title: 500 ml of blood loss does not decrease non-invasive tissue oxygen saturation (StO2) as measured by near infrared spectroscopy - A hypothesis generating pilot study in healthy adult women.
abstract: BACKGROUND
  The goal when resuscitating trauma patients is to achieve adequate tissue perfusion. One parameter of tissue perfusion is tissue oxygen saturation (StO2), as measured by near infrared spectroscopy. Using a commercially available device, we investigated whether clinically relevant blood loss of 500 ml in healthy volunteers can be detected by changes in StO2 after a standardized ischemic event.
  
  
  METHODS
  We performed occlusion of the brachial artery for 3 minutes in 20 healthy female blood donors before and after blood donation. StO2 and total oxygenated tissue hemoglobin (O2Hb) were measured continuously at the thenar eminence. 10 healthy volunteers were assessed in the same way, to examine whether repeated vascular occlusion without blood donation exhibits time dependent effects.
  
  
  RESULTS
  Blood donation caused a substantial decrease in systolic blood pressure, but did not affect resting StO2 and O2Hb values. No changes were measured in the blood donor group in the reaction to the vascular occlusion test, but in the control group there was an increase in the O2Hb rate of recovery during the reperfusion phase.
  
  
  CONCLUSIONS
  StO2 measured at the thenar eminence seems to be insensitive to blood loss of 500 ml in this setting. Probably blood loss greater than this might lead to detectable changes guiding the treating physician. The exact cut off for detectable changes and the time effect on repeated vascular occlusion tests should be explored further. Until now no such data exist.
authors.affiliation: Department of Emergency Medicine, University and University Hospital of Berne (Inselspital), Berne, Switzerland. exadaktylos@exadaktylos.ch.
authors.forename: Victor
authors.initials: V
authors.lastname: Jeger
authors.forename: Stephan M
authors.initials: SM
authors.lastname: Jakob
authors.forename: Stefano
authors.initials: S
authors.lastname: Fontana
authors.forename: Martin
authors.initials: M
authors.lastname: Wolf
authors.forename: Heinz
authors.initials: H
authors.lastname: Zimmermann
authors.forename: Aristomenis K
authors.initials: AK
authors.lastname: Exadaktylos
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