**Question:** % of COHb than can cause death -

A. 90%
B. 80%
C. 70%
D. 60%

**Core Concept:** Carbon monoxide (CO) is an odorless, colorless gas that binds to hemoglobin (Hb) and prevents oxygen (O2) from binding, leading to hypoxia and potential organ damage. The percentage of carboxyhemoglobin (COHb) that can cause significant clinical manifestations depends on the severity and duration of CO exposure.

**Why the Correct Answer is Right:** The correct answer is D, 60%. According to the World Health Organization (WHO), a COHb level above 10% is considered clinically significant. However, the severity and duration of CO exposure are crucial factors to consider. For example, acute exposure to high concentrations of CO can lead to severe symptoms at lower COHb levels.

**Why Each Wrong Option is Incorrect:**

A. 90% is too high for a clinically significant COHb level. Acute exposure to extremely high CO concentrations can lead to severe symptoms at much lower COHb levels.

B. 80% is also too high for a clinically significant COHb level. Acute exposure to high concentrations of CO can lead to severe symptoms at much lower COHb levels.

C. 70% is closer to the correct answer, but still too high. A higher percentage indicates a more severe COHb level, which typically requires immediate medical attention.

**Clinical Pearl:** The severity of CO poisoning depends on the concentration and duration of CO exposure. If you suspect CO poisoning, seek immediate medical attention regardless of COHb levels. Monitoring COHb levels is essential for assessing the severity of exposure and guiding treatment strategies.