Armored/ re-inforced tubes

Author: 
Claas Siegmueller

 

FEATURES

By being more flexible than standard ET tubes, armored tubes are less likely to kink and occlude when bent to an angle, which is their biggest single advantage over standard ETTs.

Armored or re-inforced ET tube

 

Just like standard ET tubes, armored or re-inforced tubes have the typical left-facing bevel at the tip and the Murphy eye. Their distinctive feature is a metal wire coil embedded in the wall of the tube shaft which keeps the lumen of the tube open when it is bent. The fact that this type of ET tube contains a metal wire coil means there is no need for a radio-opaque line.

Close-up view of the tip of an armored/ re-inforced ET tube

 

In contrast to ‘standard’ ET tubes, the tube connector of armored tubes is firmly fixed to the tube shaft and not detachable.

The fact that armored tubes are 'bendier' and therefore not as well pre-formed as standard tubes means they are more likely to require a stylet for successful intubation since they don't keep their curved shape quite as well.

Side-by-side comparison of 'kink-resistance' for s standard ETT (left) and an armored ETT (right)

 

Although armored tubes are less likely to occlude through bending because of the wire-coil re-inforcement, they are not a substitute for a bite block. Whilst it is significantly more difficult for a patient to totally occlude an armored compared to a regular tube by biting onto it, the armored tube has the disadvantage of having a ‘memory’, meaning it won’t expand back to a round diameter once the bite is released, significantly increasing resistance to airflow.

'Bite mark' on an armored ETT; note that the tube does not spring back to its original shape after compression

 

MRI compatibility of armored ETTs

For medical equipment there are three levels MRI compatibility and safety

  1. MRI-safe: Equipment that does not contain any metal parts. With regards to endotracheal tubes this would apply to uncuffed ETTs.
  2. MRI-conditional: Equipment which has some metal parts such as the stainless steel spring in the pilot balloon valve of cuffed endotrachel tubes.
  3. MRI-unsafe: Equipment that must not be used in an MRI environment.

With regards to MRI safety, armored endotracheal tubes are classified as MRI-conditional, which means they are generally safe to use in an MRI environment, with no increased risk of clinically significant heating in the magnetic field. Actually, most endotracheal tubes are only classed as MRI-conditional and not MRI-safe, because the pilot balloon usually contains a metal spring-loaded valve. For any medical equipment to be MRI-safe, it must not contain any metal at all. It might still be worth to avoid using armored tubes in the MRI environment as the metal coil can adversely affect picture quality, especially if the scanned area is in close vicinity to the tube, i.e. in c-spine and brain MRIs.


USES

Reinforced tubes have certain advantages over standard endotracheal tubes in several situations due to their resistance to occlusion when bent and their overall greater flexibility:

  • The most common reason to use armored ETT is arguably for certain head & neck and neurosurgical cases, i.e. when access to the airway is limited and bulky equipment in front of the patient's mouth and face can get in the way of the surgeon. In these situations an armored tube is a great alternative to an oral RAE tube.
  • They can be advantageous in fiberoptic intubation via either the oral or nasal route. Since they are usually easier to 'railroad' off the scope due to their superior flexibility. 
  • They might be useful for intubation through a tracheotomy. Again, the greater flexibility of these tubes makes for an easier navigation of the angle between the tracheotomy site at the skin and the trachea and makes an armored ETT potentially less traumatic than a standard one.
  • Reinforced tubes can be useful in patients positioned prone. Forces applied at to the part of the tube outside of the patients airway are less likely to be transmitted.
There are some disadvantages to using armored/ re-inforced tubes:
  • 'Misting' of the ET tube, one of the confirmatory signs of successful tracheal intubation, is more difficult to see when an armored/ re-inforced tube is used because of the wire coil and overall higher opacity of the tube wall.
  • The fact that the connector at the proximal end is fixed and cannot be detached means armored/ re-inforced ETTs cannot be used with the AirQ supraglottic airway or for intubation through an operating laryngoscope (as is occasionally done by our ENT surgeon colleagues).
  • They might not be suitable for airway management in the MRI scanner (see above).
  • They are more expensive!