Cyanosis associated with respiratory causes are often found at later stages of disease processes. The presence of cyanosis in respiratory distress requires rapid decision. The clinician must determine whether the patient is likely to respond to medical therapy (typically — oxygen supplementation, sedation, bronchodilators) or require intubation and possible ventilation.

Respiratory failure is typically classified into dysfunction of oxygenation (inability to oxygenate – most common problem in our veterinary patients) or ventilatory failure (inability to eliminate CO2). Additionally, it is further characterized as to whether it is acute or chronic.

This is a more precise classification scheme however, while oxygenation can be estimated in the awake patient not receiving oxygen supplementation by a pulse oximeter, it does require access to blood gas analysis for CO2 measurement.

Another possible classification is to define the respiratory failure according to the patients breathing pattern. The advantages of this classification is that it is readily done in a clinical setting, it can help delineate treatment options and anticipated response to therapy.

Respiratory distress can be divided into either an increased respiratory effort or decreased thoracic excursions (previously described as increased or decreased effort by Dr S. Haskins – UCDavis). While these patients have a decreased ability to expand their thoracic cage, some are anxious, struggling to breathe and can have increased work of the abdominal musculature in an effort to do so. We felt that, for the purposes of this description, decreased thoracic excursions reflected more accurately to what we tend to see clinically.

Increased effort is often associated with a normal nervous system but an inability to adequately meet oxygen demands due to respiratory diseases. Decreased thoracic excursions is related to a problem with the nervous system (brain, cervical cord, neuromuscular).

Cyanosis associated with the respiratory system is a late warning sign of low oxygen tension and is a life-threatening emergency. Abnormal breathing patterns, a hallmark of respiratory distress, can rapidly exhaust the patient and lead to respiratory arrest. The diagnostic work up can be stressful in itself for such a patient.

Cyanosis is a late sign of respiratory failure. It is an indicator of the severity of the disease process, but, in itself, does not help narrow the possible etiologies.