Intra-arterial nitrovasodilators do not increase cerebral blood flow in angiographically normal territories of arteriovenous malformation patients

Dynamic cerebral autoregulation during step-wise increases in blood pressure during anaesthesia: A nonrandomised interventional trial

BACKGROUND

Classically, cerebral autoregulation (CA) entails cerebral blood flow (CBF) remaining constant by cerebrovascular tone adapting to fluctuations in mean arterial pressure (MAP) between ∼60 and ∼150 mmHg. However, this is not an on-off mechanism; previous work has suggested that vasomotor tone is proportionally related to CA function. During propofol-based anaesthesia, there is cerebrovascular vasoconstriction, and static CA remains intact. Sevoflurane-based anaesthesia induces cerebral vasodilation and attenuates CA dose-dependently. It is unclear how this translates to dynamic CA across a range of blood pressures in the autoregulatory range.

OBJECTIVE

The aim of this study was to quantify the effect of step-wise increases in MAP between 60 and 100 mmHg, using phenylephrine, on dynamic CA during propofol- and sevoflurane-based anaesthesia.

DESIGN

A nonrandomised interventional trial.

SETTING

Single centre enrolment started on 11 January 2019 and ended on 23 September 2019.

PATIENTS

We studied American Society of Anesthesiologists (ASA) I/II patients undergoing noncardiothoracic, nonneurosurgical and nonlaparoscopic surgery under general anaesthesia.

INTERVENTION

In this study, cerebrovascular tone was manipulated in the autoregulatory range by increasing MAP step-wise using phenylephrine in patients receiving either propofol- or sevoflurane-based anaesthesia. MAP and mean middle cerebral artery blood velocity (MCA Vmean ) were measured in ASA I and II patients, anaesthetised with either propofol ( n  = 26) or sevoflurane ( n  = 28), during 10 mmHg step-wise increments of MAP between 60 and 100 mmHg. Static CA was determined by plotting 2-min averaged MCA Vmean versus MAP. Dynamic CA was determined using transfer function analysis and expressed as the phase lead (°) between MAP and MCA Vmean oscillations, created with positive pressure ventilation with a frequency of 6 min -1 .

MAIN OUTCOMES

The primary outcome of this study was the response of dynamic CA during step-wise increases in MAP during propofol- and sevoflurane-based anaesthesia.

RESULTS

MAP levels achieved per step-wise increments were comparable between anaesthesia regiment (63 ± 3, 72 ± 2, 80 ± 2, 90 ± 2, 100 ± 3 mmHg, and 61 ± 4, 71 ± 2, 80 ± 2, 89 ± 2, 98 ± 4 mmHg for propofol and sevoflurane, respectively). MCA Vmean increased more during step-wise MAP increments for sevoflurane compared to propofol ( P ≤0.001). Dynamic CA improved during propofol (0.73° mmHg -1 , 95% CI 0.51 to 0.95; P  ≤ 0.001)) and less pronounced during sevoflurane-based anaesthesia (0.21° mmHg -1 (95% CI 0.01 to 0.42, P  = 0.04).

CONCLUSIONS

During general anaesthesia, dynamic CA is dependent on MAP, also within the autoregulatory range. This phenomenon was more pronounced during propofol anaesthesia than during sevoflurane.

TRIAL REGISTRATION

NCT03816072 ( https://clinicaltrials.gov/ct2/show/NCT03816072 ).

Pediatric liver transplantation in severe hepatopulmonary syndrome and use of inhaled nitric oxide for post-transplant hypoxemia-a single center experience

Data on pediatric patients with HPS undergoing LT are limited. Our aim was to study the spectrum and outcomes of pediatric patients with HPS undergoing LDLT. The role ofiNO for post-LDLT refractory hypoxemia was also assessed. Patients (aged < 18 years) undergoing LT were retrospectively studied. HPS was diagnosed based on European Respiratory Society Taskforce 2004 criteria. HPS was graded based on oxygenation criteria and contrast-enhanced echocardiogram. Post-operative course was studied. Refractory post-operative hypoxemia was treated with iNO by institutionally developed protocol. 23/150 pediatric patients undergoing LDLT had HPS. BA was the most common underlying cause (52.2%). By oxygenation criteria, 6 (26.1%) had VS-HPS. VS-HPS was associated with longer LOS (p = .031) and prolonged oxygen requirement (p = .001) compared with other HPS patients. 4/6 patients with VS-HPS had pO2 < 45 mm Hg. Among these, 2 developed ICH post-operatively and 1 died. 3 developed refractory post-operative hypoxemia, successfully treated with iNO. Mean duration of iNO was 26.3 days. In the group of patients with HPS, the incidence of HAT and portal vein thrombosis was 17.3% and 4.3%, respectively. One year post-LDLT survival of patients with HPS was similar to non-HPS patients (86.9% vs 94.4%; p = .88). We concluded that, pediatric patients with VS-HPS, especially those with pre-operative pO2 < 45 mm Hg, have long and difficult post-LT course. Refractory postoperative hypoxemia can be successfully overcome with strategic use of iNO. Vigilant monitoring and good intensive care support are essential.

Reassessing the Role of Intra-Arterial Drug Delivery for Glioblastoma Multiforme Treatment

Effective treatment for glioblastoma (GBM) will likely require targeted delivery of several specific pharmacological agents simultaneously. Intra-arterial (IA) delivery is one technique for targeting the tumor site with multiple agents. Although IA chemotherapy for glioblastoma (GBM) has been attempted since the 1950s, the predicted benefits remain unproven in clinical practice. This review focuses on innovative approaches to IA drug delivery in treating GBM. Guided by novel in vitro and in vivo optical measurements, newer pharmacokinetic models promise to better define the complex relationship between background cerebral blood flow and drug injection parameters. Advanced optical technologies and tracers, unique nanoparticles designs, new cellular targets, and rational drug formulations are continuously modifying the therapeutic landscape for GBM. Personalized treatment approaches are emerging; however, such tailored approaches will largely depend on effective drug delivery techniques and on the ability to simultaneously deliver multidrug regimens. These new paradigms for tumor-selective drug delivery herald dramatic improvements in the effectiveness of IA chemotherapy for GBM. Therefore, within this context of so-called "precision medicine," the role of IA delivery for GBM is thoroughly reassessed.

Cerebral vasospasm

Cerebral vasospasm causes delayed ischemic neurologic deficits after aneurysmal subarachnoid hemorrhage. This is a well-established clinical entity with significant associated morbidity and mortality. The underlying patholphysiology is highly complex and poorly understood. Large-vessel vasospasm, autoregulatory dysfunction, inflammation, genetic predispositions, microcirculatory failure, and spreading cortical depolarization are aspects of delayed neurologic deterioration that have been described in the literature. This article presents a perspective on cerebral vasospasm, as guided by the literature to date, specifically examining the mechanism, diagnosis, and treatment of cerebral vasospasm.

Cerebral autoregulation of blood velocity and volumetric flow during steady-state changes in arterial pressure

The validity of using transcranial Doppler measurement of cerebral blood flow velocity (CBFV) to assess cerebral autoregulation (CA) still is a concern. This study measured CBFV in the middle cerebral artery using transcranial Doppler and volumetric cerebral blood flow (CBF) in the internal carotid artery (ICA) using color-coded duplex ultrasonography to assess CA during steady-state changes in mean arterial pressure (MAP). Twenty-one healthy adults participated. MAP was changed stepwise by intravenous infusion of sodium nitroprusside and phenylephrine. Changes in CBFV, CBF, cerebrovascular resistance (CVR=MAP/CBF), or cerebrovascular resistance index (CVRi=MAP/CBFV) were measured to assess CA by linear regression analysis. The relationship between changes in ICA diameter and MAP was assessed. All values were normalized as percentage changes from baseline. Drug-induced changes in MAP were from -26% to 31%. Changes in CBFV and CVRi in response to MAP were linear, and the regression slopes were similar between middle cerebral artery and ICA. However, CBF in ICA remained unchanged despite large changes in MAP. Consistently, a steeper slope of changes in CVR relative to CVRi was observed (0.991 versus 0.804; P<0.05). The ICA diameter changed inversely in response to MAP (r=-0.418; P<0.05). These findings indicate that CA can be assessed with transcranial Doppler measurements of CBFV and CVRi in middle cerebral artery. However, it is likely to be underestimated when compared with the measurements of CBF and CVR in ICA. The inverse relationship between changes in ICA diameter and MAP suggests that large cerebral arteries are involved in CA.

Maintained cerebrovascular function during post-exercise hypotension

The post-exercise period is associated with hypotension, and an increased risk of syncope attributed to decreases in venous return and/or vascular resistance. Increased local and systemic vasodilators, sympatholysis, and attenuated baroreflex sensitivity following exercise are also manifest. Although resting cerebral blood flow is maintained, cerebrovascular regulation to acute decreases in blood pressure has not been characterized following exercise. We therefore aimed to assess cerebrovascular regulation during transient bouts of hypotension, before and after 40 min of aerobic exercise at 60 % of estimated maximum oxygen consumption. Beat to beat blood pressure (Finometer), heart rate (ECG), and blood velocity in the middle cerebral artery (MCAv; transcranial Doppler ultrasound) were assessed in ten healthy young humans. The MCAv-mean arterial pressure relationship during a pharmacologically (i.v. sodium nitroprusside) induced transient hypotension was assessed before and at 10, 30, and 60 min following exercise. Despite a significant reduction in mean arterial pressure at 10 min post-exercise (-10 ± 6.9 mmHg; P < 0.05) and end-tidal PCO2 (10 min post: -2.9 ± 2.6 mmHg; 30 min post: -3.9 ± 3.5 mmHg; 60 min post: -2.7 ± 2.0 mmHg; all P < 0.05), neither resting MCAv nor the cerebrovascular response to hypotension differed between pre- and post-exercise periods (P > 0.05). These data indicate that cerebrovascular regulation remains intact following a moderate bout of aerobic exercise.

Contribution of arterial Windkessel in low-frequency cerebral hemodynamics during transient changes in blood pressure

The Windkessel properties of the vasculature are known to play a significant role in buffering arterial pulsations, but their potential importance in dampening low-frequency fluctuations in cerebral blood flow has not been clearly examined. In this study, we quantitatively assessed the contribution of arterial Windkessel (peripheral compliance and resistance) in the dynamic cerebral blood flow response to relatively large and acute changes in blood pressure. Middle cerebral artery flow velocity (MCA(V); transcranial Doppler) and arterial blood pressure were recorded from 14 healthy subjects. Low-pass-filtered pressure-flow responses (<0.15 Hz) during transient hypertension (intravenous phenylephrine) and hypotension (intravenous sodium nitroprusside) were fitted to a two-element Windkessel model. The Windkessel model was found to provide a superior goodness of fit to the MCA(V) responses during both hypertension and hypotension (R² = 0.89 ± 0.03 and 0.85 ± 0.05, respectively), with a significant improvement in adjusted coefficients of determination (P < 0.005) compared with the single-resistance model (R² = 0.62 ± 0.06 and 0.61 ± 0.08, respectively). No differences were found between the two interventions in the Windkessel capacitive and resistive gains, suggesting similar vascular properties during pressure rise and fall episodes. The results highlight that low-frequency cerebral hemodynamic responses to transient hypertension and hypotension may include a significant contribution from the mechanical properties of vasculature and, thus, cannot solely be attributed to the active control of vascular tone by cerebral autoregulation. The arterial Windkessel should be regarded as an important element of dynamic cerebral blood flow modulation during large and acute blood pressure perturbation.

Ultrahigh-dose intraarterial infusion of verapamil through an indwelling microcatheter for medically refractory severe vasospasm: initial experience

Object

Vasospasm is one of the leading causes of morbidity and death following aneurysmal subarachnoid hemorrhage (SAH). Many patients suffer devastating strokes despite the best medical therapy. Endovascular treatment is the last line of defense for cases of medically refractory vasospasm. The authors present a series of patients who were treated with a prolonged intraarterial infusion of verapamil through an in-dwelling microcatheter.

Methods

Over a 1-year period 12 patients with medically refractory vasospasm due to aneurysmal SAH were identified. Data were retrospectively collected, including age, sex, Hunt and Hess grade, Fisher grade, aneurysm location, aneurysm treatment, day of the onset of vasospasm, intracranial pressure, mean arterial pressures, intraarterial treatment of vasospasm, dosages and times of verapamil infusion, presence of a new ischemic area on CT scan, modified Rankin scale score at discharge and at the last clinical follow-up, and discharge status.

Results

Twenty-seven treatments were administered. Between 25 and 360 mg of verapamil was infused per vessel (average dose per vessel 164.6 mg, range of total dose per treatment 70–720 mg). Infusion times ranged from 1 to 20.5 hours (average 7.8 hours). The number of treated vessels ranged from 1 to 7 per patient. The number of treatments per patients ranged from 1 to 4. There was no treatment-related morbidity or death. Blood pressure and intracranial pressure changes were transient and rapidly reversible. Among the 36 treated vessels, prolonged verapamil infusion was completely effective in 32 cases and partially effective in 4. Only 4 vessels required angioplasty for refractory vasospasm after prolonged verapamil infusion. There was no CT scanning evidence of new ischemic events in 9 of the 12 patients treated. At last clinical follow-up 6–12 months after discharge, 8 of 11 patients had a modified Rankin Scale score ≤2.

Conclusions

Prolonged intraarterial infusion of verapamil is a safe and effective treatment for medically refractory severe vasospasm and reduces the need for angioplasty in such cases.

AUGMENTATION OF CEREBRAL BLOOD FLOW AND REVERSAL OF ENDOTHELIN-1-INDUCED VASOSPASM

OBJECTIVE

Local intra-arterial infusions of verapamil and nicardipine have been used to treat human cerebral vasospasm. Only a few reports of early clinical experience with these medications are currently available, and limited data are available regarding their cerebral physiological activity. We assessed the efficacy of intracarotid administration of verapamil and nicardipine on augmenting cerebral blood flow of New Zealand White rabbits and compared the ability of these drugs with reverse topical endothelin (ET)-1-triggered vasospasm.

METHODS

In the first group of New Zealand white rabbits, cerebral blood flow (laser Doppler) and systemic hemodynamic measurements were recorded at baseline and with increasing intracarotid doses of verapamil and nicardipine. In the second group, topical ET-1 (10(-4) mol/L) was applied in an acutely implanted cranial window. Dose responses to nonspecific reversal of ET-1-induced vasospasm were evaluated with intra-arterially administered nicardipine and verapamil.

RESULTS

The dose-response studies revealed that intracarotid administration of nicardipine, compared with verapamil, was more effective in augmenting cerebral blood flow. Topical ET-1-induced vasospasm was completely reversed by nicardipine and partially reversed by verapamil.

CONCLUSION

This study suggests that intra-arterially administered nicardipine is a more potent cerebral vasodilator and is superior to verapamil for treating ET-1-induced experimental cerebral vasospasm and supports further investigation of these agents in subarachnoid hemorrhage-induced vasospasm.

Postoperative hyperperfusion associated with steal phenomenon caused by a small arteriovenous malformation

A 41-year-old woman presented with a small occipital arteriovenous malformation (AVM) manifesting as headache. Cerebral angiography showed an AVM in the right occipital lobe fed by the right temporooccipital artery and draining into the superior sagittal sinus and right transverse sinus. Single photon emission computed tomography showed the steal phenomenon in the ipsilateral temporal cortex fed by the main feeding artery preoperatively, and hyperperfusion in the same cortex after removal of the AVM. Postoperative systolic blood pressure was maintained between 100 and 120 mmHg to avoid disastrous hemorrhagic complications. Cerebral blood flow evaluation before and after surgery is important to avoid postoperative disastrous complications even in patients with small AVM.

Pial Arterial Response to Topical Verapamil in Acute Closed Cranial Windows in Rabbits

We have previously observed that intraarterial verapamil increases cerebral blood flow, whereas nitric oxide donors, such as nitroglycerin, do not. Clinically, both verapamil and nitroglycerin dilate large cerebral arteries. Therefore, we hypothesized that topical verapamil would dilate both the large proximal and the small distal cerebral arteries, whereas nitroglycerin would preferentially dilate only the large proximal arteries. We tested our hypothesis in acute cranial windows implanted in 10 New Zealand White rabbits. After predrug measurements, we superfused 4 increasing concentrations of verapamil or nitroglycerin (10(-8), 10(-6), 10(-4), and 10(-3) M) in the cranial windows for 5 min each. The maximum increase in diameter was expressed as a percentage change from predrug diameters. There was a 30-min period of rest between the two drug challenges. Topical verapamil increased the arterial diameter of the larger proximal arterioles (>60 microm) by 32% +/- 18% and that of the smaller distal arterioles (<60 microm) by 62% +/- 42%. A modest increase in arterial diameters of 11% +/- 11% was observed after topical nitroglycerin that was significant only for the large-proximal arterioles. Within the 10(-8) to 10(-3) M range, topical verapamil, compared with nitroglycerin, proved to be a more potent cerebral vasodilator and had a more robust vasodilator effect on the distal small pial arteries.

Lesion-induced pseudo-dominance at functional magnetic resonance imaging: implications for preoperative assessments

OBJECTIVE

To illustrate how lesion-induced neurovascular uncoupling at functional magnetic resonance imaging (fMRI) can mimic hemispheric dominance opposite the side of a lesion preoperatively.

METHODS

We retrospectively reviewed preoperative fMRI mapping data from 50 patients with focal brain abnormalities to establish patterns of hemispheric dominance of language, speech, visual, or motor system functions. Abnormalities included gliomas (31 patients), arteriovenous malformations (AVMs) (11 patients), other congenital lesions (4 patients), encephalomalacia (3 patients), and tumefactive encephalitis (1 patient). A laterality ratio of fMRI hemispheric dominance was compared with actual hemispheric dominance as verified by electrocortical stimulation, Wada testing, postoperative and posttreatment deficits, and/or lesion-induced deficits. fMRI activation maps were generated with cross-correlation (P < 0.001) or t test (P < 0.001) analysis.

RESULTS

In 50 patients, a total of 85 functional areas were within 5 mm of the edge of a potentially resectable lesion. In 23 of these areas (27%), reduced fMRI signal in perilesional eloquent cortex in conjunction with preserved or increased signal in homologous contralateral brain areas revealed functional dominance opposite the side of the lesion. This suggested possible lesion-induced transhemispheric cortical reorganization to homologous brain regions (homotopic reorganization). In seven patients, however, the fMRI data were inconsistent with other methods of functional localization. In two patients with left inferior frontal gyrus gliomas and in one patient with focal tumefactive meningoencephalitis, fMRI incorrectly suggested strong right hemispheric speech dominance. In two patients with lateral precentral gyrus region gliomas and one patient with a left central sulcus AVM, the fMRI pattern incorrectly suggested primary corticobulbar motor dominance contralateral to the side of the lesion. In a patient with a right superior frontal gyrus AVM, fMRI revealed pronounced left dominant supplementary motor area activity in response to a bilateral complex motor task, but right superior frontal gyrus perilesional hemorrhage and edema subsequently caused left upper-extremity plegia. Pathophysiological factors that might have caused neurovascular uncoupling and facilitated pseudo-dominance at fMRI in these patients included direct tumor infiltration, neovascularity, cerebrovascular inflammation, and AVM-induced hemodynamic effects. Sixteen patients had proven (1 patient), probable (2 patients), or possible (13 patients) but unproven lesion-induced homotopic cortical reorganization.

CONCLUSION

Lesion-induced neurovascular uncoupling causing reduced fMRI signal in perilesional eloquent cortex, in conjunction with normal or increased activity in homologous brain regions, may simulate hemispheric dominance and lesion-induced homotopic cortical reorganization.

De novo cerebral arteriovenous malformation: case report

OBJECTIVE AND IMPORTANCE

Arteriovenous malformations (AVMs) are generally thought to have a congenital cause. This is the first report of an angiographically proven de novo cerebral AVM in an adult patient without previous vascular abnormality.

CLINICAL PRESENTATION

A 26-year-old African-American woman developed multiple cranial nerve deficits and ataxia over the course of a few days after a streptococcal throat infection. T2-weighted magnetic resonance imaging scans revealed a hyperintense signal in the midbrain with extension into the diencephalon. A cerebral angiogram performed at that time to exclude vasculitis revealed normal cerebral vasculature. The patient was treated with corticosteroids, and symptoms resolved. Subsequently, at the age of 32, this patient presented with a severe headache and emesis, but with no focal neurological deficit.

INTERVENTION

The patient's cranial computed tomographic and magnetic resonance imaging scans revealed a right posterior temporal intraparenchymal hemorrhage, and cerebral angiography revealed a new 3- by 2-cm AVM. The patient underwent microsurgical resection of the AVM and associated hematoma. Postoperative angiography revealed no evidence of residual AVM.

CONCLUSION

This study details the case of a woman who developed a de novo cerebral AVM during a 6-year period. This report challenges the conventional belief that all AVMs have a congenital cause.

In nonhuman primates intracarotid adenosine, but not sodium nitroprusside, increases cerebral blood flow

Intracarotid infusion of short-acting vasodilators, such as adenosine and nitroprusside, in doses that lack significant systemic side effects, may permit controlled manipulation of cerebrovascular resistance. In this experiment we assessed changes in cerebral blood flow (CBF) after intracarotid infusion of nitroprusside and adenosine. The study was conducted on six adult baboons under isoflurane anesthesia and controlled ventilation. Intracarotid drug infusion protocol avoided hypotension during nitroprusside infusion and tested for autoregulatory vasoconstriction. CBF (intraarterial (133)Xe technique) was measured four times during infusions of 1) intracarotid saline, 2) IV phenylephrine (0.2 microg x kg(-1) x min(-1)) aimed to increase mean arterial pressure by 10-15 mm Hg, 3) IV phenylephrine and intracarotid nitroprusside (0.5 microg x kg(-1) x min(-1)), and 4) intracarotid adenosine (1 mg/min). IV phenylephrine increased mean arterial pressure (69 +/- 8 to 91 +/- 9 mm Hg, P < 0.0001, n = 6), and concurrent infusion of intracarotid nitroprusside reversed this effect. However, compared with baseline, CBF did not change with IV phenylephrine or with concurrent infusion of IV phenylephrine and intracarotid nitroprusside. Intracarotid adenosine profoundly increased CBF (from 29 +/- 8 to 75 +/- 32 mL x 100 g(-1) x min(-1); P < 0.0001). In nonhuman primates, intracarotid adenosine increases CBF in doses that lack significant systemic side effects, whereas intracarotid nitroprusside has no effect. Intracarotid adenosine may be useful for manipulating cerebrovascular resistance and augmenting CBF during cerebral ischemia.

IMPLICATIONS

Intraarterial (133)Xe cerebral blood flow (CBF) measurements suggest that intracarotid adenosine, in a dose that lacks significant systemic side effects, profoundly increases CBF, whereas nitroprusside has no effect.(5-12)

Epidemiology and natural history of arteriovenous malformations

The epidemiology and natural history of cerebral arteriovenous malformations (AVMs) remains incompletely elucidated. Several factors are responsible. With regard to the incidence and prevalence of AVMs, the results of prior studies have suffered because of the retrospective design, the use of nonspecific ICD-9 codes, and a focus on small genetically isolated populations. Recent data from the New York Islands AVM Hemorrhage Study, an ongoing, prospective, population-based survey determining the incidence of AVM-related hemorrhage and the associated rates of morbidity and mortality in a zip code–defined population of 10 million people, suggests that the AVM detection rate is 1.21/100,000 person-years (95% confidence interval [CI] 1.02–1.42) and the incidence of AVM-hemorrhage is 0.42/100,000 person-years (95% CI 0.32–0.55). Contemporaneous data from the Northern Manhattan Stroke Study, a prospective, longitudinal population-based study of nearly 150,000 patients in which the focus is to define the incidence of stroke, suggest the crude incidence for first-ever AVM-related hemorrhage to be 0.55/100,000 person-years (95% CI 0.11–1.61). Efforts are ongoing to study the natural history of both ruptured and unruptured AVMs in these datasets to examine the relevance of prior studies of patients selected for conservative follow up in Finland. In addition, data are being gathered to determine whether risk factors for future hemorrhage, which have previously been established in small case series, are valid when applied to whole populations. Together, these data should help inform therapeutic decisionmaking.

Effect of intracarotid papaverine on human cerebral blood flow and vascular resistance during acute hemispheric arterial hypotension

This study assessed the feasibility of augmenting cerebral blood flow (CBF) and decreasing hemispheric cerebrovascular resistance (CVR) by intracarotid papaverine during acute cerebral hypotension. Awake patients (n = 10) undergoing transfemoral balloon occlusion of an internal carotid artery (ICA) with nitroprusside (SNP)-induced systemic hypotension (10% reduction of mean arterial pressure) were studied. We measured mean femoral artery pressure (MAP), mean distal ICA pressure (P(ica)), and CBF (intracarotid 133Xe) at two time points: before and after intracarotid papaverine infusion (1 or 7 mg/min). Two patients became symptomatic immediately after ICA occlusion and were excluded. One patient developed a focal seizure during papaverine infusion. In another, the occlusion balloon deflated prematurely. Of the remaining six patients, two of the three patients who received high-dose papaverine (7 mg/min) developed transient obtundation. The remaining three patients, who received low-dose papaverine (1 mg/min), did not develop any neurologic symptoms. There was a trend for intracarotid papaverine to increase hemispheric CBF by 36% (33 +/- 10 versus 45 +/- 22 ml x 100 g(-1) x min(-1), P = .084, n = 6); papaverine decreased CVR from 1.3 +/- 0.4 to 1.0 +/- 0.3 mm Hg x ml(-1) x 100 g(-1) x min(-1) (P = .049). There was no significant change in heart rate, MAP, or P(ica) during experimental protocol. Manipulation of CVR by intracarotid papaverine during acute hemispheric arterial hypotension appears to be feasible. Further studies are needed to establish safety and efficacy.

Influence of nitrovasodilators and cyclooxygenase inhibitors on cerebral vasoreactivity in conscious rabbits

Since the nitric oxide (NO) and cyclooxygenase pathways have been suggested to have important roles in most vasodilations, our aim was to study the influence of cyclooxygenase inhibitors and nitrovasodilators on cerebrovascular reserve capacity. Corticocerebral blood flow was measured by hydrogen polarography during hypercapnia and acetazolamide stimuli in conscious rabbits. The measurements were repeated in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME) and indomethacin as nitric oxide synthase (NOS) and cyclooxygenase inhibitors. The effects of nitroglycerin and isosorbide-5-nitrate were also tested. L-NAME completely, while indomethacin markedly inhibited the hypercapnic corticocerebral blood flow response. Nitroglycerin and isosorbide-5-nitrate significantly attenuated hypercapnia elicited corticocerebral blood flow increase. The different treatments reduced only moderately the acetazolamide-induced corticocerebral blood flow response. These results lend support to the hypothesis that antithrombotic and antiinflammatory medication (cyclooxygenase inhibitors) and nitrovasodilator treatments could interfere with the measurement of cerebrovascular reactivity resulting in underestimation of the cerebrovascular reserve capacity in patients taking these drugs.

Anaesthesia for interventional neuroradiology

Neuroradiologists have extended their treatment modalities in the field of vascular neurosurgery. The rapidly emerging and re-engineered neuroradiological techniques confront the anaesthetist with an increasing number of patients with severe neurological disease. More of these patients will need general anaesthesia in order to facilitate the endovascular procedure, including catheter placement, deposition of embolic material, and improved imaging. Anaesthetists are challenged by additional anaesthesiological aspects previously not encountered in neuroanaesthesia. A safe anaesthetic management is based on a broad understanding of pathophysiological and technical issues that arise with the endovascular treatment of cerebral vasculopathy.

New concepts in adult brain arteriovenous malformations

Brain arteriovenous malformations are currently attracting increasing attention among clinicians as modern brain imaging techniques facilitate both diagnostic and follow-up evaluation. Their frequent presentation in young individuals, at times with flagrant clinical effects caused by cerebral hemorrhages or seizure disorders, keeps clinicians alert to any improvement in treatment strategies. Recent technical advances in surgical, endovascular, and radiation therapy add to the constantly accumulating data on clinical features, natural course, and treatment outcome in adult arteriovenous malformation patients. This review focuses on new concepts in arteriovenous malformation etiology, classification, treatment, and study approaches.

The feasibility of intracarotid adenosine for the manipulation of human cerebrovascular resistance

To assess the feasibility of manipulating human cerebrovascular resistance with adenosine, we measured cerebral blood flow (CBF) by determining the initial slope (IS) of tracer washout 20-80 s after intracarotid 133Xe injection (standard IS) during sequential 3-min intracarotid infusions of (a) saline; (b) adenosine 1.2-mg bolus followed by an infusion of 1 mg/min (bolus + infusion); (c) saline; and (d) nicardipine (0.1 mg/min). During 133Xe washout, adenosine caused a rapidly clearing compartment. Therefore, tracer washout was also analyzed 5-25 s after injection (early IS). Nicardipine (n = 8) increased both standard IS (from 39+/-12 to 53+/-16 mL 100g.min(-1); P < 0.005) and early IS (from 40+/-9 to 55+/-20 arbitrary units; P < 0.02) to a similar degree. Adenosine bolus + infusion increased early IS (from 33+/-6 to 82+/-43 arbitrary units; P < 0.02) but did not increase standard IS (from 41+/-12 to 43 +/-16 mL 100g(-1) min(-1)). Standard and early IS values were then determined before and after adenosine delivered either by infusion alone (2 mg/min for 3 min, n = 5) or bolus alone (2 mg in 1 s, n = 3). Neither standard nor early IS changed after adenosine infusion alone. Early IS increased after adenosine bolus alone. Increase in early IS, but not standard IS, suggests a transient (<30 s) increase in CBF.

IMPLICATIONS

Intracarotid adenosine, in the 1- to 2-mg dose range, may cause a transient, but not a sustained, increase in cerebral blood flow. Intracarotid adenosine in such a dose range does not seem to be an appropriate drug for sustained manipulation of cerebrovascular resistance.