What are the best markers of essential tissue hypoperfusion in haemorrhagic shock?

Introduction: The pathophysiology of haemorrhagic shock is related to a reduction in end organ tissue perfusion and oxygenation. Until recently, studies have relied on global, surrogate markers of tissue oxygenation, or overall morbidity and mortality. Although important, these studies are complicated by multiple confounding variables, and do not look directly at the presumed site of the pathology-the end organ tissue itself. Objectives: To correlate traditional global markers of shock severity (lactate, vital signs, central venous O2 saturation and cardiac output) with actual tissue oxygenation and perfusion in the renal cortex, brain and skeletal muscle, using an ovine (sheep) model. Methods: Under full anaesthesia, controlled haemorrhage of 30% total blood volume was affected. Sheep were instrumented to allow monitoring of continuous cardiac output, central venous oxygenation and arterial blood gas status. Direct tissue oximetry was measured and continuously monitored in the brain, skeletal muscle and renal cortex using combined tissue oximeters and perfusion probes. Findings: Graphical representation of vital signs, arterial blood gas status, continuous cardiac output, central venous O2, compared to renal, cerebral and skeletal muscle perfusion and oxygenation during haemorrhage. Data: All sheep, with minutely vitals/cardiac output, oxygen delivery etc/tissue O2 from 15 min before haemorrhage to half hour post haemorrhage, compared with the half hourly gases and lactate Conclusion: The data suggests that measurement of serum lactate and other global markers underestimate the severity of end organ hypoxia and hypoperfusion