**Core Concept**
Carbon monoxide (CO) poisoning occurs when carbon monoxide binds to hemoglobin in red blood cells, forming carboxyhemoglobin, which reduces oxygen delivery to tissues. This results in tissue hypoxia, leading to a range of clinical manifestations.

**Why the Correct Answer is Right**
Carbon monoxide binds to the iron in hemoglobin's heme group with high affinity, forming carboxyhemoglobin. This binding is irreversible, making it difficult to treat CO poisoning. The presence of carboxyhemoglobin is a key postmortem finding in CO poisoning, and it can be detected in blood samples using spectrophotometry. The cherry-red discoloration of the skin and mucous membranes is also a classic sign of CO poisoning.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CO poisoning does not primarily affect the lungs. While oxygen saturation may be decreased, the primary issue is the formation of carboxyhemoglobin, which reduces oxygen delivery to tissues.
**Option B:** This option is incorrect because while there may be some inflammation and edema in CO poisoning, it is not a primary postmortem finding.
**Option C:** This option is incorrect because while CO poisoning can lead to cardiac arrhythmias and sudden death, the primary postmortem finding is the presence of carboxyhemoglobin.

**Clinical Pearl / High-Yield Fact**
In CO poisoning, the presence of carboxyhemoglobin is a key diagnostic clue, and it can be detected in blood samples using spectrophotometry. This is a critical differentiator from other causes of tissue hypoxia, such as cyanide poisoning.

**Correct Answer: D. Carboxyhemoglobin in blood**