Cerebrovascular and cerebral effects of nimodipine--an update

Dose-response relationship of locally applied nimodipine in an ex vivo model of cerebral vasospasm

INTRODUCTION

Cerebral vasospasm is a severe complication of subarachnoid hemorrhage (SAH). The calcium channel inhibitor nimodipine has been used for treatment of cerebral vasospasm. No evidence-based recommendations for local nimodipine administration at the site of vasospasm exist. The purpose of this study was to quantify nimodipine's local vasodilatory effect in an ex vivo model of SAH-induced vasospasm.

METHODS

SAH-induced vasospasm was modeled by contracting isolated segments of rat superior cerebellar arteries with a combination of serotonin and a synthetic analog of prostaglandin A(2). A pressure myograph system was used to determine vessel reactivity of spastic as well as non-spastic arteries.

RESULTS

Compared to the initial vessel diameter, a combination of serotonin and prostaglandin induced considerable vasospasm (55 ± 2.5 % contraction; n = 12; p < 0.001). Locally applied nimodipine dilated the arteries in a concentration-dependent manner starting at concentrations as low as 1 nM (n = 12; p < 0.05). Concentrations higher than 100 nM did not relevantly increase the vasodilatory effect. Nimodipine's vasodilatory effect was smaller in spastic than in non-spastic vessels (n = 12; p < 0.05), which we assume to be due to structural changes in the vessel wall.

CONCLUSION

The described ex vivo model allows to investigate the dose-dependent efficacy of spasmolytic drugs prior to in vivo experiments. Low concentrations of locally applied nimodipine have a strong vasodilatory effect, which is of relevance when considering the local application of nimodipine in cerebral vasospasm.

The haemodynamic effect of transcranial Doppler-guided high-dose nimodipine treatment in established vasospasm after subarachnoid haemorrhage

Eleven patients (7 females) with aneurysmal subarachnoid haemorrhage (SAH) and transcranial Doppler (TCD) signs of vasospasm during prophylactic intravenous nimodipine treatment (2 mg/h) were treated with TCD-guided high-dose (4 mg/h) intravenous nimodipine. The patients were followed clinically and with serial TCD investigations. Increasing nimodipine to high-dose treatment led to a reduction of the abnormally elevated mean flow velocities (FV) in all patients. There was also a reversal of clinical signs of delayed ischaemia. In one patient, repeated computer tomographic (CT) investigations revealed a reversal of ischaemic changes. Reduction of nimodipine from 4 to 2 mg/hr resulted in a return to abnormally elevated mean FV as well as a return of clinical signs of cerebral ischaemia. The outcome was favourable in 82% of the patients and there was no mortality or vegetative survival. No patient deteriorated clinically due to vasospasm during treatment with high-dose nimodipine. The individual effect of nimodipine treatment can be monitored by the use of serial TCD investigations. TCD-guided high-dose nimodipine treatment appears to be an effective treatment in SAH patients developing vasospasm despite prophylactic standard dose treatment. The data give support for a direct vascular effect of nimodipine on cerebral vasospasm.

Transcranial Doppler sonography, angiography and SPECT measurements in traumatic carotid artery dissection

In two young patients with traumatic internal carotid artery dissection, early transcranial Doppler sonography (TCD) primarily indicated the lesion. A subsequent carotid angiogram confirmed the diagnosis. The course of the disease was followed by daily TCD recordings and repeated SPECT measurements. Beside CT and angiography, TCD and SPECT are helpful guidelines for different therapeutic approaches aiming to reduce cerebral ischaemia and infarction.

[Anesthesia in surgery for intracranial aneurysms]

The two major neurological complications of subarachnoid haemorrhage (SAH) due to an intracranial aneurysm are rebleeding and delayed cerebral ischaemia related to cerebral vasospasm. The best way to prevent rebleeding is early surgery. Even when surgery is performed within the first 72 hours posthaemorrhage, the risk of cerebral ischaemia due to vasospasm is high. Conventional medical treatment of cerebral vasospasm includes haemodilution, hypervolaemia and increase of arterial blood pressure. Haemodilution is of limited value as the patients suffering from SAH have usually a low haematocrit. The effectiveness of hypervolaemia is controversial and it may worsen cerebral and pulmonary oedema. Systemic hypertension is an effective therapy of vasospasm, but which can only be used once the aneurysm is controlled. Nimodipine and nicardipine, two calcium antagonists, have a beneficial effect on neurologic outcome following SAH. Today, it is still debated whether the beneficial effect of nimodipine results from the vascular effect of the drug or from a direct cerebral cytoprotective mechanism. Early surgery implies that surgeons operate on brains in acute inflammatory state. Thus, it is mandatory to use peroperative techniques improving cerebral exposure. These techniques include infusion of mannitol, lumbar cerebrospinal fluid (CSF) drainage, administration of anaesthetic agents known to decrease cerebral blood flow (CBF) and hypocapnia. Usually, the effect of CSF drainage is very effective and sufficient by itself. The second objective in the peroperative period is to avoid ischaemia. In areas with decreased flow distal to vasospasm, autoregulation is impaired and CBF is directly dependent on cerebral perfusion pressure. Furthermore, the safe practice of transient clipping of vessels supplying the aneurysm has dramatically reduced the indications of controlled hypotension. During temporary clipping, some authors recommend a pharmacological brain protection using barbiturates, etomidate or propofol, but this practice has not been validated by randomized studies. However, it is generally agreed that the arterial pressure should be increased during temporary clipping to improve collateral blood flow and to maintain it after the aneurysm has been secured. To conclude, together with lumbar CSF drainage and transient clipping, the anaesthetic management of the patients should include: maintenance of the arterial blood pressure close to its preoperative level, maintenance of PaCO2 between 30 and 35 mmHg and of normovolaemia through replacement of fluid and blood losses. After completion of surgery, recovery from anaesthesia should be rapid to allow fast diagnosis of neurological complications. The monitoring of the status of consciousness is the key of the diagnosis of early postoperative complications.

Pharmacokinetics of nimodipine in multimorbid elderly patients with chronic brain failure

Twenty-one elderly patients with chronic brain failure received a single 30 mg oral dose of the calcium channel blocker nimodipine followed by two weeks of 30 mg three times a day (t.i.d.) administration. The aim of this study was to assess if drug accumulation occurred in our frail elderly subjects under this dose regimen. Plasma concentrations of nimodipine and three main metabolites were determined by gas chromatography. During the 2-week period we did not find significant changes in peak plasma concentrations and corresponding areas under the plasma concentration-time curves. Trough nimodipine plasma concentrations before administration of the morning dose were similar on days 7 and 14. Therefore, no evidence of drug accumulation was found. Blood pressure and heart rate remained stable throughout the study period and no adverse effects were observed. During the study period, there was a decline in the proportion of patients who complained about dizziness and insomnia. Overall, our data suggest that there is no need to alter the usual adult dose of nimodipine if this drug is administered to multimorbid frail elderly patients suffering from chronic brain failure.

Anesthesia for intracranial aneurysm surgery

Aneurysmal rupture represents the most common cause of subarachnoid hemorrhage. Approximately two-thirds of persons who experience a subarachnoid hemorrhage will die or become disabled. Although advances in neurosurgical techniques, neuroanesthetic management, and neuroradiology have resulted in great progress in reducing the operative risk for patients with intracranial aneurysms, the overall outcome following subarachnoid hemorrhage remains disappointing. This article provides an overview of some current concepts related to the perioperative management of patients with intracranial aneurysms, such as the risk and management of rebleeding and vasospasm, and considerations related to the timing of surgery. The anesthetic management of these patients is reviewed, emphasizing principles relating to the facilitation of surgery--by optimizing operative conditions and minimizing the risks of intraoperative aneurysmal rupture or the aggravation of neurologic deficits--and to the provision of a smooth, stable recovery. Despite the disappointing overall prognosis following subarachnoid hemorrhage, adherence to these principles can optimize the outcome for those patients who reach the operating room.

Haemodynamic considerations in the management of patients with subarachnoid haemorrhage

Cerebral vasospasm occurs, following subarachnoid haemorrhage, in the majority of patients and is accompanied by cerebral ischaemia in 30%. The objectives of this article are to review (1) the effects of subarachnoid haemorrhage and vasospasm on cerebral blood flow (CBF); (2) the effects of induced hypotension and hypocapnia on CBF in these patients; (3) current therapy for cerebral ischaemia from vasospasm. The medical literature was searched using Index Medicus; for the period 1983-90 this search was done on a computer with the CD-ROM version of Index Medicus, Silver Platter. Papers were selected on the basis of validity and applicability to clinical practice; animal studies are included when human data is lacking. Cerebral vasospasm may decrease cerebral blood flow, disturb autoregulation and place the patient at risk for delayed cerebral ischaemia. Intraoperative induced hypotension and hypocapnia can decrease CBF further, although effects of either on outcome have not been evaluated. Calcium antagonists are effective for both the prevention and the treatment of delayed cerebral ischaemia. Of the mechanical treatments, systemic-arterial hypertension has the firmest scientific foundation, although this is frequently combined with haemodilution and blood volume expansion. There is a need for randomized clinical trials to assess the efficacy of these latter treatments.

The acute effect of nimodipine on cerebral blood flow, its CO2 reactivity, and cerebral oxygen metabolism in human volunteers

The present study was undertaken in 8 healthy volunteers to examine the effect of a clinically relevant dose of nimodipine (NIM) (15 and 30 microgram/kg/h) on CBF, its CO2 reactivity, and CMRO2. Mean arterial blood pressure (MABP) was measured intra-arterially. Regional CBF was measured by SPECT of inhaled Xenon-133. During the CO2 reactivity tests changes in CBF were estimated by the arterio-venous-oxygen-difference method. Median CBF was 52 ml/100 g/min (48-53) with a normal regional distribution, and median baseline MABP was 96 mmHg (92-99). MABP was slightly reduced, by 8 mmHg (7-9), and 9 mmHg (4-11) after infusion of NIM for 2 and 4 hours, respectively. CBF, however, remained constant, although correction for changes in PaCO2, revealed a slight increase after 4 hours (p = 0.08). CMRO2 was 3.5 ml/100g/min (3.2-3.5) and was not changed by the infusion of NIM. At arterial CO2 tensions ranging from 4.0 to 6.5 Kpa the CO2 reactivity was 3.0% CBF/0.1 kPa (2.6-3.7) and decreased significantly to 2.6% CBF/0.1 kPa (1.8-3.2) after the infusion of NIM for 3 hours (p = 0.02). The median slope of the LnCBFsat/PaCO2 relationship was 1.5 at baseline compared to 1.3 after NIM (p less than 0.01). No side effects were observed. The present study shows a decreased CO2 of the cerebral vessels and a maintained coupling of CBF and CMRO2 during the infusion of nimodipine.

Does nimodipine eliminate arterial hypertension as a prognostic risk factor in subarachnoid haemorrhage?

Several studies have demonstrated an association between arterial hypertension (AH) and an increased morbidity and mortality from both cardiovascular diseases and stroke (including subarachnoid haemorrhage, SAH). Among the functional disturbances implicated in hypertension much interest has been focused on the calcium handling in the vascular smooth muscle cells, and it has been proposed that a defect in the calcium gating mechanisms in the cell membrane is of major importance. Clinical trials have confirmed that calcium antagonists of the dihydropyridine type (nimodipine) are useful in preventing secondary ischaemia after SAH. The purpose of this retrospective study was to determine if the protective effect of nimodipine differs between normotensive and hypertensive patients focused on delayed ischaemia, total morbidity and mortality. In the group (137 patients) without nimodipine treatment 17 out of 31 individuals (55%) with AH had an unfavourable outcome. In the nimodipine group (also 137 patients) four out of 25 individuals (16%) with AH had an unfavourable outcome. In terms of vasospasm and delayed ischaemia only, the difference was even more evident. These results indicate that nimodipine seems to significantly reduce the prognostic difference between normo- and hypertensive individuals with an aneurysmal SAH.