Neuroanesthesia Flashcards
What are the stimulation and response sites for SSEPs and MEPs?
SSEPs:
Stimulation - median nerve
Response - scalp electrodes over sensory cortex
MEPs:
Stimulation - scalp electrodes over motor cortex
Response - EMG in abductor pollicis brevis
What is normal ICP?
15 mm Hg or less
What is the equation for cerebral perfusion pressure (CPP)?
CPP = MAP - (the greater of CVP or ICP)
What is the ideal EtCO2 range for reduction in ICP? What PaCO2 does it reflect?
EtCO2 of 25 to 30 mm Hg, which reflects a PaCO2 of 30 to 35 mm Hg
Describe cerebral blood flow autoregulation? What are its limits?
The intrinsic ability of the cerebral vasculature to adjust resistance to maintain constant CBF over a wide range of MAPs
Autoregulation occurs from 60 to 160 mm Hg
- Above or below this range, CBF is pressure dependent
How do changes in PCO2 effect CBF?
For every 1 mm Hg change in PCO2, CBF will change by 1mL/100g/min in the same direction
What is autonomic hyperreflexia? Where is the transection usually located? What anesthetic technique is preferred? How is it treated?
Autonomic hyperreflexia is a disorder of sympathetic dysinhibition seen after spinal cord transection
- Stimulation below the level can result in generalized vasoconstriction and hypertension
- Bradycardia can occur secondary to activation of baroreceptor reflexes
Above lesion, parasympathetic predominantly - flushing and sweating
Below lesion, sympathetic predominantly - pale, cool, and goosebumps
About 85% of pts have transection above T6
Anesthetic technique should involve deep general or spinal/epidural with local anesthetic
Treatment of acute episode is with alpha-antagonists and vasodilators
- beta-blockers should not be used
What is the normal cerebral metabolic rate for oxygen per minute?
3.5 mL/100 g brain tissue
Order (most to least) of neuromonitoring sensitivity to interference from anesthetics
Visual evoked potentials
Somatosensory evoked potentials
Brainstem auditory evoked responses
What are the most sensitive monitors for venous air embolism?
TEE is the gold standard
Precordial doppler is the most sensitive non-invasive monitor
- can detect as little as 0.25 mL of air
What is normal cerebral blood flow? What is the critical low value?
Normal CBF is 50cc/100g tissue/min
The critical low value is 20cc/100g tissue/min, under which EEG changes begin to occur
How does ischemia effect autoregulation? What is the difference between intracerebral steal syndrome and Robin Hood syndrome?
During focal cerebral ischemia, ischemia areas of the brain are unable to participate in autoregulatory changes of vessel resistance
Intracerebral steal syndrome occurs with hypercarbia, when normal vessels vasodilate shunting blood away from the unchanged ischemic area
Robin Hood syndrome is reverse steal caused by hypocarbia, when normal vessels constrict shunting blood to the “poor” ischemic areas
What is the treatment for venous air embolism?
Flood the field and pack the wound 100% O2 Jugular venous compression Aspirate air through central line Place pt head down and in left lateral position
Describe the Glascow Coma Scale
Motor response: Obeys commands - 6 Localizes stimulus - 5 Withdraws from pain - 4 Flexion posture - 3 Extension posture - 2 No response - 1
Verbal response: Oriented - 5 Confused - 4 Inappropriate - 3 Incomprehensible - 2 No response - 1
Eye opening: Spontaneous - 4 To speech - 3 To pain - 2 Nothing - 1
What is neurogenic pulmonary edema?
NPE is pulmonary edema caused by massive sympathetic discharge after neurologic/spine injury
Occurs in up to 20% of pts with severe head injury
Typically develops within 4 hours of inciting event
