Overcoming Perfusion Impairment in the Ischemic Brain: A Review

Perfusion impairment is one of the major barriers to using machine perfusion to prepare brain tissue for research and clinical applications. As ischemia progresses, multiple mechanisms, including intravascular obstructions, perivascular cellular edema, mural cell contraction, and vessel wall breakdown, progressively limit the uniform delivery of preservative solutions. This problem is particularly important for connectomics, wherein successful preservation requires both widespread distribution of preservative chemicals and the maintenance of the cellular ultrastructure needed for circuit reconstruction. We conducted a narrative review of interventions used to ameliorate perfusion impairment across multiple fields, including organ transplantation, resuscitation medicine, forensic pathology, embalming, and neuroscience. We evaluated the evidence for these approaches in their original contexts and considered their potential application for brain banking aimed at preserving tissue for connectome reconstruction. We classify interventions into several categories, including anticoagulants, fibrinolytics, vasodilators, washout solutions, surfactants, osmotic agents, colloids, hypothermia, and perfusion pressure optimization. Many of these interventions have the potential to improve perfusion, but each also carries tradeoffs that may adversely affect tissue preservation. As connectomics advances toward profiling larger volumes of human brain tissue, overcoming perfusion impairment is likely to become an increasingly important challenge. This review provides a mechanistic framework for evaluating existing interventions and guiding the development of future perfusion protocols.