The pulmonary system is complex with various anatomical structures performing highly specialized functions. When evaluating
the system it is useful to examine each structure for its unique function and associated potential complications. Physical
assessment and monitoring tools such as pulse oximetry and arterial blood gas analysis are used to localize respiratory problems
and guide treatment which may include supplemental oxygen therapy, appropriate drugs or pulmonary physiotherapy. Generally,
problems are divided into two categories; ventilatory, that is the ability to move air in and out of the pulmonary system
and respiratory, that is the ability to effectively exchange oxygen and carbon dioxide. Regardless of the specific problem,
animals in respiratory distress are always regarded as medical emergencies due to the high potential for brain damage, respiratory
failure and cardiac arrest. Rapid localization of the problem is the key to successful outcome
The upper airway
Upper airway anatomy includes the nose, mouth, pharynx, larynx and trachea. The primary purpose of these structures is the
act as a conduit for the passage of air into the lower airway (ventilation). Although considered anatomical "dead space"
because gas exchange (respiration) does not occur, several vital functions are provided by the upper airway. Humidification
and protection from infection are provided by mucous production. Cilia that line the respiratory tract move mucous and bacteria out of the airway in a sweeping motion.
Problems with the upper airway are related to complete or partial obstruction of one or more of its structures. Obstruction
may be caused by a number of factors including:
• foreign body
• laryngeal spasm/paralysis
• brachycephalic disease
Specific breathing patterns and presenting signs are unique to patients with upper airway obstruction. Most notably these
patients have audible "noisy" inspiratory sounds (stridor) and present in a state of hysteria or panic due to the acute onset
of disease. In animals with partial obstruction, respiration will most likely be prolonged and forceful on inspiration in
an effort to move air through a narrowed airway. Tachypnea, cyanosis and foaming are likely to be present in patients with
more complete obstruction.
Diagnosis of upper airway disease is made chiefly by observing breathing pattern and visualization of the airway itself.
Radiographs may be helpful as well but often patients are not stable enough to undergo radiography, initially. In fact, many
patients will require sedation immediately to eliminate stress, relax the airway and allow removal of the obstruction if possible.
Patients require oxygen supplementation until airway patency can be established. In some cases this may necessitate endotracheal
intubation or tracheostomy.
The lower airway
Lower airway anatomy includes the bronchi, bronchioles, alveoli, and lung tissue. Gas exchange (respiration) is the primary
function of the lower airway.
Problems of the lower airway are related to interference, by a number of processes, with the ability to take in oxygen and
expel carbon dioxide. Common lower airway diseases/disorders are:
• asthma(bronchial irritation/inflammation/constriction)
• pulmonary edema
• pulmonary contusions
• smoke inhalation/near drowning
• pulmonary thromboembolism
Many of the breathing patterns associated with lower airway disease are related to damaged or fluid filled alveoli. Patients
are often tachypnea with shallow respiration. Moist sounds, harshness and wheezing are often heard on auscultation. Because
patients with lower airway problems are often hypoxic, they frequently present with pale or cyanotic mucous membranes.
Diagnosis of lower airway disorders can be confirmed with radiographs. Arterial blood gas analysis and pulse oximetry are
useful tools in assessing the degree of respiratory compromise as well as in guiding therapy. Treatment for lower airway
disorders may include bronchodilators, steroids, and/or antibiotics. In most cases, supplemental oxygen is beneficial. In
extreme cases, mechanical ventilation may be required.