Relationship between blood viscosity and cerebral ischemia after surgical treatment of ruptured intracranial aneurysms

Risk Factors Associated With Inadequate Brain Relaxation in Craniotomy for Surgery of Supratentorial Tumors

Introduction: Cerebral swelling often occurs during craniotomy for cerebral tumors. Poor brain relaxation can increase the risk of cerebral ischemia, possibly worsening the outcome. The surgical team should identify any risk factors that could cause perioperative brain swelling and decide which therapies are indicated for improving it. The present investigation aimed to elucidate the risk factors associated with brain swelling during elective craniotomy for supratentorial brain tumors.

Methods: This prospective, nonrandomized, observational study included 52 patients scheduled for elective supratentorial tumor surgery. The degree of brain relaxation was classified upon the opening of the dura according to a four-point scale (brain relaxation score: 1, perfectly relaxed; 2, satisfactorily relaxed; 3, firm brain; and 4, bulging brain). Moreover, hemodynamic and respiratory parameters, arterial blood gas, and plasma osmolality were recorded after the removal of the bone flap.

Results: This study showed that the use of preoperative dexamethasone was associated with a brain relaxation score of ≤2 (p = 0.005). The median midline shift of 6 (3-0) mm and median hemoglobin level of >13 g/dL were associated with a brain relaxation score of ≥3 (p = 0.02 and p = 0.01, respectively). The dosage of mannitol (0.25 g/kg versus 0.5 g/kg), physical status, intraoperative position, tumor diameter and volume, peritumoral edema and mass effect, World Health Organization (WHO) grading, mean arterial pressure, PaCO₂, osmolality, and core temperature were not identified as risk factors associated with poor relaxation.

Conclusion: The use of preoperative dexamethasone was associated with improved brain relaxation, whereas the presence of a preoperative midline shift and a higher level of hemoglobin were associated with poor brain relaxation.

[The importance of clinical hemorheology in the study of cerebral blood flow in normal conditions and in cerebrovascular ischemia]

A critical review on the importance of hemorheology for establishing clinical management of acute cerebrovascular insufficiency is presented. With this purpose a revision is made on cerebral blood flow, acute cerebrovascular insufficiency, and clinical hemorheology. Data support an evaluation on main drugs presently used in the management of stroke, and on general principles adopted for medical treatment and prevention of stroke.

Optimum degree of hemodilution for brain protection in a canine model of focal cerebral ischemia

The ability of hemodilution to lower blood viscosity and increase cerebral blood flow has been proven experimentally; however, the optimum hematocrit for maximum oxygen delivery to ischemic brain tissue is not known, and a study was designed to determine this. Fifty dogs were selected for inclusion in the study using criteria based on changes in somatosensory evoked potentials at the time of arterial occlusion, which were found in a previous study to predict the development of a moderate infarction of relatively constant size. Infarctions were induced by permanent occlusion of the left middle cerebral artery and the azygous anterior cerebral artery. The animals selected for inclusion were divided into five groups of 10 dogs each: 1) a control group; 2) a group with 25% hematocrit; 3) a group with 30% hematocrit; 4) a group with 35% hematocrit; and 5) a group with 40% hematocrit. Isovolemic hemodilution was accomplished 1 hour after occlusion of vessels using dextran infusion and blood withdrawal. The animals were sacrificed after 6 days and infarction volume was determined from fluorescein-stained sections. Statistical analysis was performed using Student's t-test and one-way analysis of variance. Mean infarction volume for each group, expressed as a percentage of total hemispheric volume +/- 1 standard error of the mean, was 28.3% +/- 2.8% for the control group, 33.6% +/- 3.4% for the 25% hematocrit group, 17.1% +/- 2.2% for the 30% hematocrit group, 29.2% +/- 4.3% for the 35% hematocrit group, and 29.9% +/- 2.1% for the 40% hematocrit group. The 30% hematocrit group showed the smallest average infarction size and this size differed significantly (p = 0.02) from the average infarction size in the control animals. These results show that, in this model of focal ischemia, a hematocrit of approximately 30% is optimum for protecting the brain.

Hematogenous factors and prediction of delayed ischemic deficit after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Delayed ischemic deficits contribute to the high morbidity and mortality rates associated with subarachnoid hemorrhage. We evaluated the potential usefulness of measuring coagulation and hemorheological variables and cardiolipin antibodies for prediction of delayed ischemic deficit after subarachnoid hemorrhage.

METHODS

Consecutive patients with subarachnoid hemorrhage were studied. Coagulation and hemorheological variables and cardiolipin antibodies were measured on admission, within 7 days of subarachnoid hemorrhage. A subset of patients was studied on admission and at two subsequent occasions.

RESULTS

Sixty-nine patients were studied. Sixty-one of these were without clinical manifestations of vasospasm at admission, and 16 developed delayed ischemic deficit during their hospitalization. None of the laboratory variables measured were significantly different between patients with or without later development of delayed ischemic deficit. Elevation of the fibrin fragment D-dimer was found in the group of eight patients admitted with ischemic symptoms and in 49% (34 of 69) of all patients, but this was not associated with delayed ischemic deficit. Sixteen patients were studied on three occasions; this group showed a significant decrease in hematocrit, an increased white blood cell count, and no change in fibrinogen concentration. Fibrin D-dimer levels rose significantly after surgery (from 5.01 +/- 0.69 to 5.53 +/- 0.58 ln-ng/ml, p less than 0.025) and after onset of delayed ischemic deficit (from 4.71 +/- 0.64 to 5.84 +/- 0.34 ln-ng/ml, p less than 0.01).

CONCLUSIONS

Hemostatic measurements, hemorheological variables, and cardiolipin immunoreactivity did not predict delayed ischemic deficit in this population.

Cognitive performance following rupture and repair of intracranial aneurysm

Modern microsurgical techniques enable most survivors of subarachnoid haemorrhage following ruptured intracranial aneurysm to make a good functional recovery. Nevertheless, it has been suggested that such patients suffer from a persistent disturbance of cognitive function. When tested 6 weeks after their discharge from the neurosurgical unit, patients from a consecutive series of 76 cases of aneurysmal subarachnoid haemorrhage demonstrated a moderate impairment of performance across a broad range of cognitive tasks. This was more pronounced in the case of patients who had suffered generalized postoperative vasospasm, but was unrelated to the site of the ruptured aneurysm. However, when patients were tested 6 months after discharge, the only consistent deficits were in the speed of retrieval of verbal items from semantic memory, and there was little evidence of any generalized cognitive impairment.

Isovolemic hemodilution in experimental focal cerebral ischemia. Part 2: Effects on regional cerebral blood flow and size of infarction

Seventy-six splenectomized dogs were entered in a study of the value and effects of isovolemic hemodilution. Of these, seven were not included in the analysis because of technical errors. Of the remaining 69 dogs, 35 were treated with hemodilution; 28 were subjected to a 6-hour period of temporary occlusion of the distal internal carotid artery and the proximal middle cerebral artery, and seven underwent a sham operation only, with arterial manipulation but no occlusion. The other 34 dogs were not subjected to hemodilution; 26 of these underwent temporary arterial occlusion and eight had a sham operation only. In each group the animals were about equally divided into 1) an acute protocol with regional cerebral blood flow measurements by a radioactive microsphere technique and sacrifice at the end of the acute experiment, and 2) a chronic protocol with survival for 1 week to permit daily neurological assessment and final histopathological examination but without blood flow measurements. The general experimental protocol, the hemodynamic and rheological measurements, and the changes in intracranial pressure are described in Part 1 of this report. In the animals with arterial occlusion, blood flow decreased significantly in the territory of the ischemic middle cerebral artery. This decrease was partially reversed by hemodilution in the animals so treated. When the changes in blood flow before and after hemodilution in treated animals are compared with the changes at equivalent times in animals without hemodilution, the increases in flow in the gray matter of the ischemic hemisphere brought about by hemodilution are statistically significant. The neurological condition of the animals in the chronic protocol (sacrificed 1 week after occlusion) with hemodilution, as evaluated by daily neurological assessment, was significantly better than that of the control animals. In the animals sacrificed acutely (8 hours after arterial occlusion), the volume of infarction as estimated by the tetrazolium chloride histochemical method was 7.36% of the total hemispheric volume in the control animals and 1.09% in the hemodiluted animals, showing a statistically significant difference (p less than 0.005). In the chronic animals these values were 9.84% and 1.26%, respectively (p less than 0.005), as calculated by fluorescein staining. By histopathological examination the volume of infarction in the chronic animals was calculated as 10.92% in the control animals and 1.20% in the hemodiluted animals (p less than 0.005).(ABSTRACT TRUNCATED AT 400 WORDS)