Neurophysiology & Pathophysiology Flashcards
Cerebral metabolic O2 consumption (CMRO2) is normally…..
3.5 mL/100 g/min. (~50mL/min)
The brain uses what percentage of total body O2 consumption?
20%
What part of the brain has the highest CMRO2?
Gray matter
CMRO2 usually parallels what?
Glucose consumption
What parts of the brain are most sensitive to hypoxia injury?
Hippocampus and cerebellum
The average CBF is what percentage of the cardiac output?
15-20%
What is the average value for CBF?
50 mL/100 g/min. (~750mL/min)
What is CPP?
Cerebral perfusion pressure.
CPP = MAP - ICP (or CVP)
What are the CPP values for normal pts, isoelectric EEG and irreversible brain damage?
Normal CPP = 80-100 mmHg
Isoelectric EEG = 25-40 mmHg
Brain damage = <25 mmHg
What is a normal ICP?
Less the 10 mmHg
In normal patients, CBF remains constant between MAP of …..?
50-150 mmHg
What happens to CBF when the MAP falls outside of the normal range (150 mmHg)?
It becomes more pressure dependent
150 usually represents edema
What effect does chronic arterial HTN have on the cerebral auto regulation curve?
Shifts is to the Right.
How is CBF related to PaCO2?
CBF is directly proportional to PaCO2 between 20-80 mmHg
For every 1 mmHg change in PaCO2, how is the CBF affected?
CBF increases 1-2 mL/100 g/min
Why does PaCO2 have such a profound influence in CBF?
CO2 can readily cross the blood brain barrier, but H+ ions do not
What effect does PaO2 have on CBF?
Only severe hypoxemia (PaO2 < 50 mmHg) significantly increase CBF
What is the blood brain barrier?
A lipid barrier that lets the lipid-soluble substances pass, but restricts ionized substances or those with large molecular weight
Passage through the blood brain barrier depends on what four characteristics?
Size
Charge
Lipid solubility
Degree of protein binding in the blood
What is the function of cerebrospinal fluid?
Protects CNS from trauma
What are the normal values for production rate and total volume of CSF?
Production rate: 0.3-0.4 mL/min (~500mL/day)
Total Volume: 150mL
Where is CSF produced?
CSF is formed by the choroid plexuses
Which drugs decrease CSF production?
Corticosteroids
Diuretics
Vasoconstrictors
The cranial vault is a rigid structure with a fixed total volume consisting of what three parts?
Brain (80%)
Blood (12%)
CSF (8%)
What is ICP?
Intracranial pressure is the supratentorial CSF pressure measured in lateral ventricles or over the cerebral cortex
What is the normal range for ICP?
5 to 10 mmHg
What are some compensatory mechanisms for decreasing ICP?
- Displacement of CSF (brain -> spinal cord)
- Increased CSF absorption
- Decreased CSF production
- Decrease in CBV
How is intracranial hypertension defined?
Sustained ICP > 15 mmHg
What are some possible causes of intracranial hypertension?
- Expanding tissue or fluid mass
- Depressed skull fracture
- CSF absorption abnormality
- Excessive CBF
- Systemic disturbances resulting in brain edema
What are some of the signs and symptoms associated with intracranial hypertension?
Headache N/V Papilledema Mental status changes Visual changes Cushing reflex (HTN & Bradycardia) Fixed, dilated pupils Seizures Altered breathing pattern
How is intracranial hypertension treated?
- Treat underlying cause
- Fluid restriction
- Decrease CSF volume (drain or diuretics)
- Decrease CBF (hyperventilation)
- Decrease brain volume (decadron, mannitol)
What is intracranial compliance?
Change in ICP in response to change in intracranial volume
Arnold-Chiari malformation is associated with what type of brain herniation?
The cerebellar tonsils through the foramen magnum
What is the worst site for a brain herniation?
Cerebellar tonsils through the foramen magnum
Which inhalational agents produce the greatest and least effect on cerebral metabolic rate?
Isoflurane = greatest depression Halothane = least effect
Which inhalational agents is best for a patient with intracranial hypertension?
Isoflurane
Has little to no effect on ICP
What phenomenon is possible with volatile anesthetics in the setting of focal ischemia?
Circulatory steal
What is the circulatory steal phenomenon?
Increasing blood flow in normal areas of the brain, but not in ischemic areas where arterioles are already maximally vasodilated.
end result = redistribution of blood flow away from ischemic -> normal areas
All intravenous agents either have little effect on or reduced CMR and CBF with the exception of which drug?
Ketamine
Ketamine is the only intravenous anesthetic that does what to the cerebral vasculature?
Dilates cerebral vasculature thus causing an increase in CBF (50-60%)
What are the most commonly used monitors for neurosurgical procedures?
EEG
Evoked potentials
EEG activation (As with light anesthesia and surgical stimulation) Shows what type of activity?
A shift to predominantly high-frequency and low-voltage activity
EEG activation is associated with what drugs and physiologic states?
Inhalational agents (Subanesthetic) Barbiturates (small doses) Benzodiazepines (small doses) Etomidate (small doses) N2O Ketamine Mild hypercapnia Sensory stimulation Early hypoxia
EEG depression is associated with which drugs and physiologic states?
Inhalational agents (1-2 MAC) Barbiturates Etomidate Propofol Opioids Hypocapnia Marked hypercapnia Hypothermia Late hypoxia
What are the four types of evoked potentials monitored?
Somatosensory (SSEP)
Motor (MEP)
Brainstem auditory (BAEP)
Visual (VEP)
What is the pathophysiology of cerebral ischemia?
Impairment resulting from cerebral perfusion or metabolic substrate interruption or severe hypoxemia
How long can the brain tolerate ischemia before irreversible neuronal injury occurs?
3 to 8 minutes
What are the different types of ischemia?
Focal (Characterized by presence of surrounding nonischemic brain and possible collateral bloodflow to the ischemic region)
Global incomplete (Insufficient blood supply or oxygen delivery to the whole brain)
Global complete (Characterized by absent CBF)
What is the ischemic penumbra?
Brain tissue surrounding a severely damaged area may suffer functional impairment but still remain viable
- marginal perfusion
- loss of autoregulation
What is the most effective method for protecting the brain during focal and global ischemia?
Hypothermia
Some anesthetic agents can prove useful in protection against what type of ischemia?
Focal ischemia
What are the four main anesthetic considerations for maintaining optimal CPP?
- Normal BP
- Avoid increased ICP
- Maintain normocarbia
- Avoid hyperglycemia
What are some potential causes of intracranial mass lesions?
Congenital Neoplastic Infectious Vascular Primary tumor sites
Intracranial Mass lesions present according to what three factors?
Growth rate
Location
ICP
The majority of intracranial mass lesions are located where?
Supratentorial (70%)
Infratentorial (30%)
What are some of the signs and symptoms associated with intracranial mass lesions?
Headache
Seizures
Decline in cognitive/Neurological functions
Focal neurological deficits
Name 3 types of supratentorial masses?
Meningiomas
Gliomas
metastatic lesions
Supratentorial masses are associated with what signs and symptoms?
Seizures
Hemiplegia
Aphasia (loss of speech)
Infratentorial masses are commonly what type?
Posterior fossa tumors
What are the signs and symptoms commonly associated with infratentorial masses?
Cerebellar dysfunction (Ataxia, nystagmus, dysarthria)
Brainstem compression (Cranial nerve palsies, altered consciousness, abnormal respiration)
What is an astrocytoma?
Primary intracranial tumor derived from astrocyte brain cells
- Slow-growing lesion
- Usually not metastatic, but tends to recur
What is glioblastoma multiforme?
Glial cell dysfunction
- Most aggressive
- Often in cerebral hemisphere surrounded by edema
- Non-metastatic
- Poor prognosis
Medulloblastoma is generally arise in the cerebellum of what patient population?
Pediatrics
What are the characteristics of a meningioma?
- Highly vascular
- Slow-growing
- Benign
- Infiltrates skull
What are the two types of pituitary adenomas?
Nonfunctioning (enlarge and compress gland)
Hypersecreting (secrete GH and prolactin)
What are the signs and symptoms commonly associated with pituitary adenomas?
Headaches
Impaired vision
Cranial nerve palsy
Hypopituitarism
What are the characteristics of an acoustic neuroma?
- Benign neurofibroma of cranial nerve VIII
- Causes Unilateral deafness and ataxia
What are the most common primary sites for metastatic tumors?
Lung and breast
What is the most aggressive primary brain tumor?
Glioblastoma multiforme
Where do intracranial aneurysms most often develop?
At the bifurcation of larger arteries commonly in the anterior circle of Willis
Intracranial aneurysms are more common in what patient population?
Females
50-60 years old
What is the main risk with intracranial aneurysms?
Rupture into a fixed space
What are some risk factors for subarachnoid hemorrhage?
Smoking HTN Alcohol/Drug abuse Oral contraceptives Hypercholesterolemia Familial
What is the most common cause of subarachnoid hemorrhage?
Ruptured aneurysm
What is the classic presentation of subarachnoid hemorrhage?
Acute severe headache Stiff neck Photophobia N/V Transient loss of consciousness
What are some potential complications of subarachnoid hemorrhage?
Re-rupture (kiss of death) Reactive vasospasm Intracranial HTN Hydrocephalus Hyponatremia Seizures
How are subarachnoid hemorrhages classified?
Hunt and Hess scale (I-V)
I = asymptomatic II = moderate headache III = confusion IV = coma V = moribund
What is an AVM?
Arteriovenous malformation
- Congenitally malformed capillary beds
- High flow, low resistance
- Circulatory steal and cerebral ischemia
How is a stroke defined?
Second neurologic insult that results from restriction/cessation of blood flow
How are strokes classified?
Ischemic/infarction (80-85%)
Hemorrhagic (15-20%)
What are some possible causes of an ischemic stroke?
- Thrombosis (atherosclerosis most common)
- Embolism (cardiac source- A fib most common)
- Vasoconstriction (Cerebral vasospasm following SAH)
What is the pathophysiology of a hemorrhagic stroke?
Rupture of intracerebral vascular lesions
Ischemia is secondary consequence
What is a subdural hematoma?
Blood collection between the Dura and cerebral cortex
What are the signs and symptoms of a subdural hematoma?
Balance problems/gait changes
Mental status changes
Seizures
What is hydrocephalus?
Imbalance between CSF production and reabsorption resulting in an increased ICP
What are some causes of hydrocephalus?
CSF overproduction
Venous drainage obstruction
CSF flow obstruction
What is pseudotumor Cerebri?
Increased ICP without a mass lesion
-Idiopathic intracranial hypertension
How is pseudotumor Cerebri treated?
VP shunt
What is the pathophysiology behind seizure disorders?
- Abnormal synchronized electrical activity in the brain
- Loss of inhibitory GABA activity
- Enhanced excretory amino acid release
- Enhanced narrow firing due to abnormal voltage mediated calcium channels
Seizure disorders can be classified into what 2 main categories?
Partial (Focal)
Generalized
What is a partial seizure disorder?
Disorder that affects either motor, sensory or autonomic symptoms depending on affected area of the brain
Simple = Consciousness preserved
Complex = Consciousness impaired, not lost
Generalized seizure disorders can be broken down into what groups?
- Convulsive (tonic, clonic, tonic-clonic)
- non-convulsive (absence, myoclonic, atonic)
- Unclassified
Signs and symptoms of seizure disorders fall into what 4 main categories?
- Motor (Muscle spasms)
- Sensory (Paresthesias)
- Autonomic (Pallor, sweating, vomiting)
- Psychiatric (Memory distortions)
What are some of the anesthetic management concerns for patients with seizure disorders?
- Avoid ketamine, etomidate and N2O
- non-depolarizer resistance with chronic therapy
What do you do if a seizure occurs?
- Maintain open airway and adequate oxygenation
2. Give IV propofol, thiopental, midazolam, diazepam or phenytoin
What is epilepsy?
Recurrent paroxysm of cerebral function
-Sudden, brief attacks of altered consciousness, motor activity, sensory phenomena, or inappropriate behavior
What is status epilepticus?
Continuous or intermittent seizure activity lasting more than 20 minutes during which the patient does not regain consciousness
What is the hemodynamic response to status epilepticus?
- Tachycardia and hypertension
- Bradycardia and hypotension
- Respiratory failure and cardiac arrest
What are the three types of cerebral palsy?
- Spastic (70-80%)
- Increased muscle tone - Athetoid/dyskinetic (10-20%)
- Constant, uncontrolled movement of limbs, head and eyes - Ataxic (5-10%)
- Balance and depth perception problems
What is the etiology of cerebral palsy?
Hypoxia/ischemia at birth
Kernicterus (High bilirubin levels)
What is the pathophysiology of Parkinson’s disease?
- Loss of dopamine producing neurons in the substantia nigra that causes dopamine deficiency
- Increased GABA nuclei activity
- Thalamic inhibition suppresses motor system in cortex resulting in hallmark symptoms
What is the purpose of the deep brain stimulator (DBS)?
Promotes dopamine release
What are the signs and symptoms of Parkinson’s?
Resting tremor Trembling Rigidity Bradykinesia Postural instability/impaired balance and coordination
What are some anesthetic management concerns for a patient with Parkinson’s?
- No metoclopramide or droperidol (Because of anti-dopaminergic activity)
- Limit premeds
- Treat hypotension w/ phenylephrine (Labile circulation)
- Anti-cholinergics and antihistamines are effective against acute symptoms
What is the pathophysiology of Alzheimer’s disease?
- Marked cortical atrophy with ventricular enlargement
- Severe loss of hippocampal and cortical neurons (Short-term memory and reasoning)
- Morphological and biochemical neuron changes
What are the signs and symptoms of Alzheimer’s?
Slow decline in intellectual function Memory loss Language deterioration Poor judgment Confusion Restlessness
What are some anesthetic management concerns for a patient with Alzheimer’s?
- Likely to be disoriented/uncooperative
- Altered responses to drugs
- Limit premeds
- Likely to be confused after extubation
