title: Mild hypothermia has minimal effects on the tolerance to severe progressive normovolemic anemia in Swine.
abstract: BACKGROUND
  The benefits of hypothermia during acute severe anemia are not entirely settled. The authors hypothesized that cooling would improve tolerance to anemia.
  
  
  METHODS
  Eight normothermic (38.0 +/- 0.5 degrees C) and eight hypothermic (32.0 +/- 0.5 degrees C) pigs anesthetized with midazolam-fentanyl-vecuronium-isoflurane (0.5% inspired concentration) were subjected to stepwise normovolemic hemodilution (hematocrit, 15%, 10%, 7%, 5%, 3%). Critical hemoglobin concentration (Hgb(CRIT)) and critical oxygen delivery (DO(2CRIT)), i.e., the hemoglobin concentration (Hgb) and oxygen delivery (DO2) at which oxygen consumption (VO2, independently measured by indirect calorimetry) was no longer sustained, and Hgb at the moment of death, defined prospectively as the point when VO2, decreased below 40 ml/min, were used to assess the tolerance of the two groups to progressive isovolemic anemia.
  
  
  RESULTS
  At hematocrits of 15% and 10% (Hgb, 47 and 31 g/l), VO2 was maintained in both groups by an increase (P < 0.001) in cardiac output (CO) and extraction ratio (ER; P< 0.001) with unchanged mean arterial lactate concentration (L(art)). At hematocrit of 7% (Hgb, 22 g/l), all normothermic but no hypothermic animals had DO2-dependent VO2. No normothermic and three hypothermic animals survived to 5% hematocrit (Hgb, 15 g/l), and none survived to 3%. Hgb(CRIT) was 23 +/- 2 g/l and 19 +/- 6 g/l (mean +/- SD) in normothermic and hypothermic animals, respectively (P = 0.053). Hgb at death was 19 +/- 3 g/l versus 14 +/- 4 g/l (P = 0.015), and DO(2CRIT) was 8.7 +/- 1.7 versus 4.6 +/- 0.8 ml x kg(-1) x min(-1) (P < 0.001).
  
  
  CONCLUSIONS
  During progressive normovolemic hemodilution in pigs, hypothermia did not significantly change Hgb(CRIT), but it decreased the Hgb at death, i.e., short-term survival was prolonged.
authors.affiliation: Department of Pediatric Anesthesia and Intensive Care, University Hospital of Lund, Sweden. Valeria.Sa@anest.lu.se
authors.forename: Valéria
authors.initials: V
authors.lastname: Perez-de-Sá
authors.forename: Roger
authors.initials: R
authors.lastname: Roscher
authors.forename: Doris
authors.initials: D
authors.lastname: Cunha-Goncalves
authors.forename: Anders
authors.initials: A
authors.lastname: Larsson
authors.forename: Olof
authors.initials: O
authors.lastname: Werner
mesh_terms: D000740:Anemia / Q000401:mortality* / Q000503:physiopathology; D000818:Animals; D005260:Female; D006400:Hematocrit; D006438:Hemodilution; D006439:Hemodynamics; D006454:Hemoglobins / Q000032:analysis; D007036:Hypothermia, Induced; D008297:Male; D010101:Oxygen Consumption; D013552:Swine
chemical_list: D006454:Hemoglobins