In a woman on magnesium sulphate for pre-eclampsia, loss of the patellar reflex comes before respiratory depression, and respiratory depression before cardiac arrest. Checking the knee jerk, respiratory rate and urine output each hour catches toxicity early, without waiting for a serum level. Oliguria is the usual reason magnesium accumulates, because it is renally cleared.
- Check patellar reflex, respiratory rate and urine output every hour while magnesium sulphate runs.
- Withhold the next dose if reflexes are absent, respiratory rate is under 12–16 per minute, or urine output is under 30 mL an hour.
- Keep 10 mL of 10% calcium gluconate at the bedside and give it slowly IV for respiratory depression.
- In oliguria with reflexes and breathing preserved, reduce the IV maintenance rate (or withhold the IM dose, as above), review renal function and check a serum level where available.
Why it matters
Where serum magnesium levels are not available on demand, these three checks are the whole monitoring plan.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for obstetrics & gynaecology, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free