Final answer:
The nurse should monitor the client for signs of muscle weakness and disorientation as these are manifestations associated with hypomagnesemia caused by long-term therapy with lansoprazole.
Step-by-step explanation:
Hypomagnesemia, which is a condition of having low levels of magnesium in the blood, can cause numerous physiological disturbances. Having developed hypomagnesemia due to long term therapy with lansoprazole, which is a type of proton pump inhibitor, a client may experience various symptoms. Proton pump inhibitors can lead to a decrease in gastric acid, which in turn can affect the absorption of certain minerals like magnesium.
The nurse should monitor the client for several manifestations of hypomagnesemia. The symptoms of hypomagnesemia can include muscle weakness, disorientation, arrhythmias, and seizures. Since the question specifies monitoring for specific symptoms related to hypomagnesemia, the most appropriate answer is disorientation and muscle weakness.