OSCE 10

What is this device? What are the indications for its use?

This was an older style college OSCE; the original text read "Miscellaneous  Equipment  including  examples  of  types  of  double  lumen  tubes, laryngoscopes, pulmonary artery catheters, cricothyrotomy kits and airway exchange catheters",  which was unhelpful.

Anyway: this is a double lumen tube. Ideally, you should hand them a right-sided one.

General indications for use include:

• Prevention of cross-contamination of one lung by the other, eg. in the following cases:
  • Infection (e.g. unilateral pulmonary abscess)
  • Massive pulmonary haemorrhage

• Enable the ventilation of each lung with a different ventilation setting in settings where the each hemithorax is wildly different from the other, for example:
  • Severe chest injury
  • Bronchopleural fistula
  • Open chest (eg. mid thoracic surgery)
  • Giant unilateral lung cyst or bulla
• Bypass a damaged section of the airway
  • Tracheobronchial tree disruption /Major airway trauma
• Permit the lavage of each lung independently - pulmonary alveolar proteinosis is frequently mentioned as an indication, and I suppose if one finds oneself bringing it up during a viva, one should then be prepared to discuss what it is.

How do you tell whether this is a left or right-sided DLT?

iewed side by side, the difference is obvious.

• The right-sided tube has a weirdly shaped "eccentric" cuff, to prevent the occlusion of the right upper lobe bronchus.
• The left sided tube has a normal straight cuff.

When would you need to use a right-sided DLT?

• The only indications for the insertion of a right-sided tube is an operation which is performed on the left main bronchus.
•  In every other case, a left sided tube is preferred.
• The left main bronchus is about 50-60mm long, whereas the right main bronchus is only about 20-25mm long. The left sided tubes have a much greater margin of safety, as they are much easier to insert. 

Describe how you would insert this tube and check that it is in correct position

To insert a left sided DLT:

The blind method

• Intubate the patient with the DLT, with the bronchial part facing anteriorly
• Rotate 90º left (i.e. now aim the brochial part to the left) as soon as it is through the cords
• Advance the tube and inflate the tracheal cuff once some resistance is met 
• Ventilate both lungs
• Inflate the bronchial balloon
• Each lumen is sequentially clamped, and the hemithorax auscultated to ensure ventilation.
• In the case of a right sided tube, one must auscultate the right apex, to ensure that the right upper lobe bronchus has not been blocked by the balloon.

The bronchoscope-guided method

• The patient is intubated routinely, and both balloons are inflated.
• A bronchoscope is passed though the tracheal lumen and the position of the left endobronchial tube is confirmed: it should be obvious whether the tube is in the left mainstem bronchus, or the right, or whether it is dangling above the carina. The DLT is then adjusted into a correct position.
• In practice, one very rarely needs to go down the endobronchial lumen. On the left, there really is nothing to see down there. On the right, one might be tempted to assure oneself of correct position, particularly whether the right upper lobe bronchus is blocked - but realistically, one might get more information about that by auscultating the right apex.

Pros and cons of each method

• The blind approach is slower to achieve good position
• The blind approach frequently will still require bronchoscopy to troubleshoot a malposition
• The bronchoscope-guided approach is typically more accurate and faster, but takes a long time to set up.

How would you ensure that lung isolation is achieved?

• By the measurement of expired CO₂ in the clamped tracheal lumen
• By auscultating the chest
• By inspecting the bronchial cuff with a bronchoscope (looking for visible bubbles of air leak)

How do you determine the correct size of this tube for insertion?

• These tubes are not sized according to their internal diameter, but rather according to the French catheter gauge (i.e. the diameter in mm. times 3), which corresponds to their external diameter.
• Girls get sizes 28-37, and boys get sizes 37-41.

What is the expected depth of insertion, for a 170 cm tall adult?

• It should be 29 cm at the teeth, +/- 1cm

What are the safety features of this device?

The DLT shares all of the safety features of the single lumen ETT, which are as follows:

• Standardised 15mm connector to fit all airway devices
• Low-allergen PVC construction, free of latex
• Transparent body,to see blood or vomit
• Markings to indicate depth of insertion
• High volume low pressure cuff to seal the trachea
• Pilot cuff to gauge cuff pressure
• Rounded atraumatic edges
• Murphy's eye to protect against occlusion
• Radio-opaque line to help gauge position on chest X-rays

However, the dual lumen tube has a few added extras:

• Blue designation for the endobronchial components
• Soft silicon portion of the ventilator connector, to ensure that it can be clamped safely without fracturing
• Small volume endobronchial cuff, to prevent bronchial mucosal ulceration
• Specially designed eccentric balloons for right-sided DLTs, preventing the obstruction of the right upper lobe bronchus

Once lung isolation is achieved, how will you set the ventilator to ventilate just the right lung?

• 6ml/kg tidal volume
• PEEP 5-8
• FiO2 50-100% initially
• Permissive hypercapnia

What are the risks of using this device?

• Failure of intubation - as previously mentioned, these things are not exactly quick or easy to insert. The chance of getting it wrong is considerably greater, even with expertise.
• Success of tracheal intubation, but failure of lung isolation - the tube fails to isolate the correct lung
• Tracheal injury - the tube is rigid and thick, more likely to damage the trachea on insertion, and there is a large cuff to inflate which may put additional pressure on the tracheal walls.
• Bronchial injury - the bronchial cuff may put too much pressure on the bronchial wall (which is far from robust) and cause a pressure area; on top of that it is possible to rupture the bronchus with a rough intubation.
• Airway oedema - the size of the tube and its rigidity may give rise to greater tracheobronchial injury, with more oedema and therefore an increase in the difficulty of re-intubation.
• Need for sustained neuromuscular junction blockade and heavy sedation: even a 1cm migration may result in incomplete lung isolation, so the patient is not allowed to cough or move very much

What are the alternatives to the use of this device, if lung isolation is desired? What are their advantages and disadvantages?

• Bronchial blocker
  • Advantages:
    • Easy to use with a normal endotracheal tube
    • Easier to use with patients who have a difficult airway
    • It is even possible to isolate specific lobes
    • Easy to stop lung isolation when it is no longer required
  • Disadvantages:
    • May actually take longer than a DLT to deploy
    • Correct positioning requires bronchoscopy
    • Suctioning of the isolated lung is not possible
    • Bronchoscopy of the isolated lung is impossible
    • Differential ventilation of each lung is impossible
• Advance the endotracheal tube into bronchus
  • Advantages:
    • Fastest!
    • Easier in an emergency
    • Can be bronchoscope-guided to access the correct bronchus
  • Disadvantages:
    • Difficult to ventilate the left lung, if blind insertion
    • Difficult to alternate one-lung ventilation to the other lung
    • Bronchoscopic access to the other lung is lost

Disclaimer: the viva stem above may be an original CICM stem, acquired from their publicly available past papers. Or, perhaps it is a slightly altered version of the original CICM stem. Or, it is a completely original viva stem, concocted by the monstrously amoral author of Deranged Physiology for nothing more than his own personal amusement. In either case, because the college do not make the main viva text or marking criteria available, almost everything here has been confabulated. It might sound like a plausible viva and it could be used for the purpose of practice, but all should be aware that it does not represent the "true" canonical CICM viva station.