Ideal Permissive Hypotension to Resuscitate Uncontrolled Hemorrhagic Shock and the Tolerance Time in Rats

Background: Studies have shown that permissive hypotension for uncontrolled hemorrhagic shock can result in good resuscitation outcome. The ideal target mean arterial pressure (MAP) and the tolerance time for permissive hypotension have not been determined. Methods: To elucidate the ideal target MAP and tolerance time for permissive hypotension with uncontrolled hemorrhagic shock rats, the effects of different target MAPs (40, 50, 60, 70, 80, and 100 mmHg) and 60-, 90-, and 120-min permissive hypotension (50 mmHg) on uncontrolled hemorrhagic shock were observed. Results: Rats in normotensive groups (80 and 100 mmHg) had increased blood loss (101%, 126% of total blood volume), decreased hematocrit, decreased vital organ (liver and kidney) and mitochondrial function, and decreased animal survival rate (1 of 10). Rats in the 50- and 60-mmHg target MAP groups had decreased blood loss (52% and 69%, respectively), good hematocrit and vital organ and mitochondrial function, stable hemodynamics, and increased animal survival (8 of 10 and 6 of 10, respectively). Rats in the 40-mmHg target MAP group, although having decreased blood loss (39%), appeared to have very inferior organ function and animal survival (2 of 10). Animal survival (1 of 10) and vital organ function in the 120-min permissive hypotension group were significantly inferior to the 60- and 90-min groups. The 60- and 90-min groups had similar animal survival (8 of 10 and 6 of 10) and vital organ function. Conclusion: A target resuscitation pressure of 50-60 mmHg is the ideal blood pressure for uncontrolled hemorrhagic shock. Ninety minutes of permissive hypotension is the tolerance limit; 120 min of hypotensive resuscitation can cause severe organ damage and should be avoided.