Tracheal Tubes

• functions of endotracheal tubes

• physical construction

• preformed tubes (e.g. RAE tubes)

• paediatric tubes

• reinforced tubes

• laser resistant tubes

• introduction to double lumen tubes

• bronchial blockers

What are the functions of endotracheal tubes ?

An endotracheal tube (ET tube) :

• provides a passage for gases to flow between a patients lungs and an anaesthesia breathing system .

• allows one to provide positive pressure ventilation.

• protects the lung from contamination from gastric  contents and nasopharyngeal matter such as blood.

It is a commonly used device that  is critical for patient safety so it is important that you understand its design and use.

ET tubes come in various sizes and shapes, but the basic concepts underlying them is the same for all.

An "ET tube" is a "tube" !

An ET tube, as the name suggests, is a tube !  Like any tube, it is:

• made out of certain materials

• has a diameter

• has a length

What are ET tubes made out of ?

Most ET tubes that you will encounter will be made out of plastic (Polyvinyl Chloride, PVC).

These ET tubes may be visually clear or opaque.

Plastic is not radio opaque and therefore have a line of radio opaque material that makes them more visible on a chest X ray.

Diameter

ET tubes have an inner diameter and an outer diameter.

The “size” of an ET tube refers to its internal diameter. Therefore if you ask for a “size 6 ” ET tube, you are asking for one with an internal diameter of 6 mm. The image below shows a size 6 mm ET tube. In this particular ET tube, the internal diameter is labeled as “ID 6.0” and similarly, the outside diameter is labeled as 8.8 OD.

Narrower tubes increase the resistance to gas flow. A size 4 mm ET tube has sixteen times more resistance to gas flow than a size 8 mm ET tube. This can be especially relevant in the spontaneously breathing patient who will have to work harder to overcome the increased resistance. Thus one should choose the largest diameter ET tube that is suitable for a given patient.

Paediatric ET tubes have a much smaller internal diameter.

Length

The length of the ET tube is measured from the end that goes into the trachea and is marked in centimeters.

After intubation, you should note the "length marking" of the ET tube with reference to a landmark such as incisor teeth or lips. This will help you to monitor the ET tube position and detect if the ET tube has moved into the left or right bronchus.

An ET tube that is too long for a given patient maybe more prone to kinking and become obstructed. It can be cut to an more appropriate length if necessary.

To help correct depth of placement, some ET tubes have black markings proximal to the cuff .

As shown below, in ET Tubes with one mark, the vocal cords should be at the black mark.

The ET Tube below has two marks. In this case, keep the vocal cords between the two marks. However, these marking systems only provide a rough estimate and correct ET tube position depth should always be confirmed by auscultation.

Bevel

To make it easier to pass through the vocal cords and to give you a better vision ahead of the tip, ET tubes have a “slant” called a bevel .

As the ET tube is advanced near the cords, the left facing bevel gives a better view .

Murphy Eye

Some ET tubes have an additional hole at the tip called a Murphy's Eye . If the main opening of the ET tube gets blocked by for example abutting against the tracheal wall (represented in the image by the finger) gas flow can still occur via the Murphy Eye. Without the Murphy Eye , the ET tube would have been completely obstructed .

Cuff

A cuff is an inflatable region at the patient end of an ET tube. ET tubes may or may not have a cuff. In the image below , ET tube 1 does not have a cuff. The ET tube 2 has a cuff that is deflated, and ET tube 3 has a inflated cuff.

The inflated portion forms a seal against the tracheal wall . This seal prevents gases from leaking past the cuff and allows positive pressure ventilation. The seal also prevents matter such as regurgitated gastric contents going into the trachea.

After intubation, the cuff is inflated with air. As shown in the image below, this is done by attaching a syringe to the pilot balloon . The pilot balloon is connected to the cuff by a thin tube. As the syringe supplies pressurised air, the pilot balloon and cuff inflate. Once the cuff is inflated the syringe is removed. Air does not leak out as there is a one way valve at the pilot balloon. By feeling the pilot balloon, one can estimate the amount of pressure in the cuff. If the cuff is leaking, e.g. due to damage by the surgeon during a thyroidectomy, the pilot balloon will collapse.

Cuffs are designed to have either a high volume or a low volume.

As explained below, cuffs with a high volume have a low pressure and are called "High volume Low pressure" cuffs. Similarly, cuffs with a low volume have a high pressure and are called "Low volume High pressure" cuffs.

High volume low pressure cuffs: As shown in the image below, because of their large volume, they have a larger surface area in contact with the trachea. This means that they apply a lower pressure against the tracheal wall and have a lower incidence of tracheal wall ischemia and necrosis. The seal is not as good as the seal in high pressure cuffs because of the lower pressures and because the large cuff may develop wrinkles that allow material to pass by the cuff.

Low volume high pressure cuffs: These cuffs have a lower volume and the surface area in contact with the trachea is small. This results in a high pressure seal that is more effective than the one caused by  high volume low pressure cuffs. However, this high pressure is more likely to  cause tracheal ischaemia and necrosis if used for a prolonged period of time.

Connectors

ET tube connectors connect the ET tube to the breathing system. One end of the connector connects to the ET tube and this end has a diameter that depends on the ET tube size (see small arrows in image below). The other end connects to the  breathing system and has a 15 mm outer diameter (British Standard).

ET tubes are often not directly connected to breathing systems. Instead , to provide a more flexible connection, ET tubes are often connected to a  flexible “Catheter Mount” (see image below). The catheter mount is then connected to the breathing system.

Special Endotracheal Tubes

PREFORMED ET TUBES

Preformed ET tubes are molded into special shapes that permit  good surgical access in the oro nasal area.

For an example (refer to picture below),a “South” facing preformed ET tube provides good access for the ENT surgeon needing to work in the nasal passages.

Similarly, a “North” facing (i.e. the tube emerges from the patient and faces towards the patients top) preformed  ET tube provides very good access  to the mouth for dental work . 

Below are some pictures of real pre formed ET Tubes

The pre formed ET Tube below has a special name. It is called a "RAE" tube, named after its inventors Ring, Adair, and Elwyn.

PEDIATRIC ET TUBES

ET tubes for paediatric patients are  smaller than those meant for adults. Because the paediatric trachea is susceptible to damage by pressure, most paediatric  ET tubes are uncuffed. However, cuffed versions  similar to adult ET tubes exist and when used , must be inflated with care.  A wide range of sizes are available.

Formulae are available to guide size selection. After intubation, depending if the fit is too tight or loose, one may have to use a different sized ET tube. For this reason, one should always keep a wide range of paediatric  ET tube sizes.

The ET tubes may have a mark to guide optimum depth of placement.  In these ET tubes, the vocal cords should be at the junction of the black line (see red arrow) and clear area as shown below.

Reinforced or armoured ET tubes are specially designed to be resistant to kinking . 

As shown below, they achieve this property by having a  spiral of wire embedded into the wall of the ET tube to give it strength and flexibility at the same time. These are particularly useful for head and neck surgery where the ET tube may be sharply bent and also compressed by the surgeons. Armoured ET tubes can be easily bent away from the area of surgery and thus improve surgical access.

 

Some airway surgery involves the use of laser beams to burn away tissue.  These beams can ignite ordinary ET tubes and  in the presence of Oxygen  may cause major airway fires.  Special ET tubes are available (example shown below) which resist  damage by laser beams.

In the ET tube shown, there is a laser resistant metal foil wrapped around it for protection. 

In this ET tube, the cuff is filled with methylene blue coloured saline.

If the laser manages to damage the cuff,  the colouring will help identify rupture and the saline will help prevent an airway fire.

In thoracic surgery, there are times that you may need to isolate and selectively not ventilate one lung. For an example, during an oesophagectomy , one may choose to not ventilate one lung to provide better surgical access to the oesophagus.  There are special ET tubes called “double lumen tubes” (DL tubes) to achieve this. A DL tube can be thought of as  two ET tubes joined together (see graphic below).  One tube is shorter and ends in the trachea and there is cuff at this level called the  tracheal cuff (colored red in the image).  The other tube extends further and enters a main bronchus and has its own cuff (bronchial cuff, usually coloured blue).

Using a special connector and clamp, one can not ventilate one lung and let it collapse to provide good surgical access.

An alterative to using a double lumen tube to isolate one lung is to use a standard ET tube along with a special device called a "bronchial blocker". The bronchial blocker has a thin tube with a cuff at one end.

Let us isolate the left lung using a bronchial blocker. First the trachea is intubated with a standard ET tube. As expected, you will be now ventilating the left lung and the right lung.

The bronchial blocker is inserted, using a special connector, through the standard ET tube you just inserted. It is guided into the left lung, often using a fiber optic scope.

Once positioned correctly, the cuff of the bronchial blocker is inflated. This cuff blocks air entry into the left lung. The air in the left lung escapes through the thin bronchial blocker tube (shown in pink ) making the left lung collapse. Ventilation to the right lung continues through the standard ET Tube (shown in green).

After the surgery, if you want to continue to ventilate the patient, the bronchial blocker is pulled out, leaving behind the standard ET tube to ventilate both lungs.

There are various advantages and disadvantages of double lumen tubes and bronchial blockers.

Both lumens of a double lumen tube are wide so you can individually suction both lungs. On the other hand, the lumen of bronchial blockers are generally too small for effective suction, so secretion removal from the blocked lung can be difficult. Double lumen tubes are bulky and are therefore difficult to insert in a difficult airway. On the other hand, bronchial blockers need only a standard size ET tube so are easier to insert in this situation. Due to their size, double lumen tubes are also more traumatic and are usually not used postoperatively for continued ventilation. Bronchial blockers need only a standard ET tubes which are much less traumatic and can be easily kept in for postoperative ventilation.