Using a diagram, explain the effect of PaO2, PaCO2 and MAP (mean arterial pressure) on cerebral blood flow (60% marks). Outline the effects of propofol and ketamine on cerebral blood flow (CBF), cerebral metabolic requirement for oxygen (CMRO2), and cerebral venous oxygen saturation (40% marks). 

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College Answer

Graphical depictions of the effect of Mean Arterial Pressure, oxygen tension and carbon dioxide 
tension on cerebral blood flow were common and in general accurate. Mention of factors that 
affected, and regulation of, the MAP vs CBF graph was expected in order to pass this question 
well. 
The effect of propofol and ketamine on the CBF was well answered. Propofol and ketamine have 
an opposite effect on cerebral haemodynamic and metabolic rate. Propofol produces a dose 
dependent reduction in CBF with proportionate reduction in CMRO2, and thus a minimal change 
in cerebral venous O2 Sat. Propofol doesn’t affect the autoregulatory curve of CBF and the 
PaCO2 response. Ketamine produce a dose dependent increase in CBF and a mild increase in 
CMRO2. 

Recommended sources: Guyton Textbook of Medical Physiology Chp 61; Goodman and Gilman 
The pharmacological basis of therapeutics 11th edition pgs 350-352.