Final answer:
Slurred speech is the expected manifestation of mild hypothermia in the provided options, as decreased body temperature impacts peripheral nerve function and subsequently affect speech clarity.
Step-by-step explanation:
A nurse assessing a client with mild hypothermia in an emergency department should expect certain physiological manifestations. Among the listed options, C. Slurred Speech is a common symptom experienced by individuals with mild hypothermia. This condition occurs as the body's temperature drops below the normal range and efforts to conserve heat lead to decreased blood flow to non-essential body parts, including the peripheral nervous system, which affects speech. In contrast, stupor is more associated with more severe hypothermia, decreased pulse can be a result of various conditions and is not a specific indicator of mild hypothermia, and while dysrhythmias can occur in hypothermia, it is not the most likely initial symptom in mild cases.