Table 1.

Expected signs and symptoms for a given percentage methemoglobin level assuming normal starting hemoglobin [6, 7].

Percentage methemoglobin	Expected symptoms
<10%	None
10–20%	Peripheral and central cyanosis
20–30%	Anxiety, tachycardia, lightheadedness, and headache
30–50%	Confusion, dizziness, fatigue, tachypnea, and worsening tachycardia
50–70%	Acidosis, arrhythmia, seizures, and coma
>70%	Death