Subcutaneous Perfusion and Oxygen During Acute Severe Isovolemic Hemodilution in Healthy Volunteers

Hypothesis Acute severe isovolemic anemia (to a hemoglobin [Hb] concentration of 50 g/L) does not decrease subcutaneous wound tissue oxygen tension (PsqO2). Setting University hospital operating room and inpatient general clinical research center ward. Subjects Twenty-five healthy, paid volunteers. Methods Subcutaneous oxygen tension and subcutaneous temperature (Tsq) were measured continuously during isovolemic hemodilution to an Hb level of 50 g/L. In 14 volunteers (initially well-perfused), normal perfusion (Tsq \u3e34.4°C) was achieved by hydration and systemic warming prior to starting isovolemic hemodilution, while in 11 volunteers (perfusion not controlled [PNC]), no attempt was made to control perfusion prior to hemodilution. Main Outcome Measures Measurements of PsqO2, Tsq, and relative subcutaneous blood flow (flow index). Results While PsqO2, Tsq, and flow index were significantly lower in PNC vs well-perfused subjects at baseline, there was no significant difference between them at the Hb of 50 g/L (nadir). Subcutaneous PO2 did not decrease significantly in either group. Arterial PO2 was not different between the groups, and did not change significantly over time; Tsq and flow index increased significantly from baseline to nadir Hb in both groups. Conclusions The level of PsqO2 was maintained at baseline levels during hemodilution to Hb 50 g/L in healthy volunteers, whether they were initially well-perfused or mildly underperfused peripherally. Given the significant increase in Tsq and flow index, this resulted from a compensatory increase in subcutaneous blood flow sufficient to maintain oxygen delivery. Wound healing depends to a large extent on tissue oxygen delivery, and these data suggest that even severe anemia by itself would not be sufficient to impair wound healing. Thus, transfusion of autologous packed red blood cells solely to improve healing in surgical patients with no other indication for transfusion is not supported by these results