capillary refill time

**Technique:** Raise the extremity to about heart level. Apply firm pressure to the nail bed, sternum, or forehead for about 5 seconds until the skin blanches. Release and time how long it takes for normal color to return. Use a warm environment, because cold causes false prolongation.

**Normal values:** ≤2 seconds is the usual cutoff in children and adults. Some references allow up to 3 seconds in older adults. Neonates are often cited as ≤3 seconds.

**Pathophysiology:** CRT reflects skin microcirculation and the balance of cardiac output, intravascular volume, and sympathetic vasoconstriction. In hypovolemia or low cardiac output, baroreceptor-mediated sympathetic activation constricts cutaneous arterioles to shunt blood to vital organs. This slows return of blood to the blanched capillary bed and prolongs CRT.

**Causes of prolonged CRT (>2–3 s):** - Hypovolemic shock (hemorrhage, dehydration) and cardiogenic shock - Obstructive shock (tamponade, tension pneumothorax, massive PE) - Distributive shock in its "cold" phase. Early "warm" septic shock may have a *flash* (<1 s) CRT from vasodilation. - Hypothermia or cold exposure - Peripheral arterial disease or acute limb ischemia - Raynaud phenomenon - Severe anemia can contribute

**Clinical significance:** - **Pediatrics:** CRT is a key part of the rapid assessment of dehydration and shock (PALS). CRT >2 s is a sign of moderate to severe dehydration. In children, compensated shock is characterized by a prolonged CRT with normal BP, because hypotension is a *late* sign of pediatric shock. - **Adults:** CRT is less sensitive and specific. It is often unreliable as an isolated measure of volume status. It is used as an adjunct in trauma (ATLS) and sepsis. Recent evidence suggests CRT-targeted resuscitation in septic shock may be useful (ANDROMEDA-SHOCK trial: CRT-targeted vs lactate-targeted resuscitation). - **Limb assessment:** Asymmetric CRT, along with the "6 Ps" (pain, pallor, pulselessness, paresthesia, paralysis, poikilothermia), suggests acute arterial occlusion.

**Limitations:** Interobserver variability, ambient temperature, lighting, skin pigmentation, age, and site of measurement all affect the result. Interpret CRT together with heart rate, blood pressure, mental status, urine output, pulses, skin temperature, and lactate.

**High-yield pearls for boards:** - CRT >2 s, tachycardia, and cool extremities with normal BP suggest compensated shock. - In children, hypotension is a late and ominous sign. - Warm, flushed skin with a brisk CRT suggests early distributive (septic) shock.