Cyanosis (Blue Coloration) in Dogs
Dr. Arnold Plotnick
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.