Lung Separation Techniques
Andrew D. Shaw
Lung separation allows the anesthesiologist to provide one-lung ventilation (OLV) in patients undergoing lung resection surgery. It is also utilized to facilitate access to other thoracic structures such as the heart, the esophagus, mediastinal lymph nodes, the thoracic aorta, and the thoracic vertebrae.1,2 In addition to facilitating surgical exposure, lung separation is also indicated for prevention of contamination of the contralateral lung from bleeding, pus material, or saline lavage (in cases of hemoptysis, purulent drainage, and lung lavage, respectively), and to allow positive pressure ventilation and adequate gas exchange in the presence of a large bronchopleural fistula.
Two main techniques are used for lung separation. The first one involves a device made of disposable polyvinylchloride material, the double-lumen endotracheal tube (DLT).3 The DLT is a bifurcated tube with both an endotracheal and an endobronchial lumen and can be used to achieve isolation of either the right or left lung. The second technique involves blockade of a mainstem bronchus to allow lung collapse distal to the occlusion.4
This chapter reviews the insertion techniques and complications for both types of devices and will provide some practical recommendations for their safe and effective use.
Double-lumen endotracheal tubes (DLT) have been used in thoracic anesthesia for lung separation and one-lung ventilation (OLV) for more than 50 years, since the report of Carlens and Bjork in 1950.5 They provide excellent operating conditions when sized and placed correctly, and allow access to both ventilated and collapsed lungs for secretion clearance, independent ventilation, and bronchoscopic inspection. Today they are the commonest method of securing lung isolation and are available in sizes ranging from 26 to 41 F, with the Bronco-Cath DLT from Mallinckrodt being the most popular in North America. Other manufacturers include Argyle (Sheridan), Rusch and Portex. The Silbroncho, a newer DLT by Fuji Systems, is also available in a left-sided version only (Figure 5–1A). This device features a shorter, wire-reinforced endobronchial tip and a reduced bronchial cuff size.6 This design should provide a greater margin of safety, although its clinical effectiveness has not been reported.
Figure 5–1. A. The Silbroncho left-sided DLT. B. The Cliny right-sided DLT. Notice the long oblique bronchial cuff and the two ventilation slots for the right upper lobe (arrows). (Reproduced with permission from Campos J. Lung isolation. In: Slinger P., ed. Principles and Practice of Anesthesia for Thoracic Surgery. New York: Springer, 2011, p. 235. Copyright © Springer Science + Business Media, LLC 2011.)
Choices—Left or Right?
Traditionally, thoracic anesthesiologists would place a DLT on the side contralateral to the surgical procedure. However, before the advent of routine fiberoptic bronchoscopy, incorrect placement was common and lead to a high incidence of avoidable hypoxemia secondary to right upper lobe obstruction. In light of this, it became the norm to place a left-sided tube for all procedures except a left pneumonectomy or left-sided main bronchial sleeve resection. This practice has become widespread and is probably the most common policy in use today. Some practitioners even advocate that a left-sided tube be used for all procedures, and withdrawn into the trachea when necessary. It is true that a right-sided tube is harder to insert and place correctly, but it is also true that a well-placed right-sided tube makes surgery on the proximal left lung airways far easier. Indications for right-sided tube placement are summarized in Table 5–1.
There are important anatomic differences between the two main bronchi, and appreciation of these allows understanding of the problems one is likely to encounter when placing a DLT. The right main bronchus is shorter, arises from the carina at a more acute angle, and gives off the right upper lobe bronchus much earlier (ie, closer to the carina—usually at about 1.5-2 cm) than its left-sided equivalent. As a result, it is very easy to inadvertently occlude the right upper lobe with the bronchial portion of the tube and thus leave only the middle and lower lobes available for ventilation. There are some design features of right-sided tubes that reduce the chance of this happening, but they do not eliminate this problem entirely.
All the currently available right-sided DLT have an orifice cut through the bronchial portion of the tube, usually distal to the cuff, which may itself be offset (Figure 5–2). This is to permit ventilation of the right upper lobe (RUL), and ideally the orifice is placed directly opposite the right upper lobe bronchus. In practice this is difficult and most practitioners are happy if they can see the RUL bronchus through the orifice, as this usually permits good ventilation of the RUL during OLV. Newer designs attempt to facilitate positioning and ventilation of the RUL. An example is the right-sided DLT by Cliny (Create Medic Co. Ltd, Yokohama, Japan), which has a long bronchial cuff with two ventilation slots for the right upper lobe (Figure 5–1B). This device may prove useful in patients with a very short right mainstem bronchus.7
Figure 5–2. A. The Sheridan right-sided DLT. B. The Mallinckrodt right-sided DLT.
In about 1 in 250 patients a porcine bronchus will be encountered.8 Here, the right upper lobe bronchus originates directly from the trachea, usually within 2 cm of the carina, but sometimes as much as 6 cm. In this situation, a right-sided tube necessarily occludes the RUL, and a left-sided tube is preferable.
Much has been written about the best size DLT to use, and how best to make the selection. In general, most female patients will be well served with a 37-F size, and most male patients with a 39 F. This is of course an oversimplification, but is not a bad starting point. When considering whether to vary from this policy, patient height is more important than weight as it better predicts tracheal length, which is the prime determinant of whether a tube of a given size provides effective lung isolation. Tubes that are too small cause far more trouble than tubes that are too large, because the problems they cause do not declare themselves until the case is well underway and lung isolation unsatisfactory. A tube that is too large will not fit, a situation that declares itself much earlier in the case, when there is still time to correct the problem. Tubes that are too small do not sit well in the main bronchus, require higher cuff volumes (the bronchial cuffs are not designed to contain more than 3 mL of air) and become dislodged easily. This leads to repeated attempts to improve their position, disruption to the surgery, repeated need for bronchoscopy, and repeated interruptions to ventilation. A correctly sized tube passes smoothly through the glottis and comes to rest at a distance of approximately 29 cm from the incisors in both men and women. In one study performed in adult cadavers, it was shown that the cricoid ring diameter never exceeds the diameter of the glottis. Thus, if a DLT encounters resistance when passing the glottis, it is likely that the DLT would also encounter resistance while passing the cricoid ring.9
Most of the published literature focuses on the left-sided DLT in part because the right-sided DLT is used less commonly. There are reports of complications related to the use of an undersized DLT. A tension pneumothorax and pneumomediastinum occurred after the endobronchial tip of an undersized DLT had migrated too far into the left lower bronchus, and the whole tidal volume was delivered into a single lobe.10 Smaller DLTs also provide more resistance to gas flow and will develop more auto-positive end-expiratory pressure when compared with larger DLTs.11 Airway-related complications have similarly been reported with the use of undersized left-sided DLTs.12
Brodsky et al13 reported that measurement of the tracheal diameter at the level of the clavicle on the preoperative posteroanterior chest radiograph can be used to determine the proper left-sided DLT size. This approach lead to the use of larger left-sided DLTs (ie, 41 F in men and 39 F in women). However, a study involving Asian patients by Chow et al14 using the same method found this approach less reliable. In their study, Chow et al found that the overall positive predictive value for the correct size of a left-sided DLT was 77% for men and 45% for women. Therefore, this method may be less useful in patients of smaller stature such as women and people of Asian descent.
Amar et al15 have shown that the use of a smaller DLT (35-F left-sided) was not associated with any difference in clinical intraoperative outcomes, regardless of patient size or gender. However, in their study, of the 35% of patients who received a DLT, 92 (65%) were female. In practice, many women will usually receive a 35-F DLT anyway; therefore the question of whether or not a 35 F for all patients is favorable remains unclear.
A different alternative that has been suggested in order to predict the proper size of a right-sided or left-sided DLT is a three-dimensional image reconstruction of tracheobronchial anatomy generated from spiral computed tomography (CT) scans combined with superimposed transparencies of DLTs.16 This is unlikely to become an everyday habit however, because of the time required to generate the 3D images, and the fact that most of the time a 37- or 39-F tube will suffice.
Taken as a group, these studies suggest that chest radiographs and CT scans may be valuable tools for selection of the correct DLT size. As such these images should certainly be reviewed before placement of a DLT as they will alert the operator to the presence of abnormal anatomy. In addition, the preoperative CT scan will provide the distance to the epidural space should an epidural catheter be part of the anesthetic plan.
DLT Insertion Technique
Double-lumen tubes may be placed “blind” or using a fiberoptic bronchoscope. In the blind technique the DLT is introduced into the glottis during direct laryngoscopy. The tip is passed through the glottis with the tip pointing anteriorly and the entire tube then turned 90 degrees to the left (for a left-sided DLT) or right (for a right-sided DLT) after the endobronchial cuff has passed beyond the vocal cords. The DLT is then advanced further into the trachea until the depth of insertion at the teeth is approximately 29 cm (for patients who are at least 170 cm tall).17 Rotating the patient’s head slightly to the opposite side as the tube is advanced into its final position helps the tip of the DLT find the correct main bronchus. Correct location may then be confirmed using a fiberoptic bronchoscope—see the following pages for details.
The second technique employs fiberoptic bronchoscopy, where the tip of the endobronchial lumen is guided into position bronchoscopically after the DLT passes the vocal cords. A study by Boucek et al18 compared the blind technique with the fiberoptic technique and showed that of the 32 patients who underwent the blind technique, primary success occurred in 30 patients. In contrast, in the 27 patients receiving the bronchoscopy-guided technique, primary success was achieved only in 21 patients and eventual success in 25 patients. This study also showed that the time spent placing a DLT was an average of 88 seconds for the blind technique and 181 seconds for the fiberoptic method. Although both methods resulted in successful placement in the majority of patients, more time was required when the fiberoptic technique was used. Figure 5–3 shows both the blind technique and the fiberoptic technique for placement of a left-sided DLT. The most important aspect of the fiberoptic technique is to confirm visualization of the trifurcation of the RUL bronchus from the right main bronchus—there is no other place in the tracheobronchial tree where this image is seen, and it therefore confirms that the position is correct. Figure 5–4A and B illustrates the optimal position of a right- and left-sided DLT, respectively, together with the bronchoscopic views that should be obtained in each case.
Figure 5–3. A. The blind method technique for placement of a left-sided DLT. The endobronchial lumen is in an anterior position during initial insertion (left figure); the DLT is then passed through the glottic opening using direct laryngoscopy and rotated 90 degrees to the left (center figure); the DLT is finally advanced until moderate resistance is felt, indicating the endobronchial lumen of the DLT has entered the bronchus (right figure). (Reproduced with permission from Campos JH.68) B. The fiberoptic bronchoscopy guidance technique for placement of a left-sided DLT. The DLT is inserted into the trachea using direct laryngoscopy (left figure). The fiberoptic bronchoscope is then inserted through the endobronchial lumen and the tracheal carina and the left main stem bronchus visualized (center figure). The DLT is rotated 90 degrees to the left and, with the aid of the fiberoptic bronchoscope; the tube is advanced to the optimal position into the left main stem bronchus (right figure). (Reproduced with permission from Campos JH.68)
Figure 5–4. A. Optimal position of a right-sided DLT. Insert A shows the take-off of the right-upper lobe bronchus with its three segments (apical, anterior and posterior) as seen when the fiberoptic bronchoscope emerges from the opening slot located in the endobronchial lumen of the DLT. Insert B shows an unobstructed bronchoscopic view of the entrance of the left mainstem bronchus when the fiberscope is passed through the tracheal lumen of the DLT and the edge of the fully inflated endobronchial cuff is positioned below the tracheal carina in the right mainstem bronchus. (Reproduced with permission from Campos JH.67) B. Optimal position of a left-sided DLT. Insert (a) shows an unobstructed bronchoscopic view of the entrance of the right mainstem bronchus when the fiberscope is passed through the tracheal lumen of the DLT and the edge of the fully inflated endobronchial cuff is below the tracheal carina in the left mainstem bronchus. Insert (b) shows the take-off of the right-upper lobe bronchus with its three segments (apical, anterior and posterior); this landmark should be used to reconfirm the location of the right bronchus. Insert (c) shows an unobstructed bronchoscopic view of the left-upper and left-lower bronchi when the fiberoptic bronchoscope is advanced through the endobronchial lumen of the DLT. (Reproduced with permission from Campos JH.67)
With either technique, the final position will be confirmed fiberoptically prior to surgery commencing. This is best performed immediately after tube placement and again once the patient is placed in the lateral position for surgery. Tubes often migrate out during patient positioning, and often a small degree of neck flexion will replace the tip of the bronchial lumen into its correct location. Ideally, the blue edge of the bronchial cuff will be visible in the main bronchus when it is inflated and in good position. The bronchial cuff is unlike the tracheal cuff and is not designed to minimize inflation pressure. It is essential therefore that the bronchial cuff is not overinflated as all this will do is increase the pressure applied to the bronchial mucosa and increase the risk of an ischemic lesion.
Problems and Complications
The most common problems and complications arising from the use of DLTs are incorrect placement and damage to the airways. A malpositioned DLT does not permit collapse of the operative lung, and may partially collapse the ventilated or dependent lung, producing hypoxemia. A common cause of malposition is dislodgement of the endobronchial cuff because of overinflation, surgical manipulation of the bronchus, or extension of the head and neck during or after patient positioning.19
Airway trauma and damage to the membranous part of the trachea or main bronchus continue to be associated with the use of DLTs.12,20 This complication can develop at any time the DLT is in position or during extubation.21–23 A 25-year review of the literature by Fitzmaurice and Brodsky24 found that most airway injuries were associated with undersized DLTs, particularly in women who received a 35- or 37-F disposable DLT. It is likely that airway damage occurs when an undersized DLT migrates distally into the bronchus and the main tracheal body of the DLT comes into contact with the bronchus, producing lacerations or rupture of the airway. Airway damage during the use of DLTs can present as unexpected air leaks, subcutaneous emphysema, and massive airway bleeding into the lumen of the DLT, or protrusion of the endotracheal or endobronchial cuff into the surgical field.
Another serious problem that may occur is the development of tension pneumothorax in the dependent, ventilated lung.25,26 This complication is particularly important to detect promptly as the treatment is immediate decompression of the non-operative-side pneumothorax. This can be achieved either directly, across the mediastinum, or by turning the patient and placing a cannula through the chest wall. If the diagnosis is wrong however, the patient now has an extra pneumothorax and chest tube to deal with postoperatively. We routinely place an esophageal stethoscope (a regular stethoscope attached to an esophageal temperature probe) and confirm auscultation of breath sounds during OLV in order to either confirm or rule this diagnosis out whenever it is suspected.
Less serious complications with the use of the DLT have been reported by Knoll et al.27 In their comparative study between the DLT and the endobronchial blocker, the development of postoperative hoarseness occurred significantly more commonly in the DLT group when compared to the endobronchial blocker group; however, the incidence of bronchial injuries was comparable between groups.