Week 3 - Neuro Review Flashcards
What determines ICP under normal conditions?
The volume of the intracranial contents in relation to the rigid skull
*brain matter, blood, CSF
How does a brain tumor change ICP?
Varies depending on tumor location
- Supratentorial lesions cause intracranial hypertension
- Infratentorial lesions cause obstructive hydrocephalus with mass effect of brain stem
What are the determinants of cerebral blood flow?
CBF is tied to CMRO2
Autoregulation holds CBF constant between pressures of 50-150 mmHg – outside these limits, CBF becomes more pressure dependent and autoregulation is less effective
What specific issues are associated with posterior fossa pathology?
Every major efferent pathway from the brain passes through it – tight space
Masses within this space can affect CN’s in brainstem – impair clearance of airway secretion
What is Cerebral Steal Syndrome?
Brain areas with intact autoregulation may “steal” blood from regions when they vasodilate by shunting blood into normal brain tissue and potentially under perfuse disease areas
*caused by intracranial disease causing dysfunction of cerebral autoregulation affecting CBF
What are physiologic changes associated with sitting position?
- Increased dural sinus pressure = increases bleeding
- Increased risk of venous air embolus
- Associated with arterial hypotension, decreased CO and SV, venous pooling in lower extremities, dysrhythmias
- Inadequate cerebral perfusion due to arterial hypotension
What are anesthetic goals for craniotomy?
Avoid increases in ICP
Avoid brain ischemia from hypoperfusion or hypoxia
Optimize the surgical field – provide slack brain and regulation of cerebral volume
What can you do to prevent intracranial hypertension?
- Diuretics
- Corticosteroids
- Adequate ventilation (PaO2 >100 mmHg, PaCO2 = 26-32)
- Optimize hemodynamics to maintain CPP
- Normovolemia
- Head up position – increases venous return
What can you do to reduce intracranial volume?
- Hyperventilation
- Hypertonic IV fluids/Diuretics
- CSF removal (Ventriculostomy)
- Deliberate hypotension
What is a venous air embolus?
Occurs when atmospheric air enters an open vein, venous sinus in operative area
- incidence ranges from 25-50%
- major complications result 5-20% as a result of air entering the arterial circulation via intrapulmonary or intracardiac shunts
What are the most sensitive ways to detect a venous air embolus?
- Precordial doppler is gold standard*****
- Right heart catheterization
- TEE
- End tidal nitrogen
- Capnography
- Esophageal stethoscope
- Pulse oximetry
How do you treat a venous air embolus?
- Have surgeon flood the field with fluids
- Increase O2 to 100%
- If CVC aspirate if possible
- Support hemodynamics
- Place pt in left lateral position
What are indications for surgical intervention in the management of carotid atherosclerotic disease?
- TIA’s with angiographic evidence of stenosis
- Reversible ischemic neuro deficits with greater than 70% stenosis of vessel wall or presence of ulcerated plaque
- Unstable neurological status that persists despite medical therapy (anticoagulation)
What are the different surgical approaches to Carotid endarterectomy?
Open surgical treatment with or without patch graft, shunt
Endovascular treatment
What is normal CBF?
50mL / 100g / minute for the entire brain
*blood flow is four times higher in gray matter than white matter
How does PCO2 affect CBF?
Hypercarbia = vasodilation
Hypocarbia = vasoconstriction
What are the principle determinants in CBF?
- Nerve cell activity
- Cerebral perfusion pressure
- PaCO2
- Brain extracellular fluid pH
- PO2
- Neurogenic influences
What is luxury perfusion? Where is it often seen?
Blood flow that is in excess of metabolic need
it is most often seen in tissues surrounding tumors or areas of infarction, also areas recently manipulated by surgery
What is intracerebral steal?
Paradoxical response to CO2 where hypercapnia decreases blood flow in an ischemic area – consequence of vasodilation
Chronic ischemic vascular beds are maximally vasodilated, therefore they can’t dilate in response to hypercapnea
What is inverse steal?
Paradoxical effect of hypocapnia that produces increased blood flow to ischemic regions of the brain
What anesthetic techniques are available for CEA?
GETA
Cervical plexus block / Awake
remember SSEPs, EEG monitored if GA
What is reperfusion injury following CEA?
Cerebral hemorrhage or the development of cerebral edema after relief of carotid artery obstruction
Rare complication, but often fatal
Poorly controlled BP after cross clamp is removed is often responsible for this phenomenon
What is the most common complication after CEA?
MI
What are cardiovascular effects of SAH?
Injury to posterior hypothalamus from SAH causes release of Norepi from adrenal medulla
-causes increase in afterload and direct myocardial injury = subendocardial ischemia
