A patient with preeclampsia is on magnesium sulfate. Which sign indicates magnesium toxicity?

GMCH Nursing Officer-2025

Obstetrics & Gynaecology

Easy

Appeared in: GMCH Nursing Officer-2025

Explanation

Magnesium sulfate is a central nervous system (CNS) depressant used to prevent seizures in patients with preeclampsia.
When serum levels become toxic, the drug suppresses the respiratory center in the brainstem, leading to respiratory depression.
A respiratory rate of 10 breaths per minute is below the critical threshold of 12 breaths/min, indicating significant toxicity that can progress to respiratory arrest.
This is a life-threatening emergency requiring immediate cessation of the magnesium infusion and potential administration of the antidote, calcium gluconate.

Option A: Positive ankle clonus is a sign of neuromuscular hyper-excitability.
Option C: A blood pressure of 160/110 mmHg is a diagnostic criterion for severe preeclampsia.
Option D: Hyperreflexia (exaggerated deep tendon reflexes) is a classic sign of CNS irritability associated with severe preeclampsia.

Visual 1: Chart: Comparison of Signs - Worsening Preeclampsia vs. Magnesium Toxicity. This visual helps differentiate the symptoms of the disease (CNS irritability) from the symptoms of drug toxicity (CNS depression).
Visual 2: Flowchart: Nursing Actions for Suspected Magnesium Toxicity. This outlines the immediate steps: 1. Stop the infusion. 2. Assess airway, breathing, and circulation. 3. Notify the healthcare provider. 4. Prepare to administer calcium gluconate.

Clinical Relevance

Nursing practice connection: Use the key finding related to Assessment and recognition of magnesium sulfate toxicity in a patient with preeclampsia to guide bedside assessment, documentation, and the next nursing action.
A nurse's primary responsibility for a patient on magnesium sulfate is vigilant monitoring for signs of toxicity. This includes hourly checks of respiratory rate, deep tendon reflexes, and urine output.
The antidote for magnesium sulfate toxicity, calcium gluconate, must be immediately accessible at the patient's bedside. Delay in administration during respiratory arrest can be fatal.
What if? If the patient's deep tendon reflexes become absent but their respiratory rate is still 14/min, the nurse must still stop the infusion and notify the provider. Loss of reflexes is the first sign of toxicity and precedes the more dangerous respiratory depression.

How to Approach the Question

First, identify the key elements: The patient has preeclampsia and is receiving magnesium sulfate. The question asks for a sign of drug toxicity.
Recall the mechanism of action of magnesium sulfate. It is a central nervous system (CNS) depressant.
Analyze the options in the context of CNS depression. A depressant would cause functions to slow down or cease.
Evaluate Option A (Positive ankle clonus) and D (Hyperreflexia). These are signs of hyper-excitability or irritability, which is the opposite of depression. These are signs of worsening preeclampsia.
Evaluate Option C (High blood pressure). This is a sign of the disease itself (preeclampsia), not a side effect of the treatment.
Evaluate Option B (Respiratory rate of 10/min). This represents a depressed or slowed function, consistent with the effects of a CNS depressant. A rate below 12/min is the established threshold for toxicity.

Concept Tested & Keywords

Concept Tested: Assessment and recognition of magnesium sulfate toxicity in a patient with preeclampsia.
Stem keywords: preeclampsia, magnesium sulfate, magnesium toxicity
Lead-in keywords: Which sign indicates
Clinical cues: A patient with preeclampsia on magnesium sulfate therapy, which signals the need to monitor for drug-specific adverse effects.
Negative lead-in flag: false

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