Page 59 - Problem-Based Feline Medicine

5 – THE DYSPNEIC OR TACHYPNEIC CAT 51

● Weakness of ventilatory, muscles or diseases
INTRODUCTION
which restrict thoracic expansion (myopathies,
neuropathies, neuromuscular disease, obesity and
MECHANISM? organomegaly).
● Pulmonary vascular disease (pulmonary hyperten-
Dyspnea is the distressful feeling associated with diffi- sion, pulmonary thromboembolism, shock).
cult or labored breathing. In animals, the term dyspnea ● Diminished oxygen-carrying capacity (methemo-
is often applied to labored breathing that appears to be globinemia, anemia).
uncomfortable. ● Cardiac disease (congestive heart failure, cyanotic
Tachypnea is rapid breathing (not necessarily labored). heart disease with right-to-left shunting).
● Miscellaneous (pain, fever, anxiety, hyperthermia).
Hyperpnea is deep breathing.

Hyperventilation refers to increased air entering the
pulmonary alveoli, brought about by prolonged, rapid
WHERE?
and deep breathing.
Upper respiratory tract (nasal cavity, paranasal
Panting, however, refers to swift and shallow breath-
sinuses, pharynx, larynx, trachea). With upper respira-
ing, with a rapid respiratory frequency and a small tidal
tory tract obstructions, stertor and stridor may be evi-
volume.
dent. Stertor is a snoring sound. Stridor is a harsh,
Respiratory causes of dypsnea include upper and high-pitched whistling respiratory sound created by
lower airway obstruction. upper airway obstructive diseases. Stridor arises from
luminal narrowing in the upper airways, generally
Upper airway obstructions may be fixed or dynamic.
involving the pharynx, soft palate, laryngeal structures
Airflow through a narrowed upper airway has increased
and the upper trachea. Nasal stridor may also be
resistance and becomes more turbulent. This resistance
encountered.
is a function of the diminished luminal diameter of the
tube, the resistance increasing to the fourth power of Lower respiratory tree (bronchial tree, small airways).
the radius.
Lung parenchyma, pleural space, chest wall and venti-
● Fixed obstructions affect both inspiration and
latory muscles. Pleural space disease often has dyspnea
expiration.
with excessive chest wall excursions accompanied by
● With dynamic obstructions, dyspnea occurs dur-
minimal nasal airflow.
ing inspiration, because the negative intraluminal
airway pressure creates a vacuum, pulling the walls Oxygen delivery system (blood vessels, RBCs, heart).
inwardly. Any weakened area of the airway wall
will tend to move into the lumen, decrease the lumi-
nal diameter, and create an obstruction.
What?
Lower airway obstructions may be obstructive or
Acute severe dyspnea in cats is often caused by an
restrictive.
acute asthmatic attack, decompensating congestive
● Obstructions include intraluminal masses and for-
heart failure or trauma.
eign bodies, bronchoconstriction, extraluminal
compression by masses or left atrial enlargement, The dyspneic cat is extremely fragile, and needs to be
and rarely tracheobronchial collapse. handled very gently and with minimal restraint. Cats
● Restrictive obstructions include pleural space dis- with open-mouth breathing and cyanosis have very lit-
ease (pneumothorax, hydrothorax, pleural masses) tle respiratory reserve left, and the slightest additional
and primary pulmonary disease (pulmonary fibro- stress may be lethal.
sis, pneumonia) that restrict expansion of the lung.
In most cases, we need to resist the temptation to make
Non-respiratory causes of dyspnea are varied and a definitive diagnosis until our patient is more stable.
include: These cats are focusing on their next breath, and are