title: Subcutaneous PO2 as an index of the physiological limits for hemodilution in the rat.
abstract: 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 (VO2) becomes dependent on O2 delivery (QO2). Twelve pentobarbital-anesthetized male Sprague-Dawley rats (315-375 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%). VO2 became delivery dependent when QO2 fell below 21 ml x min(-1) x kg body wt(-1) (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 QO2 during hemodilution.
authors.affiliation: Walter Reed Army Institute of Research, Dept. of Resuscitative Medicine, Rm. 1A34, 503 Robert Grant Ave., Silver Spring, MD 20910, USA. frederick.pearce@na.amedd.army.mil
authors.forename: Frederick J
authors.initials: FJ
authors.lastname: Pearce
authors.forename: Christine
authors.initials: C
authors.lastname: Waasdorp
authors.forename: Howard
authors.initials: H
authors.lastname: Hufnagel
authors.forename: David
authors.initials: D
authors.lastname: Burris
authors.forename: Joseph
authors.initials: J
authors.lastname: DeFeo
authors.forename: Peter
authors.initials: P
authors.lastname: Soballe
authors.forename: William R
authors.initials: WR
authors.lastname: Drucker
mesh_terms: D000818:Animals; D006400:Hematocrit / Q000379:methods*; D006438:Hemodilution / Q000379:methods*; D008297:Male; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012867:Skin / Q000098:blood supply* / Q000378:metabolism*
chemical_list: D010100:Oxygen