Abstract
BackgroundThe 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.MethodsIn 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.ResultsEleven 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/mm2, 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.ConclusionIn 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.
Highlights
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
Demographic and systemic hemodynamic data Eleven brain dead patients and eleven healthy control individuals were recruited in this study
Summary
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. Over the last decade improved microcirculatory imaging techniques such as sidestream dark field (SDF) videomicroscopy have allowed the direct observation of the microcirculation to assess capillary flow and density in humans in various clinical conditions [1,2,3,4]. Close anatomical proximity to the brain, common root of blood supply and availability for direct evaluation makes ocular conjunctiva a tempting window for a quick, noninvasive and dynamic assessment of cerebral perfusion. In a study published in abstract an inverse relationship between SDF-derived conjunctival microvascular flow and rise in intracranial pressure (ICP) was observed in head trauma patients [14]. Doppler-based measurements of OA and central retinal artery have been used to assess intracranial perfusion pressure [15, 16]
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