title: Hyperoxic ventilation enables hemodilution beyond the critical myocardial hemoglobin concentration.
abstract: BACKGROUND
  When initiated in anemic hypoxia, hyperoxic ventilation (ventilation with pure O2, FiO2 1.0, HV) reverses hypoxia-induced ECG-changes and enables survival for several hours. The quantification of the HV-induced gain in anemia tolerance and particularly the Hb-equivalent of HV in this situation are unknown.
  
  
  METHODS
  Nine anaesthetized pigs were hemodiluted under normoxia (FiO2 0.21) by exchange of whole blood for hydroxyethyl starch (HES) until predefined, ischemia associated ECG-changes occurred (timepoint Hb(crit)). From that time on all animals were ventilated with 100% O2 (FiO2 1.0). In the case of disappearance of the ECG changes with onset of HV, the animals were further hemodiluted until ECG changes reoccurred.
  
  
  RESULTS
  HV initiated in anemic hypoxia (Hb 2.3 +/- 0.2 g/dl) improved ECG-readings of all animals, and allowed for a further exchange of 14 +/- 11 ml/kg blood until ECG-changes reoccurred at Hb 1.2 +/- 0.4 g/dl.
  
  
  CONCLUSIONS
  HV initiated in anemic hypoxia creates a margin of safety for myocardial tissue oxygenation and thus further increases anemia tolerance. The Hb equivalent of HV in this situation amounts to approximately 1g/dl.
authors.affiliation: Department of Anesthesiology, Intensive Care Medicine and Pain Control, Johann Wolfgang Goethe-University, Hospital Center, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany. Meier@em.uni-frankfurt.de
authors.forename: J
authors.initials: J
authors.lastname: Meier
authors.forename: G
authors.initials: G
authors.lastname: Kemming
authors.forename: F
authors.initials: F
authors.lastname: Meisner
authors.forename: A
authors.initials: A
authors.lastname: Pape
authors.forename: O
authors.initials: O
authors.lastname: Habler
mesh_terms: D000818:Animals; D016063:Blood Loss, Surgical / Q000517:prevention & control; D001803:Blood Transfusion; D004562:Electrocardiography; D006400:Hematocrit; D006438:Hemodilution; D006439:Hemodynamics; D006454:Hemoglobins / Q000378:metabolism*; D006895:Hydroxyethyl Starch Derivatives / Q000627:therapeutic use; D018496:Hyperoxia / Q000503:physiopathology*; D017202:Myocardial Ischemia / Q000503:physiopathology; D009206:Myocardium / Q000378:metabolism; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology; D010952:Plasma Substitutes / Q000627:therapeutic use; D012121:Respiration, Artificial; D034421:Sus scrofa / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology
chemical_list: D006454:Hemoglobins; D006895:Hydroxyethyl Starch Derivatives; D010952:Plasma Substitutes; D010100:Oxygen