Nursing care
Magnesium Imbalances nursing care: what to assess and what to do first
Written and reviewed by Dana Whitfield, RN, MSN · 5 min read · Updated September 2026
Short answer
Hypomagnesaemia causes neuromuscular irritability, tremors, hyperreflexia and arrhythmias, while hypermagnesaemia causes depressed reflexes, weakness and respiratory failure at high levels. The clue experienced nurses look for is a potassium that will not correct despite replacement, since magnesium is required for potassium to move into cells and stay there.
The pathophysiology in one pass
Magnesium is the second most abundant intracellular cation and acts as a cofactor for hundreds of enzyme systems, including the sodium-potassium ATPase pump that keeps potassium inside the cell. It is lost through the same routes as potassium, poor intake, diarrhoea, diuretics and alcohol use, which is why the two electrolytes so often fall together and why magnesium follows potassium in clinical practice.
Because magnesium is needed to run the pump that retains potassium, a magnesium deficit causes the kidneys to keep wasting potassium even while it is being replaced intravenously. This is the single most useful fact on this page: a potassium level that will not correct despite adequate replacement is usually a magnesium problem, and checking and correcting magnesium first is what actually fixes the potassium. High magnesium is rarer and almost always a renal excretion problem, since healthy kidneys clear excess magnesium efficiently.
Assessment findings that matter
In hypomagnesaemia, look for tremors, muscle twitching, hyperreflexia and, in severe cases, tetany that can mimic hypocalcaemia because the two often coexist. Check the cardiac monitor for a prolonged QT interval and be alert to torsades de pointes, since low magnesium is a recognised cause of this arrhythmia independent of calcium status. Ask about alcohol use, chronic diarrhoea, malabsorption and diuretic therapy, the commonest contributors on general wards.
In hypermagnesaemia, the picture is one of central nervous system and neuromuscular depression: diminished or absent deep tendon reflexes, hypotension, bradycardia and, as the level climbs further, respiratory depression. This is almost always seen in renal failure or in obstetric patients receiving magnesium sulfate for pre-eclampsia, so the deep tendon reflex check is a standard part of monitoring anyone on a magnesium infusion. A disappearing patellar reflex is the earliest reliable warning sign and should prompt reassessment before the respiratory rate falls.
What the exam asks about this
NCLEX questions frequently pair hypomagnesaemia with alcohol use disorder or malnutrition and ask which assessment finding to expect, favouring hyperreflexia, tremor or a positive Chvostek's sign over vaguer distractors. A common scenario tests whether you recognise that a low potassium unresponsive to replacement points to magnesium, so learn to spot that pattern rather than simply repeating the potassium infusion.
For hypermagnesaemia, the exam leans heavily on the magnesium sulfate infusion for pre-eclampsia, testing whether you know to check deep tendon reflexes, respiratory rate and urine output before each dose, and to hold the infusion if reflexes are absent or the respiratory rate falls below 12 per minute. Expect a question asking which antidote to have at the bedside, and the correct answer is calcium gluconate, not calcium chloride, which is reserved for different indications.
Nursing interventions in priority order
For hypomagnesaemia, place the patient on seizure and fall precautions given the neuromuscular irritability, and put them on continuous cardiac monitoring if the level is significantly low or the QT interval is prolonged. Check the potassium and calcium at the same time, since correcting magnesium is often the step that finally allows those levels to stabilise, and reassess after replacement rather than assuming one round fixes everything.
For hypermagnesaemia, the priority before any scheduled dose of magnesium sulfate is to assess deep tendon reflexes, respiratory rate and urine output; hold the dose and notify the prescriber if reflexes are absent, respiratory rate is below 12, or output is below 30 mL per hour. Keep calcium gluconate at the bedside as the antidote, and maintain continuous fetal and maternal monitoring in the obstetric setting, since this population is the one most likely to receive therapeutic magnesium.
Medications and monitoring
Hypomagnesaemia is corrected with oral magnesium oxide for mild deficits or intravenous magnesium sulfate for symptomatic or severe cases, infused slowly because rapid administration can cause flushing, hypotension or cardiac arrest. Monitor the ECG during IV replacement and recheck the magnesium level after the infusion rather than relying on symptom resolution alone, since the neuromuscular signs can lag behind the corrected level.
Magnesium sulfate given therapeutically, most often for pre-eclampsia or eclampsia prophylaxis, requires reflex, respiratory and renal monitoring before every dose and typically hourly during a continuous infusion. Therapeutic serum levels are generally 4 to 7 mEq/L for seizure prophylaxis, and levels above that range risk loss of reflexes, respiratory depression and, eventually, cardiac arrest, so the infusion is titrated and monitored closely rather than given as a fixed rate throughout.
When to escalate
Escalate hypomagnesaemia immediately if there is a seizure, a new arrhythmia such as torsades de pointes, or tetany affecting the airway, since these represent an unstable neuromuscular or cardiac state rather than a level that can wait for the next scheduled dose. A potassium that remains uncorrectable after magnesium has also been checked and treated should prompt a call to the prescriber, since it may signal an ongoing loss the current orders are not addressing.
Escalate hypermagnesaemia at once if deep tendon reflexes are absent, the respiratory rate falls below 12, or there is bradycardia or hypotension, since this trajectory can progress to respiratory arrest. In an obstetric patient on magnesium sulfate, any of these findings means stopping the infusion, administering calcium gluconate as ordered, and notifying the provider immediately rather than simply slowing the rate.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our reduction of risk potential practice questions are the closest set to what this page covers.
One question from the reduction of risk potential set
Four hours after a cardiac catheterization via the right femoral artery, the nurse notes the client's right dorsalis pedis pulse is now faint and the foot is cool and pale. What is the nurse's priority action?
Rationale
A pulse that was present and is now faint, with a cool, pale extremity distal to the puncture site, is arterial occlusion until proven otherwise — a limb-threatening complication that needs the provider now. Documenting and rechecking wastes the window, warming treats the symptom and masks the change, and asking the client to move the ankle neither restores flow nor gives you new information.
Answer: C
Common questions
What is the normal range for serum magnesium?
Normal serum magnesium is generally 1.5 to 2.5 mg/dL (0.65 to 1.05 mmol/L). Because it is largely an intracellular ion, a normal serum level does not always rule out a total-body deficit, particularly after prolonged diuretic use or malabsorption.
Why won't my patient's potassium correct?
If potassium replacement is not raising the level despite adequate dosing, check magnesium. Magnesium is needed for the sodium-potassium pump to hold potassium inside the cell, so a coexisting magnesium deficit will keep the kidneys wasting potassium until it is corrected.
What do you assess before giving magnesium sulfate?
Check deep tendon reflexes, respiratory rate and urine output before every dose or at regular intervals during a continuous infusion. Hold the dose and notify the prescriber if reflexes are absent, respiratory rate is below 12 per minute, or output is under 30 mL per hour.
What is the antidote for magnesium toxicity?
Calcium gluconate is the antidote, kept at the bedside whenever a patient is receiving a magnesium sulfate infusion. It is given if reflexes disappear or respiratory depression develops, alongside stopping the infusion and notifying the provider.
Does low magnesium cause the same signs as low calcium?
Yes, largely, because both cause neuromuscular irritability, and Chvostek's and Trousseau's signs can appear in either. The two deficiencies frequently coexist, so a patient with tetany-like signs should have both levels checked rather than one assumed to explain the picture.
More on reduction of risk potential