WEEK 1 - Acute Cerebral Injury
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How much of cardiac output does the brain receive?
20% (800-1000mL)
Which gas is the primary regulator of cerebral blood flow?
CO2 (also controls pH)
Which three organ work together to ensure the brain has adequate blood flow all the time?
Brain, heart and lungs
What makes up cerebral blood flow (CBF)? (equation?)
CBF = CPP/CVR, CPP - cerebral perfusion pressure CVR - cerebral vascular resistance
What makes up vascular resistance? (3 parts)
• Vessel diameter • Vessel length • Blood viscosity
What can CBF be affected by?
• Metabolism - PaO2, PaCO2, pH • BP (cardiac function) • Blood viscosity
What is CBF autoregulation?
Brain’s intrinsic ability to maintain a constant CBF despite marked changes in systemic BP through vessel constriction and dilation
What are the parameters within which CBF aims to keep MAP?
60-140 mmHg
What is pulse pressure?
Recoil of an artery following the heart beat
Causes of acidosis?
• Increased CO2 • Decreased O2 • Increased H+ • Decreased pH
Causes of alkalosis?
• Decreased CO2 - Increase of pH
Equation to form H+?
CO2 + H2O = H2CO3 (carbonic acid) = dissociates to form H+
Names of all the ventricles in the brain?
Lateral ventricles (left and right), third ventricle and fourth ventricle
What is contained in the ventricles and where is it made?
CSF in the ventricles Made by the choroid plexus (lies in the lateral ventricles)
Describe the pathway CSF takes through the brain
Choroid plexus - lateral ventricles - interventricular foramen of Monro - 3rd ventricle - cerebral aqueduct - 4th ventricle - subarachnoid space - absorption via subarachnoid villi - venous blood
What is intracranial pressure (ICP?)
The pressure exerted by CSF that circulates around the brain and into the ventricles
What proportions of the cranial volume do CSF, blood and brain tissue make up?
• CSF = 10% • Blood = 10% • Brain tissue = 80%
What is ICP determined by?
Changes in intracranial blood volume and changes in pressure exerted by CSF that circulates around the brain, spinal cord and ventricles
Why is ICP talked about as a RANGE of pressures and not as a single pressure?
Because ICP is in reference to atmospheric pressure = different areas of the brain vary in their pressures
What is the ICP reference range?
5-10 mmHg though 15 is considered the upper limit of the norm
What is a burr hole and when/why would this be used?
Burr hole - small hole drilled into the cranium This would be used when ICP is elevated - holes help to relieve the pressure and let it out
What is the CPP of an adult?
80 mmHg
Equation for CPP?
CPP = MAP - ICP
If the volume of one component of the cranium is increased, the others must decrease to compensate. What happens if this doesn’t occur?
Compliance of the brain is exhausted and ICP rises - also supercedes the ability of the brain to regulate CPP