Tetany can be produced by which of the following electrolyte disturbance?

HPSSC - 2015

Medical & Surgical Nursing

Easy

Appeared in: HPSSC - 2015

Explanation

Hypocalcemia is the most direct cause of tetany.
Low extracellular calcium increases the permeability of neuronal membranes to sodium ions, which lowers the threshold for depolarization.
This heightened excitability leads to spontaneous nerve impulses and sustained muscle contractions, known as tetany.
Classic clinical indicators of hypocalcemia-induced tetany are Chvostek's sign and Trousseau's sign.

Option A: Although hypomagnesemia can cause tetany, it is often an indirect cause. Low magnesium levels impair the secretion of parathyroid hormone (PTH), leading to secondary hypocalcemia, which then causes tetany. Because hypocalcemia is a direct cause and is also an option, it is the better answer.
Option B: Hypermagnesemia causes the opposite of tetany. It decreases neuromuscular excitability by blocking the release of acetylcholine at the neuromuscular junction, leading to muscle weakness, hypoactive reflexes, and, in severe cases, respiratory depression and flaccid paralysis.
Option D: Hypercalcemia causes decreased neuromuscular excitability. High levels of calcium stabilize the cell membrane, making it more difficult for an action potential to be generated. This results in muscle weakness, lethargy, and diminished reflexes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pathophysiology of Tetany and Electrolyte Imbalances as background academic context rather than a clinical decision trigger.
Nurses must be able to recognize the signs of tetany (Chvostek's and Trousseau's signs) as they indicate a potentially life-threatening electrolyte imbalance.
Patients at high risk for hypocalcemia include those who have undergone thyroid or parathyroid surgery, individuals with pancreatitis, kidney disease, or malabsorption syndromes.
Nursing interventions for a patient with tetany include implementing seizure precautions, maintaining a quiet environment, and preparing for the potential administration of intravenous calcium gluconate.

How to Approach the Question

First, identify the key term in the question: 'Tetany'. Recall that tetany signifies neuromuscular hyperexcitability (spasms, cramps).
Next, analyze the options, which are all electrolyte imbalances involving calcium and magnesium.
Recall the general principle: for calcium and magnesium, 'hypo-' (low levels) tends to cause increased excitability, while 'hyper-' (high levels) causes decreased excitability.
This principle immediately helps you eliminate Hypermagnesemia and Hypercalcemia, as they cause muscle weakness, not hyperexcitability.
You are left with Hypomagnesaemia and Hypocalcemia. Both can cause tetany.
At this point, recall the primary physiological mechanisms. Calcium has the most direct and critical role in regulating neuronal membrane stability and muscle contraction. Hypocalcemia is the classic, direct cause of tetany. Hypomagnesemia is also a cause but often acts indirectly by inducing hypocalcemia. Therefore, Hypocalcemia is the best and most direct answer.

Concept Tested & Keywords

QVMRUw-RskeNIRLLFmq2mj

E6 Nursing Fundamentals Taylor p. 779-781

E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 53-55

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 1244-1246