Chapter Outline
Tracheal Tubes (Endotracheal Tubes) 111
Endotracheal Tube Cuffs 114
Connectors/Catheter Mounts/Tracheal Tube Adaptors 115
Common Problems with Endotracheal Tubes and Safety Considerations 115
Nitrous Oxide And The Endotracheal Tube 116
Specially Designed Tracheal Tubes 117
Preformed Tubes 117
Reinforced Tubes 118
Microlaryngeal Tubes 118
Carden Tubes 119
Laser Surgery Tubes 110
Hunsaker Tubes 120
Laryngectomy Tubes 120
Other Endotracheal Tube Variations 120
Tracheostomy Tracheal Tubes 120
Common Issues With Tracheostomy Tubes And Safety Issues 121
Minitracheostomy And Other Emergency Cricothyrotomy Tubes 122
Double Lumen Endobronchial Tubes 122
Endobronchial Tubes 123
Endobronchial Blocker 124
Other Subglottic Airway Devices 124
Conclusion 125
Endotracheal airway devices provide a means of oxygenation and ventilation by directly accessing the trachea, allowing gas delivery and exchange to the lungs. Endotracheal tubes are endotracheal airway devices inserted orally or nasally, whereas tracheostomy tubes are placed surgically or percutaneously through the trachea. Additional types of subglottic airway devices, including those used for jet ventilation, can be used for short-term oxygenation requirements.
Endotracheal tubes and tracheostomy tubes, commonly with a tracheal cuff, are used when a patient’s airway needs to be definitively secured from aspiration or when positive pressure ventilation is required. Indications for endotracheal intubation for invasive airway management take into account patient risk factors for aspiration. This includes unsatisfactory NPO status common in traumatic and emergent presentations. Pathophysiological states such as symptomatic gastric reflux, ileus, or bowel obstruction often require definitively securing the airway. Elevated risk of aspiration may also be present with anatomic variation due to a history of certain gastrointestinal operations (i.e., esophagectomy or gastrectomy). Additionally, patients who are morbidly obese or with primary lung disease should be strongly considered for endotracheal intubation, as effective ventilation with supraglottic airway devices may be difficult.
Situational factors warranting strong consideration of endotracheal airway management include the need for surgical access to the oropharynx, lengthy procedures, and positioning requirements limiting access to the airway. Postoperative intubation requirements also need to be factored into the decision to use an endotracheal tube ( Table 8–1 ).
| Patient Factors | Situational Factors |
|---|---|
GENERAL RISK FACTORS FOR ASPIRATION
| PLAN OF CARE FOR PATIENT
|
| ANATOMIC RISK FACTORS FOR ASPIRATION | SURGICAL CONCERNS |
|
|
| Physiologic Risk Factors for Aspiration | POSITIONING CONCERNS |
|
|
| PULMONARY STATUS CONCERNS | |
| |
| ANTICIPATED DIFFICULT AIRWAY |
Tracheal Tubes (Endotracheal Tubes)
A properly positioned, cuffed endotracheal tube is currently the definitive method to secure an airway via the oropharynx or nasopharynx. It should be noted that uncuffed endotracheal tubes have traditionally been used for small children due to anatomic differences between children and adults. In adults, the narrowest part of the upper airway is the glottis whereas in children the cricoid cartilage is commonly believed to be the narrowest point in the airway. Thus, cuffless tubes theoretically provide an adequate seal between the trachea and endotracheal tube while decreasing the risk of pressure injury and postintubation croup in children. Studies have shown, however, that when endotracheal cuff pressures are properly monitored, the incidence of croup and other complications in full-term neonates and young children are not statistically different between cuffed and uncuffed endotracheal tubes ( Figure 8–1 ). Uncuffed endotracheal tubes may also need to be replaced with a larger sized tube if an adequate seal is not established, requiring reinstrumentation of the airway.
Endotracheal intubation provides the ability to ventilate with positive pressure while precisely titrating gas delivery. Intubation reduces the risk of aspirating native or foreign material in patients who cannot protect their own airway, which would include anyone under a general anesthetic. Finally, a properly secured endotracheal tube is intuitively less likely than a supraglottic device to be accidentally displaced during patient positioning and surgical manipulation.
Material
Endotracheal tubes were historically made of opaque rubber or soft latex. The elasticity of these materials and the low-profile cuff made insertion less traumatic, a particularly helpful characteristic for nasally inserted tubes. Although sterilization can be difficult to verify after each use, studies show that sterilization according to the Centers for Disease Control and Prevention guidelines results in properly sterilized reusable endotracheal tubes.
Reports of foreign objects or dried mucus occluding the lumen of rubber or latex endotracheal tubes after sterilization are not uncommon. The integrity of the endotracheal tube and cuff can also become compromised over time and with repeated sterilization. This can result in easier kinking of the tube lumen and cuff herniation past the distal opening of the endotracheal tube ( Figure 8–2 ). Additionally, these cuffs are at higher risk of transmitting pressures capable of causing tracheal mucosal ischemia due to the higher inflation pressures required. Finally, the use of natural rubber and latex poses a greater risk of irritation and allergic reactions in patients. For all these reasons, plastic endotracheal tubes made of polyvinyl chloride (PVC) and polyurethane have largely replaced rubber and latex endotracheal tubes.
Single use polyvinyl chloride (PVC) and polyurethane endotracheal tubes are often transparent, allowing easier visual inspection of the airway up to the point of entry to the body. They are reliably supplied sterilized from the manufacturer. Plastic endotracheal tubes can also be reproduced to more precise specifications than rubber or latex endotracheal tubes, which is especially important in endotracheal tubes with a very small inner diameter (ID). As noted, endotracheal tubes made with these newer materials are less allergenic and are ubiquitous in modern anesthesia practice.
Recently, newer endotracheal tubes have been designed to address ventilator associated pneumonias (VAP) during prolonged intubation and ventilatory support. The incidence of VAP in the critical care setting was studied with silver-coated endotracheal tubes in multiple randomized controlled trials. Silver-coated endotracheal tubes were determined to reduce the bacterial burden and incidence of VAP while increasing the length of time to development of VAP, though long-term mortality was not affected.
Design
Endotracheal tubes are shaped to follow the anatomic curve of the oropharynx ( Figure 8–3 , A) . The distal end is beveled with the opening facing left of the laryngoscopist, allowing for visualization of the beveled tip as it passes between the vocal cords. Opposite the bevel may be a port referred to as a Murphy eye. If the beveled opening is obstructed by having its opening against the tracheal wall or becomes occluded by a foreign body, the Murphy eye theoretically enables some degree of oxygenation and ventilation ( Figure 8–3 , C ). Endotracheal tubes without the Murphy eye are referred to as Magill endotracheal tubes.
At the distal end of the endotracheal tube is the tracheal cuff, providing occlusion of the space between the tracheal wall and endotracheal tube. Once the cuff is properly positioned and inflated, effective positive pressure ventilation can be delivered and the airway is considered “protected” against aspiration. The cuff is inflated via tubing that connects to a self-sealing valve and pilot balloon. The tubing is integrated closely to the endotracheal tube body.
Several notable markings are on the endotracheal tube. This includes the size of the endotracheal tube, which is a measure of the ID in millimeters, and the length of the endotracheal tube, marked by a radio-opaque line that can be visualized on a chest radiography. Numbers oriented to be easily read by the laryngoscopist, usually in intervals of 2 cm, show the length of the endotracheal tube from the distal end. Markings relating to certification that the plastic has been tested for tissue toxicity (i.e., I.T.Z. 79 or CE) are also printed on the endotracheal tube ( Figure 8–3 , B ).
Size
Increasing the ID of an endotracheal tube exponentially decreases the resistance to gas flow through the tube, whereas decreasing the length linearly decreases the resistance. This relationship is given by the Poiseuille equation:
R = ( 8 η ) / ( πr 4 )
Resistance directly relates to the work a patient exerts to maintain sufficient ventilation through the narrow endotracheal tube. Thus, the largest ID endotracheal tube to pass through the narrowest part of the airway without trauma is typically chosen. Endotracheal tube size guidelines for adults and children based on this concept are shown in Table 8–2 .
Routine use of larger diameter endotracheal tubes has come into question for brief procedures (such as operating room anesthetics) supported by mechanical ventilation. Positive pressure ventilation by the ventilator makes work of breathing by patients less relevant. Even with spontaneous ventilation modes, pressure support settings on most modern ventilators compensate for the increased resistance of endotracheal tubes.
Although narrower endotracheal tubes do not effectively increase work of breathing for the ventilated patient, they do decrease trauma to the oropharynx and trachea. Endotracheal tubes size 7 mm ID and greater lead to an increased incidence of sore throats and vocal hoarseness, likely due to the increased area of contact between the tube and vocal cords and trachea. However, narrower endotracheal tubes are associated with more kinking and difficulty in passing a suction catheter or bronchoscope. Larger endotracheal tubes are routinely used if fiberoptic bronchoscopy is to be performed through the tube.
The shortest length of endotracheal tube would ideally be used as well, but tubes are not routinely cut to minimize the length for each patient solely to decrease resistance. This is partly due to the safety and practical aspects of cutting each tube. There is risk with certain patient conditions such as edema after burns or prone positioning with large volume resuscitation, and patient positioning changes during surgery that can lead to displacement of shorter endotracheal tubes.
Special tubes preformed for oral or nasal intubation (i.e., RAE tubes) have a fixed length correlating to their internal diameters. It is more difficult to choose narrower internal diameters in these tubes because of considerations involving the height of the patient and the possibility of having an endotracheal tube that is too short or a cuff that is too small to achieve a satisfactory seal.
Endotracheal Tube Cuffs
Endotracheal tube cuffs can be categorized according to the pressure required to properly inflate the cuff.
High pressure (also referred to as low volume) cuffs are inflated in a spherical shape, allowing for minimal surface contact area between the tracheal mucosa and endotracheal cuff when properly inflated. The trachea tends to conform to the cuff shape, rather than the cuff conforming to the trachea. This design theoretically increases the chance of transmitting cuff pressure that exceeds the capillary perfusion pressure to the tracheal mucosa, which is about 25 to 34 cm H 2 O in normotensive adults, and likely lower in children. Conversely, overinflation of the cuff quickly leads to a significant amount of pressure transmission through the cuff and can lead to tracheal mucosal ischemia.
Medium pressure cuffs are made of more distensible material and need less pressure to properly inflate than high pressure cuffs. There is less risk of exceeding the transmucosal capillary perfusion pressure with inadvertent overinflation of the cuff. However, the cuffs are more susceptible to damage due to the compliant construction material ( Figure 8–4 ).
