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NewsletterJune 2002 Newsletter:
Conventional Double-Lumen Endotracheal Tubes are Best when Lung Separation is Required
Safe and dependable isolation and selective ventilation of the lungs is essential for the practice of thoracic anesthesia. In adults, lung separation is accomplished with either a double-cuffed double-lumen tube (DLT) or by bronchial blockade using one of a variety of balloon-tipped (BB) catheters. There are certain situations when one technique is clearly superior to the other,(1) so it is difficult to support the broad general statement that "conventional double-lumen endotracheal tubes are best when lung separation is required". However, I believe that for most thoracic procedures a DLT offers important advantages over a BB. Lung tissue distal to an obstruction slowly collapses. In 1935 Magill accomplished bronchial blockade using a long, narrow rubber tube with an inflatable cuff at its end. His BB was passed alongside a single-lumen endotracheal tube. The blocker catheter was positioned under direct (rigid) bronchoscopic guidance using a stylette in its lumen. The small lumen allowed air trapped beyond the blocker to escape and secretions to be suctioned. The many catheters that have since been used for bronchial blockade are all variations of the original Magill blocker. The first modern tube designed specifically for bronchial blockade was the Univent tube (Fuji Systems Corp., Tokyo, Japan), introduced in 1982. It follows the basic BB plan, but physically incorporates its retractable blocker catheter within the body of the single-lumen endotracheal tube. Catheters commonly used for bronchial blockade (Fogarty, Foley, pulmonary-artery) are intended for other uses. They have low-volume balloons that generate high pressures, which increase the potential for airway injury. Recently, a wire-guided low-pressure, high volume endobronchial blocker (WEB) (Cook Critical Care, Bloomington, IN) was developed specifically for bronchial blockade.(2) Like all BBs, the WEB device must be positioned using a fiberoptic bronchoscope (FOB). Its unique feature is its guide wire loop, which couples the WEB to the FOB thus allowing the scope to visually guide the blocker into position. Removal of the wire after placement provides a small lumen for insufflating oxygen or removing gas from the blocked lung segment. This ingenious means of positioning the WEB blocker may make placement less difficult and perhaps less time consuming than required for other BBs, but there has been too little experience yet with this device to be certain. During pulmonary resections the operated non-dependent lung must be periodically inflated and then re-collapsed to check for air leaks. This process may be difficult to accomplish with a BB because the balloon is so easily displaced, especially when changing patient position or from surgical manipulation. If the blocker's balloon slips into the trachea it can obstruct ventilation to the non-operated lung and/or will fail to protect the healthy lung from contamination. A BB in the operated bronchus may be transected during resection. If the BB balloon is deflated and withdrawn from the bronchus during surgery, the contra-lateral healthy airway is at risk from contamination by pus or blood. To overcome these problems, Carlens introduced the first DLT for thoracic surgery in 1950. The major advantage of a DLT compared to a BB is that either or both lungs can be deflated, re-expanded, and examined with a FOB and/or suctioned, at will during the procedure without interrupting ventilation to the other lung. With both cuffs inflated each lung is completely isolated and protected from cross-contamination. One argument against DLTs centers on the potential for airway trauma. In contrast to the low volume/high pressure cuffs of most BBs, the bronchial cuffs of plastic DLTs have high volume/low pressure characteristics that reduce the danger of ischemic pressure damage. Serious complications from plastic DLTs are rare.(3) Mild laryngitis can occur with DLTs, but the actual incidence, and whether that rate is greater than that which follows intubation with an endotracheal tube, is unknown. Concerns about difficulty with DLT positioning are usually listed as another disadvantage.(4) This was a problem in the past with the bulky, rubber tubes before the introduction of fiberoptic bronchoscopy. By choosing an appropriate size (large) plastic left-DLT, advancing the tube to a depth based on the patient's height, and using a FOB or other adjunct when needed, modern DLTs are safely, easily and quickly placed.(5) Since a BB is always passed through or alongside an endotracheal tube, bronchial blockade may be the best choice for patients with "difficult" airways in whom placement of a DLT may be challenging or perhaps not even possible. Many anesthesiologists feel a DLT must be replaced with a single-lumen endotracheal tube for postoperative ventilation. Since changing tubes at the completion of surgery is potentially dangerous, use of a BB has been cited as advantageous if postoperative ventilation is anticipated. Actually, flow resistances of modern plastic DLTs are significantly less than commonly perceived.(6) In most clinical situations there will be no decrease in flow resistance when a DLT is replaced by a single-lumen endotracheal tube. Although DLTs may be less well tolerated in the conscious patient, they should not cause an increase in the work of spontaneous breathing during separation from mechanical ventilation or emergence from anesthesia The majority of patients undergoing thoracic surgery do not have "difficult" airways. No differences were reported in patients with normal airways between bronchial blockade with a Univent tube and a DLT in the time required to position either tube, the number of bronchoscopic interventions to confirm or check tube position, or the time required for lung collapse.(7) However, although satisfactory tube placement was obtained in all patients in the supine position, when patients were turned to the lateral decubitus position the blocker was displaced from its intended position more frequently than was the DLT. In some instances the blocker was in too far and only a segment of lung could be collapsed. More patients required assistance to achieve lung collapse in the Univent group. The investigators suggested that for operations when complete and rapid lung collapse is required, the Univent tube BB might not be as reliable as a DLT.(7) In that same study, the surgeons who were unaware of which technique was being used found that exposure was excellent in 90% of the DLT patients but only in 70% in whom the Univent tube had been used. Since the most common indication for one-lung ventilation is improved surgical exposure, the DLT again appeared superior to bronchial blockade.(7) Other advantages of DLTs include their relatively large lumens that allow easy passage to either lung of a suction catheter or FOB. The non-dependent lung can be thoroughly suctioned or visually examined before re-expansion. In addition, CPAP can be easily applied to the collapsed lung to improve oxygenation. The transparent material of plastic DLTs allows continuous observation of moisture during ventilation, and the presence of secretions or blood in either lumen. For the above reasons I believe that for the majority of patients a DLT is the better choice. A BB is indicated in situations when placement of a DLT may be difficult or not possible. These include patients with "difficult" airways requiring one-lung ventilation during surgery and/or mechanical ventilation following thoracotomy. A BB can also be used in the critical care setting for lung isolation in a patient whose trachea is already intubated, especially when changing from an endotracheal tube to a DLT would be hazardous. Finally, BB remains the only practical method for lung separation in small children. There is no "best" method
for lung separation in all patients. Choice depends on the specific
surgical requirements, the patient's airway, and the individual preferences
and experience of the anesthesiologist. For most patients a DLT is easier
to use and offers more advantages than a BB. Even the developer of the
WEB blocker stated that a BB "is not a replacement for DLTs
... It will allow the clinician to achieve one-lung ventilation
in ... (those situations) ... when management is optimal with
a single-lumen endotracheal tube".(2)
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