Mechanical Ventilation- Endotracheal tube.

Bevelled end

So the distal end of the endotracheal tube (ETT) is cut at a slant. This is known as a bevelled end. This is designed this way for a couple of reasons.

Firstly it aids the viewing of the cords when it is being passed through them. If it were not bevelled then that view would be obstructed.

It is also less likely to become completely blocked by the wall of the trachea if pushed against it.

Murphy eye

Most ETT have a small opening on the side just above the beveled end which is known as the Murphy eye. This is another way of ensuring that tube can still function if the end becomes occluded. It is the escape route for the air if you like


On adult tubes there will be a cuff. The cuff is a balloon which inflates to help seal the airway. The cuff has two main functions.

Firstly it ensures that the air that is put into the lungs, which is under pressure, will not then come back out of the patients mouth or nose.

It also ensures that the chances of aspiration of secretions by the patient is much less likely. It does not cause complete occlusion beyond it, so some secretions will still travel past as there will be some fine folds around it.

However it will prevent aspiration of larger objects/secretions.

This cuff is the main part of the tube which will help protect the airway in for example the patient who has taken a drug overdose.

Intubation marker line

Some tubes have a black marker line just above the cuff. This is a visual indicator to help when intubating. When this marker goes through the cords you need to stop advancing the tube, otherwise you run the risk of putting the tube down the right main bronchus.

Centimetre markings

The tube will have the centimeter markings running up it going up in value from the distal end in 2cm increments, ending at about 30cm at the proximal end of the tube.

On a normal adult, if orally intubated, the tube will be at 21-23cm at the lips.

This can vary with body habitus. The bigger patient may need the tube to go further down to reach the glottis for example.

This should be charted to allow consistency and to ensure that the tube has not moved.

Pilot tube and balloon

At the distal end the pilot tube has a one way valve that will be opened when a syringe is inserted into it.

This then allows the user to inject air into the cuff of the ETT, which will inflate the cuff allowing a seal to be created.

As the cuff inflates, so does the pilot balloon giving the user a visual reference.

The cuff should always be completely deflated when intubating and extubating the patient as this will ensure minimal trauma to the airway as the tube passes through it.

Internal Diameter

This can range from 2.5mm to 10mm.

Normal range for females is 7-7.5 and for male is 7.5-8.

Size of the tube is often marked at the proximal end so that when the patient is intubated the user will know what size tube they have in.

15mm Adapter

Plastic connector at the end which will ensure that bags used for ventilation, and ventilation tubing will connect to the ETT.

Guidelines for the management of tracheal intubation in critically ill adults

Having read the guidelines I made these infographics. They are FREE. Just let me know your email address and they will be sent to you.