Noninvasive cardiac output monitor to quantify hydration status in ischemic stroke patients: A feasibility study

BACKGROUND

Individuals who are dehydrated, volume contracted or both at the time of hospitalization for acute ischemic stroke have worse clinical outcomes than do individuals with optimal volume status. Currently, there is no gold standard method for measuring hydration status, except indirect markers of a volume contracted state (VCS) including elevated blood urea nitrogen (BUN)/creatinine ratio. We sought to test the feasibility and acceptability of a non-invasive cardiac output monitor (NICOM) for the measurement of hydration status in a group of hospitalized ischemic stroke patients, and explore the relationship with a common indirect laboratory-based measure of VCS.

METHODS

We performed a prospective observational feasibility study of hospitalized acute ischemic stroke patients. We collected hemodynamic parameters using the NICOM device before and after fluid auto-bolus via passive leg raise and BUN/creatinine ratio. Successful acquisition of relevant hemodynamic data was the primary objective of this study. We explored agreement between the NICOM results and BUN/creatinine ratio using Cohen's kappa statistic.

RESULTS

Thirty patients hospitalized with acute ischemic stroke were enrolled. We found that 29/30 patients tolerated assessment with NICOM. Hemodynamic data were collected in all 30 patients. Data capture took an average of 10 min(SD ± 112 s). Agreement between NICOM and BUN/creatinine ratio was 70%; (expected agreement 51%; kappa 0.38). Agreement was stronger in the cohort without history of diabetes (81% agreement, kappa 0.61).

CONCLUSIONS

NICOM assessment was feasible in hospitalized stroke patients. The identification of an objective, real-time measure of hydration status would be clinically useful, and could allow precise, goal-directed care.

Effect of Early vs Standard Approach to Tracheostomy on Functional Outcome at 6 Months Among Patients With Severe Stroke Receiving Mechanical Ventilation: The SETPOINT2 Randomized Clinical Trial

IMPORTANCE

Many patients with severe stroke have impaired airway protective reflexes, resulting in prolonged invasive mechanical ventilation.

OBJECTIVE

To test whether early vs standard tracheostomy improved functional outcome among patients with stroke receiving mechanical ventilation.

DESIGN, SETTING, AND PARTICIPANTS

In this randomized clinical trial, 382 patients with severe acute ischemic or hemorrhagic stroke receiving invasive ventilation were randomly assigned (1:1) to early tracheostomy (≤5 days of intubation) or ongoing ventilator weaning with standard tracheostomy if needed from day 10. Patients were randomized between July 28, 2015, and January 24, 2020, at 26 US and German neurocritical care centers. The final date of follow-up was August 9, 2020.

INTERVENTIONS

Patients were assigned to an early tracheostomy strategy (n = 188) or to a standard tracheostomy (control group) strategy (n = 194).

MAIN OUTCOMES AND MEASURES

The primary outcome was functional outcome at 6 months, based on the modified Rankin Scale score (range, 0 [best] to 6 [worst]) dichotomized to a score of 0 (no disability) to 4 (moderately severe disability) vs 5 (severe disability) or 6 (death).

RESULTS

Among 382 patients randomized (median age, 59 years; 49.8% women), 366 (95.8%) completed the trial with available follow-up data on the primary outcome (177 patients [94.1%] in the early group; 189 patients [97.4%] in the standard group). A tracheostomy (predominantly percutaneously) was performed in 95.2% of the early tracheostomy group in a median of 4 days after intubation (IQR, 3-4 days) and in 67% of the control group in a median of 11 days after intubation (IQR, 10-12 days). The proportion without severe disability (modified Rankin Scale score, 0-4) at 6 months was not significantly different in the early tracheostomy vs the control group (43.5% vs 47.1%; difference, -3.6% [95% CI, -14.3% to 7.2%]; adjusted odds ratio, 0.93 [95% CI, 0.60-1.42]; P = .73). Of the serious adverse events, 5.0% (6 of 121 reported events) in the early tracheostomy group vs 3.4% (4 of 118 reported events) were related to tracheostomy.

CONCLUSIONS AND RELEVANCE

Among patients with severe stroke receiving mechanical ventilation, a strategy of early tracheostomy, compared with a standard approach to tracheostomy, did not significantly improve the rate of survival without severe disability at 6 months. However, the wide confidence intervals around the effect estimate may include a clinically important difference, so a clinically relevant benefit or harm from a strategy of early tracheostomy cannot be excluded.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02377167.

Hemoglobin concentrations and RBC transfusion thresholds in patients with acute brain injury: an international survey

Background

The optimal hemoglobin (Hb) threshold at which to initiate red blood cell (RBC) transfusion in patients with acute brain injury is unknown. The aim of this survey was to investigate RBC transfusion practices used with these patients.

Methods

We conducted a web-based survey within various societies of critical care medicine for intensive care unit (ICU) physicians who currently manage patients with primary acute brain injury.

Results

A total of 868 responses were obtained from around the world, half of which (n = 485) were from European centers; 204 (24%) respondents had a specific certificate in neurocritical care, and most were specialists in anesthesiology or intensive care and had less than 15 years of practice experience. Four hundred sixty-six respondents (54%) said they used an Hb threshold of 7–8 g/dl to initiate RBC transfusion after acute brain injury, although half of these respondents used a different threshold (closer to 9 g/dl) in patients with traumatic brain injury, subarachnoid hemorrhage, or ischemic stroke. Systemic and cerebral factors were reported as influencing the need for higher Hb thresholds. Most respondents agreed that a randomized clinical trial was needed to compare two different Hb thresholds for RBC transfusion, particularly in patients with traumatic brain injury, subarachnoid hemorrhage, and ischemic stroke.

Conclusions

The Hb threshold used for RBC transfusion after acute brain injury was less than 8 g/dl in half of the ICU clinicians who responded to our survey. However, more than 50% of these physicians used higher Hb thresholds in certain conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1748-4) contains supplementary material, which is available to authorized users.

Practice guideline summary: Reducing brain injury following cardiopulmonary resuscitation: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology

OBJECTIVE

To assess the evidence and make evidence-based recommendations for acute interventions to reduce brain injury in adult patients who are comatose after successful cardiopulmonary resuscitation.

METHODS

Published literature from 1966 to August 29, 2016, was reviewed with evidence-based classification of relevant articles.

RESULTS AND RECOMMENDATIONS

For patients who are comatose in whom the initial cardiac rhythm is either pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF) after out-of-hospital cardiac arrest (OHCA), therapeutic hypothermia (TH; 32-34°C for 24 hours) is highly likely to be effective in improving functional neurologic outcome and survival compared with non-TH and should be offered (Level A). For patients who are comatose in whom the initial cardiac rhythm is either VT/VF or asystole/pulseless electrical activity (PEA) after OHCA, targeted temperature management (36°C for 24 hours, followed by 8 hours of rewarming to 37°C, and temperature maintenance below 37.5°C until 72 hours) is likely as effective as TH and is an acceptable alternative (Level B). For patients who are comatose with an initial rhythm of PEA/asystole, TH possibly improves survival and functional neurologic outcome at discharge vs standard care and may be offered (Level C). Prehospital cooling as an adjunct to TH is highly likely to be ineffective in further improving neurologic outcome and survival and should not be offered (Level A). Other pharmacologic and nonpharmacologic strategies (applied with or without concomitant TH) are also reviewed.

Multimodal MRI characterization of experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is associated with significant morbidity and mortality. We implemented an in-scanner rat model of mild SAH in which blood or vehicle was injected into the cistern magna, and applied multimodal MRI to study the brain prior to, immediately after (5min to 4h), and upto 7days after SAH. Vehicle injection did not change arterial lumen diameter, apparent diffusion coefficient (ADC), T2, venous signal, vascular reactivity to hypercapnia, or foot-fault scores, but mildly reduce cerebral blood flow (CBF) up to 4h, and open-field activity up to 7days post injection. By contrast, blood injection caused: (i) vasospasm 30min after SAH but not thereafter, (ii) venous abnormalities at 3h and 2days, delayed relative to vasospasm, (iii) reduced basal CBF and to hypercapnia 1-4h but not thereafter, (iv) reduced ADC immediately after SAH but no ADC and T2 changes on days 2 and 7, and (v) reduced open-field activities in both SAH and vehicle animals, but no significant differences in open-field activities and foot-fault tests between groups. Mild SAH exhibited transient and mild hemodynamic disturbances and diffusion changes, but did not show apparent ischemic brain injury nor functional deficits.

Early tracheostomy in ventilated stroke patients: Study protocol of the international multicentre randomized trial SETPOINT2 (Stroke-related Early Tracheostomy vs. Prolonged Orotracheal Intubation in Neurocritical care Trial 2)

BACKGROUND

Tracheostomy is a common procedure in long-term ventilated critical care patients and frequently necessary in those with severe stroke. The optimal timing for tracheostomy is still unknown, and it is controversial whether early tracheostomy impacts upon functional outcome.

METHOD

The Stroke-related Early Tracheostomy vs. Prolonged Orotracheal Intubation in Neurocritical care Trial 2 (SETPOINT2) is a multicentre, prospective, randomized, open-blinded endpoint (PROBE-design) trial. Patients with acute ischemic stroke, intracerebral hemorrhage or subarachnoid hemorrhage who are so severely affected that two weeks of ventilation are presumed necessary based on a prediction score are eligible. It is intended to enroll 190 patients per group (n = 380). Patients are randomized to either percutaneous tracheostomy within the first five days after intubation or to ongoing orotracheal intubation with consecutive weaning and extubation and, if the latter failed, to percutaneous tracheostomy from day 10 after intubation. The primary endpoint is functional outcome defined by the modified Rankin Scale (mRS, 0-4 (favorable) vs. 5 + 6 (unfavorable)) after six months; secondary endpoints are mortality and cause of mortality during intensive care unit-stay and within six months from admission, intensive care unit-length of stay, duration of sedation, duration of ventilation and weaning, timing and reasons for withdrawal of life support measures, relevant intracranial pressure rises before and after tracheostomy.

CONCLUSION

The necessity and optimal timing of tracheostomy in ventilated stroke patients need to be identified. SETPOINT2 should clarify whether benefits in functional outcome can be achieved by early tracheostomy in these patients.

The neurocritical care research network: NCRN

Neurocritical care diseases carry a high morbidity and mortality. Therapeutic and technological advances in neurocritical care have greatly improved the outcome of a variety of life-threatening disorders including traumatic brain injury, acute ischemic stroke, intracerebral and subarachnoid hemorrhage, and anoxic injury following cardiac arrest. These advances have stemmed from a better understanding of the physiology of neurocritical care illnesses, improved neuromonitoring techniques, and the introduction of more efficacious treatments. Despite all the advances in neuromonitoring, diagnostic imaging, and emerging treatments, much research needs to be undertaken in neurocritical care. Many of the clinical trials carried out in the general critical care population have excluded neurocritical care patients. For instance, the landmark ARDSNET trial that demonstrated the beneficial effects of low tidal volume ventilation in patients with ARDS cannot be directly applied to neurocritical care patients who frequently may experience this pulmonary complication. There is a need for a more cohesive and integrated research system or network to establish a track record for high-quality, investigator-initiated clinical research in neurocritical care. Such a system may help us overcome potential impediments to the future advancement of neurocritical care research. We propose the creation of the neurocritical care research network. The mission of the Network is to facilitate multicenter and multidisciplinary collaboration and patient enrollment in clinical trials of specific neurocritical care diseases.

Research priorities in neurocritical care

This summary of the last session of the First Neurocritical Care Research Conference reviews the discussions about research priorities in neurocritical care. The first presentation reviewed current projects funded by the National Institute of Neurological Disorders and Stroke at the National Institutes of Health and potential models to follow including an independent Neurocritical Care Network or the creation of such a network with the goal of collaborating with already existing ones. Experienced neurointensivists then presented their views on the most common and important research questions that need to be answered and investigated in the field. Finally, utility of clinical registries was discussed emphasizing their importance as hypothesis generators. During the group discussion, interests in comparative effectiveness research, the use of physiological endpoints from monitoring and alternate trial design were expressed.

Research and technology in neurocritical care

The daily practice of neurointensivists focuses on the recognition of subtle changes in the neurological examination, interactions between the brain and systemic derangements, and brain physiology. Common alterations such as fever, hyperglycemia, and hypotension have different consequences in patients with brain insults compared with patients of general medical illness. Various technologies have become available or are currently being developed. The session on "research and technology" of the first neurocritical care research conference held in Houston in September of 2009 was devoted to the discussion of the current status, and the research role of state-of-the art technologies in neurocritical patients including multi-modality neuromonitoring, biomarkers, neuroimaging, and "omics" research (proteomix, genomics, and metabolomics). We have summarized the topics discussed in this session. We have provided a brief overview of the current status of these technologies, and put forward recommendations for future research applications in the field of neurocritical care.

Acute motor-sensory axonal neuropathy associated with active systemic lupus erythematosus and anticardiolipin antibodies

Acute motor-sensory axonal neuropathy (AMSAN) is an axonal variant of Guillian-Barré syndrome (GBS) that presents with acute ascending quadriparesis. This has generally been described in association with Campylobacter jejuni infections or with anti-ganglioside antibodies. Known cases have shown a slow recovery and a poor prognosis. We report a case with clinical and electrophysiological evidence of AMSAN in association with active systemic lupus erythematosus (SLE) and anticardiolipin antibodies but not the other associations, with a rapid response to combination immunosuppressant and intravenous immunoglobulin (IVIg) therapy. The association between AMSAN and SLE has not been previously described. This case illustrates that early recognition and the utilization of electrophysiologic techniques may be beneficial in the diagnosis and management of GBS associated with SLE. Fulminant or rapidly progressive cases should be managed in specialized intensive care units. Combination therapy of immunosuppressants and IVIg may be beneficial in non-vasculitic axonal radiculo-neuropathies associated with SLE, resulting in good outcomes.

Hypertonic saline for cerebral edema and elevated intracranial pressure

The use of HS solutions has been shown to reduce ICP both in animal models and in human studies in a variety of underlying disorders, even in cases refractory to treatment with hyperventilation and mannitol. There are several possible mechanisms of action, and important complications such as central pontine myelinolysis and intracranial hemorrhage have not been reported in the human studies. Different types of HS solutions with different methods of infusion (bolus and continuous) have been used in the past, and so far there are not enough data to recommend one concentration over another. Many issues remain to be clarified, including the exact mechanism of action of HS, the best mode of administration and HS concentration to be given, and the relative efficacy of HS vis-à-vis available treatments, particularly mannitol.

Hypertonic saline for cerebral edema

Raised intracranial pressure (ICP) is a major contributor to the mortality of many conditions encountered in a neurologic intensive care unit. Achieving a sustained reduction in ICP in patients with intracranial hypertension remains a challenge. Treatment with hyperosmolar agents is one of the few options that are available, and mannitol is currently the most commonly used agent. However, hypertonic saline solutions have recently emerged as a potentially safer and more efficacious alternative to mannitol.

Ketamine for refractory status epilepticus: a case of possible ketamine-induced neurotoxicity

A 44-year-old man with treated neurosyphilis presented with subclinical status epilepticus (SE) refractory to intravenous high-dose lorazepam, phenytoin, and valproic acid over 4 days. Ketamine infusion was instituted after low-dose propofol sedation with gradual control of electrographic seizures over 72h. Reevaluation 3 months later revealed diffuse cerebellar and worsened cerebral atrophy, consistent with animal models of N-methyl-D-aspartate antagonist-mediated neurotoxicity. Animal studies of prolonged ketamine therapy are required before widespread human use in SE.

Thrombolytic therapy for acute extra-cranial artery dissection: report of two cases

Extra-cranial arterial dissection accounts for 10% of strokes in young people. Information on safety of thrombolytic administration in this group is limited. The literature, however, does not favor use of thrombolytics for myocardial ischemia when peripheral arterial dissection coexists. Based on the clinical and radiological features, two patients who presented with acute stroke secondary to arterial dissection were considered for thrombolysis. One of them received intra-venous recombinant tissue plasminogen activator (rtPA), and the other patient received intra-arterial rtPA. There were no post thrombolysis complications. This report supports feasibility of administering thrombolytics in acute ischemic strokes resulting from extra-cranial arterial dissection. Future larger studies are necessary to determine the efficacy, safety and long-term outcome in this patient population.

Risk factors for subarachnoid hemorrhage

OBJECTIVE

Cigarette smoking has been demonstrated to increase the risk of subarachnoid hemorrhage (SAH). Whether cessation of smoking decreases this risk remains unclear. We performed a case-control study to examine the effect of smoking and other known risk factors for cerebrovascular disease on the risk of SAH.

METHODS

We reviewed the medical records of all patients with a diagnosis of SAH (n = 323) admitted to Johns Hopkins Hospital between January 1990 and June 1997. Controls matched for age, sex, and ethnicity (n = 969) were selected from a nationally representative sample of the Third National Health and Nutrition Examination Survey. We determined the independent association between smoking (current and previous) and various cerebrovascular risk factors and SAH by use of multivariate logistic regression analysis. A separate analysis was performed to determine associated risk factors for aneurysmal SAH.

RESULTS

Of 323 patients admitted with SAH (mean age, 52.7+/-14 yr; 93 were men), 173 (54%) were hypertensive, 149 (46%) were currently smoking, and 125 (39%) were previous smokers. In the multivariate analysis, both previous smoking (odds ratio [OR], 4.5; 95% confidence interval [CI], 3.1-6.5) and current smoking (OR, 5.2; 95% CI, 3.6-7.5) were significantly associated with SAH. Hypertension was also significantly associated with SAH (OR, 2.4; 95% CI, 1.8-3.1). The risk factors for 290 patients with aneurysmal SAH were similar and included hypertension (OR, 2.4; 95% CI, 1.8-3.2), previous smoking (OR, 4.1; 95% CI, 2.7-6.0), and current smoking (OR, 5.4; 95% CI, 3.7-7.8).

CONCLUSION

Hypertension and cigarette smoking increase the risk for development of SAH, as found in previous studies. However, the increased risk persists even after cessation of cigarette smoking, which suggests the importance of early abstinence from smoking.

Safety of intra-arterial thrombolysis in the postoperative period

BACKGROUND AND PURPOSE

Limited systemic fibrinolysis and reduced dosage are features of intra-arterial thrombolyis (IAT) that may be advantageous in the treatment of postoperative strokes. However, IAT may increase the risk of surgical bleeding. We sought to determine the safety of postoperative IAT.

METHODS

This was a retrospective case series from 6 university hospitals. All cases of IAT within 2 weeks of surgery were identified. Demographics, stroke mechanism, stroke severity, imaging and angiographic findings, time between surgery and lysis, thrombolytic agent used, surgical site bleeding, intracranial bleeding, and mortality rates were determined. Death or complications directly related to IAT were determined.

RESULTS

Thirty-six patients (median age, 71.5 years; range, 45 to 85) were identified. Median time from surgery to stroke was 21.5 hours (range, 1 to 120). Open heart surgery was done in 18 (50%), carotid endarterectomy in 6 (17%), craniotomy in 3 (8%), ophthalmologic-ear, nose and throat surgery in 2 (6%), urologic-gynecologic surgery in 4 (11%), orthopedic surgery in 2 (6%), and plastic surgery in 1 (3%). The stroke causes were cardioembolism in 24 (67%), large-vessel atherosclerosis in 4 (11%), dissection in 3 (8%), postendarterectomy occlusion in 4 (11%), and radiation arteriopathy in 1 (3%). Median time to angiogram was 2.5 hours (0.1 to 5.5). Occlusion sites were M1 in 19 (53%), M2 in 9 (25%), internal carotid artery in 5 (14%), basilar artery in 2 (6%), and posterior communicating artery in 1 (3%). Thrombolysis was completed at a median of 4.5 hours (range, 1 to 8.0). Tissue plasminogen activator was used in 19 (53%) and urokinase in 17 (47%). Nine (26%) patients died. Surgical site bleeding occurred in 9 (25%) cases (minor in 6, major in 3). The major surgical bleeds were 2 post-craniotomy intracranial hemorrhages and 1 hemopericardium after coronary artery bypass grafting; all were fatal. Six deaths were non-IAT related: 3 caused by cerebral edema and 3 by systemic causes. Major bleeding complications were significantly more common among patients with craniotomy (P<0.02).

CONCLUSIONS

Postoperative IAT carries a risk of bleeding in up to 25% of patients but is usually minor surgical site bleeding. Avoiding IAT in intracranial surgery patients may reduce complications. Mortality rate in this series was similar to that reported in prior IAT trials. IAT remains a viable therapeutic option for postoperative strokes.

Benefits of perfusion MR imaging relative to diffusion MR imaging in the diagnosis and treatment of hyperacute stroke

BACKGROUND AND PURPOSE

The development of thrombolytic agents for use with compromised cerebral blood flow has made it critical to quickly identify those patients to best treat. We hypothesized that combined diffusion and perfusion MR imaging adds vital diagnostic value for patients for whom the greatest potential benefits exist and far exceeds the diagnostic value of diffusion MR imaging alone.

METHODS

The cases of patients with neurologic symptoms of acute ischemic stroke who underwent ultra-fast emergent MR imaging within 6 hours were reviewed. In all cases, automatic processing yielded isotropic diffusion images and perfusion time-to-peak maps. Images with large vessel distribution ischemia and with mismatched perfusion abnormalities were correlated with patient records. All follow-up images were reviewed and compared with outcomes resulting from hyperacute therapies.

RESULTS

For 16 (26%) of 62 patients, hypoperfusion was the best MR imaging evidence of disease distribution, and for 15 of the 16, hypoperfusion (not abnormal diffusion) comprised the only imaging evidence for disease involving large vessels. For seven patients, diffusion imaging findings were entirely normal, and for nine, diffusion imaging delineated abnormal signal in either small vessel distributions or in a notably smaller cortical branch in one case. In all cases, perfusion maps were predictive of eventual lesions, as confirmed by angiography, CT, or subsequent MR imaging.

CONCLUSION

If only diffusion MR imaging is used in assessing patients with hyperacute stroke, nearly one quarter of the cases may be incorrectly categorized with respect to the distribution of ischemic at-risk tissue. Addition of perfusion information further enables better categorizing of vascular distribution to allow the best selection among therapeutic options and to improve patient outcomes.

Use of hypertonic saline solutions in treatment of cerebral edema and intracranial hypertension

OBJECTIVES

To review the literature on the use of hypertonic saline (HS) in treating cerebral edema and intracranial hypertension.

DATA SOURCES

Review of scientific and clinical literature retrieved from a computerized MEDLINE search from January 1965 through November 1999.

STUDY SELECTION

Pertinent literature is referenced, including clinical and laboratory investigations, to demonstrate principles and efficacy of treatment with HS in patients with intracranial space-occupying pathology.

DATA EXTRACTION

The literature was reviewed to summarize the mechanisms of action, efficacy, adverse effects, systemic effects, and comparisons with standard treatments in both clinical and laboratory settings.

DATA SYNTHESIS

HS has an osmotic effect on the brain because of its high tonicity and ability to effectively remain outside the bloodbrain barrier. Numerous animal studies have suggested that fluid resuscitation with HS bolus after hemorrhagic shock prevents the intracranial pressure (ICP) increase that follows resuscitation with standard fluids. There may be a minimal benefit in restoring cerebral blood flow, which is thought to be mitigated through local effects of HS on cerebral microvasculature. In animal models with cerebral injury, the maximum benefit is observed in animals with focal injury associated with vasogenic edema (cryogenic injury). The ICP reduction is seen for < or =2 hrs and may be maintained for longer periods by using a continuous infusion of HS. The ICP reduction is thought to be caused by a reduction in water content in areas of the brain with intact blood-brain barrier such as the nonlesioned hemisphere and cerebellum. Most comparisons with mannitol suggest almost equal efficacy in reducing ICP, but there is a suggestion that mannitol may have a longer duration of action. Human studies published to date reporting on the use of HS in treating cerebral edema and elevated ICP include case reports, case series, and small controlled trials. Results from studies directly comparing HS with standard treatment in regard to safety and efficacy are inconclusive. However, the low frequency of side effects and a definite reduction of ICP observed with use of HS in these studies are very promising. Systemic effects include transient volume expansion, natriuresis, hemodilution, immunomodulation, and improved pulmonary gas exchange. Adverse effects include electrolyte abnormalities, cardiac failure, bleeding diathesis, and phlebitis. Although unproven, a potential for central pontine myelinolysis and rebound intracranial hypertension exists with uncontrolled administration.

CONCLUSIONS

HS demonstrates a favorable effect on both systemic hemodynamics and intracranial pressure in both laboratory and clinical settings. Preliminary evidence supports the need for controlled clinical trials evaluating its use as resuscitative fluid in brain-injured patients with hemorrhagic shock, as therapy for intracranial hypertension resistant to standard therapy, as firstline therapy for intracranial hypertension in certain intracranial pathologies, as small volume fluid resuscitation during spinal shock, and as maintenance intravenous fluid in neurocritical care units.

Long-term outcome after medical reversal of transtentorial herniation in patients with supratentorial mass lesions

OBJECTIVE

To determine the short- and long-term outcomes after successful reversal of transtentorial herniation by medical treatment. Although it has been recognized that aggressive medical management can reverse transtentorial herniation, it is believed that overall outcome in such patients is poor.

DESIGN

Prospective cohort study.

SETTING

Neurocritical care unit of a university hospital.

PATIENTS

A total of 28 consecutive patients who underwent an episode of transtentorial herniation (defined as decrease in level of consciousness accompanied by pupillary dilation) secondary to a supratentorial mass lesion followed by successful reversal.

INTERVENTION

Herniation was reversed by using a combination of hyperventilation, mannitol and hypertonic saline.

MEASUREMENTS AND MAIN RESULTS

The following outcomes were analyzed: risk of second herniation, radiologic evidence of structural damage or vascular compromise related to herniation on post-herniation computed tomographic scan, in-hospital mortality, and long-term functional outcome using Rankin score and Barthel index. A total of 32 episodes of transtentorial herniations were reversed in 28 patients during a 14-month period. The most common precipitating cause were edema (n = 23) or new/expanding intracerebral hematoma (n = 5). After first reversal of transtentorial herniation in 28 patients, a second herniation episode was observed in 16 patients after a mean interval of 88.2 hrs (range, 23-432 hrs); four were successfully reversed. On follow-up computed tomographic scan, hypodense lesion in midbrain (n = 6), temporal lobe contusion (n = 2), posterior cerebral artery (n = 3), and middle cerebral artery (n = 1) infarction were visualized in a minority of patients. The in-hospital mortality was 60% (n = 15) with brain death being the cause of death in 13 patients; care was withdrawn in eight patients. Second episode of herniation (p = .002) and midbrain involvement during herniation (p = .02) were associated with in-hospital mortality. During a mean follow-up period of 11.4+/-4.2 months, two patients died of cerebral neoplasm and human immunodeficiency virus-related sepsis, respectively. Of the 11 survivors, 7 were functionally independent (Rankin score <3 and Barthel index >60).

CONCLUSIONS

Although mortality after transtentorial herniation is high, we found a prominent potential for meaningful recovery with aggressive medical reversal of transtentorial herniation. Our study implies that timely medical intervention for reversing transtentorial herniation can result in preservation of neurologic function.

Prediction and timing of tracheostomy in patients with infratentorial lesions requiring mechanical ventilatory support

OBJECTIVES

To determine the frequency and predictors of successful extubations and tracheostomy in patients with infratentorial lesions requiring mechanical ventilation and to determine the optimal time for tracheostomy based on probability of successful extubation and in-hospital survival according to the duration of translaryngeal intubation.

DESIGN

Retrospective chart review.

SETTINGS

A neurocritical care unit at a university hospital.

PATIENTS

A total of 69 patients with infratentorial lesions who were mechanically ventilated during their intensive care unit stay.

MEASUREMENTS AND MAIN RESULTS

Of the 69 patients who were mechanically ventilated, 23 (33%) were successfully extubated. In logistic regression analysis, both the presence of a Glasgow Coma Scale score >7 at time of intubation (odds ratio, 4.8; 95% confidence interval, 1.2-21.7) and the absence of brainstem deficits (odds ratio, 4.3; 95% confidence interval, 1.3-16.7), were independently associated with successful extubation. After extubation, 11 patients were reintubated; seven were reintubated within the same day because of poor control over secretions, airway spasm, or hypoventilation. Tracheostomy was performed in 23 (33%) patients, of whom 19 were successfully weaned off mechanical ventilatory support over a mean period of 3.7+/-4.0 days after tracheostomy. Patients undergoing tracheostomy had a significantly longer intensive care unit stay (19.1+/-9.0 vs. 8.7+/-6.6 days, p < .01) and total hospital stay (34.8+/-18.7 vs. 20.1+/-9.9 days, p < .01) compared with patients who were successfully extubated. The probability of successful extubation or death before extubation or tracheostomy was 67% on the day of intubation, which decreased to 5.8% after translaryngeal intubation for >8 days.

CONCLUSIONS

An aggressive policy toward tracheostomy is justified based on the low frequency of successful extubations and high frequency of extubation failures and tracheostomies in patients with infratentorial lesions. The decision regarding tracheostomy should be made on day 8 of mechanical ventilatory support because of the low probability of subsequent extubation or in-hospital death.

Early predictors of outcome in patients receiving hypervolemic and hypertensive therapy for symptomatic vasospasm after subarachnoid hemorrhage

OBJECTIVE

Symptomatic vasospasm after subarachnoid hemorrhage (SAH) is associated with a high incidence of permanent disability and death. For early identification of patients who are at risk for poor outcome, we determined the predictors of outcome in patients with symptomatic vasospasm after SAH.

DESIGN

We retrospectively determined the prognostic value of clinical characteristics and computed tomographic scan both at admission and at the time of initiation of hypervolemic and hypertensive therapy.

SETTINGS

Neurosciences critical care unit at a University hospital.

PATIENTS

A total of 70 consecutive patients who developed symptomatic vasospasm after SAH.

INTERVENTION

Treatment with oral nimodipine, hypervolemic therapy, and hypertensive therapy. Angioplasty and intra-arterial papaverine were used in patients with vasospasm resistant to standard treatment.

MEASUREMENTS AND MAIN RESULTS

Poor outcome, defined as Glasgow Outcome Scale Score of 3-5 at 2 months or discharge, was observed in 32 (46%) patients. In the logistic regression analysis, a Glasgow Coma Scale (GCS) score of < or =11 (odds ratio, 11.0; 95% confidence interval, 3.6-39.3) and hydrocephalus (odds ratio, 4.3; 95% confidence interval, 1.2-18.2) at the time of initiation of hypervolemic and hypertensive therapy were significantly associated with poor outcome. Poor outcome was observed in 91% of the patients who had both a GCS score of < or =11 and hydrocephalus compared with 15% of patients with a GCS score of >11 and no hydrocephalus at the time of initiation of hypervolemic and hypertensive therapy. A GCS score of < or =11 was also independently associated with length of intensive care unit stay (F ratio = 18.0; p = .0011) and hospital stay (F ratio = 9.2; p = .0034) after initiation of hypervolemic and hypertensive therapy.

CONCLUSIONS

The results of this study suggest that outcome in patients with symptomatic vasospasm can be effectively predicted by routinely available information, including GCS score at the time of initiation of hypervolemic and hypertensive therapy. This information can be used for selection and stratification of patients in future treatment studies of patients with symptomatic vasospasm.

Use of hypertonic saline/acetate infusion in treatment of cerebral edema in patients with head trauma: experience at a single center

BACKGROUND

Hypertonic saline (HS) recently has been introduced as a new form of hyperosmolar treatment in patients with brain injury from diverse causes. We reviewed our experience with the use of continuous hypertonic saline/acetate infusion in patients with cerebral edema attributable to head trauma.

METHODS

We performed a retrospective chart review of all patients admitted with severe head injury, defined as admission Glasgow Coma Scale score of 8 or less, in the neurocritical care unit of a University hospital. Intravenous infusion of 2% or 3% saline/acetate for treatment of cerebral edema was introduced in the unit in April of 1993. The clinical characteristics, interventions required, and outcomes in patients who received HS were compared with patients who received 0.9% saline infusion only. Multivariate analyses were used to evaluate the impact of HS use on in-hospital mortality and Glasgow Outcome Scale score at discharge.

RESULTS

Thirty-six patients with cerebral edema caused by head trauma received infusion of HS initiated within 48 hours of admission for a mean period of 72 +/- 85 hours. Compared with 46 patients who did not receive HS, there were no differences observed in age and admission Glasgow Coma Scale scores. Patients who received HS were more likely to have a penetrating injury (p = 0.07) and a mass lesion on initial computed tomographic scan (p = 0.07). There was no difference between frequency of use of hyperventilation, mannitol, cerebrospinal fluid drainage, and vasopressors between the two groups. The requirement for pentobarbital coma was higher in HS group (n = 7 patients) versus control group (n = 2,p = 0.04). After adjusting for differences between both groups, infusion of HS was associated with higher in-hospital mortality (OR, 3.1; 95% CI, 1.1-10.2).

CONCLUSION

HS administration as prolonged infusion does not seem to favorably impact on requirement for other interventions and in-hospital mortality in our experience. Further efforts should be directed toward use of HS as bolus administrations or short infusions.

Predictors of clinical improvement, angiographic recanalization, and intracranial hemorrhage after intra-arterial thrombolysis for acute ischemic stroke

BACKGROUND AND PURPOSE

We sought to evaluate predictors of clinical outcome, angiographic success, and adverse effects after intra-arterial administration of urokinase for acute ischemic stroke.

METHODS

We designed a Brain Attack program at University Hospitals of Cleveland for diagnosis and treatment of patients presenting within 6 hours of onset of neurological deficit. Patients with ischemia referable to the carotid circulation were treated with intra-arterial urokinase. Angiographic recanalization was assessed at the end of medication infusion. Intracerebral hemorrhage was investigated immediately after and 24 hours after treatment. Stroke severity was determined, followed by long-term outcome.

RESULTS

Fifty-four patients were treated. There was improvement of >/=4 points on the National Institutes of Health Stroke Scale from presentation to 24 hours after onset in 43% of the treated patients, and this was related to the severity of the initial deficit. Forty-eight percent of patients had a Barthel Index score of 95 to 100 at 90 days, and total mortality was 24%. Cranial CT scans revealed intracerebral hemorrhage in 17% of patients in the first 24 hours, and these patients had more severe deficits at presentation. Eighty-seven percent of patients received intravenous heparin after thrombolysis, and 9% of them developed a hemorrhage into infarction. Angiographic recanalization was the rule in complete occlusions of the horizontal portion of the middle cerebral artery, but distal carotid occlusions responded less well to thrombolysis.

CONCLUSIONS

The intra-arterial route for thrombolysis allows for greater diagnostic precision and achievement of a higher concentration of the thrombolytic agent in the vicinity of the clot. Disadvantages of this therapy lie in the cost and delay. Severity of stroke and site of angiographic occlusion may be important predictors of successful treatment.

Administration of hypertonic (3%) sodium chloride/acetate in hyponatremic patients with symptomatic vasospasm following subarachnoid hemorrhage

A retrospective study was carried out to evaluate the effect of hypertonic (3%) saline chloride/acetate on various hemodynamic parameters in mildly hyponatremic patients with symptomatic vasospasm following aneurysmal subarachnoid hemorrhage (SAH). We identified 29 hyponatremic (serum sodium < 135 mEq/L) patients who received hypertonic (3%) sodium chloride/acetate as a continuous infusion. Administration of hypertonic (3%) sodium chloride/acetate resulted in higher central venous pressures and positive fluid balance, with a concomitant increase in serum sodium and chloride concentrations without metabolic acidosis. There were no changes in mean cerebral blood flow velocities after infusion of hypertonic (3%) sodium chloride/acetate. We found no reports of congestive heart failure, pulmonary edema, metabolic acidosis, coagulopathy, intracranial hemorrhages, or central pontine myelinolysis in any of these patients. We conclude that hypertonic (3%) sodium chloride/acetate can be administered to patients with mild hyponatremia in the setting of symptomatic vasospasm following SAH without untoward effects. Sample size and limitations of a retrospective analysis preclude conclusions about safety and efficacy of hypertonic (3%) sodium chloride/acetate administration in this patient population. However, our results support justification for a prospective, randomized, double-blind trial of hypertonic (3%) sodium chloride/acetate versus normal saline in patients with symptomatic vasospasm following SAH.

In vivo determination of absolute cerebral blood volume using hemoglobin as a natural contrast agent: an MRI study using altered arterial carbon dioxide tension

The ability of the magnetic resonance imaging transverse relaxation time, R2 = 1/T2, to quantify cerebral blood volume (CBV) without the need for an exogenous contrast agent was studied in cats (n = 7) under pentobarbital anesthesia. This approach is possible because R2 is directly affected by changes in CBF, CBV, CMRO2, and hematocrit (Hct), a phenomena better known as the blood-oxygenation-level-dependent (BOLD) effect. Changes in CBF and CBV were accomplished by altering the carbon dioxide pressure, PaCO2, over a range from 20 to 140 mm Hg. For each PaCO2 value, R2 in gray and white matter were determined using MRI, and the whole-brain oxygen extraction ratio was obtained from arteriovenous differences (sagittal sinus catheter). Assuming a constant CMRO2, the microvascular CBV was obtained from an exact fit to the BOLD theory for the spin-echo effect. The resulting CBV values at normal PaCO2 and normalized to a common total hemoglobin concentration of 6.88 mmol/L were 42+/-18 microL/g (n = 7) and 29+/-19 microL/g (n = 5) for gray and white matter, respectively, in good agreement with the range of literature values published using independent methodologies. The present study confirms the validity of the spin-echo BOLD theory and, in addition, shows that blood volume can be quantified from the magnetic resonance imaging spin relaxation rate R2 using a regulated carbon dioxide experiment.

Pallidal activity during dystonia: somatosensory reorganisation and changes with severity

A woman with progressive, medically intractable right upper limb dystonia underwent a pallidotomy with only transient improvement. During the procedure her dystonia became more severe as she repeatedly made a fist to command in order to provoke dystonia transiently (movement provoked dystonia). Comparisons within cells in the internal segment of the globus pallidus (Gpi) disclosed that the firing rate was the same at rest, with making a fist, and during movement provoked dystonia. However, the firing rate compared between cells decreased significantly throughout the procedure as the patient made a fist repeatedly. During the second half of the procedure the firing rate of cells in the Gpi was similar to that in hemiballismus. The proportion of cells in the GPi which responded to sensory stimulation was significantly higher in dystonia (53%) than in hemiballismus (13%). These results suggest that pallidal activity can correlate inversely with the severity of dystonia, perhaps due to activity dependent changes in neuronal function resulting from repeated voluntary movement.

Risk factors for multiple intracranial aneurysms

OBJECTIVE

Risk factors that predispose to the formation of multiple intracranial aneurysms, which are present in up to 34% of patients with intracranial aneurysms, are not well defined. In this study, we examined the association between known risk factors for cerebrovascular disease and presence of multiple intracranial aneurysms.

METHODS

We reviewed the medical records and results of conventional angiography in all patients with a diagnosis of intracranial aneurysms admitted to the Johns Hopkins University hospital between January 1990 and June 1997. We determined the independent association between various cerebrovascular risk factors and the presence of multiple aneurysms using logistic regression analysis.

RESULTS

Of 419 patients admitted with intracranial aneurysms (298 ruptured and 121 unruptured), 127 (30%) had multiple intracranial aneurysms. In univariate analysis, female gender (odds ratio [OR] = 1.9; 95% confidence interval [CI], 1.1-3.3) and cigarette smoking at any time (OR = 1.8; 95% CI, 1.1-3.0) were significantly associated with presence of multiple aneurysms. In the multivariate analysis, cigarette smoking at any time (OR = 1.7; 95% CI, 1.1-2.8) and female gender (OR = 2.1; 95% CI 1.2-3.5) remained significantly associated with multiple aneurysms. Hypertension, diabetes mellitus, and alcohol and illicit drug use were not significantly associated with presence of multiple aneurysms.

CONCLUSION

Cigarette smoking and female gender seem to increase the risk for multiple aneurysms in patients predisposed to intracranial aneurysm formation. Further studies are required to investigate the mechanism underlying the association between cigarette smoking and intracranial aneurysm formation.

Malignant cerebral edema in patients with hypertensive intracerebral hemorrhage associated with hypertonic saline infusion: a rebound phenomenon?

Hypertonic saline was recently introduced as a new hyperosmolar agent for treatment of intracranial hypertension and cerebral edema. It has the potential to cause a rebound phenomenon similar to other osmotic agents. The authors report on two patients with cerebral edema caused by hypertensive intracerebral hemorrhage who were treated with hypertonic saline infusion. Both patients improved clinically after 24 hours of hypertonic saline administration. However, both patients deteriorated clinically, 48 and 96 hours after initiation of therapy, despite continued hypertonic saline administration. Compared with pre-treatment computed tomographic scans, edema volume on repeat scans increased from 131 cc to 262 cc, and from 171 cc to 239 cc in the first and second patients, respectively, despite the lack of change in hematoma volume. Malignant edema formation late in the course of intracerebral hemorrhage after prolonged administration of hypertonic saline may represent a rebound phenomenon of hyperosmolar therapy. Further studies are warranted to identify the occurrence of this phenomenon and the subset of patients susceptible to it.

Treatment of refractory intracranial hypertension with 23.4% saline

OBJECTIVE

To evaluate the effect of intravenous bolus administration of 23.4% saline (8008 mOsm/L) on refractory intracranial hypertension (RIH) in patients with diverse intracranial diseases.

DESIGN

Retrospective chart review.

SETTING

A neurosciences intensive care unit in a university hospital.

PATIENTS

We present eight patients and a total of 20 episodes of increased intracranial pressure (ICP) resistant to standard modes of therapy. Five patients had subarachnoid hemorrhage, one patient had traumatic brain injury, one had a brain tumor, and another had spontaneous basal ganglia hemorrhage. Seven patients had intraventricular catheters, and one had a subarachnoid pressure screw placed. We monitored continuously mean ICP, serum sodium concentrations, mean arterial pressure, cerebral perfusion pressure (CPP), central venous pressure, and urine output before and after the administration of hypertonic saline (HS). Post mortem examination of the brain was performed in two patients.

INTERVENTION

Intravenous bolus administration of 30 mL of 23.4% saline.

MEASUREMENTS AND MAIN RESULTS

There was a significant (p < .05) decrease in ICP from a median of 41.5 mm Hg before HS to 17 mm Hg at 1 hr, 16 mm Hg at 2 hrs, and 14 mm Hg at 3 hrs after HS administration. In 80% of cases, ICP decreased by >50% of the pretreatment value over a duration of 21.2+/-10.3 mins. ICP decreased to <20 mm Hg in 65% of all cases and the mean time for it to again exceed 20 mm Hg was 6.3+/-4.9 hrs. There was a significant improvement in CPP, from 64.7+/-19 (SD) mm Hg before HS to 85.6+/-18 mm Hg (1 hr) and 83+/-18 mm Hg (3 hrs) after HS. There were no significant differences in the other variables measured. The post mortem examinations showed no white matter changes or subdural collections.

CONCLUSIONS

This preliminary case series suggests that the intravenous bolus administration of 23.4% saline reduces ICP and augments CPP in patients with resistant increased ICP. This reduction can be maintained for several hours while other therapeutic measures are being considered. The patient population most likely to respond to this therapy needs to be further defined. Although more research is needed, this treatment is promising as a new modality for RIH because of its ICP-lowering effect without intravascular volume depletion.

Use of hypertonic (3%) saline/acetate infusion in the treatment of cerebral edema: Effect on intracranial pressure and lateral displacement of the brain

OBJECTIVE

To determine the effect of continuous hypertonic (3%) saline/acetate infusion on intracranial pressure (ICP) and lateral displacement of the brain in patients with cerebral edema.

DESIGN

Retrospective chart review.

SETTINGS

Neurocritical care unit of a university hospital.

PATIENTS

Twenty-seven consecutive patients with cerebral edema (30 episodes), including patients with head trauma (n = 8), postoperative edema (n = 5), nontraumatic intracranial hemorrhage (n = 8), and cerebral infarction (n = 6).

INTERVENTION

Intravenous infusion of 3% saline/acetate to increase serum sodium concentrations to 145 to 155 mmol/L.

MEASUREMENTS AND MAIN RESULTS

A reduction in mean ICP within the first 12 hrs correlating with an increase in the serum sodium concentration was observed in patients with head trauma (r2 = .91, p = .03), and postoperative edema (r2 = .82, p = .06), but not in patients with nontraumatic intracranial hemorrhage or cerebral infarction. In patients with head trauma, the beneficial effect of hypertonic saline on ICP was short-lasting, and after 72 hrs of infusion, four patients required intravenous pentobarbital due to poor ICP control. Among the 21 patients who had a repeat computed tomographic scan within 72 hrs of initiating hypertonic saline, lateral displacement of the brain was reduced in patients with head trauma (2.8 +/- 1.4 to 1.1 +/- 0.9 [SEM]) and in patients with postoperative edema (3.1 +/- 1.6 to 1.1 +/- 0.7). This effect was not observed in patients with nontraumatic intracranial bleeding or cerebral infarction. The treatment was terminated in three patients due to the development of pulmonary edema, and was terminated in another three patients due to development of diabetes insipidus.

CONCLUSIONS

Hypertonic saline administration as a 3% infusion appears to be a promising therapy for cerebral edema in patients with head trauma or postoperative edema. Further studies are required to determine the optimal duration of benefit and the specific patient population that is most likely to benefit from this treatment.

Pallidotomy for hemiballismus: efficacy and characteristics of neuronal activity

A patient with unremitting, medically intractable hemiballismus underwent a pallidotomy that abolished his involuntary movements. Firing rates of cells in the internal segment of the globus pallidus (GPi) recorded during this procedure were significantly lower than those observed during pallidotomy for Parkinson's disease, either "on" or "off" medication. Firing patterns in hemiballismus were characterized by low-frequency modulation of the firing rate. These results are consistent with the hyperkinetic model, which suggests that hemiballismus results from decreased inhibition of the pallidal relay nucleus of the thalamus by the GPi. The efficacy of surgery in the case of hemiballismus demonstrates that pallidotomy can be an effective treatment for this condition and suggests that patterned neuronal activity in the GPi is important in the mechanism of hyperkinetic disorders.

Acute intermittent porphyria: clinicopathologic correlation. Report of a case and review of the literature

Acute intermittent porphyria (AIP), an autosomal dominant disorder, results from a deficiency of the enzyme hydroxymethylbilane synthase. Despite important advances in the characterization of AIP, the pathophysiology of the neurologic manifestations is not clearly understood. We present a patient with AIP followed for 31 years with multiple episodes of hyponatremia during AIP exacerbations. We discuss the clinicopathologic correlation and possible explanations for the morphologic findings, including discrete hypothalamic changes.

Torsional eye movements in patients with skew deviation and spasmodic torticollis: responses to static and dynamic head roll

We measured torsional eye movements induced by sinusoidal rotation or static tilt, of the head in roll while viewing a far or near target in 4 patients with skew deviation due to brainstem lesions, 4 patients with spasmodic torticollis (ST), 2 patients with unilateral eighth nerve section (VIIIS), and 10 normal subjects. Torsional nystagmus was present in all 4 patients with skew deviation. In subjects and patients, responses to both sinusoidal and static roll were larger while viewing the far target, consistent with factors dictated by geometry. Response gains to sinusoidal roll were abnormal in 3 patients with skew (increased in one, decreased in two), abnormal in 3 with ST (increased in 1, decreased in 2), and in abnormal both VIIIS patients (decreased). Greater abnormalities were evident in 3 skew patients while rolling away from the side of their brainstem lesions and in both VIIIS patients while rolling toward their lesioned ears. There were similar but less pronounced changes during static head roll. We conclude that patients with skew, ST, and VIIIS may all have abnormal ocular counter-rolling that is more evident during dynamic testing while viewing a far target. Such abnormalities endure because of the limited influence exerted by vision on torsional eye movements.

Neuronal specification of direction and distance during reaching movements in the superior precentral premotor area and primary motor cortex of monkeys

1. Single-unit neuronal activity was recorded in the primary motor and superior precentral premotor areas of two rhesus monkeys during an arm reaching task. The task involved moving a cursor displayed on a video terminal using a draftsman's arm-type manipulandum. From a centrally located start box the animal was required to move to 1 of 48 target boxes at eight different directions (0-360 degrees in 45 degrees intervals) and six distances (1.4-5.4 cm in 0.8-cm increments). Both direction and distance for the upcoming movement were unpredictable. 2. The activity of 197 arm movement-related cells was recorded and evaluated for each of the 48 targets. Histological examination showed the cells to be primarily in the primary motor cortex or in the premotor area around the superior precentral sulcus. Each cell's discharge was aligned on movement onset and averaged over five trials for each target. Movement kinematics including hand path velocity were also determined. The task time was divided into three epochs, a premovement period (PT), a movement period (MT), and total time (TT = PT+MT). For each epoch the average firing was correlated with the direction and distance of the movement using various regression procedures. 3. An analysis of variance (ANOVA) showed that the majority of neurons were modulated significantly by movement direction in each of the three time periods, PT (73.7%), MT (68.3%), and TT (78.5%). The relationship of the firing to direction was fit to a cosine tuning function for each significantly modulated cell. In 86.3% of the cells the firing was correlated significantly with a cosine function of movement direction in TT. A cell's preferred direction varied little for different movement distances. The mean difference in preferred direction for the smallest possible change in distance (0.8 cm) was 12.8 +/- 11.4 degrees (SD) and 17.1 +/- 14.7 degrees for the largest change in distance (4.0 cm). 4. Correlation analysis revealed that the activity of the majority of cells was modulated significantly by distance along at least one direction in each of the three time periods, PT (46.8%), MT (68.8%), and TT (67.7%). Subsequently, a univariate linear regression model was used to quantify a cell's discharge as a function of distance. For the regressions of firing with distance with a statistically significant correlation (r > 0.8), the mean slope was 3.59 +/- 0.17 spikes.s-1.cm-1 for the total time. The existence of a significant distance modulation was not invariably correlated with a cell's preferred movement direction.(ABSTRACT TRUNCATED AT 400 WORDS)