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From the Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada.
Address correspondence to: Dr. Peter Slinger, Toronto General Hospital, 200 Elizabeth Street, Toronto, Ontario, Canada M5G 2C4. Phone: 416-340-5164; Fax: 416-340-3698; E-mail: peter.slinger{at}uhn.on.ca
THE routine separation and isolation of one of the body's major paired organs, which is frequently necessary during lung surgery, is unique in medicine. Apart from the fascinating patho-physiological changes which occur during one-lung or independent-lung ventilation, the clinical usefulness of this separation is a cornerstone of thoracic anesthesia. The evolution of elective thoracic surgery was delayed more than half a century following the introduction of ether because anesthesiologists did not have the technology to manage general anesthesia with an open hemi-thorax and were unable to protect healthy lung regions from secretions or hemorrhage in affected parts of the lung. In the 1930's several different practitioners pioneered the use of single-lumen endobronchial tubes,1 bronchial blockers,2 and double-lumen tubes3 to achieve lung isolation. In spite of numerous modifications these three methods continue into this millennium as the basis of modern lung isolation techniques.
All of these early techniques of lung isolation proved to be extensively dependent on the clinical experience of the practitioner and were frequently unreliable. The double-lumen tube design introduced by Carlens3 in the late 1940's is a landmark in the development of thoracic anesthesia. The Carlens tube could be placed reliably in the vast majority of cases using only laryngoscopy and its position confirmed with auscultation. The use of the Carlens and other derivative double-lumen tubes rapidly became the predominant method of providing lung isolation.4 As the indications for lung isolation extend beyond thoracic surgery and the types of patients requiring lung separation expand to include patients with difficult upper airways and other concurrent problems, the limitations of the Carlens-style tubes are now becoming more evident. This review will examine the recent developments in equipment and techniques for lung isolation that have increased the safety and reliability of lung separation in anesthesia.
Indications
The indications for isolation of a lung, lobe or segment from the rest of the tracheo-bronchial tree have been traditionally grouped into relative ("like to have it") and absolute ("really need it"). This division is somewhat arbitrary, as a relative indication may suddenly become an absolute indication if the surgery is unable to continue with the ipsilateral lung ventilated. Lung isolation is used in a widening spectrum of situations ranging from facilitation of elective pulmonary resection surgery to emergency treatment of life-threatening hemoptysis. The original indications for lung isolation still arise although with less frequency than 50 yr ago. These include: pulmonary hemorrhage, infected secretions, bronchial fistulae and bullae. These can be remembered as representing the three categories "blood, pus, and air" that are complications of central line placement and other procedures. It is not uncommon for any obstructing lung lesion to have some infected secretions distal to the blockage that are released by surgical manipulation. Even small amounts of pus spilling into the contralateral dependent lung can cause severe post-operative pneumonia.5
The commonest indication for lung isolation is to facilitate exposure in elective lung cancer surgery. However, several recent developments in thoracic surgery including transplantation, volume reduction surgery and video-assisted thoracoscopic procedures (VATS) are essentially impossible without lung isolation.6 Apart from lung surgery, lung isolation is used in many centres for minimally invasive cardiac surgery and other intra-thoracic procedures such as aortic, esophageal and vertebral surgery. Independent lung ventilation is also an established therapeutic option whenever there is a large discrepancy between the optimal gas exchange parameters of the two lungs. Such indications include predominantly unilateral lung contusion or adult respiratory distress syndrome or following pulmonary embolectomy or single-lung transplantation.7 The provision of lung isolation is always based on an individual risk-benefit assessment for a particular case.
Contraindications
While there are no absolute contraindications to lung isolation there are contraindications to specific techniques in certain clinical situations. For example, the use of a left-side double-lumen tube in the presence of a left maintem bronchial carcinoid tumour would normally be contraindicated. Double-lumen tube placement can be hazardous if there is bronchial compression from a thoracic aortic aneurysm8 or pulmonary artery compression from an anterior mediastinal mass.9 Intubation with a double-lumen tube in a patient with an increased risk of aspiration in not contraindicated. The intubation can be performed in a "rapid sequence" fashion appreciating that the time to get control of the airway is slightly longer than with a single-lumen tube and this theoretical increase in the risk of aspiration needs to be weighed against the need for lung isolation. Similar considerations apply to lung isolation in patients who are hypoxemic or have altered coagulation.10 These individual clinical situations represent increased risk but not definite contraindications.
Lung isolation methods
Double-lumen tubes (DLTs)
TUBE DESIGN
The second half of the past century has seen refinements of the DLT from that of Carlens to a tube specifically designed for intra-operative use (Robertshaw)11 with larger, D-shaped, lumens and without a carinal hook. Current disposable polyvinyl-chloride (PVC) DLTs have incorporated high-volume low-pressure tracheal and bronchial cuffs.12 The designs of left-side double-lumen tubes of the majority of the commercial suppliers have evolved in the past five years to include the recommendations of Benumof13 increasing the angle of the distal bronchial curve, shortening the distal bronchial cuff and eliminating the bevel of the distal bronchial lumen. This increases the margin of safety while positioning these tubes in the left mainstem bronchus and facilitates surgery on the left mainstem bronchus distal to the tube.14 The modern DLTs have a far lower resistance to airflow than the older reusable red-rubber double-lumen tubes. The resistances of these newer DLTs for the spontaneously breathing patient compare favourably with the resistances of commonly used sizes of single-lumen tube and there is no reason that a patient cannot be gradually weaned from positive pressure ventilation with an in situ DLT rather than change to a single-lumen tube.15 Disposable left DLTs with carinal hooks are available but are not in widespread use as most practitioners position their tubes with bronchoscopy and prefer those without hooks.
There is a large variation in the designs of commercially available disposable right-sided DLTs. All of these designs are an attempt to deal with the short and variable length of the right mainstem bronchus and they all include a side slot on the distal bronchial lumen to ventilate the right upper lobe bronchus. With the routine use of fiberoptic bronchoscopy right-sided DLTs can be used with a higher rate of reliability than previously appreciated.16
TUBE SIZE
There is little consensus among anesthesiologists on how to choose the correct size of double-lumen tube for an individual patient. Since these tubes are not circular in cross-section, it is not useful to describe their sizes according to diameters, as is done for single-lumen tubes. They are grouped according to French gauges which are related to circumference and commonly used adult sizes are 35–41F. Selecting the correct size is more important for double than single-lumen tubes. Too large a tube is prone to cause tracheo-bronchial trauma17 and with a large tube, the bronchial cuff seals the bronchus with a volume less than 1 ml. Thus, the bronchial cuff will be incompletely inflated and more prone to inadequate isolation and risk of soiling.18 With too small a tube, the tube is more prone to displacement and excessively high volumes and pressures are required in the bronchial cuff to get a seal and this too can lead to bronchial trauma.19 Ideally the DLT size will seal the bronchus with the bronchial cuff fully inflated in the range of its resting volume but before it assumes the high-pressure characteristics of over-inflation.20 This bronchial cuff volume varies slightly with tube size and manufacturer, but is in the range of 1–3 ml for most commonly used adult DLTs.
One method of choosing the size of double-lumen tube is based on the size of the tracheal diameter determined from the chest x-ray since there is a very close correlation between tracheal and bronchial diameters.21 A 35F DLT is suggested if the tracheal diameter is <15 mm, a 37F, 15–16 mm, a 39F, 16–18 mm; and a 41F >18 mm. This protocol leads to choosing large sizes of tubes: 39 and 41F, for many men and women and may tend to overestimate the size for some smaller patients.22 A method has been described using the CT-derived left mainstem bronchial diameter for each patient23 but this information is not always readily available. A simple and useful technique as a starting point for adults is based on the patient's height. Males >170 cm (5'7"): 41F; males <170 cm: 39 F; males <160 cm (5'3"): may require 37F or less. Females >160 cm: 37F; females <160 cm 35F; short females <152 cm (5'0") may require 32F. The widest diameter of a 35F tube is slightly larger than a 9.0 mm ID single-lumen tube and the anesthesiologist must always consider whether it would be acceptable to place a comparable size single-lumen tube in the patient. For the smaller size DLTs the comparable ID single-lumen tubes are approximately: 32F= 9.0 mm; 28F=7.5 mm; and 26F=6.5 mm.
TECHNIQUE OF PLACEMENT
As with tube size, there is little agreement among anesthesiologists who do a large volume of thoracic cases on the optimal method to place a double-lumen tube. Commonly used variations following laryngoscopy include: tube rotation with vs without the stylet; tube advancement with vs without the stylet;24 head in neutral position vs right lateral rotation/flexion; and fiberoptic bronchoscopy during vs immediately after intubation vs after patient positioning.25
Personally, I keep the patient's head in the neutral position, remove the stylet once the bronchial tip passes through the vocal cords, and rotate and advance the tube to a predetermined depth providing there is no undue resistance. The average depth of placement of a DLT for a person of 170 cm (5'7") height (either sex) is 29 cm at the gums.26 This depth increases or decreases approximately 1 cm for each 10 cm increase or decrease in the patient's height. Inserting DLTs until they meet resistance is a habit left over from the use of reusable red-rubber Carlens or Robertshaw tubes. Modern disposable PVC will often not meet resistance until they are all the way into the lower lobe bronchus. Using this older technique with modern tubes leads to mal-positioning and trauma.27 I confirm tube position initially with auscultation and if completely satisfied do not bronchoscope until the patient has been moved to the final operative position since these tubes always move during patient positioning in spite of the best efforts of the anesthesia team.28 If there is any question about the tube position, I pass the fiberoptic bronchoscope immediately after intubation. With severe chronic obstructive pulmonary disease (COPD) it is often practically impossible to verify the DLT position with auscultation. Repositioning is then done under direct vision with the bronchoscope and lateral flexion or rotation of the patient's neck is occasionally required at this stage to get a misplaced DLT to enter the left main bronchus. Bronchoscopy will need to be repeated after patient positioning.
Bronchial blockers
As the clinical indications for lung isolation have expanded, the limitations of double-lumen tubes have become more evident and there has been a renewed interest in finding alternative methods to provide lung isolation. Because of the fixed distances and sizes of the tracheal and bronchial orifices and cuffs of double-lumen tubes they function optimally in patients with normal airway anatomy but have very limited adaptability in patients with abnormal upper or lower airways. Bronchial blockers are useful in many of these situations. Blockers can be placed through or external to existing single-lumen endotracheal (ET) tubes and this can obviate the need for a tube change both at the start or at the end of surgery, which may be useful in trauma or other difficult airway cases. With single-lumen tubes 7.5 mm ID or larger, both the blocker and a 4-mm diameter fiberoptic bronchoscope scope can be passed intra-luminally for positioning. With smaller ID ET tubes the blocker is passed through the glottis beside the ET tube. Blockers can provide either lobar or lung isolation. The major problem with all blockers to date is that the reliability of isolation is not as good as with a double-lumen tube. Bronchial blockers tend to become dislodged intra-operatively29 and this is particularly a concern in the presence of infected secretions. Also, they do not allow easy access to the non-ventilated lung for suctioning, to verify position, or to aid deflation. This can be a problem during thoracoscopic surgery when there is less access for the surgeon in the operative hemi-thorax and less tolerance for incomplete collapse.
General principles to increase the isolation success rate with blockers are: 1) position the deflated blocker in the correct bronchus while the patient is supine before turning, as it can be difficult to manoeuver the blocker into the non-dependent bronchus in the lateral position; 2) use a blocker preferentially for left vs right thoracotomies and position the blocker as distal as possible in the mainstem bronchus; this increases the margin of safety to maintain isolation if the blocker moves intra-operatively; 3) when possible use blockers for non-pulmonary intra-thoracic procedures such as esophageal or vascular cases as there is less lung manipulation and less accidental dislodgement of the blocker; 4) use blockers for open thoracotomies vs thoracoscopies as the surgeon can more easily move an incompletely deflated lung out of the field if the chest is open; 5) use a video camera and monitor attached to the bronchoscope to position the blocker as this allows an assistant to help in controlling the bronchoscope. Positioning and placing a blocker requires four hands.
The most widely used blocker in the past two decades has been an 8F Fogarty venous embolectomy catheter with a 4 or 10 ml balloon.30 This is a closed-end catheter and is not specifically designed as a blocker. There has been a large effort in the industry to improve on this. The Univent tube is a single-lumen tube with a blocker enclosed in a separate channel within the tube.31 Recently, the Univent blocker has been redesigned to make it more flexible and easier to manipulate. The Univent tubes are silicon and tend to be relatively stiff and, although they have been described for use in difficult airways,32 they have not received universal acceptance.
The newest commercially available blocker is the Arndt Catheter (Cook Inc., Bloomington, IN).33 The blocker balloon has a modified pear shape which seems to make it more stable in the bronchus. As with the Univent, there is a narrow suction channel in the blocker. Also, it comes with an elegantly designed three-way connector that permits separate air-tight access for the catheter, the bronchoscope and the anesthetic circuit. However the wire guide-loop, that is used to position the catheter in the bronchus with a bronchoscope, can be awkward to manipulate particularly with an ET tube <8 mm ID. The newer blockers are generally more expensive than Fogarty catheters or double-lumen tubes.
Single-lumen endobronchial tubes
The original method of lung isolation was the distal advancement of a single-lumen tube into the desired mainstem bronchus.34 Some anesthesiologists continue to use a standard 32 cm long 7.5 mm ID ET tube advanced with bronchoscopic guidance as an endobronchial tube when needed. Naturally, there is no access to the non-ventilated lung for suctioning, for continuous positive airway pressure (CPAP), to confirm positioning, etc. Some surgeons prefer single-lumen endobronchial tubes to DLTs for procedures involving the carina since they are more flexible, permitting better mobilization and exposure.35 Bilateral endobronchial tubes can be used with lesions close to the carina.36
The ABC's of lung isolation
Which ever method of lung isolation is chosen for a particular patient in a specific clinical situation, there are several general principles of lung isolation that should be followed to improve the safety and reliability of the procedure. I will refer these as the ABC's of lung isolation. They are: know the tracheo-bronchial Anatomy, always use the fiberoptic Bronchoscope and examine the Chest x-ray and CT scan preoperatively.
Anatomy
Lung isolation requires a thorough knowledge of bronchial anatomy. Just as advances in invasive monitoring have mandated that anesthesiologists develop a more complete understanding of vascular anatomy to achieve reliable central venous access, lung isolation requires detailed knowledge of bronchial anatomy. Minor variations in subsegmental anatomy are common. However, the anatomy of the lobar and segmental bronchi is consistent enough to use as a guide for positioning endobronchial tubes and blockers.
The left mainstem bronchus is narrower (mean adult diameter 13 mm) than the right (16 mm) and makes a more acute angle at the carina (45 vs 30) this means that it is generally more difficult to get a tube or blocker into the left side. However, the left mainstem bronchus is longer (48 ± 8 mm) than the right (21 ± 8 mm) and thus there is a larger margin of safety in positioning tubes or blockers on the left.13
Bronchoscope
The use of the bronchoscope to position double-lumen tubes was first described in 1982 by Shinnick.37 Improvements in fiberoptic technology have led to the development of fiberscopes that are specifically designed for airway management by anesthesiologists. Although some anesthesiologists and authors continue to advise that the use of a bronchoscope is not routinely necessary,38 the placement of modern PVC double-lumen tubes using auscultation or other techniques without direct visualization has consistently been shown to result in a rate of mal-positioning that exceeds 30% and a large number of these misplacements are potentially critical.39,40 In Britain, the National Confidential Enquiry into peri-operative deaths41 published in 1998 described problems with the double- lumen tube in 30% of the deaths in patients undergoing esophago-gastrectomy. These problems ranged from multiple tube changes to hypoxemia and hypoventilation. In all these cases, no anesthesiologist reported using a fiberoptic bronchoscope to confirm the position of the tube before or during surgery even when mal-positioning was recognized. Given these data, it was pointed out in a recent editorial that it would be very difficult to defend an anesthesiologist who was involved with a complication during thoracic surgery if a double-lumen tube or blocker was placed without confirmation by bronchoscopy.42 Similarly, it would be difficult for an institution where elective thoracic surgery is done on a regular basis to defend itself if suitable fiberoptic equipment was not made available.
The tracheal carina and the orifices of all lobes should be verified each time the bronchoscope is used. The ability to use a fiberoptic bronchoscope to recognize normal and abnormal tube placement is a skill that all anesthesiologists who manage thoracic cases should possess. Like any skill it is best learned under appropriate guidance in elective situations. A fiberoptic bronchoscopic guide to correct and incorrect positioning of double-lumen tubes has been published.43 The photographs from this article are also posted on the Internet under "double- lumen tubes" in the Review Articles section at: <www.thoracicanesthesia.com>.
Chest x-ray and CT scan
All anesthesiologists are familiar with the clinical assessment of the upper airway for the difficulty of endotracheal intubation. In a similar fashion, each thoracic surgical patient should be assessed for the difficulty of endobronchial intubation. The single most important predictor of difficult endobronchial intubation is the plain chest x-ray.44 Major abnormalities of tracheal or bronchial anatomy due to congenital malformations, distortion by tumour, etc., are usually readily visible. The anesthesiologist must view the chest x-ray him/herself prior to induction since neither the radiologist's nor the surgeon's report of the x-ray is made with the specific consideration of lung isolation in mind. It is also worthwhile to examine the CT scan of the chest when available since endobronchial problems that can lead to problematic lung isolation that may not be evident on the plain chest film can sometimes be seen on the CT scan.45
Techniques for lung separation
Since it is impossible to describe one technique as best in all indications for one-lung ventilation (OLV), the various indications will be considered separately starting with the commonest.
Pulmonary resection, right-sided
This is the commonest adult indication for one-lung ventilation. The first choice is a left double-lumen tube. There is a wide margin of safety in positioning left DLTs.13 With blind initial placement the incidence of malpositioning is high but is correctable in virtually all cases by fiberoptic adjustment.46 Some authors advocate the routine use of a bronchoscope during intubation to guide initial DLT positioning.7
A partial resection can proceed to a pneumonectomy, if required, without loss of lung isolation. There is continuous access to the non-ventilated lung for suctioning, fiberoptic monitoring of position, and CPAP. There are differences in the designs of the bronchial cuffs which result in different mean bronchial cuff inflation volumes and pressures during one-lung ventilation.48
Possible alternatives are: (a) single lumen endobronchial tube. A standard 7.5 mm ID or smaller ET tube can be advanced over a fiberoptic bronchoscope (FOB) into the left mainstem bronchus; (b) Univent tube or other bronchial blocker. This is one of the least favourable clinical situations in which to use a blocker since the margin of safety for optimal positioning is small and blockers tend to move intra-operatively especially during surgical lung manipulation.
Elective pulmonary resection, left-sided
(A) NOT A PNEUMONECTOMY
There is no definite superior choice. Double-lumen tubes are generally preferred because of increased intra- operative stability thus requiring less intra-operative repositioning29 but any of the bronchial blocker systems function well in the majority of these cases. The use of a left DLT for a left thoracotomy is occasionally associated with obstruction of the tracheal lumen by the lateral tracheal wall and subsequent problems with gas exchange in the ventilated lung. A right DLT is an alternate choice. Problems with lung isolation and/or positioning with routine FOB placement of right DLTs occur much less frequently than previously thought and are comparable to the incidence of problems with left DLTs for left thoracotomies.16
(B) LEFT PNEUMONECTOMY
There is no completely satisfactory choice. Any left pulmonary resection may unforeseeably become a pneumonectomy. When a pneumonectomy is foreseen, a right DLT is the best choice. A right DLT will permit the surgeon to palpate the left hilum during OLV without interference from a tube or blocker in the left mainstem bronchus. The disposable right DLTs currently available in North America vary greatly in design depending on the manufacturer (Mallinckrodt, Rusch, Kendall). The Mallinckrodt design is currently the most reliable. Positioning the ventilating side-slot can be time-consuming. These tubes require relatively high bronchial intra-cuff pressures (40–50 cm H2O vs 20–0 cm H2O for left DLTs). However, this is lower than the range of pressures required by a Univent49 or non-disposable DLTs.50 Some clinicians prefer the non-disposable Robertshaw right DLT which has a larger ventilating side-slot. Rarely, left lung isolation is impossible in spite of high pressures in the right DLT bronchial cuff. In these cases a Fogarty catheter can be passed into the left main bronchus after estimation of depth with a FOB to isolate the left lung.51 As an alternative to a right DLT, there is no clear preference among a Univent, left DLT or other bronchial blocker. These will all require repositioning intra-operatively, but this usually is not a major problem.
Thoracoscopy
Lung biopsies, wedge resections, bleb/bullae resections, volume reduction surgery, even some lobectomies can be done using this technique. VATS under general anesthesia requires OLV.52 During open thoracotomy the lung can be compressed by the surgeon to facilitate collapse prior to inflation of a bronchial blocker. This is not possible during thoracoscopy. The operative lung deflates more easily when the non-ventilated lung lumen of a DLT is open to atmosphere than via the 2 mm suction channel of a Univent tube or Arndt catheter. A left DLT is preferred for thoracoscopy of either hemithorax.53 Spontaneous ventilation without lung isolation is an alternative in some patients.54
Pulmonary hemorrhage
Instances of life-threatening pulmonary hemorrhage can occur due to a wide variety of causes (aspergillosis, tuberculosis, pulmonary artery catheter trauma, etc.). The anesthesiologist is often called to deal with these cases outside the operating suite. The primary risk for these patients is asphyxiation from blood, and first-line treatment is lung isolation. There are several problems associated with using any sort of bronchial blocker in the acute situation: (a) it is often not known which side to occlude; (b) visualization below the vocal cords to aid placement is difficult; (c) after the blocker is placed there is no access to the involved lung to monitor bleeding. In patients with pulmonary hypertension, endobronchial blockade can lead to lobar rupture from continued bleeding.55 A left DLT avoids these problems but the optimal choice to manage the airway in these patients depends on the clinical scenario.56 If the contralateral lung is already filled with blood it will not be possible to suction adequately with a double-lumen tube.57 Often it will not be possible to use a bronchoscope to confirm the position of a DLT in the presence of hemorrhage, but immediate lung isolation is the important first step in resuscitating these patients. If a DLT is not available a single lumen uncut ETT should be placed in the trachea and then isolation can be attempted, after suctioning, by passing the ETT as an endobronchial tube34 or with a blocker. Tracheobronchial hemorrhage from blunt chest trauma will usually resolve with suctioning, only rarely is lung isolation necessary.58 Pulmonary artery catheter-induced hemorrhage during weaning from bypass should be dealt with by resumption of full bypass, bronchoscopy, localization of the bleeding site and lung isolation. It is important to resist the temptation to reverse the anticoagulation and try to wean from bypass before a proper examination, diagnosis and therapy are instituted. Weaning may then proceed without pulmonary resection in some cases, depending on the site and severity of the injury.59,60
Bronchopleural fistula
The anesthesiologist is faced with the triple problem of avoiding tension pneumothorax, ensuring adequate ventilation, and protecting the healthy lung from the fluid collection in the involved hemithorax. Management depends on the site of the fistula and the urgency of the clinical situation. For a peripheral bronchopleural fistula in a stable patient, some form of bronchial blocker may be acceptable. For a large central fistula, and in urgent situations, the most rapid and reliable method of securing one-lung isolation and ventilation is a DLT. In life-threatening situations, a DLT can be placed in the awake patient with direct FOB guidance.61 In high-risk patients who can maintain adequate spontaneous ventilation, there is the option to use thoracic epidural regional anesthesia, avoiding general anesthesia for some of these patients.62
Purulent secretions
Lung abscess, hydatid cysts, etc. Lobar or segmental blockade is the ideal. Loss of lung isolation in these cases is not merely a surgical inconvenience, but may be life-threatening. Thus, the most reliable method to maintain lung isolation is preferred and this is with a left-sided double-lumen tube. Bronchial blockers or Univent tubes can be used for lobar blockade in certain selected cases. A secure technique to consider in some high-risk cases is the combined use of a bronchial blocker and a DLT.63
Non-pulmonary thoracic surgery
Thoracic descending aortic surgery, esophageal surgery and some trans-thoracic spine surgery require OLV. Many of these patients will require post-operative ventilation. Since there is no risk of ventilated lung contamination and since these are often left-chest operations with minimal manipulation of the non-ventilated lung these are frequently good indications to use a bronchial blocker instead of a DLT. The use of a blocker will avoid the difficulty of changing the tube at the end of surgery.
Bronchial surgery
An intra-bronchial tumour, bronchial trauma, or a bronchial sleeve resection during a lobectomy require that the surgeon have intra-luminal access to the ipsilateral mainstem bronchus. Either a single lumen endobronchial tube35 or a DLT in the ventilated lung is preferred.
Lung lavage
Unilateral broncho-pulmonary lavage is an established treatment for pulmonary alveolar proteinosis and has been tried with varying success for cystic fibrosis, silicosis, radioactive dust inhalation and other indications.64 Continuous access to both lungs and secure isolation are absolute necessities for general anesthesia for this procedure. A left- sided double lumen tube is the most reliable method. Some authors who have a large experience with these cases prefer the disposable left-sided tube with a carinal hook to decrease the chance of misplacement during this procedure.65
Independent lung ventilation
Disease processes which affect the two lungs to different degrees may require independent ventilation and the anesthesiologist may be required to separate the lungs to accomplish this for a ventilated patient in the intensive care unit7. Potential indications include unilateral pulmonary contusion, aspiration, post-pulmonary embolectomy and post-lung transplantation.66,67 Once the lungs are separated, different levels of PEEP can be applied and/or entirely different ventilatory strategies can be used for each lung depending on the underlying pathology. A recently reported use of this technique was for the administration of bronchodilator to a severe refractory unilateral bronchospasm following cardio-pulmonary bypass.68
Lung transplantation
Because of the need to have continuous access to both lungs during single and "off-pump" bilateral lung transplantation the best option is a double-lumen tube using a right sided tube for left-sided single-lung transplantation and left-sided tubes in other cases. During "on-pump" cases (severe pulmonary hypertension, children, etc.) lung isolation is not strictly necessary and these cases can be managed with a single lumen ET tube. However it is useful, when possible, in the "on pump" cases to place a DLT since this will allow the first lung installed to be ventilated sooner. Recent modifications to the design of the left double-lumen tube have shortened the bronchial segment and this facilitates making the left mainstem bronchial anastomosis with the left DLT in situ.14 Left single lung transplants can be done with a left-sided tube, but it is frequently necessary to adjust the tube position.
Upper airway abnormalities
It is occasionally necessary to provide one-lung ventilation in patients who have abnormal upper airways due to previous surgery or trauma or in patients who are known or unanticipated difficult intubations. There are four basic options for these patients: (a) fiberoptic guided intubation with a double-lumen tube; (b) secure the airway with a single-lumen tube and then use a "tube exchanger" to place a double-lumen tube; (c) a bronchial blocker or Univent tube; and (d) use an uncut single lumen tube as an endobronchial tube.
The optimal choice will depend on the patient and the operation. Accepted guidelines to manage the difficult airway must always be observed.69 At all times it is best to maintain spontaneous ventilation and to do nothing blindly in the presence of blood or pus. Awake fiberoptic bronchoscopic intubation with a double-lumen tube requires thorough topical anesthesia of the airway and a cooperative patient.61 The rigid fiberoptic laryngoscopes such as the Bullard and Wu scopes can be used with some DLTs.70 These scopes are in the process of being improved to deal with DLTs. At present, the Bullard scope requires a special guide to easily accommodate a DLT and the Wu scope cannot easily manage tubes >37F. A lighted stylet can also be used to intubate with a DLT.71
Securing the airway with a single-lumen tube and then changing to a double-lumen tube using one of the commercially available tube exchangers designed for DLTs is a viable option in many patients.72 It is extremely important when performing this exchange to use a second person to do a direct larygngoscopy to expose as much of the glottis as possible during the tube change. Direct laryngoscopy decreases the angles between the oropharynx and trachea and reduces the chance of trauma to the airway from the DLT.
Bronchial blockers are often the best choice for these patients.33 If the ET tube is too narrow to easily accommodate both a bronchoscope and a blocker, the blocker can be introduced through the glottis independently external to the ET tube with fiberoptic guidance.73 Bilateral bronchial blockers can be used for bilateral resections74 or the same blocker can be manipulated from side to side. Bilateral single lumen endobronchial tubes can be used for lung isolation in patients with tracheal fistulas, trauma or other abnormalities in the region of the carina.75
Chest trauma
The use of a double-lumen tube to isolate the lungs in cases of chest trauma has been suggested in order to decrease the risk of systemic air embolism which could be caused by positive pressure ventilation of a traumatized lung.76 Although this complication is a concern, it is not clear if lung isolation has ever actually prevented a case of fatal air embolus. It is very common in both open and closed chest trauma to have some hemoptysis from alveolar hemorhage.58 The majority of these cases can be managed without lung isolation following bronchoscopy and suction and the majority of the deaths in these patients will be due to their other injuries and not from airway hemorrhage or air embolus. Lung isolation may be helpful in some of these cases, but if resources and time are limited the priority must be the resuscitation of the patient.
Avoiding airway trauma
Iatrogenic injury has been estimated to occur in 0.5–2 per 1000 cases with DLTs.77 Suggestions to decrease the risk of this complication are: (a) follow the "ABC's" of lung isolation. Anticipate difficult endobronchial intubation from the chest x-ray and CT; (b) use an appropriate size tube; (c) avoid nitrous oxide: Nitrous oxide 70% can increase the bronchial cuff volume from 5 to 16 ml intra-operatively and has been associated with bronchial rupture;78 (d) inflate the bronchial cuff/blocker only to the minimal volume required for lung isolation and for the minimal time. This volume is usually <3 ml.48 Inflating the bronchial cuff does not stabilize the DLT position when the patient is turned to the lateral position;28 (e) endobronchial intubation must be done gently and with fiberoptic guidance if resistance is met. A significant number of case reports are from cases of esophageal surgery,79 where the elastic supporting tissue may be weakened and predisposed to rupture from DLT placement.
Summary
Although the incidence of cases with the original indications for lung isolation such as abscess and hemoptysis has decreased, lung isolation is required with increasing frequency in an ever-widening spectrum of clinical situations. The preference of anesthesiologists has oscillated between bronchial blockers and single or double-lumen tubes for the past 50 yr. At present, double-lumen tubes continue to have the widest application for providing safe reliable lung separation in the majority of cases. However the optimal method of lung isolation in any individual case will depend on multiple factors which include the patient's underlying pathology and anatomy and the skill and training of the anesthesiologist.
References
1
Gale JW, Waters RM. Closed endobronchial anesthesia in thoracic surgery. Anesth Analg 1932; 11: 283–5.
2 Mushin WW, Rendell-Baker L. The origins of Thoracic Anesthesia. Wood Library. Museum of Anesthesiology, Park Ridge IL, 1953, reprinted 1991.
3 Bjork VO, Carlens E. The prevention of spread during pulmonary resection surgery by the use of a double- lumen catheter. J Thorac Surg 1950; 20: 151–7.
4
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