Endotracheal tubes

FEATURES

Endotracheal tubes are mostly made of polyvinylchloride (PVC) and are single-use. They have a number of characteristic features that are listed below. Many variations of these designs exist in endotracheal tubes for particular purposes, as described in the links on the left.

Tube tip design

Endotracheal tubes (ETTs) typically have a left-facing bevel at the tip and, as a second design feature, a Murphy eye.

The bevel is left-facing rather than right-facing to allow the ETT tip an easier pass through the vocal chords. Endotracheal tubes are usually placed with the right hand in a right-to-left direction towards the larynx (see diagram below).

  

Whilst a tube with a bevelled tip is obviously easier to pass through the vocal chords, it is more likely to occlude when the opening makes contact with the tracheal wall. The Murphy eye provides an alternate gas passage should occlusion occur.

 

Cuff design

The majority of endotracheal tubes used in the operating room are of the low pressure- high volume type. These cuffs have a comparatively large volume and consequently large contact area between cuff and trachea. The cuff can develop folds in this contact area when inflated, resulting in an increased risk of aspiration secondary to regurgitated fluid tracking along these fold into the trachea.

In contrast, high pressure-low volume cuffs are thought to provide better protection against aspiration. Because of their much smaller cuff-trachea contact area and higher inflation pressures used, cuff folds are less likely to develop. The downside of this cuff type is that the higher cuff pressures are more likely to lead to tracheal mucosal ischemia. The cuff of the laser tube is of the high pressure- low volume design.

Low pressure- high volume cuff inflated with blue dye inside a 20ml syringe; cuff folds are visible within the large cuff contact area

High pressure- low volume cuff inflated with blue dye inside a 20ml syringe; no cuff folds are visible within the much smaller cuff contact area; high pressure- low volume cuff tubes are now uncommon, we have used a laser tube here to demonstrate this cuff design

Other features

Polyvinylchloride (PVC), the material which most endotracheal tubes are made of, does not absorb x-rays. PVC tubes therefore contain a radio-opaque line, which makes them visible on chest radiographs.

The radio-opaque line of the ETT is clearly visible on this chest X-ray.

In addition, most ETTs have a pilot balloon with non-locking Luer connector and a metal spring valve through which the cuff can be inflated. The pilot balloon allows visual and tactile assessment of whether the cuff is inflated or not.


USES

Endotracheal tubes are used to establish and maintain airway patency, prevent aspiration into the lungs, i.e. 'secure' the airway, and allow mechanical ventilation.