A client with bipolar disorder has advanced lithium toxicity with a lithium level of 1.7 mEq/L. Which symptom would the nurse expect to assess?

Choice A reason: Clonic movements are not typical of advanced lithium toxicity (levels >1.5 mEq/L). Lithium affects sodium-potassium ATPase, disrupting neuronal signaling, leading to renal and neurological symptoms, but clonic movements are more associated with seizures from other causes, not lithium’s mechanism. Choice B reason: Muscle hyperirritability is not a hallmark of advanced lithium toxicity. Lithium’s disruption of renal tubular function and neuronal signaling causes symptoms like polyuria and confusion. Muscle-related symptoms are less prominent compared to renal or neurological effects at toxic levels. Choice C reason: Polyuria is a common symptom of advanced lithium toxicity due to impaired renal concentrating ability from disrupted aquaporin-2 expression in the collecting ducts. Lithium’s interference with sodium-potassium ATPase also contributes, leading to excessive urine output, a key clinical sign at toxic levels. Choice D reason: Fine tremor occurs in therapeutic lithium levels (0.6-1.2 mEq/L) due to mild neuronal excitability. In advanced toxicity (>1.5 mEq/L), symptoms escalate to severe neurological and renal effects like confusion and polyuria, making fine tremor less prominent.