Page 331 - Clinical Small Animal Internal Medicine

30 Feline Bronchial Asthma 299

asthmatic cats and can provide evidence that is crucial samples collected from healthy cats, though growth of
VetBooks.ir in reaching a diagnosis. Mycoplasma spp. has not been documented. Therefore,
a diagnosis of secondary bacterial infection in an asth-
Airway cytology remains the most definitive means of
diagnosing feline bronchial asthma after other conditions
are excluded. Bronchoalveolar lavage (BAL) can be matic patient must be based on growth of a large number
of colonies of a single organism or intracellular bacteria
accomplished with bronchoscopic guidance to collect seen cytologically. Organisms that have been detected on
samples from specific segments of the lower airways for airway samples collected from cats with bronchopulmo-
cytologic analysis. Alternatively, BAL can be performed nary disease include Pasteurella multocida, Streptococcus
using an unguided technique in patients with diffuse dis- spp., Staphylococcus spp., Mycoplasma spp., Moraxella
tribution of disease when bronchoscopy is not available spp., and Bordetella spp.
or feasible. The procedure is performed under general Due to the degree of invasiveness, lung biopsies are not
anesthesia that is induced and maintained with short‐ routinely performed in the diagnostic evaluation of cats
acting injectable anesthetic agents such as propofol. Prior with lower airways disease. Histopathology of postmor-
to inducing anesthesia, the patient is preoxygenated for tem lung samples from cats with experimentally induced
5–10 minutes with flow‐by or mask oxygenation meth- asthma revealed epithelial hypertrophy and hyperplasia,
ods. The procedure is performed with the patient in ster- marked smooth muscle hypertrophy of the terminal and
nal or lateral recumbency with the most diseased side respiratory bronchioles, and mucous cell metaplasia.
positioned ventrally. While avoiding oropharyngeal con- Pulmonary function testing, though not employed
tamination as much as possible, the patient is intubated standardly in clinical settings, has been investigated as a
with a sterile endotracheal tube. A sterile red rubber or means of assessing asthmatic cats. Specifically, baro-
polypropylene catheter is then inserted through the metric whole‐body plethysmography (BWBP) has been
lumen of the endotracheal tube and advanced until resist- employed to assess airway responsiveness in cats with
ance is met, indicating that the catheter is wedged within experimentally induced asthma. This noninvasive tech-
a distal airway. Using a syringe, a 5 mL/kg bolus of nique measures pressure changes generated by an
warmed, sterile 0.9% saline or phosphate buffered saline awake, spontaneously breathing cat in a transparent,
is instilled through the catheter followed by a 5 mL bolus ventilated chamber. Pause and enhanced pause are
of air. The empty syringe is then used to aspirate the fluid variables used to estimate lung resistance. These values
from the airways. This may be repeated twice to obtain an have been shown to increase significantly following
adequate sample. Retrieval of 46–68% of the total infusate bronchoprovocation in healthy cats and cats with artifi-
has been reported. The caudal half of the patient may be cially induced asthma. Tidal breathing flow‐volume
elevated during aspiration to facilitate retrieval of fluid. loops have also been utilized to assess lung resistance in
Supplemental oxygen is administered postprocedurally cats with bronchial disease. These loops are generated
for 5–10 minutes. Samples reserved for cytologic analysis in awake cats using a facemask attached to a pneumot-
should be kept on ice and processed within one hour of achograph to assess airflow. Cats with bronchial disease
collection to avoid deterioration of cells. Hypoxemia is a have reduced expiratory flows and tidal breathing expir-
significant complication associated with BAL but can atory volumes and prolonged expiratory time compared
usually be reversed with oxygen supplementation. to healthy cats. Additionally, ventilator‐acquired
Bronchospasm may also occur as a consequence of BAL mechanics have been used to measure airway resistance,
and can be managed with bronchodilators. positive end‐expiratory occlusion pressure, and end‐
Increased numbers of eosinophils are classically noted expiratory breath hold pressure following bron-
in cytologic samples collected from the airways of choprovocation in anesthetized cats with experimentally
asthmatic cats. However, a significant neutrophilic induced asthma.
component has also been reported in cats with both nat- Advances in the diagnostic approach to feline asthma
urally occurring and experimentally induced asthma. have included the development of minimally invasive
Discrepancy exists regarding the percentage of eosino- methods that may have utility in a future clinical setting.
phils considered abnormal within feline airway cytology In particular, exhaled breath condensate (EBC) can be
samples. Eosinophil proportions ranging from 16% to collected from nonanesthetized cats briefly housed
28% have been documented in airway samples collected within an acrylic chamber and analyzed for hydrogen
from healthy cats. As such, cytologic findings must be peroxide, a marker of oxidative stress. The concentration
interpreted in light of other diagnostic results in order of hydrogen peroxide in the EBC of artificially sensitized
for a diagnosis of asthma to be verified. cats has been shown to correlate with the degree of
Bacterial culture of airway lavage samples collected eosinophilic lower airway inflammation, suggesting that
from cats with lower airways disease produces variable analysis of EBC may prove to be a useful screening tool
results. Bacterial growth has been found in airway for suspected asthmatics.