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: BHU NO-2019

Explanation

• Magnesium sulfate toxicity presents with a predictable sequence of symptoms as serum levels rise.
• The earliest and most sensitive clinical sign is the disappearance of deep tendon reflexes (DTRs), such as the patellar (knee-jerk) reflex.
• This sign typically appears when serum magnesium levels reach approximately 10 mEq/L, serving as a critical warning before more severe complications like respiratory depression occur.

Why Other Options Were Wrong

• Option B: This is a late and severe complication of magnesium toxicity, occurring at much higher serum levels than the initial signs.
• Option C: This is the opposite of the expected effect. Magnesium sulfate is a central nervous system (CNS) depressant.
• Option D: This is the opposite of the expected effect. Magnesium toxicity causes respiratory depression, which is a decrease in respiratory rate and depth.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Early recognition of magnesium sulfate toxicity to guide bedside assessment, documentation, and the next nursing action.
• Nurses caring for a patient on magnesium sulfate must perform hourly assessments of deep tendon reflexes, respiratory rate, level of consciousness, and urine output.
• The antidote for magnesium sulfate toxicity, calcium gluconate, must be kept at the bedside for immediate administration in case of respiratory depression.
• What if? If the patient's urine output drops below 30 mL/hr, the nurse must notify the provider immediately. Since magnesium is cleared almost exclusively by the kidneys, oliguria significantly increases the risk of toxicity, and the infusion rate may need to be decreased or stopped.

How to Approach the Question

• First, identify the key components of the question: the drug is magnesium sulfate, the condition is severe preeclampsia, and the question asks for the initial sign of toxicity.
• Recall the mechanism of action of magnesium sulfate—it is a CNS depressant.
• Remember the predictable, dose-dependent progression of magnesium toxicity symptoms.
• Mentally list the sequence of toxic effects: 1. Loss of deep tendon reflexes (DTRs), 2. Respiratory depression, 3. Cardiac arrest.
• Evaluate each option based on this sequence. The loss of the knee-jerk reflex (a DTR) is the first sign in the progression.
• Eliminate the other options: cardiac dysrhythmia is a late sign, while hyperactive sensorium and increased respiratory rate are opposite to the drug's depressant effects.

Concept Tested & Keywords

• Concept Tested: Early recognition of magnesium sulfate toxicity.
• Stem keywords: magnesium sulfate therapy, severe preeclampsia, toxicity, initial sign
• Lead-in keywords: initial sign

Question ID

QoajNJoV8hrBNfJLQlkDzY

Copy ID

Reference Book

E6 Obstetrics Williams p. 31-51

E6 Pharmacology Nursing Lilley 11e Part 3 p. 213-215