Detecting and treating microvascular ischemia after subarachnoid hemorrhage

Dexamethasone retrodialysis attenuates microglial response to implanted probes in vivo

Intracortical neural probes enable researchers to measure electrical and chemical signals in the brain. However, penetration injury from probe insertion into living brain tissue leads to an inflammatory tissue response. In turn, microglia are activated, which leads to encapsulation of the probe and release of pro-inflammatory cytokines. This inflammatory tissue response alters the electrical and chemical microenvironment surrounding the implanted probe, which may in turn interfere with signal acquisition. Dexamethasone (Dex), a potent anti-inflammatory steroid, can be used to prevent and diminish tissue disruptions caused by probe implantation. Herein, we report retrodialysis administration of dexamethasone while using in vivo two-photon microscopy to observe real-time microglial reaction to the implanted probe. Microdialysis probes under artificial cerebrospinal fluid (aCSF) perfusion with or without Dex were implanted into the cortex of transgenic mice that express GFP in microglia under the CX3CR1 promoter and imaged for 6 h. Acute morphological changes in microglia were evident around the microdialysis probe. The radius of microglia activation was 177.1 μm with aCSF control compared to 93.0 μm with Dex perfusion. T-stage morphology and microglia directionality indices were also used to quantify the microglial response to implanted probes as a function of distance. Dexamethasone had a profound effect on the microglia morphology and reduced the acute activation of these cells.

The effects of ventricular drainage on the intracranial pressure signal and the pressure reactivity index

In subarachnoid hemorrhage (SAH) patients intracranial pressure (ICP) is usually monitored via an extraventricular drain (EVD), which can produce false readings when the drain is open. It is established that both the ICP cardiac pulse frequency and long term trends over several hours are often seriously corrupted. The aim of this study was to establish whether or not the intermediate frequency bands [respiratory, Mayer wave and very low frequency (VLF)] were also corrupted. The VLF range is of special interest because it is important in cerebral autoregulation studies. Using a pattern recognition algorithm we retrospectively identified 718 cases of EVD opening in 80 SAH patients. An analysis of differences between closed and open-drain periods showed that ICP amplitude decreased significantly in all of the three lower frequency bands when the EVD was open. A similar analysis of systemic arterial pressure signal revealed similar changes in the same frequency bands that were positively correlated with the ICP changes. Therefore we concluded that the changes in the ICP signal represented real, physiological changes and not artifact. Pressure reactivity index (PRx) values were also computed during closed and open-drain periods. We found a small but statistically significant decrease during open-drain periods. Based on analysis of the change in the PRx distribution during open drainage we concluded that this decrease also represented physiological changes rather than artifact. In summary the ICP respiratory, Mayer wave, and VLF frequency bands are not corrupted when the EVD is open, and it safe to use these for autoregulation studies.

Effects of topical administration of nimodipine on cerebral blood flow following subarachnoid hemorrhage in pigs

We sought to explore whether topical administration of nimodipine improves the abnormal cerebral perfusion following subarachnoid hemorrhage (SAH) in pigs. Fourteen pigs were randomly divided into three groups: sham (n=4), SAH (n=5), or SAH + nimodipine (n=5). The SAH model was established by injecting fresh autologous nonheparinized arterial blood into the suprasellae cistern. Nimodipine or saline placebo (0.04 g/mL) were administered to the operative area on the fourth day after the SAH model was established. The cerebral blood flow (CBF) was measured 60 min after topical administration of nimodipine by cranial SPECT/CT scans with 5 mCi 99mTc-ECD injected intravenously. The CCR (corticocebellar ratio) was calculated by dividing the counts/voxel of the whole cerebral hemisphere by the average count/voxel in the cerebellar region of reference and RD (relative dispersion). A predictor for impaired autoregulation of CBF was calculated by dividing standard deviation (SD) of regional perfusion by mean perfusion (RD=SD/Mean). CCR and RD were applied to describe hemisphere CBF and perfusion heterogeneity. Cerebral perfusion significantly decreased in the SAH group (CCR: 1.382±0.192, RD: 0.417±0.015) compared to sham (CCR: 1.988±0.346, RD 0.389±0.015) (p<0.05). Abnormal cerebral perfusion status, however, was not significantly improved in the nimodipine + SAH group (CCR: 1.503±0.107, RD: 0.425±0.018) compared to the SAH group (p>0.05). Topical administration of nimodipine did not significantly improve CBF following SAH. These findings were not consistent with our previous data demonstrating that the topical administration of nimodipine significantly alleviates cerebral vasospasm following SAH detected by TCD. Potential mechanisms governing these disparate outcomes require further investigation.

Delayed cerebral ischaemia after subarachnoid haemorrhage: looking beyond vasospasm

Despite improvements in the clinical management of aneurysmal subarachnoid haemorrhage over the last decade, delayed cerebral ischaemia (DCI) remains the single most important cause of morbidity and mortality in those patients who survive the initial bleed. The pathological mechanisms underlying DCI are still unclear and the calcium channel blocker nimodipine remains the only therapeutic intervention proven to improve functional outcomes after SAH. The recent failure of the drug clazosentan to improve functional outcomes despite reducing vasoconstriction has moved the focus of research into DCI away from cerebral artery constriction towards a more multifactorial aetiology. Novel pathological mechanisms have been suggested, including damage to cerebral tissue in the first 72 h after aneurysm rupture ('early brain injury'), cortical spreading depression, and microthrombosis. A greater understanding of the significance of these pathophysiological mechanisms and potential genetic risk factors is required, if new approaches to the prophylaxis, diagnosis, and treatment of DCI are to be developed. Furthermore, objective and reliable biomarkers are needed for the diagnosis of DCI in poor grade SAH patients requiring sedation and to assess the efficacy of new therapeutic interventions. The purpose of this article is to appraise these recent advances in research into DCI, relate them to current clinical practice, and suggest potential novel avenues for future research.

Effect of dexamethasone on gliosis, ischemia, and dopamine extraction during microdialysis sampling in brain tissue

Microdialysis sampling of the brain is an analytical technique with numerous applications in neuroscience and the neurointensive care of brain-injured human patients. Even so, implanting microdialysis probes into brain tissue causes a penetration injury that triggers gliosis (the activation and proliferation of glial cells) and ischemia (the interruption of blood flow). Thus, the probe samples injured tissue. Mitigating the effects of the penetration injury might refine the technique. The synthetic glucocorticoid dexamethasone is a potent anti-inflammatory and immunosuppressant substance. We performed microdialysis in the rat brain for 5 days, with and without dexamethasone in the perfusion fluid (10 μM for the first 24 h and 2 μM thereafter). On the first and fourth day of the perfusion, we performed dopamine no-net-flux measurements. On the fifth day, we sectioned and stained the brain tissue and examined it by fluorescence microscopy. Although dexamethasone profoundly inhibited gliosis and ischemia around the probe tracks it had only modest effects on dopamine no-net-flux results. These findings show that dexamethasone is highly effective at suppressing gliosis and ischemia but is limited in its neuroprotective activity.

[Protective measures against cerebral ischemia following subarachnoid hemorrhage: Part 1]

BACKGROUND AND OBJECTIVES

Cerebral vasospasm following aneurysmal subarachnoid hemorrhage contributes significantly to morbidity and mortality. Many studies on the various treatments aimed at preventing cerebral vasospasm have been carried out, but evidence of efficacy is limited. Our aim was to review the literature on the various therapies for which there is scientific evidence of protection against cerebral vasospasm following aneurysmal subarachnoid hemorrhage.

METHODS

MEDLINE search (1950 to the october 2009) and review of articles found on the prevention of cerebral vasospasm following aneurysmal subarachnoid hemorrhage. The search was restricted to articles in English, French, and Spanish. The keywords were cerebral vasospasm, subarachnoid hemorrhage, therapy, nimodipine, triple H, clazosentan, statins, and magnesium in addition to the word forms derived from them. We also searched manually for references cited in the selected articles. A title was included if it was a randomized controlled trial, meta-analysis, nonrandomized clinical trial, descriptive study, observational study with statistical analysis, opinion article, or expert review.

RESULTS

Part 1 analyzed treatment with calcium antagonists and triple-H therapy (hypertension, hemodilution, and hypervolemia). Part 2 analyzed new therapies such as clazosentan, magnesium, and statins. A total of 597 titles were located; 283 were initially selected. The 61 articles finally selected for review were of the following types: 2 opinion articles, 21 randomized controlled trials, 22 expert review articles, 3 meta-analyses, 4 nonrandomized clinical trials, 1 descriptive study, and 5 observational studies with statistical analysis. Three studies (2 meta-analyses and 1 randomized controlled trial) demonstrated that nimodipine use confers benefits (reduced morbidity and mortality) for patients with aneurysmatic subarachnoid hemorrhage. Statistically significant clinical benefits could not be demonstrated for the other drugs (clazosentan, statins, and magnesium).

CONCLUSIONS

Insufficient evidence is available to support the use of the triple-H therapy, clazosentan, statins, or magnesium sulfate for the prevention of cerebral vasospasm following subarachnoid hemorrhage. Nimodipine is the only preventative treatment that can be recommended.

Recurrent spreading depolarizations after subarachnoid hemorrhage decreases oxygen availability in human cerebral cortex

OBJECTIVE

Delayed ischemic neurological deficit (DIND) contributes to poor outcome in subarachnoid hemorrhage (SAH) patients. Because there is continuing uncertainty as to whether proximal cerebral artery vasospasm is the only cause of DIND, other processes should be considered. A potential candidate is cortical spreading depolarization (CSD)-induced hypoxia. We hypothesized that recurrent CSDs influence cortical oxygen availability.

METHODS

Centers in the Cooperative Study of Brain Injury Depolarizations (COSBID) recruited 9 patients with severe SAH, who underwent open neurosurgery. We used simultaneous, colocalized recordings of electrocorticography and tissue oxygen pressure (p(ti)O(2)) in human cerebral cortex. We screened for delayed cortical infarcts by using sequential brain imaging and investigated cerebral vasospasm by angiography or time-of-flight magnetic resonance imaging.

RESULTS

In a total recording time of 850 hours, 120 CSDs were found in 8 of 9 patients. Fifty-five CSDs ( approximately 46%) were found in only 2 of 9 patients, who later developed DIND. Eighty-nine ( approximately 75%) of all CSDs occurred between the 5th and 7th day after SAH, and 96 (80%) arose within temporal clusters of recurrent CSD. Clusters of CSD occurred simultaneously, with mainly biphasic CSD-associated p(ti)O(2) responses comprising a primary hypoxic and a secondary hyperoxic phase. The frequency of CSD correlated positively with the duration of the hypoxic phase and negatively with that of the hyperoxic phase. Hypoxic phases significantly increased stepwise within CSD clusters; particularly in DIND patients, biphasic p(ti)O(2) responses changed to monophasic p(ti)O(2) decreases within these clusters. Monophasic hypoxic p(ti)O(2) responses to CSD were found predominantly in DIND patients.

INTERPRETATION

We attribute these clinical p(ti)O(2) findings mainly to changes in local blood flow in the cortical microcirculation but also to augmented metabolism. Besides classical contributors like proximal cerebral vasospasm, CSD clusters may reduce O(2) supply and increase O(2) consumption, and thereby promote DIND.

Performance of bedside transpulmonary thermodilution monitoring for goal-directed hemodynamic management after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Early goal-directed hemodynamic therapy is of particular importance for adequate cerebral circulation of patients with vasospasm after subarachnoid hemorrhage but is often precluded by the invasiveness of established cardiac output determination using a pulmonary artery catheter. This study was undertaken to validate the usefulness of less invasive goal-directed hemodynamic monitoring by transpulmonary thermodilution technique in patients after subarachnoid hemorrhage.

METHODS

One hundred sixteen patients with subarachnoid hemorrhage who underwent surgical clipping within 24 hours of ictus were investigated. Validation of transpulmonary thermodilution-derived intermittent/continuous cardiac output and cardiac preload (global end diastolic volume) were compared with pulmonary artery catheter-derived reference cardiac output and pulmonary capillary wedge pressure or central venous pressure in 16 patients diagnosed with vasospasm. In a subsequent trial of 100 consecutive cases, clinical results between the new and standard management paradigms were compared.

RESULTS

Transpulmonary thermodilution-derived intermittent cardiac output and transpulmonary thermodilution-derived continuous cardiac output showed close agreement to catheter-derived reference cardiac output with high correlation (r=0.85 and 0.77) and low percentage error (13.5% and 18.0%). Fluid responsiveness to defined volume loading was predicted better with global end diastolic volume than with pulmonary capillary wedge pressure and central venous pressure for larger receiver operating characteristic curve area. Patients receiving early goal-directed management by transpulmonary thermodilution experienced reduced frequencies of vasospasm and cardiopulmonary complications compared with those managed with standard therapy (P<0.05), whereas their functional outcomes at 3 months were not different (P=0.06).

CONCLUSIONS

Goal-directed hemodynamic management guided by transpulmonary thermodilution appears to have a therapeutic advantage for optimizing the prognosis of patients with subarachnoid hemorrhage with vasospasm over conventional methods.

Microdialysis patterns in subarachnoid hemorrhage patients with focus on ischemic events and brain interstitial glutamine levels

BACKGROUND

This observational microdialysis (MD) study of 33 subarachnoid hemorrhage patients explores brain interstitial levels of glutamine, glutamate, lactate and pyruvate, and their relationship to clinical status and clinical course at the neurointensive care unit.

METHODS

The focus was on ischemic events, defined by clinical criteria or by radiology, and the significance of brain interstitial glutamine levels and lactate/pyruvate (L/P) ratio.

RESULTS

Eleven out of 12 periods with an ischemic MD pattern, defined as lactate/pyruvate (L/P) ratios exceeding 40, were either related to delayed ischemic neurological deficits (DIND) or CT-verified infarcts, confirming that L/P above 40 is a specific ischemic and pathological MD measure. Poor admittance WFNS grade (WFNS 4-5) patients had lower glutamine at the onset of monitoring than what good admittance WFNS grade (WFNS 1-3) patients had (P < 0.05). Interstitial glutamine increased over time in most patients. A "glutamine surge" was defined as a period where the interstitial glutamine concentration increased at least 150 microM over 12 h. Fifteen patients had a DIND and associated MD patterns were glutamine surges (n = 12) and/or L/P>40 (n = 6). Seven patients received vasospasm treatment; in five of these the only DIND-associated MD pattern was a glutamine surge. Seventy percent of the glutamine surges occurred during ongoing propofol sedation, and there was no association between extubations and glutamine surges. There was no difference in mean glutamine levels during the monitoring period between patients with favorable 6-month outcome and patients with poor 6-month outcome.

CONCLUSION

We suggest that an increasing interstitial glutamine trend is a dynamic sign of augmented astrocytic metabolism with accelerated glutamate uptake and glutamine synthesis. This pattern is presumably present in metabolically challenged, but yet not overt ischemic tissue.

Do Statins Improve Outcomes and Reduce the Incidence of Vasospasm After Aneurysmal Subarachnoid Hemorrhage

Background and Purpose— Subarachnoid hemorrhage (SAH) is a relatively rare cause of stroke with a high rate of morbidity and mortality, primarily due to the occurrence of delayed vasospasm. To date, many therapies have been proposed to help prevent vasospasm, but very few have been proven effective. The initiation of statin therapy after SAH may be effective in reducing the incidence of vasospasm; however, the only studies that have examined this effect have been small. This meta-analysis attempted to determine whether statins reduce morbidity and mortality after aneurysmal SAH.

Methods— MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched for randomized, controlled trials relating to the use of statins in SAH. Foreign language and abstract articles were included. Two independent reviewers assessed studies for eligibility, data extraction, and quality. Primary outcome was the incidence of radiographically confirmed clinical vasospasm; secondary outcomes were incidence of delayed ischemic deficits and mortality.

Results— The incidence of vasospasm (relative risk [RR]=0.73; 95% CI, 0.54 to 0.99), delayed ischemic deficits (RR=0.38; 95% CI, 0.17 to 0.83), and mortality (RR=0.22; 95% CI, 0.06 to 0.82) were significantly reduced in the statin group. For these outcomes, we calculated a number needed to treat of 6.25, 5, and 6.7, respectively.

Conclusions— Initiation of statin therapy after aneurysmal SAH significantly reduces the incidence of vasospasm, delayed ischemic deficits, and mortality. This is consistent with animal research and retrospective studies and supports the routine use of statins in the care of patients with aneurysmal SAH.

[Ischemic complications in neurosurgery: use of calcium antagonists]

Dysregulation of the intracellular calcium concentration is thought to play a key role in the so-called ischemic cascade, as well as for the development of cerebral vasospasm after subarachnoid haemorrhaging (SAH). Therefore, the prophylactic/therapeutic administration of cerebral calcium channel blockers for neurosurgical patients appears to be a compelling idea to prevent ischemic complications. There are abundant data on the efficacy of cerebral calcium antagonists in various animal models of central nervous system pathologies, however, very little clinical evidence exists to justify their use in humans in respective situations. So far there is only evidence for a long-term treatment effect of oral nimodipine in patients suffering from SAH, and this is based essentially on one large controlled clinical trial. Experimental results suggest that blockers of other calcium channel subtypes may be promising for future clinical roles in primary or secondary ischemic brain injury. However, it is also possible that calcium-independent mechanisms play a more important role during the development of the ischemic damage than previously assumed. Currently, there is no clinical evidence to support the prophylactic use of calcium antagonists to prevent ischemic complications in neurosurgical patients without SAH.

Intensive care management of patients with subarachnoid haemorrhage

PURPOSE OF REVIEW

The aim of this article is to summarize recent concepts regarding the intensive care management of patients with subarachnoid haemorrhage, emphasizing the detection and treatment of cerebral vasospasm and the management of systemic complications.

RECENT FINDINGS

Aneurysmal subarachnoid haemorrhage is a potentially devastating disease that requires complex treatment strategies and extended monitoring. The prognosis of subarachnoid haemorrhage depends on the severity of the initial bleed, the success of the procedure to secure the aneurysm and the occurrence and severity of sequelae, including cerebral vasospasm. Patients with subarachnoid haemorrhage benefit from multidisciplinary neurointensive care where management is targeted at securing the ruptured aneurysm, optimizing cardiovascular variables, detecting and treating cerebral vasospasm and managing systemic complications.

SUMMARY

The complex treatment strategies applied after subarachnoid haemorrhage call for interdisciplinary collaboration between neurosurgeons, neuroradiologists, neurointensivists and specialist nurses. Specialized neuromonitoring and neuroimaging techniques must also be available. The neurointensive care unit serves as the focal point for these combined efforts.

A number of marketed dihydropyridine calcium channel blockers have mineralocorticoid receptor antagonist activity

Calcium channel blockers are widely used antihypertensives. Mineralocorticoid receptor antagonists are also used to treat hypertension and heart failure. We report here that a number of widely used dihydropyridine class calcium channel blockers are able to inhibit aldosterone-induced activation of mineralocorticoid receptor. These dihydropyridines varied in the extent of their effect on mineralocorticoid receptor, with nimodipine and felodipine the most potent and amlodipine the least. In contrast, both diltiazem and verapamil, nondihydropyridine calcium channel blockers, had no effect on mineralocorticoid receptor. These dihydropyridines compete with aldosterone for binding and block aldosterone-induced coactivator recruitment to mineralocorticoid receptor. The mineralocorticoid receptor S810L mutant, which is activated by steroidal mineralocorticoid receptor antagonist such as eplerenone, is inhibited by these drugs. Furthermore, nimodipine decreased aldosterone-induced expression of the mineralocorticoid receptor target gene epithelial sodium channel gamma subunit in adrenalectomized rats, demonstrating that dihydropyridine calcium channel blockers can function as mineralocorticoid receptor antagonists in vivo. Molecular modeling indicates that dihydropyridines dock into the ligand binding domain of mineralocorticoid receptor in a consensus pose that partially overlaps with steroidal mineralocorticoid receptor antagonists. Together, our data suggest that, in addition to their calcium channel blocking activity, a number of dihydropyridine calcium channel blockers also have mineralocorticoid receptor antagonist activity at high doses, a finding which may thus prove useful for the design of novel antihypertensive drugs in the future.

The Application of Near-infrared Oximetry to Cerebral Monitoring During Aneurysm Embolization: A Comparison With Intraprocedural Angiography

Near-infrared spectroscopy (NIRS) has been used to monitor regional cerebral oxygen saturation (rSO2) in patients at risk of cerebral desaturation during surgical and neurointerventional procedures. However, the quantitative capabilities of the method have been questioned, as has its validation compared with jugular bulb oximetry. Here, we compare NIRS data acquired during coil embolization procedures with incidence of vasospasm as detected from angiography. Thirty-two subarachnoid hemorrhage patients underwent embolization. Bilateral SomaSensor strips (Invos 4100, Somanetics) were affixed to the forehead at constant anatomic positions, avoiding frontal sinuses and scalp hair. Mean arterial pressure, SaO2, end-tidal pCO2, temperature and Hb were held within a narrow range during the procedure. Ipsilateral angiography was performed every 10 to 15 minutes. An independent neuroradiologist classified any vasospasm in the parent vessel as mild (25% baseline), moderate (50%), severe (75%), or total (100%). Of all, 15/32 (46.9%) patients developed spasm; in 2 it was severe or total. There was no significant association between World Federation of Neurological Surgeons grade and baseline rSO2 signal (either ipsilateral or contralateral to the side of the aneurysm) (P=0.598). There was no significant association between side of aneurysm and baseline rSO2 signal (P=0.243). However, episodes of angiographic spasm were strongly associated with reduction in trend ipsilateral NIRS signal (P<0.001); furthermore, the degree of spasm (especially more than 75% vessel diameter reduction) was associated with a greater reduction in same-side NIRS signal (P<0.001) (2-level random effects regression model, Stata 8.2, Stata Corp, TX). NIRS may have a useful role to play in the detection of cerebral desaturation secondary to vasospasm during neuroendovascular procedures.