Neuroanesthesia Practice Questions

Q: Which of the following drugs does not affect the absorption and secretion of cerebrospinal fluid?

Nitrous oxide. The dynamics of Cerebrospinal Fluid (CSF) are governed by its rate of production (secretion) and its rate of reabsorption. Most anesthetic agents alter these parameters, which is a critical consideration in neuroanesthesia for managing intracranial pressure (ICP). **Explanation of the Correct Answer:** **Nitrous Oxide (N₂O)** is the correct answer because it has **no significant effect** on either the production or the reabsorption of CSF. While it is a potent cerebral vasodilator (which can increase cerebral blood volume), it remains neutral regarding CSF kinetics. **Analysis of Incorrect Options:** * **Halothane:** This volatile anesthetic **increases the resistance** to CSF reabsorption and may also increase production. This dual effect contributes to a significant rise in ICP, making it less favorable for patients with space-occupying lesions. * **Ketamine:** It is known to **increase the rate of CSF production** without significantly affecting reabsorption. This, combined with its vasodilatory effect, leads to an increase in ICP. * **Thiopentone Sodium:** Barbiturates like thiopentone **decrease the rate of CSF production**. By reducing cerebral metabolic rate (CMRO₂) and cerebral blood flow, they are traditionally used for "brain protection" and to lower ICP. **High-Yield Clinical Pearls for NEET-PG:** * **Etomidate and Propofol:** Both decrease the rate of CSF production, similar to thiopentone. * **Acetazolamide and Furosemide:** These are non-anesthetic drugs frequently tested; both **decrease** CSF production. * **Isoflurane:** Unique among volatiles as it **facilitates (increases) CSF reabsorption**, making it a preferred volatile agent in neurosurgery compared to Halothane. * **Summary Rule:** Most intravenous induction agents (except Ketamine) decrease CSF production, while most volatile agents (except Isoflurane) increase resistance to reabsorption.

Q: Which of the following increases cerebral oxygen consumption?

Ketamine. **Explanation:** The primary determinant of cerebral metabolic rate for oxygen (**CMRO2**) is neuronal activity. In neuroanesthesia, most intravenous anesthetics are "cerebro-protective" because they decrease both CMRO2 and Cerebral Blood Flow (CBF). **1. Why Ketamine is Correct:** Ketamine is a unique intravenous anesthetic (an NMDA receptor antagonist) that causes **dissociative anesthesia**. Unlike most other induction agents, it **increases CMRO2**, CBF, and intracranial pressure (ICP). It stimulates the sympathetic nervous system and increases neuronal activity in certain brain regions, leading to an increase in oxygen demand. **2. Why the Other Options are Incorrect:** * **Propofol (Option A):** A potent cerebral metabolic suppressant. It causes a dose-dependent decrease in CMRO2 and CBF, making it a preferred agent for neurosurgery. * **Thiopentone (Option C):** A barbiturate that significantly reduces CMRO2 by suppressing neuronal electrical activity. It is historically used for "brain protection" during focal ischemia. * **Alfentanil (Option D):** As an opioid, it generally causes a mild decrease or maintains stability in CMRO2 and CBF, provided ventilation is controlled and $PaCO_2$ remains normal. **Clinical Pearls for NEET-PG:** * **The "Rule of Exceptions":** Almost all IV anesthetics decrease CMRO2 and CBF; **Ketamine** is the notable exception. * **Inhalational Agents:** Most volatile anesthetics (like Isoflurane) **decrease CMRO2** but **increase CBF** (due to vasodilation), a phenomenon known as "uncoupling." * **Drug of Choice:** Propofol is the induction agent of choice in neurosurgery due to its rapid onset and ability to reduce ICP. * **Ketamine Caution:** Traditionally contraindicated in patients with space-occupying lesions or high ICP, though it may be used if the patient is adequately ventilated and co-administered with benzodiazepines/propofol.

Q: Which muscle relaxant is known to increase intracranial pressure?

Suxamethonium. **Explanation:** **Suxamethonium (Succinylcholine)** is the correct answer because it is the only muscle relaxant listed that consistently increases intracranial pressure (ICP). The underlying mechanism is attributed to a transient increase in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen ($CMRO_2$). Additionally, the intense fasciculations caused by this depolarizing agent increase central venous pressure and muscle spindle activity, which further contributes to the rise in ICP. While this increase is usually modest and transient, it can be clinically significant in patients with severely reduced intracranial compliance. **Analysis of Incorrect Options:** * **Mivacurium & Atracurium:** These are benzylisoquinolinium non-depolarizing relaxants. While they can cause histamine release (which might lead to vasodilation and a theoretical rise in ICP), they do not directly increase ICP. In clinical practice, they are generally considered safe for neurosurgery if hypotension is avoided. * **Vecuronium:** This is an aminosteroid non-depolarizing relaxant. It is considered "neuro-neutral" as it has no effect on ICP, heart rate, or blood pressure, making it a preferred choice for maintenance in neuroanesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **The "Pre-curarization" Technique:** The rise in ICP caused by Suxamethonium can be attenuated by administering a small "defasciculating" dose of a non-depolarizing muscle relaxant (e.g., Vecuronium) 3 minutes prior to induction. * **Rocunorium** is the preferred alternative to Suxamethonium for Rapid Sequence Induction (RSI) in neurosurgical emergencies where increased ICP is a concern. * **Pancuronium** should be avoided in neuroanesthesia because it causes tachycardia and hypertension, which can indirectly increase ICP.

Q: If pneumocephalus is created either by surgery or by performance of a pneumoencephalogram, it is suggested that nitrous oxide be avoided for how many days?

7 days. **Explanation:** The correct answer is **7 days**. This recommendation is based on the physical properties of **Nitrous Oxide ($N_2O$)** and its interaction with closed gas spaces in the body. **1. Underlying Medical Concept:** Nitrous oxide is 34 times more soluble in blood than nitrogen. When $N_2O$ is administered, it diffuses from the blood into an air-filled cavity (like a pneumocephalus) much faster than nitrogen can diffuse out. This leads to a rapid increase in the volume or pressure of the air pocket. In the rigid intracranial vault, this expansion can cause **Tension Pneumocephalus**, leading to brain herniation or neurological deterioration. Studies on gas reabsorption show that it takes approximately **7 days** for intracranial air to be sufficiently absorbed to safely allow $N_2O$ use without risking expansion. **2. Analysis of Options:** * **Options A, B, and C (4, 5, 6 days):** These timeframes are insufficient. While some air may be absorbed, a significant volume often remains. Clinical guidelines and standard textbooks (like Miller’s Anesthesia) specify a 7-day safety window to ensure complete or near-complete resolution of the air pocket. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "Second Gas Effect" and "Diffusion Hypoxia"** are other key $N_2O$ concepts often tested. * **Contraindications for $N_2O$:** Pneumothorax (most common), air embolism, bowel obstruction, intraocular gas bubbles (post-vitrectomy), and middle ear surgeries. * **Post-Vitrectomy Rule:** If **SF6 (Sulfur hexafluoride)** was used in the eye, avoid $N_2O$ for **7–10 days**. If **C3F8 (Perfluoropropane)** was used, avoid it for **8 weeks**. * **Tension Pneumocephalus Sign:** Look for the **"Mount Fuji Sign"** on a CT scan (separation of frontal lobes by air).

Q: Which inhalational agent is used in patients with raised intracranial tension?

Isoflurane. ### Explanation In neuroanesthesia, the primary goal is to maintain the balance between **Cerebral Blood Flow (CBF)** and **Cerebral Metabolic Rate of Oxygen (CMRO₂)** while preventing increases in **Intracranial Pressure (ICP)**. **Why Isoflurane is the Correct Answer:** Isoflurane is considered the gold standard inhalational agent for neurosurgery. It provides a potent reduction in CMRO₂ (neuroprotection) while having a relatively modest effect on cerebral vasodilation compared to older agents. Most importantly, at concentrations below 1 MAC, the decrease in CMRO₂ offsets the direct vasodilatory effect, resulting in minimal changes to CBF and ICP. It also preserves **cerebral autoregulation** better than other agents, making it the safest choice among the options for patients with raised ICT. **Analysis of Incorrect Options:** * **Enflurane:** It is strictly contraindicated in neurosurgery because it can induce **seizure-like activity** on EEG, which significantly increases CMRO₂ and ICP. * **Desflurane:** It can cause sympathetic stimulation and a rapid increase in CBF, especially during induction or dose escalation, which can lead to a dangerous rise in ICP. * **Sevoflurane:** While commonly used, it can impair cerebral autoregulation more than isoflurane at higher concentrations. However, in modern practice, it is a close second to isoflurane. In the context of standard PG exams, Isoflurane remains the classic "textbook" answer for raised ICT. **High-Yield Clinical Pearls for NEET-PG:** * **Ideal Agent:** **Propofol** (IV) is actually superior to all inhalational agents for raised ICT as it reduces both CBF and CMRO₂ (coupling). * **Nitrous Oxide (N₂O):** Should be avoided in neurosurgery as it increases CBF and can expand a pneumocephalus. * **Hyperventilation:** If an inhalational agent must be used, mild hypocapnia (PaCO₂ 30-35 mmHg) can blunt the vasodilatory response and help lower ICP.

Q: A patient is scheduled for neurosurgery for posterior fossa tumor. During the surgery the BP crashes and Et CO2 suddenly decreases to zero. What is the most likely diagnosis?

Venous air embolism. ***Venous air embolism*** - Neurosurgery in the **posterior fossa** often involves the **sitting position**, which creates a hydrostatic gradient favoring air entrainment into open veins from the surgical field, leading to **venous air embolism (VAE)**. - VAE classically presents with a sudden decrease in **end-tidal CO2 (EtCO2)** due to increased dead space, along with **hypotension** (BP crash) from cardiovascular collapse. *Trauma to respiratory center* - While trauma to the brainstem's respiratory center could cause respiratory arrest, it would primarily lead to **cessation of respiration**, not a sudden drop to zero in EtCO2 with accompanying hypotension, unless combined with severe cardiovascular compromise. - The sudden onset of both **BP crash** and **zero EtCO2** is more indicative of an acute circulatory or pulmonary event. *Dislodgement of endotracheal tube* - A dislodged endotracheal tube would lead to a sudden decrease (**or absence**) of EtCO2, but primarily due to **ventilation failure**. - While it could cause some degree of hypotension from hypoxia, a complete **BP crash** to zero is less likely to be the primary and immediate result compared to the profound cardiovascular effects of a large air embolism. *Wearing off effect of inhalation anesthesia* - The "wearing off effect" of inhalation anesthesia would typically lead to the patient **waking up and becoming more responsive**, with an **increase in blood pressure and heart rate**, not a sudden drop to zero in EtCO2 and a BP crash. - This scenario describes a **catastrophic complication**, not a normal physiological response to anesthetic metabolism.

Q: The position of the patient as shown below is favored for which of the following conditions?

Raised ICP. ***Raised ICT*** - The image depicts the patient in a **reverse Trendelenburg position** (head elevated). This position is often used to reduce **intracranial pressure (ICP)** by promoting venous drainage from the brain. - Elevating the head above the trunk aids in gravity-assisted drainage of cerebral venous blood and cerebrospinal fluid, thereby lowering ICP and preventing complications like brain herniation. *CHF* - Patients with **congestive heart failure (CHF)** often prefer a **Fowler's position** (sitting upright) to ease breathing and reduce pulmonary congestion, not the reverse Trendelenburg as shown. - Lying flat or with feet elevated in CHF can worsen dyspnea and increase cardiac workload due to increased venous return. *Air embolism* - For suspected **air embolism**, the patient is typically placed in the **Trendelenburg position** (head down, feet up) with a left lateral tilt to trap air in the right ventricle and prevent it from entering the pulmonary circulation. - This position helps prevent air from crossing into the left side of the heart thereby reducing the risk of systemic arterial air embolization. *Neurosurgery* - While neurosurgery often involves specific patient positioning, the depicted position isn't uniquely favored for neurosurgery in general. Positioning depends on the surgical site. - The **reverse Trendelenburg** is specifically used when reducing ICP is a primary goal during or after neurosurgical procedures, but not all neurosurgeries.

Q: Anesthetic agent contraindicated in raised ICT is?

Ketamine. ***Ketamine*** - **Ketamine** is known to increase **cerebral blood flow** and metabolic rate, which can lead to a significant increase in **intracranial pressure (ICP)**. - This effect makes **ketamine** contraindicated in situations of elevated ICP, as it can worsen neurological outcomes. *Thiopentone* - **Thiopentone** is a barbiturate that typically causes a dose-dependent **decrease in cerebral blood flow** and **metabolic rate**, leading to a *reduction* in ICP. - It is often used to *lower* ICP in neurosurgical settings rather than being contraindicated. *Etomidate* - **Etomidate** also causes a **reduction in cerebral blood flow** and **cerebral metabolic rate**, leading to a *decrease* in ICP. - It is considered a relatively **hemodynamically stable** induction agent, making it suitable in many cases with neurological concerns. *Sevoflurane* - **Sevoflurane**, an inhaled anesthetic, can cause **cerebral vasodilation** at higher concentrations, potentially *increasing* ICP. - However, this effect is often *attenuated* by concurrent hyperventilation, and its overall impact on ICP is less pronounced than **ketamine's** and often manageable.

Q: All of the following lower intracranial pressure except?

Corticosteroids. ***Corticosteroids*** - While corticosteroids can **reduce cerebral edema**, particularly in cases of **vasogenic edema** from tumors or inflammation, their effect on directly lowering acute intracranial pressure is slower and less pronounced than other immediate interventions. - They primarily stabilize the **blood-brain barrier** to decrease fluid extravasation, rather than rapidly reducing brain volume or cerebrospinal fluid. *Hyperventilation* - **Hyperventilation** reduces cerebral blood flow by causing **cerebral vasoconstriction**, which decreases the arterial partial pressure of carbon dioxide (PaCO2). - This rapid reduction in cerebral blood volume is an effective, but temporary, method to **lower intracranial pressure (ICP)** in acute settings. *Furosemide* - **Furosemide** acts as a diuretic, reducing total body water and enhancing the osmotic effect of agents like mannitol by preventing volume expansion. - It also directly **reduces cerebrospinal fluid (CSF) production** by inhibiting sodium transport in the choroid plexus. *Mannitol* - **Mannitol** is an osmotic diuretic that creates an osmotic gradient, drawing water from the brain parenchyma into the intravascular space. - This dehydrates brain tissue, rapidly **reducing brain volume** and consequently **intracranial pressure**.

Question 1

Which of the following drugs does not affect the absorption and secretion of cerebrospinal fluid?

Accepted Answer

Nitrous oxide

Answer

Halothane

Answer

Ketamine

Answer

Thiopentone sodium

Question 2

Which of the following increases cerebral oxygen consumption?

Accepted Answer

Ketamine

Answer

Propofol

Answer

Thiopentone

Answer

Alfentanil

Question 3

Which muscle relaxant is known to increase intracranial pressure?

Accepted Answer

Suxamethonium

Answer

Mivacurium

Answer

Atracurium

Answer

Vecuronium

Question 4

If pneumocephalus is created either by surgery or by performance of a pneumoencephalogram, it is suggested that nitrous oxide be avoided for how many days?

Accepted Answer

7 days

Answer

4 days

Answer

5 days

Answer

6 days

Question 5

Which inhalational agent is used in patients with raised intracranial tension?

Accepted Answer

Isoflurane

Answer

Enflurane

Answer

Desflurane

Answer

Sevoflurane

Question 6

A patient is scheduled for neurosurgery for posterior fossa tumor. During the surgery the BP crashes and Et CO2 suddenly decreases to zero. All are true regarding the condition leading to this catastrophe except:

Accepted Answer

High pressure in cerebral venous sinuses is a major risk factor

Answer

Mill wheel murmur

Answer

TEE is the most sensitive investigation step

Answer

Nitrous oxide accentuates the hemodynamic collapse

Question 7

A patient is scheduled for neurosurgery for posterior fossa tumor. During the surgery the BP crashes and Et CO2 suddenly decreases to zero. What is the most likely diagnosis?

Accepted Answer

Venous air embolism

Answer

Trauma to respiratory center

Answer

Dislodgement of endotracheal tube

Answer

Wearing off effect of inhalation anesthesia

Question 8

The position of the patient as shown below is favored for which of the following conditions?

Accepted Answer

Raised ICP

Answer

CHF

Answer

Air embolism

Answer

Neurosurgery

Question 9

Anesthetic agent contraindicated in raised ICT is?

Accepted Answer

Ketamine

Answer

Thiopentone

Answer

Etomidate

Answer

Sevoflurane

Question 10

All of the following lower intracranial pressure except?

Accepted Answer

Corticosteroids

Answer

Hyperventilation

Answer

Furosemide

Answer

Mannitol

Neuroanesthesia — MCQs

Neuroanesthesia — MCQs

On this page

Practice by Chapter

Want unlimited practice?