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Cerebral protection in experimental cardiopulmonary resuscitation (with special reference to the effects of methylene blue)

Objective: The present study was designed to study the effects of cardiac arrest and cardiopulmonary resuscitation (CPR) on blood-brain barrier (BBB) permeability and subsequent neurological injury. It also tests the cerebral effects of MB on the maintenance of BBB integrity, the production of nitric oxide (NO) and regulation of nitric oxide synthases (NOS) in cerebral cortex.Intervention: The control group (CA, n=16) underwent 12 min cardiac arrest without subsequent CPR, after which the brain of the animals was removed immediately or after 15 and 30 min. The other two groups with 12 min cardiac arrest and subsequent 8 min CPR received either an infusion of saline (CA-MB group, n=10) or an infusion of saline with MB (CA+MB, n= 12) started one minute after the start of CPR and continued 50 min after return of spontaneous circulation (ROSC). In both the latter (CA-MB and CA+MB) groups the brains were removed for histological analysis at the following time points: 30, 60, 180 min after ROSC.Main Results: In all the groups an increase of necrotic neurons and albumin immunoreactivity was demonstrated with increasing duration of ischemia and reperfusion time. The immunohistochemistry analysis indicated less blood brain barrier disruption in the animals receiving MB (CA+MB group) evidenced by decreased albumin leakage (P<0.01), water content (P=0.02), potassium (P=0.04), but also decreased neuronal injury (P<0.001) in this group in comparison with the group that was not treated with MB (CA-MB). Similarly, MB treatment reduced nitrite/nitrate ratio (P=0.02), iNOS expression (P<0.01), nNOS expression (P<0.01).Conclusion: Cerebral edema, increase BBB permeability and neurologic injury are observed early in ischemia induced by cardiac arrest. MB markedly reduced BBB disruption and subsequent neurologic injury. These cerebral cortical effects after the exposure to MB appear to be associated with a decrease of NO measured by nitrate/nitrite and different effects on NOS.