title: Conjunctival microcirculatory blood flow is altered but not abolished in brain dead patients: a prospective observational study.
abstract: BACKGROUND
  The conjunctival microcirculation has potential as a window to cerebral perfusion due to related blood supply, close anatomical proximity and easy accessibility for microcirculatory imaging technique, such as sidestream dark field (SDF) imaging. Our study aims to evaluate conjunctival and sublingual microcirculation in brain dead patients and to compare it with healthy volunteers in two diametrically opposed conditions: full stop versus normal arterial blood supply to the brain.
  
  
  METHODS
  In a prospective observational study we analyzed conjunctival and sublingual microcirculation using SDF imaging in brain dead patients after reaching systemic hemodynamic targets to optimize perfusion of donor organs, and in healthy volunteers. All brain death diagnoses were confirmed by cerebral angiography. Microcirculatory images were obtained and analyzed using standardized published recommendations. Study registered at ClinicalTrials.gov, number NCT02483273.
  
  
  RESULTS
  Eleven brain dead patients and eleven apparently healthy controls were enrolled in the study. Microvascular flow index (MFI) of small vessels was significantly lower in brain dead patients in comparison to healthy controls in ocular conjunctiva (2.7 [2.4-2.9] vs. 3.0 [2.9-3.0], p = 0.01) and in sublingual mucosa (2.8 [2.6-2.9] vs. 3.0 [2.9-3.0], p = 0.02). Total vessel density (TVD) and perfused vessel density (PVD) of small vessels were significantly lower in brain dead patients in comparison to healthy controls in ocular conjunctiva (10.2 [6.6-14.8] vs. 18.0 [18.0-25.4] mm/mm(2), p = 0.001 and 5.0 [3.5-7.3] vs. 10.9 [10.9-13.5] 1/mm, p = 0.001), but not in sublingual mucosa.
  
  
  CONCLUSIONS
  In comparison to healthy controls brain dead patients had a significant reduction in conjunctival microvascular blood flow and density. However, the presence of conjunctival flow in case general cerebral flow is completely absent makes it impossible to use the conjunctival microcirculation as a substitute for brain flow, and further research should focus on the link between the ocular microcirculation, intracranial pressure and alternative ocular circulation.
authors.affiliation: Department of Intensive Care Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, LT-50009, Kaunas, Lithuania.
authors.forename: Tomas
authors.initials: T
authors.lastname: Tamosuitis
authors.affiliation: Department of Intensive Care Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, LT-50009, Kaunas, Lithuania. a.pranskunas@gmail.com.
authors.forename: Andrius
authors.initials: A
authors.lastname: Pranskunas
authors.affiliation: Department of Intensive Care Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, LT-50009, Kaunas, Lithuania.
authors.forename: Neringa
authors.initials: N
authors.lastname: Balciuniene
authors.affiliation: Department of Intensive Care Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, LT-50009, Kaunas, Lithuania.
authors.forename: Vidas
authors.initials: V
authors.lastname: Pilvinis
authors.affiliation: Department of Intensive Care Medicine, Medical Center Leeuwarden, Henri Dunantweg 2, Leeuwarden, 8901 BR, The Netherlands.|Department of Translational Physiology, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: E Christiaan
authors.initials: EC
authors.lastname: Boerma
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001926:Brain Death; D016022:Case-Control Studies; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008833:Microcirculation / Q000502:physiology*; D008875:Middle Aged; D011446:Prospective Studies; D055815:Young Adult
keywords: Brain death; Conjunctiva; Microcirculation