capillary refill
Capillary refill is a quick bedside test of how well blood is reaching the smallest vessels of the skin. Press firmly on a fingertip or nail bed for a few seconds and the pressed area turns pale as blood is squeezed out; release, and watch how fast the pink color floods back. The time it takes — normally under about two seconds — is the capillary refill time.
The idea is that good circulation refills the emptied capillaries almost instantly, while sluggish flow returns the color slowly. A prolonged refill can reflect poor perfusion from a failing or low-output heart, severe dehydration, blood loss, or shock, when the body shunts blood away from the skin to protect vital organs. It is a small, immediate clue about whether the periphery is being adequately supplied.
Its great virtue is speed and simplicity, useful for a rapid first impression in an emergency. Its weakness is that many non-cardiac factors — cold hands, age, lighting, and the examiner's technique — affect the result, so it is a rough screen rather than a precise measurement. It is interpreted alongside pulse, blood pressure, and the overall clinical picture.
In a patient with cardiogenic shock, pressing the fingertip leaves it pale for more than four seconds before color returns, signaling severely reduced perfusion of the skin.
A markedly prolonged capillary refill time is one bedside marker of poor tissue perfusion.
Cold ambient temperature alone can lengthen capillary refill in a perfectly healthy person, so a slow result must be judged together with other signs of circulation rather than on its own.