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1Department of Resuscitative Medicine, Walter Reed Army Institute of Research, Silver Spring; and 2Department of Surgery, Uniformed Services University of the Health Sciences, Bethesda, Maryland
Submitted 1 August 2003 ; accepted in final form 9 May 2005
This study was designed to test the hypothesis that changes in subcutaneous PO2 (PscO2) during progressive hemodilution will reliably predict a "critical point" at which tissue O2 consumption (
O2) becomes dependent on O2 delivery (
O2). Twelve pentobarbital-anesthetized male Sprague-Dawley rats (315375 g) underwent stepwise exchange of plasma for blood (1.5 ml of plasma for each 1 ml of blood lost). The initial exchange was equal to 25% of the estimated circulatory blood volume, and each subsequent exchange was equal to 10% of the estimated circulatory blood volume. After nine exchanges, the hematocrit (Hct) fell from 42 ± 1 to 6 ± 1%. Cardiac output and O2 extraction rose significantly. PscO2 became significantly reduced (P < 0.05) after exchange of 45% of the blood volume (Hct = 16 ± 1%).
O2 became delivery dependent when
O2 fell below 21 ml·min1·kg body wt1 (mean Hct = 13 ± 1%). Eight control rats undergoing 1:1 blood-blood exchange showed no change in PscO2, pH, HCO3, or hemodynamics. Measurement of PscO2 may be a useful guide to monitor the adequacy of
O2 during hemodilution.
optode; oxygen delivery; oxygen consumption; hemodynamics; critical hematocrit; colloid
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