Determination of the Optimal Mean Arterial Pressure for Postbleeding Resuscitation after Hemorrhagic Shock in Rats

BACKGROUND: The authors previously found that 50-60 mmHg mean arterial blood pressure (MAP) was an optimal target resuscitation pressure for hemorrhagic shock before bleeding was controlled in rats. However, the optimal target resuscitation pressure for hemorrhagic shock after bleeding has been controlled has not been determined. METHODS: A model of uncontrolled hemorrhagic shock was initiated in anesthetized Wistar rats. After 1-h hypotensive resuscitation and bleeding was stopped, rats received fluid resuscitation to different target MAPs (50, 70, or 90 mmHg) with lactated Ringer's solution (LR), 6% hydroxyethyl starch (HES), LR+HES (2:1) or LR+whole blood (2:1) for 2 h. Animal survival, hemodynamic parameters, and vital organ functions were observed. RESULTS: After bleeding had been controlled, mildly hypotensive resuscitation at a target MAP of 70 mmHg increased the survival time and survival rate compared with a target MAP of 50 mmHg and 90 mmHg (P < 0.05 or 0.01). Hemodynamic parameters, cardiac output, oxygen delivery, and vital organ function (including mitochondrial function) in 70 mmHg target MAP groups were better than in other two-target pressure groups (P < 0.05 or 0.01). Among the fluids tested, LR+whole blood (2:1) or LR+HES130 (2:1) had better effects than LR or HES alone at each level of target blood pressure. CONCLUSION: Mildly hypotensive resuscitation is also needed for hemorrhagic shock after bleeding has been controlled, irrespective of whether crystalloids or colloids are used. The optimal target pressure was 70 mmHg in our rat model. A resuscitation pressure that is too low or too high cannot produce a good resuscitative effect.