Authors: Krantz, T.¹; Warberg, J.²; Secher, N. H.¹

Source: Acta Anaesthesiologica Scandinavica, Volume 49, Number 8, September 2005 , pp. 1149-1156(8)

Publisher: Wiley-Blackwell

Abstract:

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 (S_vO₂) 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 S_vO₂ followed by normovolaemic haemodilution with 6% hydroxyethyl starch. Results: 

Volume loading increased S_vO₂ 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 (S_cvO₂; 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, S_vO₂ and S_cvO₂ 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. Conclusion: 

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 ∼50%. Accordingly, volume therapy should be directed to maintain a high venous oxygen saturation rather than a change in cardiac output.

Keywords: anaemia; atrial natriuretic peptide; blood pressure; cardiac output; central venous pressure; electrical admittance; heart rate; pulmonary artery pressure; shock; wedge pressure

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1399-6576.2005.00778.x

Affiliations: 1: Copenhagen Muscle Research Center, Department of Anesthesia, Rigshospitalet and 2: Department of Medical Physiology, the Panum Institute, University of Copenhagen, Denmark

Publication date: 2005-09-01

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