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Difficulty: HardPharmacological and Parenteral Therapies

A nurse is monitoring a client at 3636 weeks of gestation who is receiving a continuous intravenous (IV) infusion of magnesium sulfate for the management of severe preeclampsia. Which of the following assessment findings indicate potential magnesium toxicity or impaired clearance, requiring immediate intervention by the nurse? Select all that apply.

  1. Patellar deep tendon reflexes (DTRs) graded as 00 (absent)Answer
  2. Respiratory rate of 1010 breaths per minuteAnswer
  3. Urinary output of 15 mL15 \text{ mL} per hour over the last two hoursAnswer
  4. D
    Client reports a generalized sensation of warmth and facial flushing
  5. E
    Fetal heart rate tracing demonstrating early decelerations with moderate variability
  6. F
    Serum magnesium level of 5.8 mEq/L5.8 \text{ mEq/L}

Answer

The findings requiring immediate intervention are absent patellar deep tendon reflexes, a respiratory rate of 10 breaths per minute, and a urinary output of 15 mL per hour.
The correct options identify the classic signs of magnesium toxicity and impaired clearance. Because magnesium sulfate is a central nervous system depressant, toxicity sequentially manifests as the loss of deep tendon reflexes (often the first sign), followed by respiratory depression (fewer than 12 breaths per minute), and eventually cardiac arrest. Furthermore, because magnesium is excreted exclusively by the kidneys, severe oliguria (urine output less than 30 mL/hr) causes rapid accumulation of the medication, requiring an immediate decrease or cessation of the infusion to prevent toxic serum levels.

Step-by-Step Solution

1
Identify the purpose and mechanism of the medication.
Magnesium sulfate is a central nervous system depressant used to prevent seizures in severe preeclampsia.
Understanding the mechanism of action is essential to anticipate therapeutic effects and differentiate them from clinical toxicity.
2
Evaluate the assessment findings against known signs of toxicity and clearance failure.
Findings of absent DTRs (grade 0), respiratory rate < 12 breaths per minute, and severe oliguria (< 30 mL/hr) are critical indicators of toxicity or poor renal clearance.
Magnesium toxicity progresses predictably from loss of reflexes to respiratory depression and eventual cardiac arrest; renal impairment exacerbates this by preventing drug excretion.
3
Differentiate critical toxicity from expected side effects and therapeutic levels.
Flushing and warmth are expected vasodilatory side effects. A serum magnesium level of 5.8 mEq/L is within the therapeutic range (4.0 - 7.0 mEq/L). Early FHR decelerations are a normal labor finding.
Unnecessary intervention for expected or therapeutic findings can disrupt essential seizure prophylaxis and jeopardize maternal safety.

Key Concept

Recognition of magnesium sulfate toxicity and therapeutic monitoring in severe preeclampsia.
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Topics

Pharmacological and Parenteral Therapies

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