A client with renal impairment is receiving intravenous magnesium sulfate. Which monitoring plan is most important for detecting magnesium toxicity?
1Monitor bilirubin, aminotransferases, and abdominal girth because hepatic injury is the earliest sign of toxicity.
2Monitor respiratory rate, deep tendon reflexes, urine output, and magnesium level, with an injectable calcium salt available.✓ Correct answer
3Monitor capillary glucose and ketones because magnesium toxicity first produces severe insulin-mediated hypoglycemia.
4Monitor visual acuity and extraocular movements because nystagmus is the most reliable early toxicity finding.
Explanation
Magnesium is eliminated by the kidneys, so renal impairment and low urine output increase the risk of accumulation. Diminished or absent deep tendon reflexes and respiratory depression are key clinical toxicity findings, while serum magnesium and urine output help assess exposure and clearance. An injectable calcium salt should be immediately available for significant toxicity. The alternative assessments do not identify the expected toxicity pattern.
Clinical reasoning As magnesium accumulates, neuromuscular transmission is depressed before respiratory paralysis can occur. Reduced renal clearance accelerates this progression.
Decision rule Track respiratory rate, patellar or other deep tendon reflexes, urine output, and serum magnesium. Stop escalation and prepare calcium treatment if toxicity develops.
Scenario 58-year-old female on PPI 1 year, Mg 1.2 mEq/L, prescribed magnesium sulfate 2 g IV over 1 hour.