Cyanosis

Definition: Bluish discolouration skin and mucous membrane is called cyanosis.

Or,

Cyanosis is defined as a bluish discoloration, especially of the skin and mucous membranes, due to excessive concentration of deoxyhemoglobin in the blood caused by deoxygenation.
Cyanosis is divided into two main types: Central (around the core, lips, and tongue) and Peripheral (only the extremities or fingers).

Type:

[A] Central cyanosis:

Site: Tongue and mouth.

Cause: Hypoxemia, where there is an increase in amount of Hb not found.

[B] Peripheral cyanosis:

Site: Toe, fingure, earlobes.

Cause: Due to poor circulation in the cold weather.

Causes:

Central cyanosis

Central cyanosis may be due to the following causes:
1. Central nervous system (impairing normal ventilation):

• Intracranial hemorrhage
• Drug overdose (e.g. Heroin)
• Tonic–clonic seizure (e.g. grand mal seizure)

2. Respiratory system:

• Pneumonia
• Bronchiolitis
• Bronchospasm (e.g. Asthma)
• Pulmonary Hypertension
• Pulmonary embolism
• Hypoventilation
• Chronic obstructive pulmonary disease, or COPD (emphysema)

3. Cardiovascular diseases:

• Congenital heart disease (e.g. Tetralogy of Fallot, Right to left shunts in heart or great vessels)
• Heart failure
• Valvular heart disease
• Myocardial infarction

4. Blood.
5. Others:

• High altitude, cyanosis may develop in ascents to altitudes >2400 m.
• Hypothermia
• Obstructive sleep apnea

Peripheral cyanosis

Peripheral cyanosis may be due to the following causes:

• All common causes of central cyanosis
• Reduced cardiac output (e.g. heart failure, hypovolaemia)
• Cold exposure
• Arterial obstruction (e.g. peripheral vascular disease, Raynaud phenomenon)
• Venous obstruction (e.g. deep vein thrombosis)

Differential cyanosis

Differential cyanosis is the bluish coloration of the lower but not the upper extremity and the head. This is seen in patients with a patent ductus arteriosus. Patients with a large ductus develop progressive pulmonary vascular disease, and pressure overload of the right ventricle occurs. As soon as pulmonary pressure exceeds aortic pressure, shunt reversal (right-to-left shunt) occurs. The upper extremity remains pink because the brachiocephalic trunk, left common carotid trunk and the left subclavian trunk is given off proximal to the PDA.

Approach to diagnosis:

• Inquire about duration (cyanosis since birth suggests congenital heart disease) and exposures (drugs or chemicals that result in abnormal hemoglobins).
• Differentiate central from peripheral cyanosis.
• Check for nail clubbing. Combination of clubbing and cyanosis suggests congenital heart disease and occasionally pulmonary disease.
• If cyanosis is localized to an extremity evaluate for peripheral vascular obstruction.
• Evaluate abnormal hemoglobins by hemoglobin electrophoresis, spectroscopy, and measurement of methemoglobin level.