Anesthesia for Neurosurgery Flashcards
What arteries supply blood flow to the brain?
Internal carotid artery and the Vertebral arteries
Where do the two vertebral arteries arise?
Branches of the subclavian artery and enter the base of the skull through the foramen magnum
What are the three branches of the internal carotid artery?
Middle cerebral artery
Posterior communicating artery
Anterior cerebral artery
Where is the circle of willis located?
At the base of the brain and forms an anastomotic ring that includes vertebral and internal carotid flow
What is the purpose of the circle of willis?
If one portion of cerebral blood flow becomes obstructed, other blood flow will compensate and give collateral flow
What artery supplies majority of the blood flow to the brain?
Internal carotid artery 85%, supplies anterior 2/3 surface of the brain
What is normal cerebral blood flow?
50mL/100gm brain tissue/min (750mL/min or 15-20% total cardiac output)
Decreasing blood flow to the brain by how much will cause cerebral impairment?
Decreased flow by 50% (20-25mL/100gm/min)
Decreasing blood flow to the brain by how much will cause isoelectric EEG?
Flow 6-15mL/100gm/min
Decreasing blood flow to the brain by how much will cause neuronal death?
Less than 6mL/100gm/min
How is cerebral perfusion pressure calculated?
CPP = MAP - ICP
What is normal CPP?
80-100mmHg
What is CPP dependent on in a healthy individual?
MAP because ICP is usually less than 10mmHg
At what ICP does CPP become significantly compromised?
ICP greater than 30mmHg
What metabolic factors regulate CBF?
Hydrogen ion (pH of blood)
Carbon dioxide
Oxygen tension
What is the most potent determinant of CBF?
Carbon dioxide
Blood flow increases 1-2mL/100gm/min for every 1mmHg change in PaCO2
Why isn’t hyperventilating a patient for increased ICP always the best decision?
Once PaCO2 less than 20mmHg there is no further vasoconstriction effects, may cause cerebral impairment
How does oxygen tension affect CBF?
Only affected by marked changes in PaO2 less than 50mmHg will cause vasodilation and increase CBF
How is CBF impacted by temperature?
CBF changes 5-7% per 1C
At what temperate will an EEG become isoelectric?
20C
What is optimal Hct for CBF?
30-34%
What ANS control is predominately in cerebral circulation?
Extensive SNS innervation
At what MAPs is CBF auto regulated extremely well?
50-150mmHg, beyond these limits CBF become pressure dependent
How does chronic HTN cerebral auto regulation?
Cerebral auto regulation curve is shifted to the right so higher presses are necessary to maintain CBF
How does the metabolic rate of the brain differ than that of the rest of the body?
Overall metabolic rate of brain is 7 times greater than the average metabolic rate of the body
Why isn’t the brain able to sustain anaerobic glycolysis when no oxygen is present?
Metabolic rate of neurons is too great
What becomes a source of energy in the brain when glucose stores are depleted?
Ketone bodies
How does hyperglycemia contribute to global hypoxic brain injury?
Accelerates cerebral acidosis and cellular injury
What is the major function of the CSF?
Protect the CNS against trauma
About how much CSF is produced in a day?
21mL/hr (500mL/day) –> Total CSF volume is only about 150mL
What is a normal ICP?
5-15mmHg
What are the three components of the cranial vault?
Blood
Brain tissue
CSF
What is the first mechanism to compensate for an increase in ICP?
Displacement od CSF from cranial to the spinal compartment
What ICP is considered mild, moderate and severe intracranial HTN?
Mild: 12-25mmHg
Moderate: 25-40mmHg
Severe: greater than 40mmHg
Why is normal ICP said to have high compliance?
Small increases in volume can be tolerated without an increase in pressure
What are the three components of cushings triad?
HTN
Bradycardia
Irregular respirations
What medications can be given to a patient for increased ICP?
Mannitol, Lasix and Corticosteroids
What is a target PaCO2 if hyperventilation for increased ICP?
30-35mmHg
What anesthetic interventions have a Robin hood effect on CBF?
Barbiturates and Hyperventilation (good for focal ischemia or tumors)
What is the most important mechanism for protecting the brain during focal and global ischemia?
Hypothermia
What are strategies for cerebral protection?
Avoid hyperglycemia
Maintain normocarbia
Maintain O2 carrying capacity
Maintain normal or slightly increased BP
What should be considered if a patient undergoing neurosurgery is on anticonvulsants?
Anesthetic drug requirement
Therapeutic level of drug
Continue drug intraoperatively
Why is it important for the provider to have a smooth induction and emergence in neurosurgies?
To avoid swings in ICP
What are the types of mass lesions?
Congenital
Neoplastic
Infectious
Vascular
What are typical presentations for brain lesions?
HA
Seizures
Neurological decline
Focal neurologic deficits
What are the three tissue types of primary intracranial tumors?
Glial cells
Ependymal cells
Supporting tissues
What are secondary intracranial tumors?
They evolve from lesions that metastasize from primary cancers in the lungs, breast or skin
What are three major considerations in managing patients with intracranial lesions?
Tumor location (blood loss, hemodynamic changes)
Growth rate and size
ICP elevation
Why shouldn’t you monitor TOF on the hemiplegic side with an intracranial lesion?
May end up overdosing paralytic
Why do we zero the arterial line at the external auditory meatus in neurosurgical procedures?
It approximates the MAP at the level of the circle of willis
What is a major risk in neurosurgical procedures since the bed is turned 90-180 degrees away?
Unrecognized disconnects (vent, IV) may be increased
Why should PEEP be avoided in neurosurgical procedures?
Could potentially increase ICP
What is the best anesthetic technique if cerebral edema is present?
TIVA
How should fluid be managed in patients undergoing neurosurgical procedures?
Normovolemia, fluids replacements will be below calculated maintenance
Replace blood loss with blood or colloids
Why isnt using volatiles an effective method in controlling blood pressure in patients with elevated ICP?
BP is centrally mediated
What complications can occur if bucking or coughing happens during extubation?
Intracranial hemorrhage or worsening cerebral edema
What are the components of the posterior fossa?
Cerebellum
Brainstem
Cranial nerves
Large venous sinuses
What nerve is responsible for stimulating cushing’s reflex?
Trigeminal nerve (HTN and Bradycardia)
Stimulation of which cranial nerves causes bradycardia and HoTN?
Vagus and Glossophsryngeal
What are concerns for anesthesia in patients with posterior fossa lesions?
Risk injury to cranial nerves, respiratory centers and circulatory centers
What cranial nerves control the pharynx and larynx?
IX, X, XI
What is the preferred position for a posterior fossa lesion for the surgeon?
Sitting position
Why is the sitting position not preferred to used in posterior fossa lesions?
Most detrimental to physiologic status due to a lack of perfusion
What are cardiac complications are associated with the sitting position?
Postural hypotension, arrhythmias and venous pooling
What precautions can be taken to avoid CV compromise in the sitting position?
Light anesthesia during positioning Paralysis Volume/Vasopressors SCDs Move to sitting position slowly
How does a pneumocephalus occur?
Open dura and CSF leakage causes air to enter
What can occur if the air is not evacuated prior to closing the cranium?
The air can act as a mass lesion as CSF reaccumulates
What is the treatment for a tension pneumocephalus?
Burr holes
What are the symptoms of the pneumocephalus?
Delayed awakening, HA, lethargy and confusion
What are nerve injuries associated with the sitting position?
Ulnar compression
Sciatic nerve stretch
Lateral peroneal compression
Brachial plexus stretch
What can be done to prevent ulnar nerve compression and brachial plexus stretch in the sitting position?
Arms across abdomen, pad elbow and under the arms to support the shoulders
What can be done to avoid sciatic nerve stretch and lateral peroneal compression?
Place a pillow under the knees and pad the knees appropriately
When does a venous air embolism occur?
When the pressure within an open vein is sub atmospheric and the incision is greater than the level of the heart
What occurs when there is slow entrainment of air into the veins?
Small bubbles enter and travel to the heart
PVR increased from air lodging in capillary beds
Gas eventually diffuse into the alveoli and are excreted
When does pulmonary artery pressure begin to rise from small bubble entering the circulation?
When the amount of entrained air exceeds pulmonary clearance
What occurs when air is rapidly entrained in the veins?
Large bubbles enter and lodge into the SVC, RA and RV
Impedes flow through the right heart
Slow increase in PAP, CV collapse
What is a paradoxical air embolism?
Air enters the left side of the heart and travels to systemic circulation
What vessels are most at risk with a paradoxical air embolism?
Coronary and cerebral circulations
What causes a paradoxical air embolism to occur?
When the right heart pressure is greater than the left
What population is a paradoxical air embolism common?
Patients with PFOs
What are signs and symptoms of a VAE?
Mill wheel murmur Decreased ETCO2/ Increased PaCO2 Detection of ET nitrogen Dysrhythmias HoTN Sudden appearance of vigorous spontaneous ventilation
What tool can be used for early detection of a VAE?
Precordial doppler most common
Capnography
CVP/PA line
What should be used to confirm diagnosis of VAE?
Do NOT rely n only one monitor alone to diagnose, used 2-3 monitors of varying sensitivity to confirm diagnosis
What is the most sensitive indicator of a VAE?
TEE
Where should the precordial doppler be positioned to detect VAE?
Over right atrium
What is the treatment for a VAE?
100% O2
Have surgeon flood field or pack the wound
Call for help
Aspirate CVP line
Volume/inotropes
Position in LLD with slight trendelenberg
What is the leading cause of non traumatic intracranial hemorrhage?
Cerebral aneurysms
Where do cerebral aneurysms occur?
At a brand of a large cerebral artery (most turbulent blood flow)
Located in the base of the brain in the anterior circle of willis
What treatment should be given to patient with a ruptured cerebral aneurysm to avoid vasospasm?
Triple H therapy
Hemodilution
HTN (SBP 160-200)
Hypervolemia CVP greater than 10
Why is triple H therapy beneficial in preventing vasospasm after an aneurysm rupture?
It is intended to increase CBF to areas in the brain that become ischemia due to intense vascular narrowing
Why is it that in vasospasm increasing CBF will help prevent ischemia?
With a vasospasm the vascular beds become passive
What are the treatment goals of Cerebral aneurysm?
Diagnose early, airway management, control ICP, hemodynamic stabilization and seizure prophylaxis
What grading system is used with subarachnoid hemorrhage?
Hunt and Hess Gradin System (ranges from 0-5)
What is the most common method of treating an aneurysm?
Microsurgical clip ligation, clips it off from circulation
When might circ arrest be required for an aneurysm clipping?
Greater than 2.5cm
How should fluids be managed in a patient undergoing an iracranial aneurysm repair?
Run patient dry, expand blood volume with colloid (no glucose in fluids)
When are the most likely times an aneurysm will rupture?
Dural incision
Excessive brain retraction
Aneurysm dissection
During clipping or releasing clip
What should be done if an aneurysm ruptures intra operatively?
Immediate fluid resuscitation
Decrease MAP to decrease blood loss
What kind of anesthetic should be provided for endovascular therapy?
GETA with complete muscle paralysis
What is an arteriovenous malformation?
Congenital abnormality that involves a direct connection from an artery to a vein without a pressure modulating capillary bed
What are the treatment options for an AV malformation?
Intravascular embolization
Surgical excision
Radiation
How should the AV malformation be managed?
Similar to aneurysms however potential for larger amounts of blood loss, need multiple IV access
What is the leading cause of death in individuals less than 24 years old?
Head trauma
What are the determining factors of the significance of the head injury?
The extent of irreversible neuronal damage at the time of injury
Occurrence of of secondary insult
What is the goal of anesthetic and surgical intervention of head trauma?
Prevention of the secondary insult
If a skull fracture is present, what other injury is likely present?
Intracranial lesion
What type of skull fracture is associated with subdural and epidural hematoma?
Linear skull fracture
What are symptoms associated with basilar skull fracture?
CSF rhinorrhea
Pneumocephalus
Cranial nerve palsies
What type of skill fracture is associated with a brain contusion?
Depressed skull fracture
What type of injuries produce coup contra coup injuries?
Deceleration injuries
What is the range of the Glasgow coma scale?
3-15
What is the general rule of thumb of controlling an airway based on a score?
Less than 8, intubate
What are the three components that make up the Glasgow coma scale?
Eye opening
Verbal responses
Motor response
How should the airway be manipulated in a trauma patient?
In line stabilization to maintain the head in a neutral position
When is a blind nasal contraindicated in a trauma patient?
Basilar skull fracture Raccoon Sign (ecchymosis into periorbital) Battle Sign (ecchymosis behind ears)
Why might HoTN be seen in a spinal cord injury?
Sympathectomy associated with spinal shock and bradycardia id the cardia accelerator center
What should the provider be assessing for if there is pituitary insult?
Urine output for DI
How do VP shunts function?
One way pressure dependent valves to regulate flow of CSF
How should the provider control ventilation for placing a VP shunt?
Avoid hyperventilation and hypocarbia because they make the cannulation of the ventricle more difficult
When is an awake craniotomy indicated?
Epilepsy surgery
Resection of tumors in frontal and temporal lobe (speech and motor assessed intraoperatively
What is a major challenge of the anesthetic provider for an awake craniotomy?
Technique that provides adequate sedation, analgesia and respiratory and hemodynamic control but also awake and cooperative for neurological testing
What is the most common non endocrine symptom of enlarging pituitary tumors?
Frontal or temporal HA
When do pituitary tumors become apparent?
With mass effect or Hypersecretion of pituitary hormones
What hormones are commonly secreted by functional pituitary tumors?
Prolactin (lactation)
Growth hormone (acromegaly)
ACTH (adrenal hyperplasia)
When is a transphenoidal approach appropriate for pituitary surgery?
Tumor under 10mm in diameter
What can the anesthetic provider do to optimize the view for the surgeon resecting a pituitary tumor?
Avoid hyperventilation because reductions in ICP result in retraction of pituitary into the sella tursica making access difficult
What vascular structures are close to the suprasellar area when resecting a pituitary tumor?
Carotid arteries lie adjacent to the supra stellar area
What anesthetic agent should be avoided in pituitary surgery?
Halothane
What are Epi and Cocaine used for in pituitary surgery?
Topical to vasoconstrictor vessels, may produce HTN and dysrhythmias
What is a common complication that occurs after pituitary surgery?
Diabetes insipidus, usually self limiting and resolves within 7-10 days
What can DI be treated with?
DDAVP and vasopressin
Why might you need to d/c nitrous for pituitary surgery?
The surgeon may wish to inject air or saline to delineate suprasellar margins
