Subcutaneous perfusion and oxygen during acute severe isovolemic hemodilution in healthy volunteers

Hypothesis: Acute severe isovolemic anemia (to a hemoglobin [Hb] concentrat ion of 50 g/L) does not decrease subcutaneous wound tissue oxygen tension ( PsqO(2)). 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) wer e measured continuously during isovolemic hemodilution to an Hb level of 50 g/L. In 14 volunteers (initially well-perfused), "normal" perfusion (Tsq > 34.4 degreesC) was achieved by hydration and systemic warming prior to star ting isovolemic hemodilution, while in 11 volunteers (perfusion not control led [PNC]), no attempt was made to control perfusion prior to hemodilution. Main Outcome Measures: Measurements of PsqO(2), Tsq, and relative subcutane ous blood flow (flow index). Results: While PsqO(2), 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 decreas e significantly in either group. Arterial PO2 was not different between the groups, and did not change significantly over time; Tsq and flow index inc reased significantly from baseline to nadir Hb in both groups. Conclusions: The level of PsqO(2) was maintained at base line levels during hemodilution to Hb 50 g/L in healthy volunteers, whether they were initial ly well-perfused or mildly underperfused peripherally. Given the significan t increase in Tsq and flow index, this resulted from a compensatory increas e 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 impai r wound healing. Thus, transfusion of autologous packed red blood cells sol ely to improve healing in surgical patients with no other indication for tr ansfusion is not supported by these results.