Which of the following local anesthetics is more cardiotoxic?

Correct Answer: B

Rationale: The correct answer is B: Bupivacaine. Bupivacaine is more cardiotoxic compared to the other local anesthetics listed. This is due to its higher potency in blocking cardiac sodium channels, leading to a higher risk of cardiac toxicity, including arrhythmias and cardiac arrest. Procaine, lidocaine, and mepivacaine are less cardiotoxic as they have lower affinity for cardiac sodium channels and are less likely to cause significant cardiac adverse effects. It is important to be cautious when using bupivacaine to minimize the risk of cardiotoxicity.

Correct Answer: A

Rationale: The correct answer is A: Myasthenia gravis. In myasthenia gravis, there is a decrease in the number of available acetylcholine receptors at the neuromuscular junction, leading to muscle weakness. Nondepolarizing muscle relaxants work by blocking acetylcholine receptors, so in myasthenia gravis, there are fewer receptors available for the drug to bind to, resulting in an augmented neuromuscular blockade. Burns (B), asthma (C), and Parkinsonism (D) do not directly affect the number of acetylcholine receptors at the neuromuscular junction, so they would not enhance the blockade produced by nondepolarizing muscle relaxants.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Epinephrine is a sympathomimetic agent that constricts blood vessels, reduces bleeding, and prolongs the effect of local anesthetics. 2. By vasoconstriction, epinephrine delays systemic absorption of the anesthetic, leading to a longer duration of action. 3. Xylometazoline is a nasal decongestant, not used for nerve blocks. 4. Isoproterenol and dobutamine are primarily used for cardiac conditions, not for local anesthesia. Summary: Epinephrine is the correct choice due to its vasoconstrictive properties prolonging the effect of local anesthetics. Xylometazoline, Isoproterenol, and Dobutamine are incorrect as they do not serve the same purpose in nerve blocks.

Correct Answer: A

Rationale: The correct answer is A: Labetalol. Labetalol is a non-selective beta blocker with additional alpha-1 blocking properties. This combination of alpha-1 and beta-blocking effects makes it unique among the choices. Alpha-1 blockade helps reduce peripheral vascular resistance, while beta-blocking action decreases heart rate and contractility. This dual mechanism makes labetalol effective in treating hypertension. Betaxolol (B) is a selective beta-1 blocker, Propranolol (C) is a non-selective beta blocker, and Timolol (D) is a non-selective beta blocker as well. These choices lack the alpha-1 blocking effect present in labetalol, making them incorrect for this question.

Correct Answer: A

Rationale: The correct answer is A, depression of the medullar respiratory center. Hypnotics can suppress the central nervous system, leading to respiratory depression, which can result in death. This is the most common cause of death in hypnotic overdoses. B: Hypothermia is not a usual cause of death in hypnotic overdoses. C: Cerebral edema is not a direct result of hypnotic overdose and would not typically be the cause of death. D: Status epilepticus is not a typical outcome of hypnotic overdose and would not directly lead to death in this context.