The hemodynamic effect of STA-MCA bypass.

259

115

SUMMARY Cerebral blood flow (CBF) was measured by xenon-133 inhalation tomography in 18 patients with cerebrovascular disease before and 4 months after extracranial-intracranial bypass surgery. Only patients who showed a reduced CBF In areas that were intact on the CT scan and relevant to the clinical and angiographical findings were operated. The majority of the patients had suffered a minor stroke with or without subsequent transient lschemic attacks. They were studied at least 6 weeks following the stroke. All patients had an occlusion of the relevant internal carotid artery.To identify preoperatively the patients with a compromised collateral circulation and hence reduced CBF due to reduced perfusion pressure, a cerebral vasodilatory stress test was performed using acetazolamide (Dlamox*). In normal subjects, Diamox has been shown to increase tomographic CBF without change of the flow distribution. In the present series 9 patients showed a significant redistribution of flow in favor of the non-occluded side ("positive" Diamox test). Two of these 9 patients showed even a paradoxical decrease in focal CBF preoperatively, i.e., a "steal" effect. These 2 patients were the only patients who improved in focal CBF after shunting. The remaining 9 patients all showed uniform flow responses ("negative" Diamox test), and none of these increased in focal CBF postoperatively. The finding of an unchanged flow map postoperatively confirmed that the low flow areas were not due to restricted flow via collateral pathways. However, an increase in the regional vasodilatory capacity was observed postoperatively in the majority of patients.

Section: The Diamox Testsupporting

confidence: 91%

Evaluation of the cerebral vasodilatory capacity by the acetazolamide test before EC-IC bypass surgery in patients with occlusion of the internal carotid artery.

Vorstrup¹,

Brun²,

Lassen

1986

259

115

“…They found that surgery improved intracerebral hemodynamics ipsilateral to ICA stenosis only in patients who preoperatively had a reduced cerebral perfusion pressure at the side of ICA stenosis of at least 20% (indicating inadequate intracerebral collateralization) compared with the pressure in the common carotid artery. Halsey et al, 24 Widder et al, 25 and our group 26 reported a significant inverse correlation between the preoperative CBF reactivity, flow velocity reactivity, or CR, reactivity ipsilateral to ICA occlusion or stenosis and the change in reactivity after surgery. Correspondingly, Vorstrup et al, 27 Russel et al, 28 and Karnik et al 29 found that surgery significantly improved CBF or flow velocity reactivity (as evaluated by the acetazolamide test) only in patients who had an abnormal side-to-side asymmetry in reactivity before surgery.…”

Section: -23mentioning

confidence: 50%

Effect of carotid endarterectomy on patterns of cerebrovascular reactivity in patients with unilateral carotid artery stenosis.

Hartl

Janssen

Fürst

1994

Patients with unilateral significant carotid artery stenosis present with a variable intracranial hemodynamic status. In the majority of patients, hemodynamics are normal because of sufficient collateral flow. One subgroup shows poor ipsilateral hemodynamics because of a severely reduced blood supply, whereas in another subgroup of patients a steal phenomenon from the contralateral to the ipsilateral hemisphere can be observed during pharmacological provocation. The present study examined the effect of carotid endarterectomy (CEA) on these patterns of cerebrovascular hemodynamics in patients with carotid artery stenosis. The CO2 reactivity of the cerebral resistance index (CRi) was determined with transcranial Doppler sonography in 63 patients with unilateral high-grade to threadlike carotid artery stenosis before and 3 months after CEA and in 37 control subjects. The interhemispheric asymmetry of CRi reactivity of the control group was used to differentiate between normal and abnormal findings. In patients with normal CRi asymmetry (comparable CRi reactivities at both hemispheres, n = 41), CEA did not change hemispheric CRi reactivity. In patients in whom CRi reactivity was absent at the contralateral hemisphere (intracerebral steal during hypercapnia, n = 12), CEA abolished the steal phenomenon by significantly increasing CRi reactivity at the contralateral hemisphere (preoperative, -1.0 +/- 2.1 %CRi/vol%CO2; postoperative, 5.2 +/- 0.7 %CRi/vol%CO2; P < .01). Patients who showed severely diminished ipsilateral CRi reactivity, compatible with a significantly reduced perfusion pressure at the poststenotic hemisphere (n = 10), demonstrated an improvement of ipsilateral CRi reactivity after surgery (preoperative, 0.6 +/- 0.8 %CRi/vol%CO2; postoperative, 3.7 +/- 1.1 %CRi/vol%CO2; P < .01). Most patients do not respond significantly to CEA. One small subgroup of patients who presented with severely disturbed ipsilateral hemodynamics demonstrated postoperative improvement at the poststenotic hemisphere, whereas in another small subgroup, who showed a steal phenomenon at the contralateral hemisphere, CEA improved contralateral hemodynamics. Determination of preoperative CRi reactivity allowed precise prediction of the effect of CEA on intracerebral hemodynamics.

“…independent of surgical procedure) related to a diaschisis phenomenon, such as seen following stroke. 18 However, three arguments suggest that in our patients we are dealing not with this type of a spontaneous modification, but rather with a direct hemodynamic effect of the EIAB. First of all the postoperative CMRO 2 increase selectively occurred in patients with a bilateral proximal arterial disease ( fig.…”

Section: Absolute Valuesmentioning

confidence: 87%

Effects of extra-intracranial arterial bypass on cerebral blood flow and oxygen metabolism in humans.

Samson¹,

Baron²,

Bousser³

et al. 1985

124

SUMMARY Twelve patients, eleven with a carotid obstruction and one with an occlusion of the middle cerebral artery, were studied before and after a successful unilateral extra-intracranial arterial by-pass, (EIAB) using PET and the 15-0 steady-state technique to measure regional cerebral blood flow (CBF), oxygen extraction fraction and oxygen metabolic rate (CMRO 2 ). In the whole group of patients, both CBF and CMRO, increased significantly on both cerebral hemispheres after EIAB, returning toward control levels defined in age-matched subjects. Mean oxygen extraction fraction, on the other hand, was not affected. Individually, three different effects of EIAB emerged: 1) Alleviation of a state of long standing unilateral "misery-perfusion", as reported earlier; 2) parallel increase of CBF and CMRO2 bilaterally, which appeared due to improvement of a hemodynamic depression of metabolism, the precise mechanism of which remains obscure; 3) Complex, unexpected changes in the CBF-CMRO 2 couple again resulting in increases in CMRO 2 . This metabolic improvement afforded by EIAB in our patients has not been reported before; it suggests that long-standing hemodynamic failure may induce a metabolic depression that is still potentially reversible by surgical revascularization. Stroke Vol 16, No 4, 1985 THE CONTINUOUS OXYGEN 15 INHALATION METHOD provides a regional measurement of the cerebral blood flow (CBF) and oxygen metabolic rate (CMRO,). Earlier semi-quantitative studies carried out by this method 1 -2 showed the disappearance, after an extra-intracranial by-pass operation (EIAB), of two different patterns of focal functional anomaly. The first one, termed misery-perfusion, consists of a lowered CBF and an increased oxygen extraction fraction (OEF) downstream from a carotid occlusion. This pattern reflects the relative maintenance of the CMRO, and was interpreted as evidence of a drop in the cerebral perfusion pressure to a point beyond the lower threshold of CBF auto-regulation. For the second type, involving a reduced CBF with no rise in the OEF, no satisfactory pathophysiological interpretation was put forward. 2However in these semi-quantitative studies it was possible neither to measure the CMRO, nor to detect bilateral effects of the EIAB, both of which objectives form the centre of present work. Patients and MethodsThe study involved 12 consecutive patients in whom the permeability of the EIAB was verified. One preoperative study was an isolated CBF measurement (case No. 3). Eleven of these patients suffered from internal carotid artery (ICA) obstruction and the last a middle cerebral artery (MCA) occlusion. Mean age was 56 ± 9.3 years.Individual clinical, angiographic and CT Scan data Received July 16, 1984; revision #1 accepted December 7, 1984. are summed up in table 1. The advisability of EIAB was judged on the basis of clinical and angiographic criteria, independently of pre-operative PET results. Clinical signs of "hemodynamic" ischemia was the deciding factor in 5 cases (patients No. 5,6,9,11,12) ...