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Tracheal Tubes 2017 Description: Tracheal tubes are widely used in anaesthesia to provide gas transfer between a breathing system and a patient’s trachea. This module will help you to understand the design and use of standard tracheal tubes. You will also be introduced to variants of the tracheal tube which have been modified for use in different clinical situations.
Session Introduction • • Learning Objectives: Recognize the purpose of tracheal tubes Recognize and describe the design features of tracheal tubes Identify the basic features of specialized versions of tracheal tubes Identify and recognize the basic features of rigid stylets and bougies
Introduction to Tracheal Tubes A tracheal tube provides a passage for gases to flow between a patient’s lungs and an anaesthesia breathing system. It is a commonly used device that is critical for patient safety. Therefore, it is important that you understand its design and proper use. Tracheal tubes come in various sizes and shapes, but the basic concepts underlying them is the same for all. The function of tracheal tubes will be described, followed by a discussion of the many features that can be attributed to them. Finally, we will introduce specially designed tracheal tubes that may be used in specific clinical situations. This session will end with some self assessment questions, to test your knowledge of tracheal tubes and their applications. A tracheal tube
What are the Functions of Tracheal Tubes? Tracheal tubes provide a route for gases to flow between a patient’s trachea and the anaesthetic breathing system. In addition, when tracheal tubes are cuffed (which will be explained later in the session) they allow positive pressure ventilation to be used more effectively. The cuff of a tracheal tube also protects the lung from contamination from gastric contents and nasopharyngeal matter such as blood. Tracheal tube
Basic Design The basics of tracheal tubes A tracheal tube has a diameter and a length and is made out of special materials such as polyvinyl chloride (PVC) or red rubber. It also usually has a curvature and markings. It may have a cuff at the tracheal end to provide a seal between the tube and the tracheal wall. If a cuff is present, to inflate and deflate it, there will be a thin tube attached to a small one-way valve and balloon.
Construction Material Most tracheal tubes encountered will be made out of polyvinyl chloride (PVC). These are disposable. The plastic PVC tracheal tubes may be visually clear or opaque as shown in the image (Fig 1). Plastic is not radio-opaque (i. e. it is not visible on x-ray) and therefore plastic tracheal tubes have a line of radio-opaque material that makes them more visible on a chest x-ray (Fig 2). Tracheal tubes may also be made out of rubber. These may be reused after cleaning and autoclaving (Fig 3).
size Tracheal tubes have an inner diameter and an outer diameter. The ‘size’ of a tracheal tube refers to its internal diameter. Therefore if you ask for a size 6 tracheal tube, you are asking for one with an internal diameter of 6 mm. Narrower tubes increase the resistance to gas flow. A size 4 mm tracheal tube has 16 times more resistance to gas flow than a size 8 mm tube. This can be especially relevant in the spontaneously breathing patient who will have to work harder to overcome the increased resistance. Therefore, the largest suitable internal diameter tracheal tube should be used. An average sized male will usually require a size 8. 5– 9 mm internal diameter tracheal tube and an average sized female will require a size 7. 5– 8 mm internal diameter tube. Paediatric tracheal tubes are available in much smaller internal diameters based on the age and weight of the child. Fig 1 shows a size 6 mm internal diameter tracheal tube. In this particular tube, the internal diameter is labelled as ‘ID 6. 0’ and similarly, the outside diameter is labelled as ‘ 8. 8 OD’.
Length The length of a tracheal tube is measured from the end that goes into the trachea and is marked in cm on the outside of the tube as shown (Fig 1). After intubation, you should note the length marking of the tracheal tube with reference to a landmark such as incisor teeth or lips. This will help you to monitor the position of the tracheal tube and detect if the tube has inadvertently got pushed too far (into a bronchus) or pulled outwards (resting on vocal cords). A tracheal tube that is too long for the patient maybe more prone to kinking and becoming obstructed. It can be cut to a more appropriate length if necessary.
Length To help the accurate placement of the tracheal tube tip within the trachea, some tracheal tubes have black intubation depth markings located proximal to the cuff (Fig 2). The vocal cords should be at the black mark in tracheal tubes with one mark (Fig 3). Or should be between marks if there are two such marks (Fig 4). However, these are only rough estimates and correct tube position depth should always be confirmed by auscultation.
Bevel To make it easier to pass the tracheal tube through the vocal cords and to improve the view of the vocal cords during intubation, tracheal tubes have a 'slant' called a bevel (Fig 1). As the tracheal tube is advanced near the cords, the left-facing bevel gives a better view (Fig 2).
Murphy Eye Some tracheal tubes have an additional hole at the tip called a Murphy eye. If the main opening of the tracheal tube gets blocked by, for example abutting against the tracheal wall (represented in Fig 1 by the finger) gas flow can still occur via the Murphy eye. Without the Murphy eye the tracheal tube would have been completely obstructed (Fig 2).
Cuff A cuff is an inflatable region at the patient end of a tracheal tube. Tracheal tubes may or may not have a cuff. The tracheal tube (top) does not have a cuff. The tracheal tube (middle) has a cuff that is deflated, and the tracheal tube (bottom) has an inflated cuff (Fig 1). The inflated portion forms a seal against the tracheal wall (Fig 2). 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.
Cuff After intubation, the cuff is inflated with air. This is done by attaching a syringe to the pilot balloon (Fig 1). The pilot balloon is connected to the cuff by a thin tube. As the syringe supplies pressurized air, the pilot balloon and cuff inflate. Cuff inflation has to be done gently to prevent over-inflation and exerting too high a pressure on the tracheal mucosa. Continuous listening for an air leak should be used and the inflation should stop when the leak stops. 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, the amount of pressure in the cuff can be estimated. If the cuff is leaking, e. g. due to damage by the surgeon during a thyroidectomy, the pilot balloon will collapse. Cuff pressure can also be checked using a specially designed pressure gauge.
Cuff Volume and pressure Cuffs can either have a high volume with low pressure or have a low volume with high pressure (Fig 1). High volume/low-pressure cuffs Because of their large volume, these cuffs 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 highpressure cuffs because of the lower pressures and because the large cuff may develop wrinkles that allow material such as regurgitated gastric contents to pass by the cuff (Fig 2).
Cuff Volume and pressure 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 created 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 (Fig 3).
Cuff Volume and pressure
Tracheal Tube Connectors Tracheal tube connectors connect the tracheal tube to the breathing system (Fig 1 a). One end of the connector connects to the tracheal tube and this end has a diameter that depends on the size of the tube; see small arrows (Fig 1 b). The other end connects to the breathing system and has a 15 mm outer diameter (British Standard) (Fig 1 c). Often tracheal tubes are not directly connected to breathing systems. Instead, to provide a more flexible connection, tracheal tubes are often connected to a flexible ‘catheter mount’ (Fig 2). The catheter mount is connected to the tracheal tube via an L-shaped connector called an 'angle piece' (Fig 3).
Tracheal Tube Connectors
Specialized Versions of Tracheal Tubes Preformed tracheal tubes are moulded into special shapes that permit good surgical access into the oronasal area. A north-facing tracheal tube emerges from the patient and faces towards the patient’s forehead (Fig 1). Such preformed tracheal tubes provide very good access to the mouth for dental work.
Specialized Versions of Tracheal Tubes Similarly, south-facing preformed tracheal tubes provide good access for the ear, nose and throat (ENT) surgeon needing to work in the nasal passages (Fig 2). For some real examples of preformed tracheal tubes, see Fig 3. The tube marked ‘South’ shows a RAE tube, named after its inventors Ring, Adair and Elwyn.
Specialized Versions of Tracheal Tubes Tracheal tubes for paediatric patients are smaller than those meant for adults. Because the paediatric trachea is very susceptible to damage by pressure, many paediatric tracheal tubes are uncuffed. However, cuffed versions similar to adult tracheal tubes do exist and when used, must be inflated with care. A wide range of sizes are available (Fig 1) and (Fig 2).
Specialized Versions of Tracheal Tubes Paediatric tubes Tables and formulae are available to guide size selection (Fig 3). After intubation, depending on whether the fit is too tight or too loose, a different sized tracheal tube may have to be used. For this reason, a wide range of paediatric tracheal tube sizes should be readily available. The tracheal tubes may have a mark to guide optimum depth of placement. In these tubes, the vocal cords should be at the junction of the black area and the rest of the tube (Fig 4)
Specialized Versions of Tracheal Tubes Armoured tracheal tubes Reinforced or armoured tracheal tubes are specially designed to resist kinking (Fig 1). They achieve this property by having a spiral of wire embedded into the wall of the tracheal tube to give it strength and flexibility at the same time (Fig 2). These tracheal tubes are particularly useful for head and neck surgery where the tracheal tube may be sharply bent or compressed by the surgeons. Armoured tracheal tubes can be easily bent away from the area of surgery and thus improve surgical access.
Basic Features Rigid stylet Sometimes it is useful to stiffen a tracheal tube by inserting a metal rigid stylet into the lumen of the tube prior to intubation. The rigid metal stylet enables the tracheal tube to be bent in a direction more suited to the patient. They are also often used with armoured tracheal tubes, which because they are naturally 'floppy', often need to be made rigid using a stylet. Once intubation is achieved, the rigid stylet is removed, taking care not to dislodge the tracheal tube in the process. Unlike a bougie (discussed later), a rigid stylet must never project beyond the tip of an tracheal tube. A protruding rigid stylet can cause serious damage to airway structures.
Basic Features Bougie A bougie is a relatively flexible stylet that can assist difficult intubation. It has a curved tip that can help intubate an anterior trachea. If only the epiglottis is seen, it can even be passed ‘blindly’ into the trachea. Once the bougie is in the trachea, the tracheal tube is ‘railroaded’ over it. The bougie is held in place, while the tracheal tube is pushed into the trachea. Once in the trachea, the tracheal tube is held in place while the bougie is pulled out.
Session Key Points • Tracheal tubes provide a path for gas flow, protect the airway, and allow positive pressure ventilation for the patient • The 'size' usually refers to the internal diameter • The cuff may be high volume/low pressure or low volume/high pressure • Paediatric tracheal tubes are smaller and their size must be chosen carefully • Specialized versions exist such as preformed, armoured, double lumen, and laser resistant
Session Summary Learning Objectives: • Recognize the purpose of tracheal tubes • Recognize and describe the design features of tracheal tubes • Identify the basic features of specialized versions of tracheal tubes • Identify and recognize the basic features of rigid stylets and bougies When you next work in theatre, have a look at the tracheal tubes on the airway trolley. Ask your operating department practitioner to show you the specialized tracheal tubes