A client is receiving magnesium sulfate therapy for severe preeclampsia. What initial sign of toxicity should alert the nurse to intervene?

1. A

   Lack of knee jerk reflex

2. B

   Development of a cardiac dysrhythmia

3. C

   Hyperactive sensorium

4. D

   Increase in respiratory rate

Appeared in: NORCET-7 Mains-2024

Explanation

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• The loss of deep tendon reflexes (DTRs), such as the patellar (knee-jerk) reflex, is the earliest clinical sign of magnesium sulfate toxicity.
• Magnesium sulfate is a central nervous system (CNS) depressant that blocks neuromuscular transmission, causing reflexes to diminish and then disappear as serum levels rise.
• This sign typically appears when serum magnesium levels reach 8 to 10 mEq/L, serving as a crucial warning before the onset of more severe complications like respiratory depression.
• Assessing DTRs is a primary nursing responsibility to ensure patient safety during magnesium sulfate infusion.

Why Other Options Were Wrong

• Option B: The development of cardiac dysrhythmias is a late and life-threatening sign of severe magnesium toxicity, occurring at serum levels significantly higher than those that cause loss of reflexes.
• Option C: Magnesium sulfate is a CNS depressant. Therefore, toxicity leads to a hypoactive sensorium (drowsiness, lethargy, confusion), which is the opposite of a hyperactive state.
• Option D: Magnesium toxicity causes respiratory depression, which is a decrease in the rate and depth of breathing, due to its depressant effects on the CNS and respiratory muscles.

Related Visual

• Visual 1: Diagram: Illustration of the patellar reflex arc to show the neuromuscular junction where magnesium acts.
• Visual 2: Chart: A visual timeline showing the progression of magnesium toxicity signs correlated with increasing serum magnesium levels.

Clinical Relevance

• Nursing practice connection: Use the key finding related to Initial signs of magnesium sulfate toxicity to guide bedside assessment, documentation, and the next nursing action.
• Nurses must perform frequent (often hourly) assessments of DTRs, respiratory rate, level of consciousness, and urine output for any patient on magnesium sulfate to detect toxicity early and prevent harm.
• The antidote for magnesium sulfate toxicity, calcium gluconate, must always be readily available at the bedside for emergency administration.
• Patients with impaired renal function (indicated by low urine output or elevated serum creatinine) are at a much higher risk for toxicity because magnesium is cleared by the kidneys.

How to Approach the Question

• First, identify the keyword 'initial' in the question. This directs you to find the very first sign of toxicity, not just any sign.
• Recall the primary action of magnesium sulfate: it is a central nervous system (CNS) depressant and smooth muscle relaxant.
• Think about the progressive effects of increasing CNS depression. The effects on neuromuscular transmission (reflexes) occur at lower concentrations than the effects on the respiratory center (breathing) or the heart.
• Evaluate each option based on this progression: Loss of reflexes is an early sign of neuromuscular blockade. Cardiac issues are a very late, severe sign. Hyperactivity and increased respirations are the opposite of the drug's depressant effect.
• Select the option that represents the earliest detectable warning sign in this progression, which is the loss of the knee-jerk reflex.

Concept Tested & Keywords

• Concept Tested: Initial signs of magnesium sulfate toxicity
• Stem keywords: magnesium sulfate, severe preeclampsia, toxicity, initial sign
• Lead-in keywords: initial sign
• Clinical cues: Client receiving magnesium sulfate for severe preeclampsia
• Negative lead-in flag: false

Question ID

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