Which of the following symptoms is least likely to occur with first use syndrome?

First use syndrome is a reaction that can occur in patients with end-stage renal disease when they start dialysis for the first time, especially when switching to a new dialysis membrane or solution. This syndrome is characterized by a variety of acute symptoms that stem primarily from the body's reaction to dialysis.

Among the symptoms associated with first use syndrome, trouble breathing, nausea, and itching are commonly reported. Trouble breathing could occur due to an allergic-like reaction or fluid overload; nausea often results from the abrupt changes in the body’s chemistry that occur during the initial dialysis sessions; and itching, or pruritus, can arise from the release of histamines or other mediators from mast cells in response to the new dialysis materials.

Fatigue, while it can be a symptom experienced by dialysis patients, is less direct and typically does not occur abruptly during the first use in the manner that the more acute symptoms do. Fatigue usually develops over time as a result of the chronic nature of kidney disease and the demanding treatment schedule, rather than being a predominant immediate symptom from the first encounter with dialysis.

Thus, the least likely symptom to occur with first use syndrome is fatigue, making it a distinguishing characteristic in the context of immediate reactions to dialysis treatments.