Abnormal cerebral vasodilation in aneurysmal subarachnoid hemorrhage: use of serial 133Xe cerebral blood flow measurement plus acetazolamide to assess cerebral vasospasm

Cerebral autoregulation, spreading depolarization, and implications for targeted therapy in brain injury and ischemia

Cerebral autoregulation is an intrinsic myogenic response of cerebral vasculature that allows for preservation of stable cerebral blood flow levels in response to changing systemic blood pressure. It is effective across a broad range of blood pressure levels through precapillary vasoconstriction and dilation. Autoregulation is difficult to directly measure and methods to indirectly ascertain cerebral autoregulation status inherently require certain assumptions. Patients with impaired cerebral autoregulation may be at risk of brain ischemia. One of the central mechanisms of ischemia in patients with metabolically compromised states is likely the triggering of spreading depolarization (SD) events and ultimately, terminal (or anoxic) depolarization. Cerebral autoregulation and SD are therefore linked when considering the risk of ischemia. In this scoping review, we will discuss the range of methods to measure cerebral autoregulation, their theoretical strengths and weaknesses, and the available clinical evidence to support their utility. We will then discuss the emerging link between impaired cerebral autoregulation and the occurrence of SD events. Such an approach offers the opportunity to better understand an individual patient's physiology and provide targeted treatments.

Mechanisms of Global Cerebral Edema Formation in Aneurysmal Subarachnoid Hemorrhage

A growing body of clinical literature emphasizes the impact of cerebral edema in early brain injury following aneurysmal subarachnoid hemorrhage (aSAH). Aneurysm rupture itself initiates global cerebral edema in up to two thirds of cases. Although cerebral edema is not a universal feature of aSAH, it portends a poor clinical course, with quantitative analysis revealing a direct correlation between cerebral edema and poor outcome, including mortality and cognitive deficits. Mechanistically, global cerebral edema has been linked to global ischemia at the time of aneurysm rupture, dysfunction of autoregulation, blood breakdown products, neuroinflammation, and hyponatremia/endocrine abnormalities. At a molecular level, several culprits have been identified, including aquaporin-4, matrix metalloproteinase-9, SUR1-TRPM4 cation channels, vascular endothelial growth factor, bradykinin, and others. Here, we review these cellular and molecular mechanisms of global cerebral edema formation in aSAH. Given the importance of edema to the outcome of patients with aSAH and its status as a highly modifiable pathological process, a better understanding of cerebral edema in aSAH promises to hasten the development of medical therapies to improve outcomes in this frequently devastating disease.

Vasospasm in cerebral inflammation

All forms of cerebral inflammation as found in bacterial meningitis, cerebral malaria, brain injury, and subarachnoid haemorrhage have been associated with vasospasm of cerebral arteries and arterioles. Vasospasm has been associated with permanent neurological deficits and death in subarachnoid haemorrhage and bacterial meningitis. Increased levels of interleukin-1 may be involved in vasospasm through calcium dependent and independent activation of the myosin light chain kinase and release of the vasoconstrictor endothelin-1. Another key factor in the pathogenesis of cerebral arterial vasospasm may be the reduced bioavailability of the vasodilator nitric oxide. Therapeutic trials in vasospasm related to inflammation in subarachnoid haemorrhage in humans showed a reduction of vasospasm through calcium antagonists, endothelin receptor antagonists, statins, and plasminogen activators. Combination of therapeutic modalities addressing calcium dependent and independent vasospasm, the underlying inflammation, and depletion of nitric oxide simultaneously merit further study in all conditions with cerebral inflammation in double blind randomised placebo controlled trials. Auxiliary treatment with these agents may be able to reduce ischemic brain injury associated with neurological deficits and increased mortality.

Hyperperfusion syndrome after clipping an unruptured cerebral aneurysm: two case reports

A 68-year-old woman presented with severe headache 9 days after undergoing successful clipping of a right middle cerebral artery aneurysm. Postoperative imaging revealed increased perfusion and diffuse edema in the right frontotemporal cortex. A 57-year-old woman exhibited perseveration soon after undergoing successful clipping of an anterior communicating artery aneurysm. Postoperative imaging studies revealed increased perfusion and diffuse edema in the left frontal and insular cortex. The symptoms and diffuse edema gradually resolved in both patients. These two cases of hyperperfusion syndrome occurred in a series of 190 patients treated by clipping of unruptured cerebral aneurysms. Hyperperfusion syndrome is a rare complication following aneurysm surgery, especially surgery for unruptured cerebral aneurysms without temporary clipping.

"Optimal cerebral perfusion pressure" in poor grade patients after subarachnoid hemorrhage

BACKGROUND

Cerebrovascular pressure reactivity depends on cerebral perfusion pressure (CPP), with the optimal CPP (CPPopt) defined as pressure at which cerebrovascular reactivity is functioning optimally, reaching minimal value of pressure reactivity index (PRx). The study investigates the association between vasospasm, PRx, and CPPopt in poor grade patients (WFNS 4&5) after subarachnoid hemorrhage (SAH).

METHODS

Data of intracranial pressure (ICP), arterial blood pressure (ABP), and flow velocities (FV) in the Middle Cerebral Artery (MCA) on transcranial Doppler from 42 SAH patients were analyzed retrospectively. PRx was calculated as a correlation coefficient between 10 s mean values of ABP and ICP calculated over a moving 3 min window. Data recorded during the first 48 h were available in 25 cases and during the first 3 days in 29 patients. Recordings obtained from day 4 to day 24 were available in 23 patients.

RESULTS

PRx at optimal CPP measured during the first 48 h showed better cerebrovascular reactivity in patients who were alive at 3 months after ictus than in those who died (PRx value -0.17 +/- 0.05 vs. 0.1 +/- 0.09; P < 0.01). PRx below zero at CPPopt during the first 48 h had 87.5% positive predictive value for survival. CPPopt was lower before than during vasospasm (78 +/- 3 mmHg, N = 29 vs. 98 +/- 4 mmHg; N = 17, P < 0.0001). The overall correlation between CPPopt and Lindegaard ratio was positive (R = 0.39; P < 0.01; N = 45).

CONCLUSION

Most WFNS 4&5 grade SAH patients with PRx below zero at optimal CPP during the first 48 h after ictus survived. Optimal CPP increases during vasospasm.

Efficacy of intracarotid propofol infusion and impact of cerebral blood flow alteration

BACKGROUND

Intracarotid propofol infusion was studied in canines as an experimental basis for application of propofol in the Wada test.

METHODS

First, efficacy and side-effects of propofol anaesthesia were studied in eight mongrel dogs that received intracarotid and i.v. propofol infusions for 30 min according to a cross-over design. Auditory evoked potentials were used to guide anaesthesia. Secondly, eight mongrel dogs received intracarotid propofol infusion during both normal and cerebral hyperperfusion states using nicardipine. Haemodynamics and clinical endpoints were compared between the two infusion conditions.

RESULTS

We required 33 (7.6) mg propofol intracarotically vs 113 (17) mg propofol i.v. to achieve an anaesthetic state. The mean arterial pressure (MAP) decreased about 15-27% from the baseline during i.v. infusion. However, no obvious decrease of MAP was observed after intracarotid infusion. Administration of nicardipine increased the blood flow in the internal carotid artery by 17%. Then, the propofol dosage for achieving the anaesthetic effect increased from 7.7 (0.9) mg in the normal control to 11.3 (0.8) mg in the nicardipine group. The onset time of anaesthetic effect was prolonged and the recovery time was shortened during intracarotid infusion during cerebral hyperperfusion.

CONCLUSIONS

Compared with i.v. propofol infusion, intracarotid infusion could reach and maintain the target anaesthetic depth with less dosage and without affecting MAP. In addition, increase of cerebral blood flow requires a higher propofol dose, prolongs onset, and shortens recovery time during intracarotid propofol anaesthesia, indicating that patients with a cerebral hyperperfusion state may need higher dose of anaesthetics during the Wada test.

Cerebrovascular inflammation following subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage frequently results in complications including intracranial hypertension, rebleeding and vasospasm. The extravasated blood is responsible for a cascade of reactions involving release of various vasoactive and pro-inflammatory factors (several of which are purported to induce vasospasm) from blood and vascular components in the subarachnoid space. The authors review the available evidence linking these factors to the development of inflammatory lesions of the cerebral vasculature, emphasizing: 1) neurogenic inflammation due to massive release of sensory nerve neuropeptides; 2) hemoglobin from lysed erythrocytes, which creates functional lesions of endothelial and smooth muscle cells; 3) activity, expression and metabolites of lipoxygenases cyclooxygenases and nitric oxide synthases; 4) the possible role of endothelin-1 as a pro-inflammatory agent; 5) serotonin, histamine and bradykinin which are especially involved in blood-brain barrier disruption; 6) the prothrombotic and pro-inflammatory action of complement and thrombin towards endothelium; 7) the multiple actions of activated platelets, including platelet-derived growth factor production; 8) the presence of perivascular and intramural macrophages and granulocytes and their interaction with adhesion molecules; 9) the evolution, origins, and effects of pro-inflammatory cytokines, especially IL-1, TNF-alpha and IL-6. Human and animal studies on the use of anti-inflammatory agents in subarachnoid hemorrhage include superoxide and other radical scavengers, lipid peroxidation inhibitors, iron chelators, NSAIDs, glucocorticoids, and serine protease inhibitors. Many animal studies claim reduced vasospasm, but these effects are not always confirmed in human trials, where symptomatic vasospasm and outcome are the major endpoints. Despite recent work on penetrating vessel constriction, there is a paucity of studies on inflammatory markers in the microcirculation.

Predicting delayed ischemic deficits after aneurysmal subarachnoid hemorrhage using a transient hyperemic response test of cerebral autoregulation

OBJECTIVE

To assess whether the development of delayed ischemic deficits (DIDs) after aneurysmal subarachnoid hemorrhage can be predicted using transcranial Doppler ultrasonography and the transient hyperemic response test (THRT).

METHODS

An increase in the middle cerebral artery peak flow velocity (FV) of more than 9% of baseline values after 5 to 9 seconds of carotid artery compression was defined as a normal THRT result, indicating good autoregulatory reserve. The transcranial Doppler criteria for vasospasm were a FV of more than 120 cm/s and a Lindegaard ratio of more than 3. Twenty patients with no immediate postoperative neurological deficits were studied. The FVs at all of the major cerebral arteries were measured daily after surgery, and the THRT results were assessed bilaterally.

RESULTS

Five of six patients with abnormal THRT results in the first examination after surgery (primary THRT impairment) developed DIDs; none of the remaining patients developed DIDs (Fisher exact test, P = 0.0004). All five patients with DIDs initially exhibited low FVs but all subsequently developed increases in FVs to values of more than 150 cm/s and four exhibited FVs of more than 200 cm/s. The time of onset of DIDs corresponded to the time of onset of moderate vasospasm (FV > 150 cm/s). None of the patients with initially normal THRT results developed DIDs, although four patients did exhibit late (secondary) THRT impairment, which was associated with FVs of more than 120 cm/s.

CONCLUSION

When the effects of primarily impaired (after surgery) autoregulation are magnified by vasospasm, the risk of DIDs seems to be very high. Vasospasm alone does not seem to cause DIDs. The development of DIDs could therefore be predicted using the THRT for patients after aneurysm clipping.

Estimation of vessel flow and diameter during cerebral vasospasm using transcranial Doppler indices

OBJECTIVE

An important limitation of transcranial Doppler (TCD) ultrasonography is its inability to directly measure blood flow or vessel diameter. To extend the ability of TCD ultrasonography, indices were derived from an intensity-weighted mean of the entire Doppler spectrum. The objective of this article is to test the behavior of these indices under conditions of diameter constancy (hyper- and hypoventilation) and when vessel diameter decreases (vasospasm).

METHODS

A flow index (FI) was calculated by averaging several heartbeats of spectral data and calculating the first spectral moment. An area index (AI) was defined as the FI divided by the mean velocity, motivated by the knowledge that vessel flow is the product of vessel diameter and mean velocity. To test the FI and the AI under conditions of diameter constancy, middle cerebral artery Doppler signals were obtained from 20 patients during conditions of hypercarbia, hypocarbia, and normocarbia. To test the ability of these indices to evaluate a decrease in vessel diameter, signals from 41 sites on 23 arteries were obtained from patients who underwent both TCD and angiographic studies on two separate occasions after the occurrence of subarachnoid hemorrhage. The changes in the AI were compared with the arterial diameters measured from angiograms.

RESULTS

The FI was proportional to the mean velocity in the cohort of healthy patients (r=0.97). The AI changed by less than 3% in the same cohort. The AI predicted the direction of the diameter change in all vessels showing angiographic changes in area. Changes in the AI and the measured angiographic changes in cross-sectional areas were correlated (overall, r=0.90; with two outlines removed, r=0.86).

CONCLUSION

This variant of the intensity-weighted mean predicts changes in vessel cross-sectional area under conditions of changes in CO2 and cerebral vasospasm. This preliminary study suggests that careful use of this tool may provide accurate evaluation of cerebral blood flow through the large vessels and quantitative changes in diameter, which occur frequently after subarachnoid hemorrhage.

Elevated transcranial Doppler ultrasound velocities following therapeutic arterial dilation

BACKGROUND

Elevated transcranial Doppler (TCD) velocities seen after cerebral angioplasty are commonly interpreted as evidence of residual or recurrent stenosis but may conceivably arise from hyperemia and require different clinical management.

SUMMARY OF REPORT

Four cases of abnormally elevated mean TCD velocities obtained after therapeutic arterial dilation with either balloon angioplasty or intra-arterial administration of papaverine are described. In each case, cerebral angiography revealed a dilated vessel, suggesting that hyperemia and impaired autoregulation were the causes of the high velocities.

CONCLUSIONS

These examples suggest that high TCD velocities after vessel dilation may be produced by unpredictable amounts of vessel narrowing and flow alteration. Although a normalizing TCD velocity after angioplasty suggests effective vessel dilation, high velocities may be due partly to hyperemia and cannot be interpreted as arising solely from recurrent stenosis.

Time course of variations in rabbit cerebrospinal fluid levels of calcitonin gene-related peptide- and substance P-like immunoreactivity in experimental subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Cerebral vasospasm after subarachnoid hemorrhage may result partially from the imbalance between vasodilator and vasoconstrictor factors. The vasodilator peptides substance P and calcitonin gene-related peptide contained in the trigeminovascular system are involved in the vasomotor phenomenon occurring after subarachnoid hemorrhage. The delayed arterial narrowing may reflect the time course of the release of these peptides. Therefore, we followed the time course of the changes in cerebrospinal fluid immunoreactivity of substance P and calcitonin gene-related peptide in a model of experimental subarachnoid hemorrhage.

METHODS

Cerebrospinal fluid samples were taken in the basal state and at 30 minutes, 24 hours, and 3 days after a single injection of 1 mL autologous arterial blood into the cisterna magna of rabbits using a percutaneous suboccipital route. Substance P-like and calcitonin gene-related peptide-like immunoreactivities were determined in centrifuged cerebrospinal fluid and plasma by use of enzyme immunoassay.

RESULTS

Early (30 minutes) after induced subarachnoid hemorrhage, there was a large increase in cerebrospinal fluid substance P-like immunoreactivity (P < .01) and calcitonin gene-related peptide-like immunoreactivity (P < .01). Arterial and hemorrhagic cerebrospinal fluid levels of substance P-like immunoreactivity were different (P < .03), indicating that the increased cerebrospinal fluid level did not result only from the blood contamination. Twenty-four hours after induced subarachnoid hemorrhage, the immunoreactivities of substance P and calcitonin gene-related peptide remained significantly higher than the basal level (P < .01). At day 3, both immunoreactivities had decreased to a level nonsignificantly different from the basal level.

CONCLUSIONS

The early high values of the cerebrospinal fluid immunoreactivities for substance P and calcitonin gene-related peptide, apart from the contamination by arterial blood, probably resulted from the depletion of neurotransmitter peptides from the trigeminovascular fibers.