Effects of intermittent reperfusion during temporal focal ischemia

Does the impact of elective temporary clipping on intraoperative rupture really influence neurological outcome after surgery for ruptured anterior circulation aneurysms?--A prospective multivariate study

BACKGROUND

Elective temporary clipping (ETC) is increasingly used in surgery for aneurysms. This study was to assess whether the impact of ETC on intraoperative aneurysmal rupture (IAR) translates into neurological outcome.

METHODS

Patients who underwent surgery for ruptured anterior circulation aneurysms were prospectively studied for various factors related to ETC, IAR and neurological outcome at 3 months. Univariate and multivariate analyses were performed using SPSS20.

RESULTS

Of the total 273 ruptured aneurysm surgeries studied, IAR was observed in only six out of 132 aneurysms (4.5 %) who had ETC, compared with 78 out of 141 (55.3 %) without ETC (p < 0.001). Aneurysms complicated by IAR had significantly longer clipping time (8.3 min) compared with those without IAR (1.9 min) (p < 0.001). IAR had significant association with unfavorable outcome (38 % vs. 24 %) (p = 0.02). Patients with ETC had significantly shorter clipping time (2.9 min) compared with those without ETC (4.8 min) (p = 0.02). Unfavorable outcome was noted in 30 out of 132 with ETC (23 %), compared with 48 out of 141 without ETC (34 %) (p = 0.04). This beneficial effect was nonsignificantly greater in younger and good clinical grade patients. While episodes of ETC within clipping time of 20 min did not show significant difference in outcome, repeated rescue clipping (45 % unfavorable outcome, p = 0.048) and total clipping time of at least 20 min (75 % unfavorable outcome, p = 0.008) had significant impact on outcome. In multivariate analysis, the use of ETC (p = 0.027) and total temporary clipping less than 20 min (p = 0.049) were noted to result in significantly better outcome, independent of other factors.

CONCLUSIONS

The use of ETC decreased the occurrence of IAR and the total clipping time, thereby leading to significantly better outcome, independent of other factors. While repeated elective clipping within total clipping time of 20 min did not influence outcome, repeated rescue clipping and total clipping time of at least 20 min had significant impact on outcome.

Surgical management of aneurysmal subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a common and often devastating condition that requires prompt neurosurgical evaluation and intervention. Modern management of aSAH involves a multidisciplinary team of subspecialists, including vascular neurosurgeons, neurocritical care specialists and, frequently, neurointerventional radiologists. This team is responsible for stabilizing the patient on presentation, diagnosing the offending ruptured aneurysm, securing the aneurysm, and managing the patient through a typically prolonged and complicated hospital course. Surgical intervention has remained a definitive treatment for ruptured cerebral aneurysms since the early 1900s. Over the subsequent decades, many innovations in microsurgical technique, adjuvant maneuvers, and intraoperative and perioperative medical therapies have advanced the care of patients with aSAH. This report focuses on the modern surgical management of patients with aSAH. Following a brief historical perspective on the origin of aneurysm surgery, the topics discussed include the timing of surgical intervention after aSAH, commonly used surgical approaches and craniotomies, fenestration of the lamina terminalis, intraoperative neurophysiological monitoring, intraoperative digital subtraction and fluorescent angiography, temporary clipping, deep hypothermic cardiopulmonary bypass, management of acute hydrocephalus, cerebral revascularization, and novel clip configurations and microsurgical techniques. Many of the topics highlighted in this report represent some of the more debated techniques in vascular neurosurgery. The popularity of such techniques is constantly evolving as new studies are performed and data about their utility become available.

Risk of stroke with temporary arterial occlusion in patients undergoing craniotomy for cerebral aneurysm

OBJECTIVE

This study was performed to elucidate the technical and patient-specific risk factors for postoperative ischemia in patients undergoing temporary arterial occlusion (TAO) during the surgical repair of their aneurysms.

METHODS

Eighty-nine consecutive patients in whom TAO was performed during surgical repair of an aneurysm were retrospectively analyzed. The demographics of the patients were analyzed with respect to age, Hunt and Hess grade on admission, Fisher grade of hemorrhage, aneurysm characteristics, timing of surgery, duration of temporary occlusion, and number of temporary occlusive episodes. Outcome was analyzed at the 3-month follow-up, along with the occurrence of symptomatic and radiological stroke.

RESULTS

In overall, twenty-seven patients (29.3%) had radiologic ischemia attributable to TAO and fifteen patients (16.3%) had symptomatic ischemia attributable to TAO. Older age and poor clinical grade were associated with poor clinical outcome. There was a significantly higher rate of symptomatic ischemia in patients who underwent early surgery (p = 0.007). The incidence of ischemia was significantly higher in patients with TAO longer than 10 minutes (p = 0.01). In addition, patients who underwent repeated TAO, which allowed reperfusion, had a lower incidence of ischemia than those who underwent single TAO lasting for more than 10 minutes (p = 0.011).

CONCLUSION

Duration of occlusion is the only variable that needs to be considered when assessing the risk of postoperative ischemic complication in patients who undergo temporary vascular occlusion. Attention must be paid to the patient's age, grade of hemorrhage, and the timing of surgery. In addition, patients undergoing dissection when brief periods of temporary occlusion are performed may benefit more from intermittent reperfusion than continuous clip application. With careful planning, the use of TAO is a safe technique when used for periods of less than 10 minutes.

The effect of temporary aneurysm clip on the common carotid artery of atherosclerotic rabbits

BACKGROUND

We compared the effect of temporary aneurysm clips on atherosclerotic and nonatherosclerotic CCA of rabbits by morphometric and ultrastructural methods.

METHODS

The rabbits (N = 12) were divided into 2 groups: the first group was fed a 2% cholesterol diet, and the second group, a normal diet for 4 weeks. Atherosclerotic lesions developed after 4 weeks. Temporary aneurysm clips were placed on the left CCA of both groups; the right CCA of both groups served as control. Thus, a total of 4 groups were used: atherosclerotic (A), atherosclerotic/clip (AC), nonatherosclerotic (NA), and nonatherosclerotic/clip (NAC). Temporary aneurysm clips were applied for 1, 5, and 10 minutes in the AC and NAC groups. No temporary clip was placed on the right CCA (A and NA groups). The affected parts of the CCA via clips were examined under light microscope and SEM.

RESULTS

Comparison of atherosclerotic and nonatherosclerotic CCA of rabbits under light microscope indicated that the wall of atherosclerotic CCA was thicker than that of nonatherosclerotic CCA. The difference between the thickness of atherosclerotic and nonatherosclerotic CCAs was significant. SEM analyses showed that in nonatherosclerotic CCAs, the effect of temporary aneurysm clips was seen after 10 minutes, but in atherosclerotic CCAs, the effect was seen within the 1st minute of clipping and continued in the 5th and 10th minutes.

CONCLUSION

The duration of temporary clipping should be decreased for the neurovascular surgery of atherosclerotic patients.

Clampage vasculaire temporaire

In many situations, temporary artery occlusion is an integral component of aneurysm surgery. The use of temporary clip may allow safer and easier aneurysmal dissection and clipping. Several points, concerning the duration and overall risks of temporary occlusion and the method of choice for cerebral function monitoring have to be discussed.

MATERIAL AND METHODS

Non exhaustive review of neurosurgical literature.

DISCUSSION

Temporary clip application decreases the risk of intraoperative aneurysmal rupture. The analysis of data published in the literature showed that several questions remain open concerning the optimal method of neuroprotection and cerebral function monitoring, as well as the limit of occlusion duration. Other clinical trials are needed to assess the efficacy and safety of this technique.

Functional evaluation of temporary focal cerebral ischemia: experimental model

OBJECTIVE: Despite cerebral ischemia being a frequent clinical pathologic state, the tolerance of neural tissue to oxygen absence and to reperfusion is controversial. This study aims to evaluate the effects of focal cerebral ischemia/reperfusion, by analyzing the mitochondrial respiration. METHOD: Sixty-four adult rats underwent focal cerebral ischemia by middle cerebral artery occlusion, during 15, 30 and 60 minutes, followed by 10 minutes or 19 hours of reperfusion. The effects of ischemia were analyzed measuring the O2 consumption by mitochondria in the ischemic and non-ischemic areas. RESULTS: There was compromise of the mitochondrial respiration after 30 and 60 minutes of ischemia, followed by 10 minutes of reperfusion but there was no alteration in this function after 19 hours of reperfusion. CONCLUSION: Compromise of the mitochondrial function occurred after 30 minutes of ischemia but, until one hour of ischemia, if the reperfusion was prolonged there was no evidence of ischemic/reperfusion injuries.

[Evaluation of microsurgical treatment in a series of 121 intracranial aneurysms]

OBJECTIVE

The results obtained with therapy of intracranial aneurysms, in terms of morbidity and mortality, are very important when the patient has to choose between microsurgical techniques or endovascular management. The aim of this paper is to review the information regarding current microsurgical treatment of intracranial aneurysms, and presenting our experience over the last five years.

MATERIAL AND METHODS

We studied 101 consecutive patients with 121 intracranial aneurysms admitted between 1996 and 2000 with the initial diagnosis of subarachnoid hemorrhage. We paid special attention to the day of admission from the onset of the symptomatic hemorrhage to the grade of Hunt&Hess scale and the possibility of early or delayed microsurgical treatment. The diagnosis was based on four vessels cerebral angiography and in a few cases with CT-angiography. All patients were treated by microsurgical technique and such treatment was completed by nimodipine, intensive care unit management and in some cases of postoperative suspected vasospasm, induced arterial hypertension was applied. Post surgical angiography was carried out in all patients to confirm the clipping of the cerebral aneurysm. The 12 months assessment was based on the Glasgow Outcome Scale (GOS).

RESULTS

The 92.1% of the patients were admitted with a grade equal or below III in the Hunt&Hess scale. A 80% were operated within the 72 hours of admission and in the remaining cases, the surgical treatment was delayed due to a grade IV or V or to a medical contraindication. Four patients died (3.9%). At 12 months follow up, 88.9% presented a score I or II in the GOS.

CONCLUSION

According to our results, there are a substantial improvements in the microsurgical treatment of cerebral aneurysms, specially in patients admitted early after the onset of the symptoms of their hemorrhage, who have a grade I to III in the Hunt&Hess scale and showed a good level of consciousness. We think that the improvement of our results are due to: l. the high percentage of patients admitted with grades I to III. 2. the high percentage of patients operated within the first 72 hours from the onset of their symptomatic hemorrhage. 3. surgery was always carried out by the same two experienced vascular neurosurgeons. 4. intraoperative measures taken to prevent the rupture of the aneurysm. 5. early administration of nimodipine, ICU management, doppler studies and in seldom cases, induced hypertension therapy to treat the vasospasm and postoperative hypotension.

Eubaric hyperoxemia and experimental cerebral infarction

We explore three questions concerning arterial hyperoxygenation and focal ischemia. (1) Does greater benefit accrue with higher levels of arterial hyperoxemia? (2) Is the net effect of continuous (intraischemic plus postischemic) oxygen therapy toxic, or beneficial to middle cerebral artery infarction? (3) In view of free radical theories of reperfusion injury, does hyperoxia isolated to the reperfusion period damage tissue? Rats subjected to transient, focal, normothermic, normoglycemic ischemia were assessed at 2 weeks' survival. Arterial hyperoxygenation from 98.9 +/- 4.0 to 312.2 +/- 48.4mm Hg during ischemia improved (p < 0.05) neurological function, as did isolated reperfusion hyperoxemia, but treatment with continuous hyperoxemia both during and after ischemia yielded greatest benefit (p < 0.001). Cortical infarcts constituted 6.5 +/- 1.8% of the hemisphere at normoxia, but 2.3 +/- 0.9% at hyperoxic levels (p < 0.01). Hyperoxia isolated to the reperfusion period also reduced cortical necrosis, from 6.5% to 2.7 +/- 1.2%. However, continuous intraischemic and reperfusion hyperoxemia led to only 0.2 +/- 0.1% cortical necrosis (p = 0.0005). Increasing the degree of hyperoxemia did not augment the benefit. We conclude that (1) eubaric hyperoxemia improves neurological and neuropathological outcome, (2) continuous oxygen therapy offers the greatest benefit, and (3) reperfusion hyperoxemia is beneficial. The findings should allay clinical concerns regarding oxygen-induced reperfusion injury, and, by obviating hyperbaric chambers, encourage clinical trials studying arterial hyperoxemia in treating stroke.

Temporary arterial occlusion in the repair of ruptured intracranial aneurysms: an analysis of risk factors for stroke

OBJECT

This study was performed to further elucidate technical and patient-specific risk factors for perioperative stroke in patients undergoing temporary arterial occlusion during the surgical repair of their aneurysms.

METHODS

One hundred twelve consecutive patients in whom temporary arterial occlusion was performed during surgical repair of an aneurysm were retrospectively analyzed. Confounding factors (inadvertent permanent vessel occlusion and retraction injury) were identified in six cases (5%) and these were excluded from further analysis. The demographics for the remaining 106 patients were analyzed with respect to age, neurological status, aneurysm characteristics, intraoperative rupture, duration of temporary occlusion, and number of occlusive episodes; end points considered were outcome at 3-month follow up and symptomatic and radiological stroke.

CONCLUSIONS

Overall 17% of patients experienced symptomatic stroke and 26% had radiological evidence of stroke attributable to temporary arterial occlusion. A longer duration of clip placement, older patient age, a poor clinical grade (Hunt and Hess Grades IV-V), early surgery, and the use of single prolonged clip placement rather than repeated shorter episodes were associated with a higher risk of stroke based on univariate analysis. Intraoperative aneurysm rupture did not affect stroke risk. On multivariate analysis, only poorer clinical grade (p = 0.001) and increasing age (p = 0.04) were significantly associated with symptomatic stroke risk.

Análise da respiração mitocondrial em tecido cerebral de gato após isquemia e reperfusão

INTRODUÇÃO: A isquemia cerebral é uma doença freqüente e de difícil tratamento médico. De particular interesse neurocirúrgico são as situações de vasoespasmo após hemorragia subaracnóidea, de oclusão temporária de vasos nas neurocirurgias e de tromboses de artérias intracranianas. A lesão cerebral resultante da isquemia depende da sua duração e pode ser agravada pela reperfusão do território isquêmico. Vários estudos clínicos e experimentais têm sido realizados para melhor entender esses fenômenos. OBJETIVO: Este trabalho visou a avaliação precoce dos efeitos da isquemia focal seguida da reperfusão no cérebro de gatos. MÉTODOS: A isquemia cerebral foi provocada por clipagem temporária da artéria cerebral média por tempos determinados com reperfusão durante 10 minutos, e avaliação foi efetuada através da análise da respiração mitocondrial no tecido isquemiado. Resultados - Houve redução significativa no consumo de O2 nas amostras de tecido cerebral isquemiado por 60 minutos, seguidos de 10 minutos de reperfusão, quando comparadas ao tecido cerebral contralateral (não isquemiado). CONCLUSÕES: Com base nos resultados obtidos, pode-se concluir que o tempo de duração da isquemia foi um fator determinante na alteração da respiração mitocondrial de gatos submetidos à isquemia e reperfusão de curta duração (alterações significativas apenas após 60 minutos de isquemia seguidos de 10 de reperfusão).

Possible control of intermittent cerebral ischemia by monitoring of direct-current potentials

OBJECT

Neurosurgically induced temporary occlusion of intracranial arteries carries the risk of cerebral ischemic damage. Because negative shifts in the cortical direct-current (DC) potential indicate tissue depolarization and, thus, critical ischemic stress, the authors hypothesized that recordings of these potentials could help to determine the optimal duration and frequency of induced intermittent focal ischemia to prevent brain injury. The investigators related the results of DC recordings both to simultaneously recorded decreases in extracellular Ca++ concentration ([Ca++]o), which reflect Ca++ entry into cells, and to histological outcome.

METHODS

In cats anesthetized with halothane the effects of intermittent brief (10 minutes long, six times [6 x 10-min group]) and prolonged (20 minutes long, three times [3 x 20-min group]) episodes of middle cerebral artery occlusions were compared with those of a single continuous episode (1 x 60-min group). Laser Doppler flow probes and ion-selective microelectrodes were used to measure cerebral blood flow, DC potentials, and [Ca++]o in cortical tissues of ectosylvian gyri. Negative shifts in DC potential were evaluated in the three groups during the entire 60-minute-long period of ischemia and were smallest in the 6 x 10-min group, larger in the 3 x 20-min group, and largest in the 1 x 60-min group. Accordingly, infarct volumes were smallest in the 6 x 10-min group, intermediate in the 3 x 20-min group, and largest in the 1 x 60-min group. Decreases in ischemic [Ca++]o were significantly greater in the 1 x 60-min group than in the two groups in which there were repetitive occlusions, and recovery of [Ca++]o after reperfusion normalized only in the 1 x 60-min group.

CONCLUSIONS

The DC potential may provide a reliable measure to optimize intermittent ischemia and to achieve minimal ischemic brain injury during temporary neurosurgical occlusion of cerebral arteries.

Effects of interrupted and uninterrupted occlusion of the basilar artery on cerebral blood flow, and on neurological and histological outcome in rats with subarachnoid hemorrhage

Most neurosurgeons consider temporary vessel occlusion for aneurysmal clipping an effective technique that facilitates dissection between the aneurysm and the parent vessel. It is generally believed that repeated short periods of cerebral ischemia are safer for the brain than a single long episode. The aim of this study was to identify whether interrupted and uninterrupted vessel occlusion differs with regard to changes in brain tissue and cerebral hemodynamics after subarachnoid hemorrhage (SAH). Fifty Spraque Dawley rats (300-350 g) were placed under general anaesthesia and ventilated. The basilar artery was exposed through a transclival approach. Baseline local cerebral blood flow (LCBF) values was measured, and then the basilar artery was punctured, causing subarachnoid hemorrhage (SAH). Group I (n = 24) was subjected to 60 min of interrupted basilar artery occlusion, defined as 5 min of reperfusion after every 10 min of occlusion, group II (n = 26) 60 min of uninterrupted artery occlusion. Three days after completion of the experiment, each rat was neurologically evaluated and decapitated. Coronal brain slices were obtained and stained to assess infarct volume. Immediately after SAH, LCBF fell by 58% in group I, and by 52% in group II. In group I, each ischemic insult brought a similar reduction in LCBF, and after each release of the occlusion there was a rapid rise in flow. In group II, the LCBF values dropped initially and remained at low levels until the end of the study. The 2,3,5 triphenyltetrazolium chloride stained sections showed similar volumes of brainstem infarction in both groups (38.3 +/- 9.2 mm3 vs. 34.3 +/- 8.7 mm3, respectively; p > 0.05). The results suggest that there is no neuroprotective advantage to either interrupted or uninterrupted temporary blockage of blood flow during neurovascular procedures after SAH in the basilar artery region.

Ischemic brain injury caused by interrupted versus uninterrupted occlusion in hypotensive rats with subarachnoid hemorrhage: neuroprotective effects of citicoline

This study investigated the neuroprotection provided by cytidine 5'-diphosphocholine (citicoline) during interrupted and uninterrupted occlusion of the basilar artery after subarachnoid hemorrhage (SAH) in 121 hypotensive rats. Animals were anesthetized and the basilar artery was exposed through a transclival approach. Baseline local cerebral blood flow (LCBF) values were recorded, and then the basilar artery was punctured, causing SAH. Blood was drawn to induce hypotension [60-70 mmHg mean arterial blood pressure (MABP)]. Control rats received intraperitoneal (i.p.) injections of 0.5 ml saline immediately after SAH before hypotension induction and after 60 min of occlusion. Experimental rats received 400-mg/kg citicoline i.p. at the same time points. Control group I and treatment group III were subjected to 60 min of interrupted occlusion (5 min of reperfusion after each 10 min of occlusion). Control group II and treatment group IV were subjected to 60 min of uninterrupted occlusion. MABP and LCBF were recorded every 5 minutes. Brain edema was evaluated in seven rats from each group at 24 hours after ischemic injury. At 3 days after occlusion, another set of 28 rats was killed and coronal brain slices were stained to assess infarct volume. The groups' physiological and edema findings were similar. In all groups, LCBF fell immediately after SAH and remained below baseline throughout the experiment. In the citicoline-treated rats, arterial pressure increased significantly after 30-40 min of occlusion, and brain slices showed significantly smaller infarct volumes compared to control slices (p < 0.05). Mortality was significantly lower in the citicoline-treated animals (p < 0.001). The results suggest that citicoline provides significant neuroprotection during cerebral ischemia, and that it significantly reduces mortality. Part of the neuroprotective effect may be mediated by recovery of arterial pressure.

Prospective analysis of aneurysm treatment in a series of 103 consecutive patients when endovascular embolization is considered the first option

OBJECT

The aim of this study was to evaluate prospectively the results of treating cerebral aneurysms with coil embolization (CE) or with surgical clipping when CE was considered the first option.

METHODS

Whenever an aneurysm was to be treated, CE was first considered by our neurovascular team. Surgical clipping was reserved for cases excluded from CE or cases in which CE failed. The study consisted of 103 consecutive patients with 132 aneurysms, of which 127 were treated. Coil embolization was performed using Guglielmi detachable coils, and surgery was performed using Zeppelin clips. Three groups were defined: Group A consisted of 64 aneurysms that were treated by CE (neck/sac ratio < 1:3); Group B, 63 aneurysms that were surgically clipped; and Group C, 12 aneurysms that failed to be satisfactorily (> or = 95%) embolized and were subsequently clipped. The percentages of residual aneurysm were 31.2% in Group A, 1.6% in Group B, and 0% in Group C. The percentages of patients with poor Glasgow Outcome Scale (GOS) scores (GOS Scores 1-3) were 13.3% in Group A, 6.1% in Group B, and 8.3% in Group C. The percentages of poor outcome (GOS Scores 1-3) in patients with good clinical status before treatment were 10.7% in Group A, 0% in Group B, and 8.3% in Group C.

CONCLUSIONS

Even with preselection, CE remains associated with a significant number of treatment failures and poor outcomes, even in patients with good preoperative clinical status. Surgical clipping can offer better results than CE, even for more complex aneurysms of the anterior circulation, especially for those involving the middle cerebral artery cases. However, because CE can be effective and causes less stress and invasiveness for the patient, it should be considered first in aneurysms strictly selected by a neurovascular team.

Neuronal damage in gerbils caused by intermittent forebrain ischemia

OBJECT

The purpose of this study was to investigate the possibility of preventing cumulative neuronal damage after repetitive severe ischemia.

METHODS

The authors monitored ischemic depolarization in the gerbil hippocampus, which has recently been shown to be a good experimental model of the effects of brief ischemia on the brain, and evaluated neuronal damage in the CA1 subregion 7 days after the ischemic insult. In a single-ischemia paradigm, the results indicate that induction of ischemia-induced neuronal damage depended on the duration of ischemic depolarization. Neuronal damage can be detected in the CA1 subregion after a period of depolarization lasting 210 seconds. Using a double-ischemia paradigm in which the animals were subjected to two periods of ischemia, there was apparently no accumulation of neuronal damage from the first ischemic episode to the second, provided the duration of the first period of ischemic depolarization did not exceed 90 seconds. Neuronal damage accumulated when the duration of the first ischemia episode exceeded 90 seconds, regardless of the duration of the reperfusion interval between the two ischemic insults. Finally, when the ischemic insult was spread over four separate episodes, each lasting 90 seconds (with a reperfusion interval of 5 minutes), neuronal damage was not found when the total depolarization period was less than 420 seconds.

CONCLUSIONS

The authors conclude that cumulative neuronal damage may be avoided by adopting an intermittent ischemia approach. The implications of these results for human surgery requiring temporary occlusion of the cerebral arteries are discussed.

A critical reevaluation of the intraluminal thread model of focal cerebral ischemia: evidence of inadvertent premature reperfusion and subarachnoid hemorrhage in rats by laser-Doppler flowmetry

BACKGROUND AND PURPOSE

The intraluminal thread model for middle cerebral artery occlusion (MCAO) has gained increasing acceptance. Numerous modifications have been reported in the literature, indicating that the technique has not been standardized. The present study was performed to evaluate and optimize the reliability of this model.

METHODS

One hundred Sprague-Dawley rats were subjected to MCAO by 2 different intraluminal filaments. Cortical blood flow was continuously monitored over both hemispheres by laser-Doppler flowmetry (LDF). In part I (3-0 filament), we evaluated the incidence of adequate MCAO, subarachnoid hemorrhage (SAH), intraluminal thrombus formation, and the effects of heparinization. In part II (silicone-coated 4-0 filament), we also determined the influence of insufficient MCAO on morphological and functional outcome and the incidence of postischemic hyperthermia.

RESULTS

In part I, SAH occurred in 30% and premature reperfusion in 24%. All animals with a decrease in contralateral flow had suffered SAH. Thrombus formation was not observed in any group. In part II, SAH occurred in 8% and premature reperfusion in 26%. There was no difference in outcome between rats with primary MCAO and rats with filament correction. Animals with uncorrected premature reperfusion had significantly smaller infarct volumes and fewer neurological deficits.

CONCLUSIONS

SAH and insufficient MCAO may be more common in the intraluminal thread model than previously reported. Inadvertent premature reperfusion contributes to the interanimal variability associated with this model. The incidence of valid experiments increases with the use of a silicone-coated 4-0 filament. Continuous bilateral LDF is indispensable to monitor adequate MCAO and is highly sensitive to recognize SAH.

Intraoperative monitoring of substrate delivery during aneurysm and hematoma surgery: initial experience in 16 patients

The effects of proximal occlusion of the parent artery during aneurysm surgery in humans are not fully understood, although this method is widely used. The reduction in substrate that can be tolerated by normal and subarachnoid hemorrhage (SAH)-affected brain is unknown. Therefore, the authors measured brain oxygen tension (brain PO2), carbon dioxide tension (brain PCO2), pH, and hemoglobin oxygen (HbO2) saturation before and after temporary occlusion in 12 patients with aneurysms. The effect of removal of a traumatic intracranial hematoma on cerebral oxygenation was also studied in four severely head injured patients. A multiparameter sensor was placed in the cortex of interest and locked by means of a specially designed skull bolt. The mean arterial blood pressure, inspired O2 fraction, and end-tidal PCO2 were analyzed. Brain PO2 and HbO2 saturation data were collected every 10 seconds. Descriptive and nonparametric analyses were used to analyze the data. A wide range in baseline PO2 was seen, although a decrease from baseline in brain PO2 was found in all patients. During temporary occlusion, brain PO2 in patients with unruptured aneurysm (seven patients) dropped significantly, from 60 +/- 31 to 27 +/- 17 mm Hg (p < 0.05). In the SAH group (five patients), the brain PO2 dropped from 106 +/- 74 to 87 +/- 73 mm Hg (not significant). Removal of intracranial hematomas in four severely head injured patients resulted in a significant increase in brain PO2, from 13 +/- 9 to 34 +/- 13 mm Hg (p < 0.05). The duration of safe temporary occlusion could not be determined from this group of patients, because none developed postoperative deterioration in their neurological status. However, the data indicate that this technique is useful to detect changes in substrate delivery during intraoperative maneuvers. This study also reemphasizes the need for emergency removal of intracranial hematomas to improve substrate delivery in severely head injured patients.

Temporary occlusion of the middle cerebral artery in intracranial aneurysm surgery: time limitation and advantage of brain protection

The risk of focal infarction secondary to the induced reversible arrest of local arterial flow during microsurgical dissection of middle cerebral artery (MCA) aneurysms was evaluated further to define the optimal approach to temporary arterial occlusion. To compare the effectiveness of potential brain-protection anesthetics, a group of patients treated with the intravenous agents propofol, etomidate, and pentobarbital, administered individually or in combination, was compared to a group treated with the inhalational agent isoflurane. Forty-nine consecutive MCA aneurysm surgeries involving the temporary clipping of the parent vessel were retrospectively reviewed. Thirty-eight patients received intravenous brain-protection (IVBP) anesthesia. Groups of patients with and without infarctions, and receiving and not receiving IVBP anesthesia, were compared based on the duration and nature of temporary arterial occlusion. Postoperative radiographic evidence of new infarction was used as the threshold for failure of occlusion tolerance. The overall infarction rate was 22.4% (11 of 49 patients), including 15.8% (six of 38 patients) in the IVBP group versus 45.5% (five of 11 patients) in the group that did not receive brain protection (NBP). In the NBP group, the mean duration of temporary occlusion was 3.9 +/- 2.2 minutes for patients without infarction versus 12.2 +/- 4.3 minutes for patients with focal infarction (p < 0.01). In contrast, the mean duration was 13.6 +/- 10.6 minutes for patients without infarction and 18.5 +/- 9.9 minutes for patients with infarction in the IVBP group. All patients (four of four) in the NBP group who underwent occlusion lasting 10 minutes or longer suffered an infarction versus five of 23 patients in the IVBP group (p < 0.0001). Patients with multiple aneurysms were found to be at increased risk of developing focal infarction, whereas those treated with intermittent temporary clip application were at decreased risk. It is concluded that patients in whom focal iatrogenic ischemia is induced during MCA aneurysm clip ligation have a significant advantage compared with those receiving isoflurane when they are given pentobarbital as the primary neuroprotective agent or when they receive propofol or etomidate titrated to achieve electroencephalographic burst suppression, particularly if more than 10 minutes of occlusion time is required. It is also concluded that 10 minutes is a general guideline for safe, temporary occlusion of the MCA. The use of intermittent temporary arterial occlusion and its use in patients with multiple aneurysms need further evaluation before specific recommendations can be made.

Temporary occlusion of the middle cerebral artery in intracranial aneurysm surgery: time limitation and advantage of brain protection

The risk of focal infarction secondary to the induced reversible arrest of local arterial flow during microsurgical dissection of middle cerebral artery (MCA) aneurysms was evaluated further to define the optimal approach to temporary arterial occlusion. To compare the effectiveness of brain-protection anesthetics, a group of patients treated with the intravenous agents, propofol, etomidate, and pentobarbital, administered individually or in combination, was compared to a group treated with the inhalational agent isoflurane.

Forty-nine consecutive MCA aneurysm surgeries involving the temporary clipping of the parent vessel were retrospectively reviewed. Thirty-eight patients received intravenous brain-protection (IVBP) anesthesia. Groups of patients with and without infarctions, and receiving and not receiving IVBP, were compared based on the duration and nature of temporary arterial occlusion. Postoperative radiographic evidence of new infarction was used as the threshold for failure of occlusion tolerance. The overall infarction rate was 22.4% (11 of 49 patients), including 15.8% (six of 38 patients) in the IVBP group versus 45.5% (five of 11 patients) in the isoflurane (ISO) group. In the ISO group, the mean duration of temporary occlusion was 3.9 ± 2.2 minutes for patients without infarction versus 12.2 ± 4.3 minutes for patients with focal infarction (p < 0.01). In contrast, the mean duration was 13.6 ± 10.6 minutes for patients without infarction and 18.5 ± 9.9 minutes for patients with infarction in the IVBP group. All patients in the ISO group who underwent occlusion lasting 10 minutes or longer suffered an infarction versus five of 23 patients in the IVBP group. Patients with multiple aneurysms were found to be at increased risk of developing focal infarction, whereas those treated with intermittent temporary clip application were at a decreased risk.

It is concluded that patients in whom focal iatrogenic ischemia is induced during MCA aneurysm clip ligation have a significant advantage compared with those receiving ISO when they are given pentobarbital as the primary neuroprotective agent or when they receive propofol or etomidate titrated to achieve electroencephalographic burst suppression, particularly if more than 10 minutes of occlusion time is required. It is also concluded that 10 minutes is a general guideline for safe, temporary occlusion of the MCA. The use of intermittent temporary arterial occlusion and patients with multiple aneurysms need further evaluation before specific recommendations can be made.

Temporary vessel occlusion during intracranial aneurysm repair

Any method that decreases the risk of intraoperative rupture should improve outcome if complications associated with its use do not negate positive effect. If application time is limited and a form of cerebral protection and appropriate monitoring of cerebral function are used, temporary clip application may meet these requirements. The efficacy of temporary occlusion as an adjunct to aneurysm clipping may be limited by technical considerations with respect to regional anatomy, aneurysm size, and aneurysm consistency. In areas of limited access, positioning proximal clips may not be feasible. The use of endovascular techniques of balloon occlusion may provide proximal control in these situations (9, 106). The decision to use total circulatory arrest and profound hypothermia, as opposed to temporary clip application, remains largely a matter of the surgeon's judgment. The role of proximal parent vessel ligation must also be considered in the decision-making process regarding the treatment of giant or technically difficult aneurysms (114). Further refinements in cerebral monitoring that can accurately reflect intracellular processes in all territories affected by the application of temporary clips or balloon occlusion and development of more effective forms of cerebral protection may permit safer use of this technique. An adequately controlled clinical trial of temporary occlusion with or without putative "cerebral protection" is needed to confirm the efficacy of this technique.

Cerebral protection by intermittent reperfusion during temporary focal ischemia in the rat

Temporary arterial occlusion has been routinely used as an adjunct in intracranial aneurysm surgery. This has commonly been performed using a protocol of multiple short periods of occlusion alternating with periods of restoration of normal circulation. Recently, the logical basis of this method has come under scrutiny. There is extensive experimental evidence to suggest that repetitive, brief periods of global ischemia may cause more severe cerebral injury than an equivalent single period of global ischemia. Only recently has this issue begun to be addressed with regard to focal ischemia. Hence, despite the common use of temporary clipping, little experimental data are available regarding the ischemic consequences of temporary arterial occlusion with periods of reperfusion versus uninterrupted temporary occlusion. To investigate this issue, a protocol of occlusion/reperfusion that simulates the temporal profile that occurs during surgery was performed in a rat model of focal ischemia. Sixteen anesthetized Sprague-Dawley rats were divided into two groups. The animals in Group I underwent 60 minutes of uninterrupted middle cerebral artery occlusion and the animals in Group II were subjected to six separate 10-minute occlusion periods with 5 minutes of reperfusion between occlusions. Histopathological analysis was performed 72 hours postischemia. Group I had significantly increased mean infarction volumes (50.0 +/- 12.1 mm3) compared to Group II (8.7 +/- 3.1 mm3) (p = 0.008). Injuries in Group I occurred in both the cortex and striatum, whereas Group II showed only striatal injuries. Furthermore, the extent of the injuries in Group II was less severe, characterized by ischemic neuronal injury rather than frank infarction. The results indicate that intermittent reperfusion is neuroprotective during temporary focal ischemia and support the hypothesis that intermittent reperfusion is beneficial if temporary clipping is required during aneurysm repair.

Intraoperative endovascular surgery for cerebral aneurysms

The application of a number of procedures that can be considered intraoperative endovascular neurosurgery has enhanced our ability to treat cerebral aneurysms from the abluminal surface. This study identifies a role for these techniques in the management of difficult aneurysms. A review of the last 1202 aneurysms undergoing direct clipping by the authors disclosed that these methods were used in 62 cases. Of these aneurysms, 36 arose from the internal carotid artery, 12 from the middle cerebral artery, eight from the vertebrobasilar distribution, and six from the anterior cerebral artery. The indications for applying these methods were large size (12-60 mm), intraluminal thrombus, broad neck, plaque at the neck, the potential compromise of branches at the base of the aneurysm, or a combination of these problems. The most frequently chosen intraoperative technique was suction decompression with direct removal of plaque and thrombus using suction, dissection, and/or ultrasonic aspiration. The application of temporary clips was required in all cases in which the aneurysm was opened before definitive clipping. No special pharmacological cerebral protective regimen was used. In one case in which a greater occlusion time was anticipated, cardiopulmonary bypass with profound hypothermia was performed. A favorable outcome was achieved in 73% of these difficult cases. An increased neurological deficit after surgery was seen in 11%, and the mortality rate was 8%. These methods should be considered and can be anticipated before surgery for unusual aneurysms. Many cases now being considered for embolization may be more suitable for definitive surgical obliteration.

Interrupted arterial occlusion reduces ischemic damage in a focal cerebral ischemia model of rats

It is generally thought by neurosurgeons that when temporary clipping of a major cerebral vessel is necessary during aneurysm surgery, repeated short periods of cerebral ischemia are safer for the brain than a single long episode. This study was performed to investigate whether repetitive short episodes of cerebral ischemia would alter the resulting brain injury as compared with a single long period of ischemia in a rat model for focal cerebral ischemia. Middle cerebral artery occlusion and reperfusion were performed by the intraluminal thread technique. The experimental design consisted of a single 90-minute occlusion period in the continuous ischemia group versus three 30-minute occlusion periods with 15-minute reperfusion periods in the repetitive group. Local cerebral blood flow was measured by the hydrogen clearance technique. During the ischemic period, local cerebral blood flow values significantly decreased in both the continuous and the repetitive groups. Cerebral blood flow restoration was demonstrated after each episode of reperfusion in both groups. The neurological status scores 2 hours after surgery in the rats subjected to repetitive insults were significantly better compared with those in the rats of the continuous ischemia group. However, the scores on Days 1, 3, and 7 did not show a significantly better difference. The animals were killed 7 days after the induction of ischemia for the measurement of the infarction area under the microscope. The total area of infarction was significantly reduced (4.05 +/- 4.56 versus 47.2 +/- 37.3 mm2, P < 0.001) by interruption of the ischemic time period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intermittent reperfusion and nitric oxide synthase inhibition on infarct volume during reversible focal cerebral ischemia

The authors examined the effects of both intermittent reperfusion and nitric oxide synthase (NOS) inhibition, caused by NG-nitro-L-arginine methyl ester (L-NAME) during episodes of focal cerebral ischemia induced to simulate the neurosurgical setting. Seventy-eight Wistar rats underwent single (60 minutes of ischemia) or repetitive (four 15-minute periods of ischemia separated by 5 minutes of reperfusion) episodes of middle cerebral artery occlusion while under anesthesia (1.0% halothane). Twenty-four hours after the procedure, the animals were given neurological examinations and then sacrificed for histological preparation and examination. The intermittent reperfusion groups tended to have smaller mean cortical infarctions. There was also a trend showing a decrease in infarction size in groups given L-NAME. The combination of intermittent reperfusion and preischemic administration of L-NAME (10 mg/kg) resulted in a 65% reduction in infarction size (p < 0.05) when compared to that caused by 60 minutes of single occlusion without L-NAME. The use of NOS inhibition combined with intermittent reperfusion may be a technique to provide intraoperative cerebral protection during neurovascular procedures that require temporary vascular occlusion.

Effects of intermittent reperfusion on brain pHi, rCBF, and NADH during rabbit focal cerebral ischemia

BACKGROUND AND PURPOSE

The use of intermittent reperfusion versus straight occlusion during neurovascular procedures is controversial. This experiment studied the effects of intermittent reperfusion and single occlusion on intracellular brain pH (pHi), regional cerebral or cortical blood flow, and nicotinamide adenine dinucleotide (NADH) fluorescence during temporary focal ischemia.

METHODS

Twenty fasted rabbits under 1.0% halothane anesthesia were divided into four groups: (1) nonischemic controls, (2) 60 minutes of uninterrupted focal ischemia, (3) 2 x 30-minute periods of focal ischemia separated by a 5-minute reperfusion, and (4) 4 x 15-minute periods of focal ischemia separated by three 5-minute reperfusion periods. Focal ischemia was produced by occlusion of both the middle cerebral and ipsilateral anterior cerebral arteries. After the final occlusion, there was a 3-hour reperfusion period in all groups. Regional cerebral and cortical blood flow, brain pHi, and NADH fluorescence were measured with in vivo panoramic fluorescence imaging.

RESULTS

During occlusion, regional cerebral and cortical blood flows and NADH fluorescence values were not different among the groups. Brain pHi was significantly lower in the 4 x 15-minute group compared with the 1 x 60-minute group (6.57 +/- 0.02 versus 6.73 +/- 0.06; P < .03) but not significant when compared with the 2 x 30-minute group. During the short reperfusion periods, all parameters returned to normal except for NADH fluorescence levels, which remained elevated. During the postischemic final reperfusion period, there was a mild brain alkalosis of approximately 7.1 in all groups. There were no significant differences in NADH fluorescence among groups during the final reperfusion. Regional cerebral and cortical blood flow returned to near normal values in all groups.

CONCLUSIONS

This study demonstrates that intermittent reperfusion during temporary focal ischemia has different effects on the intracytoplasmic and the intramitochondrial compartments: worsening of brain cytoplasmic pHi but no significant differences in the oxidation/reduction level of mitochondrial NADH.

[Neuro-anesthetic contribution to the prevention of complications caused by mechanical cerebral retraction: concept of a chemical brain retractor]

During most intracranial procedures, the microscope is used to allow the surgeon to work on structures which are deeply located in the brain. Under these circumstances, brain retraction is required for adequate exposure. It was rapidly suspected and later confirmed that brain retraction causes secondary brain damage. This is due not only to direct effect of the retractor on the cortical surface, but also because a pressure is generated under the retractor, on the brain tissue, which compromises local cerebral blood flow and local cerebral perfusion pressure, thus causing cerebral ischaemia. The need for retraction is increased if the lesion is located deeply and/or if the brain is tensed; thus the risk to generate ischaemic conditions is enhanced. These secondary surgical lesions are promoted and worsened by associated systemic conditions such as hypotension, hypoxaemia, hypercapnia. As an attempt to respond to the problem generated by surgical retraction, the "chemical brain retractor" concept is proposed. By compulsively rendering the brain as relaxed and compliant as possible, the chemical brain retractor should allow the surgeon to operate on without the use of a surgical brain retractor and, if such a retractor is still needed, to reduce the pressure under it. These goals are achieved with an osmotic agent like mannitol to improve brain compliance, and intravenous anaesthetic agents, moderate hypocarbia and a normal or elevated blood pressure, to minimize cerebral blood volume. In conjunction with the chemical brain retractor, two other manoeuvres should be used to enhance cerebral compliance: CSF drainage and moderate head up position during the procedure.

Cerebral damage caused by interrupted, repeated arterial occlusion versus uninterrupted occlusion in a focal ischemic model

Temporary intracranial arterial occlusion is often utilized during the surgical treatment of intracranial aneurysms. Although numerous experimental studies have suggested that repetitive, brief periods of global ischemia cause more severe cerebral injury than a similar single period of global ischemia, this issue has not been extensively studied in relation to focal ischemia. It remains controversial whether it is safer to use brief periods of interrupted, temporary occlusion separated by reperfusion periods, or a more prolonged, single temporary occlusion. This question is addressed in studies on a rabbit model of transient, focal cerebral ischemia. Sixteen anesthetized rabbits underwent transorbital occlusion of the left internal carotid, middle cerebral, and anterior cerebral arteries, with one of two paradigms:uninterrupted occlusion (1 hour of temporary occlusion followed by 5 hours of reperfusion in eight rabbits), or interrupted occlusion (three separate 20-minute periods of occlusion, with 10 minutes of reperfusion between occlusions, followed by 4 hours, 40 minutes of reperfusion in eight rabbits). Histopathological evaluation for ischemic neuronal damage and magnetic resonance imaging studies for ischemic edema were conducted 6 hours after the initial arterial occlusion. The animals in the interrupted, repeated occlusion group showed a 59% decrease in the area of cortical ischemic neuronal damage (mean +/- standard error of the mean 10.0% +/- 1.7%) compared with the uninterrupted occlusion group (24.4% +/- 5%, p = 0.016). There was no difference between the groups in the extent of striatal ischemic damage or area of ischemic edema. These results suggest that interrupted, repeated focal ischemia causes less cortical ischemic injury than uninterrupted transient ischemia of a similar total duration. Although caution should be exercised in extrapolating from these results to the clinical situation, they may have important implications for temporary arterial occlusion during intracranial surgery.

Temporary vessel occlusion in spontaneously hypertensive and normotensive rats. Effect of single and multiple episodes on tissue metabolism and volume of infarction

Temporary occlusion of an intracranial artery is frequently necessary in the surgical management of intracranial aneurysms, arteriovenous malformations, and tumors. While the risks of vessel damage associated with clip application have been lessened by improved design, the threat of ischemic damage remains. It is unclear whether multiple, brief periods of clip application are more or less safe than a single period of occlusion, and whether the underlying cerebrovascular status influences the outcome from either method. The effect of each of these paradigms (single: 1-hour occlusion; multiple: three 20-minute episodes separated by 10 minutes of reperfusion) on histopathological outcome was assessed in a middle cerebral artery (MCA) occlusion model using both normotensive and spontaneously hypertensive rats. The mean volume of infarction (+/- standard error of the mean) was not different between the single-ischemic (49.4 +/- 17.3 cu mm) and the multiple-ischemic (42.9 +/- 12.9 cu mm) episode groups of normotensive rats, whereas in the spontaneously hypertensive rats a significant difference existed between the volume of infarction for the single-occlusion group (126.7 +/- 18.7 cu mm) and the multiple-occlusion group (162.4 +/- 15.5 cu mm) (p < 0.05). The metabolic data obtained from spontaneously hypertensive animals did not provide an explanation for the larger infarction in that there were no significant differences between the single- and multiple-occlusion groups with respect to tissue glucose, adenosine triphosphate, or lactate levels. The results suggest that intermittent reperfusion may have different effects depending not only on the degree and duration of ischemia and reperfusion, but also on the underlying cerebrovascular status.

A review of brain retraction and recommendations for minimizing intraoperative brain injury

Brain retraction is required for adequate exposure during many intracranial procedures. The incidence of contusion or infarction from overzealous brain retraction is probably 10% in cranial base procedures and 5% in intracranial aneurysm procedures. The literature on brain retraction injury is reviewed, with particular attention to the use of intermittent retraction. Intraoperative monitoring techniques--brain electrical activity, cerebral blood flow, and brain retraction pressure--are evaluated. Various intraoperative interventions--anesthetic agents, positioning, cerebrospinal fluid drainage, operative approaches involving bone resection or osteotomy, hyperventilation, induced hypotension, induced hypertension, mannitol, and nimodipine--are assessed with regard to their effects on brain retraction. Because brain retraction injury, like other forms of focal cerebral ischemia, is multifactorial in its origins, a multifaceted approach probably will be most advantageous in minimizing retraction injury. Recommendations for operative management of cases involving significant brain retraction are made. These recommendations optimize the following goals: anesthesia and metabolic depression, improvement in cerebral blood flow and calcium channel blockade, intraoperative monitoring, and operative exposure and retraction efficacy. Through a combination of judicious retraction, appropriate anesthetic and pharmacological management, and aggressive intraoperative monitoring, brain retraction should become a much less common source of morbidity in the future.