An endotracheal tube（ett tube）is placed between the vocal cords through the trachea, which is made of polyvinylchloride (PVC) and is single-use. PVC is not radiopaque and therefore contains radiopaque linear material throughout the length of the tube to make it easier to show the placement on x-ray. 

The endotracheal tube is used for supplying oxygen and inhaling gas to the lungs and to protect them from contamination, such as stomach contents or blood. To assist you comprehend the ett tube better, we will introduce the specs of the ett tube and the functions of the main parts through this post.

Endotracheal Tube Size 

An ett tube has a length and a diameter. For example a 6.0 inch tube, 6.0 refers to its inner diameter in millimeters (mm).

ET Tube Size Chart

As shown in the diagram above, the inner diameter is the ID and the outer diameter is the OD. 

The greater the resistance to airflow, the narrower the tube. Therefore, healthcare providers should choose the largest tube that fits the patient; this is critical for spontaneously breathing patients who have to overcome the higher resistance.

The Cuff

The cuff is an inflatable balloon attached to the ETT's end. Paediatric ETTs are manufactured with and without a cuff. When the cuff is inflated, it forms a seal against the tracheal wall, preventing stomach contents from entering the trachea and assisting in positive pressure ventilation. The cuff is inflated by attaching an appropriately sized syringe (10 to 20 ml for the adult ETT).

The syringe delivers pressurized air and inflates the balloon and cuff. Once the cuff has been inflated, the syringe must be removed otherwise the air in the cuff will redistribute back to the syringe, deflating the cuff. 

The Bevel

The bevel is to facilitate placement through the vocal cord and to provide better visualization in front of the tip of the nose. The leftward bevel provides the best view when the tracheal tube is close to the cord.

The Murphy Eye

The ETT has a built-in safety mechanism at the end called the Murphy Eye, which is an additional opening. If the end of the ETT is blocked by the tracheal wall or touching the bulge, gas can still flow through the Murphy Eye, which prevents the catheter from becoming completely blocked.

The Connector

The ETT connector connects the ETT to the mechanical ventilator tubing or an Ambu bag. For adult and pediatric ETTs, a universal 15 mm connector is usually used.

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