Drowsiness, Absent Reflexes and 20 mL of Urine on Magnesium Sulfate
Mrs Salma, 29, gravida 2 para 1, is 34 weeks pregnant and was admitted six hours ago with severe pre-eclampsia: BP 168/112 mmHg, 3+ proteinuria, headache and visual flashes. She received a 4 g intravenous loading dose of magnesium sulfate over 20 minutes, followed by a maintenance infusion of 1 g/hour. At 03:00, the third hourly check, the nurse finds her drowsy but rousable, reporting flushing and feeling hot. Respirations are 10/min and shallow, deep tendon reflexes are absent, and she has passed 20 mL of urine in the last two hours. BP 146/94 mmHg, pulse 60, SpO2 95% on room air. The fetal heart rate is 136 bpm. The infusion is still running at 1 g/hour. The chart shows the last reflex and respiratory check was recorded two hours ago. You are the only nurse on a ward of seven patients; the obstetrician is in theatre performing an emergency caesarean and the midwife has gone to collect blood.
1. What is happening to Mrs Salma, and what are your first five actions?
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Recognition. This is magnesium sulfate toxicity. The therapeutic range is narrow (roughly 2–3.5 mEq/L, or 1–2 mmol/L depending on units used), and the signs progress in a predictable order: loss of deep tendon reflexes, then respiratory depression, then cardiac arrest. She has a respiratory rate of 10, absent reflexes, oliguria (20 mL in 2 hours) and drowsiness, on a 1 g/h infusion with a two-hour assessment gap. Magnesium is cleared by the kidney, so poor output accelerates accumulation.
First five actions:
- Stop the infusion at the pump immediately. Do not wait for the obstetrician; the prescription can be rewritten, a respiratory arrest cannot.
- Call for help. Pull the emergency bell, ask any available colleague to bring the resuscitation trolley, oxygen and calcium gluconate, and call the obstetrician and anaesthetist out of theatre.
- Airway and breathing. Position her in a left lateral tilt, give oxygen at 10–15 L/min by mask, and monitor respiratory rate and SpO2 continuously. Be ready to assist ventilation with a bag-valve mask if her breathing deteriorates further.
- Antidote. Give calcium gluconate 10% 10 mL intravenously over about 10 minutes (or calcium chloride 10% 10 mL through a large patent vein) as prescribed or under the unit's standing order.
- Monitor and reassess. Cardiac monitor, urinary catheter to measure hourly output, fetal heart auscultation, and blood for magnesium level, creatinine, urea and electrolytes. Record the exact times of stopping the infusion, giving the calcium and calling for help, and state the observations factually.
2. Which assessments should have been done hourly during this infusion, and how would you explain the failure to the reviewing committee without apportioning blame inaccurately?
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The hourly bundle for magnesium sulfate:
- Respiratory rate and depth, with a hard stop below 12/min.
- Deep tendon reflexes, usually the biceps and patellar.
- Urine output, minimum 30 mL/h (roughly 0.5 mL/kg/h); magnesium is renally excreted.
- Level of consciousness, plus any nausea, flushing, visual change or slurred speech.
- BP, pulse, SpO2 and continuous or regular fetal heart monitoring.
- Serum magnesium and renal function at the prescribed intervals.
- Calcium gluconate at the bedside as the known antidote.
Explaining the gap honestly. The record shows a two-hour gap. On a ward with seven patients and one nurse, the checks were missed, not because no one knew they mattered, but because the workload and skill mix did not support the monitoring the drug requires. A fair review would separate three issues:
- A clinical monitoring failure - the checks stopped.
- A systems failure - a high-alert infusion on a general ward, with the only midwife sent for blood and the obstetrician in theatre, means no one was free to do an hourly round.
- A documentation failure - the chart was not completed, so the gap was invisible until the patient became symptomatic. Present the facts in time order, state what you did when you found her, and propose the fix: a magnesium observation chart with mandatory hourly signatures, a one-to-one or co-located high-dependency bed, and an escalation trigger. Avoid blaming individual staff by name in a way that stops others reporting honestly.
3. Once she stabilises, the ward nurse asks whether the magnesium can simply be restarted at the same rate. How do you answer, and what teaching does Mrs Salma need?
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Restarting. Not at the same rate, and not on a verbal message. The infusion restarts only on a fresh written order, after the deep tendon reflexes have returned, the respiratory rate is safely above 12–16/min and urine output is at least 30 mL/h. The prescriber will consider a reduced rate, review the magnesium level and creatinine, and keep calcium gluconate at the bedside. If toxicity recurs, the alternative is not 'push through it' - it is to weigh continuing magnesium against delivering the baby, which is the definitive treatment for severe pre-eclampsia. Magnesium is usually continued for 24 hours after delivery for seizure prophylaxis, so the question of restarting is not hypothetical.
What Mrs Salma needs to know:
- Why she is receiving magnesium: to prevent eclamptic seizures, not to treat her blood pressure.
- The warning sensations to report immediately - feeling very hot or flushed, weakness, difficulty breathing, feeling sleepy or 'far away', reduced urine, blurred vision, severe headache, epigastric pain.
- That she will be checked hourly, including her reflexes and breathing, and that this is expected, not an inconvenience.
- That the fetal heart will be listened to regularly.
- Who to call (call bell within reach) and that she must not get up alone.
Also hand over clearly to the next shift: the event, the time the infusion was stopped and restarted, the new rate, the calcium gluconate location, and that a review of the observation chart is expected.