Failure of intravascular volume expansion without hemodilution to elevate cortical blood flow in region of experimental focal ischemia

Analytic Reviews : Potential New Therapies for Acute Ischemic Stroke

Evidence from animal models of acute stroke suggests ischemia may be reversible if blood flow is restored in the first few hours. Studies of human stroke using posi tron emission tomography demonstrate areas with re duced blood flow and relatively preserved metabolism, indicating potentially reversible ischemic brain. Resto ration of blood flow during this reversible phase should improve outcome after stroke.

Many therapeutic strategies for treatment of acute ischemic stroke have been proposed, including increas ing collateral flow, removing vascular obstructions, and interfering with the intracellular cascade of events that lead to neuronal cell death. Hypervolemic hemodilution reduces viscosity and increases cerebral blood flow, and this may hopefully raise blood flow above the critical threshold of irreversible ischemia. Naloxone, calcium channel blockers, and glutamate antagonists alter blood flow and influence intracellular events during and after acute ischemia. Thrombolytic therapy restores blood flow by lysis of obstructing clot. These therapies show promise in preliminary studies, but additional ran domized controlled studies are needed.

Analytic Reviews : Hypervolemic Hemodilution in Acute Ischemic Stroke

In patients with acute ischemic stroke, reversibility of the neurologic deficits depends on the depth and dura tion of the ischemic insult. The rapid elevation of cere bral blood flow (CBF) above ischemic thresholds may minimize or prevent infarction. Reduction of blood vis cosity has been shown to augment CBF and improve cerebral neuronal activity after stroke. Hypervolemic hemodilution decreases hematocrit, increases blood volume, augments cardiac output, and, in randomized clinical trials, improves the long-term outcome in acute ischemic stroke. Similarly, administration of drugs that decrease plasma fibrinogen and increase erythrocyte flexibility reportedly causes a decrease in the incidence of recurrent ischemia after an initial transient ischemic attack. Thus, the pharmacologic manipulation of blood viscosity appears to be effective in managing patients with acute ischemic stroke.

CONTROVERSIES IN THE ENDOVASCULAR MANAGEMENT OF CEREBRAL VASOSPASM AFTER INTRACRANIAL ANEURYSM RUPTURE AND FUTURE DIRECTIONS FOR THERAPEUTIC APPROACHES

CEREBRAL VASOSPASM IS one of the leading causes of morbidity and mortality after aneurysmal subarachnoid hemorrhage. Despite maximal medical therapy, however, up to 15% of patients surviving the ictus of subarachnoid hemorrhage experience stroke or death from vasospasm. For those cases of vasospasm that are refractory to medical treatment, endovascular techniques are frequently used, including balloon angioplasty with or without intra-arterial infusion of vasodilators, combined endovascular modalities, and aortic balloon devices. In this article, we review each of these therapies and their expanding role in the management of this condition. Moving forward, rigorous prospective outcome assessments after endovascular treatment of cerebral vasospasm are necessary to clearly delineate the efficacy and indications for these techniques.

Hypertensive, hypervolemic, hemodilutional therapy for aneurysmal subarachnoid hemorrhage. Is it efficacious? Yes

Vasospasm is an important contributor to death and disability after aneurysmal SAH. CBF is decreased after SAH and correlates inversely with the severity of the clinical grade. It is necessary to avoid hypotension and hypovolemia, which can exacerbate an already reduced CBF, resulting in critically low perfusion. There have been no human, prospective, randomized trials of HHH therapy. This is attributable, perhaps, to the fact that such trials are difficult to blind. Nevertheless, there is strong evidence that HHH therapy can reverse the delayed onset of profound neurologic deficits by restoring blood flow to ischemic regions, and its prophylactic use can reduce the incidence and severity of DID.

Hemorheological and hemodynamic analysis of hypervolemic hemodilution therapy for cerebral vasospasm after aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Hypervolemic hemodilution therapy is effective for treating neurological deficits due to cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). We monitored various hemorheological and hemodynamic parameters to assess the effects of hypervolemic hemodilution therapy in SAH patients with cerebral vasospasm.

METHODS

Ninety-eight patients who underwent early craniotomy for aneurysm clipping surgery after SAH were studied. Fifty-one patients (52.0%) developed symptomatic vasospasm. The hematocrit level and red blood cell aggregability were measured daily from day 1 to day 14, whereas the circulating blood volume and cerebral blood flow were measured periodically. Cardiac output and pulmonary capillary wedge pressure were also measured using a Swan-Ganz catheter.

RESULTS

The hematocrit level was decreased significantly to 29% to 32% by hypervolemic hemodilution therapy. Red blood cell aggregability increased until day 6 but was significantly reduced by therapy. Hypovolemia tended to develop after SAH. However, patients receiving hypervolemic hemodilution therapy became normovolemic to hypervolemic, with a significant increase of cardiac output and pulmonary capillary wedge pressure. At the onset of vasospasm, cerebral blood flow was significantly lower on the operated side than on the contralateral side, and it increased on both sides with therapy.

CONCLUSIONS

Patients with SAH develop hypovolemia, hemodynamic depression, and increased red blood cell aggregability. Hypervolemic hemodilution therapy decreases hematocrit level and red cell aggregability while increasing cardiac output. Improvement of hemorheological and hemodynamic parameters by this therapy can reverse neurological deterioration due to cerebral vasospasm.

[The injured brain. Basis for hydroelectrolytic and hemodynamic resuscitation]

Brain insult in neurosurgical patients is highly dependent on hydroelectrolytic and haemodynamic disturbances. The magnitude of their effect is related to blood-brain barrier integrity and characteristics of cerebral perfusion pressure. Moderate disturbances in ionic balance or CPP may lead to interstitial oedema or worsening of cerebral ischaemia. As a consequence, intracranial pressure (ICP) may rise and neurological status worsen. This study discusses the cerebral effects of intercompartimentary water and electrolyte movements, which themselves are either secondary to early neurological dysfunction, as insipid diabetes, the syndrome of inappropriate ADH secretion, and/or to renal losses of sodium, or iatrogenic, after administration of mannitol or furosemide. Understanding the early mechanism underlying these disorders is essential for treatment. Early interstitial oedema is mainly a consequence of low plasma osmolality, whereas low oncotic pressure plays a minor role. Worsening of cerebral ischemia by hyperglycaemia should contra-indicate glucose for perioperative infusion. Keeping CPP at normal levels is essential, especially in case of disturbances of the autoregulation of the cerebral circulation. Normovolaemia and the choice of an appropriate agent for plasma volume expansion are essential. Correction of hypovolaemia is best obtained with (except for packed red cells when necessary) normal saline, 4% human albumin or hydroxyethylstarch. The benefit of utilizing hypertonic electolytic or HES solutions in neurosurgical patients has still to be assessed.

Role of hypervolemic hemodilution in focal cerebral ischemia of rats

This study was designed to better define a protocol for hypervolemic hemodilution in acute cerebral ischemia and investigate the mechanism of action of this therapy. Anesthetized rats (n = 40) were subjected to 6 h of middle cerebral artery (MCA) occlusion. At 45 min after MCA occlusion, each rat received one of the following treatment modalities: (1) control, (2) isovolemic hemodilution, (3) hypervolemic nonhemodilution (whole blood), (4) hypervolemic hemodilution (normal saline), and (5) hypervolemic hemodilution (hetastarch). Local cerebral blood flow (CBF) was determined with hydrogen clearance technique, and cardiac output was assessed by measuring the descending aorta blood flow (DAF). Infarction volume was estimated by 2,3,5-triphenyltetrazolium chloride staining method. Hetastarch infusion increased both DAF and local CBF more than the other treatments, by 98% and by 89%, respectively. Hetastarch also reduced infarction volume the most to 71 +/- 19 mm3 (p < 0.01 versus control 117 +/- 32 mm3). A significant correlation between percent (%) changes in local CBF and % changes in DAF existed in ischemic brain regions, and the hetastarch infusion improved local CBF more prominently in profoundly ischemic regions in contrast to isovolemic hemodilution. These data demonstrated the superiority of hypervolemic hemodilution with hetastarch as compared to other similar treatment modalities for acute cerebral ischemia, and indicate that cardiac output augmentation may be more responsible than decreased blood viscosity for the beneficial effect of hypervolemic hemodilution on local CBF in profoundly ischemic regions, as such ischemic brain tissue can severely lose its regulatory control of CBF to alterations in cardiac output.

Hyperdynamic therapy for focal cerebral ischemia of rats: use of colloidal volume expansion and dobutamine

The effects of hyperdynamic therapy with colloidal volume expansion and pharmacological augmentation of cardiac function with dobutamine on local cerebral blood flow (CBF) and the size of ischemic injury were investigated in rats subjected to 6 h of middle cerebral artery (MCA) occlusion. At 45 min after MCA occlusion, each rat was randomly assigned to one of the following treatment groups: (1) control; (2) hetastarch infusion (HES); and (3) hetastarch plus dobutamine (12 micrograms/kg/min) infusion (HES/DOB). In both the HES and HES/DOB groups, cardiac output and local CBF in ischemic brain markedly increased after treatment and infarction volumes were significantly reduced as compared to the control group. There were, however, no significant differences between both groups apart from a dobutamine-induced tachycardia. Colloidal volume expansion augmented cardiac output, increased CBF in ischemic brain, and substantially modified the extent of ischemic injury. However, the addition of dobutamine did not bring about adjunctive beneficial effects of cardiac performance, CBF, or the degree of ischemic brain damage in the rat focal ischemic model.

Intracranial complications of hypervolemic therapy in patients with a delayed ischemic deficit attributed to vasospasm

This investigation has revealed the frequency of various intracranial complications that may result from hypervolemic therapy for a delayed ischemic deficit following subarachnoid hemorrhage (SAH). Among 323 patients with SAH, 112 patients developed a delayed ischemic deficit, 94 of whom underwent hypervolemic therapy. Infarction due to vasospasm was found ultimately in 43 of these 94 patients. Twenty-six patients (28%) developed an intracranial complication during hypervolemic therapy: cerebral edema was aggravated in 18, and a hemorrhagic infarction developed in eight. In 13 of 18 patients with aggravation of edema, delayed ischemic deficit developed within 6 days after the SAH; at that time, a massive new infarction was found in four and edema in 10 patients. After hypervolemic therapy, the 18 patients with aggravation of edema deteriorated rapidly, and 14 of them died. In every case in which hemorrhagic infarction followed hypervolemic therapy, a new infarct was found on computerized tomography (CT) when the delayed ischemic deficit became apparent. Hemorrhagic infarction developed as the delayed ischemic deficit resolved, with one exception. In patients who sustained no complication from hypervolemia, the incidence of both massive new infarction and edema at the time when the delayed ischemic deficit was manifested was only 1%. In 44 of 68 patients who sustained no complication from hypervolemia, the delayed ischemic deficit was manifested on or after the 7th day following the SAH. This study suggests that hypervolemic therapy is contraindicated in a patient who is found to have a massive abnormality on CT at the time when a delayed ischemic deficit is manifested, especially when it occurs within 6 days after the SAH. To avoid hemorrhagic infarction, it is important to discontinue hypervolemic therapy as soon as the delayed ischemic deficit resolves.

Focal cerebral ischemia in rats: effect of hemodilution with alpha-alpha cross-linked hemoglobin on CBF

Hemodilution has had limited success as a treatment of cerebral ischemia. When using a nonoxygen binding fluid, the therapeutic efficacy of hemodilution-induced increases in CBF are offset by concomitant decreases in oxygen content. The effect of hemodilution, with diaspirin alpha-alpha cross-linked hemoglobin (DCLHb), on CBF during middle cerebral artery occlusion was assessed. Rats were hemodiluted to one of the following hematocrits (Hct): (a) 44/Hct, (b) 37/Hct, (c) 30/Hct, (d) 23/Hct, (e) 16/Hct, or (f) 9/Hct. After 10 min of ischemia, CBF was determined with 14C-iodoantipyrine. Coronal brain sections were evaluated for areas with a CBF of 0-10 and 11-20 ml 100 g-1 min-1. In addition, oxygen delivery was calculated. In the center of the ischemic zone, both areas of low CBF were less in the 30/Hct, 23/Hct, and 16/Hct groups compared with the 44/Hct and 37/Hct groups; and both areas were less in the 9/Hct group compared with the other five groups (p < 0.05). For the hemisphere contralateral to occlusion, there was a direct correlation between hematocrit and oxygen delivery. However, for the hemisphere ipsilateral to occlusion, oxygen delivery increased as hematocrit decreased (44/Hct, 8.6 +/- 0.3 vs. 9/Hct, 13.6 +/- 0.4 [mean +/- SD, ml 100 g-1 min-1]). The results of this study support a hypothesis that hemodilution with DCLHb decreases the extent of focal cerebral ischemia.

The effects of isovolumic hemodilution on ocular blood flow

Techniques by which retinal blood flow may be increased safely are potentially important in the treatment of retinal vascular disease. It was hypothesized that hemodilution, which increases cerebral blood flow, would also increase retinal blood flow. To investigate the physiological effects of hemodilution in the eye, ocular blood flow was measured in 14 cats using the radioactively labeled microsphere method. After the animals were anesthetized with halothane and oxygen, intraocular and systemic arterial pressure were recorded; blood flows were measured before and after isovolumic hemodilution to a hematocrit of 20-22% using 6% hydroxyethyl starch (a synthetic plasma expander with a molecular weight of 450 in 0.9% saline). In hemodiluted cats, retinal blood flow increased 71% from its baseline value (36.7 +/- 6.4 ml 100 g-1 min-1 to 62.9 +/- 6.4 ml 100 g-1 min-1, mean +/- S.E.M., P < 0.0001). Calculated retinal O2 delivery remained approximately constant, as the increased blood flow countered a significant decrease in arterial O2 content. Choroidal blood flow decreased (1297 +/- 140 ml 100 g-1 min-1 to 1051 +/- 144 ml 100 g-1 min-1) but the change was not statistically significant. Blood flows in the iris and sclera were not significantly altered. Hemodilution increased retinal blood flow without causing a redistribution in ocular blood flow.

Cardiac performance indices during hypervolemic therapy for cerebral vasospasm

The effect of hypervolemic preload enhancement on cardiac performance was systematically analyzed in nine patients following aneurysmal subarachnoid hemorrhage. The patients ranged in age from 34 to 63 years, and none had a history of cardiac disease. Each patient underwent placement of a flow-directed balloon-tipped catheter and the following measurements were taken during hypervolemic therapy: pulmonary artery wedge pressure (PAWP), central venous pressure (CVP), cardiac index (CI), stroke volume index (SVI), and left ventricular stroke work index (LVSWI). After baseline measurements were recorded, hetastarch or plasmanate was infused intravenously at 300 cc/hr. Thermal output determination and pressures were measured every 15 minutes. The PAWP did not correlate in a statistically significant fashion with the CVP in the ranges recorded; however, a statistically significant correlation did exist between PAWP increases and increases in CI, SVI, and LVSWI (p less than 0.01). There was no statistical correlation between PAWP increases above 14 mm Hg and improvement in cardiac performance as evidenced by CI, SVI, and LVSWI measurements. It is concluded that CVP is an unreliable index of cardiac performance during hypervolemic therapy and that, in previously healthy individuals, a PAWP of 14 mm Hg is associated with maximum cardiac performance.

Relationship between cardiac output and cerebral blood flow in patients with intact and with impaired autoregulation

Intravascular volume expansion has been successfully employed to promote blood flow in ischemic brain regions. This effect has been attributed to both decreased blood viscosity and increased cardiac output resulting from volume expansion. The physiological mechanism by which changes in cardiac output would affect cerebral blood flow (CBF), independent of blood pressure variations, is unclear, but impaired cerebral autoregulation is believed to play a role. In order to evaluate the relationship between cardiac output and CBF when autoregulation is either intact or defective, 135 simultaneous measurements of cardiac output (thermodilution method) and CBF (by the 133Xe inhalation or intravenous injection method) were performed in 35 severely head-injured patients. In 81 instances, these measurements were performed after manipulation of blood pressure with phenylephrine or Arfonad (trimethaphan camsylate), or manipulation of blood viscosity with mannitol. Autoregulation was found to be intact in 55 of these cases and defective in 26. A wide range of changes in cardiac output occurred after administration of each drug. No correlation existed between the changes in cardiac output and the changes in CBF, regardless of the status of blood pressure autoregulation. A significant (40%) increase in CBF was found after administration of mannitol when autoregulation was defective. These data support the hypothesis that, within broad limits, CBF is not related to cardiac output, even when autoregulation is impaired. Thus, the effect of intravascular volume expansion appears to be mediated by decreased blood viscosity rather than cardiac output augmentation.

Normovolaemic induced hypertension therapy for cerebral vasospasm after subarachnoid haemorrhage

We showed that normovolaemic induced hypertension therapy was effective in reducing ischaemic symptoms attributed to cerebral vasospasm in 41 patients after subarachnoid haemorrhage. By inducing hypertension to 25% to 50% above normal systolic arterial blood pressure, we observed that in 17 of 24 cases (71%) neurological deficits improved. In four cases of haemorrhagic infarction, the blood pressure rose to over 50% of systolic arterial pressure, and a low density area was confirmed on computerized tomography (CT) scan prior to vasospasm. Induced hypertension was therefore not considered when a low density area was revealed on CT scan. Restriction of fluid input is usually a factor in producing hypovolaemia after a neurosurgical operation. Intravascular volume expansion has been reported effective in reversing ischaemic deficits. However, according to Poiseuille's equation, increasing blood volume to a state of hypervolaemia can not enhance flow. The cerebral blood flow (CBF) was raised by increasing perfusion pressure, reducing viscosity, or increasing blood vessel diameter. Intravascular volume expansion elevates not only systemic arterial pressure, but also pulmonary artery wedge pressure over 18 mmHg and cardiac index over 2.2. Since pulmonary oedema and congestive heart failure may develop, one should monitor haemodynamic parameters with the Swan-Ganz catheter as a preventive measure. We emphasize that normovolaemic induced hypertension, maintaining haemodynamics subset 1 of the comparable haemodynamic subsets, is effective in raising perfusion pressure of CBF.

The novel dihydronaphthyridine Ca2+ channel blocker CI-951 improves CBF, brain pHi, and EEG recovery in focal cerebral ischemia

The effects of the novel dihydronaphthyridine Ca2+ antagonist CI-951 on focal cerebral ischemia were assessed during MCA occlusion in 30 white New Zealand rabbits under 1.0% halothane anesthesia. In vivo brain pHi and focal CBF were measured with umbelliferone fluorescence. Baseline normocapnic brain pHi and CBF were 7.02 +/- 0.02 and 48.4 +/- 2.9 ml/100 g/min, respectively. In the severe ischemic regions, 15 min postocclusion brain pHi and CBF were 6.62 +/- 0.04 and 14.4 +/- 0.7 ml/100 g/min in controls vs. 6.60 +/- 0.02 and 12.9 +/- 2.3 ml/100 g/min, respectively, in animals destined to receive CI-951. Twenty minutes after MCA occlusion, CI-951 was administered at 0.5 microgram/kg/min and brain pHi and CBF were determined in both regions of severe and moderate ischemia for 4 h postocclusion. Control severe ischemic sites demonstrated no significant improvement in brain pHi and only mild increases in CBF over the next 4 h. CI-951 caused significant improvement in both of these parameters. Postocclusion 4 h brain pHi and CBF measured 6.69 +/- 0.04 and 18.5 +/- 3.2 ml/100 g/min in controls vs. 7.01 +/- 0.04 and 41.7 +/- 5.3 ml/100 g/min, respectively, in CI-951 animals (p less than 0.001). Similar improvements were observed in moderate ischemic sites. In animals that demonstrated postocclusion EEG attenuation, 75% of CI-951 animals had EEG recovery as compared to 18% in controls. CI-951 may be a useful therapeutic agent for focal cerebral ischemia if histological and outcome studies verify these data.

Randomized clinical trials of hemodilution in acute ischemic stroke

The effects of hemodilution in acute ischemic stroke have been investigated, first in a single-center, then in a multicenter trial. Patients with hematocrit levels of 38-50% were randomized, within 48 h of onset of symptoms, to treatment with repeated venesections (total 250-1000 ml) and concomitant dextran 40 administration, or to a control group. The single-center study, performed in a research-oriented stroke unit, involved 102 patients. Case fatality rate was not grossly affected by hemodilution. In survivors, hemodilution improved neurological outcome. More hemodiluted patients were independent in walking and more were at home 3 months after the stroke. The ensuing multicenter trial involved 383 patients in 15 Scandinavian centers. Three-month case fatality rate was 16% in hemodiluted and 12% in control patients. Neurological scoring and ADL performance at 3 months was not improved by hemodilution. No subgroup with beneficial effects was discerned. It is concluded that the present standardized hemodilution regime cannot be recommended for general use in patients with ischemic stroke.

The effect of nimodipine and dextran on axonal function and blood flow following experimental spinal cord injury

There is evidence that posttraumatic ischemia is important in the pathogenesis of acute spinal cord injury (SCI). In the present study spinal cord blood flow (SCBF), measured by the hydrogen clearance technique, and motor and somatosensory evoked potentials (MEP and SSEP) were recorded to evaluate whether the administration of nimodipine and dextran 40, alone or in combination, could increase posttraumatic SCBF and improve axonal function in the cord after acute SCI. Thirty rats received a 53-gm clip compression injury on the cord at T-1 and were then randomly and blindly allocated to one of six treatment groups (five rats in each). Each group was given an intravenous infusion of one of the following over 1 hour, commencing 1 hour after SCI: placebo and saline; placebo and dextran 40; nimodipine 0.02 mg/kg and saline; nimodipine 0.02 mg/kg and dextran 40; nimodipine 0.05 mg/kg and saline; and nimodipine 0.05 mg/kg and dextran 40. The preinjury physiological parameters, including the SCBF at T-1 (mean +/- standard error of the mean: 56.84 +/- 4.51 ml/100 gm/min), were not significantly different (p greater than 0.05) among the treatment groups. Following SCI, there was a significant decrease in the SCBF at T-1 (24.55 +/- 2.99 ml/100 gm/min; p less than 0.0001) as well as significant changes in the MEP recorded from the spinal cord (MEP-C) (p less than 0.0001), the MEP recorded from the sciatic nerve (MEP-N) (p less than 0.0001), and the SSEP (p less than 0.002). Only the combination of nimodipine 0.02 mg/kg and dextran 40 increased the SCBF at T-1 (43.69 +/- 6.09 ml/100 gm/min; p less than 0.003) and improved the MEP-C (p less than 0.0001), MEP-N (p less than 0.04), and SSEP (p less than 0.002) following SCI. With this combination, the changes in SCBF were significantly related to improvement in axonal function in the motor tracts (p less than 0.0001) and somatosensory tracts (p less than 0.0001) of the cord. This study provides quantitative evidence that an increase in posttraumatic SCBF can significantly improve the function of injured spinal cord axons, and strongly implicates posttraumatic ischemia in the pathogenesis of acute SCI.

Haemodilution with dextran 40 and hydroxyethyl starch and its effect on cerebral microcirculation

The effect of haemodilution with Ringer's solution, hydroxyethyl starch (HAES) 200/0.5 10% and dextran 40 on cerebral blood flow (CBF) was measured in ten cats by means of the hydrogen clearance technique. As expected from theoretical considerations the haemodilution effect was short and not significant with Ringer's solution, but was 25% with HAES and 35% with dextrane 40. The corresponding rise in CBF was significant in both the latter but not with Ringer's solution. CBF was similarly highly correlated with diminution of haematocrit (Hct). The different effects of the substances on CBF could all be explained by their different effects on the Hct. Data analysis, together with recent literature, suggests that the dominating factor determining CBF was the O2-transport capacity, which in these experiments was in close relation to Hct. The results support the assumption that the increase of CBF by haemodilution is caused by a regulatory mechanism and not by a change of rheological parameters.

[Surgical treatment of intracranial aneurysm]

The author reviews his personal experience in the surgical treatment of 325 patients presenting intracranial aneurysms. The patients were operated at Cristo Redentor Hospital between January 1979 and December 1986. Pre and post surgical management of sub-arachnoid haemorrhage and its complications is described. Internal carotid aneurysms were 122; anterior carotid artery, 100; middle cerebral artery, 69; vertebro-basilar system, 4; and multiple aneurysms, 30. 321 of those aneurysms were approached directly. 177 patients Grade I were surgically treated, with a mortality rate of 5.08%; 78 in Grade II with mortality rate of 16.66%; 55 in Grade III with mortality rate of 36.36%; and 15 in Grade IV with mortality rate of 66.6%. The general mortality rate was 16%. The results of surgeries in the former group (1961-1978) of 277 patients were compared to the group of 325 cases. The final mortality rate in 552 operated patients in the two groups is 18.11%.

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)

Multicenter trial of hemodilution in acute ischemic stroke. Results of subgroup analyses. Scandinavian Stroke Study Group

In a multicenter trial, 183 patients with acute ischemic stroke of less than 48 hours' duration and hematocrits of 38-50% were randomized to standardized hemodilution treatment (venesection and dextran 40 administration) and 190 to a control group. We have previously reported that there were no beneficial effects of hemodilution in the total patient population. In this report, the case fatality rates and neurologic outcome in survivors (3 months' follow-up) in subsets of patients have been analyzed. The patients were subgrouped by sex, age, medical history, smoking habits, delay from the onset of symptoms to the start of treatment, hematocrit at entry, venesection volume, neurologic score at entry into the study, blood pressure changes in the acute phase, presence of atrial fibrillation, location of brain lesion by computed tomography, type of diagnostic procedures, and hospital setting. No subset in which hemodilution reduced mortality or improved neurologic outcome could be identified. Case fatality rate was apparently higher in hemodiluted patients with infarction affecting deep brain structures than in control patients with such lesions. By simple clinical criteria, we have been unable to define subsets of stroke patients who benefit from the present standardized regimen of moderate hemodilution. The sample sizes are, however, too small to refute the possibility that a modest clinical effect of hemodilution may be present in some patients with stroke.

Isovolemic hemodilution in stroke. A study in gerbils

Isovolemic hemodilution has been reported to increase cerebral perfusion in humans and has been advocated as a treatment for acute cerebral infarction. This study examines the effect of isovolemic hemodilution with low-molecular-weight dextran on mortality and the incidence of neurological deficit in gerbils after internal carotid ligation. Sixty-four Mongolian gerbils were anesthetized with pentobarbital and the left internal carotid artery was ligated in both control and experimental animals. In the experimental group, blood was removed and an equal volume of dextran was injected to reestablish normal blood volume and lower hematocrit to a mean of 30.5. Control animals were not so treated. Animals were observed for neurological deficits for 24 hours after carotid ligation. The incidence of neurological deficit in control animals was 67%; it was 64% in the experimental group. Mortality within the first 24 hours was 28% in the controls and 75% in animals that were treated by hemodilution (p less than 0.001). Isovolemic hemodilution with dextran did not reduce the incidence of neurological deficit after carotid ligation in gerbils and was associated with a significant increase in mortality during the first 24 hours.

Early operation of ruptured basilar artery aneurysm associated with bilateral carotid occlusion (moyamoya disease)

A 34-year-old Caucasian man presented with subarachnoid hemorrhage. Angiography revealed bilateral carotid occlusion at the cavernous sinus and an aneurysm at the basilar artery bifurcation. The whole brain was supplied with blood from the basilar artery and posterior cerebral arteries through a large number of collateral vessels to the internal carotid artery bifurcation, middle cerebral and anterior cerebral arteries: the moyamoya phenomenon. The aneurysm was clipped within hours of the subarachnoid hemorrhage. The relation between moyamoya disease and basilar artery aneurysms is discussed and some surgical and management considerations are given.

Comparison of the effects of infusion with hydroxyethyl starch and low molecular weight dextran on cerebral blood flow and hemorheology in normal baboons

Cerebral blood flow (CBF) and hemorheological parameters, such as hematocrit, plasma viscosity, and erythrocyte aggregation, were measured before and up to 7 h after 60-min infusions with 10% hydroxyethyl starch (HES), or 0.9% NaCl solution and 10% low molecular weight dextran (LMWD) in a total of 12 normal baboons. Infusion of HES increased CBF up to 48% from the resting level, and decreased hematocrit without an increase in plasma viscosity. Infusion of LMWD decreased hematocrit with an increase in CBF of up to 9.6%, but increased plasma viscosity at the same time. The disaggregating effect for erythrocytes was rather more obvious with LMWD than with HES but without significant difference between them. These data show different rheological effects with infusions of HES and LMWD on the physiological conditions of normal baboons.

The role of plasma hyperviscosity in subcortical arteriosclerotic encephalopathy (Binswanger's disease)

Five haemorheological variables (haematocrit, plasma viscosity, red cell aggregation, red cell deformability and yield shear stress) and the plasma fibrinogen concentration were determined in blood samples from 21 untreated patients with subcortical arteriosclerotic encephalopathy (SAE, Binswanger's disease). The results were compared with those obtained in blood samples from 40 untreated patients with lacunar infarcts and from 275 healthy control subjects without vascular risk factors. Pathological ("solid body") flow behaviour was detected in the blood of both groups of patients (SAE and lacunar infarcts). However, highly elevated plasma viscosity was a consistent feature only of SAE. The authors present the hypothesis that the high plasma viscosity in patients with SAE may account for the progressive degeneration of cerebral white matter. It is postulated that microcirculatory abnormalities due to microrheological changes may be one of the many missing links in the pathophysiology of SAE.

Focal cerebral ischemia: pathophysiologic mechanisms and rationale for future avenues of treatment

Although approximately 500,000 patients suffer from a stroke each year in the United States, treatment of these patients to date has consisted primarily of prevention, supportive measures, and rehabilitation. The modification of experimental cerebral infarction by new pharmacologic agents, along with encouraging results from the restoration of blood flow to areas of focal ischemia in both laboratory and clinical trials, suggests that a more aggressive approach might be considered in selected patients with acute stroke.

Cerebral protection

Cerebral protection from an ischemic/hypoxic insult implies that tissue injury can be controlled or even prevented by certain therapeutic maneuvers. For example, physiological thresholds may be altered so that tissue vulnerability to the insult is reduced, or the intensity of an insult may be blunted by enhancing brain homeostasis. Such a therapeutic maneuver is carotid endarterectomy to improve blood flow in the disordered hemisphere. Alternatively, drugs with protective properties can be used before or even after the insult to "stabilize" injured tissue and prevent the harmful secondary effects that often follow. Various past and present approaches to cerebral protection employing physiological, pharmacological, and surgical intervention are reviewed. The mechanisms by which each allegedly protects the brain from ischemia and hypoxia are discussed briefly. Promising, but not always successful, approaches used in the past have pointed the way for new and more rational therapies. Truly effective protection of the brain from ischemia and hypoxia depends directly upon our capability to explore basic mechanisms of injury and our willingness to measure accurately and objectively the outcome of newly developed protective measures.

Observations on the perioperative management of aneurysmal subarachnoid hemorrhage

Thirty-two patients with aneurysmal subarachnoid hemorrhage (SAH) were managed according to a protocol based on pain control and hemodynamic manipulation, monitored by an arterial line and Swan-Ganz catheter. Hemodynamic parameters were adjusted to four clinical situations. 1) For the unoperated patient with no neurological deficit, the regimen aims to maintain pulmonary wedge pressure (PWP) at 10 to 12 mm Hg, and the cardiac index (CI) and blood pressure (BP) at normal levels. 2) For the unoperated patient presenting with or developing neurological deficit, the PWP is increased until the deficit is reversed or the CI falls; the CI is high, and the BP normal. 3) For the postoperative patient with no neurological deficit, the PWP is maintained at 12 to 14 mm Hg, the CI is a high normal, and the BP is normal. 4) For the postoperative patient developing neurological deficit but showing no surgical complication on the computerized tomography scan, the PWP is increased until the deficit is reversed or the CI falls; the CI is high and the BP is increased with vasopressors if necessary. Fourteen patients developed neurological deficits either preoperatively, postoperatively, or both. Neurological deficits were repeatedly reversed by increasing the PWP, as measured hourly. In several patients an optimal wedge pressure was determined, below which deficits would reappear. In one patient whose neurological deficit was reversed on several occasions by increasing the PWP, the optimal PWP rose after each episode until it reached 22 mm Hg. Detailed event-related analysis of these patients' course illustrates these phenomena well. The optimal PWP varied from patient to patient, but ranged most frequently from 14 to 16 mm Hg. Meticulous monitoring of the patients' neurological status coupled with prompt correction of low PWP (assuming an adequate CI) has proven to be an effective way to prevent and reverse neurological deficits following aneurysmal SAH.

Do different ischemic brain lesions have different hemorheological profiles?

The following hemorheological parameters were determined in 68 patients with ischemic brain lesions and in 28 controls: yield shear stress, erythrocyte aggregation, erythrocyte rigidity, plasma viscosity, and hematocrit. The patients were classified into various groups on the basis of etiological criteria. The results revealed differences between certain hemorheological variables (erythrocyte aggregation, plasma viscosity) in some of the stroke groups. Plasma viscosity was significantly higher in patients with Binswanger's disease and significantly lower in the control group compared with values measured in patients with macroangiopathy and microangiopathy. Erythrocyte aggregation was significantly lower in the controls than in the other groups. Discriminant analysis revealed that plasma viscosity, erythrocyte aggregation and hematocrit were the most useful variables for classification.

Induced hypertension for the treatment of cerebral ischemia after subarachnoid hemorrhage. Direct effect on cerebral blood flow

The best treatment for symptomatic cerebral ischemia from presumed vasospasm after aneurysmal subarachnoid hemorrhage remains a matter of controversy. A direct effect of any treatment modality on regional cerebral blood flow has never been documented. In a series of 43 patients operated on for ruptured anterior circulation aneurysms, five patients (11.6%) developed clinical signs of cerebral ischemia postoperatively. In four of those patients, the diagnosis of "vasospasm" was made with measurements of cerebral blood flow (133Xe inhalation or intravenous injection, 10-16 detectors, cerebral blood flow infinity). Treatment with induced arterial hypertension with phenylephrine was instituted. Hemodilution was instituted in one patient; the other three patients already had hematocrits in the range of 33. Within 1 hour, the cerebral blood flow measurement was repeated to document the effect of treatment. The average pretreatment hemispherical blood flow on the operated side was 18.8 mL/100 g per minute, on the contralateral side 21.0 mL/100 g per minute. With treatment these flows increased to 30.8 and 35.8 mL/100 g per minute, respectively. There was also an immediate and obvious positive clinical effect in all patients. The role of measurement of cerebral blood flow in the clinical management of vasospasm is discussed. We stress the theoretical and practical advances of measurements of cerebral blood flow over cerebral angiography, especially in comatose patients.

Effects of rapid mannitol infusion on cerebral blood volume. A positron emission tomographic study in dogs and man

Positron emission tomography was used to study the effect of a rapid infusion of mannitol on cerebral blood volume (CBV) in five dogs and in three human subjects. The ability of mannitol to reduce intracranial pressure (ICP) has always been attributed to its osmotic dehydrating effect. The effects of mannitol infusion include increased osmolality, total blood volume, central venous pressure (CVP), and cerebral blood flow, and decreased hematocrit, hemoglobin concentration, serum sodium level, and viscosity. Mannitol's ability to dilate the cerebral vasculature, either directly or indirectly, and thus to transiently increase ICP, is a subject of controversy. By in vivo labeling of red cells with carbon-11, the authors were able to demonstrate an early increase in CBV in dogs of 20%, 27%, and 23% (mean increase, p less than 0.05) at 1, 2, and 3 minutes, respectively, after an infusion of 20% mannitol (2 gm/kg over a 3-minute period). The animals' muscle blood volume increased by 27% (mean increase, p less than 0.05) 2 minutes after infusion. In the human subjects, lower doses and a longer duration of infusion (1 gm/kg over 4 minutes) resulted in an increase in CBV of 8%, 14% (p less than 0.05), and 10% at 1, 2, and 3 minutes, respectively, after infusion. In dogs, ICP increased by 4 mm Hg (mean increase, p less than 0.05) 1 minute after the infusion, before decreasing sharply. The ICP was not measured in the human subjects. Hematocrit, hemoglobin, sodium, potassium, osmolality, heart rate, mean arterial pressure (MAP), and CVP were measured serially. Results of these measurements, as well as the significant decrease in MAP that occurred after mannitol infusion, are discussed. This study demonstrated that rapid mannitol infusion increases CBV and ICP. The increase in muscle blood volume, in the presence of a decreased MAP and an adequate CVP, suggests that mannitol may have caused vasodilation in these experiments.

The haemorheological features of lacunar strokes

Clinical and haemorheological data were recorded in 40 patients with lacunar strokes confirmed clinically and by computed tomography. The following haemorheological variables were monitored: haematocrit, erythrocyte aggregation, erythrocyte deformability, plasma viscosity, fibrinogen concentration and yield shear stress. Clinically, most patients had case histories and features according to the description of Fisher. All haemorheological parameters with the exception of the haematocrit were pathological when compared with values obtained from a normal control group. In descending order of frequency the pathological changes were in erythrocyte aggregation, plasma viscosity and erythrocyte deformability.

Modification of focal cerebral ischemia by cardiac output augmentation

Intravascular volume expansion has been employed successfully for treatment of ischemic stroke from cerebral vasospasm and from cerebrovascular occlusive disease. The physiologic mechanism responsible for this success has not previously been delineated in controlled experimentation. The objective of this investigation was to delineate the effects of cardiac output and of hemodilution in a primate model of focal cerebral ischemia. Two groups of anesthetized rhesus monkeys received extensive cardiovascular monitoring, and local cerebral blood flow (lCBF) was determined in both ischemic and nonischemic brain regions by the hydrogen clearance method. Both groups were subjected to unilateral middle cerebral artery occlusion. One group then underwent blood volume expansion with Dextran 40 (cardiac output augmentation), and one group underwent isovolemic hemodilution with Dextran 40, cardiac output being maintained constant. Significant increases in lCBF occurred in ischemic regions only and occurred only in response to augmentation of cardiac output. Isovolemic hemodilution failed to produce any changes in lCBF. This investigation indicates that ischemic brain regions are selectively vulnerable to alterations in cardiac output, these effects being independent of alterations in blood pressure. Blood viscosity changes may play only a minor role. This study strongly suggests an important role of intravascular volume expansion and cardiac output augmentation in treatment of acute ischemic stroke.

Baseline hemodynamic state and response to hemodilution in patients with acute cerebral ischemia

Hemodynamic data were obtained in 9 patients (mean age 65 yrs) with carotid territory cerebral infarct within the preceding 24 hours (mean 14 +/- 8) as part of a pilot study testing the feasibility and safety of hypervolemic hemodilution. Pulmonary arterial catheters (PACs) were placed without complication in all patients, and after baseline measurements were obtained, up to 1500 cc of 6% hetastarch in 0.9% sodium chloride was administered the first day and up to 1000 cc per day the second and third days. Pulmonary wedge pressure (PWP) rose from 6.3 +/- 3.5 to 14.4 +/- 3.4 mm Hg (p less than 0.001) without development of congestive heart failure in any patient. This was accompanied by a drop in hematocrit (Hct) from 40.3 +/- 3.4 to 32.9 +/- 2.0 (p less than 0.001) and rise in cardiac output (CO) from 4.3 +/- 1.0 to 5.3 +/- 0.6 (p less than 0.05). Phlebotomy of 250 cc was performed in 2 patients and 500 cc in one in order to reduce Hct to desired levels. The volume of fluid needed to raise PWP to 15 was unpredictable (2361 +/- 1106 cc) and therefore PACs were necessary to monitor the rate and volume of fluid administration. The data show that PWP is sufficiently low and Hct sufficiently high following stroke in most patients that hemodilution by volume expansion with phlebotomy added if necessary can be undertaken safely with appropriate monitoring of hemodynamic function, and that this therapy results in optimal reduction of Hct and increased CO without risk of hypotension.

The effects of rapid infusions of saline and mannitol on cerebral blood volume and intracranial pressure in dogs

The role of osmotic brain dehydration in the early reduction of intracranial pressure (ICP) following mannitol administration has recently been questioned and a decrease in cerebral blood volume (CBV) proposed as the mechanism of action. To evaluate this hypothesis, relative CBV changes before and after mannitol infusion were determined by collimated gamma counting across the biparietal diameter of the exposed skull in six dogs. Red blood cells were labelled with chromium-51. Cerebral blood volume (CBV), total blood volume (TBV), ICP, mean arterial pressure (MAP), central venous pressure (CVP), haematocrit and osmolality were serially measured after infusions of 10 ml X kg-1 of normal saline (control study) and of 20 per cent mannitol (mannitol study). The solutions were administered over a two-minute period; a 30-minute equilibration period intervened between the saline and mannitol infusions. We demonstrated that the mannitol infusion was associated with significant increases in relative CBV (25 per cent), ICP (7 mmHg), CVP (11 cm H2O), and TBV (50 per cent). MAP declined significantly (14 per cent) after mannitol infusion. The administration of saline, although associated with an increase in TBV (18 per cent), was not associated with any significant change in CBV, ICP, MAP or CVP. The increase in relative CBV persisted for 15 minutes after mannitol infusion, while the ICP returned to control within five minutes and continued to decrease. This study supports the fact that after rapid mannitol infusion, ICP begins to decrease only once the dehydrating effect has counteracted the increase in brain bulk caused by the increase in cerebral blood volume.

Acute cerebral revascularization

Fifteen patients evaluated for acute cerebral ischemia underwent acute cerebral revascularization between March, 1979, and May, 1983. Clinical presentation included crescendo transient ischemic attacks (TIA's) in eight cases, progressing neurological dysfunction in three cases, and completed nonfluctuating deficits in four cases. Nine patients received intravenous heparin but did not improve neurologically. The patients with crescendo TIA's were operated on within 4 hours of their last event; those with progressing deficits were operated on while the deficit was developing, and those with established deficits were operated on 4, 6, 9, and 12 hours, respectively, after the event began. The clinical picture for 10 patients had resolved within 10 hours after surgery. One patient with crescendo TIA's, two with progressing deficits, and two with established deficits had postoperative residual deficits, of which three were mild and two severe. One patient, who had a saphenous vein graft to the middle cerebral artery, developed an intracerebral hematoma. In this prospective noncontrolled nonrandomized study, acute cerebral revascularization was performed safely, had limited risks, and offered the potential to help some patients. Further controlled randomized studies are indicated.

Beneficial effects of induced hypertension on experimental stroke in awake monkeys

The authors performed a controlled study of induced hypertension therapy for treatment of experimental stroke in unanesthetized monkeys. Ten control and 10 treated animals were subjected to a 4-hour occlusion of the middle cerebral artery (MCA) by an implanted tourniquet. Neurological status and local cerebral blood flow (CBF) were monitored serially. Local CBF was determined by hydrogen clearance in and around the elevated 20% to 40% by intravenous infusion of phenylephrine hydrochloride. Neuropathological evaluation was performed after about 2 weeks. A 4-hour occlusion of the MCA in control animals caused moderate stable neurological deficits, moderate stable decreases in local CBF, and medium-sized infarcts. With induced hypertension, five of 10 treated animals showed neurological improvement, and eight exhibited increased CBF in the ischemic zone. Average infarct size tended to be smaller in the treated group, although the difference did not reach statistical significance. Hemorrhagic infarcts were not observed. In four animals, phenylephrine caused cardiac dysrhythmias and hypotension which were reversed by appropriate measures. In this unanesthetized primate model of moderate experimental stroke, induced hypertension had beneficial effects on neurological status, local CBF, and infarct size without causing hemorrhagic infarction. Induced hypertension may be beneficial for some clinical cases of focal cerebral ischemia.

Cerebral vasospasm after subarachnoid hemorrhage: an update

Symptomatic vasospasm, or delayed cerebral ischemia associated with arteriographic evidence of arterial constriction, is currently the most important cause of morbidity after acute subarachnoid hemorrhage. The development of vasospasm is directly correlated with the presence of thick blood clots in the basal subarachnoid cisterns, which can be detected by an early computed tomographic scan. Symptomatic vasospasm usually develops between 4 and 12 days after subarachnoid hemorrhage. The onset is gradual, occurring over hours or days. There is typically a gradual deterioration of the level of consciousness, accompanied by focal neurological deficits that are determined by the arterial territories involved. Hyponatremia frequently occurs and may exacerbate the symptoms. The patients are usually volume depleted, and therefore many authorities now treat them with replenishment and expansion of their intravascular volume with colloid and blood. Volume expansion, together with elevation of the systemic blood pressure and reduction of the intracranial pressure when elevated, constitute the only currently available effective therapy for symptomatic vasospasm. The cause of vasospasm remains obscure. Mechanisms of smooth muscle cell contraction and relaxation and experimental efforts to elucidate the nature of vasospasm are reviewed.

Hypervolemic hemodilution in experimental focal cerebral ischemia. Elevation of cardiac output, regional cortical blood flow, and ICP after intravascular volume expansion with low molecular weight dextran

Cerebrovascular and cardiac alterations evoked by intravascular volume expansion with low molecular weight dextran (LMD, molecular weight 40,000), an advocated adjunct in the clinical prevention or therapy of acute stroke and cerebral vasospasm, were studied in splenectomized dogs. Clipping of the right distal internal carotid artery and the proximal middle cerebral artery (MCA) in eight dogs decreased regional cortical blood flow (rCoBF) by 58% without changing cardiac output (CO), and caused 10% +/- 5% (SE) hemispheric infarction. Ten other dogs underwent similar cerebral arterial occlusion and were infused twice with LMD within 2 hours; each infusion equaled 20% of the respective dog's total blood volume. Both CO and rCoBF in the territory of the occluded MCA increased significantly by 119% +/- 13% and 42% +/- 6%, respectively. following the two LMD infusions. Although the mean arterial blood pressure was unaltered, the hematocrit decreased significantly and the intracranial pressure (ICP) increased significantly. The mean hemispheric infarction in these 10 treated dogs was 4% +/- 2%. Another nine dogs underwent arterial manipulation without clipping. Two hemodiluting LMD infusions, similar to those in the 10 dogs, significantly elevated CO and ICP but not rCoBF. These data suggest that hypervolemic hemodilution with LMD effectively elevates collateral perfusion to ischemic regions of brain distal to occluded MCA segments and concomitantly raises the CO and ICP.

Microsurgical removal of a balloon embolus to the internal carotid artery. Case report

✓ A complication of treatment of posttraumatic carotid-cavernous fistulas by detachable balloon techniques is presented. During occlusion of the fistula, a balloon embolus migrated from the cavernous sinus into the bifurcation of the internal carotid artery. The resultant neurological deficit was immediately treated with hypertension and volume expansion. The patient underwent direct microsurgical embolectomy and suffered no postoperative neurological sequelae. The significance and management of this complication are discussed.