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Feline
chronic small airway disease comprises a spectrum of conditions
involving the small airways (bronchioles) within the lungs.
The condition is also known as chronic bronchitis, allergic
airway disease, allergic bronchitis and asthma.
Some
cases bear similarities to asthma in humans, hence it is frequently
known as 'feline asthma', however the majority of cases are
not proven to have an allergic cause. Inhalation of irritants
such as pollens, cigarette smoke, dust and household cleaning
sprays are sometimes implicated.
The
airways respond to an irritant by contraction of the bronchial
smooth muscle in order to prevent the irritant from moving
deeper into the lung, production of mucus to trap the irritant
and initiation of a cough to expel the irritant. Contraction
of the smooth muscle, mucus production and airway inflammation
all contribute to narrowing of the airways which results in
difficulty breathing.
Can
any cats develop the condition?
Cats
of any age, breed or sex can develop chronic airway disease,
however young to middle aged cats are most frequently affected.
Siamese cats appear to be particularly predisposed.
What
clinical signs do cats show?
Signs
vary from chronic coughing and/or wheezing to the development
of sudden onset laboured breathing without any prior clinical
signs. An increase in respiratory rate (>30-40 breaths
per minute) or effort (particularly expiratory effort) may
also be noticed. Symptoms may come and go or may be so mild
that they go unnoticed by owners for sometime.
How
is it diagnosed?
Other
diseases such as bacterial infections, foreign bodies, heart
disease, airway parasites and lung cancer can present with
similar clinical signs and therefore these all need to be
eliminated before a diagnosis of chronic small airway disease
can be made.
X-rays
of the chest are required and usually demonstrate evidence
of thickening of the bronchial (small airways) walls and air
trapping within the airways. Air trapping occurs because when
the airways have constricted, inspired air cannot be exhaled.
The lungs therefore appear larger than normal on X-rays, as
they are over inflated. The diaphragm may seem flattened due
to this over-inflation. Not all cats however will have these
changes, X-rays can appear normal.
Another
diagnostic technique that can be useful is bronchoscopy. This
is a technique whereby a fibreoptic endoscope is passed into
the airways to enable direct visualisation of the airways.
Excessive mucus, roughening and reddening of the airways may
be seen in cats with chronic airway disease, although again
the gross appearance can be normal in some cats. Very small
endoscopes are required to examine the airways of cats and
therefore this procedure is most frequently carried out at
specialist institutions.
Airway
washes (bronchoalveolar lavage) can also be collected and
examined under a microscope for the presence of inflammatory
cells, bacteria and cancer cells. These washes can also be
cultured to assess whether bacteria are present within the
lungs. Lots of inflammatory cells are usually evident in washes
taken from cats with chronic small airway disease.
How
is small airway disease treated?
1.)
Anti-inflammatories
Reducing
the inflammation within the airways is the most important
part of treatment. Corticosteroids are potent anti-inflammatories
that are used to achieve this. This treatment can be administered
in different ways:
Systemically
- in the form of tablets (eg, prednisolone) or injections
(eg, dexamethasone)
In
the past corticosteroid tablets or injections have been
used to treat the condition. However, treatment is required
for life and long-term treatment with these drugs can result
in side effects such as increases in appetite and thirst,
weight gain, diabetes mellitus, and thin fragile skin.
Inhalational (eg,
fluticasone)
More
recently inhalational steroids have been used for treatment,
with the big advantage that the drug is delivered directly
to the lungs where it is required, but is not absorbed into
the body therefore avoiding side effects with long-term
use.
2.)
Bronchodilators
Drugs
to help dilate the airways are usually used in conjunction
with corticosteroids. These can also be given in the form
of oral or injectable medication (eg, terbutaline) or by inhalational
treatment (Salbutamol).
3.)
Mucolytics
In
some cats excessive production of mucus can be a problem.
Adding a mucolytic powder (eg, bromhexine) to the food can
help in these cases.
4.)
Reducing exposure to irritants
Some
actions can be taken in the home to reduce the severity of
the signs, namely avoidance of smoking and the use of household
sprays around the cat. Using a low dust type of litter may
also help.
The
feline inhaler
A
special 'spacer' has been designed for the delivery of inhalational
drugs to cats (for more details see www.aerokat.com ).
One end of the spacer is made to fit the inhaler, whilst a
facemask is attached to the other end (see figure 1). One
to two puffs are administered into the spacer chamber and
then the cats' face is held in facemask for 7 – 10 seconds
(see figure 2). This is usually performed twice daily. Cats
tolerate the procedure surprisingly well and with the majority
of cats it is easier than administering tablets.
What
is the prognosis?
The
prognosis for this condition depends on the severity of the
disease and on the time delay before treatment is initiated.
Whilst the majority of cats respond well to treatment, acute
severe attacks can prove fatal if treatment is not initiated
promptly. In addition, if the condition is chronic and treatment
has been delayed, irreversible fibrotic changes within the
airways can occur.
How
is inhaled treatment used in cats?
To
administer a dose of inhaled therapy to a patient:
1.)
Attach the MDI to the AeroKat unit
2.)
Hold the unit over the cat's face
3.)
Actuate a dose (press down the MDI) to supply drug to the
spacer chamber
4.)
Allow
the cat to take 10 – 15 breaths
Some
cats dislike having the face mask on when the dose is actuated
and in this case, the dose can be actuated and then the mask
placed over the cats face. This is thought to result in a
lower dose reaching the airways so, in some cases, a second
dose may be needed to provide sufficient drug.
In
cats needing two puffs of treatment, this should be given
as two separate administrations (i.e. follow steps 1 to 4
and then repeat).
What
medications and dosing regime?
1.)
Bronchodilator
therapy: b 2-adrenergics
such as salbutamol and albuterol are most commonly used. They
have a rapid speed of onset (5–10 minutes) and relatively
short duration of action (2 – 4 hours) meaning that they are
suitable for use 'as needed' including in emergency situations.
Some longer acting preparations of bronchodilators (eg salmeterol
– onset of action 15 –30 minutes, duration greater than 12
hours) are also available and can be helpful treatments in
those cats benefiting from long-term bronchodilator therapy.
2.)
Glucocorticoid
therapy: Fluticasone propionate given twice daily is a commonly
recommended glucocorticoid, having high potency but virtually
no systemic absorption and therefore no systemic side-effects.
Cheaper glucocorticoids (eg, beclomethasone dipropionate)
can also be used but at high doses may have systemic effects.
High strength MDIs of these products (generally 200-250 m
g/actuation) have been used in
cats (1-2 doses twice daily) but this can be reduced according
to response.
Suggested
dosing regimes:
Mild cases: Fluticasone (110 µg/puff strength MDI) one puff
twice daily with salbutamol ( 100 µg/puff strength) given
as needed.
More severely affected cases: Fluticasone (250 µg/puff strength)
one puff twice daily with salbutamol given as needed. When
starting therapy, it can be helpful to also prescribe oral
prednisolone (starting at 1- 2 mg/kg/day and weaning off
therapy over a two week period) as the inhaled glucocorticoid
therapy can take some time to become fully effective.
Emergency cases: oxygen therapy, intravenous glucocorticoid
( eg prednisolone sodium succinate 30 mg/kg) and terbutaline
(0.01 mg/kg).
Side-effects
are very rare when using these agents. b 2-adrenergics can
be associated with causing excitability, anorexia and muscular
twitching.
Where
can Aerokat units be obtained?
AeroKat
units are made by Trudell Medical in the US. They are available
in the UK through:
BreathEazy
Ltd
8
Woodford Road
South
Woodford
London
E18 2BH
Phone:
0871 219 2335
Fax:
0871 521 5489
E-Mail:
sales@Breatheazy.co.uk
website:
www.breatheazy.co.uk
and www.felineasthma.co.uk
BreathEazy
supplies AeroKat units to the following veterinary wholesalers:
NVS
Centaur
Veterinary
surgeons supply (Northern Ireland)
Dunlop
(Scotland)
GenusXpress
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