cyanosis
Meaning of cyanosis: The color depends on how much hemoglobin is traveling without oxygen rather than on the percentage, so anemia can hide it entirely.
Definition of cyanosis
Cyanosis is a blue or gray discoloration of the skin, lips or mucous membranes caused by an increased amount of hemoglobin circulating without its oxygen. It is a sign rather than a diagnosis, and it points either to poor oxygen loading in the lungs and heart or to sluggish blood flow through the skin, depending on where the color appears.
What does the location of the color tell?
| Feature | Central | Peripheral |
|---|---|---|
| Where it shows | Lips, tongue, inside of the mouth, and the skin generally | Fingers, toes, nose and ears only |
| Oxygen in the arteries | Low | Often normal |
| Temperature of the hands | Usually warm | Usually cold |
| Underlying problem | Lung disease, blood bypassing the lungs through a heart defect, altitude, abnormal hemoglobin | Cold, shock, heart failure, or a blocked artery or vein in the limb |
The tongue is the useful place to look, because it has no local blood supply problem of its own to confuse the picture. Central cyanosis is nearly always accompanied by peripheral cyanosis, since the blood reaching the fingers started out short of oxygen. The reverse is not true, and cold hands on a winter morning turn dusky in people whose lungs and heart are entirely healthy.
Why can the sign be absent when oxygen is dangerously low?
Because the eye responds to an absolute amount of oxygen poor hemoglobin in the small vessels, not to a proportion. Someone with severe anemia has so little hemoglobin in total that the threshold amount may never be reached even when saturation has fallen to a level causing real harm, so the skin stays pink. Someone with an unusually high red cell count crosses that threshold easily and may look blue while carrying enough oxygen. Skin tone, lighting and jaundice all interfere with judging the color, and detection is documented to be less reliable in people with darker skin, in whom the lips, tongue and nail beds are the more dependable places to check. Measurement rather than appearance settles the question, though even a fingertip oxygen monitor has known limits.
What produces it?
Central causes fall into groups. Lungs that cannot load oxygen into blood account for most: pneumonia, a severe asthma or emphysema attack, fluid in the lungs, or a clot in a lung artery. Structural heart defects can shunt blood past the lungs altogether, which is the mechanism behind blue coloring in some infants. Abnormal forms of hemoglobin produce a distinctive picture, with the person looking blue while the measured oxygen in the blood is normal and extra oxygen brings no improvement. Peripheral causes are largely about circulation: cold constricting the small vessels, shock or failing heart output slowing flow so tissues strip out more oxygen than usual, or a blockage in the artery or vein of a single limb, in which case the color affects that limb alone.
Used in a sentence
Cyanosis of the lips was noted on examination, prompting evaluation of the patient's oxygen levels.
Good to know
Central cyanosis, affecting the lips and tongue, generally points toward a problem with oxygen levels in the blood itself, while peripheral cyanosis, limited to the fingers and toes, more often reflects reduced local blood flow.
Word origin
Where “cyanosis” comes from
Formed from Greek kyanos, meaning dark blue, and -osis, meaning a condition.