Which of the following symptoms is a healthy pt likely to complain of when carbon monoxide levels reach 20%?

• A. Headache, nausea and vomiting
• B. Dry lips, tachypnea, lethargy
• C. Confusion, lethargy, polyuria
• D. Polydipsia, lethargy, headache

Answer: (A)

Carbon monoxide poisoning disrupts oxygen delivery by binding to hemoglobin to form carboxyhemoglobin, which robs tissues of oxygen and leads to hypoxia. When exposure reaches a moderate level around 20%, the brain and other organs react with symptoms like a throbbing headache, nausea, and sometimes vomiting as the body responds to hypoxia. This combination fits the typical presentation at this level, reflecting the brain’s sensitivity to reduced oxygen.

The other signs listed don’t match the common early pattern of CO exposure. Dry lips and rapid breathing aren’t characteristic hallmarks of CO poisoning at this stage, and polyuria or excessive thirst aren’t typical features of its early or moderate effects. More confusion or lethargy tend to appear with higher levels of carboxyhemoglobin, after hypoxia becomes more severe.