Reperfusion injury/ Reperfusion Hemorrhage/ Hemorrhage
Large Vessel Occlusion (LVO) if treated successfully can undoubtedly
improve patient outcomes as evidenced by the current literature. The
restoration of blood flow to viable brain tissue permits for salvage of
the penumbra but at the same time opens the door for a process known as
cerebral re-perfusion injury. Cerebral reperfusion injury may be defined
as deterioration of salvageable brain tissue, which was initially
ischemic, after reperfusion. (\cite{Pan_2006}) Although research is ongoing with the mechanisms by
which the injury occurs, several studies have demonstrated various
processes involved. Inflammatory response and release of free radicals
to injured tissue by restored blood flow is one mechanism in addition to
the involvement of leukocyte infiltration and breakdown of the blood
brain barrier. Reperfusion injury occurs on a microvascular or cellular
level, but is certainly related to a more overt and conspicuous
phenomena which is reperfusion hemorrhage or hemorrhagic transformation.
An endpoint in clinical trials, symptomatic intracranial hemorrhage
(SICH) after ischemic stroke is not an uncommon consequence of
recanalization of LVO by either tPA or mechanical thrombectomy.\cite{Hao2017} determined that a number of factors may predispose patients to SICH following thrombectomy. These
factors included cardioembolic stroke, poor collateral circulation,
delayed endovascular treatment, multiple passes with stent retriever
device, lower pretreatment ASPECTS, and a high baseline neutrophil
ratio. SICH has potentially devastating ramifications for patients
depending on the severity of the bleed. The potential of worsening a
patient’s poor clinical exam or increasing their post procedure NIHSS is
a risk undertaken. Therefore, patient selection and evaluation of the
risk benefit profile is imperative. Of the modifiable factors studied by
Hao et. al, the neurointeventionist should pay close attention to the
time at which endovascular treatment is rendered with regard to the
onset of stroke and the number of passes attempted with the stent
retriever as these can be directly impacted. Delays in treatment are
modifiable only to a certain extent, however. Expediting door to groin
times and streamlining the process by which patients receive
interventions is a constant effort by providers to prevent delays. With
the introduction of the ADAPT technique, intervention may not require
the use of stent retrievers. Stent retrievers may have the deleterious
effect of endothelial damage and weakening of what in many cases might
be unhealthy atherosclerotic vessel lumens. New clinical trials such as
the DAWN trial demonstrate that the therapeutic time of window of 6
hours may be extended for intervention while still providing benefit to
patients. However, with longer periods of ischemia, cerebral tissue may be
exposed to a higher risk of injury and potential SICH (DO WE HAVE REFERENCE TO BACK THIS UP?).