Comparison of local measurement of cerebral metabolism and to cerebral PvO2 during alterations in intracranial pressure, PaCO2 and arterial pressure--an experimental study in goat.
OBJECTIVE
to assess the changes in local brain PO2, PCO2, pH (PO2br, PCO2br, pHbr) measured by a intraparenchymal probe (Neurotrend, Codeman) and compare them to simultaneous recording of cerebral PvO2 and blood flow (CBF).


METHODS
Arterial, venous longitudinal sinus blood samples and CBF were analyzed in 8 adult anesthetized, ventilated goats. Three step increase of intracranial pressure (ICP) (16, 22, 29 mm Hg) were performed by inflation of an epidural balloon. At each ICP level, similar changes in MAP and in PaCO2 were performed.


RESULTS
At constant PaCO2 and MAP, balloon inflation induced a fast response: a decrease of PO2br, PCO2br and pHbr (starting 14 +/- 12 sec, 45 +/- 23 sec and 55 +/- 19 sec after the peak ICP, respectively). Since the second inflation level, PO2br decreased (p < 0.05) despite an ICP returning at 22 mm Hg and a cerebral perfusion pressure (CPP) larger than 90 mmHg. During changes in PaCO2, PO2br paralleled CBF and PvO2 before the second balloon inflation but diverged at higher ICP. In the same time pH-pHbr gradient rose. Hypotension did not induce sizeable changes.


CONCLUSIONS
The direct metabolic monitoring of cerebral tissue locally compressed show fast response. At steady state, it shows alterations which are not detected by the measurement of the oxygen saturation in the longitudinal sinus or that of CBF. It confirms that the threshold for ICP which may require therapy in presence of focal brain compression is around 20 mm Hg even in the presence of a CPP > 90 mm Hg.
Ter Minassian
Aram
A
Département d'Anesthésie, CHU d'Angers, Angers, France.
Desfontis
Jean Claude
JC
Gautier
Freddy
F
Douart
Claire
C
Ursino
Mauro
M
Denizot
Benoît
B
Gogny
Marc
M
Beydon
Laurent
L
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D006041:Goats; D019586:Intracranial Hypertension; D007427:Intracranial Pressure; D008991:Monitoring, Physiologic; D010100:Oxygen / Q000032:analysis*; D012815:Signal Processing, Computer-Assisted
D010100:Oxygen