Hemorrhage produces depression in microvascular blood flow which persists despite fluid resuscitation

Although various hemodynamic changes occur during and following hemorrhagic shock, the progressive changes in microvascular blood flow (MBF) in various organs under those conditions have not been determined. To study this, non-heparinized rats were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% o the shed blood volume was returned in the form of Ringer's lactate (RL). The rats were then resuscitated with 2, 3, or 4 times (x) the volume of maximum bleedout with RL. Laser Doppler flowmetry (LDF) was used to determine the MBF in the liver, kidney, spleen, skeletal muscle, and small intestine at different intervals following hemorrhage and resuscitation. The results indicate that MBF was significantly decreased during hemorrhage and remained depressed 30-240 min post-resuscitation in all the measured organs. This was not due to the decreased hematocrit since acute hemodilution did not significantly depress MBF. These results indicate that 1) LDF is a useful technique for repeated assessment of MBF following hemorrhage and resuscitation; 2) resuscitation with 4x RL increased central venous pressure to more than twice the normal value but did not restore or maintain MBF, suggesting that pharmacological support may be needed under such conditions; 3) the lack of maintenance of MBF following hemorrhage and resuscitation may form the basis of multiple organ failure observed following severe and prolonged hemorrhagic shock.