Central and Peripheral Cyanosis

Excerpt

Cyan means ‘blue’ and the abnormal bluish discoloration of the skin and mucous membranes is referred to as “cyanosis”. It is a pathologic sign, and not a disease by itself. Underlying diseases that increase the deoxygenated hemoglobin to 5.0 g/dl or more leads to cyanosis. Cyanosis can be best appreciated in areas with rich superficial vasculature and thin overlying dermis. These include lips, nose, earlobes, oral cavity, extremities, and tips of fingers and toes. Cyanosis usually becomes evident in hypoxemia, that is, abnormally low concentration of oxygenation (<80-85%) in arterial blood. However, it is not sensitive or a specific indicator of hypoxemia. Since cyanosis is a clinical sign, a proper evaluation is important to determine the etiology of cyanosis.

Cyanosis is further classified as central, peripheral, and differential.

1. Central cyanosis is a generalized bluish discoloration of the body and the visible mucous membranes, which occurs due to inadequate oxygenation secondary to conditions that lead to an increase in deoxygenated hemoglobin or presence of abnormal hemoglobin.

2. Peripheral cyanosis is the bluish discoloration of the distal extremities (hands, fingertips, toes), and can sometimes involve circumoral and periorbital areas. Mucous membranes are generally not involved. Peripheral cyanosis is rarely a life-threatening medical emergency. However, it is essential to determine the underlying cause and its timely management to prevent potential complications.

3. Differential cyanosis is the asymmetrical bluish discoloration between the upper and lower extremities. It usually indicates serious underlying cardiopulmonary conditions.

The bluish discoloration despite adequate oxygenation is sometimes seen due to the ingestion of drugs, toxins, or metals. This is called ‘Pseudocyanosis.’