title: Hyperoxic ventilation reduces 6-hour mortality at the critical hemoglobin concentration.
abstract: BACKGROUND
  Acute normovolemic hemodilution reduces the circulating erythrocyte mass and, thus, the hemoglobin concentration. After extreme acute normovolemic hemodilution to the critical hemoglobin concentration (Hbcrit), oxygen demand of the tissues is no longer met by oxygen supply, and death occurs with increasing oxygen debt. The aim of the current study was to investigate whether ventilation with 100% oxygen (fraction of inspired oxygen [FiO2] = 1.0; hyperoxic ventilation) initiated at Hbcrit could restore adequate tissue oxygenation and prevent death.
  
  
  METHODS
  Fourteen anesthetized pigs ventilated with room air (FiO2 = 0.21) were hemodiluted by exchange of whole blood for 6% hydroxyethyl starch (200,000:0.5) until the individual Hbcrit was reached. Hbcrit was defined as the onset of oxygen supply dependency of oxygen consumption and was identified with indirect calorimetry. For the next 6 h, animals were either ventilated with an FiO2 of 0.21 (n = 7) or an FiO2 of 1.0 (n = 7).
  
  
  RESULTS
  All animals in the 0.21 FiO2 group died within the first 3 h at Hbcrit (i.e., 6-h mortality 100%). Death was preceded by an increase of serum concentrations of lactate and catecholamines. In contrast to that, six of the seven animals of the 1.0 FiO2 group survived the complete 6-h observation period without lactacidosis and increased serum catecholamines (i.e., 6-h mortality 14%; FiO2 0.21 vs. FiO2 1.0, P < or = 0.05). After 6 h at Hbcrit, the FiO2 was reduced from 1.0 to 0.21, and five of the six animals died within the next 3 h.
  
  
  CONCLUSIONS
  In anesthetized pigs submitted to lethal anemia, hyperoxic ventilation enabled survival for 6 h without signs of circulatory failure.
authors.affiliation: Department of Anesthesiology, J. W. Goethe-University, Frankfurt, Germany. meier@em.uni-frankfurt.de
authors.forename: Jens
authors.initials: J
authors.lastname: Meier
authors.forename: Gregor I
authors.initials: GI
authors.lastname: Kemming
authors.forename: Hille
authors.initials: H
authors.lastname: Kisch-Wedel
authors.forename: Stefan
authors.initials: S
authors.lastname: Wölkhammer
authors.forename: Oliver P
authors.initials: OP
authors.lastname: Habler
mesh_terms: D000758:Anesthesia; D000818:Animals; D002395:Catecholamines / Q000097:blood; D003326:Coronary Circulation / Q000502:physiology; D004562:Electrocardiography / Q000187:drug effects; D005260:Female; D006438:Hemodilution / Q000401:mortality*; D006439:Hemodynamics / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism*; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009206:Myocardium / Q000378:metabolism; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology; D010102:Oxygen Inhalation Therapy; D016019:Survival Analysis; D013552:Swine
chemical_list: D002395:Catecholamines; D006454:Hemoglobins; D019344:Lactic Acid; D010100:Oxygen