Cyanosis (Blue Coloration) in Dogs

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Cyanosis is a bluish or purplish coloration imparted to the skin or mucous membranes due to excessive amounts of poorly oxygenated hemoglobin in the circulation. The causes include certain congenital heart diseases, various respiratory diseases, and exposure to certain chemicals that result in the creation of some abnormal forms of hemoglobin which are incapable of binding oxygen properly.

Cyanosis in pets is usually an alarming clinical symptom for pet owners and for veterinarians.

What to Watch For

  • Purplish/bluish coloration of the tongue, gums, lips, and areas of the skin in which the blood vessels are superficial

  • Possible purplish/bluish coloration of the foot pads

    Diagnosis

  • Arterial blood gas measurement
  • Pulse oximetry
  • Other specific tests, depending on the disorder that is causing the cyanosis

    Treatment

    Therapy of cyanosis will depend on what is causing the condition.

  • Congenital heart disease. If the condition is caused by congenital heart disease, the treatment is surgery.

  • Chemical. If a chemical has affected the hemoglobin in such a way that it cannot carry oxygen properly, for example, by inducing the formation of methemoglobin, an abnormal type of hemoglobin that cannot carry oxygen, the treatment involves: elimination of the cause, limiting any tissue injury due to poor oxygenation, and administration of medication (methylene blue; N-acetylcysteine) if necessary.

  • Respiratory Disorder. If a respiratory disorder is the cause of the cyanosis, the underlying respiratory disease must be treated with antibiotics if pneumonia or chronic bronchitis is present, diuretics if fluid is building up in the lungs, thoracocentesis, which is removal of fluid or air from the chest cavity if fluid or air is causing the cyanosis, or supplemental oxygen as necessary.

    Emergency treatment involves making sure that the airway is unobstructed and providing oxygen by: face mask, nasal oxygen tube, oxygen cage, intubation of the trachea.

    Home Care

    There is no specific home care for cyanosis. Animals who are suspected to be cyanotic should be evaluated by a veterinarian immediately. Depending on the cause of the cyanosis, your veterinarian will make specific recommendations as warranted.

    • Notice the bluish or purplish coloration (cyanosis) of the mucous membranes of the mouth in this dog.

    Cyanosis is the bluish or purplish discoloration of the mucous membranes or skin due to excessive amounts of desaturated (poorly oxygenated) hemoglobin in the blood stream. Oxygenated blood is red. Poorly oxygenated blood is dark blue. The more deoxygenated hemoglobin in the bloodstream the more bluish coloration will be imparted to the tissues.

    There are two general "types" of cyanosis: central and peripheral.

  • Central cyanosis is a result of the entire systemic blood supply being desaturated. Central cyanosis is due to a decrease in oxygenated blood throughout the systemic circulation. All tissues are affected.

  • Peripheral cyanosis is due to desaturated hemoglobin that may be confined to a specific region of the body, for example, if a blood clot has obstructed blood flow to a particular body part or if a tourniquet has been applied. Peripheral cyanosis implies a purplish coloration in the peripheral tissues (oral mucous membranes, vaginal or penile mucous membranes, paw pads or nail beds, etc). All animals with central cyanosis also have peripheral cyanosis, because the entire bloodstream is desaturated. However, it is possible to have peripheral cyanosis without having central cyanosis, if the cause of the decreased oxygenation is localized to a specific region, such as a blood clot that interrupts the blood supply to a specific limb.

    In young animals, the most likely cause is a congenital heart disease where poorly oxygenated blood that is returning to the heart erroneously bypasses the lungs and is sent back out into the systemic circulation without picking up more oxygen. This is called "right-to-left shunting" because poorly oxygenated blood from the right side of the heart is shunted to the left side of the heart where it is pumped out into the general circulation.

    Any age animal can develop cyanosis secondary to severe pulmonary (lung) disease, such as severe pneumonia, or to diseases that prevent the lungs from expanding properly, such as fluid or air in the chest cavity.

    Genetic defects in hemoglobin can alter its ability to carry oxygen, however, these defects are rare in companion animals. Hemoglobin defects are more likely to develop secondary to ingestion of, or exposure to, chemicals and oxidants.

  • Causes

    Causes of peripheral cyanosis include:

  • Anything that would cause central cyanosis, with resultant bluish coloration in all peripheral tissues.

  • Hypothermia. The low body temperature constricts the vessels in the skin.

  • Thromboembolism, or a blood clot

  • Application of a tourniquet (accidental, deliberate or malicious)

  • Shock (inadequate blood flow to the tissues)

    Causes of central cyanosis would include:

    Heart Causes

  • Congenital heart disease

  • Tetralogy of Fallot, which is a genetic defect involving four abnormalities of the heart and great vessels

  • Atrial septal defect (the proverbial "hole in the heart"), with subsequent right-to-left shunting

  • Ventricular septal defect ("hole in the heart") with subsequent right-to-left shunting

  • Reversed patent ductus arteriosus (this congenital defect does not initially cause cyanosis. Only if it goes undetected or untreated so that blood flow in the heart reverses, can changes occur that lead to cyanosis)

    Lung Causes

  • Hypoventilation (inability to breathe properly)

  • Pleural effusion (blood, pus, lymphatic fluid, cancer-induced fluid, etc. that gathers in the chest cavity and prevents the lungs from expanding properly)

  • Pneumothorax

  • Respiratory muscle failure

  • Muscle disorder (like a diaphragmatic hernia)

  • Neurologic disease

  • Anesthetic overdose

  • Airway obstruction

  • Laryngeal paralysis

  • Tumor, abscess, granuloma, foreign body obstructing a large airway

  • Inadequate oxygen due to improperly administered anesthesia

  • Ventilation-perfusion mismatch (improper blood supply to the lung, combined with improper lung function, or both)

  • Pulmonary thromboembolism (blood clot in the lungs)

  • Infiltration of the lung tissue with fluid (edema)

  • Inflammatory cells (infection, inflammation)

  • Cancer cells

  • Acute respiratory distress syndrome (ARDS)

  • Pulmonary fibrosis (pulmonary scar tissue)

    Other Causes

    Abnormal hemoglobin (methemoglobin) can result in cyanosis due to chemicals that render the hemoglobin nonfunctional.

  • Nitrates

  • Nitrites

  • Acetaminophen (Tylenol®)

  • Methylene blue

  • Cetacaine

  • Topical benzocaine

  • Diagnosis In-depth

  • Arterial blood gas measurement. Arterial blood gas (ABG) is the "gold standard" for evaluating a cyanotic patient. The test involves obtaining an arterial blood sample. For maximal diagnostic value, the ABG should be evaluated while the animal is receiving supplemental 100 percent oxygen. The response to supplemental oxygen can be used to help rule in or rule out certain causes of cyanosis. For example, if there is peripheral cyanosis due to obstruction of blood flow to one or two limbs, giving supplemental oxygen does not raise the amount of oxygen in the arterial blood, and does not resolve the cyanosis.

    However, if the cyanosis is due to disease of the lungs (edema, infection), hypoventilation, or ventilation/perfusion mismatch, giving supplemental oxygen will raise the amount of oxygen in the arterial blood, and the cyanosis should resolve. Giving supplemental oxygen to animals who are cyanotic because of an abnormal form of hemoglobin (such as methemoglobin) will not be helpful, because methemoglobin cannot bind oxygen, regardless of how enriched the oxygen supply is.

  • Pulse oximetry. Pulse oximetry is readily available to most practitioners nowadays. It is a noninvasive way to get an idea of the amount of oxygen in the bloodstream. A probe is applied to a fold of skin in the axillary (armpit) or inguinal (groin) area, or the lip or tongue in an anesthetized animal. The major advantage of pulse oximetry is that you get a continuous reading, allowing sequential monitoring in response to supplemental oxygen.

  • Further diagnostic tests. Depending on the cause of the cyanosis, further diagnostic tests may be warranted. For example, if cardiac abnormalities are the cause of the cyanosis, cardiac ultrasound, electrocardiography, or angiocardiography may be necessary. If respiratory diseases are the cause of the cyanosis, various diagnostic tests such as thoracocentesis (removal of fluid or air from the chest cavity), a transtracheal wash, complete blood count, chemistry panel, urinalysis, chest X-rays, thoracic ultrasound, and fecal analysis may be warranted.

    Treatment In-depth

    One or more of the diagnostic tests described above may be recommended by your veterinarian. In the meantime, treatment of the symptoms might be needed, especially if the problem is severe. The following nonspecific symptomatic treatments may be applicable to some pets with cyanosis. These treatments may reduce the severity of symptoms or provide relief for your pet. However, nonspecific therapy is not a substitute for definite treatment of the underlying disease responsible for your pet's condition.

    Therapy of cyanosis is dependent on understanding the cause of the condition.

  • Peripheral cyanosis. Peripheral cyanosis is usually not life threatening. Therapy is directed more toward the underlying disease. For example, a dog with a blood clot that has cut off circulation to a leg, causing cyanosis to the foot pads, acquires this condition secondary to severe heart disease. The main concern in this instance is getting the heart disease under control. The cyanosis is of much less significance.

  • Central cyanosis is treated as an emergency until the cause of the cyanosis can be determined.

    Emergency Measures

    Provide supplemental oxygen. In cases of central cyanosis, a reduced supply of oxygen is to be assumed until it can be disproved and supplemental oxygen is to be provided until the actual cause can be ascertained. Obvious mechanical obstructions to airflow (such as a foreign body in the mouth or throat) are removed and a patent airway is established. Then, oxygen is administered immediately either by face mask, a nasal oxygen tube, an oxygen cage, or endotracheal intubation.

    If congenital heart disease is the cause of cyanosis, the treatment may involve surgery to correct the defect.

    If respiratory disease is the cause, the treatment is:

  • Thoracocentesis to remove pus, blood, lymphatic fluid (chyle), or air that may be impeding the ability of the lungs to expand

  • Antibiotics to treat infection

  • Nebulization (use of a vaporizer) to moisten and loosen tenacious secretions down in the lungs and, possibly, to deliver antibiotics or other drugs down into the lungs

    If excessive amounts of methemoglobin is the cause of the cyanosis, treatment involves:

  • Elimination of the cause of the formation of the methemoglobin

  • Acetylcysteine (Mucomyst®) can be given to dogs who have received a toxic dose of Tylenol®

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