The primary mechanism by which thiopentone offers cerebroprotection is – (AIPG 2012)
|A||Decreased brain metabolism|
|B||By acting as a free radical scavenger|
|C||Calcium channel blocker|
|D||GABA agonist mechanism|
Decreased brain metabolism
a. The barbiturates decrease both CBF and CMRO2 in humans.
b. Treatment with barbiturates does not prevent CBF auto -regulation, however, the response to hypoxia and hypercapnia is attenuated because of metabolic depression. In addition to their effect on metabolism, barbiturates may have direct effects on vascular tone causing cerebral vasoconstriction hence a decrease in CBF and ICP.
c. The mechanism for vasoconstriction appears to be due to influx of calcium into vascular smooth muscles.
d. Incremental does of pentothal may decrease the CBF and CMRO2 by 55-60 percent5.In the clinical setting, if it is desirable to pursuenear maximal brain metabolic suppression with thiopental for brain protection, an end point of complete burst suppression on the EEG introduces an increased risk of significant haemodynamic depression with little furthercerebral metabolic suppression as compared to a safer burst suppression EEG pattern with 3-6 residual bursts per min.
e. However, it may be argued that even a burst suppression pattern may not be safe, as this too requiresa relatively higher dose of pentothal.