Effects of isovolaemic haemodilution on oxygenation of liver and skeletal muscle

Background and objective: Hydroxyethyl starch is frequently used for volume substitution during surgical procedures and for isovolaemic haemodilution. Haemodilution has also been shown to improve tissue oxygen tension in skeletal muscle. However, effects of this volume substitute on tissue oxygen tension of the liver during haemodilution remains unknown. Methods: Fourteen foxhounds were anaesthetized with fentanyl/midazolam and mechanically ventilated with 30% oxygen. Following splenectomy animals were randomly assigned to a control group without haemodilution but fluid substitution with Ringer's lactate (Group C) or underwent isovolaemic haemodilution to a haematocrit of 25% with hydroxyethyl starch 70/0.5 (Group H). Haemodynamic parameters and oxygen transport during 100 min following isovolaemic haemodilution were measured. Liver oxygen tension was recorded using a flexible polarographic electrode tonometer, whereas in the muscle a polarographic needle probe was used. Results: Animal characteristics and baseline haematocrit were similar in both groups. At baseline the tissue oxygen tension of liver and skeletal muscle were not different between groups. Haemodilution with hydroxyethyl starch 70/0.5 provided augmentation of mean liver tissue oxygen tension (baseline: 46 ± 13 mmHg; 20 min: 60.3 ± 12 mmHg*; 60 min: 60 ± 16 mmHg*; 100 min: 63 ± 16 mmHg*; *P < 0.05 vs. baseline), while oxygen tensions in Group C remained unchanged (baseline: 48 ± 16 mmHg; 20 min: 52 ± 19 mmHg; 60 min: 49 ± 12 mmHg; 100 min: 52 ± 16 mmHg) and no differences could be detected between groups. Oxygen tension in skeletal muscle changed as follows: Group H - baseline: 24 ± 32 mmHg; 20 min: 32 ± 3 mmHg*†; 60 min: 33 ± 7 mmHg*†; 100 min: 33 ± 11 mmHg†. Group C - baseline: 22 ± 6 mmHg; 20 min: 21 ± 3 mmHg; 60 min: 24 ± 4 mmHg; 100 min: 18 ± 4 mmHg (*P < 0.05 vs. baseline, †P < 0.05 vs. Group C). Conclusion: In this animal model, isovolaemic haemodilution with hydroxyethyl starch 70/0.5 increased tissue oxygen tension in liver and skeletal muscle in comparison with baseline values. However, when compared between groups haemodilution only resulted in an increase of tissue oxygen tension in the muscle but not in the liver.