Red blood cell regulation of microvascular tone through adenosine triphosphate

The matching of blood flow with metabolic need requires a mechanism for sensing the needs of the tissue and communicating that need to the arterioles, the ultimate controllers of tissue perfusion. Despite significant strides in our understanding of blood flow regulation, the identity of the O(2) sensor has remained elusive. Recently, the red blood cell, the Hb-containing O(2) carrier, has been implicated as a potential O(2) sensor and contributor to this vascular control by virtue of its concomitant carriage of millimolar amounts of ATP, which it is able to release when exposed to a low-O(2) environment. To evaluate this possibility, we exposed perfused cerebral arterioles to low extraluminal O(2) in the absence and presence of red blood cells or 6% dextran and determined both vessel diameter and ATP in the vessel effluent. Only when the vessels were perfused with red blood cells did the vessels dilate in response to low extraluminal O(2). In addition, this response was accompanied by a significant increase in vessel effluent ATP. These findings support the hypothesis that the red blood cell itself serves a role in determining O(2) supply to tissue.

Molecular keys to the problems of cerebral vasospasm

The mechanisms responsible for subarachnoid hemorrhage (SAH)-induced vasospasm are under intense investigation but remain incompletely understood. A consequence of SAH-induced vasospasm, cerebral infarction, produces a nonrecoverable ischemic tissue core surrounded by a potentially amenable penumbra. However, successful treatment has been inconsistent. In this review, we summarize the basic molecular biology of cerebrovascular regulation, describe recent developments in molecular biology to elucidate the mechanisms of SAH-induced vasospasm, and discuss the potential contribution of cerebral microcirculation regulation to the control of ischemia. Our understanding of the pathogenesis of SAH-induced vasospasm remains a major scientific challenge; however, molecular biological techniques are beginning to uncover the intracellular mechanisms involved in vascular regulation and its failure. Recent findings of microvascular regulatory mechanisms and their failure after SAH suggest a role in the development and size of the ischemia. Progress is being made in identifying the various components in the blood that cause SAH-induced vasospasm. Thus, our evolving understanding of the underlying molecular mechanism may provide the basis for improved treatment after SAH-induced vasospasm, especially at the level of the microcirculation.

No reduction in cerebral metabolism as a result of early moderate hyperventilation following severe traumatic brain injury

OBJECT

Hyperventilation has been used for many years in the management of patients with traumatic brain injury (TBI). Concern has been raised that hyperventilation could lead to cerebral ischemia; these concerns have been magnified by reports of reduced cerebral blood flow (CBF) early after severe TBI. The authors tested the hypothesis that moderate hyperventilation induced early after TBI would not produce a reduction in CBF severe enough to cause cerebral energy failure (CBF that is insufficient to meet metabolic needs).

METHODS

Nine patients were studied a mean of 11.2+/-1.6 hours (range 8-14 hours) after TBI occurred. The patients' mean Glasgow Coma Scale score was 5.6+/-1.8 and their mean age 27+/-9 years; eight of the patients were male. Intracranial pressure (ICP), mean arterial blood pressure, and jugular venous oxygen content were monitored and cerebral perfusion pressure was maintained at a level higher than 70 mm Hg by using vasopressors when needed. Measurements of CBF, cerebral blood volume (CBV), cerebral metabolic rate for oxygen (CMRO2), oxygen extraction fraction (OEF), and cerebral venous oxygen content (CvO2) were made before and after 30 minutes of hyperventilation to a PaCO2 of 30+/-2 mm Hg. Ten age-matched healthy volunteers were used as normocapnic controls. Global CBF, CBV, and CvO2 did not differ between the two groups, but in the TBI patients CMRO2 and OEF were reduced (1.59+/-0.44 ml/100 g/minute [p < 0.01] and 0.31+/-0.06 [p < 0.0001], respectively). During hyperventilation, global CBF decreased to 25.5+/-8.7 ml/100 g/minute (p < 0.0009), CBV fell to 2.8+/-0.56 ml/100 g (p < 0.001), OEF rose to 0.45+/-0.13 (p < 0.02), and CvO2 fell to 8.3+/-3 vol% (p < 0.02); CMRO2 remained unchanged.

CONCLUSIONS

The authors conclude that early, brief, moderate hyperventilation does not impair global cerebral metabolism in patients with severe TBI and, thus, is unlikely to cause further neurological injury. Additional studies are needed to assess focal changes, the effects of more severe hyperventilation, and the effects of hyperventilation in the setting of increased ICP.

Sagittal sinus occlusion by intraluminal dural cysts. Report of two cases

Lesions involving the sagittal sinus typically present as masses compressing the sinus externally. The authors describe two cases of lesions entirely within the lumen of the sagittal sinus. In one of the cases, syncope was the presenting symptom and surgical resection of the cyst was performed. An entirely intraluminal cyst, consistent with a dural cyst, was resected, followed by reconstruction of the sinus and resolution of symptoms. Entirely intraluminal lesions of the sagittal sinus have rarely been reported as incidental findings. This represents the first report of symptomatic occlusion of a venous sinus by an intraluminal cyst.

Intracranial pressure monitoring during intraarterial papaverine infusion for cerebral vasospasm

PURPOSE

Intraarterial papaverine infusions are performed to reverse cerebral arterial vasospasm resulting from subarachnoid hemorrhage, but such infusions may lead to increases in intracranial pressure (ICP). This study was undertaken to determine when ICP monitoring is indicated during papaverine treatment.

METHODS

Seventy-eight vessels were treated in 51 sessions in 28 patients with symptomatic vasospasm. ICP, papaverine doses, and infusion rates were recorded during treatment sessions. The procedural data, Hunt and Hess scores, Fisher grades, Glasgow Coma Scale scores, and ages for all subjects were reviewed and analyzed retrospectively.

RESULTS

Baseline ICP ranged from 0 to 34 mm Hg. With typical papaverine doses of 300 mg per territory and infusion times ranging from 5 to 60 minutes per vessel, ICP increases above baseline during papaverine infusion ranged from 0 to 60 mm Hg. Significant (> or = 20 mm Hg) ICP increases during therapy were observed even in patients with low baseline ICP and with papaverine infused at the slowest rate. Patients with a baseline ICP of more than 15 mm Hg were much more likely to have significant ICP increases than were patients with a baseline ICP of 0 to 15 mm Hg. Hunt and Hess scores, Fisher grades, age, and Glasgow Coma Scale scores on admission and immediately before treatment did not correlate with ICP increases during papaverine infusion. Patients with ICP increases of more than 10 mm Hg during therapy were more likely to experience adverse clinical events than were patients with ICP increases of < or = 10 mm Hg. Reduction in the rate of papaverine infusion, or termination of infusion, resulted in reversal of drug-induced ICP elevation.

CONCLUSION

ICP monitoring during intraarterial papaverine infusions for cerebral vasospasm is recommended for all patients and is particularly important for patients with elevated baseline ICP. Continuous ICP monitoring facilitates safe and time-efficient drug delivery.

Posterior ventricular catheter burr-hole localizer. Technical note

Proper ventricular catheter placements are associated with improved shunt performance. When placing ventricular catheters via the posterior approach, the surgeon must determine an optimum trajectory and then pass a catheter along that trajectory. The incidence of optimal posterior catheter placements is increased by using a posterior catheter guide (PCG); however, errors may still occur because of poor selection of a posterior burr-hole site. In this report an easy-to-use posterior burr-hole localizer (Localizer) is described that defines the optimum burr-hole location based on geometric relationships involving the ear and supraorbital rims. The basic design principle of the Localizer was formulated and tested by using neuronavigational imaging tools to examine normal adult ventricular anatomy in relation to surface landmarks and by reviewing imaging studies obtained in 50 adult patients with hydrocephalus. Subsequently, the Localizer was used in 28 consecutive patients scheduled to undergo shunt surgery performed by using the PCG. In all cases the catheter entered the ventricle on the first pass and postoperative imaging studies demonstrated successful placement in the ipsilateral anterior horn. There were no catheter-related complications. These early results indicate that the Localizer and PCG devices may be safe and effective when used in combination for placement of posterior ventricular catheters.

Possible role of nitric oxide in autoregulatory response in rat intracerebral arterioles

OBJECTIVE

Cerebral autoregulation is an important regulatory mechanism that maintains a constant cerebral blood flow over a wide range of perfusion pressures. The goal of this study was to determine whether nitric oxide contributes to the autoregulatory response of cerebral arterioles to altered transmural pressure (TMP).

METHODS

Seventy-nine intraparenchymal arterioles (53.6 +/- 3.5 microm mean diameter) isolated from rats were cannulated with micropipettes and pressurized at a TMP of 60 mm Hg (control pressure). Vessel diameters were monitored continuously using a video dimensional analyzer. The autoregulatory diameter responses to varying intraluminal pressures were observed in the presence and absence of a nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). The effect of L-NMMA-induced constriction on autoregulatory response also was compared with responses after prostaglandin F2alpha and alkalosis-induced constrictions.

RESULTS

Autoregulatory responses were observed over a range from 10 to 90 mm Hg of TMP. Treatment with 10(-4) mol/L L-NMMA constricted arterioles and inhibited the autoregulatory vasodilation to TMP reductions from 60 mm Hg to 10 or 30 mm Hg. In L-NMMA-treated arterioles, elevation in TMP from 60 to 90 mm Hg caused an autoregulatory vasoconstriction. Treatment with alkaline pH 7.65 constricted arterioles to a similar degree as that induced by L-NMMA at 60 mm Hg, and under these conditions, the autoregulatory response remained intact. Arterioles severely constricted with prostaglandin F2alpha showed no significant autoregulatory response.

CONCLUSION

These results suggest that 1) vascular nitric oxide release increases in response to a decrease in TMP from 60 mm Hg, thereby contributing to the autoregulatory vasodilation intrinsic to the vessel during hypotension, 2) arteriolar nitric oxide appears not to be involved in the autoregulatory vasoconstriction induced by elevating TMP from 60 to 90 mm Hg, and 3) a marked increase in vascular tone may affect autoregulatory response.

Increased functional vascular response in the region of a glioma

Functional imaging of a language task using positron emission tomography was performed as part of the preoperative assessment of a patient with a left supplementary motor area (SMA) tumor. Positron emission tomography scans were obtained during language tasks (verb generation and word reading of visually presented nouns) that normally lead to increased blood flow in the SMA relative to a control condition (visual fixation). In the patient, the normal SMA response was an order of magnitude larger in the region of the tumor. Other regions, such as left inferior frontal cortex and right cerebellum, showed equivalent activation in the patient and normal subjects. Histopathologic study revealed an anaplastic astrocytoma. Thus, this exaggerated vascular response to local neuronal activation occurred in the setting of a proliferation of glial cells. This is consistent with models of coupling of regional CBF and neuronal activity that implicate glia as the mediator between neurons and vasculature. The concept that tumoral disruption of normal vascular responses could, in some cases, potentially enhance rather than dampen the response is proposed.

Increase in diameters of vasospastic intracranial arteries by intraarterial papaverine administration

OBJECT

This study was conducted to determine if there is a change in intracranial arterial diameters after papaverine infusion for vasospasm and to determine whether the change occurs in proximal, intermediate, and distal arteries.

METHODS

The authors measured arterial diameters retrospectively in all patients who received intraarterial papaverine for treatment of vasospasm between November 1992 and August 1995. Patients who received papaverine in the same session with or following angioplasty were excluded. Measurements were made in a blinded manner with the aid of a magnification loupe at 12 predetermined sites on each angiogram before and after papaverine infusion. Eighty-one treatments in 34 patients were included. Angiograms obtained at the time of presentation with subarachnoid hemorrhage (SAH) were examined in 26 of the 34 patients. Nine carotid territories visualized by repeated angiography on the day after infusion were examined to determine the duration of the papaverine effect.

CONCLUSIONS

In all treatment groups an increase was found in the average arterial diameters ranging from 2.8 to 73.9%, with a mean increase of 26.5%. Increases in diameter were observed in proximal, intermediate, and distal arteries. The timing of treatments ranged from Day 3 to Day 19 post-SAH, and there was no relationship between timing and arterial responsiveness (r = -0.06). There was a moderately good correlation between the degree of vasospasm in an artery and its responsiveness to papaverine (r = -0.54, -0.66, and -0.66, for proximal, intermediate, and distal arteries, respectively). The effect of papaverine did not persist until the following day in patients in whom repeated angiography was performed.

Intracranial aneurysm: anatomic factors that predict the usefulness of intraoperative angiography

PURPOSE

To correlate the size and location of intracranial aneurysm with the need to reposition the aneurysm clip after intraoperative angiography.

MATERIALS AND METHODS

In 199 consecutive patients with 234 clipped intracranial aneurysms, 273 intraoperative angiographic studies were retrospectively reviewed. Aneurysm size and location, determined with preoperative angiographic and surgical reports, were correlated with the frequency of clip repositioning because of parent- or branch-vessel compromise or unexpected residual aneurysm.

RESULTS

Findings from intraoperative angiograms resulted in clip repositioning in 46 of 273 (16.8%) studies. Clip repositioning was statistically significantly less frequent with aneurysms of the posterior communicating (three of 52 [5.7%] studies) and anterior choroidal (none of 12 studies) arteries. High rates of clip repositioning were found in aneurysms of the superior hypophyseal artery (seven of 18 [38.9%] studies), superior cerebellar artery (three of five [60.0%] studies), and bifurcation of the internal carotid artery (three of nine [33.3%] aneurysms). In 98 conventional follow-up angiographic studies, seven (7%) false-negative cases with unsuspected aneurysm neck remnant were found.

CONCLUSION

The rate of clip repositioning in aneurysms of the posterior communicating or anterior choroidal arteries was less than that at other locations (P < .05). Intraoperative angiography may not be necessary when aneurysms are at these two locations.

Convection versus conduction cooling for induction of mild hypothermia during neurovascular procedures in adults

Hypothermia for cerebral protection is usually achieved by administration of intravenous fluids at room temperature, cooling ambient air, ice packs, and a temperature-adjustable circulating water mattress. We compared cooling by conduction by using a water mattress to cool by convection by using a forced-air cooling device. Twenty patients were prospectively randomized to two groups: 10 patients cooled by convection (CC) and 10 patients cooled by traditional methods (TC). Two patients in the CC group were withdrawn from the study and excluded from the analysis; one patient for failure to cool despite the use of both techniques, and the other for the abrupt onset of arrhythmias and myocardial depression during hypothermia. Temperature was measured at the tympanic membrane, pulmonary artery, and esophageal probe sites and recorded every 15 min. The time required to reach the target temperature range of 33-34 degrees C was recorded. We found no differences in the temperatures measured at the three sites during cooling and rewarming. Baseline temperatures recorded from the pulmonary artery catheter before beginning "active cooling" were similar in both groups (TC, 35.0 +/- 0.2 degrees C vs. CC, 35.3 +/- 0.1 degrees C). We found no difference in the time to target temperature between TC and CC (TC, 178 +/- 25 min vs. CC, 142 +/- 21 min). One patient had some arrhythmias on cooling in the convective group, but her preoperative condition may have been responsible. In conclusion, cooling by convection appears to be a safe alternative to conduction cooling.

Effect of intraarterial papaverine on cerebral circulation time

PURPOSE

To measure the mean cerebral circulation time (CCT) in patients with symptomatic vasospasm stemming from subarachnoid hemorrhage and to determine any change after papaverine treatment.

METHODS

We studied 27 patients who received intraarterial papaverine from November 1992 to August 1995 to determine the CCT in 59 carotid territories. CCT was measured from the first image in which contrast was seen above the supraclinoid internal carotid artery to the peak filling of parietal cortical veins. Angiograms at the time of presentation were examined in 19 of the 27 patients. A control population of 19 patients (30 carotid territories) was also studied.

RESULTS

The mean CCT on presentation was 6.8 seconds +/- 1.1. The prepapaverine mean CCT was 6.1 seconds +/- 1.2. The immediate postpapaverine mean CCT was 3.8 seconds +/- 0.8. CCT decreased in 58 of 59 territories treated with papaverine; the mean change was -35.7%. In eight of these patients, CCT rose on the following day to 6.1 seconds +/- 1.1. In the control group, mean CCT was 5.9 seconds +/- 0.8. The mean CCT in patients with subarachnoid hemorrhage was slightly prolonged on presentation relative to that in control subjects.

CONCLUSION

Intraarterial papaverine produces a consistent decrease in CCT in patients with vasospasm.

Effects of oxyhemoglobin on local and propagated vasodilatory responses induced by adenosine, adenosine diphosphate, and adenosine triphosphate in rat cerebral arterioles

After subarachnoid hemorrhage (SAH), cerebral arteries display impaired vasomotor control, resulting in decreased regional cerebral blood flow. Recently, propagation of vasomotor responses has been recognized as an important regulatory mechanism in microcirculation. In this study, the authors tested the hypothesis that oxyhemoglobin (OxyHb) inhibits the vasodilatory effect of chemical mediators such as adenosine and adenine nucleotides at a local and/or propagated site. Penetrating intracerebral arterioles were surgically isolated from the middle cerebral arteries of rat brains, cannulated, and observed videomicroscopically in an organ bath under an inverted microscope. The effects of 10(-5) M OxyHb on vasoactive responses to adenosine, adenosine diphosphate (ADP), and adenosine triphosphate (ATP) were examined. The drugs were extraluminally applied either to the bath (10(-10)-10(-3) M) or, using pressure microejection (pipette concentration 10(-2) M), locally. The ATP and ADP initially constricted and then significantly dilated the vessels after both extraluminal application and microapplication. Furthermore, local microstimulation by these drugs produced conducted vasodilation. Adenosine elicited significant vasodilation after both extraluminal and local stimulation. Again, conducted vasodilation was observed. The vasomotor responses that were induced by a maximum local stimulation corresponded in magnitude to those observed at bath concentrations of 10(-5) to 10(-4) M of the same drug. Pretreatment with OxyHb constricted arterioles to an average of 87% of control and blunted extraluminally induced dilation at low concentrations (10(-10)-10(-8)) of ATP and ADP, but did not affect vasodilation induced by 10(-4) M or greater concentrations of ATP, ADP, or adenosine. Although the local response to local microstimulation was unaltered, propagated vasodilation as a response to ATP, ADP, and adenosine was significantly attenuated by OxyHb. These findings indicate that vasodilatory propagation plays an important role in the regulation of brain microcirculation and that its impairment by OxyHb could, in part, explain the cerebral hypoperfusion that is observed after SAH.

Hospital resource utilization in the treatment of cerebral aneurysms

The authors reviewed clinical and financial data for all patients treated for nontraumatic subarachnoid hemorrhage (SAH) and unruptured cerebral aneurysms at their institution between June 1993 and December 1994. This study sought to identify specific areas of high resource utilization that may be amenable to reduction of expenditures without compromising quality of care. Detailed hospital financial data were correlated with clinical grade and course. Areas of high resource use were identified based on patient charges and category-specific loaded hospital cost. Patients were divided into four groups: Group 1, surgically treated unruptured aneurysms (28 patients); Group 2, acute SAH (42 patients); Group 3, SAH with vasospasm (32 patients); and Group 4, SAH with negative angiogram (10 patients). Total cost per patient (mean +/- standard deviation in thousands of U.S. dollars) was highest for Group 3 (38.4 +/- 21.3; vs. Group 1, 12.7 +/- 8.8; Group 2, 22.6 +/- 20.9; and Group 4, 25.0 +/- 33.5) and correlated with hospital length of stay, Hunt and Hess grade, and Fisher grade. Areas of highest hospital cost were not always reflected in patient charges. The three areas of highest cost accounted for 48.5% of the total cost and were: 1) intensive care unit (ICU) room (Group 1, 2.5 +/- 3.5; Group 2, 7.0 +/- 9.2; Group 3, 11.0 +/- 7.8; and Group 4, 7.9 +/- 14.1); 2) arteriography (Group 1, 1.7 +/- 1.2; Group 2, 2.1 +/- 1.5; Group 3, 4.1 +/- 2.1; and Group 4, 2.2 +/- 0.7); and 3) ICU medicosurgical supplies (Group 1, 1.7 +/- 0.8; Group 2, 2.0 +/- 1.5; Group 3, 3.7 +/- 1.7; and Group 4, 2.0 +/- 3.0). It is concluded that cost containment strategies should be based on cost rather than charge and novel approaches will be required to reduce the cost of treating patients with SAH. Such approaches might include preventing vasospasm, reducing ICU stay, selective use of arteriography, and reducing the cost of supplies.

Local and conducted vasomotor responses in isolated rat cerebral arterioles

We tested the hypothesis that conduction of vasomotor responses occurs in cannulated and isolated rat cerebral penetrating arterioles. Both at the site of stimulation (local) and 500-650 microns distant from it, we observed the diameter responses and time courses thereof to pressure-ejected vasoactive stimuli. ATP locally caused an initial constriction (response onset at 0.3 s, average diameter 85% of control at 450-ms pulse with a maximum at 1.6 s after stimulation) followed by a secondary dilation (111% at 7 s). Conducted vasodilation of 111% was observed over a distance of 520 microns. Prostaglandin F2 alpha (PGF2 alpha) constricted the vessels locally (80%) and caused conducted vasodilation (110%). For both ATP and PGF2 alpha the local constriction occurred simultaneously to the conducted vasodilation. Adenosine dilated the vessels (123%) but produced only inconsistent conducted vasodilation. Hydrogen ions initially constricted the vessels (88%) and then dilated them to 113%. Thus, although ATP and PGF2 alpha are strong promoters of conduction, adenosine and hydrogen ions are not. Paradoxically, ATP and PGF2 alpha caused conducted vasodilation even though the initial local response was a vasoconstriction, indicating that in cerebral arterioles conduction may be mediated through endothelial cell mechanisms rather than through smooth muscle cell communication.

Jugular bulb temperature: comparison with brain surface and core temperatures in neurosurgical patients during mild hypothermia

Blood temperature at the jugular bulb was monitored in 10 patients undergoing neurovascular procedures that used induced mild hypothermia, and its correlation with surface brain, core, and peripheral temperatures was determined. The study was motivated by the difficulty encountered in directly measuring global brain temperature and the poor correlations between various core and peripheral sites temperatures and brain temperature, particularly during deep hypothermia. Although not statistically significant, previous studies have suggested a trend toward higher brain temperatures. Temperatures from the jugular bulb (collected using a No. 5 French Swan-Ganz catheter) as well as from subdural, pulmonary artery, esophagus, tympanic membrane, and bladder sites were analyzed during three surgical conditions: prior to incision, with the dura open, and after closure of the dura. No complications related to placement of the jugular bulb catheter, induced hypothermia, or temperature monitoring were seen. The authors found that jugular bulb temperature was similar to pulmonary artery and esophageal temperatures; although prior to incision it tended to be higher than that found at the pulmonary artery, most commonly by 0.2 degrees C. Surface brain temperature was cooler than all other temperatures (p < 0.05), except that of the tympanic membrane, and was particularly sensitive to environmental variations. Finally, as has been shown by others, bladder temperature lagged substantially behind core temperatures particularly during rapid cooling and rewarming of the patient. In summary, monitoring of jugular bulb temperature is a feasible technique, and temperatures measured in the jugular bulb are similar to core temperatures.

Magnetic neurosurgery

Because of the complex shape of many brain structures, the ideal brain probe would be highly flexible and give the neurosurgeon the ability to independently and precisely control movement of the probe tip. A magnetic surgery system has been developed that implements this concept. Flexible brain probes with small permanent magnetic tips are placed on the brain surface through a small burr hole and then magnetically manipulated within the brain. Drive forces are produced by an array of six superconducting magnets suspended within a cryostatic helmet. They produce a maximum force of 3 times the threshold needed to move the probe through the parenchymal tissues at its normal speed of 1 mm/s. Computer-controlled magnetic impulses precisely direct the probe movement in any direction desired with movement accuracy of 0.47 mm in phantom gels. Probe position is monitored 3 times per second with orthogonally oriented microchannel plate X-ray systems, X-ray dose from a 3-hour simulated procedure is comparable to that of a chest X-ray. In vivo and in vitro feasibility studies have been carried out in dog and pig brains. Preclinical trials are planned for clinical applications including implantation of flexible brachytherapy threads.

Safety of hypertensive hypervolemic therapy with phenylephrine in the treatment of delayed ischemic deficits after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Hypertensive hypervolemic therapy has been shown to reverse delayed ischemic deficits after aneurysmal subarachnoid hemorrhage. Concern has been raised about systemic complications of therapy, including pulmonary edema and myocardial ischemia, especially when high doses of vasopressors are used. Patients in whom delayed ischemic deficits were treated with hypervolemia and phenylephrine were prospectively evaluated for signs of systemic toxicity.

METHODS

Twenty-four consecutive patients treated with hypertensive hypervolemic therapy after aneurysmal subarachnoid hemorrhage were studied. Sixty-seven percent had underlying cardiac disease, vascular disease, or hypertension. No patient was excluded because of age or preexisting cardiac disease. Patients were closely monitored for signs of congestive heart failure (physical examination, chest x-ray films, arterial blood gases, cardiac index, pulmonary artery wedge pressure, and oxygen requirement). Indicators of cardiac ischemia and other extracerebral toxicity that were monitored included cardiac enzymes, electrocardiograms, serum creatinine, electrolyte and lactic acid levels, gastrointestinal motility, and urine output.

RESULTS

Volume expansion and phenylephrine infusion produced an increase in several hemodynamic parameters including pulmonary artery wedge pressure, which rose 28% (13 +/- 3.6 to 16 +/- 1.9 mm Hg), mean arterial blood pressure, which rose 25% (99 +/- 12.5 to 123 +/- 11.4 mm Hg), and systemic vascular resistance, which rose 46% (1234 +/- 294 to 1739 +/- 315 dyne.s-1.cm-5); however, there was no change in cardiac index (3.9 +/- 0.9 to 4.0 +/- 0.6 L.min-1.m-2). There were no clinically significant episodes of pulmonary edema requiring a change in vasopressor therapy and no myocardial infarctions. Phenylephrine was stopped in only one patient (incidence, 4%; 95% confidence interval, 0% to 12%), who developed an exacerbation of his preexisting bradycardia. There was no evidence of noncardiac organ system toxicity. Eighty-eight percent of the patients exhibited neurological improvement.

CONCLUSIONS

Hypertensive hypervolemic therapy with the use of high-dose phenylephrine can be administered with acceptable systemic toxicity, even in patients with previous cardiac disease, provided that close monitoring is performed. To minimize risk, aggressive treatment should probably be reserved for patients with signs of delayed ischemia rather than administered prophylactically.

Severe thrombocytopenia following intraarterial papaverine administration for treatment of vasospasm

Selective intraarterial infusion of papaverine is used in the treatment of symptomatic cerebral vasospasm. The authors report two episodes of severe thrombocytopenia in a patient that were related to intraarterial administration of papaverine. A 70-year-old man with a right internal carotid artery aneurysm underwent craniotomy and aneurysm clipping. He became lethargic 8 days after the hemorrhage occurred. Cerebral angiography revealed moderate vasospasm. In addition to hypervolemic-hypertensive therapy, the patient was treated on two occasions with intraarterial administration of papaverine. Within 24 hours of both treatments he developed severe thrombocytopenia. On one occasion epistaxis requiring transfusion of blood products occurred. Laboratory data support the diagnosis of immune-mediated papaverine-induced thrombocytopenia. The authors conclude that intraarterial administration of papaverine for treatment of vasospasm can be associated with severe, rapidly reversible thrombocytopenia.

Endovascular treatment of epistaxis in a patient with tuberculosis and a giant petrous carotid pseudoaneurysm

A 31-year-old man with pulmonary tuberculosis who did not have human immunodeficiency virus had massive epistaxis from a giant petrous internal carotid artery pseudoaneurysm. Endovascular trapping of the aneurysm was performed, curing the epistaxis. MR showed multiple enhancing brain lesions that resolved with additional antituberculous drug therapy.

Intraoperative digital subtraction angiography: a review of 112 consecutive examinations

PURPOSE

To examine the effect of intraoperative angiography on neurosurgery and angiographic technical success, safety, and accuracy.

METHODS

Angiographic studies, surgical reports, and hospital records were reviewed retrospectively for 112 consecutive procedures in which intraoperative angiography was performed during neurosurgery. The results of conventional postoperative angiograms in 28 of the 112 procedures were also reviewed. A portable digital subtraction angiography unit was used for all patients. Decisions in the operating room were based on review of stored videotaped images.

RESULTS

Eighteen studies were obtained in 14 patients after arteriovenous malformation resection. Unsuspected residual nidus was identified and resected in 3 patients. The intraoperative angiogram also altered therapy for 2 patients undergoing staged resections of arteriovenous malformations. Sixty-six studies were performed after aneurysm clipping, with clinically significant changes in surgical therapy made in 5 patients. Of 28 examinations after carotid endarterectomy, 3 led to revision. Two complications of angiography occurred. One led to a permanent neurologic deficit, yielding a complication rate of 1.5% for stroke. Two examinations could not be completed because of technical factors. Two false-negative examinations were identified on postoperative studies. One patient with a normal intraoperative study after carotid endarterectomy thrombosed the repaired internal carotid artery after surgery.

CONCLUSIONS

Intraoperative angiography altered surgery in 13 of 112 procedures on 104 patients. This study supports the use of intraoperative angiography in arteriovenous malformation resection and in complex aneurysm surgery, but not for routine carotid endarterectomy.

Polyvinyl alcohol particle size and suspension characteristics

PURPOSE

To evaluate the size and shape of commercially available polyvinyl alcohol (PVA) particles and to determine whether they change in size when suspended in nonionic contrast and in a solution of nonionic contrast and absolute alcohol.

METHODS

The two-dimensional area and the long and short axis of PVA particles from several different vendors were measured using a light microscope attached to a video system and an image-processing software program. Particles were measured as packaged (dry or suspended in saline), suspended in ioversol, and suspended in ioversol containing 30% alcohol.

RESULTS

All brands of dry particles had similar microscopic appearances. The saline-suspended particles had fewer and finer perforations. After suspension in contrast, all sizes and brands of dry particles significantly increased in size. The particles packaged in saline did not expand. The addition of alcohol to the contrast did not consistently change particle size. Particle aggregation was similar in both contrast suspensions for all groups of particles. Particles less than 50 microns in size were rarely observed in any PVA preparation after suspension.

CONCLUSIONS

The three dry PVA preparations seem to be similar. All increase significantly in size when suspended in nonionic contrast or contrast-alcohol solutions. The saline-packaged PVA particles were different from the dry variety and did not enlarge in contrast or contrast-alcohol solutions. Alcohol did not change the size or suspension characteristics of PVA particles. Particles less than 50 microns in size were rarely identified.

Nitric oxide regulates cerebral arteriolar tone in rats

BACKGROUND AND PURPOSE

Although cerebral penetrating arterioles are main regulators of the brain microcirculation, little is known about the effect of endothelium-derived relaxation factor on these vessels. This study examined the effects of nitric oxide synthase inhibitors on the spontaneous tone of isolated rat cerebral arterioles.

METHODS

Intraparenchymal penetrating arterioles (53 to 102 microns in passive diameter) isolated from Sprague-Dawley rats were cannulated with glass pipettes and subjected to 60 mm Hg of intraluminal pressure. The diameter response to intraluminal and extraluminal treatments was observed with an inverted microscope.

RESULTS

Extraluminal application of Nw-nitro-L-arginine (10(-5) mol/L) contracted the arterioles to 63.9 +/- 2.8% (P < .05) of the control diameter. This contracting effect was stereospecific and easily reversed by L-arginine dose dependently (10(-3), 10(-2) mol/L) but not by D-arginine. Intraluminally applied Nw-nitro-L-arginine also induced a similar degree of contraction. Another nitric oxide synthase inhibitor, NG-monomethyl L-arginine (10(-5), 10(-4) mol/L), applied extraluminally induced a dose-dependent contraction to 77.5 +/- 6.6% and 68.6 +/- 5.4% of the control (P < .05), which was also reversed by L-arginine. L-Arginine alone did not significantly affect vessel diameter, however. Treatment with indomethacin, a cyclooxygenase inhibitor, dilated the vessel to 115.2 +/- 7% (P < .05) but did not change the constricting effect of Nw-nitro-L-arginine.

CONCLUSIONS

Nw-Nitro-L-arginine and NG-monomethyl L-arginine produce substantial contraction in isolated brain arterioles, suggesting that nitric oxide of brain arterioles is continuously produced within the vessel wall. The dilatory effect of indomethacin appears to be independent of the vasoconstriction induced by nitric oxide synthase inhibitor. In these vessels, the effect of nitric oxide synthase inhibitors is not mediated by an indomethacin-sensitive mechanism. A balance probably exists between factors tending to constrict these arterioles and the elaboration of nitric oxide from endothelial cells, which tends to dilate them. The production of nitric oxide from isolated vessels indicates that parenchymal and vessel wall sources of nitric oxide are probably important in brain microcirculatory regulation.