In a patient on magnesium sulphate therapy, usually at what levels the patellar (knee) reflex disappears
**Core Concept**
Magnesium sulphate therapy can cause neuromuscular blockade by blocking acetylcholine release at the neuromuscular junction. This effect is utilized in the treatment of certain conditions such as eclampsia and pre-eclampsia.
**Why the Correct Answer is Right**
The patellar reflex, also known as the knee jerk reflex, is a monosynaptic reflex that involves the contraction of the quadriceps muscle in response to stimulation of the L2-L4 nerve roots. Magnesium sulphate therapy can cause a decrease in the release of acetylcholine, a neurotransmitter that plays a crucial role in the transmission of nerve impulses at the neuromuscular junction. As a result, the patellar reflex disappears when serum magnesium levels reach a certain threshold. This effect is seen when serum magnesium levels exceed 4-5 mmol/L.
**Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because the patellar reflex disappears at lower magnesium levels than those listed here.
- **Option B:** This option is incorrect because the patellar reflex disappears at higher magnesium levels than those listed here.
- **Option C:** This option is incorrect because the patellar reflex disappears at levels that are not typically associated with magnesium sulphate therapy.
**Clinical Pearl / High-Yield Fact**
It's essential to monitor serum magnesium levels in patients receiving magnesium sulphate therapy, as excessive levels can cause neuromuscular blockade and respiratory depression.
**Correct Answer:** C.