Neurosurgery: Intracranial Tumor Debulking
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Questions and Answers

What is the percentage of cardiac output that supplies the brain?

  • 10% to 15%
  • 15% to 20% (correct)
  • 20% to 25%
  • 25% to 30%

    • Which of the following structures allows bilateral communication of internal carotid and vertebral artery blood flow?

  • Basal ganglia
  • Circle of Willis (correct)
  • Cerebellum
  • Cerebral cortex

    • What is the approximate weight of the brain?

  • 1 lb
  • 4 lb
  • 3 lb (correct)
  • 2 lb

    • Where is the majority of cerebrospinal fluid produced?

    <p>Lateral ventricles</p> Signup and view all the answers

    What is the normal range of intracranial pressure?

    <p>≤10 mm Hg</p> Signup and view all the answers

    How much cerebrospinal fluid is produced per day?

    <p>400 mL/day</p> Signup and view all the answers

    What is the approximate increase in CBF for every 1 mm Hg increase in PaCO2?

    <p>1 to 2 mL/100 g/min</p> Signup and view all the answers

    What is the primary location of cerebral blood flow in the brain?

    <p>Gray matter</p> Signup and view all the answers

    What is the total cerebral blood flow in the brain?

    <p>750 mL/min</p> Signup and view all the answers

    What is the effect of a profound increase in PaO2 on CBF?

    <p>A profound increase in CBF</p> Signup and view all the answers

    Through which structure does CBF occur?

    <p>Circle of Willis</p> Signup and view all the answers

    What is the primary anesthetic concern during intracranial tumor debulking?

    <p>Preventing increases in ICP</p> Signup and view all the answers

    What is the effect of hyperventilation on cerebral blood flow?

    <p>It decreases CBF by causing cerebral vascular vasoconstriction</p> Signup and view all the answers

    What is the effect of diuretics on brain tissue?

    <p>They decrease brain tissue water content</p> Signup and view all the answers

    What is the consequence of severely increased ICP?

    <p>Brainstem herniation through the foramen magnum</p> Signup and view all the answers

    What is the effect of ventriculostomy and intrathecal catheters on ICP?

    <p>They decrease ICP by allowing CSF to drain</p> Signup and view all the answers

    What is the primary reason glioblastomas may not cause significant symptoms initially?

    <p>Compensatory physiologic mechanisms that help maintain normal ICP</p> Signup and view all the answers

    What is the result of baroreceptor stimulation in response to increased systemic vascular resistance?

    <p>Bradycardia</p> Signup and view all the answers

    What is the consequence of ICP increasing beyond the compensatory mechanisms of the Cushing reflex?

    <p>All of the above</p> Signup and view all the answers

    What is the estimated percentage of patients with elevated ICP that display all three components of the Cushing triad?

    <p>33%</p> Signup and view all the answers

    What is the primary location of glioblastoma growth in the brain?

    <p>Frontal or temporal regions</p> Signup and view all the answers

    What is the effect of increased ICP on CPP requirements?

    <p>CPP requirements exceed arterial pressure</p> Signup and view all the answers

    What is the result of the Cushing reflex on the sympathetic nervous system?

    <p>Increased sympathetic nervous system activity</p> Signup and view all the answers

    What is the consequence of tumor growth on surrounding brain tissue?

    <p>Inflammation, necrosis, and displacement of surrounding brain tissue</p> Signup and view all the answers

    What is the primary goal of complete tumor removal in intracranial tumor debulking?

    <p>To prevent tumor remnants from regrowing</p> Signup and view all the answers

    Which of the following positions is associated with an increased risk of postoperative vision loss?

    <p>Prone position</p> Signup and view all the answers

    What is the main difference between supratentorial and infratentorial tumors?

    <p>Location of the tumor in the brain</p> Signup and view all the answers

    What is the reason for biopsying tumor boundaries during intracranial tumor debulking?

    <p>To assess the absence of tumor tissues</p> Signup and view all the answers

    Which of the following positions is associated with an increased risk of brachial plexus injury?

    <p>Lateral oblique position</p> Signup and view all the answers

    What is the purpose of intraoperative biopsy during intracranial tumor debulking?

    <p>To confirm the diagnosis of the tumor</p> Signup and view all the answers

    Which of the following tumors is least likely to cause increased ICP?

    <p>Pituitary tumor</p> Signup and view all the answers

    What is the primary location of most neurosurgical procedures for tumor resection?

    <p>Cerebral hemispheres</p> Signup and view all the answers

    What is the purpose of mild head elevation during surgical procedures?

    <p>To increase venous drainage from the head</p> Signup and view all the answers

    What is the primary concern for patient positioning in surgical procedures for infratentorial tumors?

    <p>Surgical access</p> Signup and view all the answers

    What is the function of the corpus callosum in the brain?

    <p>Connects the right and left hemispheres</p> Signup and view all the answers

    What is the primary reason for discussing patient and operating room table position preoperatively?

    <p>To plan for intraoperative airway and invasive line access</p> Signup and view all the answers

    What is the consequence of neck flexion during surgical procedures?

    <p>Impaired venous drainage from the head</p> Signup and view all the answers

    What is the purpose of using foam supports or a bean bag vacuum mattress during surgical procedures?

    <p>To support the patient's head</p> Signup and view all the answers

    What is the primary goal of maintaining a minimum CPP of 70 mm Hg during intracranial tumor debulking?

    <p>To limit ischemia around the tumor during intraoperative brain retraction</p> Signup and view all the answers

    What is the benefit of giving midazolam preoperatively in patients with intracranial tumors?

    <p>It attenuates increases in blood pressure and ICP related to anxiety</p> Signup and view all the answers

    Why is it recommended to avoid narcotics preoperatively in patients with intracranial tumors?

    <p>They may depress respiratory function and raise PCO2</p> Signup and view all the answers

    What is the effect of dexamethasone given before induction in patients with intracranial tumors?

    <p>It has an antiemetic effect and attenuates inflammatory responses</p> Signup and view all the answers

    What is the consequence of small increases in MAP in patients with elevated ICP?

    <p>Profound increases in ICP</p> Signup and view all the answers

    What is the significance of the Cushing reflex in patients with intracranial tumors?

    <p>It is a sign of elevated ICP</p> Signup and view all the answers

    Why do small tumors and slow-growing tumors not always cause increases in ICP?

    <p>Because they are associated with cerebral physiologic compensation</p> Signup and view all the answers

    What is the benefit of placing at least one large-bore intravenous (IV) access preoperatively in patients with intracranial tumors?

    <p>It allows for rapid administration of medications</p> Signup and view all the answers

    What is the primary benefit of using hypertonic saline to decrease ICP?

    <p>It osmotically decreases brain water content without causing hypovolemia</p> Signup and view all the answers

    What is the effect of a 1°C decrease in body temperature on CMRO?

    <p>A 7% decrease in CMRO</p> Signup and view all the answers

    What is the primary reason why VAAs disrupt the coupling of CMRO2 and CBF?

    <p>They decrease CMRO2 and increase CBF due to their vasodilating effects</p> Signup and view all the answers

    What is the primary benefit of using benzodiazepines, etomidate, and propofol in neuroanesthesia?

    <p>They decrease CMRO2 and CBF, allowing for normal regulatory decreases in CBF</p> Signup and view all the answers

    What is the primary consequence of the steal phenomenon in ischemic brain tissue?

    <p>It diverts blood flow away from ischemic areas to nonischemic areas</p> Signup and view all the answers

    What is the primary goal of using diuretics to decrease ICP?

    <p>To decrease brain volume and reduce ICP</p> Signup and view all the answers

    What is the primary effect of hyperventilation on CBF?

    <p>It decreases CBF</p> Signup and view all the answers

    What is the primary benefit of using corticosteroids to decrease ICP?

    <p>They block inflammatory responses and prevent further brain edema</p> Signup and view all the answers

    What is the primary consequence of hyperthermia on brain tissue?

    <p>It is detrimental to brain tissue</p> Signup and view all the answers

    What is the primary rationale for using hypothermia to decrease CMRO2 and protect brain tissue?

    <p>It decreases CMRO2 and CBF, protecting brain tissue from metabolite formation</p> Signup and view all the answers

    What is the primary concern during induction of anesthesia in a patient with elevated ICP?

    <p>Hypotension and hypertension</p> Signup and view all the answers

    What is the goal of anesthetic care for a patient with elevated ICP?

    <p>Decreasing intracranial volume and maintaining adequate CPP</p> Signup and view all the answers

    What is the effect of IV agents such as propofol, etomidate, and midazolam on CMRO2?

    <p>Decrease CMRO2 and CBF</p> Signup and view all the answers

    What is the effect of VAAs on CMRO2?

    <p>Decrease CMRO2 and increase CBF</p> Signup and view all the answers

    What is the primary concern during the intraoperative period for a patient with elevated ICP?

    <p>Hypotension and hypertension</p> Signup and view all the answers

    Why is continuous blood pressure monitoring important in patients with elevated ICP?

    <p>To monitor and manage hypertension and hypotension</p> Signup and view all the answers

    What is the benefit of inducing an adequate depth of anesthesia before direct laryngoscopy?

    <p>To prevent sympathetic stimulation</p> Signup and view all the answers

    Why is it important to maintain an adequate CPP in patients with elevated ICP?

    <p>To maintain adequate cerebral blood flow</p> Signup and view all the answers

    What is the primary goal during the recovery phase of anesthesia in intracranial tumor debulking?

    <p>All of the above</p> Signup and view all the answers

    Why is sedation using central nervous system depressant medications important if the patient remains intubated?

    <p>To reduce the risk of intracranial events</p> Signup and view all the answers

    What should the anesthetist observe for in an extubated patient during the recovery phase?

    <p>Changes in mental status or signs of intracranial events</p> Signup and view all the answers

    What is the primary reason for observing the patient for changes in mental status during the recovery phase?

    <p>To detect intracranial events, such as increased ICP, vasospasm, or hemorrhage</p> Signup and view all the answers

    Why is pain control important during the recovery phase of anesthesia?

    <p>To improve patient comfort</p> Signup and view all the answers

    Study Notes

    Cranial Vault Composition

    • Composed of three components: brain tissue (80%), blood (12%), and cerebrospinal fluid (CSF) (8%)
    • These components together determine intracranial pressure (ICP)

    Brain and Blood

    • Brain tissue: 1300 grams (3 lb or 2% of total body weight)
    • Blood: 15% to 20% of cardiac output, 750 mL/min

    Cerebrospinal Fluid (CSF)

    • Total volume: 150 mL in cranium and spinal cord
    • Volume in cranium at any given time: 75 mL
    • Production rate: approximately 400 mL/day by choroid plexuses in lateral ventricles
    • Absorption: in the subarachnoid space by arachnoid villi of the venous system

    Cerebral Circulation

    • Circle of Willis: allows bilateral communication of internal carotid and vertebral artery blood flow

    Tumor Locations

    • Described as supratentorial or infratentorial

    CSF Flow Pathway

    • Produced by choroid plexus in lateral ventricles
    • Flows through interventricular foramen of Monro and into the third ventricle
    • Proceeds from the third ventricle through the aqueduct of Sylvius and into the fourth ventricle
    • From the fourth ventricle, flows through the foramen of Magendie and two foramina of Luschka into the cerebellomedullary cistern (cistern magna) and then into the subarachnoid space and spinal column

    Cerebral Blood Flow (CBF)

    • Average CBF: 50 mL/100 g/min (total 750 ml/min), with a range of 10 to 300 mL/100 g/min
    • CBF in gray matter (neuronal bodies): 80 mL/100 g/min
    • CBF in white matter (axons): 20 mL/100 g/min
    • Alterations in CBF can be either detrimental (decreasing blood flow to ischemic areas) or beneficial (providing more blood and oxygen to ischemic areas)

    Factors Affecting CBF

    • PaCO2: has a linear relationship with CBF, with a 1 mm Hg increase in PaCO2 resulting in a 1 to 2 mL/100 g/min increase in CBF
    • PaO2: has a profound effect on CBF, but only at very low PaO2 levels

    Intracranial Tumor Debulking

    • Normal ICP is ≤10 mm Hg, but temporary elevation occurs during coughing, Valsalva maneuver, and hypertensive episodes.

    ICP Management

    • Sustained elevation of ICP >15 mm Hg decreases CPP and increases the risk of cerebral ischemia.
    • Severely increased ICP may lead to brainstem herniation through the foramen magnum.
    • Intracranial tumors are space-occupying lesions that may increase ICP, depending on their size and location.

    Anesthetic Concerns

    • Preventing increases in ICP is a primary anesthetic concern.

    Decreasing ICP

    • Hyperventilation decreases CBF by causing cerebral vascular vasoconstriction, which decreases CBF.
    • Decreasing cerebral blood volume (CBV) decreases ICP.
    • Diuretics decrease brain tissue water content, thereby decreasing ICP.
    • Ventriculostomy and intrathecal catheters allow CSF to drain, which decreases ICP.

    Glioblastomas

    • Glioblastomas are tumors that rapidly expand and arise from white or gray matter usually in the frontal or temporal regions of the brain.
    • These tumors are often surrounded by inflammatory and necrotic tissue.

    Symptoms and Diagnosis

    • Glioblastomas can become large rapidly before the patient develops significant symptoms.
    • Tumors that infiltrate or displace the ventricles may cause obstructive hydrocephalus.

    Treatment

    • Treatment includes tumor debulking, CSF diversion, chemotherapy, and radiation to the affected site.
    • Despite these treatments, survival remains low.

    Pathophysiology of ICP

    • Intracranial tumors may not cause serious symptoms initially because of compensatory physiologic mechanisms that help maintain normal ICP.
    • Glioblastomas often develop rapidly and cause increases in ICP.

    Cushing Reflex

    • When CPP requirements exceed the arterial pressure, the hypothalamic sympathetic reflex increases blood pressure to restore CBF.
    • The increased blood pressure stimulates carotid bodies, which lowers the heart rate by initiating the Cushing reflex.
    • The Cushing reflex is one of the body's most potent physiologic responses that, when stimulated, dramatically increases sympathetic nervous system predominance.

    Cardiovascular Response

    • The cardiovascular response includes hypertension and bradycardia.
    • Bradycardia is the result of baroreceptor stimulation in response to increased systemic vascular resistance.

    Cushing Triad

    • The Cushing triad includes hypertension, bradycardia, and irregular respirations, reflecting severe increases in ICP and severe cerebral ischemia.
    • Up to 33% of patients with elevated ICP display all three components of the Cushing triad.
    • Impending herniation of the brainstem down through the foramen magnum can occur if ICP continues to increase.

    Intracranial Tumor Debulking

    • The surgical procedure for intracranial tumor debulking involves an open craniotomy using a parietal approach with the patient in the lateral position.

    Surgical Objectives

    • The primary objective is to completely remove the tumor to prevent regrowth of tumor remnants.
    • Intraoperative biopsy is performed to confirm and identify the tumor.
    • Tumor boundaries (margins) are biopsied to assess the absence of tumor tissues before surgical closure.

    Supratentorial and Infratentorial Tumors

    • Supratentorial tumors occupy the area of the midbrain and cerebral cortex.
    • Infratentorial tumors occupy the area of the vital centers of the cerebellum and brainstem.
    • The location of an intracranial tumor necessitates specific positioning for neurosurgical access.

    Positioning Risks

    • Sitting position: Increased risk of venous air emboli (VAE).
    • Lateral oblique position: Risk of brachial plexus injury.
    • Prone position: Risk of postoperative vision loss (POVL), especially in diabetic patients, associated with lengthy prone position cases and intraoperative hypotension.
    • Supine position: May have head and neck rotation or extension; may have cranial pinning/fixation in head tongs.

    Anesthetic Management and Considerations for Intracranial Tumor Debulking

    • Preoperative goals include maintaining or achieving normal ICP and CPP (minimum 70 mmHg) to optimize cerebral circulation and oxygenation.
    • Maintenance of adequate CPP limits ischemia around the tumor and during intraoperative brain retraction.
    • Midazolam 0.025 to 0.05 mg/kg IV may be given to attenuate increases in blood pressure and ICP related to anxiety.
    • Preoperative interventions include placing at least one large-bore IV access preoperatively and another after induction.
    • Avoid narcotics preoperatively as they depress respiratory function and raise PCO, causing cerebral vessel dilation and corresponding increases in ICP.
    • Administer antibiotics and corticosteroids (dexamethasone 4 to 10 mg IV) per surgeon preference before induction.

    Signs and Symptoms of Elevated ICP

    • Symptoms progress on a continuum from mild to severe and include headache, difficulty concentrating, memory disturbances, vision disturbances, vertigo, syncope, nausea, vomiting, severe headache, the Cushing reflex, Cushing's triad, seizures, or coma.
    • Not all intracranial tumors cause increases in ICP; small tumors and larger, slow-growing tumors associated with cerebral physiologic compensation may present with delayed increases in ICP.

    Location of Intracranial Tumors

    • The most prevalent location of intracranial tumors is supratentorial, involving the cerebral hemispheres.
    • The cerebral hemispheres are divided by the medial longitudinal fissure and composed of the frontal, parietal, temporal, and occipital lobes.
    • Infratentorial location refers to the brainstem, consisting of the midbrain, medulla, cerebellum, and pons, containing major motor and sensory pathways and cranial nerve nuclei.

    Influence of Tumor Location on Patient Positioning

    • Infratentorial tumors usually require a prone or lateral position for surgical access.
    • Supratentorial tumors are often resected while the patient is positioned supine or lateral.
    • Lateral or semi-lateral positions may use foam supports or a bean bag vacuum mattresses to support the patient.
    • The sitting position is associated with an increased risk of VAE and excessive neck flexion, impeding venous drainage from the head.
    • Mild head elevation (reverse Trendelenburg) may be done with any surgical position.
    • The patient's head may be held by a horseshoe-shaped support, a foam support, or pinned in tongs, fixing the skull to a support frame.

    Anesthetic Concerns during Induction for a Patient with Elevated ICP

    • Primary concerns during induction: hypoxia, hypercarbia, hypertension, and hypotension
    • Smooth induction with hyperventilation and proper mask ventilation is recommended
    • Rapid sequence induction may be indicated for patients with severe GERD
    • Continuous blood pressure monitoring is important, and placement of an arterial line may be beneficial
    • Induction agents may depress cardiac function and cause hypotension, while laryngoscopy can cause sympathetic stimulation and hypertension

    Primary Intraoperative Goals of Anesthesia Care for the Patient with Elevated ICP

    • Decreasing intracranial volume to prevent increases in ICP
    • Maintaining adequate cerebral perfusion pressure (CPP) by manipulating blood pressure
    • Decreasing cerebral metabolic rate of oxygen (CMRO2)

    Methods to Decrease CMRO2

    • IV agents: propofol, etomidate, and midazolam lower CMRO2 and cerebral blood flow (CBF)
    • Vasodilatory anesthetics (VAAs): decrease CMRO2, increase CBF, and uncouple the relationship between CMRO2 and CBF
    • Temperature: mild decrease in body temperature (1°C decrease corresponds to 7% decrease in CMRO2)

    Coupling and Uncoupling of CMRO2 and CBF

    • Coupling: direct relationship between CMRO2 and CBF, where an increase in one corresponds to an increase in the other
    • Uncoupling: disruption of the direct relationship between CMRO2 and CBF, caused by VAAs, which decrease CMRO2 while increasing CBF

    Methods to Lower ICP

    • Decreasing brain volume: diuretics (furosemide, mannitol) and hypertonic saline administration
    • Decreasing blood volume: hyperventilation to decrease PCO2 and cause cerebral vasoconstriction
    • Decreasing CSF volume: not mentioned in the passage

    Rationale for Each Method to Decrease Intracranial Volume

    • Brain: diuretics (furosemide, mannitol) and hypertonic saline administration to decrease brain volume
    • Blood: hyperventilation to decrease intracranial blood volume

    Postoperative Period for Intracranial Tumor Debulking

    • Goals of the recovery phase of anesthesia include pain control and maintenance of adequate blood pressure.
    • Postoperative monitoring involves observing for changes in mental status or signs and symptoms that may indicate an intracranial event, such as: • Increased ICP (Intracranial Pressure) • Vasospasm • Hemorrhage
    • If the patient is extubated, close monitoring is essential to detect any potential complications.
    • If the patient remains intubated, sedation using central nervous system depressant medications is necessary.

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    Description

    This quiz covers the key points of intracranial tumor debulking, including the composition of the cranial vault and the determination of intracranial pressure. It also discusses the normal ICP and CSF production.

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