Venous oxygen saturation during normovolaemic haemodilution in the pig.
BACKGROUND
Hypovolaemia may be considered to represent a volume-restricted cardiac output (CO), but CO varies inversely with the haemoglobin concentration (Hb) and a maximal mixed venous oxygen saturation (SvO2) may be a better target for volume administration than a maximal CO.


METHODS
In 10 anaesthetized pigs, volume loading with 6% hydroxyethyl starch was performed to obtain a maximal SvO2 followed by normovolaemic haemodilution with 6% hydroxyethyl starch.


RESULTS
Volume loading increased SvO2 from 55.0+/-5.2% to 64.8+/-9.0% (mean+/-SD) associated with an increase in CO (2.3+/-0.4 to 3.5+/-0.9 l/min) and central venous oxygen saturation (ScvO2; 68.2+/-9.3% to 79.4+/-7.2%; P<0.05). Heart rate (HR), mean arterial (MAP), central venous (CVP), pulmonary arterial mean (PAMP), and occlusion pressures (PAOP) increased as well (P<0.05). In contrast, during progressive haemodilution, SvO2 and ScvO2 remained statistically unchanged until the haemoglobin concentration had decreased from 5.5+/-0.4 to 2.9+/-0.2 mM, while CO and HR increased at a haemoglobin value of 4.4+/-0.4 and 4.0+/-0.4 mM and CVP and PAOP decreased at a haemoglobin of 4.0+/-0.4 and 2.9+/-0.2 mM, respectively (P<0.05) leaving MAP unaffected.


CONCLUSIONS
This study found that volume loading increased cardiac output and mixed and central venous oxygen saturations in parallel, but during normovolaemic haemodilution an increase in cardiac output left mixed and central venous oxygen saturations statistically unchanged until haemoglobin concentration was reduced by approximately 50%. Accordingly, volume therapy should be directed to maintain a high venous oxygen saturation rather than a change in cardiac output.
Krantz
T
T
Copenhagen Muscle Research Center, Department of Anesthesia, Rigshospitalet, Denmark. torbenkrantz@dadlnet.dk
Warberg
J
J
Secher
N H
NH
D000818:Animals; D001784:Blood Gas Analysis / Q000379:methods; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006438:Hemodilution / Q000379:methods*; D006439:Hemodynamics / Q000187:drug effects; D006454:Hemoglobins / Q000187:drug effects; D006895:Hydroxyethyl Starch Derivatives / Q000008:administration & dosage; D023421:Models, Animal; D010100:Oxygen / Q000097:blood*; D010952:Plasma Substitutes / Q000008:administration & dosage; D013552:Swine; D014680:Veins / Q000502:physiology*
D006454:Hemoglobins; D006895:Hydroxyethyl Starch Derivatives; D010952:Plasma Substitutes; D010100:Oxygen