A double lumen tube (DLT) is a specialized endotracheal tube designed for specific surgical and medical procedures. Its primary function is to facilitate one-lung ventilation (OLV), a technique that allows for the independent ventilation of each lung. This separation is often necessary in thoracic surgery to create a still and collapsed lung, providing the surgeon with a clear and unobstructed view of the operative field. OLV also serves to prevent the spread of blood, pus, or other infectious materials from a diseased lung to the healthy lung, isolating contamination.
Anatomy and Standard Dimensions of a Double Lumen Tube
A double lumen tube has two distinct lumens bonded together. The shorter, larger tracheal lumen ventilates one lung, terminating in the trachea. The longer, narrower bronchial lumen extends into a mainstem bronchus to ventilate the other lung. Each lumen has an inflatable cuff: a larger, high-volume, low-pressure tracheal cuff (typically clear), and a smaller, high-pressure, low-volume bronchial cuff (usually blue). These cuffs are inflated to create a seal, isolating each lung.
DLTs are available in standard sizes, measured in French (Fr) units, ranging from 26 Fr to 41 Fr for adults. Common adult sizes include 28, 32, 35, 37, 39, and 41 Fr. Left-sided DLTs are more frequently used than right-sided ones. This preference stems from anatomical differences: the left mainstem bronchus is longer and has a more consistent take-off angle, providing a greater margin of safety for tube placement. The right mainstem bronchus is shorter, and its upper lobe bronchus originates close to the carina, making right-sided placement challenging without potentially obstructing the upper lobe.
Key Factors for Determining Tube Size
Selecting the appropriate DLT size requires careful consideration, progressing from general estimations to precise anatomical measurements. Traditional methods use general guidelines based on gender and height. For most adult females, a 35 Fr or 37 Fr tube is used, with taller individuals often receiving the larger size. For adult males, 39 Fr or 41 Fr tubes are common, with height also influencing the choice. However, these methods are less precise due to individual variations in airway anatomy, which can lead to an inappropriately sized tube and increase the risk of airway injury.
A more accurate approach uses imaging-based measurements from pre-operative scans, particularly chest computed tomography (CT). CT imaging allows for direct and precise measurement of tracheal and bronchial diameters, which helps determine the appropriate DLT size. For a left-sided DLT, the anterior-posterior dimension of the left mainstem bronchus is measured just distal to the carina, where the bronchial cuff sits. The selected DLT should have an outer diameter of its bronchial lumen at least 1 mm smaller than this measured bronchial diameter to ensure a good fit without excessive pressure. While chest X-rays can provide some measurements, they are less accurate due to magnification and unclear bronchial borders.
Tracheal diameter, measurable from CT scans or chest X-rays, also relates to the appropriate DLT size. For example, a tracheal diameter of 18 mm or greater corresponds to a 41 Fr DLT, while a diameter less than 15 mm suggests a 35 Fr DLT. These imaging-based methods offer a tailored approach, leading to a better tube fit and reducing the need for tube repositioning and associated complications. This detailed assessment of individual airway anatomy improves tube selection.
Techniques for Placement Confirmation
After DLT insertion, confirming correct placement is essential to ensure effective one-lung ventilation and prevent complications. While initial clinical signs like auscultation and observing chest wall movement offer preliminary indications, they are unreliable for definitive confirmation. Fiberoptic bronchoscopy is the gold standard for verifying the precise position of the DLT.
Bronchoscopic confirmation involves visual inspection of the airway. A flexible bronchoscope is advanced through the DLT’s tracheal lumen. The tracheal carina, where the trachea divides, is observed. The DLT’s bronchial lumen should be correctly positioned within the intended mainstem bronchus (e.g., left main bronchus for a left-sided tube). The blue bronchial cuff should be visible just below the carina, fully inflated, without herniation above the carina.
The bronchoscope is then advanced into the bronchial lumen to confirm patency and ensure clear visualization of the distal airways.
Bronchoscopy also helps identify signs of an incorrectly sized tube. If the tube is too large, it can be difficult to advance or cause blanching of the tracheal or bronchial mucosa, indicating excessive pressure. Conversely, a tube that is too small may require an excessive volume of air to inflate the bronchial cuff, which can lead to cuff herniation above the carina or persistent air leaks, compromising lung isolation. Undersized tubes are also more likely to migrate distally, increasing the risk of airway trauma. Studies indicate that DLT malpositioning is common (35-48% of cases), even when inserted by experienced providers, highlighting the necessity of bronchoscopic confirmation.