Lung Isolation Techniques

Key Points

• Lung isolation should only be performed by well-trained and experienced practitioners who understand the significant risks and benefits of such techniques.

• Indications for lung isolation include protection of the healthy lung from contamination in the case of infection or hemorrhage; control of ventilation distribution; and bronchopulmonary lavage.

• Relative indications for lung separation are mainly for surgical exposure.

• Double-lumen tubes (DLTs) come in sizes 28, 32, 35, 37, 39, and 41 French, and the appropriate length is based on height, build, and airway examination. Positioning should be confirmed by flexible scope visualization, selective ventilation auscultation, or radiographic studies.

• DLTs are advantageous because they provide the capability of independent bilateral lung ventilation, bronchial suctioning, lung deflation, and stability, but they have the disadvantages of difficult tube placement, large size, rigidity, and difficulty in management for prolonged ventilation.

• For patients with difficult airways, anatomic anomalies, tracheal obstructions, tracheal-vascular distortions, or the need for segmental lung isolation, the use of one-lung ventilation (OLV) isolation devices should be strongly considered.

• Disadvantages of OLV isolation techniques include difficulty with lung deflation, difficulty suctioning the isolated lung, difficulty with stability and positioning, and inability to independently ventilate the isolated lung portion.

• Univent tubes are single-lumen tubes (SLTs) with an external bronchial blocker attachment; they can be used as an effective device for lung isolation, including large segmental-lobar isolation.

• Bronchial blockers come as stand-alone devices and can be used with SLTs or DLTs that have a low-volume, high-pressure cuff system; they may be used paraxially or axially for whole or segmental lung isolation.

• Pediatric lung isolation techniques are similar, if not identical, to those used for adults, although SLT techniques are often used. However, pediatric anatomy and physiology differ from those of adults in terms of positioning and ventilation.

• Successful lung isolation and protection are vastly improved with the use of a flexible scope.

Introduction

The physiology, indications, and techniques of lung isolation and one-lung ventilation (OLV) are discussed in this chapter. Lung isolation is most commonly used during thoracic, esophageal, and some cardiac procedures; however, it can often be useful and potentially lifesaving in other situations like massive hemoptysis. Modern disposable double-lumen tubes (DLTs), single-lumen tubes (SLTs) with built-in endobronchial blockers (Univent), new endobronchial blockers, and enhanced video technology are making lung isolation and OLV safer to perform. Knowledge of these topics is requisite for an anesthesia provider.

Physiology

The most common physiologic problem with OLV is the presence of a large intrapulmonary shunt through the collapsed nonventilated lung. This shunt may result in hypoxia with severe irreversible end-organ damage. Most anesthesia providers aim to maintain arterial oxygen saturation above 90% (Pa o ₂ >60 mm Hg because hemoglobin saturation and O ₂ content drop sharply below this value as a result of the characteristics of the O ₂ dissociation curve).

In most surgical cases patients are placed in lateral decubitus position with the ventilated lung dependent. The physiologic goal is to promote blood flow to the nonsurgical, dependent lung. By reducing the pulmonary vascular resistance (PVR) of the dependent lung to minimal levels, improved ventilation-perfusion (V/Q) matching may occur. Excess positive end-expiratory pressure (PEEP), high airway pressures, hypoxia, hypercapnia, and hypovolemia may contribute to an increase in PVR of the dependent lung, thereby increasing the shunt fraction. Improvement of the shunt fraction can be accomplished by decreasing the blood flow and/or supplying O ₂ to the nondependent lung.

Hypoxic pulmonary vasoconstriction is a powerful protective reflex that increases the PVR of the hypoxic alveoli and lung, thus diverting blood to the well-oxygenated areas of the lung. It is therefore useful to limit agents that inhibit hypoxic pulmonary vasoconstriction, such as nitrates and high concentrations of volatile agents.

The supplementation of O ₂ to the nondependent lung may also alleviate hypoxia. This can be accomplished via apneic oxygenation by the application of an external continuous positive airway pressure (CPAP) circuit to the nondependent lung or simply by trapping partial inflations of the nondependent lung. The goal is to allow enough O ₂ into the nondependent lung to reverse hypoxia while not obscuring the surgical field.

Indications for Lung Separation

The current indication for lung separation distinguished between lung isolation or lung separation. Lung isolation includes protecting and isolating the nondiseased lung from the pathology of the diseased lung to maintain adequate gas exchange. Lung isolation may be lifesaving by simply preventing drowning or severe contamination of the ventilated lung by the nondependent lung. Lung protection will prevent further deterioration of overall pulmonary function. As depicted in Box 26.1 , these cases include hemoptysis, empyema, or any contaminant in the noninvolved lung that can lead to severe atelectasis, pneumonia, sepsis, and inadequate ventilation. A large bronchopleural or bronchocutaneous fistula can lead to little or no ventilation. In this situation the decreased resistance to flow in the affected lung results in most of the positive-pressure ventilation (PPV) being directed toward the diseased lung. This results in minimally ventilating the normal lung and producing inadequate gas exchange. Conversely, a relatively noncompliant transplanted lung cannot compete with the better compliance of the native lung, and, as a result, the healthy transplanted lung can be severely underventilated. Another scenario involves a lung with bullous or cystic disease or a lung with tracheobronchial disruption. Tension pneumothorax or tension mediastinum could result during these scenarios from elevated airway pressures that are often observed with OLV in the lateral decubitus position.

Patients with alveolar proteinosis may require unilateral bronchopulmonary lavage, which involves multiple instillations of large fluid volumes into the target lung with subsequent drainage of the effluent fluid. Lung isolation and protection are mandatory to avoid lung cross-contamination and drowning caused by the large volume of fluid required to perform the lavage.

Lung separation involves facilitating surgical exposure by providing a still operating field, avoiding lung trauma, and improving gas exchange. Operations such as the repair of thoracic aneurysms, pneumonectomy, pulmonary lobectomies (especially of the upper lobe), video-assisted thoracoscopic surgery (VATS), esophageal surgery, and anterior spinal surgery all benefit from the optimized surgical exposure afforded by OLV (see Box 26.1 ). Lung protection further improves recovery by minimizing lung instrumentation and trauma to the nonventilated, nondependent lung. In cases of unilateral lung trauma, oxygenation and recovery may be optimized with OLV by improving V/Q matching.

Most procedures in which OLV is used are for lung separation, while only a few require isolation for lung protection. This distinction of lung isolation versus lung separation is important when selecting the method to provide OLV. In cases where lung protection is necessary, DLTs are preferable to endobronchial blockers (BB) because the low-pressure, high-volume cuff of the BB would not provide a protective seal to prevent contamination of the dependent lung. In addition, once the balloon of the blocker is deflated, the nondiseased lung is subjected to contamination from the pathology of the diseased lung. The use of blockers limits the ability for robust suctioning and removal of debris or thick pus before balloon deflation.

Techniques

Double-Lumen Tubes

Anatomy

DLTs are essentially two tubes bonded together with a design that allows each tube to ventilate a specified lung. DLTs are right-sided or left-sided devices. Left-sided DLTs have a bronchial port that extends into the left main stem bronchus and a tracheal port that is designed to sit above the carina. In right-sided DLTs the bronchial port extends into the right main stem bronchus, and the tracheal port sits above the carina. The cuff of the right-sided DLT may be at an oblique angle to facilitate ventilation of the right upper lobe bronchus at the Murphy eye ( Fig. 26.1 ).

The original DLTs were reusable, Robertshaw-design red rubber tubes with high-pressure cuffs that became stiff and brittle over time, making placement more difficult and traumatic. Modern DLTs are made of nontoxic polyvinyl chloride (the Z-79 marking) and are disposable ( Fig. 26.2 ). As the plastic warms up from the surrounding body temperature, the DLT conforms to the anatomy of the patient. This increased malleability, however, makes it more difficult to reposition the same tube. Current DLTs employ high-volume, low-pressure, color-coded cuffs. The bronchial cuff and its pilot balloon/connector are blue. The tracheal cuff and its pilot balloon/connector are clear or white. Cuff inflation pressure requires a balance between preserving an adequate seal and maintaining mucosal perfusion. Measured cuff pressures between 15 and 30 mm Hg achieve these goals. In cases involving the use of nitrous oxide the cuff pressures should be checked periodically as the nitrous oxide will diffuse into the cuff and increase the pressure in the balloon.

DLTs come in various French sizes, namely, 28, 32, 35, 37, 39, and 41. French equals approximately 0.33-mm measurement of the outer diameter (OD). In most adult men a 39- to 41-French DLT fits well, having an adequate length and appropriate diameter while providing the capability of suctioning or intubation with a fiberoptic bronchoscope (FB). A 35- to 37-French DLT fits most adult women. A 32-French will fit a small adult, while a 28-French will be adequate for an adolescent. A left-sided DLT size can also be estimated by using tracheal width measurements obtained from imaging. A radiopaque line may be seen at the end of each lumen to allow for radiographic positioning. A Y-adapter for the proximal end allows ventilation of both lumens through a single circuit. The cross-section of the DLT is designed as one D-shaped lumen and one crescent-shaped tracheal lumen. Left- and right-sided DLTs are curved at the distal end to enable advancement into the respective main stem bronchus. DLTs from different manufacturers have their own characteristic feel and slight modifications to the basic design described. The depth required for insertion of the DLT correlates with the height of the patient. For any adult 170 to 180 cm tall, the average depth for a left-sided DLT is 29 cm. For every 10-cm increase or decrease in height, the DLT is advanced or withdrawn 1.0 cm.

Advantages

When properly positioned, the DLT allows independent ventilation of each lung in unison or separately. This is a great advantage in cases in which each lung needs to be ventilated using different modalities. Treatment and prevention of desaturation are also easier with DLTs, because CPAP or partial lung inflation is easy to perform on the surgical lung while the opposite lung is ventilated normally. Suctioning and flexible bronchoscopy are facilitated by the relatively large luminal accesses into each main stem bronchus. Access beyond each main stem bronchus also allows for the egress of gases and lung deflation for surgical exposure. Other advantages include the solid structure and improved cuff seals of the DLTs, which prevent easy dislodgment after proper positioning and is the tube of choice for cases of lung isolation to prevent contamination from the diseased lung.

Disadvantages

The most significant disadvantages of the DLT are related to its bulky size and stiffness. Intubation with a DLT is often more difficult than with an SLT depending upon the mouth opening and the size of the tongue. Intubation is even more complex in patients with difficult airway anatomy. In cases of a distorted or compressed tracheobronchial tree the placement of a DLT may be impossible because of its size and rigidity. DLT size can contribute to airway damage during placement or when the device is left in place for a long period. Because of some difficulty managing DLTs in the intensive care unit (ICU) with regard to weaning and pulmonary toilet, they are often exchanged for SLTs. The process of exchanging a DLT for an SLT can be dangerous, especially after procedures in which airway edema and secretion accumulation has occurred. Although DLT lumens are relatively large, flexible bronchoscopy may be cumbersome because of the extended length of each tube and the narrowed crescent shape of the tracheal lumen. Multiple ports and connections further require a good working knowledge of the DLT anatomy to prevent errors in ventilation and management.

Novel Double-Lumen Tubes