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Evaluation of splanchnic oxygen extraction ratio as an index of portal vein pressure in dogs

Catriona M. MacPhailDepartment of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523-1620.

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Eric MonnetDepartment of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523-1620.

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James S. GaynorDepartment of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523-1620.

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Abstract

Objective—To determine changes in splanchnic oxygen extraction ratio during experimentally induced portal hypertension in dogs.

Animals—6 clinically normal dogs.

Procedure—Standard midline laparotomy and median sternotomy were performed in anesthetized dogs. Baseline measurements of arterial blood pressure, aortic blood flow, portal vein blood flow, and portal vein pressure were acquired, and arterial, venous, and portal vein blood samples were obtained to determine systemic and splanchnic oxygen extraction ratios. The portal vein was gradually occluded until a pressure of 18 cm of H2O was reached; this pressure was maintained for 30 minutes, and measurements and collection of blood samples were repeated.

Results—Portal vein blood flow decreased significantly from 457 ± 136 ml/min before to 266 ± 83 ml/min after induction of portal hypertension. Oxygen content in the portal vein significantly decreased from 12.3 ± 1.85 to 8.2 ± 2.31%, and splanchnic oxygen extraction ratio significantly increased from 15.8 ± 6.2 to 37.4 ± 10.9% during portal hypertension. There was a significant inverse correlation between portal vein blood flow and splanchnic oxygen extraction ratio at baseline and during portal hypertension.

Conclusion and Clinical Relevance—An increase in splanchnic oxygen extraction ratio is evident with partial attenuation of the portal vein and the concurrent decrease in portal vein blood flow. Correlation of oxygen extraction ratio with portal vein blood flow may be a more important indicator for determination of an endpoint to prevent congestion and ischemia of the gastrointestinal tract and pancreas during ligation of portosystemic shunts. (Am J Vet Res 2002;63:15–18)

Abstract

Objective—To determine changes in splanchnic oxygen extraction ratio during experimentally induced portal hypertension in dogs.

Animals—6 clinically normal dogs.

Procedure—Standard midline laparotomy and median sternotomy were performed in anesthetized dogs. Baseline measurements of arterial blood pressure, aortic blood flow, portal vein blood flow, and portal vein pressure were acquired, and arterial, venous, and portal vein blood samples were obtained to determine systemic and splanchnic oxygen extraction ratios. The portal vein was gradually occluded until a pressure of 18 cm of H2O was reached; this pressure was maintained for 30 minutes, and measurements and collection of blood samples were repeated.

Results—Portal vein blood flow decreased significantly from 457 ± 136 ml/min before to 266 ± 83 ml/min after induction of portal hypertension. Oxygen content in the portal vein significantly decreased from 12.3 ± 1.85 to 8.2 ± 2.31%, and splanchnic oxygen extraction ratio significantly increased from 15.8 ± 6.2 to 37.4 ± 10.9% during portal hypertension. There was a significant inverse correlation between portal vein blood flow and splanchnic oxygen extraction ratio at baseline and during portal hypertension.

Conclusion and Clinical Relevance—An increase in splanchnic oxygen extraction ratio is evident with partial attenuation of the portal vein and the concurrent decrease in portal vein blood flow. Correlation of oxygen extraction ratio with portal vein blood flow may be a more important indicator for determination of an endpoint to prevent congestion and ischemia of the gastrointestinal tract and pancreas during ligation of portosystemic shunts. (Am J Vet Res 2002;63:15–18)