CNS Cells and Functions

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Questions and Answers

What percentage of cerebral blood flow (CBF) is provided by the internal carotid arteries?

50%

15%

20%

80% (correct)

Which structure is responsible for the production of cerebrospinal fluid (CSF)?

Pineal gland

Hypothalamus

Area Postrema

Choroid plexus (correct)

What is the normal rate of cerebral blood flow in mL/100g of tissue/min?

50 (correct)

What is the primary determinant of cerebral blood flow regulation when considering metabolic needs?

Cerebral Metabolic Rate (CMRO2) Signup and view all the answers

What vessel carries venous blood from the brain to the heart?

Jugular veins Signup and view all the answers

Which of the following components is least affected by an increase in intracranial pressure according to the Monro-Kellie Hypothesis?

Intracranial air volume Signup and view all the answers

Which intervention is not recommended for lowering intracranial pressure following a closed head injury?

Hypothermia Signup and view all the answers

Which parameter should peak pressure be limited to during ventilation management?

40 cmH2O Signup and view all the answers

What is the most significant factor in preoperative evaluation of patients with possible intracranial mass lesions?

Extent of intracranial hypertension Signup and view all the answers

Which of the following correctly describes the consequence of restoration of blood flow after ischemia?

Increased free radicals and inflammatory mediators Signup and view all the answers

What is the primary goal during induction regarding intracranial pressure (ICP) and cerebral perfusion pressure (CPP)?

To limit changes in ICP and CPP Signup and view all the answers

What should the ideal blood glucose level be maintained at to avoid cerebral complications?

90-280 mg/dL Signup and view all the answers

In which situation would hypotonic solutions be acceptable for a patient with diabetes insipidus?

During severe dehydration Signup and view all the answers

Which of the following agents is typically used as an induction agent to reduce sympathetic nervous system responses?

Propofol Signup and view all the answers

What should be avoided to minimize the risk of intracranial pressure complications during intubation?

Hypotension and hypoventilation Signup and view all the answers

Which of the following interventions is primarily focused on managing blood volume in critically ill patients?

Maintain euvolemia with isotonic solutions Signup and view all the answers

Which of the following interventions is recommended to decrease ICP?

Administer mannitol or hypertonic saline Signup and view all the answers

What is the recommended strategy for the maintenance of anesthesia to minimize increases in ICP?

Provide a continuous infusion of propofol and remifentanil Signup and view all the answers

Which combination of medications can potentially help attenuate opioid-induced hyperalgesia?

Low-dose ketamine or magnesium sulfate Signup and view all the answers

During emergence from anesthesia, what is essential to control in order to avoid exacerbating cerebral edema?

Hemodynamic stability Signup and view all the answers

How should the body position be modified to enhance venous drainage during surgery?

Head of bed elevated Signup and view all the answers

What is the primary factor relating to the risk of aneurysm rupture associated with a diameter greater than 2.5 cm?

Increased transmural pressure Signup and view all the answers

Which surgical approach involves clipping at the base of the aneurysm to prevent rupture?

Aneurysm clipping Signup and view all the answers

During intraoperative aneurysm rupture, which treatment priority is emphasized?

Immediate, aggressive volume replacement Signup and view all the answers

What is the percentage risk of an aneurysm located in the Posterior Cerebral Artery (PCA)?

25% Signup and view all the answers

Which factor does NOT increase the risk of cerebral aneurysm rupture?

Male gender Signup and view all the answers

What is the primary physiological concept used to calculate transmural pressure?

MAP - ICP Signup and view all the answers

Which anesthetic management strategy is recommended for tight blood pressure control during aneurysm clipping?

Keep BP 15-20% below baseline Signup and view all the answers

What is the recommended action if intraoperative rupture occurs?

Reduce MAP to 40-50 mmHg Signup and view all the answers

What is the primary function of the blood-brain barrier?

Restrict the passage of large molecules and ions from the bloodstream Signup and view all the answers

Which type of CNS cell is responsible for producing myelin in the central nervous system?

Oligodendrocytes Signup and view all the answers

Which of the following components is NOT involved in the production or flow of cerebrospinal fluid?

Central canal of the spinal cord Signup and view all the answers

Which electrolyte has a significantly lower concentration in cerebrospinal fluid compared to plasma?

K+ Signup and view all the answers

What role do astrocytes play in the central nervous system?

Maintenance of the blood-brain barrier Signup and view all the answers

What is the normal intracranial pressure range?

5 – 15 mmHg Signup and view all the answers

Which substance is permeable through the blood-brain barrier?

Nicotine Signup and view all the answers

Which cells are typically considered the 'nerve glue' in the central nervous system?

Glial cells Signup and view all the answers

What is the primary mechanism of reabsorption of cerebrospinal fluid?

Pressure gradient at arachnoid villi Signup and view all the answers

Which area of the brain contains the choroid plexus responsible for CSF production?

Ventricles Signup and view all the answers

Study Notes

CNS Cells

Neurons are the most abundant type of cell in the CNS, responsible for transmitting information
Glial cells are supportive cells in the CNS
- Astrocytes: most abundant glial cells, regulate metabolism, maintain blood brain barrier, and repair neuronal injury
- Oligodendrocytes: responsible for creating myelin sheaths for CNS nerves
- Ependymal cells: line the ventricles and produce cerebrospinal fluid
- Microglia: macrophage-like cells that phagocytize debris

Cerebrospinal Fluid (CSF)

Cushions the brain, provides buoyancy, and supports neurological function
Produced by the choroid plexus in the ventricles at a rate of 20 mL/hr
CSF volume is approximately 150 mL
Normal intracranial pressure is 5-15 mmHg
Reabsorbed by arachnoid villi in the superior sagittal sinus into the venous circulation

Blood Brain Barrier

Separates CSF from plasma
Tight junctions between endothelial cells restrict the passage of large molecules and ions
- This includes substances with a molecular weight > 500 daltons
- Polar molecules such as amino acids, glucose, and mannitol
- Water-soluble drugs
- Proteins
Permeable to lipid-soluble molecules
- This includes anesthetics, CO2, EtOH, O2, and nicotine

Cerebral Blood Flow

Arterial supply:
- Internal carotid arteries supply the hemispheres - 80% of cerebral blood flow
- Vertebral arteries supply the posterior brain and cervical spinal cord - 20% of cerebral blood flow
Venous drainage:
- Blood exits the brain through jugular veins
Normal cerebral blood flow is 50 mL/100g tissue/min (750 mL/min total)
Cerebral blood flow is regulated by "flow-metabolism coupling"
Five Key Determinants of Cerebral Blood Flow
- Cerebral Metabolic Rate of Oxygen Consumption (CMRO2)
- Cerebral Perfusion Pressure (CPP)
- PaCO2
- PaO2
- Irregular respirations (medullary compression)

Intracranial Pressure

Monro-Kellie Hypothesis: The cranium is a rigid box with three volumes:
- Brain (80%)
- Blood (12%)
- CSF (8%)
An increase in one volume causes a decrease in one or both of the other volumes to maintain a constant intracranial pressure
Elevated intracranial pressure can lead to:
- Cerebral ischemia
- Decreased cerebral blood flow
- Cerebral edema
- Decreased CPP
Ways to lower ICP:
- Hyperventilation: (temporary effect, lasts for 4-6 hours)
- Mannitol: 0.25-1 g/kg
- Furosemide: 0.5-1 mg/kg
- Corticosteroids:
- Fluid Restriction:
- Elevate the Head of Bed:
- Hypothermia: (not recommended for closed head injury)
- Normotensive to slightly hypertensive:

Cerebral Protection

Ischemic and Reperfusion Injury:
- The brain is vulnerable to rapid ischemic injury: high oxygen and glucose consumption and limited storage capabilities
- Global ischemia is treated with interventions aimed at restoring total cerebral perfusion
- Focal ischemia is treated with interventions focused on the region in question.
- A "penumbra" of salvageable tissue usually surrounds the necrotic core.
Ventilation Management:
- Tidal volume (Vt): 6-8 ml/kg
- Peak pressure: < 40 cmH2O
- Avoid PEEP unless absolutely necessary for oxygenation requirement
- Positive pressure ventilation (PPV) to control ventilation and PaCO2
Fluids and Electrolytes:
- Maintain euvolemia with isotonic or slightly hypertonic solutions
- Avoid glucose-containing solutions
  - Glucose is quickly metabolized and not osmotically active. This can worsen cerebral edema.
  - Ideal blood glucose level: 90-280 mg/dL
    - Hypoglycemia results in lack of glucose for ATP production.
    - Hyperglycemia leads to an increased conversion of glucose to lactic acid during ischemia
- If the patient has diabetes insipidus, hypotonic solutions are acceptable.
- Excessive sodium chloride can lead to hyperchloremic metabolic acidosis.

Tumor Resection

Preoperative Evaluation:
- Identify potential problems for proper planning
  - Intracranial mass lesion and elevated ICP
    - Most important information: assess for presence/extent of intracranial hypertension (through history and physical, MRI, CT, etc.)
    - Symptoms may include: headaches, dizziness, visual or gait disturbances, nausea and vomiting, seizures, altered level of consciousness, confusion, papilledema, loss of strength or sensation, cranial nerve dysfunction, etc.
  - Premedication should be minimized or avoided completely
    - Be especially mindful of drugs that depress respiration (which can lead to increased PaCO2)
- Continue steroid and anticonvulsant therapy if already prescribed

Induction & Airway Management: Tumor Resection

Goals:
- Minimize changes in ICP and CPP
- Avoid hypotension and hypoventilation
Considerations:
- Obtain arterial line, administer an osmotic diuretic, or perform CSF drainage before induction
- Strict blood pressure control during intubation (to minimize risk of herniation)
Medications:
- Propofol for induction
- Blunt the sympathetic nervous system response to laryngoscopy:
  - Fentanyl (1-2 mcg/kg), Lidocaine (1-1.5 mg/kg), or Esmolol
Vascular Access:
- Two large-bore IVs plus arterial line (possible central venous line)
Mayfield Pins:
- Place Mayfield pins after induction and vascular access
Neck Positioning:
- Avoid excessive neck flexion, extension, or rotation (this can compress the internal jugular vein and impair cerebral venous drainage)
ICP Control:
- Paramount until the dura is opened
Hemodynamic Stability:
- Minimizing hemodynamic instability is very important d/t impaired autoregulation.
  - Hypotension can lead to ischemia.
  - Hypertension can increase the risk of bleeding and edema.

Decreasing ICP & Increasing Exposure: Tumor Resection

Ventilation:
- Avoid PEEP
- Hyperventilation
Anesthesia:
- Limit volatile anesthetic use
HOB:
- Elevate HOB
Fluids:
- Limit fluids to achieve euvolemia
Ventriculostomy:
- Consider placement for monitoring and CSF drainage
Osmotic Diuretics:
- Mannitol (0.25-1 g/kg) or Lasix (0.5-1 mg/kg)
Hypertonic Saline:
- 3% hypertonic saline (50-100 ml/hr)
Steroids:
- Administer if appropriate

Maintenance of Anesthesia: Tumor Resection

Goals:
- Avoid increasing intracranial pressure (at least until the dura is opened)
- Maintain CPP
- Closely monitor neurologic status
Fluid Management:
- Maintain fluid balance with dextrose-free, iso-osmolar crystalloids or colloids
Emergence:
- Rapid emergence is preferred (short-acting, easily titratable drugs)
  - Propofol, remifentanil, sevoflurane, desflurane, and potentially N2O

Maintenance of Anesthesia Meds: Tumor Resection

Volatile Anesthetics:
- Less than 0.5 MAC (to avoid cerebral vasodilation)
Propofol:
- Infusion at 50-300 mcg/kg/min (depend on volatile anesthetic use)
Remifentanil:
- Infusion at 0.05-2 mcg/kg/min (based on ideal body weight)
- Watch for opioid-induced hyperalgesia
  - Low-dose ketamine or magnesium sulfate can help prevent opioid-induced hyperalgesia

Emergence from Anesthesia: Tumor Resection

Extubation:
- Patients with a normal Glasgow Coma Scale (13-15) are usually extubated.
Hemodynamic Control:
- Careful blood pressure control is crucial (hypertension can worsen cerebral edema).
  - Consider medications such as labetalol, esmolol, nicardipine.

Aneurysm and Transmural Pressure

Transmural Pressure (TMP) = MAP - ICP
- The pressure differential between the mean arterial pressure (MAP) and intracranial pressure (ICP).
- This pressure drives blood flow into the brain.
Aneurysm rupture is more likely when:
- Transmural pressure is elevated.
- Aneurysm diameter is > 2.5 cm
- The patient has certain risk factors:
  - Smoking
  - Excessive alcohol consumption
  - Recreational drug use
  - Age > 40
  - Female
  - Systemic hypertension

Cerebral Aneurysm: Surgical Options

Clipping:
- Placement of a clip at the base of the aneurysm.
- This isolates the aneurysm from the arterial pressure, preventing rupture.
Endovascular Coiling:
- Transarterial catheterization to thread a coil into the aneurysm sac.

Cerebral Aneurysm: Induction & Airway Management

Preinduction:
- Minimize sedation to avoid hypercapnia
- Obtain an arterial line
Induction:
- Two large-bore IVs
- Prepare 2-4 units of packed red blood cells (in room)
- Administer propofol for induction
- Administer Lidocaine (1-1.5 mg/kg) and fentanyl (1-2 mcg/kg) to blunt sympathetic nervous system response
- Maintain tight blood pressure control
Maintenance:
- General anesthesia is used.
  - Consider total intravenous anesthesia (TIVA) or volatile anesthetics
- Maintain blood pressure at 15-20% below baseline
- Prevent vasospasm
- Limit excess crystalloids
- Prepare packed red blood cells in the room.
Emergence:
- Rapid awakening is necessary for neurological assessment
- Similar considerations to intracranial mass resection
- Maintain a stable blood pressure within 20% of baseline
- Prepare packed red blood cells in the room
Clipping Considerations:
- May see an increase in MAP during clipping.
- If clamping is performed, maintain the MAP between 80-100 mmHg.

Cerebral Aneurysm: Intraoperative Rupture

Most likely during:
- Dural incision (reduction in ICP)
- Excessive brain retraction
- Aneurysm dissection
- Clipping or clip release
Immediate Treatment:
- Volume: Aggressive fluid replacement with PRBCs
- Pressure: Decrease the MAP to 40-50 mmHg
- Visualization:
  - Surgeon will attempt to clip the feeder vessel.
  - Possible use of adenosine (0.3-0.4 mg/kg)

Cerebral Aneurysm: Clipping

Placement of a clip at the base of the aneurysm.
Removes the aneurysm from the arterial pressure, preventing rupture.

Cerebral Aneurysm: Endovascular Coiling

Transarterial catheterization to thread a coil into the aneurysm sac.

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Description

Explore the various types of cells in the central nervous system (CNS), including neurons and glial cells. Learn about the role of cerebrospinal fluid and the blood-brain barrier in supporting brain function and protecting against harmful substances. Test your understanding of CNS anatomy and physiology.