Neuro Flashcards
Which part of brain is most sensitive for lack of O2:
- cerebellum
- hippocampus
Brain consumption of O2:
- 3 to 3.8 mlO2/100g/min (50 ml/min, CMR-O2)
- 20% of total body O2 consumption
- > 60% neuronal electrical activity
- > 40% cellular integrity
What is glucose uptake of the brain?
- 5mg/100g/min
- 90% is metabolized aerobically(CMR-O2 parallels Glc consumption normally, cave Ketons, Lac)
What is CBF normally:
- 50 ml/100g/min (750ml/min, 15 - 20% of CI)
- varies locally: 10 - 300 ml/100g/min- > grey matter: 80 ml/100g/min
- > white matter: 20 ml/100g/min
What is relationship between EEG and CBF:
CBF: < 25 => slowing EEG
< 20 => iso - EEG
< 10 => irreversible damage
Blood-flow speed in middle cerebral artery:
55 cm/s
> 120 => Vasospasm/hyperemic blood flow
What is Lindegaard ratio:
- speed of blood flow in middle cerebral artery / external a.carotis int.
- hyperemia
- > 3 => vasospazm
Normal pO2 in brain tissue:
- 20 to 50 mmHg
How is defined CPP (cerebral perfusion pressure):
- CPP = MAP - ICP (CVP when higher)
- norm: 60 - 80 mmHg
- severe TBI: 50 - 70 mmHg
What is relationship between EEG and CPP:
CPP: slowing EEG
irreversible damage
CBF is autoregulated in range:
- MAP 60 - 160mmHg
- based on: - myogenic response
- metabolic issues (tissue metabolites)
Tension of pCO2 versus CBF:
- nearly linear relationship in range of pCO2 20 - 80
(1-2 ml/100g/min/mmHg)
Tension of pO2 versus CBF:
- independent down to 50mmHg, then log
Temperature versus CBF:
- 5 to 7% /celsius
- > 42 => neuronal cell injury
What is ideal Hct for optimal cerebral oxygen delivery:
- 30%
What usually disrupt blood-brain barrier:
- severe hypertension
- tumors / trauma
- strokes / sustained seizures
- infection / marked hypoxia / hypercapnia
Volume of CSF:
- 150ml
Speed of secretion of CSF:
- 21 ml/hr
What decreases CSF production:
- diuretics
- corticosteroids
- vasoconstrictors
- isoflurane
Cranial vault consist of:
- brain (80%)
- blood (12%)
- CSF (8%)
ICP is defined:
- cortex / lateral ventricle CSF pressure
- norm: < 10mmHg
- in lateral position = lumbar CSF pressure
When ICP raises the major compensatory mech.starts:
- initial displacement of CSF from cranial to spinal compartment
- increase of CSFabsorption
- decrease in CSF production
- decrease in total CBV (mainly venous)
Potential sites of brain herniation:
- g.cinguli -> falx cerebri
- g.uncinatus -> tentorium cerebelli
- cereb.tonsills -> foramen magnum
- any area through a defect in the skull
Effect of anesthetic agents on cerebral physiology:
- CMR goes down (reduced electrical activity)
- ICP and CBF up: Ketamine, Halotan and inhalation anestetic
