Respiratory Failure

[Kvet Forum]

Respiratory movements are involuntary and are stimulated and modified by the respiratory centers in the medulla. Respiratory failure is the terminal stage of respiratory insufficiency in which the activity of the respiratory centers diminishes to the point where movements of respiratory muscles cease. Respiratory failure can be paralytic, dyspneic or asphyxial, or tachypneic, depending on the primary disease.

Paralytic respiratory failure is caused by depression of the respiratory centers or paralysis of the muscles of respiration. Depression of the respiratory center occurs with poisoning by respiratory center depressants, such as general anesthetics or damage to the respiratory center, such as might occur with brainstem injury. Paralysis of respiratory muscles occurs in disease such as botulism, tetanus, strychnine poisoning, white-muscle disease, severe hypocalcemia, and tick paralysis. The signs of paralytic respiratory failure are a gradual or abrupt cessation of respiratory movements without preceding signs of increased respiratory effort or dyspnea. The animal is often unconscious, or unable to move, during the later stages of the disease.

The differentiation of these types of failure is of some importance in determining the type of treatment necessary. In the paralytic form of respiratory failure, the optimal treatment is mechanical ventilation, along with removal of the inciting cause. Administration of respiratory stimulants is seldom effective as sole therapy. The more complex pathogenesis of respiratory failure in most diseases requires a therapeutic approach that removes each of the underlying defects. In most cases this is achieved by treating the inciting disease, for example, administering antimicrobials to an animal with pneumonia or furosemide to an animal with pulmonary edema, in addition to supportive care, including, potentially, nasal or pharyngeal insufflation with oxygen or mechanical ventilation.


Principal Manifestations of Respiratory Insufficiency

Respiratory disease is evident as one or more of a variety of signs detectable on clinical examination. The signs vary with the etiology of the disease and its anatomic location. Diseases that impair ventilation or gas exchange have hypoxemia and hypercapnia as prominent life-threatening abnormalities.

The common signs of respiratory disease are as follows:

• Abnormalities in the rate, depth, or ease of breathing.
• Lethargy or exercise intolerance.
• Abnormal posture.
• Abnormal lung sounds.
• Abnormal respiratory noises.
• Coughing.
• Cyanosis.
• Nasal discharge.
• Epistaxis and hemoptysis.