Lung Isolation in Patients With a Difficult Airway in Thoracic Anesthesia

Introduction

One-lung ventilation (OLV) in the thoracic surgical patient who presents with a difficult airway can be achieved with the use of a single-lumen endotracheal tube with a bronchial blocker or with the use of a double-lumen endotracheal tube (DLT). It is estimated that between 5% and 8% of the patients who presented for thoracic surgery for primary lung carcinoma also have carcinoma of the pharynx, usually in the epiglottic area. Many of these patients have undergone extensive surgery of the airway or neck. In addition, some of these patients had previous radiation to the neck or previous airway surgery, such as hemi-mandibulectomy or hemi-glossectomy, making intubation difficult in general, and particularly for achievement of OLV because of distorted upper airway anatomy. The distorted anatomy can be located at or beyond the tracheal carina, such as descending thoracic aortic aneurysm compressing the left mainstem bronchus or an intrabronchial or extrabronchial tumor near the tracheobronchial bifurcation that make the insertion of a left-sided DLT difficult or impossible.

Preoperative Assessment of the Difficult Airway

An airway is termed difficult when conventional laryngoscopy reveals a class III view (just the epiglottis is seen) or class IV view (just part of the soft palate is seen). Fig. 17.1 displays the airway anatomy and class III and IV according to the modified Mallampati classification. Once the airway is recognized as being potentially difficult, a careful examination of the patient should follow. Previous anesthesia records, if available, should be examined for a history of airway management of the patient. Patients should be asked to open their mouths as wide as possible and extend their tongues. The length of the submental space should also be noted. Patients should be evaluated from side to side to assess any degree of maxillary overbite and their ability to assume the sniffing position. Also the patency of the nostrils must be assessed in patients who cannot open their mouths because a nasotracheal approach might be considered. For patients who have a tracheostomy in place, the inlet of the stoma and the circumferential diameter must be assessed when considering replacing the tracheostomy cannula with the device selected to achieve OLV. Furthermore, depending on the type and the length of surgery, the degree of fluid shift during surgery, an airway that initially was not classified as difficult may become difficult secondary to airway edema, the presence of secretion, and laryngeal trauma from the initial intubation. In addition, 10% of the patients who can be intubated with a single lumen tube can be difficult to insert a DLT into depending on the degree of the mouth opening, the size of the tongue and the composition of the teeth.

Another group of patients considered to have a difficult airway during OLV are those who have distorted anatomy from compression or intraluminal tumor at the orifice of the mainstem bronchus. Such anomalies can be recognized by reviewing chest radiographs and multidetector computed tomography scans to determine the main stem bronchus diameter and anatomy to exclude the presence of distortion or compression. In some cases, the use of flexible fiberoptic bronchoscopy will be necessary to evaluate the degree of distorted anatomy of the airway before the selection of a specific device to achieve OLV. Box 17.1 displays the patients at risk of potentially having difficult intubation during OLV.