Cyanosis

14 Cyanosis




Clinical Tip



• In most animals, cyanosis indicates very severe hypoxaemia. However, it is essential to remember that animals can be markedly hypoxaemic and on the cusp of severe deterioration without manifesting cyanosis; this is especially true in anaemic animals. A false sense of security should not therefore be derived either from the absence of cyanosis or from normal arterial oxygen saturation by pulse oximetry. In addition, cyanosis when identified must be treated as an emergency.

Cyanosis is a bluish or purplish discoloration of the mucous membranes or skin and occurs as a result of an increase in the concentration of unoxygenated (reduced) haemoglobin. Reduced haemoglobin must rise above a certain level (5 g/dl) before cyanosis is detectable. Animals can therefore be markedly hypoxaemic and on the cusp of severe deterioration without manifesting cyanosis; this is especially true in anaemic animals. Causes of cyanosis are typically classified as central or peripheral.


Central cyanosis most commonly occurs when arterial blood fails to become adequately saturated with oxygen. It may also occur if there is an increase in the concentration of other types of haemoglobin that are unable to carry oxygen (e.g. methaemoglobinaemia in paracetamol (acetaminophen) intoxication). Inadequate oxygen saturation may occur for example due to:


• Congenital cardiovascular anomalies causing right-to-left shunting such that unoxygenated blood bypasses the lungs and flows straight into the systemic arterial circulation (e.g. tetralogy of Fallot, reverse patent ductus arteriosus (PDA)). Cyanosis may also occur as a result of severe congenital pulmonic stenosis.

• Severe lung disease: this may be due to primary lung disease (e.g. aspiration pneumonia, bronchopneumonia, pulmonary contusions, neoplastic infiltration) but also to severe cardiogenic pulmonary oedema. Obstructive lower airway disease (especially feline bronchial disease) may also cause central cyanosis.

• Upper respiratory tract obstruction (e.g. laryngeal paralysis, foreign body, tumour).

• Severe hypoventilation, for example due to severe pleural effusion or pneumothorax, central nervous system depression or injury, neuromuscular disease (e.g. myasthenia gravis, tetanus) or intoxication/drug overdose.

Right-to-left shunting PDA may be associated with so-called differential cyanosis, in which unoxygenated blood flows to the caudal parts of the body but oxygenated blood flows to the cranial parts. Cyanosis is therefore only detected caudally in such cases.


Peripheral cyanosis occurs as a result of a disturbance in peripheral circulation. Slow peripheral blood flow results in a relative increase in the amount of oxygen extracted by the tissues and therefore the amount of oxyhaemoglobin that is reduced. The arterial blood in such cases may have normal or reduced oxygen saturation. The most common causes are intense peripheral vasoconstriction (e.g. severe hypothermia), low cardiac output, and thrombosis/thromboembolism (e.g. cyanotic nail beds in cats with feline aortic thromboembolism).



Approach to Cyanosis




Clinical Tip



• Central cyanosis is typically associated with a potentially life-threatening disorder and affected animals should be considered highly unstable, requiring gentle handling and minimal intervention.

• Many of the causes of central cyanosis (with the particular exceptions of right-to-left cardiovascular shunts and increased concentrations of non-oxygen-carrying haemoglobin) are responsive to oxygen supplementation that should therefore be provided from the outset. A period of oxygen supplementation prior to further examination/intervention can be invaluable in many cases. In the author’s experience, severe respiratory disease is the most commonly identified cause of cyanosis in companion animals presenting as emergencies.

• It is important to remember that both types of cyanosis – central and peripheral – may be present in the same animal at the same time.


Signalment, history


Signalment and history may allow certain differential diagnoses to be viewed with a greater or lesser index of suspicion. For example, cyanosis in a young animal is more likely to be due to a congenital cardiovascular abnormality. A chronic history of consistent signs in a breed predisposed to idiopathic pulmonary fibrosis (e.g. the West Highland White terrier) may point to this as the cause of the cyanosis.

Related posts:

  1. Hyperthermia and pyrexia
  2. Sudden loss of vision
  3. Pelvic limb paresis and paralysis
  4. Ocular emergencies

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Cyanosis

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