Final answer:
Calcium gluconate is the emergency treatment for tetany following a subtotal thyroidectomy, due to its effectiveness in elevating blood calcium levels quickly.
Step-by-step explanation:
The correct medication to provide emergency treatment if a client develops tetany after a subtotal thyroidectomy is calcium gluconate. This condition is often due to a decrease in ionized calcium in the serum, which can occur after a thyroidectomy due to accidental removal or damage to the parathyroid glands. Calcium gluconate is used to quickly elevate calcium levels in the blood, preventing or treating tetany.
The role of the parathyroid hormone (PTH) is critical in this context, as it is responsible for mobilizing calcium from the bones and reducing its excretion by the kidneys. Without the proper functioning of the parathyroid glands, which can inadvertently be compromised during thyroid surgery, these processes are inhibited, leading to hypocalcemia and subsequent tetany.