Intraoperative endogenous erythropoietin levels and changes in intravascular blood volume in healthy humans

There is accumulating evidence of a relationship between changes in intravascular blood volume and endogenous erythropoietin (EPO) levels. In this study, eight healthy adult American Society of Anesthesiologists class-I patients due for prolonged elective surgery were randomised either to preoperative hypervolaemic haemodilution using hydroxyethyl starch, followed by intraoperative crystalloid infusion, or to standard intraoperative normovolaemic fluid balance management using crystalloids (control group). Electrolytes, creatinine, urea, osmolality, urine output and blood gases were monitored pre- and intraoperatively for 6 h, Comparable cardiopulmonary and renal homeostasis were maintained in both groups. We found that central venous pressure increased and EPO levels decreased, both significantly, in the hypervolaemic haemodilution group relative to controls. There were no significant intergroup changes in any other parameters. By controlling for other known determinants of EPO levels, our data indicate a relationship between EPO levels and changes in intravascular blood volume in humans, supporting the notion of EPO as a volume-regulated, and possibly volume-regulating, hormone.