Controversy: does prevention of vasospasm in subarachnoid hemorrhage improve clinical outcome?

Blood oxygenation-level dependent cerebrovascular reactivity imaging as strategy to monitor CSF-hemoglobin toxicity

OBJECTIVES

Cell-free hemoglobin in the cerebrospinal fluid (CSF-Hb) may be one of the main drivers of secondary brain injury after aneurysmal subarachnoid hemorrhage (aSAH). Haptoglobin scavenging of CSF-Hb has been shown to mitigate cerebrovascular disruption. Using digital subtraction angiography (DSA) and blood oxygenation-level dependent cerebrovascular reactivity imaging (BOLD-CVR) the aim was to assess the acute toxic effect of CSF-Hb on cerebral blood flow and autoregulation, as well as to test the protective effects of haptoglobin.

METHODS

DSA imaging was performed in eight anesthetized and ventilated sheep (mean weight: 80.4 kg) at baseline, 15, 30, 45 and 60 minutes after infusion of hemoglobin (Hb) or co-infusion with haptoglobin (Hb:Haptoglobin) into the left lateral ventricle. Additionally, 10 ventilated sheep (mean weight: 79.8 kg) underwent BOLD-CVR imaging to assess the cerebrovascular reserve capacity.

RESULTS

DSA imaging did not show a difference in mean transit time or cerebral blood flow. Whole-brain BOLD-CVR compared to baseline decreased more in the Hb group after 15 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.01 vs -0.01 ± 0.02) and remained diminished compared to Hb:Haptoglobin group after 30 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.01 vs 0.0 ± 0.01), 45 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.01 vs 0.01 ± 0.02) and 60 minutes (Hb vs Hb:Haptoglobin: -0.03 ± 0.02 vs 0.01 ± 0.01).

CONCLUSION

It is demonstrated that CSF-Hb toxicity leads to rapid cerebrovascular reactivity impairment, which is blunted by haptoglobin co-infusion. BOLD-CVR may therefore be further evaluated as a monitoring strategy for CSF-Hb toxicity after aSAH.

Subarachnoid Hemorrhage Induces Sub-acute and Early Chronic Impairment in Learning and Memory in Mice

Subarachnoid hemorrhage (SAH) leads to significant long-term cognitive deficits, so-called the post-SAH syndrome. Existing neurological scales used to assess outcomes of SAH are focused on sensory-motor functions. To better evaluate short-term and chronic consequences of SAH, we explored and validated a battery of neurobehavioral tests to gauge the functional outcomes in mice after the circle of Willis perforation-induced SAH. The 18-point Garcia scale, applied up to 4 days, detected impairment only at 24-h time point and showed no significant difference between the Sham and SAH group. A decrease in locomotion was detected at 4-days post-surgery in the open field test but recovered at 30 days in Sham and SAH groups. However, an anxiety-like behavior undetected at 4 days developed at 30 days in SAH mice. At 4-days post-surgery, Y-maze revealed an impairment in working spatial memory in SAH mice, and dyadic social interactions showed a decrease in the sociability in SAH mice, which spent less time interacting with the stimulus mouse. At 30 days after ictus, SAH mice displayed mild spatial learning and memory deficits in the Barnes maze as they committed significantly more errors and used more time to find the escape box but still were able to learn the task. We also observed cognitive dysfunction in the SAH mice in the novel object recognition test. Taken together, these data suggest dysfunction of the limbic system and hippocampus in particular. We suggest a battery of 5 basic behavioral tests allowing to detect neurocognitive deficits in a sub-acute and chronic phase following the SAH.

Haemoglobin causes neuronal damage in vivo which is preventable by haptoglobin

After subarachnoid haemorrhage, prolonged exposure to toxic extracellular haemoglobin occurs in the brain. Here, we investigate the role of haemoglobin neurotoxicity in vivo and its prevention. In humans after subarachnoid haemorrhage, haemoglobin in cerebrospinal fluid was associated with neurofilament light chain, a marker of neuronal damage. Most haemoglobin was not complexed with haptoglobin, an endogenous haemoglobin scavenger present at very low concentration in the brain. Exogenously added haptoglobin bound most uncomplexed haemoglobin, in the first 2 weeks after human subarachnoid haemorrhage, indicating a wide therapeutic window. In mice, the behavioural, vascular, cellular and molecular changes seen after human subarachnoid haemorrhage were recapitulated by modelling a single aspect of subarachnoid haemorrhage: prolonged intrathecal exposure to haemoglobin. Haemoglobin-induced behavioural deficits and astrocytic, microglial and synaptic changes were attenuated by haptoglobin. Haptoglobin treatment did not attenuate large-vessel vasospasm, yet improved clinical outcome by restricting diffusion of haemoglobin into the parenchyma and reducing small-vessel vasospasm. In summary, haemoglobin toxicity is of clinical importance and preventable by haptoglobin, independent of large-vessel vasospasm.

Haptoglobin Genotype and Outcome after Subarachnoid Haemorrhage: New Insights from a Meta-Analysis

Haptoglobin (Hp) is a plasma protein involved in clearing extracellular haemoglobin and regulating inflammation; it exists as two genetic variants (Hp1 and Hp2). In a meta-analysis of six published studies, we confirm that Hp genotype affects short-term outcome (cerebral vasospasm and/or delayed cerebral ischemia) after subarachnoid haemorrhage (SAH) but not long-term outcome (Glasgow Outcome Score and modified Rankin Scale between one and three months). A closer examination of the heterozygous group revealed that the short-term outcome of Hp2-1 individuals clustered with that of Hp1-1 and not Hp2-2, suggesting that the presence of one Hp1 allele was sufficient to confer protection. Since the presence of the Hp dimer is the only common feature between Hp1-1 and Hp2-1 individuals, the absence of this Hp moiety is most likely to underlie vasospasm in Hp2-2 individuals. These results have implications for prognosis after SAH and will inform further research into Hp-based mechanism of action and treatment.

Functional response of cerebral blood flow induced by somatosensory stimulation in rats with subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is often accompanied by cerebral vasospasm (CVS), which is the phenomenon of narrowing of large cerebral arteries, and then can produce delayed ischemic neurological deficit (DIND) such as lateralized sensory dysfunction. CVS was regarded as a major contributor to DIND in patients with SAH. However, therapy for preventing vasospasm after SAH to improve the outcomes may not work all the time. It is important to find answers to the relationship between CVS and DIND after SAH. How local cerebral blood flow (CBF) is regulated during functional activation after SAH still remains poorly understood, whereas, the regulation of CBF may play an important role in weakening the impact of CVS on cortex function. Therefore, it is worthwhile to evaluate the functional response of CBF in the activated cortex in an SAH animal model. Most evaluation of the effect of SAH is presently carried out by neurological behavioral scales. The functional imaging of cortical activation during sensory stimulation may help to reflect the function of the somatosensory cortex more locally than the behavioral scales do. We investigated the functional response of CBF in the somatosensory cortex induced by an electrical stimulation to contralateral forepaw via laser speckle imaging in a rat SAH model. Nineteen Sprague-Dawley rats from two groups (control group, n=10 and SAH group, n=9) were studied. SAH was induced in rats by double injection of autologous blood into the cisterna magna after CSF aspiration. The same surgical procedure was applied in the control group without CSF aspiration or blood injection. Significant CVS was found in the SAH group. Meanwhile, we observed a delayed peak of CBF response in rats with SAH compared with those in the control group, whereas no significant difference was found in magnitude, duration, and areas under curve of relative CBF changes between the two groups. The results suggest that the regulation function of local CBF during functional activation induced by somatosensory stimulation might not be seriously impaired in the somatosensory cortex of rats with SAH. Therefore, our findings might help to understand the clinical phenomenon that DIND might not occur even when CVS was found in SAH patients.

Early intensive versus minimally invasive approach to postoperative hemodynamic management after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The results of previous studies suggest that early goal-directed fluid therapy (EGDT) reduces delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage, but the effects of EGDT on clinical outcomes are still unclear. This study aimed to determine whether EGDT improves outcomes compared with standard less-invasive hemodynamic therapy.

METHODS

This study included 160 patients treated within 24 hours after subarachnoid hemorrhage, randomized to receive either (1) EGDT guided by preload volume and cardiac output monitored by transpulmonary thermodilution (treatment group) or (2) standard therapy guided by fluid balance or central venous pressure, assisted by uncalibrated less-invasive cardiac output monitoring during hyperdynamic therapy in patients with clinical or radiological indications of DCI (control group). DCI determined by clinical or radiological findings and functional outcome determined by the modified Rankin Scale score at 3 months were compared between groups.

RESULTS

For all clinical grades combined, there were no significant differences in the rates of DCI (33% versus 42%; P=0.33) or modified Rankin Scale score of 0 to 3 at 3 months (67% versus 57%; P=0.22) between the 2 groups. For patients with poor clinical grade, those who received EGDT had a significantly lower rate of DCI (5% versus 14%; P=0.036), modified Rankin Scale score of 0 to 3 at 3 months (52% versus 36%; P=0.026), and shorter length of intensive care unit stay (14 versus 17 days; P=0.043) than those who received standard therapy.

CONCLUSIONS

EGDT is beneficial for reducing DCI and improving postoperative functional outcome in patients with poor clinical grade.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: UMIN000007509.