From the Guidelines
The adverse effect that should be considered when monitoring this patient receiving intravenous magnesium sulfate is respiratory depression. This 22-year-old pregnant woman presenting with seizure and hypertension (160/115 mm Hg) is likely experiencing eclampsia, for which magnesium sulfate is the first-line treatment. While magnesium sulfate effectively prevents and treats eclamptic seizures, it can cause respiratory depression, particularly at higher serum concentrations, as noted in the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1. Magnesium acts as a central nervous system depressant and can suppress respiratory drive. The initial loading dose of 6g followed by a 2g/hour infusion requires careful monitoring of respiratory rate, oxygen saturation, and deep tendon reflexes, as loss of reflexes often precedes respiratory depression, with neurological effects ranging from loss of tendon reflexes, sedation, severe muscular weakness, and respiratory depression seen at magnesium levels of 4–5 mmol/L 1. If respiratory rate falls below 12 breaths per minute or reflexes become absent, the infusion should be reduced or temporarily discontinued. Calcium gluconate should be readily available as an antidote to reverse severe magnesium toxicity. Other potential side effects of magnesium therapy include hypotension, flushing, and reduced cardiac conduction, but respiratory depression is the most concerning adverse effect requiring vigilant monitoring, especially considering the risk of iatrogenic overdose in pregnant women with oliguria 1. Key points to consider when monitoring this patient include:
- Respiratory rate and oxygen saturation
- Deep tendon reflexes
- Potential for hypotension, as magnesium produces vasodilation and may cause hypotension if administered rapidly 1
- Availability of calcium gluconate as an antidote for severe magnesium toxicity.
From the FDA Drug Label
ADVERSE REACTIONS The adverse effects of parenterally administered magnesium usually are the result of magnesium intoxication. These include flushing, sweating, hypotension, depressed reflexes, flaccid paralysis, hypothermia, circulatory collapse, cardiac and CNS depression proceeding to respiratory paralysis.
Clinical indications of a safe dosage regimen include the presence of the patellar reflex (knee jerk) and absence of respiratory depression (approximately 16 breaths or more/min).
Reflexes may be absent at 10 mEq magnesium/L, where respiratory paralysis is a potential hazard.
The adverse effect that should be considered when monitoring this patient is Respiratory depression. This is because the patient is being given a high dose of magnesium sulfate, and respiratory depression is a potential consequence of magnesium intoxication, as indicated by the absence of respiratory depression being a clinical indication of a safe dosage regimen 2, 2.
From the Research
Adverse Effects of Magnesium Sulfate
- The patient is being given intravenous magnesium sulfate, and the adverse effect to consider is respiratory depression 3.
- Magnesium sulfate can cause respiratory depression, especially in patients with myasthenia gravis, as it can exacerbate muscle weakness and lead to acute respiratory failure 3.
- Other studies have reported adverse effects such as a burning or heat sensation 4, but respiratory depression is a more critical concern in this scenario.
- It is essential to monitor the patient's respiratory status closely, especially since she has been given a large dose of magnesium sulfate (6 g) and is on a continuous infusion (2 g/hour).
- The patient's initial presentation with a seizure and lethargy also increases the risk of respiratory depression, and careful monitoring is necessary to prevent complications.
- Other options such as osmotic demyelination syndrome, QT prolongation, seizure, and tetanic muscle contractions are not directly related to the administration of magnesium sulfate in this context 5, 4, 6, 7.