Neuro-Anesthesia Flashcards
What is the most appropriate initial treatment for a stroke secondary to air embolism
Hyperbaric oxygen
Cerebral perfusion pressure should be maintained and the patient placed 100% FiO2 while awaiting hyperbaric therapy.
What is the order of evoked potential sensitivity to volatile anesthetics (i.e. visual evoked potential vs. somatosensory evoked potential vs. brain stem auditory evoked potential)?
Visual evoked potentials are the MOST sensitive to volatile anesthetics.
Brain stem evoked potentials are the least sensitive
VEP > SSEP > BAEP
What are some relative contraindications for ECT?
Relative contraindications:
- recent stroke
- high-risk pregnancy
- aortic & cerebral aneurysms
[Pregnancy, pacemakers, and AICDs are NOT contraindicated conditions]
What part of the spinal cord is involved in motor function? How is motor function tested during spine surgery?
Motor function involves the anterior horn in the spinal cord and is tested by waking the patient up and assessing their ability to move their lower extremities.
What part of the spinal cord is monitored by sensory evoked potentials?
The posterior column
How does Etomidate effect the amplitude and latency of somatosensory monitoring?
Etomidate increases both the amplitude and latency
What are the divisions of the autonomic nervous system?
1) Sympathetic (thoracolumbar, short preganglionic path with synapse near the vertebral bodies)
2) Parasympathetic (craniosacral, long pregnanglionic path with synapse near the effector organs)
3) Enteric (in the gut itself, can function without CNS input, and therefore, can function in case of spinal cord injury or spinal anesthesia)
What percentage decrease in CBF occurs for every 1 degree Celsius decrease in temperature?
CBF decreases 7% for every 1 degrees Celsius
Describe the pain pathway
It is a 3 neuron chain:
1) a peripheral nerve brings the signal into the spinal cord
2) second order neuron synapses in the gray matter of the dorsal horn, crosses, and sends the signal up the spinothalamic (and other) tracts
3) synapses with a third order neuron in the thalamus, which processes and sends the signal to the cerebral cortex for interpretation
Describe delta fibers
myelinated nerve fibers that transmit sharp, localized traumatic pain
Describe C fibers
Non- or poorly myelinated fibers that transmit the dull, poorly localized visceral pain (i.e. distended viscus, ischemia, or spasm)
How soon after spinal injury can you see an improvement from neurogenic shock symptoms?
It usually improves within 3-5 days of the injury
What are the expected results of an acute cervical spine injury immediately to a few weeks post injury? What is the role of succinylcholine?
Flaccid paralysis and spinal shock will ensue for a few days to a few weeks
Succinylcholine is acceptable for the first 48 hours, after which, hyperkalemia becomes a significant risk
Sympathetic supply to the heart will be interrupted (T1-4)
Poikilothermia and paralytic ileus (not diarrhea) are additional problems
For every 1 mmHg drop in PaCO2, what percentage drop in CBF is seen?
1-3% decrease
How long does it take for the body’s compensatory mechanisms to “neutralize the effect” of hyperventilation?
24 hours
What are some causes of postoperative visual loss (POVL)? Which is the most common cause?
Ischemic optic neuropathy (ION) (most common cause)
Retinal artery occlusion (usually secondary to pressure on the eye)
Cortical blindness
What are the cardiovascular concerns during a posterior fossa procedure?
Stimulation of the lower portion of the pons and upper part of the medulla can lead to a variety of cardiovascular responses: bradycardia, hypotension, tachycardia, hypertension, and ventricular arrhythmias
What are the major cranial nerves at risk of injury during posterior fossa procedures?
Cranial nerve dysfunction, particularly nerves IX, X, and XII can result in loss of control/patency of the upper airway
Describe the Glasgow Coma Scale
It is a way to evaluate the severity of patients who have suffered a traumatic brain injury (TBI) on a scale from 3 - 15
3 variables are evaluated: Eye opening, Verbal response, and Motor response
Eye opening (1-4): Don't open eyes = 1
Opens eyes to pain = 2
Opens to speech = 3
Opens spontaneously = 4
Verbal response (1-5): None = 1
Garbled, incomprehensible sounds = 2
Inappropriate words = 3
Confused but converses = 4
Oriented speech = 5
Motor response (1-6): None = 1
Extension (decerebrate rigidity) = 2
Flexion (decorticate rigidity) = 3
Withdrawal to pain = 4
Localizing pain = 5
Obeying commands = 6
How much of the total body oxygen does the brain consume?
20%
What is the Monro-Kellie doctrine?
Any increase in one of the 3 components of the cranial vault (80% brain, 12% blood, 8% CSF) must be offset by an equivalent decrease in the others to prevent a rise in ICP
What is the cerebral metabolic rate of oxygen (CMRO2)?
3 - 3.8 mL/100g/min (50 ml/min)
What is the normal cerebral blood flow (CBF) rate?
50 mL/100g/min
What is the critical CBF in anesthetized patients with Isoflurane?
10 mL/100g/min
Since GA reduces CMRO2, the critical level for reversible (15-20 mL/100 g/min) and irreversible ischemia (< 10-15 mL/100g/min) is lowered.
What amount of cardiac output (CO) does the brain receive?
15%
How to calculate cerebral perfusion pressure (CPP)
CPP = MAP - ICP
What is the level of ICP that is indicative of Severe Intracranial HTN?
An ICP >40 mmHg is life threatening
What are the indications for placing intracranial pressure monitoring?
- Severe TBI, Glasgow Coma Scale Score < 8
- Abnormal head CT or a normal head CT
- Two thirds of the following conditions: age > 40; unilateral of bilateral motor posturing; SBP < 90 mmHg
Obstructive hydrocephalus
Communicating hydrocephalus with signs of elevated ICP
Subarachnoid hemorrhage with abnormal GCS score
Generalized cerebral edema
Stroke involving >50% of the MCA territory
Intraparenchymal hemorrhage with > 5mm midline shift
Which volatile anesthetic is the most potent cerebral vasodilator?
Halothane
At what level of CBF does evidence of ischemia present?
< 20 mL/100g/min
The afferent input for Somatosensory-evoked potentials (SSEPs) is carried through what spinal cord tract?
Dorsal columns
Cushing’s Triad
Systemic Hypertension
Bradycardia
Irregular Respirations
When can the complication of vasospasm in a subarachnoid hemorrhage (SAH) present?
AFTER 48 hours, 7-9 days
How does Succinylcholine cause an increase in ICP?
By indirectly stimulation the reticular activating system
How is Diabetes Insipidus treated?
1) Central: IV or intranasal DDAVP (desmopressin)
2) Nephrogenic: IV hypo-isotonic replacement &/or Furosemide (?)
What part of the spinal cord contains ascending SENSORY (afferent) tracts? descending MOTOR (efferent) tracts?
- Afferent ascending sensory tracts are within the DORSAL WHITE MATTER
- Efferent descending motor tracts are with the LATERAL/VENTRAL WHITE MATTER
What differentiates spinal shock from neurogenic shock?
Patients with Neurogenic shock have profound hemodynamic instability (bradycardia w/ decreased SVR associated with injuries above T6).
Patients with Spinal shock have acute and transient sensorimotor dysfunction at ANY level
What are the acute manifestation of spinal injury?
- Flaccid paralysis for 1-4 weeks
* absence of neurologic function below the lesion (motor, sensory, autonomics, reflexes)
* atonic periphery & peripheral blood vessels are DILATED - Loss of DTRs
- Bradycardia (only efferent component of baroreflex pathway that remains intact is the vagus
- Hypotension
For C-spine and high T-spine injuries:
- Alveolar hypoventilation
- Hypoxemia
What is autonomic hyperreflexia?
Amplified sympathetic response to stimulus that cannot be modulated by parasympathetic response due to blockage of spinal cord at or above level of T6
- Flushing above level of injury
- Vasoconstriction below
What neurogenic diseases do you see hyponatremia?
1) SIADH
2) Cerebral salt wasting
What is the treatment for vasospasm s/p SAH?
Triple H Therapy: 1) Hemodilution (Hct 30-35%)
2) Hypertension (most important)
3) Hypervolemia (Euvolemia is being promoted currently due to the significant morbidity of hypervolemia)
Calcium channel blockers: Nimodipine/Nicardipine
How is t-PA induced thrombolysis treated?
Cryoprecipitate
What is the cause of anterior cord syndrome?
Disruption of the arterial blood supply to the anterior cord.
What does the anterior spinal artery supply? What is the result of injury?
The ventral 2/3rds of the spinal cord
- Loss of ipsilateral motor function (ventral corticospinal)
- Loss of contralateral pain/temperature (spinothalamic)
What area is fed by the artery of Adamkiewicz?
It is the largest radicular artery that supplies T1-T4 and the first lumbar segments
Prone to ischemia after vascular occlusions
What are RELATIVE contraindications for ECT?
Recent stroke
High-risk pregnancy
Aortic & cerebral aneurysms
(preexisting arrhythmias, pacemakers, AICDs and NOT contraindicated)
What are examples of excitatory CNS transmitters?
Glutamate and acetylcholine
What are examples of inhibitory CNS transmitters?
GABA and glycine
How do endorphins act as a CNS transmitter?
Endorphins activate descending inhibitory pathways that modulate pain in the spinal cord.
What receptors are most catecholamines linked to?
Dopamine receptors
When do the symptoms of spinal/neurogenic shock usually resolve?
Within 3-5 days
What are the manifestations of spinal shock?
- Absolute flaccidity and loss of reflexes
- hypotension
- bradycardia
- loss of vasomotor tone and sympathetic innervation of the heart
What are the signs/symptoms of autonomic hyperreflexia?
Seen with chronic spinal cord injuries at or above the level of T5-6
Sweating Nasal congestion Headache Blurred vision Severe HTN Bradycardia (baroreceptor reflex) Heart block Ventricular dysrhythmias Vasodilation and Flushing ABOVE the level of the spinal cord lesion
The constellation of a severe headache and rapid neurologic deterioration is suspicious for what diagnosis?
Subarachnoid hemorrhage
cerebral vasospasms will have the neurologic decline, yet, without the headache.
What ECG changes do patients with subarachnoid hemorrhage display?
- Absent or inverted T waves
- Prolonged QT interval
- ST segment depression/elevation
What is the normal CMRO2?
3-5 mL/100g of brain tissue/min
What is the normal CBF? At what flow does cerebral acidosis develop? At what flow is an EEG isoelectric? At what flow does brain infarction begin to develop?
Normal = 50 mL/100g/min
Cerebral acidosis = 20 mL/100g/min
EEG isolectric = 15 mL/100g/min
Brain infarction development = 6 mL/100g/min
List excitatory neurotransmitters
Glutamate
Acetylcholine (Ach)
List inhibitory neurotransmitters
GABA
Glycine
Endorphines (activate descending inhibitory pathway that modulate pain in the spinal cord)
What are unmyelinated C fibers responsible for? Small myelinated fibers? Large myelinated fibers?
Unmyelinated C fibers = pain and temperature
Small myelinated fibers = proprioception, touch, pressure
Large myelinated fibers = motor
Describe Brown-Sequard Syndrome
It is partial spinal cord transection that results in ipsilateral motor and contralateral sensory deficits BELOW the level of the lesion
What anesthetic technique for spinal cord stimulator placement is associated with the lowest failure rate?
Spinal anesthesia
*Spinal cord stimulator placement often requires both extensive surgical dissection and an AWAKE patient for intra-operative testing to optimize the surgical result.
Excessive neck flexion in the seated position has what effect?
Quadriplegia due to the compression of the cervical spinal cord in combination with lowered perfusion pressure
What is the maximal reduction in the cerebral metabolic requirement for oxygen (CMRO2) achievable exclusively through the use of high-dose barbiturates?
50%
What are the characteristics of Central Retinal Artery Occlusion (CRAO)?
- It can be associated with surgery in the prone position
- It is almost always associated with external pressure not he globe
- It is unilateral 95% of the time
- Visual acuity does NOT improve
- Examination reveals a pale retina and often a “cherry red” spot on the macula
