capillary refill

TECHNIQUE: Raise the extremity to about heart level. Apply firm pressure to the nail bed, or to the sternum or forehead in infants, for ~5 seconds until blanched. Release and time how long it takes for normal color to return. Normal is ≤2 seconds. Some sources use <3 seconds for adults, and cutoffs vary with age, sex, and ambient temperature.

PHYSIOLOGY: Blanching empties the capillaries and venules of the dermal plexus. Refill depends on arteriolar tone, cardiac output, and blood volume. When the body compensates for low perfusion, sympathetic activation (norepinephrine, α1 receptors) causes peripheral vasoconstriction. That shunts blood to vital organs and slows skin refill.

PROLONGED CRT (>2–3 s) CAUSES: - Hypovolemic shock: hemorrhage, dehydration, burns. Common in pediatric gastroenteritis. - Cardiogenic shock: pump failure. - Obstructive shock: tension pneumothorax, tamponade, massive PE. - Distributive shock, especially "cold" late septic shock. Early septic and neurogenic shock can show brisk or flash refill from vasodilation ("warm shock"). - Peripheral arterial disease or acute limb ischemia (the 6 P's: pain, pallor, pulselessness, paresthesia, paralysis, poikilothermia). - Hypothermia or cold environment, which causes vasoconstriction and a false positive. - Raynaud phenomenon and other vasospastic states.

CLINICAL SIGNIFICANCE: - In pediatrics, CRT is part of the Pediatric Assessment Triangle (appearance, work of breathing, circulation to skin). It is a key early sign of compensated shock. Children maintain blood pressure until late, so hypotension is a late and ominous sign of decompensation. - ATLS: CRT is used to assess perfusion in trauma. Cool, clammy skin with delayed refill suggests hemorrhagic shock class II or higher. - Sepsis resuscitation: CRT is used as a perfusion target in some protocols. The ANDROMEDA-SHOCK trial found that CRT-targeted resuscitation was non-inferior to, and possibly better than, lactate-targeted resuscitation. - Limitations: it is subjective and varies with temperature, lighting, skin pigmentation, age, and pressure duration. It is a poor standalone test in adults, so interpret it with heart rate, blood pressure, mental status, urine output, and lactate.

BOARD PEARLS: - Normal ≤2 s. Delayed refill with tachycardia and normal blood pressure in a child means compensated shock, so give fluids. - Brisk or flash refill with bounding pulses suggests warm (distributive) shock. - Always consider and exclude a cold room or hypothermia before attributing delayed refill to shock.