Submitted on August 1, 2003
Accepted on May 9, 2005
SUBCUTANEOUS OXYGEN TENSION AS AN INDEX OF THE PHYSIOLOGICAL LIMITS FOR HEMODILUTION IN THE RAT
Frederick J. Pearce1*, Christine Waasdorp2, Howard Hufnagel2, David Burris2, Joseph DeFeo2, Peter Soballe2, and William R. Drucker3
1 Department of Resuscitative Medicine, Walter Reed Army Institute of Research, Silver Spring, MD, USA
2 Department of Surgery, Uniformed Services University, Bethesda, MD, USA
3 Department of Resuscitative Medicine, Walter Reed Army Institute of Research, Silver Spring, MD, USA; Department of Surgery, Uniformed Services University, Bethesda, MD, USA
* To whom correspondence should be addressed. E-mail: fjpearce{at}na.amedd.army.mil.
This study was designed to determine whether changes in subcutaneous oxygen pressure (PsqO2) during progressive hemodilution would reliably identify a "critical point" at which tissue oxygen consumption (VO2) becomes dependent on oxygen delivery (DO2). Methods: Twelve (12) pentobarbital anesthetized, male Sprague-Dawley rats (315-375gm), underwent stepwise exchange of plasma for blood (1.5ml plasma for each 1ml blood lost). The initial exchange involved 25% of the estimated circulatory blood volume (ECBV), each subsequent exchange was equal to 10% ECBV. Results: After 9 exchanges the hematocrit (Hct) fell from 42 ± 1% to 6 ± 1%. Cardiac output and oxygen extraction rose significantly. The PsqO2 became significantly reduced (p<0.05) after exchanging 45% of the blood volume (Hct 16 ± 1%). VO2 became delivery dependent when DO2 fell below 21 ml/min/kg body weight (BW) (mean Hct 13 ± 1%). Eight (8) control rats undergoing 1:1 blood for blood exchange showed no change in PsqO2, pH, HCO3 or hemodynamics. Conclusions: PsqO2 may be a useful guide to monitor the adequacy of QO2 during hemodilution.
