In a patient on magnesium sulphate therapy, usually at what levels the patellar (knee) reflex disappears

Ans. b (10-12 mEq/L) (Ref. William's Obstetrics 22nd ed., p 789; Dutta Obstetrics, 6th ed., p 249)MAGNESIUM SULPHATE# Magnesium sulphate is the treatment of choice for the prevention and treatment of eclamptic seizures.# It reduces motor end plate sensitivity to acetylcholine.# It induces cerebral vasodilatation, dilates uterine arteries, increases production of endothelial prostacyclin and inhibits platelet activation.# Magnesium may prevent seizures by interacting with NMDA receptors in the CNS.# The therapeutic level of serum magnesium is 4-7 mEq/L. Eclamptic convulsions are almost always prevented by maintaining plasma magnesium levels between A--7 mEq/L (2.0-3.5 mmol/L).# Repeat injections are given only if:- Knee jerks are present,- Urine output is > 30 mL/hour, and- Respiration rate is > 12/min.# Loss of DTRs serves as the earliest warning sign of impending magnesium toxicity, because a further increase leads to respiratory depression.- Patellar reflex disappears when magnesium level reaches 10 mEq/L (12 mg/dL) - curariform action.- Respiratory depression develops - when magnesium levels go > 10 mEq/L,- respiratory paralysis and arrest follows when levels = 12 mEq/L, .# Rx:- With calcium gluconate 1 g IV and withholding magnesium sulphate reverses mild to moderate respiratory depression.- Usually magnesium sulphate is otherwise discontinued 24 hours after delivery.RegimenLoading doseMaintenance dosePritchard4 g IV over 3-4 min, 10 mg deep IM5 g IM in alternate buttockZuspan4 g IV over 5-10 min1-2 g/hour IV infusionSibai6 g IV over 20 min2 g/hour IV infusionRegimens for the administration of magnesium sulphate for seizure prophylaxis in women in labor with preeclampsia# Intramuscular- 10 g (5 g IM deep in each buttock)- 5 g IM deep q4h, alternating sides# Intravenous- 6-g bolus over 15 min- 1-3 g/h by continuous infusion pump- May be mixed in 100 mL crystalloid; if given by intravenous push, make up as 20% solution; push at maximum rate of 1 g/min- 40-g MgS04.7H,0 in 1000 mL Ringer's lactate; run at 25-75 mL/h (1-3 g/h).