Sodium nitroprusside compared with isoflurane-induced hypotension: the effects on brain oxygenation and arteriovenous shunting.
We compared sodium nitroprusside (SNP)-induced hypotension with 3% isoflurane-induced hypotension with regard to brain tissue oxygen pressure (PtO(2)), middle cerebral artery (MCA) blood flow, and cerebral arteriovenous shunting. Eight dogs were anesthetized with 1.5% isoflurane. After a craniotomy, a probe was inserted into the left frontoparietal brain cortex to mea-sure tissue gases and pH. Blood flow was measured in a secondary branch of the MCA by a flowprobe. Measurements were made during baseline 1.5% isoflurane, during 1.5% isoflurane and SNP-induced hypotension or 3% isoflurane-induced hypotension to a mean pressure of 60-65 mm Hg, and during continued treatment with SNP or 3% isoflurane with blood pressure support to baseline levels with phenylephrine. Shunting was calculated from arterial, sagittal sinus, and tissue (indicating capillary) oxygen content. During hypotension with SNP, PtO(2) decreased 50%, and shunting increased 50%. During hypotension with 3% isoflurane, PtO(2) and shunting did not change. Blood pressure support increased PtO(2) and MCA flow during both SNP and 3% isoflurane treatment. These results show that SNP is a cerebrovasodilator but that hypotension will decrease PtO(2), probably because of an increase in arteriovenous shunting and a decrease in capillary perfusion.


CONCLUSIONS
We measured brain arteriovenous shunting and tissue oxygen pressure(PtO(2))during a 40% decrease in blood pressure induced by sodium nitroprusside (SNP)or 3% isoflurane. Large-dose isoflurane maintainedPtO(2) with no change in shunting. SNP infusion decreasedPtO(2) 50%and increased shunting 50%. This suggests that SNP-induced hypotension decreases PtO(2) because of a decrease in capillary perfusion.
Hoffman
W E
WE
Department of Anesthesiology, University of Illinois at Chicago, 60612, USA. whoffman@uic.edu
Edelman
G
G
Ripper
R
R
Koenig
H M
HM
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001164:Arteriovenous Fistula / Q000139:chemically induced*; D001784:Blood Gas Analysis; D001831:Body Temperature / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects*; D002560:Cerebrovascular Circulation / Q000187:drug effects; D004285:Dogs; D006439:Hemodynamics / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007022:Hypotension / Q000139:chemically induced* / Q000503:physiopathology; D007530:Isoflurane / Q000494:pharmacology*; D020768:Middle Cerebral Artery / Q000502:physiology; D009599:Nitroprusside / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects*
D018685:Anesthetics, Inhalation; D000959:Antihypertensive Agents; D009599:Nitroprusside; D007530:Isoflurane