Abstract
A 2-year-old, 4.5 kg, neutered male domestic shorthair cat was presented to the emergency service with dyspnoea, anorexia and apathetic behaviour. Thoracic radiographs showed typical signs for a thoracic trauma and a tracheal lesion in the region of the carina, consistent with pseudoairway formation. Computed tomography (CT) was performed in the conscious cat to avoid aggravation of air leakage associated with ventilation. The additional CT findings were consistent with a novel pattern of a traumatic avulsion of the left principal bronchus expanding into the carina and caudal thoracic trachea. Despite the complex avulsion pattern, successful treatment was achieved surgically by performing an end-to-end anastomosis via a fifth right intercostal lateral thoracotomy. The cat was ventilated with a feeding tube and jet ventilation throughout. The cat showed excellent recovery 6 months after surgery.
Case Report
Intrathoracic tracheal avulsion is a rare, but well described, injury in the cat.1–4 A blunt trauma with hyperextension of the head and neck is assumed to be the initiating cause, typically leadin g to an avulsion 1–4 cm cranial to the bifurcation of the trachea representing its weakest point. In some circumstances, avulsion of a principal bronchus is possible.3–5 In the presented case a novel avulsion pattern was observed involving the bifurcation, the carina and the caudal trachea. After an avulsion injury, intact tracheal adventitia, as well as thickening of mediastinal tissue, is thought to maintain the airway lumen enabling ventilation leading to a condition described as pseudoairway. 3 However, the narrowing at both avulsed ends of the injury can result in stenosis.2,3 Resection of the stenosed ends of the avulsed trachea followed by anastomosis is described as the treatment of choice.3–6 The present case describes a completely novel avulsion pattern, including its diagnostic work up, on a conscious patient and its subsequent surgical repair.
A 2-year-old, 4.5 kg, neutered male domestic shorthair cat was presented to the emergency service with dyspnoea, anorexia and apathetic behaviour of 2 days’ duration. A traumatic history was suspected. Tachypnoea and increased inspiratory lung sounds were present on the right side on auscultation, whereas lung sounds were diminished on the left side. Other vital parameters were within normal limits, as well as serum biochemistry and haematology.
Initially, the cat was treated with intravenous lactated Ringer’s solution (Fresenius Medical Care) at maintenance rate (2 ml/kg/h) and buprenorphine (20 μg/kg q6h; Temgesic, Reckitt Benckiser). Thoracic radiographs revealed moderate pneumothorax, pleural effusion, pneumomediastinum and pneumoretroperitoneum. The base of the left mainstem bronchus appeared spherically enlarged and could not be followed to the periphery, raising the suspicion of an airway laceration (Figure 1).
Ventrodorsal and left lateral projection of the thorax. (a) There is a considerable cardiac shift to the right side. A pleural fissure line is visible between left cranial and caudal lung lobes (white arrow). Lack of vascular pattern demarcates pleural gas in the left caudal aspect of the thorax (white arrowhead), while part of the left cranial lung lobe is consolidated (black arrowhead). (b) Note extensive gas in the cranial and caudal mediastinum as well as the retroperitoneum (black arrows). The focal spherical enlargement of the left mainstem bronchus is well appreciated (*)
Computed tomography (CT) was scheduled for the following day to assess the severity and extent of the lesion. Thoracocentesis was performed and examination of the fluid was consistent with the diagnosis of haemothorax.
The cat was kept in an oxygen cage with continuous respiratory monitoring.
CT was performed with a multi-row helical CT unit (Brilliance16; Philips) using 16 detector rows. Owing to continuous concern regarding ventilation-associated complications in anaesthesia, the study was performed with the animal awake in an appropriately sized conventional cardboard box, allowing oxygen supply and air circulation via small designated holes. The resulting plain scan was only minimally compromised by motion artefacts. Obliquity of patient positioning was corrected by adjusting the multiplanar reconstructions.
Scan direction was cranio-caudal using a slice thickness of 1.0 mm. Scan parameters were kV 120, mA 183, collimator pitch 0.688 and 0.75 s tube rotation time. The field of view was adjusted to the cardboard box. The raw data were reconstructed to image series with 1 mm slices in a matrix of 512 dpi with an overlap of 33% in a soft tissue, bone and lung algorithm. The images were exported to a work station (OsiriX v.4.1. 64-bit, DICOM Viewer, www.osirix-viewer.com) and multiplanar reconstructions were evaluated in appropriate windows (WL/WW): soft tissue (40/350), bone (300/1500) and pulmonary window (−500/1400).
The base of the left mainstem bronchus was extensively enlarged over a length of 11.4 mm, caudal to which it abruptly decreased in size with ill-defined bronchial borders and tapered to the periphery. The left caudal lung lobe was aerated, whereas both parts of the left cranial lung lobe appeared isoattenuating to soft tissue, with only mild volume loss and persistent bronchial aeration. The right caudal mainstem bronchus was normal. Right lung lobe borders were mildly retracted. Moderate gas accumulations were visible around the mediastinal structures, expanding caudally into the retroperitoneal space and into subcutaneous and interfascial planes (Figure 2). The resulting diagnosis was rupture of the left mainstem bronchus, involving the carina, with secondary moderate pneumomediastinum.
Corresponding CT images of the thoracic studies shown above. True extent of left mainstem bronchus rupture (*) is now evident, as well as tracheal involvement (white arrowhead marks bifurcation). Note further the extensive pneumomediastinum (white arrows)
Following intramuscular ketamine (7 mg/kg Narketan; Vétoquinol), midazolam (0.1 mg/kg Dormicum; Roche Pharma) and medetomidine (2 μg/kg; Dorbene), anaesthesia was induced with intravenous alfaxalone (1.3 mg/kg Alfaxan; Vétoquinol) and maintained with alfaxalone (4.4–8.0 mg/kg/h), medetomidine (0.5–1.0 μg/kg/h) and fentanyl (5–10 μg/kg/h Sintenyl; Sintetica) infusions. The trachea was intubated with a cuffed 4.5 mm endotracheal tube (Mallinckrodt, Covidien) just beyond the larynx. The cat was allowed to breathe spontaneously.
The bifurcation of the trachea was approached through a fifth right intercostal thoracotomy according to the description of White and Milner. 3 A 5 Fr feeding tube (Paediatric Feeding Tube; Mallinckrodt) was advanced through the endotracheal tube lumen and connected to a manual jet ventilator (Manujet III; VBM Medizintechnik). Manual jet ventilation with driving pressures between 0.1 and 0.5 bar, variable frequency and fraction of inspired oxygen (FiO2) of 1.0 was initiated thereafter. The effectiveness of ventilation was visually assessed by the degree of lung inflation.
The azygos vein was separated by blunt preparation and ligated. The caudal trachea, and the bifurcation and principal bronchi were isolated by a combination of sharp and blunt dissection, and the oesophagus and the cranial vena cava were retracted. A pseudoairway was recognised in the area of the bifurcation. It was entered with a stab incision, which allowed observation of the two avulsed sites. At this state the feeding tube was advanced into the right bronchus under visual control. An oblique avulsion of the left principal bronchus with involvement of the carina and the distal trachea was detected (Figure 3).
Schematic drawing of the avulsion pattern
When a decrease in arterial haemoglobin oxygen saturation and visual lung deflation occurred during opening of the pseudoairway membrane, the injured airway was digitally occluded. The proximal and distal end of the avulsed segment was transected in the cartilage as close as possible to the stenosed ends. Along the laceration the carina had to be resected to achieve proper anastomosis. Single interrupted 4-0 Polydioxanone (PDS; Ethicon) sutures were pre-placed in the proximal and distal segment, starting at the dorsal aspect to facilitate best visibility. Most of the sutures were placed around cartilaginous rings. Owing to the particular shape of the avulsion some of the sutures had to be placed through the end of cartilaginous rings. Mechanical ventilation was started after tying the last suture and feeding tube removal. Warm, sterile lactated RInger’s solution was used to lavage the surgical site and to check for an airtight seal. A thoracic drain was placed, the thorax was closed routinely and during closure a wound catheter (MILA Diffusion/Wound Catheter; MILA International) was placed for local bupivacaine (0.5 mg/kg q6h: Carbostesin 0.5%; AstraZeneca) administration. Anaesthetic recovery was uneventful. Medetomidine infusion (0.4–5.5 μg/kg/h), buprenorphine (20 μg/kg q6h) and intrapleural bupivacaine (0.5 mg/kg q6h) administration was continued postoperatively.
The thoracic drain was removed 36 h after surgery as thoracic radiographs showed no signs of pneumothorax or persistent pseudoairway. The cat was discharged 3 days later. Presentation at 2 weeks and 4 weeks after surgery showed the patient to be in a good condition without clinical signs of respiratory abnormalities.
At telephone follow up 6 months after surgery, the owners reported a normal condition of the cat without any signs of respiratory compromise.
A traumatic incident is considered to be the most common reason for avulsion injury of the intrathoracic trachea 4 and remains most likely in the presented case. A recent case report described an avulsion injury of a principal bronchus in a cat with a notional traumatic episode; however, in that case the bifurcation, the carina and the distal trachea remained unaffected. 5 The reason for the atypical and novel confirmation of the avulsion injury described in this case report remains unclear. Similar injuries are described as avulsion of the main bronchus with stellate tear in human medicine. The reason for this type of injury is unexplained. 7
The cat showed apathetic behaviour for 2 days prior to the time of presentation. White and Milner 3 described two distinct clinical presentations, with the first being an acute-onset dyspnoea and respiratory compromise immediately after the injury, and the second a more chronic exertional dyspnoea combined with exercise intolerance appearing several days to weeks after the traumatic episode.
Initially, thoracic radiographs had raised the suspicion of a discontinuity of the borders of the left mainstem bronchus, resulting in a pseudoairway formation. The latter is described in tracheal lacerations, 8 but is expected to develop in a similar manner in bronchial avulsions. 4 Considering the aforementioned, the history of this cat is most consistent with a more chronic avulsion injury.
The CT study allowed a distinct characterisation of the bronchial lesion, hence facilitating surgical and anaesthetic preparation. Being able to obtain a diagnostic study of a critical patient in an awake state by creating a confined environment by such a simple device as a cardboard box was beneficial.
The surgical approach via a right lateral thoracotomy to the tracheal bifurcation gave excellent exposure, as previously described. A left lateral thoracotomy would have restricted the exposure by the descending thoracic aorta and the thoracic oesophagus. 5
Conclusions
Avulsion injury of the principal bronchus with involvement of the carina, the bifurcation and the distal trachea is a rare condition, which can be successfully surgically repaired, even in cases with complex avulsion patterns. However, it has to be taken into consideration that anaesthetic management of these patients is unpredictable and challenging. Size and avulsion shape did not allow one-lung ventilation. 9 Selective bronchus intubation with subsequent jet ventilation was a feasible alternative, 9 although hypercapnia, hypoxaemia and barotrauma can occur. 10
Footnotes
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Conflict of interest
The authors do not have any potential conflicts of interest to declare.