Atropine as preanesthesia has all effects except
**Core Concept**
Atropine, a non-selective muscarinic receptor antagonist, is often administered preanesthetically to reduce salivation, bronchial secretions, and cardiac vagal tone. This results in a decrease in the parasympathetic tone, thereby reducing the risk of bradycardia and asystole during anesthesia.
**Why the Correct Answer is Right**
Atropine's preanesthetic administration leads to a decrease in salivation and bronchial secretions, reducing the risk of aspiration and facilitating endotracheal intubation. Additionally, atropine increases heart rate and cardiac output by blocking the vagal inhibitory effects on the sinoatrial node. This is primarily due to the blockade of muscarinic receptors (M2 subtype) in the heart, which are responsible for mediating the vagal inhibitory effects on heart rate.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as atropine does indeed decrease salivation and bronchial secretions. However, the mechanism is not due to its effects on the central nervous system but rather its peripheral action on muscarinic receptors in the salivary and bronchial glands.
**Option B:** This option is incorrect as atropine does indeed increase heart rate and cardiac output. However, this is not due to its direct effects on the sympathetic nervous system but rather its blockade of muscarinic receptors in the heart.
**Option C:** This option is incorrect as atropine does indeed have a role in anesthesia, particularly in reducing the risk of bradycardia and asystole. However, its primary mechanism is not through its effects on the central nervous system but rather its peripheral action on muscarinic receptors.
**Clinical Pearl / High-Yield Fact**
It's essential to note that atropine's effects can be reversed with physostigmine, a cholinesterase inhibitor that increases acetylcholine levels and counteracts atropine's effects.
**Correct Answer: D.**