25 Jul 2016
Catherine Bovens considers stabilisation and long-term treatment approaches to chronic breathing difficulties in felines, where, in the majority of cases, the prognosis is good.
Catherine Bovens
Job Title
Figure 2. Fluticasone inhalations are administered via a spacing chamber and are usually well tolerated by cats.
Feline lower airway disease includes asthma and chronic bronchitis. In feline asthma, a major feature is bronchoconstriction causing acute dyspnoea – airway inflammation is also present.
In feline chronic bronchitis, airway inflammation causes a chronic cough, but bronchoconstriction is not present. Cats with chronic bronchitis can develop dyspnoea due to airway inflammation, remodelling and mucus accumulation, so these conditions can be difficult to differentiate based on clinical signs.
Lower airway disease tends to develop in younger cats (four to five years), but can occur at any age. Siamese cats may suffer more commonly from asthma. Asthma is caused by hypersensitivity to inhaled allergens, while the cause of chronic bronchitis is not completely understood.
Signs vary from coughing to tachypnoea, wheezing, upper respiratory rattling from secretions, cyanosis and/or expiratory dyspnoea. A cough may be mistaken for trying to expel hairballs. Vomiting may occur after paroxysmal coughing. Exercise intolerance may be present, but is difficult to assess in sedentary cats. The signs are often intermittent, with asymptomatic periods, and vary from mild to severe.
Acute flare-ups can occur on a background of milder chronic signs (for example, dyspnoea in a cat with chronic cough). Examination may be normal or reveal tachypnoea, expiratory dyspnoea, wheezes and/or crackles on thoracic auscultation.
If a cat presents with dyspnoea, oxygen needs to be administered immediately (an oxygen cage or tent is best) and handling should be minimal. Investigation should be delayed until the cat is more stable. A mild sedative can be used to reduce anxiety, such as butorphanol (0.2mg/kg to 0.3mg/kg IM/SC/IV), but respiratory depression should be avoided.
If auscultation reveals dull pulmonary sounds, thoracocentesis should be attempted to drain any pulmonary effusion. Furosemide (2mg/kg IM/SC/IV, repeated if needed) can be administered in case cardiogenic pulmonary oedema is present, until the cat is more stable and the origin of the dyspnoea can be determined.
If bronchoconstriction is suspected, a fast-acting bronchodilator can be administered: salbutamol inhalation (100mg) administered via a space chamber or injection of terbutaline (0.01mg/kg IM/SC/IV) – repeat if needed. These bronchodilators can cause tachycardia, so should be used with caution if a cardiac cause is possible. Steroids (dexamethasone 0.2mg/kg to 0.3mg/kg IM/IV) can be considered if there is no response to furosemide and bronchodilators, but are best avoided if possible until a cardiac cause is excluded and after investigation. An IV catheter should be placed as soon as it is safe.
A basic echocardiography can usually be performed conscious and is useful in cats with dyspnoea to establish if left atrium enlargement is present (a normal left atrial size makes left-sided congestive heart failure unlikely). Thoracic ultrasonography also allows detection of pleural effusions.
Thoracic radiographs are usually the first diagnostic step to confirm the localisation of the disease to the lower airways and exclude many other causes of coughing or dyspnoea (Table 1). Common radiographic changes with lower airway disease (Figure 1) include a diffuse bronchial or bronchointerstitial pattern, bronchial mineralisation and pulmonary hyperinflation (with a flattened diaphragm and an increased distance between the caudal border of the heart and diaphragm).
Increased density of the right middle lung lobe may be present due to accumulation of mucus in this lobe’s main bronchus with gravity (this bronchus is orientated ventrally) and subsequent lobe atelectasis. If other focal changes are present, consider other differential diagnoses, such as a foreign body or neoplasia. Normal radiographs do not rule out lower airway disease, as bronchoconstriction or mild inflammation may not be visible.
Thoracic CT scanning may not be more useful than radiographs in many cases, but may pick up subtle changes in affected cats with normal thoracic radiographs, and allows better characterisation of airway structural changes, such as bronchiectasis. CT also allows better visualisation of other conditions, such as airway foreign bodies or neoplasia.
Once imaging has confirmed lower airway disease is present, and if the cat is sufficiently stable, sampling of the lower airways under general anaesthesia is recommended to confirm the diagnosis, determine the severity and type of airway inflammation, and look for bacterial infections. Bacterial infections are usually secondary to chronic lower airway disease, but can occasionally be the primary cause.
Regardless, if an infection is present it will require appropriate treatment. If airway sampling is not possible due to finances, or the cat being too unstable, empirical treatment can be attempted, but airway sampling should be considered again if the response is poor.
It is essential to stabilise the cat prior to anaesthesia and sampling to reduce risks. Terbutaline (0.01mg/kg SC) is recommended prior to bronchoscopy as it has been shown to reduce the risk of life-threatening complications. Terbutaline also doesn’t interfere with sample results. Steroids and antibiotics should be avoided if possible as they would interfere with results. The risks of the procedure should be discussed with owners, including risks of anaesthesia, significant dyspnoea after the procedure, failure to return to spontaneous ventilation and pneumothorax.
Once the cat is under anaesthesia, the oral cavity should be examined carefully, including the larynx, with laryngoscopy. Local anaesthesia of the larynx with a lidocaine spray is essential to reduce the risk of laryngospasm after the procedure. Close monitoring is important during anaesthesia, particularly of the respiratory rate and pattern, cardiac rate and rhythm, and peripheral capillary oxygen saturation (SpO2). If the SpO2 reduces too much during the procedure, or if the cat is unstable during anaesthesia, the procedure should be interrupted or abandoned. An oxygen cage and equipment for patient warming should be ready for recovery after the procedure.
The ideal method of lower airway sampling is to perform a bronchoscopy with bronchoalveolar lavage (BAL). Bronchoscopy allows visualisation of the airways, with useful information, such as the amount of secretions present, the presence and severity of bronchial static or dynamic collapse, and the presence of bronchiectasis. Bronchoscopy also allows sampling of specific lung lobes or areas where the disease appears more severe. If diffuse disease is present, BAL is usually performed in both sides of the thorax.
If bronchoscopy cannot be performed due to a lack of equipment or financial constraints, a blind endotracheal wash can be performed under anaesthesia. This is less ideal than bronchoscopy as the airways cannot be examined and the site of sampling cannot be chosen. The samples collected are also often of lesser quality than a BAL, but it should still yield useful samples.
The airway samples are placed in ethylenediamine tetra-acetic acid and plain tubes, and some fresh smears prepared. The samples are submitted for cytology and bacterial culture. PCR for Bordetella bronchiseptica and Mycoplasma felis is also recommended.
Cats with asthma have an eosinophilic airway inflammation on cytology, while chronic bronchitis causes a non-degenerate neutrophilic inflammation; however, mixed inflammation is frequent and it may be difficult to differentiate the two conditions. Secondary bacterial infections may add a neutrophilic component. Up to 20% to 25% of eosinophils can be present in the BAL of healthy cats – this should not be overinterpreted. Neutrophils are abnormal if they represent more than 5% of BAL cells. Signs of mucus overproduction can be present, such as Curschmann’s spirals.
A faecal Baermann test is recommended to look for the lungworm Aelurostrongylus abstrusus, which can cause airway inflammation. In cats that have travelled in affected areas, testing for heartworm (Dirofilaria immitis) is recommended.
The mainstay of treatment for lower airway disease involves steroids to control inflammation.
Antibiotics should be used if secondary infections are detected on BAL culture/PCR, and chosen based on antibiogram. Amoxicillin and clavulanate or doxycycline are most commonly used and a three to four-week antibiotic course is recommended.
Because the lack of A abstrusus larvae in BAL and faeces does not exclude the disease, a fenbendazole course is recommended at the start of treatment (30mg/kg PO once daily for five days).
Steroids usually involve a course of oral prednisolone to bring the disease under control, followed by long-term fluticasone inhalations. The initial oral prednisolone course will vary in dose and duration depending on the severity of the disease (usually 1mg/kg twice daily PO for 10 to 14 days, followed by gradual tapering of the dose by 20% to 25% every one to two weeks). Alternatively, ciclosporin can be used for cats where oral prednisolone is contraindicated (such as cats with concurrent heart failure or diabetes mellitus).
Long-term oral prednisolone is effective, but has many side effects, including obesity and predisposing to diabetes mellitus. Long-term treatment with inhaled fluticasone is safer and effective, in most cases. It has little systemic absorption and minimal to no side effects. Fluticasone inhalations should be introduced at the start of treatment, as they can take up to two weeks to become fully effective.
A 250mg/actuation inhaler is recommended. One actuation is administered via a spacing chamber (Figure 2) twice daily (count 7 to 10 breaths). Once a cat is stable on the inhalations without systemic steroids, after three to six months a dose reduction can be considered (125mg twice daily). In most cases, long-term treatment with fluticasone is required and relapse commonly occurs if all treatments are discontinued.
Other measures include reducing exposure to airway irritants (such as smoke, perfumes, chemicals, and dust created by insufficient or excessive vacuum cleaning – use of a vacuum cleaner with a high-efficiency particulate air [HEPA] filter for particles should be considered), weight control and regular worming effective against A abstrusus.
For cats where bronchospasm and acute dyspnoea are part of the disease, it is useful for owners to have an inhaler of salbutamol at home to administer in case of emergency prior to transport. Inhaled salbutamol produces bronchodilation within 15 minutes; however, chronic use of inhaled salbutamol is not recommended as it has pro-inflammatory effects. Long-term use of oral terbutaline as a bronchodilator can be considered, if needed. Theophylline is a less potent bronchodilator and has variable effects in cats.
While feline lower airway disease is usually a chronic condition that cannot be cured, most cats can be stabilised with appropriate long-term treatment and have a good prognosis. The prognosis is more guarded in cats with episodes of severe respiratory distress, with poor response to treatment, or with severe remodelling of the airways (such as severe bronchiectasis).
Fluticasone inhalations are often sufficient for long-term treatment and are generally well-tolerated – usually much better than oral medications. Relapses of clinical signs can occur if inflammation flares up or if a secondary airway infection develops. Repeat imaging is recommended in case of relapse to ensure no other disease has developed, as well as repeat airway sampling, so the treatment can be tailored to the pathology present.
