title: Renal blood flow, fractional excretion of sodium and acute kidney injury:  time for a new paradigm?
abstract: OBJECTIVE
  Global renal blood flow is considered pivotal to renal function. Decreased global renal blood flow (decreased perfusion) is further considered the major mechanism of reduced glomerular filtration rate responsible for the development of acute kidney injury (AKI) in critically ill patients. Additionally, urinary biochemical tests are widely taught to allow the differential diagnosis of prerenal (functional) AKI and intrinsic [structural AKI (so-called acute tubular necrosis)]. In this review we will examine recent evidence regarding these two key clinical paradigms.
  
  
  RESULTS
  Recent animal experiments and clinical studies in humans using cine-phase contrast magnetic resonance technology are not consistent with the decreased perfusion paradigm. They suggest instead that changes in the intra-renal circulation including modification in efferent arteriolar function and intra-renal shunting are much more likely to be responsible for AKI, especially in sepsis. Similarly, recent human studies indicate the urinary biochemistry has limited diagnostic or prognostic ability and is dissociated form biomarker and microscopic evidence of tubular injury.
  
  
  CONCLUSIONS
  Intra-renal microcirculatory changes are likely more important than changes in global blood flow in the development of AKI. Urinary biochemistry is not a clinically useful diagnostic or prognostic tool in critically ill patients at risk of or with AKI.
authors.affiliation: Adult Critical Care Unit, The Royal London Hospital, Bart's and the London NHS Trust, London, UK.
authors.forename: John
authors.initials: J
authors.lastname: Prowle
authors.forename: Sean M
authors.initials: SM
authors.lastname: Bagshaw
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Bellomo
mesh_terms: D058186:Acute Kidney Injury / Q000175:diagnosis* / Q000503:physiopathology*; D015415:Biomarkers / Q000652:urine; D016638:Critical Illness; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000098:blood supply*; D012039:Regional Blood Flow; D012964:Sodium / Q000378:metabolism / Q000652:urine*; D014508:Urea / Q000652:urine
chemical_list: D015415:Biomarkers; D014508:Urea; D012964:Sodium