Effect of acute normovolemic hemodilution on distribution of blood flow and tissue oxygenation in dog skeletal muscle

Acute normovolemic hemodilution (ANH) is efficient in reducing allogenic bl ood transfusion needs during elective surgery. Tissue oxygenation is mainta ined by increased cardiac output and oxygen extraction and, presumably, a m ore homogeneous tissue perfusion. The aim of this study was to investigate blood flow distribution and oxygenation of skeletal muscle. ANH from hemato crit of 36 +/- 3 to 20 +/- 1% was performed in 22 splenectomized, anestheti zed beagles (17 analyzed) ventilated with room air. Normovolemia was confir med by measurement of blood volume. Distribution of perfusion within skelet al muscle was determined by using radioactive microspheres. Tissue oxygen p artial pressure was assessed with a polarographic platinum surface electrod e. Cardiac index (3.69 +/- 0.79 vs. 4.79 +/- 0.731 min(-1).m(-2)) and muscl e perfusion (4.07 +/- 0.44 vs. 5.18 +/- 0.36 ml.100 g(-1).min(-1)) were inc reased at hematocrit of 20%. Oxygen delivery to skeletal muscle was reduced to 74% of baseline values (0.64 +/- 0.06 vs. 0.48 +/- 0.03 mi O-2.100 g(-1 ).min(-1)). Nevertheless, tissue PO2 was preserved (27.4 +/- 1.3 vs. 29.9 /- 1.4 Torr). Heterogeneity of muscle perfusion (relative dispersion) was r educed after ANH (20.0 +/- 2.2 vs. 13.9 +/- 1.5%). We conclude that a more homogeneous distribution of perfusion is one mechanism for the preservation of tissue oxygenation after moderate ANH, despite reduced oxygen delivery.