Intraoperative monitoring of cerebral blood oxygenation and hemodynamics during extracranial-intracranial bypass surgery by a newly developed visible light spectroscopy system

BACKGROUND: Cerebrovascular reconstruction procedures run the risk of changing the balance between oxygen supply and consumption during surgery. We assessed the value of visual light spectroscopy for detecting changes in cerebral blood oxygenation (CBO) during superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis. METHODS: We developed a VLS monitoring system which permits continuous monitoring of CBO changes during surgery. Using the VLS, we evaluated the CBO changes in the MCA territory on the lesion side in 18 patients who underwent STA-MCA anastomosis. RESULTS: Temporary occlusion of the MCA (M4 portion) did not change the CBO in 17 patients. However, in the patient with dissecting aneurysm, it caused decreases of oxyhemoglobin and cortical oxygen saturation (CoSo(2)) associated with an increase of deoxyhemoglobin, although these CBO changes were normalized by STA blood flow. In 5 patients, STA blood flow increased the oxyhemoglobin and CoSo(2) and decreased the deoxyhemoglobin, indicating that cortical blood flow (CoBF) was increased. The CoSo(2) before anastomosis was significantly low in the patients who showed an increase of CoSo(2) by STA blood flow (63.0% +/- 2.5%) as compared with those who did not (72.0 +/- 6.1%, P = .024). CONCLUSION: Temporary occlusion of a cortical artery during bypass surgery did not affect the CBO in patients who had chronic cerebral ischemia, but caused acute ischemia in the patient who did not. STA blood flow increased the CoBF during surgery more frequently in patients who showed a low perfusion pressure. The VLS monitoring system is considered useful for evaluating bypass function and facilitates safe and accurate bypass surgery.     

Hemodynamic compensation via an excimer laser-assisted, high-flow bypass before and after therapeutic occlusion of the internal carotid artery

OBJECTIVE: High-flow, extracranial-intracranial (EC-IC) bypass operations are performed to prevent strokes among patients with giant aneurysms who cannot tolerate internal carotid artery (ICA) occlusion. However, the volume flow through the bypass, compared with preoperative ICA flow, has not been evaluated for any type of bypass. We describe a prospective case study that tested the ability of the high-flow EC-IC bypass to replace the volume flow of the ipsilateral ICA after deliberate ICA occlusion. METHODS: Seven consecutive patients with giant aneurysms of the ICA who experienced test occlusion failure underwent nonocclusive, excimer laser-assisted, EC-IC bypass surgery before permanent ICA occlusion. Volume flow values in the ICAs, the basilar artery, the EC-IC bypass, and the middle cerebral arteries were measured with magnetic resonance angiography. RESULTS: No significant changes in volume flow to the ipsilateral and contralateral hemispheres were observed after bypass surgery and therapeutic ICA occlusion. Before bypass surgery, the volume flow through the ipsilateral ICA was 243 +/- 74 ml/min, that through the contralateral ICA was 264 +/- 32 ml/min, and that through the basilar artery was 141 +/- 43 ml/min. After bypass surgery and therapeutic occlusion of the ipsilateral ICA, the volume flow through the bypass was 199 +/- 72 ml/min, that through the contralateral ICA was 303 +/- 82 ml/min, and that through the basilar artery was 153 +/- 72 ml/min. No significant preoperative versus postoperative changes in middle cerebral artery flow were observed on either side. CONCLUSION: The flow through the high-flow EC-IC bypass was able to replace the volume flow of the ipsilateral ICA after deliberate ICA occlusion for the treatment of giant aneurysms.     

Measurement of cerebral blood flow by single photon emission computed tomography in cases of internal carotid artery occlusion

Cerebral blood flow (CBF) was measured with 133xenon inhalation and single photon emission computed tomography in 33 cases of internal carotid artery occlusion, in the resting state and 25 minutes after acetazolamide (Diamox) administration. The patient population consisted of 24 males and nine females with a mean age of 57 years, who presented with transient ischemic attacks or stroke. Acetazolamide inhibits carbonic anhydrase, and CBF increases as a result of dilatation of cerebral arteries due to CO2 accumulation. The mean CBF was 46 ml/100/g/min on the affected hemisphere and 56 ml/100/g/min on the unaffected hemisphere. The mean CBF value obtained by the same method in 10 normal volunteers was 55 ml/100/g/min. Thus, in the patients, CBF decreased on the affected side. The average increase in CBF after acetazolamide administration was 9% on the affected side and 17% on the unaffected side. The average increase in 10 normal volunteers was 32%. The reduced cerebral arterial reactivity to acetazolamide administration was bilateral in the patient group, which suggests that the cerebral arteries were dilated in order to maintain normal CBF. Extra-intracranial (EC-IC) bypass surgery was performed in nine patients. Preoperatively, the mean CBF was 48 ml/100 g/min on the affected side and 57 ml/100 g/min on the unaffected side; the postoperative CBF was 48 ml/100 g/min on the affected side and 56 ml/100 g/min on the unaffected side. Thus, there was no notable change in CBF on either side after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Somatosensory evoked potentials and cortical blood flow during craniotomy for vascular disease

It has been demonstrated that central conduction time (CCT) is slowed and that attenuation of cortical potentials occurs with reduced cerebral perfusion. During 11 craniotomies for aneurysm, arteriovenous malformation (AVM), or extracranial-intracranial (EC-IC) bypass, we continuously monitored somatosensory evoked potentials (SSEPs) and regional cortical blood flow (rCBF) as determined by a thermal flow probe. The CCT was calculated and correlated with the rCBF. In 8 of the 11 cases, the rCBF values varied within 1 SD of normal values derived from 25 measurements of nonischemic cerebral cortex. All initial CCT values were within 1 SD of normal, but 4 of 11 patients had a prolonged CCT intraoperatively. Three of these were associated with a low rCBF (14 to 31 ml/100 g/minute). One patient had postoperative confusion at the time of discharge. One patient who underwent AVM embolization had a permanent loss of SSEPs postoperatively, and his preexisting hemiparesis was more profound after operation. Finally, 1 patient's CCT improved after EC-IC bypass. This is a preliminary study that demonstrates the feasibility of monitoring CCT and rCBF during craniotomy. When rCBF values fall and the CCT slows, neurological deficit will probably occur.     

Clinical results of extracranial-intracranial bypass surgery in patients with hemodynamic cerebrovascular disease

The importance of hemodynamic factors in the pathogenesis and treatment of cerebrovascular disease remains uncertain. The extracranial-intracranial (EC-IC) bypass trial has been criticized for failing to identify and separately analyze those patients with chronic reduction in regional cerebral perfusion pressure (rCPP) who might be most likely to benefit from surgery. Positron emission tomography (PET) measurements of regional cerebral blood flow (rCBF) and blood volume (rCBV) were performed on 29 patients with symptomatic occlusion or intracranial stenosis of the carotid arterial system prior to undergoing EC-IC bypass surgery. Twenty-four patients had evidence of reduced rCPP (increased rCBV/rCBF ratio) distal to the arterial lesion. Of 21 patients who survived surgery without stroke, three suffered ipsilateral ischemic strokes during the 1st postoperative year. A nonrandomized control group of 23 nonsurgical patients' with similar clinical, arteriographic, and PET characteristics experienced no ipsilateral ischemic strokes during the 1st year following PET. Based on these results in 44 patients, the probability that successful surgery reduces the occurrence of ipsilateral ischemic stroke 1 year later was calculated. This probability ranged from 0.045 for a 50% reduction to 0.168 for a 10% reduction. Thus, there was little evidence to suggest that measurements of cerebral hemodynamics can identify a group of patients who would benefit from EC-IC bypass surgery.     

Hemodynamic evaluation in patients with superficial temporal artery-middle cerebral artery anastomosis--stable xenon CT-CBF study and acetazolamide.

Sixteen patients with minor completed stroke in the chronic stage underwent superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis. The acetazolamide-activated regional cerebral blood flow (rCBF) was measured 20 minutes after the injection using inhalation of stable xenon and computed tomographic scanning (Xes CT-CBF study) pre- and postoperatively. Eleven patients (Group 1) showed immediate improvement in neurological state within a few days of the operation, while five (Group 2) showed no improvements. Preoperative rCBF in the ischemic areas without infarction was 30.8 +/- 3.0 ml/100 gm/min in Group 1 and 53.0 +/- 5.2 ml/100 gm/min in Group 2. Preoperative vasodilatory capacity with acetazolamide in Group 1 was 5.7 +/- 8.6 and significantly increased to 19.8 +/- 4.9 after surgery. In Group 2, pre- and postoperative vasodilatory capacity was 12.7 +/- 3.1 and 14.9 +/- 2.9, respectively, and there was no significant change. These results suggested that minor stroke patients with moderate decrease of affected side rCBF (less than 40 ml/100 gm/min) and with hemodynamic impairment may have the surgical indication for STA-MCA anastomosis.     

Improvement of oxygen metabolic reserve after extracranial-intracranial bypass surgery in patients with severe haemodynamic insufficiency

Summary The effectiveness of extracranial-intracranial arterial bypass (EC-IC bypass) surgery on impaired haemodynamic status was studied in 12 patients with reduced regional cerebral perfusion pressure (rCPP) and elevated regional oxygen extraction fraction (rOEF) in the area distal to the symptomatic arterial lesion. Postoperative positron emission tomography (PET) study demonstrated a statistically significant decrease of rOEF in the operated hemispheres with disappearance of the pre-operative interhemispheric rOEF difference. Regional cerebral blood flow (rCBF) and regional cerebral oxygen metabolism (rCMRO2) were also increased in the operated hemispheres with disappearance of the pre-operative interhemispheric differences. Regional CBF/regional cerebral blood volume (rCBV) ratios of the symptomatic hemispheres were increased after surgery, but were still lower than in the contralateral hemispheres. We conclude that EC-IC bypass surgery improves impaired cerebral oxygen metabolic reserve.     

Superficial temporal artery to middle cerebral artery anastomosis. Intraoperative evaluation by fluorescein angiography and xenon-133 clearance.

Fluorescein angiography and xenon-133 (133Xe) clearance studies were performed during surgery on 15 patients who were undergoing superficial temporal artery (STA) to middle cerebral artery (MCA) anastomosis. Fourteen patients had occlusive disease of the internal carotid artery (ICA), and one patient had severe stenosis of the MCA. Before anastomosis, fluorescein angiography showed slow filling of the MCA branches through collateral channels. Focal areas of impaired microcirculatory filling and washout were seen in the territory of severely sclerotic cortical arteries. The findings of preanastomotic 133Xe clearance studies were variable and a uniform pattern of regional cerebral blood flow (rCBF) changes was not defined. In 55% of the patients, rCBF was reduced to 25 ml/100 gm/min or less at one or more detector sites. Fluorescein angiography provided an immediate assessment of anastomotic patency and clearly displayed the distribution of blood entering the epicerebral circulation through the STA. In 67% of patients, multiple MCA cortical branches filled with fluorescein, whereas in 33% filling was restricted to the receptor artery territory. An immediate, substantial (greater than or equal to 15 ml/100 gm/min) increase in rCBF was demonstrated in 73% of patients after anastomosis. The rCBF changes were consistently better in patients with donor and receptor arteries greater than 1 mm in diameter. Redistribution of collateral input acted to increase rCBF in areas distant from the anastomotic site. Some improvement in fluorescein circulation and rCBF also was seen in cortex supplied by sclerotic MCA branches.     

Emergency EC-IC bypass for symptomatic atherosclerotic ischemic stroke

Previous studies have shown that extracranial–intracranial (EC-IC) bypass surgery has no preventive effect on subsequent ipsilateral ischemic stroke in patients with symptomatic atherosclerotic internal carotid occlusion and hemodynamic cerebral ischemia. A few studies have assessed whether an urgent EC-IC bypass surgery is an effective treatment for main trunk stenosis or occlusion in acute stage. The authors retrospectively reviewed 58 consecutive patients who underwent urgent EC-IC bypass for symptomatic internal carotid artery or the middle cerebral artery stenosis or occlusion between January 2003 and December 2011. Clinical characteristics and neuroimagings were evaluated and analyzed. Based on preoperative angiogram, responsible lesions were the internal carotid artery in 19 (32.8 %) patients and the middle cerebral artery in 39 (67.2 %). No hemorrhagic complication occurred. Sixty-nine percent of patients showed improvement of neurological function after surgery, and 74.1 % of patients had favorable outcome. Unfavorable outcome was associated with insufficient collateral flow and new infarction after bypass surgery.     

Clinical and hemodynamic effects of lipo PGE1 in cerebral infarction

Prostaglandin (PG) E1 is a potent vasodilator on the peripheral vessels and also has an inhibitory action of platelet aggregation. Lipo PGE1, the lipid emulsified PGE1 has much longer half life time in the circulation than PGE1 which is rapidly inactivated in the lung. The purpose of this investigation was to study the clinical and hemodynamic effect of Lipo PGE1 on the 15 patients with acute or subacute focal cerebral ischemia. Of these patients, five had evidence of internal carotid artery occlusion, and ten had either occlusion or severe stenosis of middle cerebral artery. Lipo PGE1 containing 15 micrograms of PGE1 was administered within 12 days of onset of ischemic events. Before the first Lipo PGE1 administration, regional cerebral blood flow (rCBF) of the affected middle cerebral artery (MCA) territory was 41.8 +/- 8.4 ml/100 g/min and on the non-affected side was 60.0 +/- 9.4 ml/100 g/min. Immediately after the Lipo PGE1 treatment, rCBF of the MCA region was increased by 6% on the affected side and by 11% on the non-affected side. rCBF of the affected MCA territory was increased more than 15% in five cases (Group 1) and was changed less than +/- 15% in seven cases (Group 2) by the first Lipo PGE1 treatment. Lipo PGE1 was administered every 8 hours for 10 to 14 days in these 12 cases. By the continuous Lipo PGE1 treatment, rCBF of the affected MCA territory increased by 18% in the Group 1 and by 3% in the Group 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of the selective endothelin A (ET(A)) receptor antagonist Clazosentan on cerebral perfusion and cerebral oxygenation following severe subarachnoid hemorrhage - preliminary results from a randomized clinical series

OBJECTIVE: To study the effects of clazosentan, a new selective endothelin receptor subtype A antagonist, on cerebral perfusion and cerebral oxygenation following severe aneurysmal subarachnoid haemorrhage (aSAH). METHODS: All 12 patients treated at our institution in the context of a phase IIa, multicenter, randomized trial on clazosentan's safety and efficacy in reducing the incidence of angiographic cerebral vasospasm were included in this substudy. The phase IIa study (n = 34) consisted of two parts: a double-blind, randomized Part A (clazosentan 0.2 mg/kg/h versus placebo) and an open-label Part B (clazosentan 0.4 mg/kg/h for 12 h followed by 0.2 mg/kg/h) for patients with established vasospasm. In parallel to the phase IIa study protocol, which included assessment of vasospasm by angiography and transcranial Doppler sonography, we determined regional cerebral blood flow (rCBF), cerebrovascular resistance, and regional tissue oxygenation. RESULTS: Cerebral perfusion was comparable between treatment groups during the early post-bleeding period (rCBF placebo, 22.6 +/- 3.5 ml/100 g/min versus rCBF clazosentan, 23.9 +/- 1.1 ml/100 g/min). By the time of control angiography (day 8 after aSAH), rCBF decreased by 50% in the placebo group (11.3 +/- 6.7 ml/ 100 g/min) while it remained stable in the clazosentan group (23.5 +/- 12.9 ml/100 g/min). During Part B of the study, all 3 patients who developed haemodynamically relevant vasospasm during placebo treatment, showed a sustained improvement in rCBF upon conversion to clazosentan. CONCLUSIONS: These preliminary data suggest that clazosentan reduces the extent of vasospasm-associated impairment of cerebral perfusion following aSAH. Furthermore, clazosentan may exert beneficial actions on overt vasospasm-associated hypoperfusion.     

Cerebral blood oxygenation changes induced by bypass blood flow in moyamoya disease and non-moyamoya cerebral ischaemic disease

Summary Background. Superficial temporal artery–middle cerebral artery (STA–MCA) anastomosis has been used to prevent stroke in patients with moyamoya disease (MD) and non-moyamoya ischaemic disease (non-MD). However, little is yet known regarding the difference between these groups of patients in the extent to which the bypass contributes to maintaining adequate cerebral blood oxygenation (CBO), or the temporal changes after surgery. In the present study, we evaluated the CBO changes induced by bypass blood flow in patients with MD and non-MD during the peri-operative periods employing optical spectroscopy. Methods. We investigated 13 patients who underwent STA–MCA anastomosis, including 5 MD and 8 non-MD patients. We evaluated the effects of STA blood flow on the CBO in the MCA territory on the anastomosis side, employing visual light spectroscopy during surgery and near infrared spectroscopy (NIRS) at one week after surgery. Findings. In 4 MD patients and one non-MD patient, the STA blood flow increased the oxyhaemoglobin and cortical oxygen saturation (CoSO₂), indicating that the bypass supplied blood flow to the ischaemic brain; the CBO changes were observed more frequently in MD than in non-MD patients (p < 0.02). The pre-anastomosis CoSO₂ (65.4 ± 5.4%) in MD was significantly lower than that (72.8 ± 7.6%) in non-MD (p < 0.05). Postoperative NIRS demonstrated that the bypass began to supply blood flow to the brain in 5 non-MD patients whose bypass did not supply blood flow during surgery. Conclusions. Although MD has vessels of small diameter as compared to non-MD, the bypass begins to supply blood flow to the ischaemic brain earlier in MD than in non-MD after anastomosis. The fact that the CoSO₂ in MD was lower than that in non-MD suggested that the perfusion pressure in MD was lower than that in non-MD, and this might account for the difference in the bypass blood supply after anastomosis between MD and non-MD. Our data suggest that, even if the bypass does not supply blood to the brain during surgery in non-MD, the bypass blood flow gradually increases after surgery.     

Extracranial-intracranial bypass in atherosclerotic cerebrovascular disease: report of a single centre experience

Despite the failure of the international extracranial-intracranial (EC-IC) bypass study in showing the benefit of bypass procedure for prevention of stroke recurrence, it has been regarded to be beneficial in a subgroup of well-selected patients with haemodynamic impairment. This report includes the EC-IC bypass experience of a single centre over a period of 14 years. All consecutive 72 patients with atherosclerotic occlusive cerebrovascular lesions associated with haemodynamic compromise treated by EC-IC bypass surgery were retrospectively reviewed. Pre-operatively, 61% of patients presented with minor stroke and the remaining 39% with recurrent transient ischemic attacks (TIAs) despite maximal medical therapy. Angiography revealed a unilateral internal carotid artery (ICA) stenosis/occlusion in 79%, bilateral ICA stenosis/occlusion in 15%, MCA stenosis/occlusion in 3% and other multiple vessel stenosis/occlusion in 3% of the cases. H(2)(15)O positron emission tomography (PET) or 99mTc-HMPAO SPECT with acetazolamide challenge was performed for haemodynamic evaluation of the cerebral blood flow (CBF). All the patients had impaired haemodynamics pre-operatively in terms of reduced regional cerebrovascular reserve capacity and rCBF. Standard STA-MCA bypass procedure was performed in all patients. A total of 68 patients with 82 bypasses were reviewed with a mean follow-up period of 34 months. Stroke recurrence took place in 10 patients (15%) resulting in an annual stroke risk of 5%. Improved cerebral haemodynamics was documented in 81% of revascularised hemispheres. Patients with unchanged or worse haemodynamic parameters had significantly more post-operative TIAs or strokes when compared to those with improved perfusion reserves (30% vs.5% of patients, p<0.05). In conclusion, EC-IC bypass procedure in selected patients with occlusive cerebrovascular lesions associated with haemodynamic impairment has revealed to be effective for prevention of further cerebral ischemia, when compared with a stroke risk rate of 15% reported to date in patients only under antiplatelet agents or anticoagulant therapy.     

Usefulness of intraoperative laser Doppler flowmetry and thermography to predict a risk of postoperative hyperperfusion after superficial temporal artery-middle cerebral artery bypass for moyamoya disease

We investigated whether postoperative hyperperfusion in moyamoya disease can be predicted using intraoperative laser Doppler flowmetry and/or thermography. A prospective study was conducted on 27 patients (39 hemispheres) with moyamoya disease who underwent superficial temporal artery-middle cerebral artery (STA-MCA) bypass. During surgery, regional cerebral blood flow (rCBF) was measured with a laser Doppler flowmeter and the temperature of the cortical surface was measured with an infrared thermograph. Postoperative hyperperfusion was assessed immediately after surgery based on CBF study under sedation (propofol) as >100% increase in corrected rCBF compared to preoperative values. Postoperative hyperperfusion on CBF was observed in two patients (7.4%). A significant correlation was observed between intraoperative rCBF changes and postoperative rCBF increase (Pearson's method: r=0.555, p=0.0003; simple regression: Y=1.22X+3.289, r (2)=0.308, p=0.0004). Furthermore, the rCBF changes measured by laser Doppler flowmetry were significantly greater in patients with postoperative hyperperfusion (p=0.0193) and CHS (p=0.0193). The present study suggests that intraoperative rCBF measurement using laser Doppler flowmetry may predict a risk of post-EC-IC bypass cerebral hyperperfusion in moyamoya disease.     

Effects of EC-IC bypass surgery on cognitive impairment in patients with hemodynamic cerebral ischemia

BACKGROUND: Chronic ischemia because of internal carotid artery (ICA) occlusive disease may result in dementia. The goal of this study was to assess cognitive impairment in symptomatic patients with hemodynamic cerebral ischemia and determine the efficacy of extracranial-intracranial (EC-IC) bypass in restoring neuropsychologic integrity. METHODS: Twenty-five patients were defined by clinical and neuroradiological criteria as suffering from hemodynamic cerebral ischemia because of unilateral ICA or middle cerebral artery occlusion. Subjects underwent assessment of cerebral blood flow and metabolism using positron emission tomography (PET) before and after bypass surgery. To provide data regarding cognition, changes in the Japanese Wechsler Adult Intelligence Scale Revised (WAIS-R) were recorded. RESULTS: Preoperative study of patients revealed significant impairment in cerebral blood flow and metabolism as well as reduced WAIS-R score. Among the factors considered, only elevated regional oxygen extraction fraction and reduced regional cerebral metabolic rates of oxygen were significantly associated with preoperative cognitive impairment (p = 0.0032 and p = 0.0255, respectively; logistic regression analysis). After bypass surgery, cerebral blood flow and metabolism improved significantly, and the WAIS-R score increased. CONCLUSIONS: Symptomatic patients with hemodynamic cerebral ischemia displayed impaired cognition that was partially alleviated with EC-IC bypass surgery.     

The effects of hyperventilation on cerebral blood flow in the rat with an open and closed carotid-jugular fistula

Perturbations in cerebral hemodynamics at the time of ablation of an arteriovenous shunt have been regarded as important in the pathogenesis of swelling and hemorrhage complicating resection of arteriovenous malformations (AVMs). A carotid-jugular fistula model in the rat had previously been investigated and found to simulate in part the nonhemorrhagic pathophysiology of a large cerebral arteriovenous fistula. Utilizing this model and measuring cerebral blood flow in 14 regions with a [14C]iodoantipyrine autoradiographic technique, the effects of hypocapnea on the cerebral circulation in opened and closed fistulas were investigated. Regional cerebral blood flow (rCBF) in control animals ranged from a median of 53 to 64 ml/100 g/min at a partial arterial carbon dioxide pressure (PaCO2) of 28 +/- 2 mm Hg and 85 to 112 ml/100 g/min at a PaCO2 of 40 +/- 5 mm Hg. In animals with an open carotid-jugular fistula created 12 weeks before the study, these median rCBF values at comparable PaCO2 levels ranged, respectively, from 15 to 39 ml/100 g/min and 50 to 68 ml/100 g/min (the 25th percentile for the open fistula in the hypocapneic group was 15 ml/100 g/min in 5 of the 14 regions studied). In contrast, median rCBF in the closed fistula group ranged from 73 to 100 ml/100 g/min in hypocapneic animals and from 118 to 187 ml/100 g/min in normocapneic animals. These results demonstrate the preservation of CO2 reactivity; hypoperfusion in the presence of a carotid-jugular fistula, hyperemia on fistula occlusion, and the potential to induce cerebral ischemia with hyperventilation in this model of a cerebral arteriovenous fistula.(ABSTRACT TRUNCATED AT 250 WORDS)     

Continuous monitoring of regional cerebral blood flow during temporary arterial occlusion in aneurysm surgery

OBJECT: Temporary arterial occlusion (TAO) during aneurysm surgery carries the risk of ischemic sequelae. Because monitoring of regional cerebral blood flow (rCBF) may limit neurological damage, the authors evaluated a novel thermal diffusion (TD) microprobe for use in the continuous and quantitative assessment of rCBF during TAO. METHODS: Following subcortical implantation of the device at a depth of 20 mm in the middle cerebral artery or anterior cerebral artery territory, rCBF was continuously monitored by TD microprobe (TD-rCBF) throughout surgery in 20 patients harboring anterior circulation aneurysms; 46 occlusive episodes were recorded. Postoperative radiographic evidence of new infarction was used as the threshold for failure of occlusion tolerance. The mean subcortical TD-rCBF decreased from 27.8+/-8.4 ml/100 g/min at baseline to 13.7+/-11.1 ml/100 g/min (p < 0.0001) during TAO. The TD microprobe showed an immediate exponential decline of TD-rCBF on clip placement. On average, 50% of the total decrease was reached after 12 seconds, thus rapidly indicating the severity of hypoperfusion. Following clip removal, TD-rCBF returned to baseline levels after an average interval of 32 seconds, and subsequently demonstrated a transient hyperperfusion to 41.4+/-18.3 ml/l 00 g/min (p < 0.001). The occurrence of postoperative infarction (15%) and the extent of postischemic hyperperfusion correlated with the depth of occlusion-induced ischemia. CONCLUSIONS: The new TD microprobe provides a sensitive, continuous, and real-time assessment of intraoperative rCBF during TAO. Occlusion-induced ischemia is reliably detected within the 1st minute after clip application. In the future, this may enable the surgeon to alter the surgical strategy early after TAO to prevent ischemic brain injury.     

Experimental simulation study on EC-IC bypass--Part 1: Optimum conditions for bypass on the basis of hydraulic and theoretical models with autoregulation mechanism

There have been several reports about unexpected occlusive change of stenotic lesion in the internal carotid artery (ICA) or middle cerebral artery (MCA) following bypass surgery, rupture or formation of an aneurysm after carotid ligation and ICA EC-IC bypass for the treatment of inaccessible ICA aneurysm. These suggest that operation for one vessel causes hemodynamic changes in others, not only near the operation site but in remote sites. Although complete hemodynamic analysis in the brain and quantitative speculation of the possible effect of a cerebrovascular operation are essential to prevent these complications, these measures are usually very difficult to carry out because multiple factors are related mutually in complex fashion in a living body. One effective means to simulate these changes would be the use of a vascular model. A hydraulic model of unilateral ICA stenosis (resistance of stenosis: R) with EC-IC bypass (resistance of bypass: Rby) has been manufactured with silicone and glass tubes. Peripheral vascular resistance (Rp) is adjusted to obtain an arterial flow of 180 ml/min at poststenotic pressures of 60, 70, 80, 90, and 100 mmHg. To simulate the autoregulation mechanism, appropriate Rp is selected for each combination of R and Rby so as to make, as far as possible, a hemispheric flow (sum of stenosis flow and bypass flow) of 180 ml/min. The Rp with the lowest value (60/180 mmHg/ml/min) is to be chosen in flow conditions of lower than 180 ml/min, where autoregulation is no longer functioning. Twelve kinds of stenosis segments with an inner diameter from 0.37 to 2.59 mm are prepared and used in the models.(ABSTRACT TRUNCATED AT 250 WORDS)     

Continuous monitoring of regional cerebral blood flow: experimental and clinical validation of a novel thermal diffusion microprobe

OBJECT: Current clinical neuromonitoring techniques lack adequate surveillance of cerebral perfusion. In this article, a novel thermal diffusion (TD) microprobe is evaluated for the continuous and quantitative assessment of intraparenchymal regional cerebral blood flow (rCBF). METHODS: To characterize the temporal resolution of this new technique, rCBF measured using the TD microprobe (TD-rCBF) was compared with rCBF levels measured by laser Doppler (LD) flowmetry during standardized variations of CBF in a sheep model. For validation of absolute values, the microprobe was implanted subcortically (20 mm below the level of dura) into 16 brain-injured patients, and TD-rCBF was compared with simultaneous rCBF measurements obtained using stable xenon-enhanced computerized tomography scanning (sXe-rCBF). The two techniques were compared using linear regression analysis as well as the Bland and Altman method. Stable TD-rCBF measurements could be obtained throughout all 3- to 5-hour sheep experiments. During hypercapnia, TD-rCBF increased from 49.3+/-15.8 ml/100 g/min (mean +/- standard deviation) to 119.6+/-47.3 ml/100 g/ min, whereas hypocapnia produced a decline in TD-rCBF from 51.2+/-12.8 ml/100 g/min to 39.3+/-5.6 m/100 g/min. Variations in mean arterial blood pressure revealed an intact autoregulation with pressure limits of approximately 65 mm Hg and approximately 170 mm Hg. After cardiac arrest TD-rCBF declined rapidly to 0 ml/100 g/min. The dynamics of changes in TD-rCBF corresponded well to the dynamics of the LD readings. A comparison of TD-rCBF and sXe-rCBF revealed a good correlation (r = 0.89; p < 0.0001) and a mean difference of 1.1+/-5.2 ml/100 g/min between the two techniques. CONCLUSIONS: The novel TD microprobe provides a sensitive, continuous, and real-time assessment of intraparenchymal rCBF in absolute flow values that are in good agreement with sXe-rCBF measurements. This study provides the basis for the integration of TD-rCBF into multimodal monitoring of patients who are at risk for secondary brain injury.     

Effects of open-heart surgery on renal function in patients with chronic renal failure--is hemodialysis during cardiopulmonary bypass really required?]

In 300 consecutive adult patients who underwent open-heart surgery in our department, 16 patients (ischemic heart disease in 8 patients, valvular heart disease in 7 and congenital heart disease in 1) were preoperatively complicated with chronic renal failure (CRF); creatinine clearance (Ccr) < 40 ml/min and serum creatinine (Scr) > 1.6 mg/dl. The effects of open-heart surgery on renal function were studied in these CRF patients who were divided into the following 3 groups according to their preoperative Ccr values: Group 1 (6 patients), 30 < Ccr < 40 ml/min; Group 2 (5 patients), 20 < Ccr < 30 ml/min; and Group 3 (5 patients, 4 of whom were on dialysis preoperatively), Ccr < 10 ml/min. In addition, Group C (38 patients, Ccr > 50 ml/min) was set up as normal controls. Instead of hemodialysis, the extracorporeal ultrafiltration method (ECUM) was employed for all patients during the cardiopulmonary bypass (CPB). The Ccr in Group 1 showed the lowest value of 24.2 +/- 12.0 ml/min on postoperative day (POD) 0 which then recovered to the preoperative level on POD 1. This quick recovery of the Ccr in Group 1 was similar to that in Group C. In contrast, the Ccr in Group 2 showed the lowest value of 13.0 +/- 6.0 ml/min on POD 1, followed by a delayed recovery that did not reach the preoperative level until POD 5. The Ccr in Group 3 was quite low (< 5 ml/min) throughout the test period.(ABSTRACT TRUNCATED AT 250 WORDS)