Ischemia
Comparison of Brain Tissue
Metabolic Changes During Ischemia
at 35° and 18°C
William E. Hoffman, Ph.D.,* Fady T. Charbel, M.D.,† Lorenzo Munoz, M.D.,†
and James I. Ausman, M.D., Ph.D.†
Departments of *Anesthesiology and †Neurosurgery, University of Illinois at Chicago,
Chicago, Illinois
Hoffman WE, Charbel FT, Munoz L, Ausman JI. Comparison of
brain tissue metabolic changes during ischemia at 35° and 18°C.
Surg Neurol 1998;49:85–9.
BACKGROUND
We evaluated brain tissue oxygen pressure (PO2), carbon
dioxide pressure (PCO2) and pH during ischemia with
brain temperature at 35° and 18°C in the same patient.
METHODS
Surgery was performed in a 60-year-old woman to clip a
large aneurysm in the left internal carotid artery (ICA). A
Paratrend 7 probe measuring PO2, PCO2, and pH was
inserted into tissue at risk for ischemia during ICA occlu-
sion and brain protection was provided with 9% desflu-
rane. One week later, hypothermic circulatory arrest with
brain temperature at 18°C was performed for aneurysm
clipping and tissue measurements were obtained during
ischemia and rewarming.
RESULTS
At 35°C, ICA occlusion for 16 minutes produced tissue
hypoxia (PO2 ϭ 0) and acidosis (pH ϭ 6.70). The rate of
increase of hydrogen ion (H
ϩ
) reached 50 nEq.L
Ϫ1
.min
Ϫ1
during ICA occlusion and there was a slow recovery of
acidosis at the end of the ischemic period. During hypo-
thermic circulatory arrest, tissue PO2 was sensitive to
decreases in blood pressure and decreased rapidly dur-
ing exsanguination. Although tissue pH decreased to 6.5
with 30 min of no pump flow, the rate of H
ϩ
increase
during hypothermic arrest was one-third of that seen
during ischemia at 35°C. During rewarming from pro-
found hypothermia, two phases of recovery from acidosis
were observed, one during CO2 clearance and one after
tissue reoxygenation. Recovery of acidosis occurred
sooner at 18°C than at 35°C.
CONCLUSIONS
These results show that tissue acidosis develops more
slowly and recovers more rapidly with hypothermic isch-
emia. This may be an important mechanism of reduced
ischemic injury during hypothermia. © 1998 by Elsevier
Science Inc.
KEY WORDS
Hypothermia, brain oxygen, carbon dioxide, hydrogen ion,
pH, ischemia.
I
t is well known that profound hypothermia will
reduce brain ischemic injury compared with to
normothermia [1,2]. Hypothermia with brain tem-
perature below 20°C has been used with total cir-
culatory arrest for 60 min or more with good cere-
bral recovery [1,3]. Although the mechanism of
hypothermic brain protection is not known, it may
involve the development of tissue acidosis. Tissue
acidosis has been closely associated with ischemic
brain injury [4,5] and it is possible that profound
hypothermia may attenuate ischemic acidosis by
decreasing brain metabolism. In this study we com-
pared tissue metabolic changes produced by isch-
emia when brain temperature was 35° and 18°C.
Case Report
This study was approved by the University of Illi-
nois Institutional Review Board for Clinical Re-
search and informed consent was received. A 60-
year-old female was admitted with a large aneurysm
identified by cerebral angiogram at the bifurcation
of the left internal carotid artery (ICA) and the pos-
terior communicating artery (PCA). A balloon oc-
clusion test of the left ICA revealed that the PCA did
not provide collateral circulation but that the ante-
rior communicating artery was patent. The patient
was anesthetized with fentanyl and thiopental, in-
tubated and ventilated with 6% end-tidal desflurane
and an inspired oxygen fraction of 0.4. Mean arterial
pressure, measured by radial artery catheter, was
maintained at 90 –95 mmHg. PaCO2 was maintained
at 31–33 mmHg. Esophageal temperature was al-
Address correspondence and reprint requests to: Dr. William E. Hoff-
man, Anesthesiology Department, Suite 3200, University of Illinois Hospi-
tal, 1740 West Taylor, Chicago, IL 60612.
Received January 17, 1997; accepted May 5, 1997.
© 1998 by Elsevier Science Inc. 0090-3019/98/$19.00
655 Avenue of the Americas, New York, NY 10010 PII S0090-3019(97)00297-8