The effect of nimodipine on autoregulation of cerebral blood flow after subarachnoid haemorrhage in rat

Cerebral Autoregulation in Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating stroke subtype with a high rate of mortality and morbidity. The poor clinical outcome can be attributed to the biphasic course of the disease: even if the patient survives the initial bleeding emergency, delayed cerebral ischemia (DCI) frequently follows within 2 weeks time and levies additional serious brain injury. Current therapeutic interventions do not specifically target the microvascular dysfunction underlying the ischemic event and as a consequence, provide only modest improvement in clinical outcome. SAH perturbs an extensive number of microvascular processes, including the “automated” control of cerebral perfusion, termed “cerebral autoregulation.” Recent evidence suggests that disrupted cerebral autoregulation is an important aspect of SAH-induced brain injury. This review presents the key clinical aspects of cerebral autoregulation and its disruption in SAH: it provides a mechanistic overview of cerebral autoregulation, describes current clinical methods for measuring autoregulation in SAH patients and reviews current and emerging therapeutic options for SAH patients. Recent advancements should fuel optimism that microvascular dysfunction and cerebral autoregulation can be rectified in SAH patients.

Calcium Channel Blockers in Acute Care: The Links and Missing Links Between Hemodynamic Effects and Outcome Evidence

Calcium channel blockers (CCBs) exert profound hemodynamic effects via blockage of calcium flux through voltage-gated calcium channels. CCBs are widely used in acute care to treat concerning, debilitating, or life-threatening hemodynamic changes in many patients. The overall literature suggests that, for systemic hemodynamics, although CCBs decrease blood pressure, they normally increase cardiac output; for regional hemodynamics, although they impair pressure autoregulation, they normally increase organ blood flow and tissue oxygenation. In acute care, CCBs exert therapeutic efficacy or improve outcomes in patients with aneurysmal subarachnoid hemorrhage, acute myocardial infarction and unstable angina, hypertensive crisis, perioperative hypertension, and atrial tachyarrhythmia. However, despite the clear links, there are missing links between the known hemodynamic effects and the reported outcome evidence, suggesting that further studies are needed for clarification. In this narrative review, we aim to discuss the hemodynamic effects and outcome evidence for CCBs, the links and missing links between these two domains, and the directions that merit future investigations.

Cerebral microvascular effects of nimodipine in combination with soman

Nimodipine, a calcium antagonist, has been shown to increase the detoxification of soman. In this study the cerebral microcirculatory effects of nimodipine and the acetylcholinesterase inhibitor soman was studied. Anaesthetised rats were administered nimodipine, 10 mg kg(-1) or vehicle intra-peritoneally, and 1h later exposed to 45 μg kg(-1) soman intravenously. The regional blood flows were measured using the microsphere method. Nimodipine and soman markedly increased the cerebral blood flow (CBF) and reduced the vascular resistance. Total CBF increased by 146% after nimodipine and by 105% after soman administration. Combined administration of nimodipine and soman caused additional but not fully additive effects on CBF and vascular resistance, indicating possible different mechanisms of the two agents. A part of the nimodipine induced increased detoxification after AChE-inhibition may be associated with this cerebral vasodilation.

Cerebrovascular Dynamics With Head-of-Bed Elevation in Patients With Mild or Moderate Vasospasm After Aneurysmal Subarachnoid Hemorrhage

• Background In patients with aneurysmal subarachnoid hemorrhage, elevation of the head of the bed during vasospasm has been limited in an attempt to minimize vasospasm or its sequelae or both. Consequently, some patients have remained on bed rest for weeks.

• Objectives To determine how elevations of the head of the bed of 20° and 45° affect cerebrovascular dynamics in adult patients with mild or moderate vasospasm after aneurysmal subarachnoid hemorrhage and to describe the response of mild or moderate vasospasm to head-of-bed elevations of 20° and 45° with respect to variables such as grade of subarachnoid hemorrhage and degree of vasospasm.

• Methods A within-patient repeated-measures design was used. The head of the bed was positioned in the sequence of 0°-20°-45°-0° in 20 patients with mild or moderate vasospasm between days 3 and 14 after aneurysmal subarachnoid hemorrhage. Continuous transcranial Doppler recordings were obtained for 2 to 5 minutes after allowing approximately 2 minutes for stabilization in each position.

• ResultsNo patterns or trends indicated that having the head of the bed elevated increases vasospasm. As a group, there were no significant differences within patients at the different positions of the head of the bed. Utilizing repeated-measures analysis of variance, P values ranged from .34 to .97, well beyond .05. No neurological deterioration occurred.

• Conclusions In general, elevation of the head of the bed did not cause harmful changes in cerebral blood flow related to vasospasm.

Laser Doppler flowmetry is valid for measurement of cerebral blood flow autoregulation lower limit in rats

Laser Doppler flowmetry (LDF) is a recent technique that is increasingly being used to monitor relative changes in cerebral blood flow whereas the intra-arterial 133xenon injection technique is a well-established method for repeated absolute measurements of cerebral blood flow. The aim of this study was to validate LDF for assessment of cerebral autoregulation and CO2 reactivity with the 133xenon injection technique as the gold standard. Simultaneous measurements of cerebral blood flow (CBF) were collected by LDF (CBF(LDF)) and the 133xenon method (CBF(Xe)) while (1) cerebral autoregulation was challenged by controlled systemic haemorrhage, or (2) cerebral blood flow was varied by manipulating the arterial partial pressure of CO2 (P(a,CO2)). LDF slightly overestimated CBF under conditions of haemorrhagic shock and haemodilution caused by controlled haemorrhage (paired t test, P < 0.05). However for pooled data, the autoregulation lower limit was similar when determined with the 133xenon and the LDF techniques: 65 +/- 3.9 mmHg and 60 +/- 5.6 mmHg, respectively. Linear regression analysis yielded CBF(Xe) = (1.02 x CBF(LDF)) + 9.1 and r = 0.90. Even for substantial changes in P(a,CO2), the two methods resulted in similar results. We conclude that even though LDF overestimated CBF during haemorrhagic shock caused by controlled haemorrhage, the lower limit autoregulation was correctly identified. The laser Doppler technique provides a reliable method for detection of a wide range of cerebral blood flow changes under CO2 challenge. Haemodilution influences the two methods differently causing relative overestimation of blood flow by the laser Doppler technique compared to the 1(33)xenon method.

Persistent autoregulatory disturbance after angioplasty for cerebral vasospasm. A case report

SUMMARY

Hyperdynamic therapy, consisting of hypervolemia, haemodilution, and hypertension, is an established treatment for cerebral vasospasm following subarachnoid haemorrhage. Angioplasty has emerged as an additional, effective treatment for symptomatic vasospasm. Loss of autoregulation, however, can occur despite effective angioplasty, underscoring the need for treatment with hyperdynamic therapy in combination with angioplasty. A 43-year-old woman underwent endovascular coiling of a ruptured left posterior communicating artery aneurysm. The patient went on to develop symptomatic vasospasm and was treated with hyperdynamic therapy and angioplasty. Autoregulation was assessed with xenon CT cerebral blood flow (CBF) measurement. An initial CBF study was obtained when the patient received dopamine and dobutamine infusions to maintain systolic blood pressure at 160 mmHg. The vasopressor drips were then temporarily held for twenty minutes, allowing the patient's systolic blood pressure to drop to 140 mmHg, and a repeat CBF study was obtained. Several days after angioplasty, CBF decreased significantly when the patient was taken off vasopressors, indicating impaired autoregulation. Hyperdynamic therapy was continued, and another CBF study one week later showed a return of autoregulation and normalization of CBF without induced hypertension. Autoregulation is disturbed during vasospasm. Although angioplasty can improve large artery blood flow during vasospasm, hyperdynamic therapy is also needed to maintain cerebral perfusion, particularly in the face of impaired autoregulation. Quantitative CBF measurement permits the maintenance of optimal CBF and monitoring of response to therapy.

Time course of the diameter of the major cerebral arteries after subarachnoid hemorrhage using corrosion cast technique

In this report, we examined whether corrosion cast method is also applicable for the measurement and estimation of the rat major arteries in which subarachnoid hemorrhage (SAH) is produced. Additionally, we have examined the diameters of the rat major arteries following SAH. A total of 0.3 ml autologous blood was injected into the cisterna magna of male Sprague-Dawley rats for the SAH model. A perfusion of a semi-polymerized casting medium was performed, 10 min, 30 min, 1 h, 4 h, 8 h, 1 day, 2 days, 3 days, 5 days, and 7 days after SAH. The brains were corroded in a 10% NaOH solution. The BA and the other major arteries were then measured using scanning electron microscopy (SEM). Macroscopic observation and hematoxylin-eosin (HE) staining were also performed. Using the corrosion cast method, the biphasic contractile response was observed in the BA; 8.3% and 11.6% contractions were observed 30 min and 1 day after SAH, respectively. In addition, there was almost no smooth muscle or adventitial thickening in the chronic stage. In contrast, the dilative response was observed in the internal carotid artery and middle cerebral artery 10 min after SAH. Macroscopic findings and HE staining revealed that the extensive basal subarachnoid hematoma had almost disappeared by day 2. These results indicate that in this model, the minimal spasm, which occurs one day after SAH, can be explained by the small capacity of the rat subarachnoid space and the rapid cerebrospinal fluid washout around major vessels at the cerebral base. Moreover, the present data also show the compensatory dilatation in the ICA and MCA in the early stage after SAH.

Cerebral autoregulation testing after aneurysmal subarachnoid hemorrhage: the phase relationship between arterial blood pressure and cerebral blood flow velocity

OBJECTIVE

Impairment of cerebral autoregulation (CA) appears to be an important cause for secondary ischemia after subarachnoid hemorrhage (SAH). It has been shown that graded CA impairment is predictive of outcome. Little is known about whether such impairment is present, what causes CA impairment, whether it precedes vasospasm, and whether it is predictive of outcome in patients with severe aneurysmal SAH.

DESIGN

Prospective, controlled study.

SETTING

Neurosurgical intensive care unit.

PATIENTS

Twelve patients after aneurysmal subarachnoid hemorrhage, 40 controls.

INTERVENTIONS

Recording of cerebral blood flow velocities and continuous measurement of arterial blood pressure at a controlled ventilatory frequency of six per minute to standardize the influence of intrathoracic pressure changes on blood pressure.

MEASUREMENTS AND MAIN RESULTS

We calculated the phase shift angles (deltaphidegrees) between slow (0.1 Hz) arterial blood pressure and cerebral blood flow velocity waves measured by transcranial Doppler ultrasound in the middle cerebral artery during a) posthemorrhage days (PHD) 1-6 (early or prevasospasm phase), and b) during PHD 7-13 (late or vasospasm phase) using a 6/min ventilation protocol, and in 40 controls spontaneously ventilating at the same rate. deltaphi <30 degrees indicated lost CA. Mean flow velocities >100 cm/sec were considered vasospasm. We combined early and late measurements to assess the CA relationship with low cerebral perfusion pressure (CPP) and/or vasospasm. We assessed the Glasgow Outcome Scale (GOS) score at discharge (1 = worst, 5 = best). The admission Hunt and Hess score was 3.6 +/- 0.7. GOS scores were n = 3 (GOS 1), n = 2 (GOS 2), n = 5 (GOS 3), n = 1 (GOS 4), and n = 1 (GOS 5). In the early phase, deltaphi was 40.4 +/- 19.8 degrees (left), and 40.4 +/- 19.2 degrees (right). CPP was 69.4 +/- 10.9, intracranial pressure (ICP) was 6.7 +/- 2.8 mm Hg. In the late phase, deltaphi worsened in six patients and none improved: 32.1 +/- 21 degrees (left), and 26.9 +/- 17.2 degrees (right); CPP was 68.1 +/- 12.1, ICP was 7.5 +/- 3.7 mm Hg. CA was significantly impaired in both phases when compared with normal subjects (deltaphi: 65.7 +/- 24.5 degrees; p < .01 for early, p < .001 for late phase). In the early phase, seven of eight patients in whom autoregulation was intact had a GOS >2 at discharge and disturbed CA on at least one side was predictive of either vegetative condition at discharge or death (p < .01). In the late phase, deltaphi was no longer predictive of outcome. Spasm was present in 8 of 17 vessels (47%) in which CA was lost; no spasm was found in 25 of 28 vessels (89%) in which CA was intact (p < .01). A low CPP was present in 6 of 17 vessels (35%) in which CA was lost; a normal CPP was found in 21 of 27 vessels (78%) in which CA was intact (p > .05, NS). However, 14 of 17 vessels (82%) with lost CA showed spasm and/or low CPP while only 8 of 27 cases (30%) with intact CA had either spasm or low CPP (p < .001).

CONCLUSIONS

CA can be assessed in a graded fashion in SAH patients. CA impairment precedes vasospasm; ongoing vasospasm worsens CA. CA assessment early after subarachnoid hemorrhage, within PHD 1-6, is predictive of outcome whereas late assessment is not. CA impairment is associated with cerebral vasospasm and low CPP.

Lactate and free fatty acids after subarachnoid hemorrhage

The hypothesis that lactate and free fatty acids (FFA) are elevated in the first minutes after subarachnoid hemorrhage (SAH) is tested. Adult rats were subjected to an endovascular SAH through the right internal carotid artery while under anesthesia. The brains were frozen in-situ at 15, 30, 60 min, and 24 h post-hemorrhage. Regional measures of tissue lactic acid and FFA were made in the hippocampi, ipsilateral cortex, contralateral cortex, and cerebellum. Lactic acid levels were significantly elevated from sham animals in each region within the first hour (p<0.0001 cerebellum, right, and contralateral cortex, p<0.01 hippocampus), but did not change significantly over the first hour. At 24 h post-hemorrhage, there was no significant difference in the lactic acid levels from controls. Similarly, total FFA were significantly higher in each region as compared to sham operated controls within the first hour (p<0.001 cerebellum, p<0.05 hippocampus, p<0.05 contralateral cortex, p<0.0001 ipsilateral cortex). By 24 h, there was no significant difference in FFA levels from shams. The data indicate that aerobic metabolism fails and cellular damage with degradation of cell membranes occurs in the first minutes after SAH, and lasts for at least 1 h. However, this process is stabilized within 24 h in our model. Although the largest effect was seen in the ipsilateral cortex, all areas of the brain were effected.

Improved survival after aneurysmal subarachnoid hemorrhage: review of case management during a 12-year period

OBJECT

Based on the concept that unfavorable clinical outcome after aneurysmal subarachnoid hemorrhage (SAH), to a large extent, is a consequence of all ischemic insults sustained by the brain during the acute phase of the disease, management of patients with SAH changed at the authors' institution in the mid-1980s. The new management principles affected referral guidelines, diagnostic and monitoring methods, and pharmacological and surgical treatment in a neurointensive care setting. The impact of such changes on the outcome of aneurysmal SAH over a longer period of time has not previously been studied in detail. This was the present undertaking.

METHODS

The authors analyzed all patients with SAH admitted to the neurosurgery department between 1981 and 1992. This period was divided in two parts, Period A (1981-1986) and Period B (1987-1992), and different aspects of management and outcome were recorded for each period. In total, 1206 patients with SAH (mean age 52 years, 59% females) were admitted; an aneurysm presumably causing the SAH was found in 874 (72%). The 30-day mortality rate decreased from 29% during the first 2 years (1981-1982) to 9% during the last 2 years (1991-1992) (Period A 22%; Period B 10%; p<0.0001) and the 6-month mortality rate decreased from 34 to 15% (Period A 26%; Period B 16%; p<0.001). At follow-up review conducted 2 to 9 years (mean 5.2 years) after SAH occurred, patients were evaluated according to the Glasgow Outcome Scale. Subarachnoid hemorrhage-related poor outcome (vegetative or dead) was reduced (Period A 30%; Period B 18%; p<0.001). There was an increase both in patients with favorable outcome (good recovery and moderate disability) (Period A 61 %; Period B 66%) and in those with severe disability (Period A 9%; Period B 16%; p<0.01).

CONCLUSIONS

This study provides evidence that the prognosis for patients with aneurysmal SAH has improved during the last decades. The most striking results were a gradual reduction in mortality rates and improved clinical outcomes in patients with Hunt and Hess Grade I or II SAH and in those with intraventricular hemorrhage. The changes in mortality rates and the clinical outcomes of patients with Hunt and Hess Grades III to V SAH were less conspicuous, although reduced incidences of mortality were seen in some subgroups; however, few survivors subsequently appeared to attain a favorable outcome.

Effect of nimodipine on cerebral blood flow and cerebrovascular reactivity after subarachnoid haemorrhage

The aim of the present study was to investigate the effect of nimodipine on autoregulation of cerebral blood flow (CBF), CO2 reactivity and cerebral oxygen metabolism (CMRO2) in patients with subarachnoid haemorrhage (SAH). Eight patients with severe SAH were studied with repeated CBF and CMRO2 measurements on the first day of the bleeding and after at least 12 h of treatment of nimodipine. An initial resting study, an autoregulation study and a hyperventilation study was performed. CBF was measured using the 133-Xenon intravenous method. CMRO2 was calculated as AVDO2 x CBF. Nimodipine did not significantly change CBF and CMRO2 in the initial resting study. After induced arterial hypotension intact autoregulation was found before as well as after treatment with nimodipine. Beneficial effects of nimodipine were found on CO2 reactivity and CMRO2 during hypotension that may be explained as a positive effect on cerebral ischaemia.

Brain energy metabolism in the acute stage of experimental subarachnoid haemorrhage: local changes in cerebral glucose utilization

An experimental model was used to investigate acute alterations of cerebral metabolic activity in rats subjected to subarachnoid haemorrhage (SAH). Haemorrhages were produced in anaesthetized animals by injecting 0.3 ml of autologous, arterial nonheparinized blood into the cisterna magna. Control rats received subarachnoid injections of mock-cerebrospinal fluid to study the effect of sudden raised intracranial pressure, or underwent sham operation. Three hours after SAH rats were given an intravenous injection of [14C]-2-deoxyglucose. Experiments were terminated by decapitation, and the brains were removed and frozen. Regional brain metabolic activity was studied by quantitative autoradiography. In comparison with sham-operated controls, cerebral metabolic activity was diffusely decreased after SAH. Statistically significant decreases in metabolic rate were observed in 23 of 27 brain regions studied. Subarachnoid injections of mock-cerebrospinal fluid also produced depression of cerebral metabolic activity, but quantitatively these changes were not as pronounced and diffuse as in SAH rats. The present study shows that a widespread depression of brain metabolism occurs in the acute stage after experimental SAH and is probably secondary to the subarachnoid presence of blood itself and/or blood products.