Which of the following is an early sign of hypoxemia that clinicians should monitor?

• A. Cyanosis
• B. Anxiety/restlessness
• C. Tachypnea
• D. Confusion

Answer: (C)

An early sign of hypoxemia is an increased breathing rate because the body responds quickly to falling oxygen levels by boosting ventilation. The receptors that sense low PaO2 (and rising CO2) signal the brain to breathe faster, so tachypnea often appears before more obvious signs like color changes or mental status changes.

Cyanosis tends to be a late indicator because it requires a substantial amount of deoxygenated hemoglobin before skin and mucous membranes look blue, and it can be unreliable in patients with darker skin tones or mild desaturation. Anxiety or restlessness can occur but is nonspecific and may reflect pain, fear, or other factors. Confusion is a sign of more advanced or prolonged hypoxemia, indicating significant cerebral hypoxia.

So, the fastest, most reliable early sign among these is tachypnea.