Introduction

Cervical injuries are common in dogs occurring as a result of bite injuries, road traffic accidents, choke chains, and gunshot injuries.^1–11 Penetrating wounds of the cervical region may cause tracheal, laryngeal, and esophageal tears; tracheal stenosis; rupture of the carotid or jugular vessels; or damage to the recurrent laryngeal nerve, mandibular salivary gland, thyroid, parathyroid gland, occipital condyle, tympanic bulla, spinal cord, or vagus nerve.³ Minor cervical tracheal tears may be self-limiting and heal without intervention, but large cervical tracheal tears including partial or complete tracheal disruption may lead to serious respiratory distress or death associated with airway obstruction secondary to tracheal displacement, soft tissue interposition, or intraluminal hematoma formation.^3–11 Several reports focusing on traumatic laryngeal or tracheal rupture in dogs have been published.^3–11 The purpose of this retrospective study was to report signalment, clinical and surgical findings, complications, and long-term follow-up of 10 dogs that were presented for penetrating trauma of the upper airway.

Materials and Methods

Medical records of 10 dogs from January 1997 to March 2011 were reviewed. Dogs that had laryngeal or tracheal perforation and laryngeal or tracheal structural compromise associated with a traumatic incident that was confirmed at the time of surgery were included in the study. In all cases diagnostic evaluation included clinical examination, routine hematology, biochemical analysis, and plain radiography. In one case (case 5), tracheoscopy was performed to aid in localization of the tear. Records were evaluated for signalment (breed, sex, age, and weight), historical data, physical examination abnormalities, duration of injury, diagnostic tests, surgical findings and treatment, complications, hospitalization time, follow-up, and outcome. Follow-up was performed by re-examination that was done by one of the authors or referring veterinarians and/or telephone contact with the referring veterinarian or the owner.

Results

Breeds represented were mixed-breed dogs (n = 6) and one of each of Greek hound, Finnish spitz, dachshund, and English setter. Eight dogs were intact males and two were spayed females. Mean age at presentation was 4 yr (range: 2.5 to 6.5 yr) and mean weight was 20.4 kg (range: 14 to 33 kg). Four dogs were injured during hunting (cases 1, 2, 7, and 8), 2 of the dogs (cases 1 and 2) sustained dog bites, and 2 of these dogs were bitten by wild boars (cases 7 and 8). Five dogs sustained dog bites (cases 3, 5, 6, 9, and 10) and one had a gunshot injury as was witnessed by the owner (case 4).

Upon arrival oxygen was administered (face mask, nasal catheter, or transtracheal catheter) to all dogs. All dogs were resuscitated with intravenous crystalloids +/- colloid fluids guided by oscillomeric blood pressure monitoring. Continuous electrocardiographic monitoring was provided in all cases. Sinus tachycardia was detected in eight dogs (cases 2, 3, 5, 6, 7, 8, 9, and 10). Ventricular premature contractions were noted in six dogs (cases 3, 4, 7, 8, 9, and 10) that were resolved without treatment.

Physical examination abnormalities included depression (cases 1, 5, 6, 7, 8, 9, and 10); respiratory distress (cases 5, 6, 7, 9, and 10); stridor (cases 6, 7, and 9); cyanosis (cases 6, 7, and 9); air leaking through the cervical wound every time the animal breathed (cases 1, 2, 5, 7, 8, 9, and 10); bite wounds over the cervical region (cases 1, 2, 3, 6 9, and 10); multiple bite wounds over the cervical region, thorax, and abdomen (case 5); a scar along the ventral cervical region reflecting a gunshot injury (case 4); a single 1.5 cm diameter wound inflicted by a boar (case 7) and a 4 cm wide wound extending from the cranial ventral thorax to the mid cervical region inflicted by a boar (case 8); localized subcutaneous emphysema over the cervical region (cases 1, 2, 7, 9, and 10) or generalized (over the entire trunk) subcutaneous emphysema (cases 3, 4, and 5); and cervical spinal pain on palpation (case 6, 9, and 10). Mean duration of clinical signs from onset to admission was 2.5 days (range: 1 to 7 days). The 10 dogs of this study are presented in Table 1.

Table 1 Clinical Data of 10 Dogs Sustaining Traumatic Upper Airway Injury

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Table 1 (Extended) Clinical Data of 10 Dogs Sustaining Traumatic Upper Airway Injury

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Radiographic examination of the cervical region, thorax, and abdomen (right and left lateral and a ventrodorsal view) confirmed subcutaneous emphysema localized over the cervical region (cases 1, 2, 7, 9, and 10) and generalized subcutaneous emphysema (cases 3, 4, and 5). It also revealed tracheal stenosis (case 6), pneumomediastinum (cases 3, 4, 5, 7), pneumothorax (case 5), a soft tissue opacity into the tracheal lumen consistent with fluid accumulation (case 7), and two gun pellets over the thorax and abdomen (case 4). Radiographic examination of the cervical region of case 8 was not performed. Thoracic radiography of case 8 was normal. Tracheoscopy of case 5 showed tracheal obstruction associated with fracture of the first tracheal ring. The ring was protruding into the tracheal lumen.

Aerobic and anaerobic cultures were obtained from seven dogs at the time of presentation. Cultures from two dogs were negative (cases 5 and 8). Cultures revealed S. intermedius in three dogs (cases 2, 3, and 9) and Enterococcus spp. in two (cases 7 and 10).

All surgeries were performed under gas anesthesia. Butorphanol^a, diazepam^b, or low dose acetylopromazine (0.02 mg/kg intramuscular)^c were administered for premedication. Anesthesia was induced with IV propofol^d and maintained with isoflurane delivered in 100% oxygen through oral endotracheal intubation using a smaller tube diameter (2–3 mm smaller than what would normally be used). All patients received mechanical ventilation. In one dog (case 7) oral endotracheal intubation was unsuccessful and a second sterile tube was placed in the distal trachea following a midline cervical approach. Before intubation of the distal trachea blood clots and tissue debris were suctioned. The dog was reintubated orally and tracheal reconstruction was completed.

Surgical exploration through a ventral cervical midline incision was performed in 10 dogs. Copious lavage with normal saline and debridement preceded surgical repair. In case 1, multiple fractures of the thyroid cartilage were identified, which precluded reconstruction. A permanent tracheostomy was recommended, but it was declined by the owner and the dog was euthanized. In case 2, separation of the cricoid and thyroid cartilage was revealed and reconstruction was performed by placing five simple interrupted 2/0 polypropylene^e sutures through the cartilages to achieve cricoid and thyroid apposition. Tenth to 11th tracheal ring perforation was identified in case 3, 9th–11th in case 6, 9th–10th in cases 7 and 8, and 11th–12th ring perforation in case 10. Caudal cervical tracheal stenosis involving rupture of 15th, 16th, and 17th rings was diagnosed in case 4. Three to five rings were excised in cases 3, 4, 6, 7, and 10 and an end to end split cartilage tracheal anastomosis was performed using simple interrupted 3/0 polypropylene or 3/0 polydioxanone^f sutures penetrating the adjacent rings. Tension relieving sutures also were placed encircling two to three rings proximal and distal to the anastomotic site using 3/0 polypropylene or 3/0 polydioxanone sutures in a simple interrupted pattern. In case 8 a minor tracheal separation of the 9th and 10th rings was noted and following limited debridement closure was achieved by inserting three 3/0 simple interrupted polydioxanone sutures around the adjacent rings.

First ring tracheal fracture was detected in case 5. The first ring was excised and the cricoid cartilage was anastomosed to the second tracheal ring by placing simple interrupted 3/0 polydioxanone sutures penetrating the cricoid and encircling the second tracheal ring. Pneumothorax associated with a thoracic injury was also present. A thoracostomy tube was placed before surgery and remained in place for 2 days after surgery for the management of pneumothorax.

In case 9 a minor tracheal separation of the third and fourth tracheal rings was identified and following limited debridement closure was achieved by inserting two 3/0 simple interrupted polydioxanone sutures around the adjacent rings. Multiple perforations of the ventral and lateral pharyngeal region were detected during exploration in addition to the tracheal wound. The most distal pharyngeal perforation was close to the epiglottis. Rupture of the cervical musculature was also detected. The pharyngeal wounds were debrided and sutured using 3/0 polydioxanone suture material in a simple interrupted pattern. The skin wound was closed in a continuous pattern after placing two Penrose drains^g, which exited through small skin incisions on either side of the cervical incision. A 20 Fr esophagostomy tube was inserted via a left cervical approach. The cervical region was dressed with a light bandage, which was changed twice daily for 8 days.

Mean hospitalization time for the 9 dogs was 5.5 days (range: 2 to 14 days). Fentanyl^h was administered postsurgery for analgesia. All animals received empirical IV antibiotics before surgery. Antibiotics were continued IV while the patient was in hospital and then switched to oral at the time of discharge for a total of 7 to 10 days. Once culture and sensitivity results were available antibiotics were changed as necessary. Antibiotics administered included cefuroximeⁱ (10 mg/kg q 12 hr) for cases 2, 3, 4, 6, and 9 and marbofloxacin^j (2 mg/kg q 24 hr) for cases 5, 7, 8, and 10.

Case 7 developed coughing secondary to aspiration pneumonia that was diagnosed by radiographic examination. Pneumonia was treated with oral marbofloxacin, IV crystalloids, nebulization, and coupage for 10 days. One dog (case 2) was aphonic and one dog (case 8) had dysphonia. In case 8, vocalization returned to normal within 3 wk.

In cases 3, 4, and 5, generalized subcutaneous emphysema was completely resolved within 2 to 3 wk, while local emphysema resolved within 7 to 10 days in cases 2, 7, 9, and 10. In case 9, the dog started to eat on its own on day 5 after surgery and the esophagostomy tube removed on day 8 after surgery. Drains were removed on day 5 when the drainage resolved.

Median follow-up time for the 9 animals was 24 mo (mean: 31.9 mo; range: 11 to 120 mo). Cases 3, 4, 5, and 9 were re-examined by one of the authors; cases 6, 7, 8, and 10 were re-examined by the referring veterinarian; and the owner of case 2 was contacted by telephone. All dogs were in good health, showed no signs of breathing difficulty, and three of them (cases 2, 7, and 8) were able to hunt. Case 2 had permanent aphonia.

Discussion

Bite wounds are among the most frequent and serious injuries encountered in small animal practice; most of them are associated with dog fights and account for 10–15% of all trauma cases.^1,12 The head and cervical regions are the most common bite wound regions in medium and large breed dogs.¹² Bite wounds of the cervical region account for 20–29% of the bite wound cases reported in dogs.^12,13 In the present study, 90% of the cervical injuries were inflicted by animal bites and 40% of the dogs were injured during hunting. Male dogs were over represented in one study.¹² Our study population comprised of 80% male dogs with a male to female ratio of 8:2.

The skin and underlying tissues in a dog fight may be lacerated, stretched, crushed, and avulsed.¹² Because the skin and subcutaneous tissue are freely movable, minimal skin wound damage may be associated with a large amount of underlying tissue trauma.^14,15 Upper airway tears may be masked by barely noticeable skin puncture wounds.³ In our study, only one dog with tracheal stenosis associated with a gunshot injury was presented with no obvious external wounds.

In one study, wild-boar-inflicted dog injuries affecting the head, cervical region, and thoracic limbs accounted for 13.5% of the total inflicted injuries, but no percentages for male and female boar inflicted trauma were provided.¹⁶ In our study, a male boar created a larger wound than that of the female. This difference in wound creation may be attributed to the fact that saber-shaped tusks of the male boars slash the victim's skin easily and can create extensive deep wounds compared to the smaller female boar teeth that depend on impact force for inflicted damage.¹⁷

Diagnosis of laryngeal or tracheal perforation may be challenging, especially in cases with signs of subcutaneous emphysema and mild or no respiratory distress. In the present study, respiratory distress was diagnosed in 50% of the dogs and emphysema was evident in 70% of the dogs. Stridor was evident in 30% of the dogs and was attributed to tracheal stenosis or obstruction. The presence of subcutaneous emphysema should raise suspicion of an upper airway injury.³

Dynamic air leakage through the cervical skin wounds, as was present in 70% of the dogs of this study, was pathognomonic for upper airway rupture.⁴ Extension of emphysema along fascial planes and into the mediastinum created a pneumomedistinum.

Tracheal perforation is rarely a specific radiographic diagnosis.¹⁸ Radiographic findings associated with tracheal perforation are mostly indirect and include peritracheal air accumulation, subcutaneous or deep fascial emphysema, and pneumomediastinum.¹⁹ Regional interruptions may be visualized in complete tracheal rupture and displacement.¹⁹ Radiographic abnormalities of the study presented here are in agreement with the above findings. Narrowing of the tracheal lumen related to tracheal stenosis was easily evaluated due to its non-dynamic nature. Positive contrast tracheography and computed tomography can also be used for the assessment of tracheal lumen abnormalities.^20,21

Upper airway endoscopy may be necessary to aid in the diagnosis of upper airway perforation. In severely compromised patients, tracheoscopy may be contraindicated since the risk may outweigh the benefits.²² During tracheoscopy, aggravation of the tracheal tear or pneumothorax may be seen.²² In the study reported here, tracheoscopy was performed in one dog to help in localization of the tear. In most of the dogs of our study, physical and radiographic examination findings were the cornerstone of diagnosis and surgical exploration was performed for diagnostic confirmation and treatment.

In view of the potential for life-threatening complications associated with upper airway rupture, definite management should not be delayed and establishment and maintenance of an unobstructed airway should be a priority.^3,6,22 In the study presented here, the decision to proceed to surgical exploration of all dogs was based on the type, progressive nature, and severity of clinical findings. Before implementing surgical reconstruction, upper airway patency may be achieved by oral intubation, intubation through an open wound, or intubation through a tracheostomy distal to the tear.^6,22 In cases of suspected tracheal disruption, endotracheal intubation should be carefully performed using a substantially smaller diameter than the tracheal lumen tube since passage of a larger tube may result in complete disruption of the trachea.⁴

Treatment of upper airway ruptures may be surgical, consisting of immediate repair of the tear, tracheal resection, and anastomosis, or delayed primary repair.^3–8,22 Adequately apposed full thickness mucosal injuries heal by epithelialization; 96 hr after injury the migrated epithelium differentiates into ciliated and goblet cells.^23,24 Inadequate apposition results in excessive granulation tissue formation and poorly differentiated epithelium lining, which leads to narrowing of tracheal lumen diameter.^24,25 A simple interrupted pattern was found to be superior to a simple continuous pattern for tracheal anastomosis in dogs because it resulted in significantly less luminal stenosis.²⁶ Tracheal stenosis may result from a traumatic injury and clinical signs, depending on the degree of structural compromise, vary from asymptomatic to coughing or respiratory distress.^5,7,27

Minor tracheal tears in animals with static emphysema and no respiratory distress, in the presence of other significant injuries or due to financial constraints, may be left to heal secondarily.^6,27,28

The split cartilage technique was used to perform the tracheal resection and anastomosis in five dogs of the present study. This technique was preferred over the annular ligament technique because of its superiority in achieving more precise alignment and apposition and decreased likelihood of dorsoventral stenosis.²⁴ Although removal of tracheal segments was limited to three to five rings, tension relieving sutures were used in five of the dogs. In our study, additional reinforcement sutures were placed to add strength to the anastomotic site. Extra tension relieving sutures were reported to add significant strength over a simple interrupted pattern in a static distraction experimental canine study.²⁹ Pharyngeal wall perforations caused by animal bites constitute an uncommon site of injury of the head and cervical region.³ Case 9 sustained a combination of pharyngeal and tracheal perforation secondary to bites inflicted by other dogs. In this dog, tube esophagostomy was performed to divert food away from the pharyngeal wounds; however, the esophageal tube ideally should have been used until the pharyngeal injury had healed.³⁰

Complications of tracheal resection and anastomosis include granulation tissue formation associated with the use of reactive non-absorbable or absorbable suture material; anastomotic dehiscence related to excessive tension resulting from removal of large number of tracheal rings; or they may result secondary to disruption of the delicate blood supply, stenosis, hemorrhage, or recurrent laryngeal nerve damage.^{3,5,8,24,26,31}

Long-term follow-up of the dogs of our study revealed no signs of respiratory distress or stridor in any of the dogs, even in the three hunting dogs that continued to hunt postsurgery. Tracheal luminal stenosis after anastomosis may be anticipated, although respiratory signs associated with stenosis are not observed until there is more than 50–75% narrowing of the tracheal lumen.³²

Dysphonia is an uncommon manifestation of diseases affecting the central nervous system, neuromuscular junction, or muscle.³³ Dysphonia is a rare postoperative complication of tracheal surgery or penetrating cervical trauma.^3,27 Injury to the vocal folds or recurrent laryngeal nerves resulting from the original bite wound or surgical manipulations during surgery may be responsible for the dysphonia.^3,27 During surgery, the recurrent laryngeal nerves should be identified and preserved. One dog in our study presented with or developed dysphonia following tracheal reconstruction. In this dog, dysphonia was evident immediately postoperatively and resolved within 3 wk after surgery. This dog, however, was not evaluated for laryngeal paralysis.^3,27 Laryngeal nerve regenerative capability is reported following nerve damage.³⁴ In another dog of our study that suffered a separation of the cricoid and thyroid cartilage, permanent aphonia was noted for 2 yr after surgery. The exact cause of aphonia in this dog could not be determined. Aspiration pneumonia was observed in one dog after a tracheal resection and anastomosis. This complication might be associated with recurrent laryngeal nerve damage, infected blood and tissue debris accumulation within the tracheal lumen, and mucostasis reflecting surgery in the trachea.²⁴

Conclusion

In the study presented here, diagnosis of traumatic upper airway perforation is based on clinical signs and radiographic examination and confirmed at surgery. Dynamic air leakage from the skin wound, emphysema, and pneumomediastinum are commonly seen. Emphysema resolves with time. Surgical exploration and reconstruction by tracheal resection and anastomosis or suturing is performed in most of the dogs with favourable results. Complications included aspiration pneumonia and abnormal vocalization, but most resolve with time.