Which of the following is an early sign of respiratory distress in an infant?

Choice A rationale Nasal flaring is a cardinal early sign of respiratory distress in infants and children, representing an involuntary attempt to decrease airway resistance. Flaring the nares widens the upper airway opening, allowing a greater volume of air to pass and maximizing gas exchange efficiency during inspiration. Choice B rationale Central cyanosis (bluish discoloration of the mucous membranes and torso) signifies inadequate oxygenation and is a late and ominous sign of severe hypoxemia. It indicates a substantial 5 g/dL or greater increase in deoxygenated hemoglobin, signaling decompensated respiratory failure. Choice C rationale Bradycardia (abnormally slow heart rate) in an infant is a late and critical sign of severe hypoxia and impending cardiorespiratory arrest. The heart slows as a compensatory response to profound oxygen deficit, indicating a failure of the body to maintain adequate oxygen delivery. Choice D rationale Hypotension (abnormally low blood pressure) is a very late and decompensated sign of shock, often due to severe prolonged hypoxemia and acidosis. The body's initial response to respiratory distress is typically to maintain or increase blood pressure, so a drop indicates circulatory collapse.