1 What are the indications for lung isolation?

There are five areas for which lung isolation may be required:

1. Thoracic surgery

Lung surgery: Thoracoscopy, lobectomy, pneumonectomy, lung transplantation, lung volume reduction

Bronchial surgery: Intraluminal tumors, bronchopleural fistula

Pleural surgery: Pleurectomy, pleurodesis, decortication

2. Surgery on the great vessels, heart, and pericardium

Heart: Via thoracotomy (as opposed to sternotomy) approach

Thoracic aorta: Descending aortic aneurysm

Pulmonary artery: Rupture, embolectomy

Pericardium: Pericardiectomy, pericardial window

2 How can lung isolation be achieved while maintaining one-lung ventilation?

There are two basic techniques:

3 How do you choose the appropriate size double-lumen endotracheal tube?

There are right and left DLTs to account for the anatomic differences between the right and left main stem bronchi. Most commonly left-sided tubes are used. The optimal tube size for a particular patient is the largest tube that will pass atraumatically through the glottis, advance down the trachea, and fit in the bronchus with a small air leak detectable when the cuff is deflated. Using the largest possible tube is associated with the least airway resistance and ensures that a bronchial seal is obtained with small cuff volumes. A DLT that is too small requires a large endobronchial cuff volume, which may result in cuff herniation across the carina. Many anesthesiologists select 41-Fr and 39-Fr DLTs for tall and short men, respectively, and 39-Fr and 35- to 37-Fr DLTs for tall and short women, respectively. There is considerable variation in left main stem bronchi diameters and a relatively weak predictive value of gender and height. Other alternatives to predict the size of the optimal DLT are to measure the patient’s trachea and left or right main stem bronchus diameters from preoperative radiologic studies such as chest x-ray films and computed tomography scans (Table 71-1).

TABLE 71-1 Conversion Measurements of Tracheal Width Based on Chest X-Ray and Bronchial Diameter Measurements*

CXR, Chest x-ray; DLT, double-lumen endotracheal tube.

* Bronchial diameter measurements based on computed tomography scan of the chest and the predicted left-sided double lumen endotracheal tube size.

Data from Brodsky JB, Macario A, Mark JBD: Tracheal diameter predicts double-lumen tube size: a method for selecting left double-lumen tubes, Anesth Analg 82:861–864, 1996; and Hannallah M, et al: Evaluation of an approach to choosing a left double-lumen tube based on chest computed tomography scan measurement of left mainstem bronchial diameter, J Cardiothorac Vasc Anesth 11:168–171, 1997.

4 How is the right main stem bronchus different from the left and how does this affect right-sided double-lumen endotracheal tube design?

The adult trachea is 11 to 13 cm long and begins at the level of the cricoid cartilage (C6) and bifurcates behind the sternomanubrial joint (T5). The main differences between the right and left main stem bronchi include the following:

The wider right bronchus diverges away from the trachea at a 25-degree angle, whereas the left bronchus diverges at a 45-degree angle.

The right bronchus has upper, middle, and lower lobe branches, whereas the left bronchus divides into only upper and lower lobe branches.

The orifice of the right upper lobe bronchus from the carina is 15 mm in women and 20 mm in men, whereas that of the left upper lobe is 50 mm from the carina.

Therefore right-sided DLTs must have a slit in the bronchial cuff for ventilating the right upper lobe. It is more difficult to correctly position a right-sided DLT because of anatomic variations between individuals in the distance between the right upper lobe orifice and the carina, often resulting in difficulties ventilating the right upper lobe (Figure 71-1).

Figure 71-1 A, Double lumen endotracheal tube correctly positioned in the left main bronchus. B, Double lumen endotracheal tube correctly positioned in the right main bronchus but notice the position of the bronchial cuff on the endotracheal tube and the right upper lobe bronchus take off.

5 Describe the placement and positioning of double-lumen endotracheal tubes

Using laryngoscopy, the DLT is passed with the distal curvature concave anteriorly and is rotated 90 degrees toward the side of the bronchus to be intubated after the tip passes the larynx. There are then two options to position the tube: auscultation or flexible fiber-optic bronchoscopy (FOB). With the auscultation method, the DLT is blindly advanced until resistance is felt as the endobronchial lumen enters the bronchus. The endobronchial and tracheal cuffs may then be inflated, and the lumens clamped in turn while auscultating the chest. However, auscultation alone is often unreliable for proper DLT placement.

Ovassapian (1996) described a reliable and reproducible method of placing DLTs on the first attempt. This technique requires advancing the tube only into the tracheal lumen. The FOB is then placed through the endobronchial lumen and advanced until the carina and main stem bronchi are identified. The FOB is then advanced into the appropriate bronchus and, using the FOB as a stylet, the DLT is slid over the FOB until its bronchial lumen comes into view just beyond the tip of the FOB. When positioning a right-sided DLT, it must be ensured that the endobronchial cuff does not block the right upper lobe orifice. Finally the FOB is passed through the tracheal lumen of the DLT to check for a carinal or subcarinal position of the bronchial cuff and ensure patency of the opposite main stem bronchus.

6 What complications may be caused by double-lumen endotracheal tubes?

Malposition: Most often occurs when a patient is turned from the supine to the lateral position. Usually there is cephalad movement of the DLT by 1 cm. Malposition can be avoided by maintaining the head in a neutral position with folded blankets to avoid flexion and extension. After repositioning, the FOB should be used to confirm that the DLT is still in good position.

Airway trauma: Inflation of the bronchial cuff beyond its resting cuff volume may result in high cuff pressures and bronchial rupture. The cuff volume depends on the size of the DLT. In a randomized, prospective controlled trial postoperative hoarseness and vocal cord lesions were significantly more frequent in patients intubated with a DLT compared to when an endobronchial blocker was used to achieve lung isolation. There was no difference in the incidence of bronchial injuries between the two groups.

Other complications: Include stapling the endobronchial lumen in the bronchus during pneumonectomy (an argument for placing right-sided DLT for left pneumonectomy) and right upper lobe collapse when using right-sided DLTs.

7 Name three methods of bronchial blockade

8 Describe the Univent tube

A Univent tube is a single-lumen tube with an incorporated channel for the bronchial blocker that can be used to block the left or right bronchus. The internal diameter of the Univent ranges from 3.5 to 9 mm, but the enclosed channel of the bronchial blocker makes the outer diameter larger than that of a standard endotracheal tube of the same internal size. The bronchial blocker catheter has a small internal lumen that can be used as a suction channel.

9 What are the advantages of using a Univent tube?

Since the shape of the Univent tube is similar to that of a standard endotracheal tube, it is useful in patients who have difficult airways for direct laryngoscopy. It may be used during awake fiber-optic intubation. Other features of the Univent tube are its efficiency as a selective lobar blocker and its ability to be used as a regular endotracheal tube without the need to exchange the tube if postoperative mechanical ventilation is contemplated.

10 What are the advantages of a double-lumen endotracheal tube?

DLTs are the best device for achieving absolute lung separation (e.g., bronchopulmonary lavage or presence of contamination of the other lung with massive bleeding or pus when a large suction lumen is needed). Although double-lumen tubes may be placed slightly more quickly than bronchial blockers (median times DLT 6.1 minutes, Univent 6.7 minutes, and Arndt blocker 8.6 minutes), there is no difference between DLTs and bronchial blockers in the success rate of accurate positioning by anesthesiologists with limited experience in thoracic anesthesia. The most critical factor in the successful placement of any lung isolation device is knowledge of endoscopic bronchial anatomy.

11 Describe the placement and positioning of a Univent tube

Before use the bronchial blocker is lubricated to facilitate passage down the side channel. After the bronchial cuff is tested, the blocker is retracted, and standard endotracheal tube placement is performed. Once the tube is in the trachea, the bronchial blocker is advanced into the appropriate main stem bronchus under direct view of the FOB, which has been passed down the main lumen of the Univent tube. The optimal position of the bronchial blocker when fully inflated (6 to 8 ml of air) in the left main bronchus is when the inflated bronchial cuff is seen with the FOB 5 mm down the left main stem bronchus without any detectable air leak. For a right-sided bronchial blocker, the optimal position is when the cuff is seen above the origin of the right upper bronchus, with no leaks detectable when the cuff is inflated. (Check the Vitaid website for videos demonstrating Univent tube placement.)

12 What complications can occur with the Univent tube?

There are two serious complications with improper use of the Univent tube:

13 Describe the wire-guided endobronchial blocker

The adult wire-guided endobronchial blocker (WEB) is a 9-Fr catheter that is available in 65- and 78-cm lengths. It has a small internal lumen measuring 1.4 mm in diameter, which contains a flexible wire that passes through the proximal end of the catheter, where it exits as a flexible wire loop. The wire loop allows the FOB and catheter to be coupled while they are guided into position. The WEB comes with a three-way multiport airway adapter, where the WEB, the FOB, and the anesthesia breathing circuit can be connected to the standard endotracheal tube. The smallest endotracheal tube that can accommodate both the WEB and an FOB is 7.0. After positioning the WEB, the wire guide is removed to convert the 1.4-mm channel into a suction port. However, once the wire is removed, it cannot be reinserted through the channel to allow repositioning of the catheter. There is a pediatric WEB that is a 5-Fr catheter, available in 50- or 65-cm lengths and 2.5 mm in diameter. When used with a 2.5-mm FOB, the pediatric WEB may be passed through a 5.0 endotracheal tube. (Check out the Cook website for links to videos and lectures on the WEB.)

14 What are the advantages of the wire-guided endobronchial blocker?

Like the Univent tube, the WEB can be used for selective lobar blockade. It is particularly useful in critically ill patients who are already intubated and ventilated who require single-lung ventilation. It is also useful in patients with difficult airways who can undergo awake fiber-optic intubation with a standard endotracheal tube followed by placement of the WEB. A final advantage is that the WEB may be used with patients who are nasally intubated.

15 How can the Fogarty embolectomy catheter be used as a bronchial blocker?

The most commonly used Fogarty catheter in adults is 8 Fr. The catheter comes with a wire stylet that can be curved at the distal end to facilitate guidance to the target bronchus. The Fogarty catheter is passed through the standard endotracheal tube and guided into position using the FOB. An advantage of Fogarty catheters is that they can be passed through standard single-lumen endotracheal tubes, including pediatric sizes. A disadvantage is the lack of a hollow center so suction or oxygen insufflation is not possible and lung collapse takes longer because it is by absorption atelectasis.

16 What tubes or bronchial blockers would you select for single-lung ventilation in children and adults?

See Table 71-2.

17 What are the standard ventilator settings for one-lung ventilation?

Most anesthesiologists use approximately the same tidal volume for one-lung ventilation as for two-lung ventilation—typically around 10 ml/kg. Higher tidal volumes increase airway pressures and vascular resistance, which may cause more blood flow to the nonventilated lung and more shunting. Lower tidal volumes may allow more atelectasis in the ventilated lung. The fractional concentration of oxygen in inspired gas (FiO₂) will usually be 0.8 to 1.0, giving the greatest margin of safety against hypoxia. The respiratory rate is adjusted to maintain a normal PaCO₂.

18 Which volatile anesthetic agent would you use for single-lung ventilation?

Comparisons of desflurane and sevoflurane with isoflurane during single-lung ventilation demonstrated that the choice of volatile anesthetic does not significantly influence arterial oxygenation.

19 What pulmonary changes occur with one-lung ventilation?

Most thoracic surgery is performed in the lateral decubitus position. When ventilation is interrupted to the nondependent (operative) lung, a right-to-left shunt is created as blood flow continues to the now unventilated lung. However, several factors decrease the blood flow to the nondependent lung and therefore decrease this shunt:

Gravity favors blood flow to the ventilated-dependent lung.

Surgical compression and retraction decrease blood flow to the nondependent lung. The surgeon may also ligate the blood supply to the nondependent lung.

Hypoxic pulmonary vasoconstriction (HPV)—hypoxia is a powerful stimulus for pulmonary vascular constriction (the opposite of its systemic effect). Factors that inhibit HPV will worsen the right-to-left shunt; they include hypocapnia and nitrovasodilators.

20 How should you manage hypoxia during one-lung ventilation?

During one-lung ventilation the change in PaO₂ is usually greater than PaCO₂ because of the greater diffusibility of CO₂. When the patient begins to desaturate on one-lung ventilation, a sequence of actions should happen:

Increase the FiO₂ to 1.0.

Optimize tidal volumes and peak inspiratory pressures.

Use the FOB to check your tube/blocker position.

Add about 5 cm H₂O pressure of continuous positive airway pressure (CPAP) to the nondependent lung. This supplies oxygen to some of the alveoli that are perfused in the nondependent lung, therefore decreasing shunt.

Consider adding 5 cm H₂O pressure of positive end-expiratory pressure (PEEP) to the dependent lung. This will help recruit any parts of the dependent lung that have developed atelectasis. However, be careful as the PEEP may have a negative effect by increasing vascular resistance in the dependent lung, causing more blood flow to the nondependent lung, thereby increasing shunt.

If severe hypoxia continues, alert the surgeon. The surgeon may be able to help by ligating or clamping the pulmonary artery to the nondependent lung, thus eliminating the shunt. Alternatively, consider a return to two-lung ventilation.