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Veterinarian Technician July 2007 (Vol 28, No 7) Focus: Medical Advances

Preventing Iatrogenic Tracheal Trauma

by Kelli Johnsen, CVT, VTS (ECC)

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    Key Points

    • Most iatrogenic tracheal tears are caused by the incorrect use of endotracheal (ET) tubes.
    • A complete understanding of ET tube management during anesthesia is necessary for preventing iatrogenic tracheal trauma.
    • Treatment of iatrogenic tracheal trauma can range from conservative to surgical.

    Click here for Glossary

    Although the veterinary staff always strives for a successful patient outcome, there are times when staff mem­bers can potentially cause problems for patients. When a condition is caused by a veterinary professional, it is classified as iatrogenic. By being alert and attentive in the care, use, and management of endotracheal (ET) tubes, technicians can often prevent iatrogenic tracheal damage, including tears. Tracheal tears can lead to a great deal of discomfort or disability for the patient, may require surgery to repair, and are potentially life threatening.


    The trachea is a cartilaginous and membranous tube that serves as the conducting airway between the cricoid cartilage of the larynx and the mainstem bronchi. It consists of a series of imperfect rings of hyaline cartilage joined by connective tissue; the trachealis muscle runs along its length. In dogs and cats, the tracheal rings are incomplete, which means that instead of forming an "O," they form a "C" and are slightly flattened dorsoventrally. These incomplete rings and the trachealis muscle are what give the trachea a great deal of flexibility and a modicum of elasticity.1-3

    The trachea is separated into two portions: the cervical or extrathoracic trachea and the thoracic or intrathoracic trachea. As the names suggest, the extrathoracic trachea lies outside the thoracic cavity. The portion of the trachea that descends into the thoracic cavity is referred to as the intrathoracic trachea.

    Possible Causes

    (see box)

    Most iatrogenic tracheal tears are caused by the incorrect use of ET tubes.4 It is important to choose an ET tube that is the appropriate size for the patient. If a tube is too large, trauma to the arytenoid cartilages is possible during intubation. An undersized ET tube requires too much air for cuff inflation, and the tube may not completely fill the lumen of the trachea as intended.

    Stiff stylets, stylets that protrude past the tip of the ET tube, placement of an ET tube past the tracheal bifurcation, overinflated cuffs, and inflated-cuff extubations can all lead to tracheal trauma.5,6 Once intubation is complete, patient handling becomes very important; patients must be moved cautiously to avoid undue pressure on the trachea. At the close of the procedure, care must also be taken in disinfecting the ET tube to prevent irritation and chemical burns to the trachea in the next patient for which it is used.

    The elasticity of the trachea is relied on to provide a small margin of safety when inflating the cuff of an ET tube. However, when too much pressure is exerted on the trachea, mucosal ischemia may result. This ischemia can create an area of pressure necrosis. Over time, this necrosis can lead to a tear in the trachealis muscle.5

    Other causes of iatrogenic tracheal trauma include the use of undersized rebreathing bags, closed pop-off valves,7,8 and oxygen flow rates that are set too high. Exceeding the recommended pressure on the rebreathing bag during positive-pressure ventilation and using incorrect systems or tubing (e.g., nonrebreathing system in a large dog) are other potential causes.9 The mechanism of these types of injury, which are termed barotraumas, is the extreme difference between atmospheric and intrathoracic pressures that results from each of these situations. Although not directly related to the misuse of the ET tube, each of these causes represents a common way that a technician can do serious intubation-related damage to a patient during general anesthesia.

    Noniatrogenic tracheal trauma can result from direct bite wounds to the trachea or as a result of vehicular trauma during which the trachea is ruptured.5,10,11 Foreign bodies and parasitic granulomas also can destroy the tracheal tissue to the extent that it ruptures.4,12

    Patient Assessment

    Iatrogenic tracheal trauma most often follows administration of anesthesia for dental prophylaxis.6 Traumatic injuries in this setting are thought to be due to (1) increased vigilance of the technician in ensuring that the ET tube cuff creates a complete seal in the trachea to preclude patient aspiration of dental debris and operator exposure to waste anesthetic gas and (2) the need for frequent repositioning of the patient in order to access all areas of the oral cavity. In less severe cases of tracheal trauma, the patient may experience coughing, gagging, or difficulty swallowing immediately upon extubation due to mucosal inflammation and edema.

    The most common clinical sign associated with a tracheal tear is subcutaneous emphysema, which can manifest a few hours to a few days after an anesthetic episode.4-6 Subcutaneous emphysema that results from a defect in the trachea is most commonly seen in the cervical region. In more severe cases, the emphysema can progress to the head and thoracic areas. If subcutaneous emphysema is present and the patient does not have surface skin wounds, a tracheal tear is highly suspected.13 A typical client complaint is that they hear "crackling" under the pet's skin. Crackling is created by air from the trachea leaking into the mediastinum and moving to the exterior of the patient's body through the thoracic inlet and into the subcutaneous tissue. Dyspnea, coughing, anorexia, lethargy, and upper airway noises have also been reported by owners.6 Associated findings on physical examination can vary widely and include dehydration, tachycardia, tachypnea, dyspnea, gagging, coughing, ptyalism, and fever.6

    Tracheal tears are often diagnosed presumptively, which means that the veterinarian uses a complete history and physical examination to arrive at a tentative diagnosis. The veterinarian makes a definitive diagnosis by using tracheoscopy, fluoroscopy, magnetic resonance imaging, or radiography or by performing surgery.6 There have been reports in which tracheoscopy did not reveal a tracheal tear that was later found during surgery.6,14 An additional diagnostic option is to conduct a positive-contrast study using a water-soluble organic iodide contrast medium.13 The water-soluble medium always should be diluted with sterile water. After dilution, the contrast medium can be instilled into the trachea by passing a red rubber catheter or a tomcat catheter through the arytenoid cartilages. If the patient has skin wounds, a tomcat catheter can also be used to instill the medium directly into the wounds. Tracheal tears are most often found on the dorsal aspect of the trachea.13

    The diagnostic findings in a patient with a tracheal tear include pneumomediastinum4 and pneumothorax due to air in the trachea leaking into the mediastinum as seen on thoracic radiography. This condition can develop if the pressure is high enough to rupture the mediastinum. On radiographs, pneumomediastinum allows clear visualization of the esophagus and descending aorta.13 Although rare, pneumoretroperitoneum or pneumopericardium may also be present.

    A complete understanding of proper ET tube placement and management provides an ideal opportunity for technicians to greatly influence the success of a procedure by using just a few preventive measures. Technicians who are delegated this task must be fully aware of the proper technique and potential to do harm because they will be expected to be diligent about always observing proper technique.

    Endotracheal Tube Cleaning

    Although they are designed for single use in human patients, ET tubes are typically sanitized, disinfected, and reused in veterinary patients. During cleaning and before use, the veterinary technician should always verify proper operation of the cuff. Any tube with a leaking cuff should be disposed of and replaced with a properly working tube.

    Caution should be used when choosing a cleaning agent. Plain water is recommended when soaking the tube is required (e.g., to remove mucus and other debris) before disinfection. To prevent a mechanical obstruction of the ET tube during its next use, it is important to completely clear the tube using a cleaning brush before disinfection. Clearing all debris particles also leads to better disinfection by allowing the agent to completely contact the tube. Short-term contact with a properly diluted chlorhexidine solution is effective for disinfection; soaking the tube for extended periods can harden the plastic. Over time, chlorhexidine also leaves a residue, which may present a nidus for bacterial or fungal growth. Therefore, it is essential to thoroughly rinse the tube with water. As a final step, a visual inspection of the tube is recommended to ensure that the lumen is not obstructed.

    In the author's opinion, ethylene oxide, when available and used properly, is the gold standard for sterilizing ET tubes. However, it is important that ethylene oxide be used with caution. It is a hazardous chemical, and personnel exposure must be prevented during use. The tubes must be completely dry before gas sterilization. It is also important to follow manufacturer recommendations for aeration times when ET tubes are gas sterilized, which allows the gas to dissipate and decreases the likelihood of the ethylene oxide causing a chemical burn to the inner lining of the trachea.

    Tube Choice

    (see figure)

    Two types of ET tube cuffs are typically used in veterinary medicine: low-pressure, high-volume (LPHV) cuffs and high-pressure, low-volume (HPLV) cuffs. LPHV cuffed tubes are often clear and have graduated numbers along their length. HPLV tubes are commonly opaque red rubber. Compared with LPHV cuffs, HPLV cuffs require a smaller amount of air for inflation. In addition, because of the larger amount of air that is needed, LPHV cuffs rise farther away from the surface of the ET tube upon inflation.

    HPLV cuffed tubes have many disadvantages; therefore, LPHV cuffed tubes currently are used more often in veterinary medicine. The opaque HPLV tubes make it impossible to see fluid reflux. Also, as the tubes age, they are more prone to cracking and the distal tip can break off. As alarming as these two problems are, they are minor compared with the possibility of damage from an improperly used HPLV cuff. These cuffs require small volumes of air to inflate but create great pressure over smaller areas of the trachea.10 In effect, they close the dead space between the cuff and the trachea by exerting a lot of pressure (using a small volume) over a small area. This increases the likelihood of pressure necrosis because the pressure of the cuff is not evenly distributed over a larger area but rather is concentrated over a smaller area on the trachea.

    LPHV tube cuffs, however, require larger volumes of air to inflate. Although this might seem counterintuitive, the larger volume of air and the design of the cuff allow for the pressure to be distributed more evenly on the trachea. However, this fact should not be interpreted to mean that it is beneficial to use large amounts of air during cuff inflation. It simply means that, compared with HPLV cuffs, the lower pressure caused by the more-even distribution of air with LPHV cuffs is preferred and is far less likely to result in pressure necrosis.

    An important point is that if LPHV cuffs are overinflated, a larger tracheal tear could be created because of the larger cuff size.5 A literature search revealed one study that reported that LPHV cuffs create an adequate seal at 15 mm Hg (20 cm H2O).10 A slight increase to 20 mm Hg (27 cm H2O) does not cause major changes in mucosal blood flow but does cause damage to the tracheal cilia if the tube is kept in place for 14 consecutive days.10 This study shows the importance of not overinflating the cuffs, particularly in patients that are intubated for longer periods, such as those on ventilators. However, compared with HPLV cuffs, which can easily reach pressures ranging from 130 to 370 mm Hg10 (177 to 503 cm H2O), LPHV cuffs are much safer.

    Proper Tube Insertion

    Some operators elect to place a stylet in the tube lumen, which stiffens the lumen and facilitates insertion of flexible ET tubes. Caution should be exercised when using stiff stylets. Particular attention should be given to ensure that the stylet does not protrude from the tip of the ET tube because it may perforate the trachea.

    A small splash (<0.2 ml) of 2% lidocaine hydrochloride on the arytenoid cartilages of cats is helpful because it leads to relaxation of these cartilages. The lidocaine should contact the tissues for approximately 1 minute before intubation is attempted. Cetacaine, a benzocaine-containing topical anesthesia, is no longer recommended as an aid in feline intubation because its use can result in methemoglobinemia.15 The ET tube should not touch the cartilages until they are relaxed --touching cartilages prematurely causes them to completely close.

    It is important to always take advantage of proper lighting in order to more clearly visualize the structures of the laryngeal pharynx and larynx during intubation. The tube should be measured from the external nares to the thoracic inlet and inserted only to that point. If the tube is inserted beyond the thoracic inlet, there is a greater chance that it will pass the tracheal bifurcation, in which case it will enter one of the mainstem bronchi. This will result in oxygenation of only that bronchus, causing a serious ventilation-perfusion mismatch, a decrease in blood oxygen saturation, and an overall lack of tissue oxygenation. During anesthetic monitoring, if oxygen saturation is decreasing, carbon dioxide concentration is increasing, and there is difficulty in maintaining the anesthetic plane, troubleshooting should include verification that the ET tube has not passed the thoracic inlet.

    It is also a good idea to use the graduated numbers along the length of the tube as a means to allow easier monitoring for tube migration. The number closest to the patient's upper canine tooth should be noted on the anesthesia record. This number should remain closest to the upper canine tooth throughout the anesthetic period. For tubes that do not have graduated numbers or for tubes on which the numbers have worn off, a permanent marker or piece of tape can be used to mark the initial location of the tube.

    Securing the Tube

    To decrease the risk of tube migration, the ET tube should be secured to the patient before the cuff is inflated. Although it is not always possible, securing the tube to the upper or lower jaw is most effective in preventing migration. There are several methods to secure the tube, but the important point is that the tube does not move proximal (out) or distal (in) from the location in which it is placed. Each of the following methods has benefits and risks:

    • Tie-gauze. To prevent the gauze from sliding down the tube, it must be tied tightly to the tube. Gauze is more likely to slip as it becomes wet and can be difficult to untie quickly.
    • Intravenous (IV) line tubing. Anecdotal evidence shows that this may work best if the line is looped rather than tied around the ET tube. The friction between the plastic IV line tubing and the ET tube is what helps keep the tube in place. The IV line tubing should be changed regularly to allow for the best friction.
    • Rubber bands. Rubber bands secure well to ET tubes, but this method carries two risks. A large amount of motion of the ET tube may be allowed if the rubber band is too large. Also, the rubber band cannot be secured to the upper or lower jaw but has to be looped around the patient's head. Any tie method that uses the upper or lower jaw will be much more secure.
    • Orange ties made specifically for ET tubes. The benefits of using these ties are that they do not get caught in the patient's hair and are less likely to break. Similar to rubber bands, however, they are able to stretch and may allow too much motion of the ET tube.
    • White porous tape. For this method, two pieces of tape are placed sticky-sides together; the resulting piece of tape is used as a tie. This method holds the ET tube in place well but is cumbersome to use and is particularly difficult with long-haired patients.

    Proper Cuff Inflation

    The cuff on an ET tube is inflated to create a seal between the tube and the trachea. This is done to prevent waste anesthetic gas from contaminating the environment near the patient, thereby protecting veterinary personnel from exposure. Inflating the cuff also prevents contaminants, such as vomitus or water, from entering the patient's mainstem bronchi, which can result in aspiration pneumonia.

    It is dangerous to rely on palpation of the tube's pilot balloon to dictate how much air to use to inflate the cuff because it is too subjective and misleading. When palpation is used, it may not seem as though the pressure is too much even in cases in which the cuff is exerting a great deal of pressure on the trachea. If the pilot balloon is the primary method used to determine the amount of air to add to the cuff of an ET tube, there is a high risk of eventually causing pressure necrosis, which can, in turn, lead to a tracheal tear.6 Using a 3-ml syringe, rather than a larger syringe, to inflate the cuff may help prevent overinflation by forcing the user to inflate the cuff more slowly.

    There are two recommended techniques for inflating ET tube cuffs. One method involves inflating the cuff slowly while watching the barrel of the syringe advance. When the barrel begins to meet resistance and push back, inflation should cease and 0.5 ml of air should be removed. The anesthesia machine pop-off valve then should be closed to close the circuit, and the technician should gently squeeze the rebreathing bag to a level of 10 to 15 cm H2O (7 to 11 mm Hg) while watching the manometer (pressure gauge) on the machine. In addition, the operator or a second person can lean down to the patient's face and listen for air leakage. A small amount of air leakage around the cuff will ensure that most of the lumen of the trachea is protected, yet it will also allow for a margin of safety against overinflation.5 If a significant leak is heard, a small amount of air should be added and the process should be repeated.

    A second recommended method is to inflate the cuff by incrementally adding 0.5 ml of air and then gently squeezing the rebreathing bag to a level of 10 to 15 cm H2O until no significant amount of air is heard escaping around the ET tube.5 In the case of dental prophylaxis, given the fact that streams of water are used, it may also be helpful to place a "dam" of gauze sponges at the back of the mouth to aid in preventing contaminants from entering the upper and lower respiratory system.6

    Patient Handling

    Moving the intubated patient may result in shifting the position of or dislodging the ET tube. The tube can also become kinked and occlude air flow. Care must be taken whenever an intubated patient is moved or repositioned. Because of the nature of the dental prophylaxis procedure, the patient must be turned and positioning must be adjusted. It is critically important to always pay attention to the angle of the trachea when turning a patient. Two staff members should turn a patient by moving the patient's feet under its body. One technician should turn the caudal portion of the patient, while the second technician grasps the patient's muzzle to further stabilize the ET tube and then turns the head and cranial portion of the body. Every effort should be made to keep the ET tube in the same position as it was before the move. The patient's neck should not be turned with either dorsoflexion or ventroflexion. When manipulating the patient's position between turnings, the technician should always stay mindful of the position of the trachea and the forces placed on it by the ET tube. The care exercised during this manipulation may mean the difference between a successful procedure and one that leads to patient discomfort and client dissatisfaction.

    Without exception, during turning, the oxygen flowmeter should always be turned to zero, the anesthetic tubing should be disconnected from the ET tube, and the turning motion should be gentle. Although it is ideal to also turn off the vaporizer, this is less important because oxygen is required to carry anesthetic gas. Once the patient has been gently turned, the anesthetic tubing should be reconnected and the oxygen turned back on. Improperly turning the patient, even when a cuff is properly inflated, can and will cause a tracheal tear.6

    It is important to pay close attention to a patient that is recovering from anesthesia. This not only is good practice but also increases the likelihood of deflating the ET tube cuff at the right time. Ideally, the cuff should be deflated after the patient has regained the ability to swallow but before being able to move its head. A properly inflated ET tube cuff in a dysphoric, thrashing patient can do just as much damage to the trachea as can an overinflated cuff. Both situations can lead to tracheal trauma. Keeping the patient intubated until it can swallow, cough, and gag increases the likelihood that the patient can once again protect its own airway. The ability to swallow also helps a patient to clear its airway in the case of vomiting on recovery. The oral cavity should be inspected before extubation, and any debris or fluid should be removed using either suction or gauze pads.

    Treatment of Tracheal Tears

    The treatment for tracheal trauma in the absence of a tear often consists of antianxiety medications or a cough suppressant with or without an NSAID to treat inflammation and pain management as indicated. These types of injuries often resolve without further intervention.

    The treatment selected for a tracheal tear depends greatly on the location of the tear. Tracheal tears can be categorized as extrathoracic and intrathoracic.

    Extrathoracic Tears

    The term extrathoracic refers to the portion of the trachea that is in the neck region or outside the thoracic cavity. Treatment of extrathoracic tracheal tears involves sedation, pain management, oxygen support if the patient has dyspnea, and possible placement of an active drain system (Jackson-Pratt drain) to remove the air from the subcutaneous space.6 Aspiration of the subcutaneous air is suggested to alleviate patient discomfort.4 In addition, a pressure bandage can be placed around areas where subcutaneous emphysema exists to facilitate drainage; however, caution must be used to ensure that the bandage does not restrict the patient's breathing. Sedation and pain management are important because rest and decreased movement will best allow a patient's trachea to heal. Typically, most of the noticeable subcutaneous emphysema should dissipate within 14 days.6 Conservative therapy is often sufficient for patients with extrathoracic tears.4-6,13 If conservative therapy alone is not successful, surgery may be required to repair the defect.

    Intrathoracic Tears

    Intrathoracic tracheal tears also involve subcutaneous emphysema. Typically, they may also lead to pneumomediastinum and sometimes pneumothorax. In severe intrathoracic tears, pneumoretroperitoneum is a frequent sequela. Thoracentesis is often required to stabilize the patient if the dyspnea is severe.13 Many intrathoracic tracheal tears require placement of a chest tube with either intermittent or continuous suction. If severe pneumothorax is present, continuous suction is required to allow proper lung expansion for ventilation. Ultimately, severe or worsening cases require surgical repair.4,5,10,13 It is possible that a patient that is initially stable can have decompensation several days after the event because of stenosis of the trachea that is caused by granulation tissue.13 This possibility should be communicated to the owner.


    Although it is never the veterinary staff's intention to harm a patient under their care, the reality is that iatrogenic trauma can occur during intubation. The good news is that this type of trauma is preventable if the proper measures are taken. Through knowledge and vigilance, veterinary technicians can play a critical role in successfully preventing complications and in treating these patients. It is important to understand the pitfalls of the equipment that is used and to use that equipment cautiously.

    Proper monitoring and management of intubated patients are essential to ensure their safety. In cases of severe tracheal tears, it is critically important to be able to respond immediately to life-threatening respiratory distress.

    1. Done SH, Goody PC, Evans SA, Stickland NC: The neck, in Color Atlas of Veterinary Anatomy, vol 3. London, Mosby, 1996, pp 3.20-3.21.

    2. Hudson LC: Respiratory system, in Hamilton WP (ed): Atlas of Feline Anatomy for Veterinarians. Philadelphia, WB Saunders, 1993, pp 137-141.

    3. Dyce KM, Sack WO, Wensing CJG: The respiratory apparatus, in Textbook of Veterinary Anatomy, ed 2. Philadelphia, WB Saunders, 1996, pp 159-161.

    4. Reiss AJ, McKiernan BC: Laryngeal and tracheal disorders, in Wingfield WE, Raffe MR (eds): The Veterinary ICU Book. Jackson Hole, WY, Teton NewMedia, 2002, pp 606-607.

    5. Hardie EM, Spodnick GJ, Gilson SD, et al: Tracheal rupture in cats: 16 cases (1983-1998). JAVMA 214:508-512, 1999.

    6. Mitchell SL, McCarthy R, Rudloff E, et al: Tracheal rupture associated with intubation in cats: 20 cases (1996-1998). JAVMA 216:1592-1595, 2000.

    7. Ko J: Anesthesia tips 1-2-3. Atl Coast Vet Conf Proc:2005.

    8. Ko J: Anesthetic mishaps. Atl Coast Vet Conf Proc:2005.

    9. King LG: Ventilator-induced complications: Recognition, prevention, and management. Int Vet Emerg Crit Care Symp Proc:2005.

    10. Nelson AW: Lower respiratory system, in Slatter D (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders, 1993, pp 780-803.

    11. White RN, Burton CA: Surgical management of intrathoracic tracheal avulsion in cats: Long-term results in 9 consecutive cases. Vet Surg 29:430-435, 2000.

    12. Krahwinkel DJ: Tracheal trauma. Atl Coast Vet Conf Proc:2004.

    13. Macintire DK, Drobatz KR, Haskin SC, Saxon WD: Respiratory emergencies, in Troy DB (ed): Manual of Small Animal Emergency and Critical Care Medicine. Philadelphia, Lippincott Williams & Wilkins, 2005, pp 124-125, 143.

    14. Suter PF, Lord P: Trauma to the thorax and airways, in Suter PF (ed): Thoracic Radiography, A Text Atlas of Thoracic Disease in the Dog and Cat. Wettswil, Switzerland, Peter F. Suter, 1984, pp 127-159.

    15. Krake AC, Arendt TD, Teachout DJ: Cetacaine-induced methemoglobinemia in domestic cats. JAAHA 21:527-534, 1985.

    References »

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