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
