title: Thoracic epidural anesthesia with ropivacaine does not compromise the tolerance of acute normovolemic anemia in pigs.
abstract: BACKGROUND
  The initial treatment of an acute blood loss with acellular fluids leads to the dilution of the red cell mass remaining in the vasculature, that is, to acute normovolemic anemia. Whether the compensation and, thus, the tolerance of acute anemia, are affected by sympathetic block induced by thoracic epidural anesthesia has not yet been investigated.
  
  
  METHODS
  Eighteen anesthetized and mechanically ventilated pigs were instrumented with thoracic epidural catheters and randomly assigned to receive an epidural injection of either 5-ml ropivacaine 0.2% (n = 9) aiming for a Th5-Th10 block or saline (n = 9) followed by continuous epidural infusion of 5 ml/h of either fluid. Subsequently, acute normovolemic anemia was induced by replacement of whole blood with 6% hydroxyethyl starch solution until a "critical" limitation of oxygen transport capacity was reached as indicated by a sudden decrease in oxygen consumption. The critical hemoglobin concentration quantified at this time point was the primary endpoint; secondary endpoints were hemodynamic and oxygen transport parameters.
  
  
  RESULTS
  Thoracic epidural anesthesia elicited only a moderate decrease in mean arterial pressure and cardiac index and a transient decrease in oxygen extraction ratio. During progressive anemia, the compensatory increases in cardiac index and oxygen extraction ratio were not compromised by thoracic epidural anesthesia. Critical hemoglobin concentration was reached at identical levels in both groups (ropivacaine group: 2.5 ± 0.6 g/dl, saline group: 2.5 ± 0.6 g/dl).
  
  
  CONCLUSIONS
  Thoracic epidural anesthesia with ropivacaine 0.2% does not decrease the tolerance to acute normovolemic anemia in healthy pigs. The hemodynamic compensation of acute anemia is fully preserved despite sympathetic block, and the critical hemoglobin concentration remains unaffected.
authors.affiliation: From the Department of Anesthesiology, Intensive-Care Medicine and Pain Therapy, University Hospital Frankfurt, Frankfurt am Main, Germany (A.P., C.F.W., M.L., M.S., S.K., O. Horn); Clinic of Anesthesiology, Ludwig Maximilians University Hospital, Munich, Germany (B.Z.); and Clinic of Anesthesiology, Surgical Intensive Care Medicine and Pain Management, Krankenhaus Nordwest, Frankfurt, Germany (O. Habler).
authors.forename: Andreas
authors.initials: A
authors.lastname: Pape
authors.forename: Christian F
authors.initials: CF
authors.lastname: Weber
authors.forename: Mohammed
authors.initials: M
authors.lastname: Laout
authors.forename: Max
authors.initials: M
authors.lastname: Steche
authors.forename: Saskia
authors.initials: S
authors.lastname: Kutschker
authors.forename: Oliver
authors.initials: O
authors.lastname: Horn
authors.forename: Bernhard
authors.initials: B
authors.lastname: Zwissler
authors.forename: Oliver
authors.initials: O
authors.lastname: Habler
mesh_terms: D000577:Amides / Q000008:administration & dosage*; D000740:Anemia / Q000175:diagnosis / Q000503:physiopathology*; D000767:Anesthesia, Epidural / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage*; D000818:Animals; D001810:Blood Volume / Q000187:drug effects / Q000502:physiology; D004361:Drug Tolerance / Q000502:physiology; D005260:Female; D008297:Male; D011897:Random Allocation; D000077212:Ropivacaine; D013552:Swine; D013904:Thoracic Vertebrae
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine