Alterations in tissue oxygen consumption and extraction after trauma and hemorrhagic shock

OBJECTIVESAlthough trauma and hemorrhage are associated with tissue hypoperfusion and hypoxemia, changes in oxygen delivery (˙DO2), oxygen consumption (O2), and oxygen extraction at the organ level in a small animal (such as the rat) model of trauma and hemorrhage have not been examined. Therefore, the objectives of this study were to determine whether blood flow, ˙DO2, O2, and oxygen extraction ratio in various organs are differentially altered after trauma-hemorrhagic shock and acute resuscitation in the rat. DESIGNProspective, randomized animal study. SETTINGA university research laboratory. SUBJECTSMale Sprague-Dawley rats (n = 6–7 animals/group) weighing 275–325 g. INTERVENTIONSMale rats underwent laparotomy (i.e., soft tissue trauma) and were bled to and maintained at a blood pressure of 40 mm Hg until 40% of shed blood volume was returned in the form of lactated Ringer’s solution. They were then resuscitated with four times the volume of shed blood with lactated Ringer’s solution for 60 mins. At 1.5 hrs postresuscitation, cardiac output and blood flow were determined by using strontium-85 microspheres. Blood samples (0.15 mL each) were collected from the femoral artery and vein and the hepatic, portal, and renal veins to determine total hemoglobin and oxygen content. Systemic and regional ˙DO2, O2, and oxygen extraction ratio were then calculated. MEASUREMENTS AND MAIN RESULTSBoth the systemic hemoglobin and systemic arterial oxygen content in hemorrhaged animals at 1.5 hrs postresuscitation were >50% lower as compared with sham-operated controls. Cardiac output and blood flow in the liver, small intestine, and kidneys decreased significantly, but blood flow in the brain and heart remained unaltered after hemorrhage and resuscitation. Systemic ˙DO2 and O2 were 73% and 54% lower, respectively, than controls at 1.5 hrs after resuscitation. Similarly, regional ˙DO2 and O2 in the liver, small intestine, and kidneys decreased significantly under such conditions. In addition, the liver had the most severe reduction in O2 (76%) among the tested organs. However, the oxygen extraction ratio in the liver of sham animals was the highest (72%) and remained unchanged after hemorrhage and resuscitation. CONCLUSIONBecause the liver experienced the most severe reduction in O2 associated with an unchanged oxygen extraction capacity, this organ appears to be more vulnerable to hypoxic insult after hemorrhagic shock.