Blue Skin and Mucus Membranes in Dogs

Cyanosis in Dogs

Cyanosis is a medical condition characterized by blue colored skin and mucous membranes, which occurs as the result of inadequate amounts of oxygenated hemoglobin -- the molecule which carries oxygen to the body tissues -- or due to hemoglobin abnormalities.

Unfortunately, dogs that are suffering from cyanosis caused by advanced lung/airway disease and severe heart disease have a poor long-term prognosis.

Symptoms and Types

• Heart murmur
• Crackles heard when listening to the lungs
• Muffled heart sounds
• Harsh sounds upon inhalation
• Honking cough
• Difficulty breathing
• Cyanotic, cool, pale, painful, swollen limbs lacking a strong pulse
• Weakness
• Posterior (hind limb) paresis or paralysis

Causes

Originating in the Respiratory System

• Larynx (voice box): can be due to paralysis (acquired or congenital); collapse; spasm; swelling; trauma; cancer; chronic inflammatory disease
• Trachea: can be due to collapse; neoplasia; foreign body; trauma; underdevelopment
• Lower airway: can be due to pneumonia (viral, bacterial, fungal, allergic, mycobacteria, aspiration); chronic swelling of the bronchioles; allergies, asthma; chronic dilation of the bronchioles; cancer; foreign body; parasites; bruising of the lungs; swelling due to inhalation, snake bite, electric shock; near drowning
• Pleural space: may be due to air in the chest cavity; infectious (bacterial, fungal); pus in the chest cavity; blood in the chest cavity; cancer; trauma
• Chest wall, or diaphragm: may be related to congenital defects such as hernia around the heart or through the diaphragm (when an organ pushes through the wall, or enclosure that normally contains it); trauma (diaphragmatic hernia, fractured ribs); neuromuscular disease

Originating in the Cardiovascular System

• Congenital defects
• Acquired disease: may be linked to mitral valve (left side of heart valve between atrium and ventricle) disease; disease of heart muscle
• Fluid collection around the heart: due to cancer or unknown causes
• Clogging of lung blood vessels with a clot
• Pulmonary hypertension: unknown origin (idiopathic); right-to-left cardiac shunts (blood is diverted to another pathway)
• Peripheral blood vessel disease

Originating in the Neuromusculoskeletal System

• Brain-stem dysfunction: due to brain swelling; trauma; bleeding; cancer; drug-induced depression of the respiratory center
• Spinal cord dysfunction: may be due to swelling; trauma; vertebral fractures; disk slippage
• Neuromuscular dysfunction: may be caused by overdose of paralytic drugs; tick paralysis; botulism; coonhound paralysis

Methemoglobinemia

• Methemoglobin (metHb) binds to water molecules rather than oxygen molecules
• Elevated concentrations of methemoglobin in the red blood cells leads to tissue hypoxia due to reduced oxygen carrying capacity of blood
• Congenitally acquired NADH-methaemoglobin reductase (NADH-MR) deficiency: deficiency of an intracellular reductive enzyme, which helps keep methemoglobin at levels of less than two percent, preventing cyanosis
• May be linked to ingestion of oxidant chemicals: acetaminophen, nitrates, nitrites, phenacetin, sulfonamides, benzocaine, aniline dyes, dapsone

Diagnosis

Your veterinarian will first stabilize your dog's oxygen levels. This is usually done in ICU (intensive care unit) in a specially equipped oxygen cage. Once your dog is stable, your veterinarian will be able to perform a full physical exam.

A blood chemical profile, complete blood count, urinalysis, electrocardiograph (EKG), thoracic radiographs (and echocardiogram with Doppler, if heart or lung disease is suspected), and an electrolyte panel should be ordered to determine the underlying cause of the disease that is causing cyanosis.

A laryngoscopic (voice box) and/or bronchoscopic (lung airway) exam should be given. If bronchopulmonary (lung disease) disease is suspected, a transtracheal wash, a bronchoalveolar lavage or fine-needle lung aspirate may be performed. For pleural space disorders, a thoracocentesis (a procedure which removes fluid from the chest cavity) will be required.

Methemoglobinemia is a condition that can be measured; one of the most obvious indications is that the color of the blood will be darker than the bright red it is supposed to be. Arterial blood can be taken so that a blood gas analysis can be performed at the laboratory. Your dog's breathing patterns will also give your veterinarian a clue as to the origin of the cyanosis.