Step 1: Think about what magnesium does in the body:
Magnesium sulfate is a membrane stabiliser. It reduces acetylcholine release at the neuromuscular junction and acts as a calcium channel blocker.
An excess therefore weakens muscles. The kidneys are the only route of loss, so poor urine output makes it worse.
Step 2: Link each action to a monitoring parameter:
Weak muscles mean the reflexes are lost first, then the respiratory muscles fail. So deep tendon reflexes and respiratory rate are the two clinical signs of toxicity.
Renal clearance depends on urine output, so this is the third parameter.
Step 3: Use the order in which signs appear:
The signs follow the blood level. At about 8 to 10 mEq/L the knee jerk disappears. At about 12 to 15 mEq/L breathing slows or stops. At higher levels the heart stops.
Watching the early sign (reflexes) lets us act before the later ones.
Step 4: Apply this to the four statements:
Respiratory rate above the safe limit (the statement gives more than 14 per minute) is a required check. So statement 1 is correct.
Presence of the knee jerk is a required check. So statement 2 is correct.
Urine output of more than 100 mL in 4 hours is a required check. So statement 3 is correct.
Serum sodium does not tell us anything about magnesium, and hourly sodium checks are not part of the routine. So statement 4 is wrong.
Step 5: What to do if a parameter fails:
Hold the next dose and, if the signs are significant, stop the infusion. Give 10 mL of 10 percent calcium gluconate intravenously over 10 minutes.
Support breathing if needed. Serum magnesium levels can be checked in a mother with renal impairment.
Keep a vial of calcium gluconate at the bedside whenever the infusion is running. Check the three parameters again after the antidote is given, because magnesium is still present in the blood and the signs can return.
Final Answer:
The routine parameters are respiratory rate, deep tendon reflexes and urine output. The correct options are 1, 2 and 3.