Brick red postmortem lividity is typically a sign of poisoning by which substance?

Brick red postmortem lividity is a characteristic finding associated with cyanide poisoning. This phenomenon occurs because cyanide impairs cellular respiration at the mitochondrial level, preventing the use of oxygen by the cells. As a result, the tissues become hypoxic and can develop a cherry-red or brick red coloration due to the increased levels of carboxyhemoglobin when cyanide is present.

In contrast, the other substances listed have different effects on the body and postmortem findings. Arsenic poisoning typically does not cause this specific discoloration; instead, it may produce a pallor or yellowish hue due to liver damage and other systemic effects. Nitrite poisoning can lead to methemoglobinemia, resulting in a brownish tint of blood, rather than brick red lividity. Carbon dioxide exposure can cause a variety of hypoxic symptoms, but its postmortem lividity usually does not present as brick red, as it primarily affects blood oxygen levels without altering the color as dramatically.

Thus, the distinct brick red postmortem lividity serves as a key indicator in forensic sciences for identifying cyanide as the toxic agent in cases of suspected poisoning.