Assessment of Global Ischemia - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 355

Chapter 25
Assessment of Global Ischemia
Fatima A. Sehba and Joshua B. Bederson
Abstract
A number of methods have been used to assess global cerebral ischemia after subarachnoid hemorrhage
(SAH). During global ischemia, vascular perfusion is reduced and brain cells are hypoxic. This chapter
describes two techniques of assessing global ischemia after SAH. The fi rst explains how cerebral vessels can
be examined for perfusion status and the second describes how cerebral interstitial fl uid can be studied for
the signs of cellular hypoxia after SAH. Each technique offers advantages and disadvantages and selection
of one over the other depends upon the operator's choice and availability of instruments.
Key words: Global ischemia, Rat, Subarachnoid hemorrhage, Perfusion, Microdialysis
1. Introduction
Ischemic brain injury after subarachnoid hemorrhage (SAH) is
global in nature, and appears in two phases; early ischemia at the
time of the initial hemorrhage ( 1-3 ), and delayed vasospasm and
ischemia that develops 3-7 days later ( 4-6 ). Studies document
that, compared to delayed cerebral ischemia; deleterious effects of
the initial injury are by far the most important cause of death after
SAH, and of neurological defi cits in survivors ( 7-9 ).
Animal models have been developed to study the mechanisms
underlying early and delayed brain injury after SAH ( 10-14 ).
These models provide a deeper insight into the changes occurring
in the brain and their contribution to the injury after SAH.
Moreover, they help in development of analytical techniques that if
found successful can later be modifi ed for use in humans.
This chapter describes two techniques for assessing global
cerebral ischemia in animals after SAH.