title: Cardiovascular and microvascular responses to mild hypothermia in an ovine model.
abstract: OBJECTIVE
  Hypothermia is used for brain protection after resuscitation from cardiac arrest and other forms of brain injury, but its impact on systemic and tissue perfusion has not been well defined. The aim of this study was to evaluate the cardiovascular and microvascular responses to mild therapeutic hypothermia (MTH) in an ovine model.
  
  
  METHODS
  Seven anaesthetised, mechanically ventilated, invasively monitored sheep were cooled from a baseline temperature of 39-40°C to 34°C using cold intravenous fluids, ice packs and transnasal cooling. After 6h of MTH, sheep were progressively re-warmed to baseline temperature. Positive fluid balance was maintained during the entire study period to avoid hypovolemia. In addition to standard haemodynamic assessment, the sublingual microcirculation was evaluated using sidestream dark-field (SDF) videomicroscopy.
  
  
  RESULTS
  MTH was associated with significant decreases in cardiac index and left (LVSWI) and right (RVSWI) ventricular stroke work indexes. There was a downward shift in the relationship between LVSWI and pulmonary artery occlusion pressure during MTH, indicating myocardial depression. During MTH, mixed venous oxygen saturation increased, in association with reduced oxygen consumption, but blood lactate concentrations increased significantly. There was a significant decrease in the proportion and density of small perfused vessels. All variables returned to baseline levels during the re-warming phase.
  
  
  CONCLUSIONS
  In this large animal model, MTH was associated with decreased ventricular function, oxygen extraction and microvascular flow compared to normothermia. These changes were associated with increased blood lactate levels. These observations suggest that MTH may impair tissue oxygen delivery through maldistribution of capillary flow.
authors.affiliation: Department of Intensive Care, Erasme University Hospital, Université Libre de Bruxelles, Belgium.
authors.forename: Xinrong
authors.initials: X
authors.lastname: He
authors.forename: Fuhong
authors.initials: F
authors.lastname: Su
authors.forename: Fabio Silvio
authors.initials: FS
authors.lastname: Taccone
authors.forename: Leonardo Kfuri
authors.initials: LK
authors.lastname: Maciel
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Vincent
mesh_terms: D000818:Animals; D003080:Cold Temperature; D005260:Female; D006321:Heart / Q000503:physiopathology; D006439:Hemodynamics; D007036:Hypothermia, Induced; D007262:Infusions, Intravenous; D019344:Lactic Acid / Q000097:blood; D008833:Microcirculation / Q000502:physiology; D010101:Oxygen Consumption; D012756:Sheep; D012965:Sodium Chloride / Q000008:administration & dosage
chemical_list: D019344:Lactic Acid; D012965:Sodium Chloride