First sign of magnesium sulphate toxicity is?
**Core Concept**
The question tests the understanding of **magnesium sulphate toxicity**, a critical aspect of obstetric care, particularly in the management of pre-eclampsia and eclampsia. Magnesium sulphate is used for its neuroprotective effects and to prevent seizures. However, its toxicity can lead to serious complications.
**Why the Correct Answer is Right**
The first sign of magnesium sulphate toxicity is related to its effects on the neuromuscular system. As magnesium levels rise, it can lead to decreased neuromuscular transmission, resulting in muscle weakness. The earliest clinical manifestation of this is often **loss of deep tendon reflexes**, which is a sensitive indicator of rising magnesium levels.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while respiratory depression is a sign of magnesium toxicity, it occurs at higher levels than the initial loss of reflexes.
**Option B:** Incorrect as cardiac arrest is a late and severe complication of magnesium sulphate toxicity.
**Option D:** Incorrect because while magnesium sulphate can cause flushing and other minor side effects, these are not the first signs of toxicity.
**Clinical Pearl / High-Yield Fact**
It's crucial to monitor patients receiving magnesium sulphate closely, checking for the absence of deep tendon reflexes as an early warning sign of potential toxicity. This allows for prompt intervention to prevent more severe complications.
**Correct Answer:** D. Loss of deep tendon reflexes.