title: Long-term measurement of renal cortical and medullary tissue oxygenation and perfusion in unanesthetized sheep.
abstract: The role of renal cortical and medullary hypoxia in the development of acute kidney injury is controversial, partly due to a lack of techniques for the long-term measurement of intrarenal oxygenation and perfusion in conscious animals. We have, therefore, developed a methodology to chronically implant combination probes to chronically measure renal cortical and medullary tissue perfusion and oxygen tension (tPO2) in conscious sheep and evaluated their responsiveness and reliability. A transit-time flow probe and a vascular occluder were surgically implanted on the left renal artery. At the same operation, dual fiber-optic probes, comprising a fluorescence optode to measure tPO2 and a laser-Doppler probe to assess tissue perfusion, were inserted into the renal cortex and medulla. In recovered conscious sheep (n = 8) breathing room air, mean 24-h cortical and medullary tPO2 were similar (31.4 ± 0.6 and 29.7 ± 0.7 mmHg, respectively). In the renal cortex and medulla, a 20% reduction in renal blood flow (RBF) decreased perfusion (14.6 ± 8.6 and 41.2 ± 8.5%, respectively) and oxygenation (48.1 ± 8.5 and 72.4 ± 8.5%, respectively), with greater decreases during a 50% reduction in RBF. At autopsy, minimal fibrosis was observed around the probes. In summary, we have developed a technique to chronically implant fiber-optic probes in the renal cortex and medulla for recording tissue perfusion and oxygenation over many days. In normal resting conscious sheep, cortical and medullary tPO2 were similar. The responses to and recovery from renal artery occlusion, together with the consistent measurements over a 24-h period, demonstrate the responsiveness and stability of the probes.
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia; Department of Intensive Care and Department of Medicine, Austin Health, Heidelberg, Victoria, Australia; Department of Anesthesia and Intensive Care, AO Melegnano, PO Uboldo, Cernusco sul Naviglio, Italy;
authors.forename: Paolo
authors.initials: P
authors.lastname: Calzavacca
authors.affiliation: Department of Physiology, Monash University, Clayton, Victoria, Australia; and.
authors.forename: Roger G
authors.initials: RG
authors.lastname: Evans
authors.affiliation: Australian and New Zealand Intensive Care Research Centre, School of Epidemiology and Preventive Medicine, Monash University, Clayton, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Bailey
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia;
authors.forename: Yugeesh R
authors.initials: YR
authors.lastname: Lankadeva
authors.affiliation: Department of Intensive Care and Department of Medicine, Austin Health, Heidelberg, Victoria, Australia;
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Bellomo
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia; clive.may@florey.edu.au.
authors.forename: Clive N
authors.initials: CN
authors.lastname: May
mesh_terms: D000818:Animals; D006439:Hemodynamics / Q000502:physiology; D000860:Hypoxia / Q000503:physiopathology*; D007668:Kidney / Q000737:chemistry* / Q000503:physiopathology; D010100:Oxygen / Q000032:analysis*; D012079:Renal Circulation / Q000502:physiology*; D015203:Reproducibility of Results; D012756:Sheep
chemical_list: D010100:Oxygen
keywords: kidney oxygenation; perfusion; renal artery occlusion; renal blood flow; tissue oxygen tension