Abstract P114: The Importance of Measuring Oxygen Debt in Hemorrhagic Shock
Introduction: Oxygen debt (OD) a discrete measure of global tissue hypoxia and is linked with survival in critical injury including hemorrhagic shock (HS). OD repayment is believed to be critical to avoid multiple organ failure. However, it is difficult to measure and most HS models do not include OD as a measured variable. We determined the correlative relationships between OD and lactate, hemoglobin (Hb), and hemorrhage volumes in HS.
Methods: Forty-one anesthetized instrumented swine (46±4.5 kg) were hemorrhaged to an OD of 80 cc/kg. OD was determined by indirect calorimetry by measuring the cumulative difference between baseline oxygen consumption (VO2) and current VO2 during every minute of hemorrhage and resuscitation. Concurrent arterial Hb and lactate levels were taken when 25%, 50%, 75% and 100% of the OD target was reached as well as every 30 min during the resuscitation period for 3 hours. Animals were resuscitated upon reaching target OD with a combination of crystalloid, colloid, and blood. Hemorrhage volumes and time necessary to reach target OD were recorded. Simple correlative analysis was performed.
Results: Hemorrhage volumes were highly correlated with OD (r=0.73 for hemorrhage volume and 0.74 for % blood volume) (p<0.0001). However, volumes ranged from 320 to 1680 cc (14 –51% of blood volume). Average time to achieve target OD was 77±25.7 min with the range between 29 and 138 min. Hb levels had an overall correlation with OD over the entire experiment of only −0.171 (p<0.0001). Hb levels during hemorrhage to reach target OD had a correlation of −0.085 (p=0.1) with concentrations ranging from 5.0 –12.7 g/dl. Hb levels during the resuscitation had a correlation with OD of −0.097 (p=0.07). Lactate levels were highly correlated with OD during hemorrhage (r=0.85; p<0.0001) but became much less correlated during resuscitation (r=0.415; p<0.001).
Conclusion: Hemorrhage volume and Hb levels correlate poorly with OD and time to reach target OD is extremely variable. While lactate levels correlate highly with OD during HS they loose much of their correlative power during resuscitation and cannot be used to ensure that OD has been repaid. These finding raise concerns for models of HS as well as in potentially assessing the adequacy of resuscitation in patients.