title: Novel 24-h ovine model of brain death to study the profile of the endothelin axis during cardiopulmonary injury.
abstract: BACKGROUND
  Upregulation of the endothelin axis has been observed in pulmonary tissue after brain death, contributing to primary graft dysfunction and ischaemia reperfusion injury. The current study aimed to develop a novel, 24-h, clinically relevant, ovine model of brain death to investigate the profile of the endothelin axis during brain death-associated cardiopulmonary injury. We hypothesised that brain death in sheep would also result in demonstrable injury to other transplantable organs.
  
  
  METHODS
  Twelve merino cross ewes were randomised into two groups. Following induction of general anaesthesia and placement of invasive monitoring, brain death was induced in six animals by inflation of an extradural catheter. All animals were supported in an intensive care unit environment for 24 h. Animal management reflected current human donor management, including administration of vasopressors, inotropes and hormone resuscitation therapy. Activation of the endothelin axis and transplantable organ injury were assessed using ELISA, immunohistochemistry and standard biochemical markers.
  
  
  RESULTS
  All animals were successfully supported for 24 h. ELISA suggested early endothelin-1 and big endothelin-1 release, peaking 1 and 6 h after BD, respectively, but there was no difference at 24 h. Immunohistochemistry confirmed the presence of the endothelin axis in pulmonary tissue. Brain dead animals demonstrated tachycardia and hypertension, followed by haemodynamic collapse, typified by a reduction in systemic vascular resistance to 46 ± 1 % of baseline. Mean pulmonary artery pressure rose to 186 ± 20 % of baseline at induction and remained elevated throughout the protocol, reaching 25 ± 2.2 mmHg at 24 h. Right ventricular stroke work increased 25.9 % above baseline by 24 h. Systemic markers of cardiac and hepatocellular injury were significantly elevated, with no evidence of renal dysfunction.
  
  
  CONCLUSIONS
  This novel, clinically relevant, ovine model of brain death demonstrated that increased pulmonary artery pressures are observed after brain death. This may contribute to right ventricular dysfunction and pulmonary injury. The development of this model will allow for further investigation of therapeutic strategies to minimise the deleterious effects of brain death on potentially transplantable organs.
authors.affiliation: Critical Care Research Group, The Prince Charles Hospital, Chermside, Queensland, Australia. ryan.watts@health.qld.gov.au.|University of Queensland, Brisbane, Queensland, Australia. ryan.watts@health.qld.gov.au.|Royal Brisbane and Women's Hospital, Herston, Queensland, Australia. ryan.watts@health.qld.gov.au.
authors.forename: Ryan P
authors.identifier: http://orcid.org/0000-0002-4837-4074
authors.initials: RP
authors.lastname: Watts
authors.affiliation: Critical Care Research Group, The Prince Charles Hospital, Chermside, Queensland, Australia. izabela.bilska@gmail.com.|Heart Foundation Research Centre, Griffith Health Institute, Griffith University, Southport, Queensland, Australia. izabela.bilska@gmail.com.
authors.forename: Izabela
authors.initials: I
authors.lastname: Bilska
authors.affiliation: Critical Care Research Group, The Prince Charles Hospital, Chermside, Queensland, Australia. sara_diab5@hotmail.com.
authors.forename: Sara
authors.initials: S
authors.lastname: Diab
authors.affiliation: Critical Care Research Group, The Prince Charles Hospital, Chermside, Queensland, Australia. k.dunster@qut.edu.au.|Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia. k.dunster@qut.edu.au.
authors.forename: Kimble R
authors.initials: KR
authors.lastname: Dunster
authors.affiliation: Heart Foundation Research Centre, Griffith Health Institute, Griffith University, Southport, Queensland, Australia. a.bulmer@griffith.edu.au.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Bulmer
authors.affiliation: Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia. a.barnett@qut.edu.au.
authors.forename: Adrian G
authors.initials: AG
authors.lastname: Barnett
authors.affiliation: Critical Care Research Group, The Prince Charles Hospital, Chermside, Queensland, Australia. John.Fraser@health.qld.gov.au.|Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia. John.Fraser@health.qld.gov.au.|University of Queensland, Brisbane, Queensland, Australia. John.Fraser@health.qld.gov.au.
authors.forename: John F
authors.initials: JF
authors.lastname: Fraser
keywords: Brain death; Endothelin; Endothelin-1; Haemodynamics; Organ transplantation; Pulmonary circulation; Receptors; Right; Sheep; Ventricular Function