Lung Ventilation – Indications, Contraindications

Single lung ventilation, also known as ‘One Lung’ ventilation, is a method of ventilation which was first conceptualized by physiologists Eduard Pflüger and Claude Bernard who studied gas exchange in dogs using a lung isolation catheter.[rx] Wolffberg isolated the two lungs using the catheter in 1871 which is the first reported concept of an endobronchial single-lumen tube. The first instance of clinical use in humans was by Loewy and von Schrotter with lower lobe bronchus catheterized under fluoroscopic control. Head designed the first double-lumen tube in 1889 which had two tracheal cannulas – one short tracheal and one longer endobronchial one. Gale and Walters in 1932 advanced Head’s design and created the prototype for the modern-day double-lumen tubes. Double lumen tubes paved the way for one-lung ventilation offering better control of ventilation and more efficient separation of the two lungs.

Single lung ventilation involves ventilating one lung and letting the other collapse for providing surgical exposure in the thoracic? cavity or isolating ventilation to one lung. The protective role of the single lung ventilation involves protecting one lung from the ill effects of fluid from the other lung – which may be blood, lavage fluid, malignant? or purulent secretions. Thus it is prudent to ensure perfect placement of the tube as a misplaced tube defeats the goals of lung isolation or differential ventilation. This is ensured by bronchoscopy done after tube placement and after any position changes thereafter. One lung ventilation is used to facilitate a wide variety of procedures on ipsilateral thoracic or mediastinal structures as well as to provide lung isolation; this is made possible by the use of double-lumen tubes, bronchial blockers, and endobronchial tubes. Familiarity with the use of these instruments and the physiology of one-lung ventilation is essential to the performance of safe anesthesia.

Anatomy and Physiology

A good understanding of airway anatomy and the tracheobronchial tree is essential to performing safe one-lung ventilation. The fiberoptic bronchoscopy enables a good visualization of the airway anatomy. The first branching point in the airway is the carina – which marks the bifurcation of the trachea into the two mainstem bronchi at the level of the sternal angle – left and right main bronchus. The trachea is about 10 to 13 cm long and has 12 concentric cartilaginous rings. These rings are deficient in their posterior aspect and thus for C-shaped rings as seen on a cross-section. The trachea divides in an area known as the carina which marks the division into left and right main bronchus.

The left main bronchus (LMB) continues for about 5 cms after which it branches into left lower lobe bronchus (LLLB) and left upper lobe bronchus (LULB). The right main bronchus (RMB) is shorter than the left side, but it is also wider and more vertical than the left side. The right main bronchus gives off the right upper lobe bronchus and then continues further as the bronchus intermedius. The take-off of the right upper lobe bronchus is about 2.0cm in adult men and about 1.6 cm in adult females. A knowledge of tracheal anatomy helps the anesthesiologist to position the double-lumen tube for selectively isolating one lung for ventilation. This anatomy must undergo careful observation once the double-lumen tube is in place and the fiberoptic scope is inserted to check the cuff position and verify correct tube placement.

Indications

The indications of single-lung ventilation aim at facilitating surgical exposure by isolating the lung away from the field of surgery or preventing further lung trauma by providing selective ventilation as well as preventing infection? or secretions from entering the healthy lung.

Surgical Exposure

• Video-assisted thoracoscopic surgery including pneumonectomy, wedge resections
• Pulmonary resections including pneumectomies and lobectomies
• Mediastinal surgery
• Thoracic? vascular surgery
• Esophageal surgery
• Spine surgery

Lung Isolation

For protective isolation:

• Massive pulmonary hemorrhage
• Infection?/purulent secretions

For control of ventilation:

• Tracheobronchial trauma
• Broncho-pleural/Broncho-cutaneous fistula

Contraindications

These are some of the relative contraindications for single lung ventilation.

• Patient unable to tolerate OLV/Dependence on bilateral ventilation
• Intraluminal airway masses (making DLT placement difficult)
• Hemodynamic instability
• Severe hypoxia
• Severe COPD
• Severe pulmonary hypertension?
• Known or suspected difficult intubation

Equipment

Single lung ventilation is achieved with the use of special airway devices such as double-lumen tubes (DLT) and bronchial blockers (BB) which selectively direct the airflow to one lung. They are used to collapse one lung selectively for surgery on the ipsilateral side.

• Double Lumen Tubes: The most common design of the double-lumen tube used in the present practice of thoracic? anesthesia is the Robertshaw design. It is available in left and right-sided types, and varying sizes from 26 Fr to 41 Fr.  The size denotes the external diameter of the tube in cms.  The Robertshaw design of the DLT comprises two semicircles placed back to back to form two independent lumens that can be ventilated independently of each other. The lumens have different openings depending on which sided DLT is present. The right-sided DLT has a curve to the right, and similarly, the left-sided DLT has a curve to the left. The double-lumen tube cuffs are high volume and low-pressure cuffs.[rx][rx]
• Connector: The connector is an important component of the Double lumen tube as it provides the user with an opportunity to selectively block either lumen or ventilate bilaterally. The connector piece is composed of a Y-shaped piece which has two openings – one each for the connection to the bronchial and tracheal lumen respectively and a common portion that fits into the anesthesia circuit. The connector usually has tracheal and bronchial lumen parts made of different colors for ease of use. Universally the blue color is used by manufacturers to denote the endobronchial lumen/cuff. The cuffs are colored similarly to the connector tubes to maintain uniformity in identification. This safety mechanism ensures correct side lung collapse and ventilation achieved by clamping the side on which lung needs to collapse temporarily.
• Bronchial Blockers: Bronchial blockers are used to achieve single lung ventilation by blocking either left or right primary bronchus. Several manufacturers produce bronchial blockers with different designs. However, their basis is on a simple design comprising an inflatable low pressure, high volume cuff at the end of a catheter. The advantages offered by a bronchial blocker over a DLT include the ability to place through an existing endotracheal tube, ability to use in patients with airway trauma and the ability to perform selective lobar blockade if needed. Bronchial blockers are not without their own disadvantages. They require a minimum of 7.5 endotracheal tubes in place for introduction into the airway. They allow the slower collapse of the lung. Owing to the variable take-off of the right upper lobe, bronchial blockers are often difficult to position to seal off the right upper lobe. They are also much more prone to dislodgement when compared to Double lumen tubes.[rx]
• Fiber-optic Bronchoscope: A fiberoptic scope is mandatory when attempting to place a double-lumen tube; this is because accurate positioning is essential to achieving a good seal and lung isolation. Malpositioned tubes are avoided by checking the tube position after the patient is in place in the final position for the procedure.
• Endobronchial Tubes: Endotracheal tubes may be placed in the endobronchial to provide one-sided ventilation. The major disadvantage of such a technique is the inability to have access to the non-intubated lung. Endobronchial tubes are preferred in specific clinical scenarios to a DLT, such as patients with previous neck or oral surgery who present with a difficult airway and require adequate lung separation. The placement of a DLT is more challenging than that of an endobronchial SLT. DLT placement has higher chances for airway injury and bleeding. Endobronchial tubes may be mandatory in patients requiring lung isolation who have a short or long-term tracheostomy present before the procedure.[rx][rx][rx]

Preparation

Anesthetic Considerations[rx]

Patients usually undergoing single lung ventilation for a variety of procedures have underlying pulmonary disease. Patients should be evaluated comprehensively for their primary disease prior to performing the surgical procedure. Echocardiography may be useful in patients with cor pulmonale and may provide information about baseline cardiac function and reserve.

A review of the relevant radiological anatomy on a case-to-case basis may help plan anesthetic management for single lung ventilation. This review will also allow proper preparation for patients who require specialized airway management. Presence of decreased baseline function due to large effusions, consolidations and atelectasis predispose patients to hypoxemia during the procedure, which may obviate the need to use higher fractions of inspired oxygen during the procedure. The presence of any bullae on the non-operative lung may provide clues to patients more likely to develop a pneumothorax in the perioperative period. Tumors need to be evaluated for the presence of any paraneoplastic syndromes as their presence may guide anesthetic management.

Special considerations need to be placed on patients age as it is an independent risk factor which decides complication rates in patients undergoing pulmonary resection using single lung ventilation. Elderly patients have been found to have higher morbidity and mortality from pulmonary resections. Patients undergoing lung resections need additional testing to predict the risks involved in lung resection besides age. The most common tests used for such an assessment are FEV1 (forced expiratory volume-one second) and DLCO (diffusing capacity of the lungs for carbon monoxide).

FEV1 is a predictor of postoperative complications including death that may arise from undergoing pulmonary resection. A reduced preoperative FEV1 (less than 60 percent predicted) was found to be the strongest predictor of postoperative complications by multiple authors.[rx][rx]

DLCO has been studied as a factor that decides postoperative morbidity as well. DLCO measured as a percent of the predicted value and predicted postoperative DLCO is considered the most valuable predictors of mortality & postoperative complications in pulmonary resections.[rx] The current ACCP guidelines do not provide numerical cutoffs for DLCO below which pulmonary resections should not be performed on patients. Instead, they give importance in determining the predicted postoperative (PPO) values. Assessment of the postoperative predicted values is the deciding factor in such cases and predicts the success of single lung ventilation. The interpretation of postoperative values are as follows:

• Patients who have both PPO FEV1 and PPO DLCO are greater than 60 percent do not need any further testing to undergo pulmonary resection.
• Patients who have either PPO FEV1 or PPO DLCO less than 60 percent, however, have both values greater than 30 percent need additional testing with stair climbing or a shuttle walk test.
• If both values are less than 30 percent, patients should undergo cardiopulmonary exercise testing with additional measurement of the maximal oxygen consumption.

The cut-off for the stair climb test is 22 meters. Incremental shuttle walk test distance greater than 400 meters denotes a maximal oxygen uptake of (VO max) greater than or equal to 15 mL/kg per minute. Such information may help the physician interpret the procedural risks and better clinical outcomes for patients undergoing single lung ventilation.

Technique

The most commonly used DLT is the left-sided DLT irrespective of which side requires the isolation; this is because placing a left-sided DLT is less challenging than the right-sided one. This comparative ease is in part due to the short take-off of the right upper bronchus which leads to higher chances of dislodgement and or impaired ventilation of the right upper bronchus.

DLT placement technique: After inducing the patient with general anesthesia and confirming complete neuromuscular blockade, the following steps are taken to place a Left-sided DLT

• A direct laryngoscopy using a Macintosh blade is used for laryngoscopy as the DLT is a large tube and this technique provides the maximum space for its insertion.
• The double-lumen tube is introduced with a rigid stylet with the endobronchial curvature facing anteriorly.
• The rigid style ensures passage through the vocal cords. After the DLT passes through the vocal cords, the style is removed.
• The tube is then rotated by a 90 degrees angle anticlockwise to the left until the blue bronchial lumen faces left and tracheal lumen faces right.
• The next step involves either advancing the tube further until we meet resistance or using a fibreoptic bronchoscope to guide further placement. At this moment the tracheal cuff may be inflated and the connector attached to start ventilation.
• The shape of the left-sided DLT facilitates the bronchial cuff to be positioned in the left bronchus when advanced, but the DLT position should be confirmed with a fibreoptic bronchoscope to make sure that the tracheal lumen opening is above the carina and bronchial lumen is in the left bronchus. The bronchial cuff can now be inflated with 1 to 2 ml of air.
• Bilateral ventilation confirmation is by auscultation. Air entry should be audible in bilateral lungs at this point.
• Next, lung isolation is confirmed with selective clamping of the tracheal and bronchial lumens.
• When ventilation through the bronchial lumen completes, only the left lung should be inflated.
• When clamping the bronchial lumen and ventilating through the tracheal lumen, only the right lung should inflate.

Inability to perform a direct laryngoscopy is a contraindication? to use of a DLT. In such a situation a bronchial blocker may be a suitable alternative.

Complications

Management of Hypoxemia[rx]

During single lung ventilation, the ventilation to one of the lungs is interrupted. However, the perfusion is still present in the non-ventilated lung, which leads to an intrapulmonary shunt in the form of wasted perfusion to the non-ventilated lung. Protective mechanisms like hypoxic pulmonary vasoconstriction can counteract hypoxia to a certain degree. However, it is mandatory for the anesthesiologist to have measures in place for hypoxemia that may arise during single lung ventilation. Ventilation and perfusion (V- Q) matching plays a significant role in the management of oxygenation in patients on single lung ventilation. Some authors note that oxygenation is much better in the lateral decubitus position when compared to the supine position.

Classically, an inspired oxygen fraction (FiO2) of 1.0 has been advocated while performing one-lung ventilation. The rationale behind using a higher inspired fraction of oxygen is to have a safety margin. Higher Fio2 also leads to vasodilatation, and this may help increase the blood to the ventilated lung. Oxygenation at FiO2 of 1.0 can lead to atelectasis, so it is advisable to initiate with a Fio2 less than 1.0 and increase if needed.

If hypoxia develops during the performance of one lung ventilation the following step s must take place :

• Check the position of the double-lumen tube/endobronchial tube/bronchial blocker. Changes in position may occur due to surgical manipulation. A repeat fiberoptic bronchoscopy through the tracheal lumen is useful in clinching the diagnosis?. Additional steps involve suctioning the lumens of the tube to clear secretions which may also contribute to hypoxia.
• FiO2 is increased to 1.0 to improve the amount of oxygen delivered.
• Recruitment maneuvers are employed on the ventilated lung which is in the dependent position; this is done to overcome any atelectasis and thus help in oxygenation. PEEP may be applied to this lung to eliminate atelectasis, resulting in a decrease in the shunt thereby improving oxygenation
• CPAP to the operative lung may be applied to decrease shunting and thus improve oxygenation. However, this does make the surgical procedure challenging to the surgeon, and should only be an option when other measures have not resulted in any improvement.
• If the hypoxemia is severe and does not resolve with the abovementioned steps, the next best step is to revert to two lung ventilation.
• Severe hypoxemia should alert the anesthesiologist to look for causes like pneumothorax on the dependent lung. Chronic? obstructive lung disease patients are more likely to experience such a complication. Intraoperative development of pneumothorax mandates aborting the surgical procedure and immediate insertion of a chest tube on the side of the pneumothorax.