Pregnancy (MFM)

Question 1

Effects of Magnesium at various serum levels?

Answer 1

Physiologic Affects of the Use of Magnesium and the Associated Concentrations

 Effect	 Serum Level in mEq/L
 Anticonvulsant prophylaxis	4-7
 EKG changes	5-10
 Loss of deep tendon reflexes	8-10
 Respiratory paralysis	12-15
 Cardiac arrest	20

Question 2

Magnesium toxicity can present with? Treat with?

Answer 2

respiratory distress as evidenced by her respiratory acidosis, accessory muscle use, and hypoxia, in the setting of a markedly elevated magnesium level concerning for magnesium toxicity and should be given IV calcium gluconate. The most common cause for severe magnesium toxicity is magnesium infusion used for the treatment of preeclampsia. Because magnesium is rapidly cleared by the kidneys, other patients with magnesium toxicity include those who are on magnesium supplementation and have renal failure (usually undiagnosed kidney disease or acute insult).

The toxic effect of magnesium is linked to the level of magnesium found in the serum. The most common findings of early onset toxicity include nausea, muscle weakness (often detected as decreased deep tendon reflexes), and low blood pressure. As serum magnesium levels rise, the sinoatrial (SA) and atrioventricular (AV) node can be affected causing EKG changes such as a prolonged PR interval and intraventricular conduction delay. Eventually there will be loss of respiratory muscle tone leading to respiratory paralysis and/or arrhythmia leading to cardiac arrest.