Physiological Assessment in Stroke Research - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 79

approach for monitoring and controlling temperature in the aware
and mobile animal and is ideal for long-term monitoring of physi-
ologic variables in most experimental stroke approaches.

4. Blood Studies:
Hematocrit, pCO2,
pO2, pH, and
Glucose

Blood sampling is necessary for periodic measurement of hemato-
logic, respiratory, and endocrine values. Relevant laboratory stud-
ies and frequency of their measurement should be determined
based on the needs of the experimental approach, with deference
to the animal size. Frequent blood sampling is not advised in small
animals due to the limited blood volume and the potential impact
on outcome. Diehl ( 35 ) reviewed the typical blood volumes in
multiple strains of mice and determined that the average circulat-
ing blood volume is 7.2 ml/100 g body weight (range 6.3-
8.0 ml/100 g body weight). Estimations for rat suggest circulating
blood volume is 6.4 ml/100 g body weight (range 5.8-
7.0 ml/100 g body weight). Good laboratory practices recom-
mend that no more than 15% of total blood volume be removed if
the blood draw is not collected as a terminal event ( 17 ). Otherwise,
collecting more blood will induce a physiologic impact that can
adversely infl uence the reproducibility of the results and increase
the risk of morbidity in the animal.
Advances in point of care technology have simplifi ed the mea-
suring of a number of standard hematologic and chemistry studies.
Devices such as Abbott Laboratory's iSTAT ® (Abbott Park, IL)
offer a reliable and easy approach to obtaining the desired lab tests.
The drawback is the initial investment as these devices tend to be
costly and the need to purchase cartridges with the relevant labora-
tory tests.

4.1. Hematology:
Hematocrit

Basic hematologic tests can be conducted at the bench with minimal
equipment and very little blood volume. The most common bench
top hematologic test is a determination of spun hematocrit.
Hematocrit (often also referred to as Packed Cell Volume) is a
measure of the percentage of red blood cells contained within the
total blood volume. Hematocrit values in healthy rodents typically
fall between 35% and 52%. Commercially available microhemat-
ocrit tubes (plain and heparinized), a centrifuge and a hematocrit
scale are all that is needed for this test.

4.2. Acid-Base (pH)
and Respiratory (pCO2
and pO2) Parameters

Monitoring of the acid-base status is usually reserved for experi-
mental stroke studies in which the animal is ventilated for a pro-
longed period of time. This is key in experimental stroke because
prolonged hypoxia leads to increased CNS injury. Additionally,
hypercarbia (elevated pCO2) leads to increased CBF due to the