 42%), and sensitivity (93% vs 86.4%) for lymph nodes < 2 cm. There were no significant differences in diagnostic accuracy, adequacy, and sensitivity for lymph nodes ≥2 cm. ^[15]

Evaluation of mediastinal lesions, intrapulmonary pulmonary nodules, and endobronchial lesions

EBUS can visualize and allow physicians to sample and diagnose various mediastinal abnormalities, ^[16] including sarcoidosis ^{[17, 18, 19, 20]} and mediastinal lymphoma. ^{[21, 22, 23, 24]} It can characterize the intraparenchymal and endobronchial lesions and help to determine the likelihood of malignancy based on appearance. EBUS-TBNA can visualize and allow sampling of pulmonary nodules that are not visualized by fluoroscopy and may avert the need for surgical procedures. ^[25] RP-EBUS is a relatively accurate tool in the investigation of peripheral pulmonary lesions. ^[26]

Guidance of endobronchial therapy

EBUS can provide useful additional information during nterventions such as resection of endobronchial lesions, stricture dilatation, stenting, laser therapy, and argon plasma coagulation. ^[27]

Contraindications

Contraindications to endobronchial ultrasound (EBUS) are similar to contraindications to flexible bronchoscopy and include following:

• Life-threatening cardiac arrhythmias

• Current or recent myocardial ischemia

• Poorly controlled heart failure

• Severe hypoxemia

• Uncooperative patient

Additional contraindications to EBUS-TBNA are related to bleeding risk and include following:

• Current antiplatelet agents ^[28]

• Current anticoagulant therapy

• Coagulopathy

• Thrombocytopenia

• Elevated blood urea nitrogen or serum creatinine

Preparation

Anesthesia

EBUS is usually performed under procedural sedation and local anesthesia. Local anesthesia on airways is done by nebulizing 1% or 2% lidocaine and spraying lidocaine spray in the posterior pharynx. A 1-2 mL of 1% to 2% lidocaine can be installed through the working channel of bronchoscope during insertion and procedure, if needed. EBUS can be done under general anesthesia. The use of a laryngeal mask airway allows access to upper paratracheal nodes, which may not be accessible with an endotracheal tube in place. The size of the endotracheal tube should be at least No. 8 or larger, to accommodate the CP-EBUS bronchoscope. The patient should be NPO for at least 6 hours.

Equipment

RP-EBUS probe

The RP-EBUS probe has an ultrasound processor and a balloon catheter attached to it. The balloon is fixed at the tip of the probe. If overinflation or excessive pressure occurs, the balloon slips from the tip and a small amount of water is released from the balloon to prevent balloon rupture. The 20 MHz miniature radial probe is the standard probe. The 30 MHz miniature radial probe provides a more detailed image of the airway wall and surrounding structures. These 2 probes have a diameter of 2.5 mm; therefore, a flexible bronchoscope with a working channel of 2.8 mm is required to use it. The 20 MHz ultra-miniature radial probe has a smaller diameter than either miniature radial probe, so it can be inserted through the 2 mm working channel of a bronchoscope and can extend further into subsegmental bronchi than the miniature radial probe.

CP-EBUS bronchoscope

The CP-EBUS bronchoscope has a linear curved-array ultrasonic transducer of 7.5 MHz at the distal tip, which has the capability of displaying B-mode and color Doppler mode. ^[29]

The field of view is 80 degrees, and the direction of view is 35 degrees forward oblique. The outer diameter of the bronchoscope is 6.2 mm, and the inner channel diameter is 2 mm. The dedicated 22-gauge needle has an echogenic dimpled tip to enhance visibility by ultrasound. The maximum extruding stroke is 40 mm with a safety mechanism that stops at 20 mm. The needle has an internal sheath that prevents contamination of samples by bronchial wall tissue.

Positioning

EBUS is usually performed with the patient in the supine position, with the operator standing at the head of the bed. The bronchoscopist should have a clear view ofthe  monitor.

The monitoring devices are placed on the patient, supplemental oxygen is administered by nasal cannula, and intravenous access is established before starting the procedure. The patient's eyes should be covered so as to prevent splashing of normal saline, secretions, or blood into the eyes. Conventional bronchoscopy with a working channel of at least 2.8 mm is required for RP-EBUS. When the bronchoscope is in the airway and around the target lesion, the radial probe is placed in a catheter sheath and inserted through the working channel of the bronchoscope. The probe is positioned at the target level, and the balloon is filled with water until it has achieved firm contact with the airway. A complete circular image of the airway wall and surrounding structures is obtained once the balloon has firm contact with the airway wall. RP-EBUS provides a 360-degree image of the airway wall and its surrounding structures.

If the patient is unable to tolerate complete obstruction of the airway, the balloon can be partially filled and applied to the airway wall in a semicircular manner.

Sequential TBNA

Sequential TBNA is defined as the localization of a lesion, followed by sampling of the lesion. When the target lesion is identified, the radial probe is removed from the working channel of the bronchoscope, and the TBNA needle is introduced. Sequential TBNA can also be used to localize and sample intraparenchymal lesions. The probe should be introduced using a catheter with an extended working channel and placed precisely on the lesion. With the guide sheath in position, the radial probe is removed and a biopsy forceps or brush is used to sample the lesion through the guide sheath. It can also be combined with a virtual bronchoscopic navigation system. ^[30]

CP-EBUS

Convex probe EBUS (CP-EBUS) is usually performed orally, because the ultrasound probe prevents use of the nasal route. The image quality of CP-EBUS is lower than that of regular bronchoscopy. A disposable latex balloon is attached to the ultrasound probe. The tip of the bronchoscope should be positioned anteriorly while passing it through the vocal cords to prevent the EBUS bronchoscope from sticking to the posterior part of the vocal cords. Once in the airway, a syringe filled with sterile water is attached to the balloon channel of the scope, and the balloon is filled with water to achieve contact with the airways.

The lymph nodes should be differentiated from vascular structures, which are also hypoechoic. Doppler ultrasound accurately differentiates lymph nodes from vascular structures. All mediastinal lymph node stations should be evaluated systematically. The subcarinal lymph node can be visualized either from the right main or left main bronchus. The bronchoscopic and ultrasound views can be toggled alternatively, or a 2-screen display can be used for simultaneous viewing. The tip should be flexed up for and ultrasound image and down for an endoscopic image. The ultrasound image can be frozen, allowing lesions to be measured.

Real-time TBNA

Real-time TBNA is defined as simultaneous sonographic visualization and sampling of the lesion. Once the target lesion is identified, the dedicated needle is inserted through the working channel of the bronchoscope and fastened to it. The tip of the bronchoscope should be in neutral position to allow the sheath to come out of the distal end of the working channel. The needle should remain within the catheter during passage through the working channel in order to prevent damaging the bronchoscope. Once the catheter emerges from the bronchoscope, the needle is advanced from the catheter and locked into position. The insertion point of the needle is localized and then pushed through the bronchial wall into the target lymph node under direct ultrasound visualization.

With the needle in the target lymph node, the internal sheath is removed. This cleans the lumen of the needle system, which usually becomes contaminated with bronchial cells. Suction is applied using a 20-mL syringe, and the catheter is moved back and forth. Suction is released, and the needle is pulled back into the flexible catheter. The entire transbronchial needle system is then removed from the bronchoscope in a single, smooth motion. The tissue core is then removed from the needle lumen by reinserting the internal sheath.

The number of needle aspirations per site can impact the yield and can range from 3 to 7 aspirations, depending on the study, but the first pass has the highest yield. ^{[31, 32]} If the TBNA is being done for staging of NSCLC, the sampling should be started from N3, followed by N2 and N1 lymph nodes, to avoid contamination and upstaging.

EBUS and EBUS-TBNA are usually safe procedures. In a systematic review of effectiveness and safety, no serious complications were found for CP-EBUS-TBNA of regional lymph nodes. ^[33] Reported complications have included agitation, sore throat, cough, hypoxia, laryngeal injury, fever, bacteremia and infection, bleeding, pneumothorax, and broken equipment becoming stuck in the airway. Mediastinal abscess has also been reported. Complications related to upper airway local anesthesia are laryngospasm, laryngeal edema, bronchospasm, methemoglobinemia, and cardiac arrhythmias. ^[34] Complications attributable to procedural sedation are respiratory depression, cardiovascular instability, vomiting, and aspiration.

If the lung is punctured, an air leak (pneumothorax) can occur and cause collapse of the lung.

Following completion of the procedure, the bronchoscope should be disinfected and hung upright to prevent the accumulation of moisture.

Specimen preparation

Aspirated specimen is smeared onto glass slides and air dried, so that an on-site cytopathologist can evaluate the specimen. The use of rapid on-site evaluation significantly improves the diagnostic yield of transbronchial aspiration, ^[35]  and it is a cost-effective approach. ^[36] It helps avoid the need for additional biopsies without loss in diagnostic yield and reduces the complication rate associated with bronchoscopy. ^{[37, 38]}  

Monitoring

Cardiac rhythm, heart rate, respiratory rate, oxyhemoglobin saturation, and blood pressure are continuously monitored after the procedure until the effects of sedation and upper airway anesthesia wear off. The patient should be monitored closely for 2-4 hours after the test. Eating and drinking can be resumed once the gag reflex returns. A chest radiograph should be performed following the procedure to look for any complications, such as pneumothorax. Outpatients must have stable vital signs and be alert and oriented with baseline ambulation status before discharge.

Patient education

A family member or friend must be available to drive or accompany the patient home. The patient may have a mild sore throat, hoarseness, cough, or fever following the procedure. If, after being discharged, the patient experiences increasing chest pain or shortness of breath or coughs up more than a few tablespoons of blood, he or she should contact the physician immediately.