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Global cerebral blood flow (CBF) is normally about 54 ml/100 g/min.

Which one of the following options is likely to result if the CBF falls below 35 ml/100 g/min?

(Please select 1 option)

More damage than complete ischaemia

Rise in lactate

Irreversible brain damage Incorrect answer selected

Liberation of free radicals

Poor prognostic EEG This is the correct answer

Explanation

Cerebral ischaemia can either be global or focal, either complete or incomplete. At blood flow levels of 30-40 ml/100 g/min EEG changes begin to appear. The EEG changes that suggest poor prognosis are low voltage, poorly reactive rhythms, periodic lateralised epileptiform discharges and fluctuations in underlying rhythms.

Incomplete ischaemia causes several insults depending on the reduction of blood flow.

Glucose will still be metabolised albeit anaerobically. The waste products of anaerobic metabolism will not be removed efficiently due to reduced blood supply. This results in worse acidosis compared to complete cessation of blood supply.

Studies to prove whether incomplete ischaemia causes more damage than complete ischaemia have been inconclusive. At 30-40 ml/100 g/min causes EEG changes as described above. When the blood flow decreases to 20 ml/100 g/min lactate levels increase. Between 20 ml/100 g/min - 10 ml/100 g/min free radicals are released and evoked potentials begin to disappear.

At flow rates lesser than 10 ml/100 g/min irreversible damage occurs due to water accumulation.

Answer Statistics

1

18%

2

17%

3

18%

4

36%

5

14%

Times answered: 244