The influence of hemorrhage on organ perfusion during deliberate hypotension in rats

There is general concern that major blood loss during deliberate hypotension could produce severe organ ischemia, but documentation of the magnitude of this response remains obscure. To examine this response, we studied 43 male Sprague-Dawley rats that were divided into seven groups: the control animals received 1 MAC (1.4%) isoflurane only; the hypotensive animals received a 1.4% isoflurane baseline anesthetic and were then rendered hypotensive by either increasing the isoflurane concentration (dISO), or by adding sodium nitroprusside (SNP), or 2-chloroadenosine (2AD) to the baseline anesthetic, decreasing the MAP to 51 mmHg; hemorrhaged animals had hypotension produced in the same manner as for the hypotensive animals, but additionally were bled 20% of estimated blood volume during deliberate hypotension produced with either deep isoflurane (dISOH), sodium nitroprusside (SNPH), or 2-chloroadenosine (2ADH). After a 25-min period of hypotension, or hypotension plus hemorrhage, cardiac output and blood flow to brain, heart, gastrointestinal tract, kidney, and liver were measured with 141Ce-labelled 15-microns microspheres. Hypotension was associated with decreased blood flow to the kidneys in all groups and to the liver in the 2AD group and an increased blood flow to the heart in the SNP and 2AD groups. Hemorrhage decreased blood flow during deliberate hypotension to the brain and the gastrointestinal tract in the dISOH and 2ADH groups and to the liver in the dISOH group. Our results suggest that hemorrhage during deliberate hypotension with dISO or isoflurane plus 2AD may be associated with compromised organ blood flow, whereas blood flow to vital organs is maintained after 20% hemorrhage during isoflurane and superimposed SNP-induced hypotension.