Pre-eclampsia on Magnesium Sulfate: Absent Reflexes and Slow Breathing

Interpretation: magnesium sulfate toxicity. The therapeutic serum range is roughly 4–7 mEq/L; 9.4 mEq/L is above it.

The expected progression of magnesium toxicity is:

• Loss of deep tendon reflexes (broadly 8–10 mEq/L).
• Respiratory depression (roughly 10–12 mEq/L).
• Cardiac conduction disturbance and arrest at higher levels (usually above 15 mEq/L).

This patient already has absent reflexes, a respiratory rate of 10/min and desaturation - she is at the respiratory depression stage, not merely at the reflex-loss stage.

Earliest and most useful bedside warning: loss of deep tendon reflexes. It occurs before respiratory depression and is assessable at the bedside every hour without a laboratory. That is why hourly reflex checks, respiratory rate and urine output are the core monitoring triad for any woman on magnesium sulfate.

Why she is accumulating:

• Magnesium is cleared almost entirely by the kidney. Her urine output (15, 12 and 18 mL/h) is well below the usual 30 mL/h threshold used to trigger review.
• The blurred vision and nausea may be magnesium effect, worsening pre-eclampsia, or both - they should not be dismissed as benign.
• Reduced fetal heart variability can reflect magnesium effect on the fetus, but also uteroplacental insufficiency, so it must be interpreted together with maternal status.

Do not miss: the drowsiness could also be a developing eclamptic process or a cerebrovascular event. The absent reflexes plus slow respiratory rate plus a high level make magnesium toxicity the leading explanation, but she still needs urgent medical assessment.

Sequence of actions:

1. Stop the magnesium sulfate infusion immediately. This is the single most important action and is within nursing authority.
2. Call for help: obstetric registrar/consultant on call and the anaesthetist, plus the midwife-in-charge. Call a rapid response or obstetric emergency team rather than waiting for the registrar to leave theatre.
3. Airway, breathing, circulation: position left lateral tilt or left lateral, suctions available, give oxygen to maintain SpO2 at 94–98%, and attach continuous pulse oximetry and cardiac monitoring.
4. Give the antidote: calcium gluconate 1 g intravenously - this is 10 mL of 10% calcium gluconate - given slowly over 3–10 minutes. Give it under a written or verbal medical order or the unit's approved standing order, and document. Do not give it as a rapid bolus: fast injection can cause hypotension, bradycardia and arrhythmia.
5. Monitor respiratory rate, oxygen saturation, reflexes, blood pressure, conscious level and urine output at least every 15 minutes until stable, then hourly. Insert or check a urinary catheter to measure output accurately.
6. Continue fetal surveillance and note the trace times; reduced variability in this context is expected with magnesium but must be re-evaluated once maternal status is stable.
7. Prepare for possible seizure and for delivery: keep the eclampsia box and airway equipment at the bedside, alert the theatre, and anticipate that delivery may be indicated.
8. Document the observations, the time the infusion was stopped, the antidote given, and the names and times of everyone contacted.

The midwife should respectfully but clearly refuse to give more magnesium and explain why, while still treating the blood pressure.

Reasoning to state to the doctor:

• The problem is not under-treatment of pre-eclampsia with magnesium - it is magnesium excess. The reflexes are absent, the respiratory rate is 10/min and the level is 9.4 mEq/L. A further 2 g would deepen respiratory depression and risks apnoea and cardiac arrest.
• Magnesium is not the antihypertensive; it is given for seizure prophylaxis. It will not correct a blood pressure of 168/112 mmHg, so increasing it does not even address the stated goal.
• The blood pressure still needs treating, and labetalol can be given as prescribed - but with the caveat that the reading must be rechecked, and that persistent severe hypertension with blurred vision, nausea and fetal compromise may indicate that delivery, not more medical therapy, is the definitive management.

How to handle it safely:

• Repeat the observations in the doctor's presence or read them back explicitly, so the decision is made on current data rather than the admission data.
• Ask for a documented plan: target blood pressure, the antihypertensive escalation route, whether a magnesium level will be repeated, and what the restart criteria for magnesium are (typically reflexes present, respiratory rate adequate, urine output adequate, level falling).
• Escalate to the consultant obstetrician and anaesthetist if the doctor insists. The midwife's accountability for a potentially fatal drug error does not disappear because a junior doctor gave a verbal order.
• Document the concern, the advice sought, and the final plan - including who authorised it - in the notes and on the obstetric early warning chart.