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Advanced Principles of Anesthesia > Week 1 - Increased ICP and Herniation > Flashcards

Week 1 - Increased ICP and Herniation Flashcards

1
Q

What are the divisions of the peripheral nervous system?

A

Cranial and Spinal Nerves and Receptors Divided into:

  • Somatic Nervous System: contains sensory neurons – controls skin, muscles, and joints
  • Autonomic Nervous System: sympathetic and parasympathetic and enteric subdivisions – responsible for “involuntary” innervations of various organ systems
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2
Q

What are the two primary cell types of the central nervous system?

A

Neurons (basic functional cells of CNS)

Neuroglial (Glial Cells)

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3
Q

What are the three components of a neuron? What are the different classifications?

A

Consists of cell body (perikaryon), dendrites, and a single axon

Vary in size and shape and classification:
-unipolar, bipolar, pseudounipolar, multipolar

*classified according to specific function (motor, sensory, and interneurons)

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4
Q

What are the four types of Neuroglial (glial cells) found in the CNS?

A

Astrocytes

Oligodendrocytes

Microglial

Ependymal Cells

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5
Q

What is the major function of Astrocytes?

A

Support (for neurons) metabolic and nutritive functions

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6
Q

What is the major function of Ependymal Cells?

A

Probable role in CSF production

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7
Q

What is the major function of Microglia?

A

Phagocytosis

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8
Q

What is the major function of Oligodendrocytes?

A

Insulation – form myelin sheath in brain and spinal cord

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9
Q

What is the major function of Schwann Cells?

A

Insulation – form myelin sheath in peripheral nerves

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10
Q

What are the five cavities of the Ventricular System within the brain?

A

Lateral Ventricles (Two) - largest of the ventricular cavities, irregular shape

Third Ventricle - located in the midline and surrounded by the diencephalon

Cerebral Aquaduct - channel between the third and fourth ventricles

Fourth Ventricle - forms the roof of the pons and the medulla

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11
Q

What are the different lobes of the cerebrum and their functions?

A
  • Frontal: regulation of personality, tact, judgement, inhibition, planning for the future, and abstract thinking
  • Parietal: interpretation of pain/temp, light touch, vibration, two-point discrimination, and proprioception
  • Occipital: macular vision and peripheral vision
  • Temporal: hearing, memory/learning, and receptive language (Wernickes area)

Gnostic Area: temporal, occipital and parietal lobes come together – most important for higher cerebral comprehension activities = intelligence

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12
Q

What are the three major divisions of the brainstem?

A

Midbrain, Pons, and Medulla

  • houses cranial nerve nuclei for CN III through XII
  • respiratory center of the brain is located in the Medulla
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13
Q

What are the 12 cranial nerves?

A 
I - Olfactory
II - Optic
III - Oculomotor
IV - Trochlear
V - Trigeminal
VI - Abducens
VII - Facial
VIII - Acoustic
IX - Glossopharyngeal
X - Vagus
XI - Accessory
XII - Hypoglossal
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14
Q

What are the three meningeal layers of the CNS?

A

Dura: thickest - overlies cerebral hemispheres and brainstem, forms a fold (falx cerebri) that functionally separates the hemispheres

Arachnoid: thin - avascular membrane joining the dura mater – the subdural space is between the dura and arachnoid mater

Pia: thin avascular membrane adherent to the brain and spinal cord – subarachnoid space is between arachnoid and pia

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15
Q

What is the blood brain barrier? What is permeable to it?

A

Protective mechanism for brain – tightly knit capillary structure within the brain

  • Highly permeable to O2, CO2, and glucose
  • Slightly permeable to electrolytes
  • Nearly impermeable to other substances

*many meds do not cross - must be lipid soluble and very small molecular size to cross

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16
Q

How is CSF produced?

A

Made hourly in the plexus of the 3rd and 4th ventricles – Made from blood

-produced by ependymal cells in the Choroid Plexus at a rate of 30mL/hr

  • entire CSF volume is replaced q3-4 hours
  • produce approx 200-225 mL/day and reabsorb it at the same rate
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17
Q

What is the function of CSF?

A

Allows the brain to float in its compartment under normal circumstances (cushions brain)

Helps maintain glucose supply

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18
Q

Describe CSF circulation within the brain

A

CSF flows from the lateral ventricles of the cerebral hemispheres through the foramen of Monro into the third ventricle, through the aqueduct of Sylvius in the midbrain, into the fourth ventricle

CSF enters the subarachnoid space through the medial foramen of Magendie and the paired lateral foramina of Luschka, openings posterior to the pons and anterior to the cerebellum

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19
Q

What happens when there is too little CSF? What about too much?

A

Too Little = collapsing ventricles and herniation through foramen magnum

Too Much = increased ICP and push brain against cranium –> herniation

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20
Q

How many pairs of spinal nerves are there?

A

31 Pairs of Spinal Nerves:

  • 8 cervical
  • 12 thoracic
  • 5 lumbar
  • 5 sacral
  • 1 coccygeal
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21
Q

How are peripheral nerves classified?

A

According to diameter – degree of myelination affects the conduction velocity of the nerves

*the larger the diameter the faster the conduction velocity

  • A alpha = largest diameter fibers - fastest conduction velocity
  • A beta, A gamma, A delta, B fibers = decreasing order of size and conduction velocity
  • C fibers = smallest diameter and slowest velocity
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22
Q

What is intracranial pressure? What is normal?

A

Relationship between intracranial contents (blood, brain, and CSF) and the pathophysiology within the cranium

Normal ICP = 0-15 mmHg

*management of ICP is aimed at balancing these volumes to achieve homeostasis

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23
Q

What is the definition of Intracranial hypertension?

A

ICP greater than 20mmHg lasting 5 minutes or more

24
Q

What is the Monroe Kellie Doctrine?

A

under normal physiological conditions, the volume of the three components brain (80%), blood (10%), and CSF (10%) remains in a constant relationship

If the volume of any one of these components increases, there is a corresponding decrease in one or both of the other two components to maintain a constant overall intracranial volume, or ICP will rise

25
Q

Increased ICP can lead to brain damage and/or death by what two mechanisms?

A

Global Hypoxic-Ischemic Injury: results from reduction of cerebral perfusion pressure (CPP) and cerebral blood flow (CBF)

Mechanical compression, displacement, and herniation of brain tissue, which results from mass effect as described by the Monroe-Kellie doctrine

26
Q

What are some causes of increased ICP?

A
  • Tumor
  • Hematoma (subdural and epidural)
  • Cerebral edema
  • CSF disturbances (Communicating and Non communicating hydrocephalus)
  • Intracranial hemorrhage
  • Other pathologies such as: hypoxia, diffuse brain injury, trauma, hepatic encephalopathy, Reye’s syndrome, infections, spinal contributions, skull abnormalities, and hypo and hyperosmolar states
27
Q

How are increases in intracranial volume initially counterbalanced? (intracranial compliance)

A

By reductions in volume in the other compartments:

  • CSF is displaced through the foramen magnum into the paraspinal space
  • Blood is displaced from the intracranial to the extracranial venous system
  • Brain parenchyma is compressed

*overtime these mechanisms are exhausted and intracranial compliance falls sharply – once this happens even small increased is intracranial volume can lead to dramatic elevations in ICP

28
Q

What is the normal rate of cerebral blood flow?

A

50 mL per 100 grams of brain tissue per minute or 750 mL/min

*when you get below 20mL/100gm you see ischemic changes

29
Q

What factors influence cerebral blood flow?

A

PaCO2: a change in PaCO2 is directly related to cerebral blood flow – CBF increases or decreases 2mL/100gm/min for every 1mmHg increase of decreased of the PaCO2 from 40mmHg

PaO2: hypoxia is a potent cerebral vasodilator and CBF increases markedly with PaO2 below 50mmHg

CMRO2: increases in CMRO2 will result in proportional changes in CBF

30
Q

How do you calculate Cerebral Perfusion Pressure?

A

CPP = MAP - ICP

Critical determinant of CBF and is vital in ICP management

  • CPP should be maintained >70 mmHg to avoid ischemia
  • can also do MAP - CVP but this is controversial
31
Q

What is autoregulation of cerebral blood flow?

A

the ability of the brain to maintain a constant cerebral blood flow over a wide range of MAP (50-150)

32
Q

What are signs and symptoms of increased ICP?

A
  • Altered level of consciousness
  • Severe headache, nausea, vomiting
  • Seizures
  • Restlessness / Agitation
  • Cranial nerve palsies (most commonly III, VI-X)
  • Visual dysfunction and/or pupillary changes
  • Papilledema
  • Motor dysfunction (weakness, decorticate or decerebrate posturing, flaccidity)
33
Q

What are considered early signs of increased ICP and herniation?

A

Hypertension

Tachycardia

Abnormal respiratory pattern – Cheyne Stokes respirations, central neurogenic hyperventilation, and apnea

34
Q

What are considered late signs of increased ICP and herniation?

A

Cushings Triad:

  • Hypertension with widening pulse pressure along with diminished level of consciousness = two most consistent signs
  • Bradycardia
  • Abnormal Respiratory Pattern – ataxic or agonal respirations
35
Q

What are the indications for ICP monitoring?

A
  • Suspect to have increased ICP
  • Patient is comatose (GCS <8, motor posturing, hypotension <90mmHg)
  • Pathology and or prognosis indicate aggressive ICU treatment is indicated
  • CT scan showing significant intracranial mass effect with midline shift or effacement of the basal cisterns
36
Q

What is the gold standard device for ICP monitoring? Describe it

A

Ventriculostomy

  • connects the intraventricular space to an external pressure transducer
  • transducer must be at the level of the foramen of Monroe (external auditory meatus)
  • system can be set for continuous drainage with intermittent ICP measurement or for continuous ICP measurement and intermittent CSF drainage.
  • disadvantage is high risk of infection- This has improved dramatically with antibiotic coated catheters
37
Q

Describe the intraparenchymal pressure transducer for monitoring ICP

A

Two examples include: Codman and Camino

  • these catheters can be placed into the brain parenchyma or the ventricle via a small burr hole and screw
  • only need to be calibrated once prior to insertion
  • unable to drain CSF
38
Q

Describe the subarachnoid bolt used to monitor ICP

A

A hallow screw that is inserted via a burr hole

Useful in monitoring ICP only and unable to drain off CSF

39
Q

What is the definition of brain herniation?

A

Displacement of brain structures resulting in a sequence of neurological signs and symptoms related to compression of brain structures and to compromised blood flow

  • it is a process that can be reversed, but is time limited
  • when the pt has herniated, the process is complete and brain death occurs
40
Q

What preventative measures can be done to prevent herniation?

A
  • Perform thorough neuro exams Q 1 hour and prn
  • Proper positioning (Midline head position, HOB elevated to >30°)
  • Fluid administration- Use only isotonic fluids such as 0.9% saline or Lactated Ringers solution
  • Monitor CVP to maintain adequate fluid resuscitation. (8-12 mmHg)
  • Temperature Management (fevers should be treated aggressively - Tylenol, cooling blankets)
  • Seizure Prophylaxis (Phenytoin or Posphenytoin – IV Keppra = treatment of choice in ICU stetting/OR)
  • Steroid Administration (dexamethasome 4-10mg IV Q6H)

*maintain Hematocrit >30% –> isn’t done as much anymore

41
Q

What is used to treat patients with cerebral edema?

A

Administration of hypertonic saline 3% to 23.4%

42
Q

What are the early treatments for increased ICP and herniation?

A
  • Elevate the head of bed 15–30 degrees or more
  • IV fluids- Replace based on patients CVP (Assume patient is dry, Monitor chest x-rays daily to assess for volume overload)
  • Intubate and hyperventilate (Permissive hypercapnia= Target pCO2 26-30 mm Hg)
  • Mannitol 20% 1-1.5 g/kg via IV bolus
  • Hypertonic Saline Bolus (3 - 23.4% saline)
  • Foley Catheter to monitor urine output
  • CT scan and Stat Neurosurgical consult
43
Q

What are the 7 components of the Columbia Stepwise Protocol for ICP management?

A

1: Surgical Decompression
2: Sedation
3: CPP Optimization
4: Osmotherapy
5: Hyperventilation
6: Pentobarbital
7: Hypothermia

44
Q

Describe the Surgical Decompression step from the Columbia Stepwise Protocol for ICP management

A
  • Consider repeat CT scan and decide if surgical intervention such as Craniotomy or Ventriculostomy should be performed
  • Ventric should be opened to drain at 5mmHg (Surgeons preference)
45
Q

Describe the Sedation step from the Columbia Stepwise Protocol for ICP management

A

– Can be very helpful in reduction of ICP
– Risky due to limited ability to perform thorough neuro exam
– Short acting agent should be utilized such as Propofol or Versed

46
Q

Describe the CPP Optimization step from the Columbia Stepwise Protocol for ICP management

A
  • Maintain CPP >70 mmHg and ICP < 20 mmHg
  • utilize vasopressor such as Phenylephrine or Norepinephrine or IV boluses to maintain CPP >70 mmHg
  • Watch for rebound hypertension when using vasopressors
  • Nicardipine, Labetolol and Hydralazine may be utilized to reduce blood pressure safely and quickly
47
Q

Describe the Osmotherapy step from the Columbia Stepwise Protocol for ICP management

A

Used when ICP remains elevated after CPP is optimized and patient is sedated:

  • Mannitol 20% IV bolus- Osmotic diuretic that lowers ICP by causing cerebral dehydration
  • Monitor serum electrolytes and serum osmolality, CVP and urine output with Mannitol administration
  • Hypertonic saline bolus infusions are gaining popularity in the ICU setting

*head to head trial of Mannitol vs. Hypertonic saline is warranted !

48
Q

Describe the Hyperventilation step from the Columbia Stepwise Protocol for ICP management

A

Goal is to maintain pCO2 to 28-32 mmHg

Respiratory alkalosis caused by hyperventilation reduces ICP by causing cerebral vasoconstriction and reduced cerebral blood volume

49
Q

Describe the Pentobarbital Therapy step from the Columbia Stepwise Protocol for ICP management

A

High dose barbiturate therapy can effectively reduce ICP in most patients

  • Loading dose of 10-20 mg/kg given in 5 mg/kg boluses until a state of flaccid coma is established
  • Maintenance infusion of 1-4 mg/kg/hr titrated to burse suppression of 1 every 5 seconds
  • Continuous EEG monitoring is needed to avoid over sedation. Usually maintained for 24-48 hours
50
Q

Describe the Hypothermia step from the Columbia Stepwise Protocol for ICP management

A
  • Systemic hypothermia to levels of 32-34 degrees Celsius can lower ICP
  • Cooling blankets placed over and under the patient, iced gastric lavage, and pharmacologic paralysis to prevent shivering
  • Studies are ongoing utilizing endovascular cooling techniques
51
Q

What are inhalational agent anesthetic considerations for CBF?

A

CBF has been consistently shown to increase with Nitrous Oxide alone and in combination with volatile anesthetics

-volatile agents cause dose dependent reductions in cerebral vascular resistance and thus increase CBF at doses of 0.6 MAC and higher

52
Q

What is the opioid of choice for neurosurgery?

A

Remifentanil due to rapid onset and offset

53
Q

Why are barbiturates often used in neurosurgical anesthesia?

A

Because of their ability to decrease the CMRO2, CBF, and ICP

  • propofol has similar effects
  • avoid ketamine due to increased ICP
54
Q

What are neurosurgical anesthetic considerations for muscle relaxants?

A

NDMRs don’t have clinically significant direct effects of CBF or CMRO2 – watch for effects from histamine release (tachycardia, hypotension)

Succinylcholine increases ICP and should be avoided

55
Q

What are intraop fluid management anesthetic considerations for neurosurgery?

A
  • Goals are to maintain normovolemia and relative hyperosmolarity
  • Avoid dextrose containing solutions
  • Normal saline is generally preferred to LR d/t its osmolarity (308 mOsm vs 273 mOsm)
  • Maintain Hct at 28-35%?? –> pt and procedure specific

Advanced Principles of Anesthesia (31 decks)

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