Abstract
An 11-year-old, 7 kg male neutered domestic shorthair cat, presented to the University Veterinary Hospital (UVH) for investigation of chronic tachypnoea and dyspnoea. Radiographs, bronchoscopy and computerised tomography (CT) demonstrated an intra-tracheal mass measuring 13 mm×5 mm×6 mm arising from the right wall of the caudal trachea immediately cranial to the carina. Due to size and position, debulking and subsequent cryosurgery were attempted to minimise the amount of tissue removed and prevent recurrence. A combination of anaesthetic techniques was required to allow cryotherapy, with the trachea open whilst maintaining adequate ventilation. This case report demonstrates that cryotherapy in conjunction with anaesthetic planning, can achieve a positive outcome for the cat.
An 11-year-old, 7 kg male neutered domestic shorthair cat was referred with a 6-month history of episodic tachypnoea and dyspnoea. Non-responsiveness to etamiphylline, (Millophylline V; Jurox), prednisolone (Solu delta cortef; Pfizer), and doxycycline (Vibravet 100 paste; Pfizer), prompted referral. Physical examination revealed increased respiratory rate and expiratory effort with increased bronchovesicular sounds and wheezes.
Radiography and endoscopy were performed under general anaesthesia to allow airway control. Anaesthesia was induced using propofol (Propofol; Hospira) after premedication with methadone 0.2 mg/kg IM. Intubation was performed using a 4.0 mm cuffed endotracheal tube and anaesthesia was maintained on isoflurane (ISO; Veterinary Companies of Australia) delivered in oxygen via a Bain circuit. A soft-tissue opacity was identified radiographically in the caudal trachea. The endoscopy confirmed a smooth rounded mass arising from the right wall of the trachea at the level of the carina, occupying approximately 80% of the cross-section of the lumen. The patient recovered from anaesthesia without complications and was discharged the following day. Histopathology from endoscopic pinch biopsies was suggestive of either an adenoma or an adenocarcinoma.
The patient was re-admitted 2 weeks later for computerised tomography (CT) prior to surgery. CT of the thorax was performed to assess potential involvement of the right mainstem bronchus and further delineate the mass. Premedication was 0.2 mg/kg methadone IM. Induction of anaesthesia was performed with propofol administered to effect for a total dose of 4 mg/kg. Oral intubation was performed with a 5.0 mm cuffed endotracheal tube. Anaesthesia was maintained using isoflurane delivered in 100% oxygen via a paediatric circle system. Manual ventilation was commenced at a respiratory rate of 10 breaths/min and an inspiratory:expiratory ratio (I:E) of 1:1 to allow sufficient time for lungs to inflate and deflate in the presence of an obstructed airway with markedly increased airway resistance. Positive end expiratory pressure (PEEP) of 5 mmHg was provided by manually limiting complete bag inflation at the end of expiration. PEEP was measured using a manometer placed within the expiratory limb of the circle breathing system. The amount of chest expansion and deflation was monitored visually to ensure adequate inflation and deflation. CT identified that the 13 mm×6 mm×5 mm mass was located immediately cranial to the carina and did not involve the right bronchi. The mass almost completely obstructed the 6.5 mm tracheal lumen.
Following CT, mandatory pressure-controlled, time-cycled, time-triggered and pressure limited ventilation (Julian; Drager) was commenced using a respiratory rate of 10 breaths/min, an I:E ratio of 1:1, a peak inspiratory pressure of 12 mmHg and a PEEP of 3 mmHg.
A remifentanil infusion was delivered at 10–30 μg/kg/h for intra-operative analgesia and minimum alveolar concentration (MAC) reduction. Hartmann's solution was administered at 10 ml/kg/h and cephazolin administered at 22 mg/kg IV every 120 min. Neuromuscular blockade was performed using atracurium administered initially at 0.2 mg/kg IV followed by increments of 0.1 mg/kg IV with monitoring by ‘train-of-four’ nerve stimuli on the facial nerve. Repeated administration was performed when the first twitch returned.
Monitoring throughout the procedure was performed with a multiparameter monitor (Surgivet V9203; Surgivet) and included heart rate (HR), respiratory rate (RR), end tidal carbon dioxide concentration (ETCO2) via side-stream capnography, oxyhaemoglobin saturation (SpO2) with the probe positioned on the tongue, blood pressure (BP) and central venous pressure (CVP). BP was measured non-invasively from the metatarsus due to technical difficulties with arterial catheter placement. CVP was measured via a triple-lumen central venous catheter (Arrow Triple-Lumen catheter; Arrow) inserted via the left jugular vein into the cranial vena cava.
A right lateral thoracotomy was performed. Two pairs of 4/0 polydioxanone stay sutures were placed: one along the right dorsolateral margin of the trachea just cranial to the carina and the other pair in the dorsal midline through the m trachealis. These allowed retraction of the trachea and access to the mass.
Cryotherapy was applied to the external wall of the trachea adjacent to the mass using a liquid nitrogen cooled, brass tipped cryosurgical probe. The probe was applied for 45 s in an attempt to vasoconstrict any vessels associated with the mass prior to its debulking. A 2 cm longitudinal incision was made through the m trachealis to the right of its midline to expose the mass and facilitate debulking, following which anaesthesia was maintained using a variable-rate infusion of propofol, (0.2–0.4 mg/kg/min). Resection of the mass and cryosurgery was performed in stages to allow intermittent mandatory ventilation, as ventilation was discontinued when the airway was open. A cut-off SpO2 of 90% was used to dictate the need for temporary closure of the trachea by crossing the pre-placed stay sutures thus allowing mandatory ventilation to recommence until an SpO2 of 98–99%and an ETCO2 of 35–45 mmHg was attained. ETCO2 monitoring was not possible whilst the patient was not being ventilated. Debulking of the mass allowed a reduction in the peak inspiratory pressure required to maintain normal ETCO2 and a change in the I:E ratio (from 1:1 to 1:2) as the initial longer inspiratory phase was no longer required.
Resection of the mass resulted in a raw base of tissue. Three separate 1 min freeze cycles of the mucosal tumour bed were performed. Thaw times averaged 5 min. After cryosurgery, the m trachealis incision was closed following which the propofol infusion was discontinued and isoflurane anaesthesia recommenced. A 3 cm×2 cm sheet of pericardium was harvested ventral to the phrenic nerve and sutured as a free graft over the external surface of the trachea at the cryosurgery site to act as a secondary fibrous seal in the event of postoperative tracheal wall necrosis.
Reduction of the remifentanil infusion to 3 μg/kg/h after thoracotomy closure was followed by a return of spontaneous ventilation. Isoflurane administration was discontinued, and extubation performed when normal swallowing was evident. The presence of a blood clot within the endotracheal tube, an SpO2 of 80% and cyanotic mucous membranes after extubation was suggestive of airway obstruction associated with airway haemorrhage. Re-intubation was performed under propofol anaesthesia followed by gentle tracheal suctioning which was productive for blood and mucous. Oxygen support during the second recovery attempt was provided initially via the endotracheal tube and then via a tight-fitting face mask following extubation. This second recovery attempt was uncomplicated. Postoperative recovery was uneventful and the patient was discharged 5 days after surgery with a normal appetite. Histopathology was consistent with a dysplastic papillary adenoma.
Follow-up radiographs 8 months after surgery did not reveal any evidence of recurrence of the mass. Recurrence of clinical signs occurred at 16 months. The surgical procedure was repeated. A pneumothorax developed postoperatively, respiratory arrest followed and the cat was subsequently euthanased.
This case report describes the surgical debulking, cryosurgical and anaesthetic management to alleviate clinical signs associated with an intra-tracheal adenoma in a cat for 16 months. This report also demonstrates how adequate ventilation and oxygenation can be maintained during intra-tracheal surgery using standard ventilation equipment.
Primary neoplasms of the trachea are rare in cats. Lymphoma and carcinomas are most commonly reported. 1,2 Treatment options include chemotherapy, radiotherapy and surgery. 3 Other reported methods include stenting, the use of endoscopic laser and the use of snares. 4 Due to the location of the mass, complete surgical resection was not possible. Debulking with snares has been reported to palliate clinical signs for up to a period of 9 months. 4 The use of cryotherapy in this case allowed palliation of clinical signs for 16 months. This was longer than that reported with snare use.
The use of cryosurgery for skin lesions in cats has been described, however, it has not been previously reported as a method for treating tracheal masses. 5 Cryotherapy has been reported for the treatment of tracheal and bronchial tumours in humans and dogs. Correctly applied cryotherapy destroys biological material via a rapid freezing and thawing process 6 whilst minimising trauma to the surrounding tissue. Frozen cells undergo dehydration, electrolyte changes and denaturation of proteins leading to cell lysis or death. 7,8 The thawing process results in further injury on a structural and whole tissue level. Repetition of the cycle causes complete cell lysis. 9 Tracheal necrosis is a potential complication of this therapy. In a study in which 11 dogs were anaesthetised for an experimental study of the application of cryotherapy to the trachea and bronchi, tracheal necrosis did occur. However, the necrosis was localised, followed by prompt regeneration of the mucosa and there was no permanent alteration to the gross structure of the trachea. 10 Also, by visualising the base of the mass, the cryotherapy could be applied directly on the mass, reducing the chance of causing necrosis at sites other than the mass. The use of the cryoprobe to produce vasoconstriction on the external wall of the trachea has not been reported in the literature. It is known that vasoconstriction occurs in association with cold temperatures. It was postulated that by applying the cryoprobe to the area it may limit the haemorrhage during the procedure and, due to the resistance of cartilage to cryotherapy, would not have caused permanent damage to the mucosa.
Maintenance of adequate ventilation during tracheal surgery may be complicated by neoplasms, an open tracheal lumen or luminal obstruction from haemorrhage, fibrosis or inflammation. Surgery of the mass at the level of the carina presented a challenge due to the need to maintain a patent communication between the trachea and the smaller mainstem bronchi. Given successful anaesthesia and ventilation via an oral endotracheal tube for the previous diagnostic procedures, a similar protocol was considered the best option for the surgery. Appropriate premedication was necessary to prevent stress and excitement during induction, in order to prevent an increase in respiratory effort in an already respiratory compromised patient. As the cat was of a placid temperament, methadone alone provided adequate sedation. Use of a neuromuscular blocker facilitates the surgeons’ access, however, inhibition of spontaneous ventilation in a patient without a means to perform positive pressure ventilation is contraindicated. A sterile endotracheal tube was available to allow intubation of the left bronchus via the surgical site to perform one-lung ventilation. A 5-French rigid urinary catheter was also available to allow insufflation of oxygen down the trachea whilst maintaining anaesthesia intravenously. The short-burst nature of cryotherapy, ie, the 60 s freeze cycle with the thaw time of 4–5 min in combination with the pre-placed stay sutures, allowed short periods of apnoea with the trachea open and then time for SpO2 and end tidal carbon dioxide to return to normal.
The second anaesthetic challenge posed by this case was the ability to maintain anaesthesia once the integrity of the airway was disrupted. Without an airway, isoflurane could not be delivered and intravenous anaesthesia was required. A variable-rate propofol infusion was used. Propofol infusions are commonly used for maintenance of anaesthesia in dogs but have a number of problems associated with their use in cats. Propofol has a longer duration of action with greater accumulation overtime, resulting in longer recovery time and has been reported to cause a Heinz body anaemia when repeatedly administered. In this case the duration and total amount of propofol administered were limited by maintaining anaesthesia with isoflurane before opening and after complete closure of the trachea. Alfaxalone could have been used as an alternative to propofol and would have negated the risk of the Heinz body anaemia associated with propofol.
This case report describes the novel use of cryotherapy and modification of routine ventilation techniques in the surgical management of an intra-tracheal mass in a cat.