**2. Considerations for One-Lung Ventilation (OLV)**

Thoracic Surgery poses unique challenges to the anesthesiologist, including surgery in the lateral decubitus position, an open thorax, manipulation of thoracic organs, potential for major bleeding, and, unique among all potential surgery scenarios, the need for lung isolation.

#### **2.1. Physiologic effects of lung isolation**

Successful lung isolation (one-lung ventilation, OLV) requires the management of oxygena‐ tion, ventilation, and pulmonary blood flow. Remarkably, OLV decreases total minute ventilation minimally. In fact, it has been shown that the non-isolated lung receives close to the same minute ventilation as ventilation to two lungs. The rate of CO2 elimination undergoes minimal changes because CO2 is readily diffusible and has no plateau in its dissociation curve.

When a patient is placed on OLV, inevitably a shunt is developed. The non-dependent lung is no longer being ventilated but is still perfused, resulting in a right to left shunt. When this occurs, the pulmonary system has physiological adaptations to decrease this shunt. Given that the patient is in the lateral decubitus position, one of the responses is a decrease in blood flow to the non-dependent lung due to gravitational forces. These effects are significant because the pulmonary system has a much lower blood pressure than the systemic circulation. Another adaptation is hypoxic pulmonary vasoconstriction of the vascular supply in the non-depend‐ ent lung. Hypoxic pulmonary vasoconstriction is a physiological phenomenon in which pulmonary arteries constrict in the presence of hypoxia (unlike the systemic circulation), redirecting blood flow to the dependent lung. Surgical compression of the non-dependent lung can also serve as a way of decreasing shunt as the pulmonary vasculature is compressed. One last factor contributing to a decrease in shunt fraction is apneic oxygenation—residual oxygen in the non-dependent isolated lung diffusing into the pulmonary circulation. All these factors combined allow for better oxygenation during OLV.

testing with maximal oxygen consumption. Climbing five flights of stairs approximates a VO2 max value of >20 ml/kg/min and less than one flight is associated with values <10 ml/kg/ min (S9). Ventilation-perfusion (V/Q) scintigraphy can also be used as a preoperative assess‐ ment when pulmonary resection is to be undertaken. This modality is particularly helpful for patients undergoing pneumonectomy or any patient with a ppoFEV1 less than 40% [2].

Anesthesia for Thoracic Surgical Procedures http://dx.doi.org/10.5772/56104 5

Slinger et al. proposed a "3-legged" stool of pre-thoracotomy respiratory assessment, which encompasses the prior mentioned pre-operative tests [7]. This model summarizes the results of those tests and reveals that patients have lower expected post-operative morbidity if they have a ppoFEV1 > 40%, cardio-pulmonary reserve with a VO2 max >15 ml/kg/min, and lung parenchymal function with a ppoDLCO >40%. These three tests are the most valid for preoperative assessment. Other tests that can be used are maximal volume ventilation (MVV), residual volume/total lung capacity (RV/TLC), and forced vital capacity (FVC), but these are less valid for respiratory mechanics. Stair climbing (two flights), a 6-minute walk, and measurement in the change in SpO2 (<4%) during exercise are other tests that can be used to measure cardio-pulmonary reserve. Measurement of arterial blood gas values can also serve as a respiratory assessment; indicators of good prognosis are PaO2 > 60 and a PaCO2 < 45.

In regards to post-thoracotomy anesthetic management, Slinger et al. devised an algorithm derived from pre-operative assessment using ppoFEV1 [7]. If the patient's ppoFEV1 is > 40% and the patient is awake, alert, warm, and comfortable, immediate postoperative extubation is recommended. If the ppoFEV1 is between 30-40%, extubation should be considered based on exercise tolerance, DLCO, V/Q scan, and associated diseases. If the ppoFEV1 < 30%, staged weaning from mechanical ventilation is recommended. However, when the patient has a functioning thoracic epidural catheter providing adequate analgesia, extubation may be

Knowledge of tracheo-bronchial anatomy is important for achieving and maintaining proper lung isolation. Other chapters in this text describe lung and bronchial anatomy in detail. Features of the anatomy that are relevant to anesthetic considerations are presented here.

A critical landmark when placing lung isolation devices is the primary carina, where the trachea splits into two main bronchi. The diversion angle differs between these main bronchi, with the right bronchi angled at 25 degrees and the left bronchus at 45 degrees. Because of the steeper angle of diversion of the right main bronchus, foreign bodies (including lung isolation devices) are more likely to travel into this bronchus. Left and right side double lumen tubes (DLTs) are designed with curvatures to accommodate left or right main bronchi diversion

Because of the steeper angle of the right mainstem bronchus, it is not uncommon to inadver‐ tently intubate the right mainstem when intending to intubate the left mainstem with a DLT (using blind or non fiberoptic guided placement techniques). Operators unfamiliar with distal bronchial anatomy sometimes confuse secondary carinas with the primary carina. For example, the right main bronchus divides at the secondary carina into the upper lobar

angles to make intubation into the specified main bronchi easier (Figure 1).

attempted even at ppoFEV1 values as low as 20% [7].

**2.3. Tracheo-bronchial anatomy for lung isolation**

#### **2.2. Preoperative anesthetic evaluation of the thoracic surgery patient**

Patients undergoing OLV should undergo a perioperative assessment of their respiratory function that includes testing of lung mechanical function, pulmonary parenchymal function, andcardiopulmonaryreserve.Thebest assessmentofrespiratoryfunctioncomes fromahistory of the patient's quality of life [1]. It is useful to think of respiratory function in three related but independent areas:respiratorymechanics,gas exchange, andcardio-respiratoryinteraction[2].

The most valid test for perioperative assessment of respiratory mechanics is the predicted postoperative forced expiratory volume in one second (ppoFEV1). This test is the best at predicting post thoracotomy respiratory complications [3].

Percentage of predicted postoperative (ppo) FEV1 after lobectomy is given by

*ppoFEV* 1= *preoperative FEV* 1 *x No*. *of segments remaining total No*. *of segments*

Nakahara et al found that patients with a ppoFEV1 of more than 40% had no or only minor post resection respiratory complications [4]. Major respiratory complications were only seen in the sub group with ppoFEV1 < 40%; post-operative mechanical ventilator support was seen in those < 30%.

For the assessment of lung parenchymal function, the most useful test of the gas exchange capacity is the diffusing capacity for carbon monoxide (DLCO). This test correlates with the total functioning surface of the alveolar-capillary interface. The DLCO is used to calculate a post resection value using the same calculation as FEV1. A ppoDLCO less than 40% of predicted correlates with increased cardiac and respiratory complications and is relatively independent of the FEV1 [5].

Stair climbing is the most traditional test of respiratory function in the assessment of cardio‐ pulmonary interaction. Ability to climb three flights or more is closely associated with a decrease in morbidity and mortality. The ability to climb fewer than two flights is associated with a very high risk [6]. The "gold standard" for assessment is formal laboratory exercise testing with maximal oxygen consumption. Climbing five flights of stairs approximates a VO2 max value of >20 ml/kg/min and less than one flight is associated with values <10 ml/kg/ min (S9). Ventilation-perfusion (V/Q) scintigraphy can also be used as a preoperative assess‐ ment when pulmonary resection is to be undertaken. This modality is particularly helpful for patients undergoing pneumonectomy or any patient with a ppoFEV1 less than 40% [2].

Slinger et al. proposed a "3-legged" stool of pre-thoracotomy respiratory assessment, which encompasses the prior mentioned pre-operative tests [7]. This model summarizes the results of those tests and reveals that patients have lower expected post-operative morbidity if they have a ppoFEV1 > 40%, cardio-pulmonary reserve with a VO2 max >15 ml/kg/min, and lung parenchymal function with a ppoDLCO >40%. These three tests are the most valid for preoperative assessment. Other tests that can be used are maximal volume ventilation (MVV), residual volume/total lung capacity (RV/TLC), and forced vital capacity (FVC), but these are less valid for respiratory mechanics. Stair climbing (two flights), a 6-minute walk, and measurement in the change in SpO2 (<4%) during exercise are other tests that can be used to measure cardio-pulmonary reserve. Measurement of arterial blood gas values can also serve as a respiratory assessment; indicators of good prognosis are PaO2 > 60 and a PaCO2 < 45.

In regards to post-thoracotomy anesthetic management, Slinger et al. devised an algorithm derived from pre-operative assessment using ppoFEV1 [7]. If the patient's ppoFEV1 is > 40% and the patient is awake, alert, warm, and comfortable, immediate postoperative extubation is recommended. If the ppoFEV1 is between 30-40%, extubation should be considered based on exercise tolerance, DLCO, V/Q scan, and associated diseases. If the ppoFEV1 < 30%, staged weaning from mechanical ventilation is recommended. However, when the patient has a functioning thoracic epidural catheter providing adequate analgesia, extubation may be attempted even at ppoFEV1 values as low as 20% [7].

#### **2.3. Tracheo-bronchial anatomy for lung isolation**

When a patient is placed on OLV, inevitably a shunt is developed. The non-dependent lung is no longer being ventilated but is still perfused, resulting in a right to left shunt. When this occurs, the pulmonary system has physiological adaptations to decrease this shunt. Given that the patient is in the lateral decubitus position, one of the responses is a decrease in blood flow to the non-dependent lung due to gravitational forces. These effects are significant because the pulmonary system has a much lower blood pressure than the systemic circulation. Another adaptation is hypoxic pulmonary vasoconstriction of the vascular supply in the non-depend‐ ent lung. Hypoxic pulmonary vasoconstriction is a physiological phenomenon in which pulmonary arteries constrict in the presence of hypoxia (unlike the systemic circulation), redirecting blood flow to the dependent lung. Surgical compression of the non-dependent lung can also serve as a way of decreasing shunt as the pulmonary vasculature is compressed. One last factor contributing to a decrease in shunt fraction is apneic oxygenation—residual oxygen in the non-dependent isolated lung diffusing into the pulmonary circulation. All these factors

Patients undergoing OLV should undergo a perioperative assessment of their respiratory function that includes testing of lung mechanical function, pulmonary parenchymal function, andcardiopulmonaryreserve.Thebest assessmentofrespiratoryfunctioncomes fromahistory of the patient's quality of life [1]. It is useful to think of respiratory function in three related but independent areas:respiratorymechanics,gas exchange, andcardio-respiratoryinteraction[2]. The most valid test for perioperative assessment of respiratory mechanics is the predicted postoperative forced expiratory volume in one second (ppoFEV1). This test is the best at predicting

combined allow for better oxygenation during OLV.

4 Principles and Practice of Cardiothoracic Surgery

post thoracotomy respiratory complications [3].

*ppoFEV* 1= *preoperative FEV* 1 *x*

independent of the FEV1 [5].

in those < 30%.

**2.2. Preoperative anesthetic evaluation of the thoracic surgery patient**

Percentage of predicted postoperative (ppo) FEV1 after lobectomy is given by

*No*. *of segments remaining total No*. *of segments*

Nakahara et al found that patients with a ppoFEV1 of more than 40% had no or only minor post resection respiratory complications [4]. Major respiratory complications were only seen in the sub group with ppoFEV1 < 40%; post-operative mechanical ventilator support was seen

For the assessment of lung parenchymal function, the most useful test of the gas exchange capacity is the diffusing capacity for carbon monoxide (DLCO). This test correlates with the total functioning surface of the alveolar-capillary interface. The DLCO is used to calculate a post resection value using the same calculation as FEV1. A ppoDLCO less than 40% of predicted correlates with increased cardiac and respiratory complications and is relatively

Stair climbing is the most traditional test of respiratory function in the assessment of cardio‐ pulmonary interaction. Ability to climb three flights or more is closely associated with a decrease in morbidity and mortality. The ability to climb fewer than two flights is associated with a very high risk [6]. The "gold standard" for assessment is formal laboratory exercise

Knowledge of tracheo-bronchial anatomy is important for achieving and maintaining proper lung isolation. Other chapters in this text describe lung and bronchial anatomy in detail. Features of the anatomy that are relevant to anesthetic considerations are presented here.

A critical landmark when placing lung isolation devices is the primary carina, where the trachea splits into two main bronchi. The diversion angle differs between these main bronchi, with the right bronchi angled at 25 degrees and the left bronchus at 45 degrees. Because of the steeper angle of diversion of the right main bronchus, foreign bodies (including lung isolation devices) are more likely to travel into this bronchus. Left and right side double lumen tubes (DLTs) are designed with curvatures to accommodate left or right main bronchi diversion angles to make intubation into the specified main bronchi easier (Figure 1).

Because of the steeper angle of the right mainstem bronchus, it is not uncommon to inadver‐ tently intubate the right mainstem when intending to intubate the left mainstem with a DLT (using blind or non fiberoptic guided placement techniques). Operators unfamiliar with distal bronchial anatomy sometimes confuse secondary carinas with the primary carina. For example, the right main bronchus divides at the secondary carina into the upper lobar

*2.5.1. DLT*

isolation.

*2.5.2. SLT with bronchial blocker*

*2.5.3. Mainstem intubation*

(MLTs), may be required.

**2.6. Difficult airway and lung isolation**

The standard device for providing lung isolation is the DLT. It provides reliable lung isolation, offers the ability to suction both lungs, allows for bilateral differential lung ventilation with minimal device manipulation, and allows for simple procedures such as bronchoalveolar lavage. DLTs range in size from 28 to 41 Fr. Posteroanterior (PA) chest x-ray is the standard method for sizing comparison between DLT, trachea, and bronchial diameter [9]. However, patient sex, age, and height are commonly used to choose DLT size. As discussed above, DLTs are made in right-side and left-side conformations to accommodate the differences in the

Anesthesia for Thoracic Surgical Procedures http://dx.doi.org/10.5772/56104 7

Bronchial blockers used with conventional single lumen tubes have advantages in difficult airways, in patients with indwelling endotracheal or tracheostomy tubes, in patients who are nasally intubated with SLTs, and in cases where sub-segmental blockade may be required [10]. Bronchial blockers have several disadvantages, however. They are easier to displace and provide limited suction and drainage to the isolated lung, which may lead to an accumulation of pus, blood or secretions [11]. They are deployed in the operative lung, which may interfere with the surgical procedure, and the device must be repositioned for contralateral lung

Despite their specific enhancements, bronchial blockers are essentially modeled after vascular embolization catheters (albeit with high compliance low pressure cuffs and a deflation port). They are manufactured as separate units or units integrated with an endotracheal tube. Separate units include the Cohen Flexi-tip BB (Cook Critical Care), Fuji Uni-blocker (Fuji Systems, Tokyo) (Figure 2A) and the Arndt wire-guided BB (Cook Critical Care, Bloomington, IN) (Figure 2B). An example of an integrated unit is the Univent tube (Fuji Systems, Tokyo).

Mainstem bronchial intubation with an SLT may be used for lung isolation in emergent scenarios or in pediatric cases. However, with this method, exhalation of the operative lung is limited, airway protection at the vocal cords is compromised, and the endotracheal tube tip is advanced into the operative lung; lastly, repositioning is required if contralateral isolation is needed. Furthermore, standard endotracheal tubes may be too short to effectively mainstem intubate either main bronchi; specialized longer tubes, such as Micro Laryngoscopy Tubes

*Campos* describes two categories of patients at risk for difficult intubation during OLV: those with complications related to the upper airway and those related to the lower airway [12]. The former include a short neck and increased neck circumference, prominent upper incisors with a receding mandible, limited cervical mobility, limited jaw opening due to previous surgery, radiation therapy of the neck, previous hemiglossectomy or hemimandibulectomy, and

anatomy of the right and left main bronchi (i.e., the right upper lobe branch).

**Figure 1.** Left (top) and right (bottom) conformations of double lumen tubes. Note the right upper lobe ventilation lumen on the right conformation tube.

bronchus and bronchus intermedius; this secondary carina may be mistaken for the primary carina when viewed under bronchoscopy. Therefore, knowledge of distal bronchial anatomy is fundamental in confirming correct placement as well as in correcting misplacement.

Knowledge of distal bronchial anatomy is essential for additional reasons. First, the operator must recognize that a right DLT has an additional slot to allow for ventilation of the right upper lobe and must place it at the correct depth and rotational alignment to assure adequate ventilation of all three lobes. Secondly, anatomy is abnormal in a small percentage of patients. For example, in up to 2% of patients, the right bronchus originates directly from the supra carinal trachea (a so-called bronchus suis) [8]. Abnormal anatomy is also seen in patients who have had previous lung surgeries. The operator must be able to recognize and respond to abnormal anatomy by selecting the appropriate device to provide effect lung isolation in any scenario.

#### **2.4. Indications for lung isolation**

Patient pathology and/or operative requirements determine the indication for OLV. Patients with lung pathology may need lung protection. For example, OLV may be used to protect the unaffected lung from contamination with pus or blood from the affected lung. Alternatively, OLV may be used to provide differential lung ventilation to minimize volutrauma and barotrauma to the affected lung while optimizing ventilation to the non-affected lung. Certain operative scenarios require OLV. Because it optimizes visualization of the operative site, OLV is absolutely indicated in closed procedures (for example, thoracoscopic surgery) but is also useful in open procedures to maximize exposure.

#### **2.5. Lung isolation devices**

Three standard methods for lung isolation include DLT, bronchial blockers, and mainstem intubation.

### *2.5.1. DLT*

bronchus and bronchus intermedius; this secondary carina may be mistaken for the primary carina when viewed under bronchoscopy. Therefore, knowledge of distal bronchial anatomy is fundamental in confirming correct placement as well as in correcting misplacement.

**Figure 1.** Left (top) and right (bottom) conformations of double lumen tubes. Note the right upper lobe ventilation

Knowledge of distal bronchial anatomy is essential for additional reasons. First, the operator must recognize that a right DLT has an additional slot to allow for ventilation of the right upper lobe and must place it at the correct depth and rotational alignment to assure adequate ventilation of all three lobes. Secondly, anatomy is abnormal in a small percentage of patients. For example, in up to 2% of patients, the right bronchus originates directly from the supra carinal trachea (a so-called bronchus suis) [8]. Abnormal anatomy is also seen in patients who have had previous lung surgeries. The operator must be able to recognize and respond to abnormal anatomy by selecting the appropriate device to provide effect lung isolation in any

Patient pathology and/or operative requirements determine the indication for OLV. Patients with lung pathology may need lung protection. For example, OLV may be used to protect the unaffected lung from contamination with pus or blood from the affected lung. Alternatively, OLV may be used to provide differential lung ventilation to minimize volutrauma and barotrauma to the affected lung while optimizing ventilation to the non-affected lung. Certain operative scenarios require OLV. Because it optimizes visualization of the operative site, OLV is absolutely indicated in closed procedures (for example, thoracoscopic surgery) but is also

Three standard methods for lung isolation include DLT, bronchial blockers, and mainstem

scenario.

**2.4. Indications for lung isolation**

lumen on the right conformation tube.

6 Principles and Practice of Cardiothoracic Surgery

**2.5. Lung isolation devices**

intubation.

useful in open procedures to maximize exposure.

The standard device for providing lung isolation is the DLT. It provides reliable lung isolation, offers the ability to suction both lungs, allows for bilateral differential lung ventilation with minimal device manipulation, and allows for simple procedures such as bronchoalveolar lavage. DLTs range in size from 28 to 41 Fr. Posteroanterior (PA) chest x-ray is the standard method for sizing comparison between DLT, trachea, and bronchial diameter [9]. However, patient sex, age, and height are commonly used to choose DLT size. As discussed above, DLTs are made in right-side and left-side conformations to accommodate the differences in the anatomy of the right and left main bronchi (i.e., the right upper lobe branch).

#### *2.5.2. SLT with bronchial blocker*

Bronchial blockers used with conventional single lumen tubes have advantages in difficult airways, in patients with indwelling endotracheal or tracheostomy tubes, in patients who are nasally intubated with SLTs, and in cases where sub-segmental blockade may be required [10]. Bronchial blockers have several disadvantages, however. They are easier to displace and provide limited suction and drainage to the isolated lung, which may lead to an accumulation of pus, blood or secretions [11]. They are deployed in the operative lung, which may interfere with the surgical procedure, and the device must be repositioned for contralateral lung isolation.

Despite their specific enhancements, bronchial blockers are essentially modeled after vascular embolization catheters (albeit with high compliance low pressure cuffs and a deflation port). They are manufactured as separate units or units integrated with an endotracheal tube. Separate units include the Cohen Flexi-tip BB (Cook Critical Care), Fuji Uni-blocker (Fuji Systems, Tokyo) (Figure 2A) and the Arndt wire-guided BB (Cook Critical Care, Bloomington, IN) (Figure 2B). An example of an integrated unit is the Univent tube (Fuji Systems, Tokyo).

#### *2.5.3. Mainstem intubation*

Mainstem bronchial intubation with an SLT may be used for lung isolation in emergent scenarios or in pediatric cases. However, with this method, exhalation of the operative lung is limited, airway protection at the vocal cords is compromised, and the endotracheal tube tip is advanced into the operative lung; lastly, repositioning is required if contralateral isolation is needed. Furthermore, standard endotracheal tubes may be too short to effectively mainstem intubate either main bronchi; specialized longer tubes, such as Micro Laryngoscopy Tubes (MLTs), may be required.

#### **2.6. Difficult airway and lung isolation**

*Campos* describes two categories of patients at risk for difficult intubation during OLV: those with complications related to the upper airway and those related to the lower airway [12]. The former include a short neck and increased neck circumference, prominent upper incisors with a receding mandible, limited cervical mobility, limited jaw opening due to previous surgery, radiation therapy of the neck, previous hemiglossectomy or hemimandibulectomy, and

sequentially clamp the tracheal and bronchial inflow limbs of the DLT and auscultate the chest. Absent breath sounds corresponding to the tracheal or bronchial lumen clamped, should be confirmed. Different malposition scenarios may be deduced depending on type of DLT (L v. R), intended mainstem to be intubated, DLT lumen occluded and the absence or presence of breath sounds. Although auscultation is an important tool in situations where fiberoptic bronchoscopy is unavailable, studies have shown a large margin of positioning error when it is not used [15-18]. Fiberoptic confirmation is required for proper positioning of bronchial blockers because they lack basic ergonomic design features that enable blind placement (like curvature or specialized ventilation port configurations of DLTs). Furthermore, because malpositioned lung isolation devices may be potentially be fatal, and auscultation is usually not an option intraoperatively, fiberoptic bronchoscopy has become the standard for proper

Anesthesia for Thoracic Surgical Procedures http://dx.doi.org/10.5772/56104 9

For thoracic surgery, the incidence of pulmonary complications now out-numbers that of cardiovascular complications [19], and pulmonary complications are the most common cause of postoperative death in esophageal cancer patients [20]. Injury from one-lung ventilation (OLV) can manifest as re-expansion pulmonary edema (REPE), acute lung injury (ALI), or acute respiratory distress syndrome (ARDS). While late causes of ALI (3-10 days after surgery) are secondary to bronchopneumonia or aspiration, early ALI is predicted by high intraoper‐ ative ventilation pressures, increased surgery duration, excessive intravenous volume replacement, pneumonectomy, and preoperative alcohol abuse [21]. Most likely, a combina‐ tion of a patient's health status, intraoperative fluid management, the use of epidural analgesia, inflammatory responses due to surgical manipulation, alveolar recruitment, and reexpansion/ reperfusion lung injury [22, 23] underlie the development of ALI following OLV [24]. While chronic patient risk factors are difficult to modify, protective ventilatory strategies and

Prior ventilatory schemes focused on the detrimental effects of atelectasis, primarily increased pulmonary shunt via local alveolar hypoxia and hyperoxia. Tidal volumes of 10-12mL/kg were advocated, as it was previously held that tidal volumes <8mL/kg resulted in decreased functional residual capacity (FRC) and worsening atelectasis in the dependent lung. The lowest positive end-expiratory pressure (PEEP) for acceptable oxygenation and normal arterial CO2 levels (35 to 38 mmHg) were suggested [24]. OLV was achieved with parameters similar to two-lung ventilation, with consequent stimulation of stretch-activated cation channels, oxygen-derived free radicals, activated neutrophils, and cytokine upregulation contributing

The current strategy to minimize OLV-associated lung injury utilizes so-called lung protective ventilation. Overdistension (volutrauma), excessive transpulmonary pressure resulting in barotrauma, repeated opening and closing of alveoli resulting in ateletotrauma, and biotrauma

placement and maintenance of lung isolation devices.

**3.1. Ventilator strategies for one-lung ventilation**

judicious fluid use may decrease the incidence of ALI [21].

to increased microvascular-alveolar permeability [25].

**3. Intraoperative care for the thoracic surgical patient**

**Figure 2.** Examples of bronchial blockers. (A) Fuji Uni-blocker (Fuji Systems, Tokyo); (B) Arndt wire-guided BB (Cook Critical Care, Bloomington, IN).

tumors of the upper airway. Lower airway risk factors include an existing tracheotomy, a distorted tracheobronchial anatomy, and compression at the entrance of the left mainstem bronchus. Patients with any of the above conditions might pose a difficulty for lung isolation with a conventional DLT and might be candidates for SLT placement with subsequent lung isolation with a bronchial blocker. However, if a DLT is indicated, fiberoptic intubation may be used to facilitate placement [13]. However, because of the long length of the DLT, it is difficult to maintain distal control of the fiberscope, especially with patients having longer oral to vocal cord distance. Additionally, the small diameter bronchoscope required (to assure fit for the DLT) results in an inferior view and restricts suction capabilities. Therefore, new generation indirect laryngoscopes may be preferable. Indirect laryngoscopes (e.g., CMAC [Storz, Tuttlingen, Germany], GlideScope [Verathon,Bothell, WA], Airtraq (Prodol Meditec S.A., Vizcaya, Spain)) improve airway grade and have been shown to improve the ease of intubation with DLTs in patients with difficult airways [14].

#### **2.7. Confirming proper lung isolation**

Regardless of the device used for lung isolation, the anesthesiologist must confirm correct placement of the device. Chest auscultation has traditionally been used to confirm correct DLT placement. The process is straightforward in patients with normal pulmonary anatomy. First, inflate both tracheal and bronchial balloons and auscultate to confirm bilateral breath sounds (if bilateral breath sounds are absent, suspect malposition – the DLT may be too deep). Next, sequentially clamp the tracheal and bronchial inflow limbs of the DLT and auscultate the chest. Absent breath sounds corresponding to the tracheal or bronchial lumen clamped, should be confirmed. Different malposition scenarios may be deduced depending on type of DLT (L v. R), intended mainstem to be intubated, DLT lumen occluded and the absence or presence of breath sounds. Although auscultation is an important tool in situations where fiberoptic bronchoscopy is unavailable, studies have shown a large margin of positioning error when it is not used [15-18]. Fiberoptic confirmation is required for proper positioning of bronchial blockers because they lack basic ergonomic design features that enable blind placement (like curvature or specialized ventilation port configurations of DLTs). Furthermore, because malpositioned lung isolation devices may be potentially be fatal, and auscultation is usually not an option intraoperatively, fiberoptic bronchoscopy has become the standard for proper placement and maintenance of lung isolation devices.
