Airway security is a cornerstone of veterinary medical practice. The ECC clinician is challenged with patients who present in acute respiratory distress (injury, disease, or dysfunction of upper airway structures) that require intervention to assure airway security. At times, standard methods for producing airway security are unsuccessful. In those cases, advanced strategies for establishing airway security may be required. The purpose of this presentation is to expand your “toolbox” with additional techniques and strategies to manage these challenging patients.

Cases Requiring Airway Management

Any case presenting with respiratory difficulty or distress is a candidate for airway support. Airway dysfunction may be clinically evident by increased respiratory effort, stridor, dyspnea, inability to move air volume, cyanosis, constant shifting movement, and struggle. Reasons for upper airway dysfunction are varied and include congenital, acquired, neoplastic, and anaphylactic etiologies, as well as acute mechanical obstruction due to injury or secondary to ingested/inhaled foreign body. The underlying cause may not be known at initial presentation prior to initiating action steps to provide comfort and support. Definitive diagnosis is, in many cases, deferred until airway patency and security can be accomplished.

Primary Action Steps

The first action step is to provide oxygen to the patient. Many cases appear cyanotic as well as dyspneic and will benefit from oxygen support. There is no downside to doing so. Use of a face mask or head enclosure is preferred; flow by oxygen provides minimal and variable results. If the patient struggles when oxygen support is offered, do not attempt to continue oxygen delivery. They may require sedation and/or anesthesia to provide oxygen support and to identify and resolve the underlying cause.

The second action step is to evaluate for mechanical airway obstruction. Sedation or light anesthesia may be necessary to facilitate the exam. A caudal oropharyngeal exam using a light source or laryngoscope may help identify the problem, such as a foreign object (ball, toy, stick, plastic disk) that may be causing an obstruction. It may also help to reposition structures in the caudal oropharynx into their normal anatomic relationship (epiglottic entrapment, soft palate entrapment).

The third action step is to support the upper airway and provide a secure conduit for oxygen administration. This can be accomplished by the use of an emergency oral airway device. These can be constructed by taking a syringe case and cutting the closed end away. The rough edge can be “fire polished” by exposing it to a low heat flame to polish the edge. The syringe case is inserted into the oral cavity and advanced past the tongue base. It is secured at this point and provides a conduit for oxygen delivery to the caudal oropharynx.

Sedation or Anesthesia

A crucial challenge is to identify the degree to which patient stress/anxiety is contributing to the overall clinical picture. Sedation for anxiolysis may be all that is needed in cases where airway stridor and/or increased respiratory effort is evident, but mucous membrane/tongue color is pink with normal oxygen saturation. Drugs used for anxiolysis include acepromazine, dexmedetomidine, opioids, benzodiazepine tranquilizers, and ketamine. Intravenous or rectal routes of administration are generally used as they provide the fastest response. There are multiple protocols using these drugs either alone or in combination; the goal of doing so is to calm the patient, reduce work of breathing, and facilitate evaluation.

In cases of exaggerated anxiety and/or respiratory effort accompanied by cyanosis and low oxygen saturation, emergency anesthetic induction may be required. Rapid sequence anesthesia using 2 mg/kg lidocaine IV (block laryngeal and tracheal reflexes) followed by 2 mg/kg ketamine IV and 4–6 mg/kg propofol or 1–3 mg/kg alfaxalone IV to effect is preferred. Ketamine is used because it increases bronchodilation and enhances lower esophageal sphincter tone thereby reducing gastroesophageal reflux during induction. Oxygen support is provided by one of several methods (face mask, enclosure, intratracheal) until airway security is present.

Basic Airway Support Techniques

Positioning

There is significant anatomic variation in the relationship of the tongue base, caudal pharynx, epiglottis, and laryngeal entrance in companion animals. As in humans, the location of each may contribute to challenges in laryngeal visualization. This may be compounded by heavy muscling of the cranial cervical region as is present in certain dog breeds. The net result is that the laryngeal location is “deeper” in the caudal pharynx and may be significantly obstructed by the tongue base even when the tongue is extended. This may be exacerbated by the position of the head relative to the cervical axis. If the centerline of the head is hyperextended and similar to the neck, this may increase the depth of the larynx relative to the tongue base because of traction placed on the hyoid bones by the sternohyoideus m. Conversely, excessive flexion of the neck and head centerlines in a perpendicular direction will also cause the laryngeal depth to increase relative to the tongue base. It is best to maintain a “normal” centerline between the head and neck to achieve the best visualization.

Even if the optimal centerline angle is maintained, visualization may be challenging. In cases where this is present, postural change may be helpful. We have been trained to intubate dogs and cats in sternal recumbency. While this is the best physiologic position, it may compromise airway visualization in cases with anatomic deviations. In those cases, rotation into lateral or dorsal recumbency may be warranted. In humans, intubation in supine, or dorsal, recumbency is the standard of care. The advantage of this posture is that the soft palate “falls” rather than “hangs” in the caudal oropharynx which is helpful in identifying laryngeal position. It also is helpful because the laryngoscope is designed to be used in dorsal recumbency. In this position, the vertical part of the laryngoscope blade is used to “sweep” the tongue to the side of the oropharynx further assisting visualization. It is important that the patient is straight in dorsal recumbency without any cervical or head rotation relative to the long axis of the torso to achieve the best visualization. This posture may be easily combined with other facilitative techniques (Sellick maneuver) to further enhance laryngeal visualization. No special equipment is required for this procedure beyond a standard laryngoscope and blade combination. In deep-chested dogs, a trough or sandbags may be helpful to assist stabilization in dorsal recumbency. Caution must be exercised to avoid regurgitation during the procedure.

Sellick Maneuver

As noted above, variation in the relationship of the tongue base, caudal pharynx, and larynx may result in the larynx being “hidden” by the tongue base even when the tongue is extended. This is especially true in dog breeds with wide, muscular tongues such as bulldogs, Staffordshire terriers, pugs, and other brachycephalic breeds. Moving the laryngeal orifice dorsal relative to the tongue base increases visualization and facilitates endotracheal tube placement. Gentle laryngeal displacement can be performed by taking two fingers and applying pressure to the ventral surface of the larynx. By applying pressure, the larynx naturally shifts dorsad relative to the tongue base resulting in improved visualization. The Sellick maneuver will work when the patient is in any recumbency. No additional equipment or supplies beyond a laryngoscope and assistant are required. The potential side effect of increasing laryngeal pressure is bradycardia due to vagal-induced feedback. If this occurs, an intravenous dose of atropine or glycopyrrolate will resolve the issue.

Stylette Assistance

One of the challenges the operator encounters during intubation is the flexibility of the endotracheal tube (ET) itself. Commercially available endotracheal tube materials include rubber, plastic, and silicone. Silicone is the least traumatic biomaterial; it is also the most flexible. Flexibility is good once intubation is achieved but can be challenging to direct the tube into the laryngeal orifice to achieve intubation. There are several options available to help the operator direct the ET in the desired direction. One option is to insert a sterile stylette, or stiffening device, into the ET tube lumen prior to introduction. The stylette can be purchased from a commercial source or can be homemade from a 6 mm aluminum rod. The stylette length must not protrude from the end of the ET tube; a distance of 5–10 mm from the end of the ET tube must be maintained. This can be achieved by bending the stylette if the material is flexible or fashioning a “stop” from the top of a blood collection tube or rubber cork that can be positioned on the stylette to prevent accidental protrusion of the stylette tip beyond the ET. The stylette is pre-positioned in the ET and the final 5 cm of the stylette before the ET tube tip is gently bent to a 15–20-degree angle. One must align the tip bend of the stylette with the ET tube bevel to make sure the bevel stays in vertical alignment for intubation. This will facilitate engagement of the ET tip and the laryngeal orifice. Once engagement occurs, the stylette is held in position and the ET tube is advanced into the larynx and trachea. Do not continue to advance the stylette once engagement occurs; this may result in injury to laryngeal and tracheal structures.

Procedural risk is associated with stylette-induced trauma from allowing the stylette to extend beyond the tip of the endotracheal tube. Momentary airway obstruction can also occur if the stylette is not removed promptly following completion of the procedure.

Stylette/Light Source

Commercially available flexible shaft flashlights are available in several sizes and may be adapted as a stylette. They may be gas sterilized prior to each use. The indications for use are the same as described above for stylette-assisted intubation. The advantage of using this device is that it provides additional lighting which is useful in identifying anatomic structures in the caudal pharyngeal area.

Guided ET Placement

In cases where restricted visualization due to anatomic distortion of oropharyngeal structures is present, pre-placement of a guide over which the ET tube is advanced can be helpful. This technique is particularly valuable in small-sized patients with restricted caudal pharyngeal access (i.e., cat). Guides may be created from several different materials. One option is to use a 5–8 F plastic male urinary catheter. The use of a catheter has the added benefit of giving the option to insufflate oxygen through the catheter into the airway during intubation. A second option is a vascular “J” wire. It has enough flexibility to be tissue friendly but enough rigidity to assist in ET placement.

The technique requires direct visualization of the laryngeal orifice. Following identification, the guide is advanced through the oral cavity and pharynx and inserted into the laryngeal orifice. Once this is achieved, the guide is stabilized by the operator and the ET is “threaded” over the guide and advanced to the laryngeal orifice. When the ET engages the laryngeal orifice, the guide is removed and the ET advanced.

Potential risks are related to guide-induced tissue trauma from either too far advancement or poor control during ET placement. Meticulous attention to guide control during the procedure will reduce the risk of laryngeal injury or the guide becoming stuck on a laryngeal structure.

Fiberoptic Intubation

In recent years, the use of fiberoptic scopes for intubation has increased in popularity in human medicine. Fiberoptic intubation has the advantage of direct visualization of the laryngeal orifice and provides verification of correct ET placement. Fiberoptic scopes designed and dedicated to ET intubation are commercially available. There are several designs including a traditional fiberoptic scope and handheld monitor or a hybrid design incorporating a traditional laryngoscope blade connected to a videoscope handle and power source. Additionally, there are non-medical sources for fiberoptic equipment that may be cost effective. The automotive industry has handheld videoscopes for engine inspection (borescopes) which may cross adapt to veterinary practice. There are also fiberoptic endoscopes available through commercial vendors (Amazon) that have integrated video displays or attach to a computer, tablet, or smartphone display. They work but are limited by the diameter of the scope head and light intensity (lumens) at the scope end. In exotic species, a small diameter rigid scope (needle scope) is used for ET placement in avians and small mammals. Its use is very effective in these species.

The principles for fiberoptic scope use are the same as described for stylette or guided placement. The ET is placed over the fiberoptic bundle which acts as a guide or stylette. The unit is advanced until visualization of the laryngeal orifice is noted at which time the ET is advanced into the stoma and airway. Following advancement, the scope is withdrawn. Potential risks associated with fiberoptic scope use have been described for guided placement.

Advanced Techniques

Cricothyroid Oxygen Administration

In specific patients, emergency placement of an endotracheal tube may not be possible despite attempting the above described procedures. In those cases, oxygen administration assumes paramount importance until airway security is established. It is highly unlikely that complete airway obstruction has occurred; if that was the case, the patient would not present for clinical evaluation. Assuming incomplete airway obstruction, emergent placement of an oxygen catheter through the cricotracheal membrane can be lifesaving. The technique is straightforward and effective when correctly performed.

The procedure requires the use of a large-bore, short-length, over-the-needle intravenous catheter (16 G x 2.5” in dogs, 18 G x 2” in cats). The catheter is attached to a 6 cc syringe filled with 4 cc saline for identification of correct placement. The operator palpates the junction of the larynx and trachea and identifies the cricotracheal membrane. It is a depressed area on the ventral midline on the distal aspect of the larynx formed by the caudal margin of the cricoid cartilage and the anterior aspect of the first tracheal ring.

There is a palpable depression immediately rostral to this point, the cricothyroid membrane. It is in the larynx and should not be used as the landmark. A small window on the midline over the cricotracheal membrane is clipped and quickly prepped.

The needle unit is inserted perpendicular to the trachea and advanced until a loss of resistance is felt. Aspiration on the saline syringe should yield air bubbles to confirm correct placement. Following confirmation, the catheter unit is pointed in a caudal direction toward the chest cavity and the catheter is advanced off the needle as far as possible. Following advancement, the catheter is secured with a loop ligature and connected to an oxygen line. An adapter from the oxygen line to the catheter can be easily made by taking the syringe barrel of a TB syringe and cutting its length down and fitting it into the oxygen line. One to two LPM/minute oxygen flow is then started. Flow rates beyond 3 LPM create too much back pressure and risk detachment of the connector from the catheter. The oxygen hose is secured to the patient for continual delivery.

Warning: You are delivering dry medical gas to the trachea. If support greater than 1–2 h is required, it is imperative that humidification is added in line. Do not use this technique for more than 24 h. A “jet” lesion characterized by mucosal injury can occur where the catheter tip is in proximity to the respiratory epithelium.

Retrograde Guided/Assisted Endotracheal Intubation

In cases where oral airway visualization is impossible (oral mass, swollen tongue, craniofacial injury, perilaryngeal swelling), a retrograde guidewire can facilitate ET placement. The procedure requires the passage of a vascular guidewire from the cricotracheal ligament retrograde through the larynx and oral cavity to the exterior. Once exteriorized, an appropriate sized endotracheal is “threaded” over the guidewire and advanced into the laryngeal area.

The procedure is similar to that described above for tracheal oxygen insufflation. A large-bore, short-length, over-the-needle intravenous catheter (16 G x 2.5” in dogs, 18 G x 2” in cats) is selected. The catheter is attached to a 6 cc syringe filled with 4 cc of saline for identification of correct placement. The operator palpates the junction of the larynx and trachea and identifies the cricotracheal membrane. A small window over the cricotracheal membrane on the ventral midline is clipped and prepped.

Local anesthetic is injected into the skin and subdermal tissues to desensitize the area. The needle unit is inserted perpendicular to the trachea, advanced until a loss of resistance is felt, and then angled 20–30 degrees toward the nose. Aspiration on the saline-filled syringe should yield air bubbles to confirm correct placement. Following confirmation, the catheter is advanced off the needle as far as possible. A 4–6 F J-tipped vascular guidewire is inserted through the catheter lumen and advanced 3–4 cm.

The catheter is then backed out and removed off the wire. The wire continues to be advanced rostral until visualized in the oral cavity. It is then grasped with forceps and advanced through the oral cavity. Once exteriorized to a length longer than the ET tube, the guidewire is inserted through the ET tube’s beveled end and exits at the breathing circuit adapter. The ET tube is then advanced forward following the path of the wire. Gentle ET tube rotation may be necessary to move around distorted tissues. The ET tube is advanced until back resistance is felt. If the inserted length visually appears to be where the guidewire was placed, the operator can withdraw the wire and advance the ET tube to its final location.

Potential risks/concerns are associated with J-wire placement. The wire may enter one of several “blind” corners of the larynx and become lodged. In that case, dislodge the wire by backing it out, gentle rotation, and readvancing the wire until it clears the laryngeal stoma. A second risk/concern is accidental introduction into the nasopharynx. If this occurs and the wire is advanced too far, it may become lodged in the nasal turbinates or exit at the nares. In that case, the wire is pulled back to the level of the oropharynx and redirected into the oral cavity.

Percutaneous Cricothyroidotomy

If upper airway structures must be bypassed and direct tracheal access is required, there are two invasive options to facilitate airway security. The first technique is the placement of a tracheostomy tube using the Melker cricothyrotomy technique. Cricothyroidotomy is a planned, semi-emergent technique that should be performed secondary to other support measures described above. It is a well-established procedure that has multiple training modules on YouTube and other Internet media. Supplies required include the Melker cricothyrotomy set, flexible guidewire, 16 or 18 G over-the-needle catheter, 6 cc syringe, sterile saline, surgical scrub, and clipper. The ventral cervical region immediately posterior to the larynx is the insertion site. A window is clipped on the ventral surface and surgically scrubbed.

Local anesthesia with 2% lidocaine infiltrated into the proposed insertion point in a semi-sedated or awake patient. The ventral midline anatomy is identified including the landmarks described above. The catheter is attached to a 6 cc syringe filled with 4 cc of saline for identification of correct placement. The operator palpates the junction of the larynx and trachea. It is a depressed area on the ventral midline on the distal aspect of the larynx formed by the caudal margin of the cricoid cartilage and the anterior aspect of the first tracheal ring. There is a palpable depression immediately rostral to this point, the cricothyroid membrane. It is in the larynx and should not be used as the landmark. The needle unit is inserted perpendicular to the trachea between the second and third laryngeal rings and advanced until a loss of resistance is felt. Aspiration on the saline syringe should yield air bubbles to confirm correct placement. Following confirmation, the catheter unit is pointed caudal toward the chest cavity and the catheter is advanced off the needle as far as possible. A 4–6 F J-tipped vascular guidewire is inserted through the catheter lumen and advanced 3–4 cm. The catheter is then backed out and removed off the wire. The Melker device, a combination of a dilator and tracheostomy tube, is threaded from the tip end of the dilator, over the wire, and advanced to the skin surface. A small incision (0.5–1 cm) is performed to facilitate insertion through the skin and deep tissues. The Melker device is advanced with firm pressure and slight twist until the dilator and tip of the tracheostomy tube are within the tracheal lumen. The dilator is held steady and the tracheostomy tube is advanced. Following tracheostomy tube insertion, the dilator is removed and the tracheostomy tube is secured. Wound dressing is applied at the surgical site. A light, padded bandage is applied to protect and help stabilize the airway.

Most complications are associated with poor procedural technique in identifying structures and attempting to advance the dilator tracheostomy tube unit without incising overlying tissues to facilitate advancement. Secondary complications are associated with the development of subcutaneous emphysema and/or fascial plane air from a leak around the tube site. Leaving an open wound distal to the tube location reduces this risk by allowing a low-pressure escape pathway. Poor placement and/or technique can produce pneumomediastinum. Tracheostomy tube patency must be constantly monitored and care provided on a regular basis to assure patency.

Tracheostomy

The most invasive procedure to establish an airway is an emergency tracheostomy. Tracheostomy may be performed on a critical emergency basis (slash tracheostomy) or as a secondary procedure following ET intubation (controlled tracheostomy). The purpose and goal of each procedure are the same; to establish and secure airway patency. The technique, and timing, are quite different between the procedures.

Emergency, or slash, tracheostomy is a primary procedure that is performed when the patient is struggling to breathe and at risk for immediate death if airway patency is not established. It can be “crude” in that, due to a sense of urgency, the degree of aseptic preparation is less and tissue trauma greater than in the controlled procedure. Equipment and supplies are minimal due to the essence of time. Several sizes of tracheostomy tubes, a lidocaine filled syringe-needle unit, scalpel, forceps, scissor, scalpel unit, and 0 nonabsorbable suture are all that are required. To perform an emergency tracheotomy, the surgical site is quickly infiltrated with local anesthetic. A 5–10 cm longitudinal skin incision on the ventral midline is performed just below the larynx.

The muscles overlying the trachea are quickly divided by blunt dissection and the trachea is identified. The tracheal incision is targeted to occur at the interspace between the 4th and 5th cartilage ring. A transverse incision of 1/3 the tracheal circumference is performed. A finger is inserted into the incision and replaced by an endotracheal or tracheostomy tube to secure the airway. One loop of suture, created by a loosely tied square knot, is passed around the tracheal ring proximal and distal to the entry point. The tube is secured to the patient and the wound is closed cranial to the tube exit point. The wound distal to the tube exit point remains open to act as a vent point for air leakage and to prevent the development of subcutaneous emphysema and/or pneumomediastinum.

A controlled tracheostomy is performed when the patient has airway patency established but requires long-term support. Appropriate size tracheostomy tubes (known from ET intubation), surgical scrub, clipper, lidocaine filled syringe, barrier drape, scalpel, forceps, scissor, scalpel unit, and 0 nonabsorbable suture are the necessary supplies/equipment. To perform a controlled tracheotomy, the surgical site is quickly infiltrated with local anesthetic. The ideal site is between the 4th and 5th laryngeal rings, high enough to avoid blockage with neck flexion but low enough to avoid interference with laryngeal function. A 5 cm longitudinal skin incision on the ventral midline is performed in this area. The muscles overlying the trachea are divided by blunt dissection and the trachea is identified. The tracheal incision may be performed by a ventral midline incision, transverse incision of 1/3 the tracheal circumference, or the creation of a “flap” combining both approaches. One loop of suture created by a loosely tied square knot is passed around the tracheal ring proximal and distal to the entry point. Following entry, the tube is secured to the patient and the wound is closed cranial to the tube exit point. The wound distal to the tube exit point remains open to act as a vent point for air leakage and to prevent the development of subcutaneous emphysema and/or pneumomediastinum.

Complications are associated with poor procedural technique in identifying structures and attempting to advance the tracheostomy tube unit without incising overlying tissues enough to facilitate advancement. Secondary complications are associated with the development of subcutaneous emphysema and/or fascial plane air from a leak around the tube site. Leaving an open wound distal to the tube location reduces this risk by allowing a low-pressure escape pathway. Poor placement and/or technique can produce pneumomediastinum. Tracheostomy tube patency must be constantly monitored and care provided on a regular basis to assure patency.

Techniques Used to Confirm Successful Airway Placement

Tracheal Palpation

If the technique results in successful placement of a regular endotracheal tube, a quick check step is to palpate the mid-cervical region for correct placement. One should palpate one rigid tubular structure which represents the endotracheal tube within the lumen of the trachea. If a second rigid structure is palpated dorsal to the most prominent one, the endotracheal tube may have entered the esophagus. Quick auscultation of the stomach while giving a breath can quickly confirm if that has occurred. This procedure only works when an endotracheal tube is placed; it is not appropriate when a tracheostomy tube is sited.

Bilateral Chest Movement During the Respiratory Cycle

Canine and feline chest anatomy resembles a clamshell. When an assisted breath is delivered, the thoracic wall on both sides should expand as well as the cranial abdominal area due to diaphragm displacement. In “barrel-chested” dogs (bulldog, Staffordshire terrier), the chest wall is stiff and most breath excursion occurs in the cranial abdominal region. Focus on this area in these breeds.

Bilateral Thoracic Auscultation

A stethoscope is placed on each side of the thorax during an assisted breath. As inflation occurs, breath sounds should be heard on both sides of the chest. Breath sounds on only one side of the chest indicate endobronchial intubation. The absence of breath sounds suggests esophageal intubation. In that case, auscultation of the stomach during a subsequent breath will help decide if esophageal intubation has occurred.

ETCO₂ Measurement

End-tidal carbon dioxide measurement is useful in determining if airway placement is correct. If correct placement has occurred, an end-tidal waveform will be noted with each breath, whether spontaneous, assisted, or controlled. If the end-tidal waveform is consistently “flat” throughout the breath cycle, one should recheck airway placement and also make sure a pulse is present. In some cases, the presence of high fermentable food in the stomach can produce CO₂ and can be a point of confusion. In those cases, the ETCO₂ waveform is “flat”and independent of the breath cycle. One should verify correct placement using the physical methods described above if there is a concern. Disposable CO₂ devices are commercially available to assist in verifying correct airway placement. They do not monitor or report end-tidal values. They only determine if CO₂ is present by colorimetric change of a dye indicator in the presence of carbon dioxide.

Table 1. Equipment and adjuncts to assist in achieving an emergent airway

References

1.  Grimm KA, Lamont LL, Tranquilli WJ, Greene SA, Robertson SA, eds. Veterinary Anesthesia and Analgesia. 5th edition of Lumb and Jones. Wiley Blackwell; 2015:32–38.

2.  Burkitt Creedon JM, Davis H. Advanced Monitoring and Procedures for Small Animal Emergency and Critical Care. Wiley Blackwell; 2012:293–339.

3.  Hardjo S, Palmer L, Haworth MD. Prehospital emergency cricothyrotomy in dogs part 1: experiences with commercial cricothyrotomy kits. Front Vet Sci. 2021. https://doi.org/10.3389/fvets.2021.705695.

4.  Vieitez V, Ezquerra LJ, Ramis VL, Santella M, de Segura IAG. Retrograde intubation in a dog with severe temporomandibular joint ankylosis: case report. BMC Vet Res. 2018;14(118).

5.  Johnson D. Endotracheal intubation of small exotic mammals. DVM 360. 2011.