A nurse needs to check the most important parameter if patient is on magnesium sulphate therapy?

SJH Nursing Officer - 2019

Pharmacology

Hard

Appeared in: SJH Nursing Officer - 2019

Explanation

Magnesium sulphate is a high-risk medication with a narrow therapeutic window, used to prevent seizures in conditions like pre-eclampsia.
Its most severe and life-threatening toxic effect is respiratory depression, which can rapidly progress to respiratory arrest and death.
Following the Airway, Breathing, Circulation (ABC) principle of prioritization in nursing, maintaining adequate breathing is the most critical assessment.
A respiratory rate falling below 12 breaths per minute is a critical sign of severe magnesium toxicity that requires immediate intervention to prevent a fatal outcome.

Option A: Monitoring urine output is crucial for preventing magnesium accumulation, as the drug is cleared by the kidneys. However, low urine output is a risk factor for toxicity, not the most immediate life-threatening sign of acute toxicity itself.
Option B: The absence of the knee jerk (patellar) reflex is the earliest sign of magnesium toxicity. While it is a vital early warning sign, it occurs at lower serum levels than respiratory depression and is not as immediately life-threatening.
Option D: Magnesium sulphate is used as an anticonvulsant, not primarily as an antihypertensive. Blood pressure is monitored to manage the patient's underlying condition (e.g., pre-eclampsia), not as a direct indicator of magnesium toxicity.

Clinical Relevance

Nursing practice connection: Use the key finding related to Monitoring for magnesium sulphate toxicity to guide bedside assessment, documentation, and the next nursing action.
Magnesium sulphate has a narrow therapeutic range (4-7 mEq/L), making vigilant, frequent monitoring of vital signs and reflexes essential for patient safety.
The antidote for magnesium toxicity, calcium gluconate, must always be readily available at the bedside of any patient receiving a magnesium sulphate infusion.
What if? If the patient's knee jerk reflex becomes absent but their respiratory rate is still normal, the nurse's first action should be to stop the magnesium infusion immediately and then notify the healthcare provider. This is because the loss of reflexes is the earliest sign of toxicity and precedes the more dangerous respiratory depression.

How to Approach the Question

Identify the question type: This is a priority-based question asking for the 'most important' parameter.
Analyze the core concept: The question is about monitoring for toxicity from magnesium sulphate, a CNS depressant.
Recall the key adverse effects: The major toxic effects are loss of deep tendon reflexes, respiratory depression, and cardiac arrest.
Apply a prioritization framework: Use the ABC (Airway, Breathing, Circulation) model. Respiratory depression is a 'Breathing' problem and represents the most immediate threat to life among the given options.
Evaluate the options based on priority: While loss of reflexes is the earliest sign and urine output is important for prevention, respiratory arrest is the most severe and fatal outcome. Therefore, monitoring respiration is the highest priority.
Select the answer that aligns with the highest priority assessment for preventing a life-threatening event.

Concept Tested & Keywords

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E6 Obstetrics Williams p. 31-51