Neuroanesthesia — MCQs

Question 1: Intracranial pressure (ICP) is raised due to:

• A. Ketamine (Correct Answer)
• B. Scoline
• C. Halothane
• D. Ether

Explanation: ### Explanation **Correct Answer: A. Ketamine** **Mechanism of Action:** Ketamine is a dissociative anesthetic that acts as an NMDA receptor antagonist. Unlike most other induction agents, Ketamine is a potent **cerebral vasodilator**. It increases Cerebral Blood Flow (CBF) and Cerebral Metabolic Rate of Oxygen ($CMRO_2$), which leads to a significant **increase in Intracranial Pressure (ICP)**. Consequently, it is generally contraindicated in patients with space-occupying lesions, head injuries, or intracranial hypertension. **Analysis of Other Options:** * **B. Scoline (Succinylcholine):** While Succinylcholine can cause a transient, mild increase in ICP (likely due to muscle fasciculations and increased CVP), it is **not** the primary answer in this context. In modern neuroanesthesia, its benefits for rapid sequence induction often outweigh this minor risk, and the effect can be blunted with defasciculating doses of non-depolarizers. * **C. Halothane:** Halothane is a potent vasodilator and can increase ICP; however, in the hierarchy of "ICP-elevating drugs" for exam purposes, Ketamine is the classic "high-yield" answer due to its profound effect on cerebral hemodynamics. * **D. Ether:** While Ether causes some vasodilation, it is obsolete in modern practice and less potent in its ICP-elevating effects compared to Ketamine. **High-Yield Clinical Pearls for NEET-PG:** * **The "Neuro-Friendly" Induction Agent:** **Thiopentone** (and Propofol) are the drugs of choice for neurosurgery as they decrease $CMRO_2$, CBF, and ICP (cerebral protection). * **Exceptions for Ketamine:** Recent studies suggest that if a patient is well-ventilated (normocapnia maintained), the ICP increase from Ketamine may be minimal, but for MCQ purposes, **Ketamine = Increased ICP**. * **Inhalational Agents:** All volatile anesthetics cause vasodilation at >1 MAC, but **Sevoflurane** is preferred over Halothane in neurosurgery because it has the least effect on cerebral autoregulation.