Intracranial pressure autoregulation

Sevoflurane has a dose-dependent effect on cerebral blood flow and intracranial pressure cerebral autoregulation is preserved (this is not the case with isoflurane). During hypocarbia, in the absence of nitrous oxide, 1 MAC does not increase intracranial pressure (ICP). It reduces the cerebral metabolic rate for oxygen (CMR02) by approximately 50% at concentrations approaching 2 MAC. This is similar to the reduction observed during isoflurane anaesthesia. 

Cerebral blood flow depends on cerebral perfusion pressure and cerebrovascular resistance. The perfusion pressure is the difference between systemic arterial pressure at the base of the brain when in the recumbent position and the venous pressure at exit from the subarachnoid space, the latter being approximated by the intracranial pressure. Cerebral perfusion pressure divided by cerebral blood flow gives the cerebrovascular resistance. In normal humans, cerebral blood flow remains almost constant when the mean systemic blood pressure is between approximately 50 and 170mmHg, which, under normal circumstances when the intracranial venous pressure is negligible, is the same as the cerebral perfusion pressure. This homeostatic mechanism to maintain a constant cerebral blood flow in the face of changes in cerebral perfusion pressure is known as autoregulation (Reed and Devous 1985 Powers 1993). Autoregulation is less effective in the elderly, and so postural hypotension is more likely to be symptomatic (Wollner et al. 1979 Parry et al. 2006). 

Damaged brain appears to have impaired responsiveness to arterial partial pressure of carbon dioxide and oxygen as well as impaired autoregulation and perfusion reserve, increasing the likelihood of further secondary insults such as systemic hypoxia, hypotension and raised intracranial pressure (Cormio et al. 1997). There are good theoretical... 

Nervous System Halothane dilates the cerebral vasculature, increasing cerebral blood flow under most conditions. This increase in blood flow can increase intracranial pressure in patients with space-occupying intracranial masses, brain edema, or preexisting intracranial hypertension. Thus, halothane is relatively contraindicated in patients at risk for elevated intracranial pressure. Halothane also attenuates autoregulation of cerebral blood flow. 

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