Cyanosis is the visible blueness to skin and mucous membranes which is due to hypoxia (low levels of oxygen in the blood). It is not a disease itself but a sign of an underlying disorder which has resulted in low blood oxygen saturation which leads to increased levels of deoxygenated hemoglobin in the bloodstream.
Cyanosis occurs either as a result of the heart not working effectively enough to circulate blood around the body, the lungs not being able to deliver oxygen to the blood or ingestion of certain toxins which leads to the abnormal form of hemoglobin which is unable to bond to oxygen properly.
Hemoglobin is a protein which carries oxygen to the cells of the body, releasing oxygen into the capillaries. Hemoglobin which is saturated with oxygen is bright red and is known as oxyhemoglobin, hemoglobin not saturated with oxygen is more mucous in colour and is known as deoxyhemoglobin.
Cyanosis is divided into two types, central and peripheral.
- Central cyanosis - This type of cyanosis occurs when the entire systemic blood is desaturated and all tissues are affected.
- Peripheral cyanosis - Due to desaturated blood in a particular region of the peripheral circulation (arms, legs, hand, feet and tail). It can be due to hypothermia, embolism which blocks blood supply to a particular limb.
All causes of central cyanosis will cause peripheral cyanosis however peripheral cyanosis only typically affects an isolated part of the body.
What causes cyanosis in cats?
- Congestive heart failure - This is a serious disorder where the heart doesn't pump blood efficiently, causing fluid to build up in the lungs while other organs don't receive enough blood to function properly.
- Hypertrophic cardiomyopathy - Thickening of the left ventricular wall which results in the heart not pumping as efficiently as it should.
- Congenital heart disorders (endocardial fibroelastosis, tetralogy of Fallot, reversed patent ductus arteriosus, aortic stenosis).
- Right to left cardiovascular shunts which causes deoxygenated blood to pass from the right to the left side of the heart where it is circulated to the rest of the body.
- Pyothorax - Pus in the pleural cavity.
- Pleural effusion - Build up of a number of types of fluid in the pleural space surrounding the lungs.
- Pulmonary edema - Build up of fluid in the alveoli (air sacs) of the lungs.
- Pulmonary embolism - Blood clot in the vessels of the lungs.
- Respiratory paralysis - Such as with tick poisoning.
- Tracheal or laryngeal collapse.
- Obstruction in the airway or lungs which could be a foreign object or cancer.
- Pneumonia - Inflammation or infection of the lungs.
- Hydrogen cyanide - Stops the cells being able to use oxygen.
- Carbon monoxide poisoning - Carbon monoxide is a toxic gas which binds to hemoglobin in the lungs forming carboxyhemoglobin which prevents oxygen attaching to the hemoglobin.
- Methemoglobin - An abnormal form of hemoglobin which oxygen molecules are unable to bind to. There are many causes of this including ingestion of oxidant chemicals such as onion, benzocaine, nitrates, nitrites and most commonly, acetaminophen (paracetamol).
- Hypoglycemia (low blood sugar).
- Hypotension (low blood pressure).
Causes of peripheral cyanosis:
- Arterial thromboembolism - Usually a blood clot which blocks delivery of blood through the vessel to a particular part of the body (legs, foot etc). This most often occurs in cats with heart disease.
- Hypothermia - During times of extreme cold, blood is diverted away from the extremities to protect the vital organs in the core and the brain.
- Constriction of an extremity such as an elastic band around the tail or limb which cuts off circulation.
Other than cyanosis, what other symptoms may my cat show?
Symptoms may vary depending on the underlying cause.
Central cyanosis reveals blue tinged mucus membranes of the mouth, tongue, and lips.
Peripheral cyanosis will reveal blue-tinged skin of the affected area. This can often be hard to see on cats due to their fur and often pigmented paw pads.
Generalised symptoms of cyanosis may include:
- Anorexia (loss of appetite)
- Loss of weight
- Poor appearance (unkempt coat)
Symptoms associated with breathing difficulty or lack of oxygen:
- Exercise intolerance
- Difficulty breathing
- Rapid breathing (tachypnea)
- If methemoglogin has occurred, the gums may have a brownish appearance
- Open-mouthed breathing
How is the cause diagnosed?
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you including any underlying conditions your cat, other symptoms you may have noticed, any medications or poisons your cat could have consumed. He will listen to the cat's heart and lungs and will need to perform some diagnostic tests including:
- Complete blood count, biochemical profile, and urinalysis are all standard tests and can give your veterinarian an overall picture on organ function and reveal anemia if it is present.
- Listen to the heart, which may reveal muffled or abnormal sounds.
- Listen to the lungs which may sound crackly.
- Watch respiration which may show a difficulty to expand the chest which may be due to asthma or pneumonia.
- Arterial blood gas test involves obtaining an arterial blood sample to measure the percentage of oxygen. This test is performed while your cat is being given oxygen. If oxygen levels are still low, it is indicative of a right to left heart disorder.
- Blood pressure monitoring.
- Imaging of the chest and heart to evaluate for heart and lung disorders, tumours, foreign object.
- Echocardiogram to evaluate the heart.
- Pulse oximetry is a non-invasive way to measure oxygen saturation.
- Lung aspiration or tracheal wash if pneumonia is suspected. This then enables the veterinarian to obtain samples for culture to determine the causative agent and prescribe the best medication.
- Thoracentesis involves removing fluid from the pleural cavity this not only relieves compression on the lungs but provides your veterinarian with a fluid sample to determine the underlying cause of pleural effusion.
How is cyanosis treated in cats?
Most importantly, treat the underlying cause as well as relieving symptoms. Most cyanotic cats are very sick and will need to be placed in an oxygen tent until he is more stable.
- Antibiotics or antifungals will be prescribed to treat pneumonia.
- Pleural effusion is treated by removing the build-up of fluid in the pleural space (thoracentesis) and treating the underlying cause.
- Surgery may be required for certain heart conditions or to remove foreign objects, blockages, tracheal or laryngeal collapse or tumours.
- Low blood sugar is treated by administration of glucose.
- N-acetylcysteine (NAC) is a medication given to cats who have paracetamol toxicity to assist in the detoxification of the drug. Vitamin C can also be of help.
- Bronchodilators to open up the airways for a cat with asthma.
- Diuretics to help to flush out excess fluids for cats with pulmonary edema as well as vasodilators to open up the vessels.
- Hypertrophic myopathy may be treated with beta blockers, ACE inhibitors, low salt diet and restricting activity.
- Diuretics to treat congestive heart failure to help flush out excess fluids, ACE inhibitors, vasodilators to open up the vessels and help with fluid build up.
- Low blood pressure usually has an underlying cause which will need to be determined and addressed.
- In addition, supportive care may be required such as fluid therapy and nutritional support as well as painkillers if necessary. Blood transfusion may be required.