Blood glucose response after oral lactulose intake in type 2 diabetic individuals

BACKGROUND

Lactulose is approved for the symptomatic treatment of constipation, a gastrointestinal (GI) complication common in individuals with diabetes. Lactulose products contain carbohydrate impurities (e.g., lactose, fructose, galactose), which occur during the lactulose manufacturing process. These impurities may affect the blood glucose levels of individuals with type 2 diabetes mellitus (T2DM) using lactulose for the treatment of mild constipation. A previous study in healthy subjects revealed no increase in blood glucose levels after oral lactulose intake. However, it is still unclear whether the intake of lactulose increases blood glucose levels in individuals with diabetes.

AIM

To evaluate the blood glucose profile after oral lactulose intake in mildly constipated, non-insulin-dependent subjects with T2DM in an outpatient setting.

METHODS

This prospective, double-blind, randomized, controlled, single-center trial was conducted at the Clinical Research Center at the Medical University of Graz, Austria, in 24 adult Caucasian mildly constipated, non-insulin-dependent subjects with T2DM. Eligible subjects were randomized and assigned to one of six treatment sequences, each consisting of four treatments stratified by sex using an incomplete block design. Subjects received a single dose of 20 g or 30 g lactulose (crystal and liquid formulation), water as negative control or 30 g glucose as positive control. Capillary blood glucose concentrations were measured over a period of 180 min post dose. The primary endpoint was the baseline-corrected area under the curve of blood glucose concentrations over the complete assessment period [AUC_{baseline_c (0-180 min)}]. Quantitative comparisons were performed for both lactulose doses and formulations vs water for the equal lactulose dose vs glucose, as well as for liquid lactulose vs crystal lactulose. Safety parameters included GI tolerability, which was assessed at 180 min and 24 h post dose, and adverse events occurring up to 24 h post dose.

RESULTS

In 24 randomized and analyzed subjects blood glucose concentration-time curves after intake of 20 g and 30 g lactulose were almost identical to those after water intake for both lactulose formulations despite the different amounts of carbohydrate impurities (≤ 3.0% for crystals and approx. 30% for liquid). The primary endpoint [AUC_{baseline_c (0-180 min)}] was not significantly different between lactulose and water regardless of lactulose dose and formulation. Also with regard to all secondary endpoints lactulose formulations showed comparable results to water with one exception concerning maximum glucose level. A minor increase in maximum blood glucose was observed after the 30 g dose, liquid lactulose, in comparison to water with a mean treatment difference of 0.63 mmol/L (95% confidence intervals: 0.19, 1.07). Intake of 30 g glucose significantly increased all blood glucose endpoints vs 30 g liquid and crystal lactulose, respectively (all P < 0.0001). No differences in blood glucose response were observed between the different lactulose formulations. As expected, lactulose increased the number of bowel movements and was generally well tolerated. Subjects experienced only mild to moderate GI symptoms due to the laxative action of lactulose.

CONCLUSION

Blood glucose AUC_{baseline_c (0-180 min)} levels in mildly constipated, non-insulin dependent subjects with T2DM are not affected by the carbohydrate impurities contained in 20 g and 30 g crystal or liquid lactulose formulations.

Arterial lactate above 2 mM is associated with increased brain lactate and decreased brain glucose in patients with severe traumatic brain injury

BACKGROUND

Lactate fuels cerebral energy-consuming processes and it is neuroprotective. The impact of arterial lactate on brain metabolism determined by microdialysis was investigated retrospectively in patients with severe traumatic brain injury (TBI).

METHODS

Cerebral microdialysis (glucose, lactate), neuromonitoring (ICP, CPP, ptiO2, SjvO2) and blood gas data collected in 20 patients during pharmacologic coma were grouped within predefined arterial lactate clusters (<1, 1-2, >2 mM). Microdialysis samples were only taken from time points characterized by normoventilation (paCO2 34.5-42 mmHg), sufficient oxygenation (paO2 >75 mmHg) and hematocrit (≥24%) to exclude confounding influences.

RESULTS

Elevated arterial lactate ≥2 mM was associated with significantly increased brain lactate which coincided with markedly decreased brain glucose despite significantly increased arterial glucose levels and sufficient cerebral perfusion indirectly determined by normal SjvO2 and ptiO2 values. At elevated arterial lactate levels signs of significantly increased cerebral lactate uptake coincided with markedly decreased cerebral glucose uptake. Infused lactate above 50 mM per 24 hours was associated with significantly decreased cerebral glucose.

CONCLUSION

Increased arterial lactate levels were associated with increased cerebral lactate uptake and elevated brain lactate. At the same time brain glucose uptake and brain glucose were significantly reduced. It remains unclear whether arterial lactate is the driving force for the increased cerebral lactate levels or if the reduced glucose uptake also contributed to the increased cerebral lactate levels. Further studies are required to assess the impact of lactate infusion under clinical conditions.

Resuscitative emergency thoracotomy in a Swiss trauma centre

BACKGROUND

Resuscitative emergency thoracotomy (ET) is performed as a salvage manoeuvre for selected patients with trauma. However, reports from European trauma centres are scarce.

METHODS

A retrospective analysis was undertaken of injured patients who underwent resuscitative ET in the emergency department (ED) or operating room (OR) between January 1996 and September 2008. Survival in the ED and to hospital discharge was analysed using logistic regression.

RESULTS

During the study interval 121 patients required a resuscitative thoracotomy, of which 49 (40·5 per cent) were performed in the ED and 72 (59·5 per cent) in the OR. Patients in the OR had higher blood pressure on arrival (median 110 versus 60 mmHg; P < 0·001), were less often in severe haemorrhagic shock (63 versus 94 per cent; P < 0·001), had fewer serious head injuries (Abbreviated Injury Score of 3 or above in 33 versus 53 per cent; P = 0·031) and more often had a penetrating stab wound as the dominating mechanism (25 versus 10 per cent; P = 0·042) compared with those in the ED. Ten patients (20 per cent) survived to hospital discharge after ED thoracotomy, compared with 53 (74 per cent) of those treated in the OR. Penetrating injury and Glasgow Coma Scale score above 8 were independent predictors of hospital survival following ED thoracotomy. No patient with a blunt injury and no detectable signs of life on admission survived. Three of 26 patients with blunt trauma and signs of life on admission survived to hospital discharge.

CONCLUSION

Resuscitative ET may be life-saving in selected patients. Location of the procedure is dictated by injury severity and vital parameters. Outcome is best when signs of life are present on admission, even for blunt injuries.

Changes in calculated arterio-jugular venous glutamate difference and SjvO2 in patients with severe traumatic brain injury

BACKGROUND

Cerebral metabolic impairment is feared to induce secondary brain damage following traumatic brain injury (TBI). The present study was designed to assess the temporal profile of calculated arterio- jugular venous differences in glutamate (AJVDglu) and SjvO(2) in patients subjected to continuous pharmacologic coma. Metabolic impairment was assumed to be reflected by increased jugular venous glutamate levels and decreased jugular venous oxygen saturation (SjvO(2)).

METHODS

Arterial and jugular venous blood was drawn once daily for up to 14 days from 14 patients to assess the temporal profile. Plasma glutamate was measured by high performance liquid chromatography. SjvO(2), lactate and paCO(2) were determined in routine blood gas analysis. Calculated AJVD indirectly reflects cerebral uptake (positive values) or cerebral release (negative values).

RESULTS

During pharmacologic coma an increase in ICP approaching 20 mmHg was associated with significantly reduced paCO(2) (4.7 ± 0.5 kPa; mean ± standard deviation), markedly decreased SjvO(2) (66.0 ± 4.2%) without reaching ischemic values, and a trend to more negative AJVDglu values (-6.0 ± 14.3 μmol/L), suggesting cerebral glutamate release. Arterio- jugular venous lactate difference (AJVDlac) remained unchanged.

CONCLUSION

During pharmacologic coma increased ICP was associated with significantly decreased SjvO(2) which coincided only with a trend to increased cerebral glutamate release. Calculated AJVDglu appears to be inferior in unmasking altered brain metabolism compared to SjvO(2) whenever ICP is increased.

Insulin differentially influences brain glucose and lactate in traumatic brain injured patients

BACKGROUND

Hypo- and hyperglycemia must be avoided to prevent additional brain damage following traumatic brain injury (TBI). However, the optimal blood glucose range requiring insulin remains unknown. Cerebral microdialysis is helpful in unmasking signs of metabolic impairment, thereby identifying deleterious blood glucose levels.

METHODS

A retrospective analysis of prospectively collected cerebral microdialysis samples obtained from 20 non-diabetic patients with severe TBI treated at the trauma surgical intensive care unit at the University Hospital Zürich, Switzerland.

RESULTS

The impact of different arterial blood glucose values and concomitant insulin administration on cerebral interstitial glucose and lactate levels was investigated. In addition, energetic impairment was determined by calculating lactate-to-glucose ratios. Insulin administration was associated with significantly reduced cerebral glucose concentrations and significantly increased lactate-to-glucose ratios with arterial blood glucose levels <5 mM. At arterial blood glucose levels >7 mM, insulin administration was associated with significantly increased interstitial glucose values, significantly decreased lactate concentrations, and markedly diminished lactate-to-glucose ratios.

CONCLUSION

Insulin exerts differential effects that depend strongly on the underlying arterial blood glucose concentrations. To avoid energetic impairment, insulin should not be administered at arterial blood glucose levels <5 mM. However, at arterial blood glucose levels >7-8 mM, insulin administration appears to be encouraged to increase extracellular glucose concentrations and decrease energetic impairment reflected by reduced interstitial brain lactate and decreased lactate-to-glucose ratios. Nevertheless, frequent analysis is required to minimize the risk of inducing impaired brain metabolism.

Granulocyte colony-stimulating factor does not affect contusion size, brain edema or cerebrospinal fluid glutamate concentrations in rats following controlled cortical impact

INTRODUCTION

Granulocyte colony-stimulating factor (G-CSF) is an established treatment in the neutropenic host. Usage in head-injured patients at risk for infection may aggravate brain damage. In contrast, evidence of G-CSF neuroprotective effects has been reported in rodent models of focal cerebral ischemia. We investigated effects of G-CSF in acute focal traumatic brain injury (TBI) in rats.

METHODS

Thirty-six male Sprague-Dawley rats were anesthetized with 1.2%) to 2.0% isoflurane and subjected to controlled cortical impact injury (CCII). Thirty minutes following CCII, either vehicle or G-CSF was administered intravenously. Animals were sacrificed 24 hours following CCII. Glutamate concentrations were determined in cisternal cerebrospinal fluid (CSF). Brain edema was assessed gravimetrically. Contusion size was estimated by 2,3,5-triphenyltetrazolium chloride staining and volumetric analysis.

RESULTS

Dose-dependent leukocytosis was induced by infusion of G-CSF. Physiological variables were unaffected. Water content of the traumatized hemisphere and CSF glutamate concentrations were unchanged by treatment. Contusion volume was similar in all groups.

CONCLUSIONS

A single injection of G-CSF did not influence cortical contusion volume, brain edema, or glutamate concentrations in CSF determined 24 hours following CCII in rats. G-CSF, administered 30 minutes following experimental TBI, failed to exert neuroprotective effects.

The Use of Neuronavigation in Transnasal Transsphenoidal Pituitary Surgery

BACKGROUND

Recurrent pituitary adenomas and localisation of microadenomas potentially cause difficulties during transsphenoidal pituitary surgery. Neuronavigation might improve tumour removal in such cases.

METHODS

Between 12/98 and 04/01 transnasal transsphenoidal adenomectomies were performed in 152 patients at our department. In 16 of these patients neuronavigation was chosen as a means of safely approaching the tumour and improving the efficacy of tumour localisation and removal. Mean age of the 7 female and 9 male patients was 51.8 +/- 13.7 years. Patients were subdivided according to the underlying pathology, i. e. microadenomas (n = 8, mean diameter: 5.75 +/- 2.1 mm), and recurrent adenomas (n = 8). The imaging of adenomas was achieved in preoperatively obtained 1 mm transversely reconstructed magnetic resonance sections from a dynamic enhanced 3D-FFE sequence (Gyroscan 1.5 Tesla, Philips). Contour-guided surgery via a transnasal transsphenoidal approach to the sella region was performed using the MKM navigation microscope (Zeiss).

RESULTS

Endocrinologic studies revealed secretion of growth hormone (GH), ACTH, and follicle stimulating hormone (FSH) in 5, 4, and 1 patient, respectively. The remaining 7 adenomas did not secrete any hormones. All pituitary tumours were accurately localised by neuronavigation. In all recurrent macroadenomas, the tumours were rapidly and safely approached through the scarred tissue and the tumour volume was significantly reduced. Neither intraoperative nor postoperative complications occurred in these patients. In hormone-secreting pituitary tumours with far lateral localisation, endocrinologic abnormalities were corrected in 5 patients, while hormone secretion was significantly decreased in 3 patients. In 1 patient with histologically verified adenoma, hormone secretion did not significantly change following surgical removal.

CONCLUSIONS

Neuronavigation in pituitary surgery is of use in only a small number of cases. Nevertheless, we suggest that contour-guided, transsphenoidal adenomectomy may prove helpful in approaching recurrent adenomas and localising lateral microadenomas.

Anesthesia increases circulating glutamate in neurosurgical patients

BACKGROUND

The excitotoxic amino acid glutamate is known to aggravate pre-existing neuropathology. Since volatile anesthetics increase plasma amino acid levels, we investigated if the anesthetics isoflurane and propofol increase plasma and cerebrospinal fluid (CSF) glutamate in neurosurgical patients.

METHODS

In discectomized patients (n = 15), plasma glutamate was determined at 30 minute intervals before and during isoflurane anesthesia. In craniotomized patients (n = 66), plasma glutamate was assessed during and up to 24 hours after routine isoflurane or propofol anesthesia. CSF samples were withdrawn upon opening of the dura, before surgical manipulations.

FINDINGS

During isoflurane anesthesia, plasma glutamate was significantly and reversibly increased in discectomized and craniotomized patients compared to healthy controls (56+/-6 microM; p<0.05), which was mostly sustained in male patients (males: 126+/-12 vs. females: 96+/-6 microM; p<0.05). With propofol, plasma glutamate was increased equally in men and women but to a lesser extent than with isoflurane (mean: 72+/-7 microM). CSF glutamate was significantly increased during isoflurane and propofol anesthesia compared to control lumbar CSF (1.2+/-0.1 microM; p<0.0001), being more prominent in patients with pre-existing brain edema receiving isoflurane (76+/-8 vs. propofol: 40+/-6 microM; p<0.05).

CONCLUSIONS

The significant increases in plasma and CSF glutamate which were mostly sustained during isoflurane compared to propofol anesthesia should prompt the identification of anesthetic agents which do not impose a possible burden of glutamate-mediated excitotoxicity in patients with underlying compromised cerebral homeostasis. Detailed neuropsychological investigations following different anesthesia regimen are important to determine if transient elevations in CSF and plasma glutamate levels are of clinical relevance.

Assessment of the relationship between age and continuous intracranial compliance

The aim of this open, descriptive and prospective study was to determine if the new monitoring parameter "continuous intracranial compliance (cICC)" decreases with age in patients with traumatic brain injury (TBI). 30 patients with severe and moderate TBI (Glasgow Coma Scale score < or = 10) contributing to a European multicenter study, organized by the Brain-IT group, underwent computerized monitoring of blood pressure, intracranial pressure (ICP), cerebral perfusion pressure and cICC. Regression analyses of individual median ICP and median cICC versus patients' age revealed no significant dependency. Median cICC declined significantly with increasing ICP (when median ICP = 10, 20 and 30 mmHg, cICC = 0.64, 0.56 and 0.42 ml/mmHg respectively, p < 0.05). These three ICP groups were then subdivided according to age (0-20, 21-40, 41-60 and 61-80 years). Median cICC declined with age in both high ICP groups (median ICP = 20,30 mmHg). Percentage cICC values below a set pathological threshold of lower than 0.05 ml/mmHg across the four age groups were 28% (0-20 yrs), 59% (21-40 yrs), 60% (41-60 yrs) and 70% (61-80 yrs) respectively. The observed phenomenon of decreased intracranial volume challenge compensation with advancing age may contribute to the well-known fact of a worse outcome in elderly patients after TBI.

The antioxidant effect of N-acethylcysteine on experimental contusion in rats

N-acethylcysteine (NAC) is known to have direct and indirect antioxidant abilities. We investigated the potential protective effect of NAC on ICP, brain edema and contusion volume after Controlled Cortical Impact (CCI) injury. A moderate CCI injury was induced on the left hemisphere in 48 Sprague Dawley rats. The animals were treated with intraperitoneal injection of NAC (163 mg/kg/KG) or physiological saline. Measurements of intracranial pressure (ICP) were performed and brains were removed at 24 hours. Gravimetric analysis of post-traumatic edema and morphometric measurements (TTC staining) of contusion volume were carried out in 24 animals, respectively. ICP measurements increased significantly over time with no significant differences between both groups. The relative difference in water content in NAC treated animals (1.45 +/- 0.1%) did not differ significantly versus placebo (1.47 +/- 0.2%). The contusion volume was diminished by 19% in the NAC group (53.52 +/- 5.3 mm3) versus placebo (66.28 +/- 4.7 mm3) without showing statistical significance. The antioxidant properties of NAC did not affect intracranial pressure or posttraumatic brain edema formation, although the moderate reduction of contusion volume might reveal beneficial effects on focal contusion.

Differential effects of prolonged isoflurane anesthesia on plasma, extracellular, and CSF glutamate, neuronal activity, 125I-Mk801 NMDA receptor binding, and brain edema in traumatic brain-injured rats

BACKGROUND

Volatile anesthetics reduce neuronal excitation and cerebral metabolism but can also increase intracellular water accumulation in normal and injured brains. While attenuation of neuronal excitation and glutamate release are beneficial under pathological conditions, any increase in edema formation should be avoided. In the present study we investigated duration-dependent effects of the commonly used isoflurane/nitrous oxide (N2O) anesthesia on EEG activity, specific NMDA receptor binding, extracellular, CSF, and plasma glutamate, and cerebral water content in brain-injured rats subjected to short (30 minutes) or prolonged (4 hours) anesthesia.

METHODS

Before controlled cortical impact injury (CCI), during prolonged (4-8 hours) or short anesthesia (7.5-8 hours after CCI), and before brain removal, changes in neuronal activity were determined by quantitative EEG analysis and glutamate was measured in arterial plasma. Brains were processed to determine acute and persisting changes in cerebral water content and 125I-Mk801 NMDA receptor binding at 8 and 32 hours after CCI, i.e., immediately or 24 hours after short or prolonged anesthesia. During prolonged anesthesia glutamate was measured via microdialysis within the cortical contusion. CSF was sampled before brain removal.

FINDINGS

Prolonged isoflurane (1.8 vol%) anesthesia significantly increased EEG activity, plasma, cortical extracellular, and CSF glutamate, cortical and hippocampal 125I-Mk801 NMDA receptor binding, and cerebral water content in brain-injured rats. These changes were partially reversible within 24 hours after prolonged anesthesia. At 24 hours, CSF glutamate was significantly reduced following long isoflurane anesthesia compared to rats previously subjected to short anesthesia despite an earlier significant increase. Conclusions. The partially reversible increases in EEG activity, 125I-Mk801 NMDA receptor binding, cerebral water content, plasma and CSF glutamate appear important for physiological, pathophysiological, and pharmacological studies requiring prolonged anesthesia with isoflurane. Increases in extracellular cortical and plasma glutamate could contribute to acute aggravation of underlying tissue damage.

Neuronal activity and cortical perfusion determined by quantitative EEG analysis and laser doppler flowmetry are uncoupled in brain injured rats

Following traumatic brain injury uncoupling of metabolism from perfusion, reflected by an increase in cellular activity in face of reduced perfusion contributes to secondary tissue damage. Standard autoradiographic techniques employed to study metabolism and perfusion are limited by the inability to perform longitudinal investigations. Therefore, the aims of this study were to investigate if metabolic uncoupling can be studied by applying noninvasive and non-radioactive methods. For this, quantitative EEG analysis and laser Doppler flowmetry were employed to determine changes in EEG activity as a global measure of neuronal activity and pericontusional cortical perfusion during the early phase following controlled cortical impact injury (CCII). In eight rats changes in neuronal activity and pericontusional cortical perfusion were determined before, at 4 and 24 hours after CCII. Neuronal activity was significantly increased by 40% at 4 hours after CCII followed by a significant decrease by 60% at 24 hours compared to pre-trauma levels. Pericontusional cortical perfusion was significantly reduced by 45% and 18% at 4 and 24 hours after CCII. respectively. Non-radioactive methods like quantitative EEG analysis and laser Doppler flowmetry can be used to reveal underlying uncoupling of EEG activity from cortical perfusion which is mostly sustained in the early phase following CCII.

Continuous monitoring of intracranial compliance after severe head injury: relation to data quality, intracranial pressure and brain tissue PO2

The objective of the present study was to test the new continuous intracranial compliance (cICC) device in terms of data quality, relationship to intracranial pressure (ICP) and brain tissue oxygenation (PtiO2). A total of 10 adult patients with severe traumatic brain injury underwent computerized monitoring of arterial blood pressure, ICP, cerebral perfusion pressure, end-tidal CO2, cICC and PtiO2 providing a total of 1726 h of data. (1) The data quality assessed by calculating the 'time of good data quality' (TGDQ, %), i.e. the median duration of artefact-free time as a percentage of total monitoring time reached 98 and 99% for ICP and PtiO2, while cICC measurements were free of artefacts in only 81%. (2) Individual regression analysis showed broad scattered correlation between cICC and ICP ranging from low (r = 0.05) to high (r = 0.52) correlation coefficients. (3) From 225 episodes of increased ICP (ICP > 20 mmHg > 10 min), only 37 were correctly predicted by a preceding decline in cICC to pathological values (< 0.5 ml/mmHg). (4) In all episodes of cerebral hypoxia (PtiO2 < 10 mmHg > 10 min), cICC was not pathologically altered. Based on the present results, we conclude that the current hardware and software version of the cICC monitoring system is unsatisfactory concerning data quality, prediction of increased ICP and revelance of cerebral hypoxic episodes.

Noninvasive analysis of conjunctival microcirculation during carotid artery surgery reveals microvascular evidence of collateral compensation and stenosis-dependent adaptation

OBJECTIVE

Hemodynamically relevant internal carotid artery (ICA) stenosis is a major cause of ischemic stroke. Despite its long-term benefit, carotid endarterectomy may also be associated with severe neurologic deficits. Intraoperative and early recognition of ischemia in the region of the ICA may reduce this risk. To date, direct imaging and quantitative analysis of microvascular structures and function in the human ICA region have not been possible. We purposed to visualize and quantify ischemia/reperfusion-induced microcirculatory changes in the terminal vascular bed of the ICA in patients undergoing unilateral ICA endarterectomy.

METHODS

Sequential analysis of the ipsilateral and contralateral conjunctival microcirculation was performed with orthogonal polarized spectral imaging in 33 patients undergoing unilateral ICA endarterectomy because of moderate or severe ICA stenosis (North American Symptomatic Carotid Endarterectomy Trial score, 75% +/- 13%), before clamping the ICA (baseline), during clamping of the external carotid artery and ICA, during reperfusion of the ICA (intraluminal shunt), during the second clamping of the ICA (shunt removal), after declamping (reperfusion) of the external carotid artery and ICA, and 15 to 20 minutes after the second ICA reperfusion.

RESULTS

During ICA clamping for shunt placement, ipsilateral and contralateral conjunctival capillary perfusion was significantly decreased, but it was completely restored after reperfusion with carotid shunting. Reclamping of the ICA for shunt removal caused microvascular dysfunction, which was significantly less pronounced than that observed during the first clamping. The individual degree of ICA stenosis was inversely correlated with the ipsilateral and contralateral decrease in conjunctival functional capillary density during the first ICA clamping.

CONCLUSIONS

These results suggest adaptive mechanisms of capillary perfusion with increasing stenosis and development of collateral compensatory circulation in the vascular region of the human ICA. Conjunctival orthogonal polarized spectral imaging during unilateral ICA reconstruction enables continuous noninvasive analysis of bilateral conjunctival microcirculation in the terminal region of the ICA and enables monitoring for efficient carotid shunt perfusion during and after endarterectomy.

Pharmacology of traumatic brain injury

The intensity of experimental and clinical research to identify a neuroprotective drug for the treatment of traumatic brain injury is motivated by the devastating morbidity and mortality of this condition. Encouraging experimental work has led so far to disappointing clinical trials and the identification of new potential therapeutic targets is critically dependent on a better understanding of the chronic pathophysiology triggered by the initial insult. Future advances in the pharmacological treatment of traumatic brain injury are likely to include the evaluation of sequentially timed therapies combining multiple and targeted agents, and manipulation of the newly discovered neurogenic potential of the adult brain together with the refinement of traditional interventions to block specific cytotoxic cascades.

Norepinephrine is superior to dopamine in increasing cortical perfusion following controlled cortical impact injury in rats

Following traumatic brain injury catecholamines are routinely applied to increase cerebral perfusion. To date, it remains controversial if infusion of catecholamines is associated with diminished cerebral perfusion due to catecholamine-mediated vasoconstriction. The aims of the present study were to investigate the effects of norepinephrine and dopamine on cortical perfusion and brain edema following controlled cortical impact injury (CCII) in rats. Four hours after CCII, rats (n = 22) received either norepinephrine or dopamine with the aim of increasing MABP to 120 mm Hg for 90 minutes. Control rats were given NaCl. Cortical perfusion was measured before, during, and after catecholamine infusion using Laser Doppler flowmetry. Brain swelling was determined directly after the study period (8 hrs after CCII). Following CCII cortical perfusion was reduced by 40% compared to pre-trauma values in all rats. Parallel to the increases in MABP, cortical perfusion was significantly elevated under norepinephrine and dopamine, respectively (p < 0.05). Despite similar MABP values this increase was mostly sustained under norepinephrine. In control rats cortical perfusion remained diminished. Brain swelling was similar in all groups. Both norepinephrine and dopamine significantly increased cortical perfusion following CCII. Norepinephrine, however, was superior to dopamine in CBF. Based on increased CBF and unchanged brain swelling catecholamine-mediated vasoconstriction does not seem to occur under the present study design.

Temporal profiles of extracellular nitric oxide metabolites following aneurysmal subarachnoid hemorrhage

The temporal profile of nitric oxide metabolite concentrations i.e. nitrite and nitrate (NOx) was investigated in brain parenchyma of patients following aneurysmal subarachnoid hemorrhage (SAH). In a subset of ten patients (7F/3M, age: 47 +/- 14 yrs) included in a prospective clinical trial on neurochemical intensive-care monitoring, microdialysis (MD) probes (CMA70, Sweden) were implanted at time of aneurysm surgery. Samples from patients clipped electively (n = 3) were considered "normal" in regard to SAH patients (n = 7). MD was performed for 162 +/- 63 hrs. NOx was measured off-line using a highly sensitive, fluorometric assay (2-3-diaminonaphtalene, DAN). NOx concentrations determined from electively operated patients averaged 36.7 +/- 9.6 microM (n = 59, pooled data). Regardless of the development of delayed ischemic neurological deficits (DIND), SAH patients showed a specific temporal profile of NOx consisting of an initial peak followed by an exponential decay. In detail, NOx decreased from initial values of 46.2 +/- 34.8 microM to 23.5 +/- 9.0 microM on day 6-7 after SAH (p < 0.05). Following SAH extracellular concentrations of NO metabolites decrease over time. This is in agreement with hypothetical NO scavenging by products of hemolysis. However, subsequent development of DIND cannot be explained by a lack of vasodilatory NO alone.

Neuronal activity determined by quantitative EEG and cortical microdialysis is increased following controlled cortical impact injury in rats

Following brain injury increased glutamate release is linked to sustained neuronal activation resulting in excitotoxic tissue damage. Isoflurane anesthesia has been shown to decrease electroencephalographic (EEG) activity and extracellular (e.c.) glutamate, possibly attenuating excitotoxic tissue damage. However, based on clinical experience EEG activity can fluctuate despite stable isoflurane concentrations. Therefore, the aims of this study were to investigate the impact of neuronal activity assessed by quantitative EEG on e.c. glutamate during isoflurane anesthesia following controlled cortical impact injury (CCII). In 10 rats balanced anesthesia using isoflurane was induced at 4 hours after CCII. Under steady-state conditions maintaining isoflurane at 1.8 vol%, EEG was recorded for 3 hours. During this period, e.c. glutamate was sampled in the pericontusional cortex by microdialysis. Despite maintaining isoflurane at 1.8 vol%, neuronal activity expressed as low frequency EEG power showed marked fluctuations. Spontaneous increases in neuronal activity coincided with elevated e.c. glutamate levels and vice versa. Overall, EEG power correlated significantly with pathologically elevated e.c. glutamate levels (n = 58; R2 = 0.54; p < 0.05). Despite unchanged isoflurance concentrations fluctuations in neuronal activity were reflected by altered EEG power and e.c. glutamate concentrations. Therefore, neuronal activity needs to be considered for the interpretation of e.c. glutamate levels.

Cortical hypoperfusion precedes hyperperfusion following controlled cortical impact injury

Impaired cerebral perfusion contributes to tissue damage following traumatic brain injury. In this longitudinal study persistence of reduced cortical perfusion employing laser doppler flowmetry was investigated following controlled cortical impact injury (CCII). Before, 30 minutes, 6, 24, and 48 hours after CCII, perfusion in pericontusional cortex was determined by moving a laser doppler probe in 50 x 0.2 mm steps over the traumatized hemisphere in 5 rats. Arterial blood gases and mean arterial blood pressure were monitored. Mean arterial blood pressure and arterial blood gases remained stable during the entire experiments. At 30 minutes and 6 hours following CCII, cortical perfusion was significantly diminished by 24% and 43% (p < 0.05), respectively compared to pre-trauma levels. At 24 and 48 hours after CCII, pericontusional blood flow was significantly increased by 64% and 123%. Cortical hypoperfusion found within the early phase following trauma is reversible and precedes a long lasting phase of hyperperfusion. Changes in tissue mediators (endothelin, acidosis, NO) could account for these findings.

Early expression of glutamate transporter proteins in ramified microglia after controlled cortical impact injury in the rat

Traumatic brain injury is followed by increased extracellular glutamate concentration. Uptake of glutamate is mainly mediated by the glial glutamate transporters GLAST and GLT-1. Extent and distribution of GLAST and GLT-1 were studied in a rat model of controlled cortical impact injury (CCII). Western Blot analysis revealed lowest levels of GLAST and GLT-1 with a decrease by 40%-54% and 42%-49% between 24 and 72 h posttrauma. By 8 h after CCII, CSF glutamate levels were increased (10.5 microM vs. 2.56 microM in controls; P < 0.001), reaching maximum values by 48 h. A significant increase in de novo GLAST and GLT-1 expressing ramified microglia was observed within 4 h, reached a stable level by 48 h, and remained high up to 72 h after CCII. Furthermore, ramified microglia de novo expressed the neuronal glutamate transporter EAAC1 after CCII. Following CCII, GLAST/GLT-1 and GFAP coexpressing astrocytes were immediately reduced, reaching minimum levels within 8 h. This reduction of expression could be either due to protein downregulation or loss of astrocytes. At 72 h, a marked population of GLAST- and GLT-1-positive reactive astrocytes appeared. These results support the hypothesis that reduced astrocytic GLAST and GLT-1 protein levels following CCII contribute to evolving secondary injury. Microglia are capable of de novo expressing glutamate transporter proteins, indicating that the expression of glial and neuronal glutamate transporters is not restricted to a specific glial or neuronal lineage. Ramified microglia may play an important compensatory role in the early regulation of extracellular glutamate after CCII.

Relation of cerebral energy metabolism and extracellular nitrite and nitrate concentrations in patients after aneurysmal subarachnoid hemorrhage

In a prospective clinical investigation on neurochemical intensive care monitoring, the authors' aim was to elucidate the temporal profile of nitric oxide metabolite concentrations-that is, nitrite and nitrate (NO(x))--and compounds related to energy-metabolism in the cerebral interstitium of patients after aneurysmal subarachnoid hemorrhage (SAH). During aneurysm surgery, microdialysis probes were implanted in cerebral white matter of the vascular territory most likely affected by vasospasm. Temporal profiles of NO(x) were analyzed in a subset of 10 patients (7 female, 3 male, mean age = 47 +/- 14 years). Microdialysis was performed for 152 +/- 63 hours. Extracellular metabolites (glucose, lactate, pyruvate, glutamate) were recovered from the extracellular fluid of the cerebral parenchyma. NO(x) was measured using a fluorometric assay. After early surgery, SAH patients revealed characteristic decreases of NO(x) from initial values of 46.2 +/- 34.8 micromol/L to 23.5 +/- 9.0 micromol/L on day 7 after SAH (P < 0.05). Decreases in NO(x) were seen regardless of development of delayed ischemia (DIND). Overall NO(x) correlated intraindividually with glucose, lactate, and glutamate (r = 0.58, P < 0.05; r = 0.32, P < 0.05; r = 0.28, P < 0.05; respectively). After SAH, cerebral extracellular concentrations of NO metabolites decrease over time and are associated with concomitant alterations in energy-or damage-related compounds. This could be related to reduced NO availability, potentially leading to an imbalance of vasodilatory and vasoconstrictive factors. On the basis of the current findings, however, subsequent development of DIND cannot be explained by a lack of vasodilatory NO alone.

Isoflurane doubles plasma glutamate and increases posttraumatic brain edema

Increased plasma and cerebral glutamate levels may contribute to posttraumatic edema formation. Since volatile anesthetics elevate plasma amino acid concentrations, the influence of isoflurane on arterial plasma glutamate levels and brain edema formation was investigated in brain-injured rats. Rats were anesthetized with chloral hydrate (380 mg/kg i.p.) or isoflurane (1.2-2.0 vol%) for four hours following controlled cortical impact injury. Isoflurane significantly increased arterial glutamate levels compared to chloral hydrate (124 +/- 12 vs. 60 +/- 5 microM; p < 0.005). At eight hours after trauma, water content was significantly increased in the traumatized hemisphere compared to the non-traumatized side (p < 0.005). In addition, four hours of isoflurane anesthesia caused a significant increase in brain water content of both hemispheres compared to chloral hydrate (80.1 +/- 0.1 vs. 79.6 +/- 0.1%; p < 0.005). Prolonged isoflurane anesthesia is associated with a significant increase in arterial plasma glutamate levels and brain water content. This increase in brain water content must be considered when performing prolonged isoflurane anesthesia.

Bradykinin 2 receptor antagonist LF 16-0687Ms reduces posttraumatic brain edema

Activation of the kallikrein-kinin system contributes to traumatic brain edema formation. Inhibition of bradykinin 2 (B2) receptors has been shown to successfully reduce brain edema formation. The purpose of this study was to investigate the protective effect of the novel nonpeptide B2 receptor antagonist LF 16-0687Ms in brain-injured rats. Contusion was produced in forty rats by controlled cortical impact injury. Five minutes after trauma rats received a single dose of 0, 3, or 30 mg/kg of LF 16-0687Ms. After 24 hours brain swelling and hemispheric water content were determined. Brain swelling was significantly decreased by 25% in the low and 27% in the high dose group compared to controls (p < 0.03). Water content of the traumatized hemisphere tended to be decreased (80.2 +/- 0.1 vs. 80.4 +/- 0.1%) while water content of the non-traumatized hemispheres tended to be increased after administering LF 16.0687Ms (79.3 +/- 0.1 vs. 79.0 +/- 0.1%). Single administration of the novel nonpeptide B2 receptor antagonist LF 16-0687Ms significantly reduces brain swelling. The missing significant reduction in water content of the traumatized hemisphere, however, could be related to an unspecific increase in water content due to LF 16.0687Ms as suggested by increased water content in the non-traumatized hemisphere.

Visualization of rat pial microcirculation using the novel orthogonal polarized spectral (OPS) imaging after brain injury

Recently, the novel optical system, orthogonal polarized spectral (OPS) imaging was developed to visualize microcirculation. Investigation of changes in microcirculation is essential for physiological, pathophysiological, and pharmacological studies. In the present study applicability of OPS imaging was assessed to study pial microcirculation in normal and traumatized rat brain. High quality images of rat pial microcirculation in normal and traumatized rats were generated with the OPS imaging, allowing to easily differentiate arterioles and venules with the dura remaining intact. In non-traumatized rats, mean vessel diameter of arterioles and venules of five different cortical regions was 19.1+/-2.7 and 22.2+/-1.4 microm, respectively. In the early phase following focal cortical contusion vessel diameter was significantly decreased in arterioles by 28% while diameter in venules was significantly increased by 27%. For technical reasons velocity in arterioles was not measurable. In venules, mean flow velocity of 0.68+/-0.08 mm/s was significantly decreased by 50% at 30 min after trauma. OPS imaging is an easy to use optical system allowing to generate high quality images and to reliably investigate pial microcirculation without having to remove the dura. This technique opens the possibility to perform longitudinal studies investigating changes in pial microcirculation.

Effects of tacrolimus on hemispheric water content and cerebrospinal fluid levels of glutamate, hypoxanthine, interleukin-6, and tumor necrosis factor-α following controlled cortical impact injury in rats

Object. Disturbance of calcium homeostasis contributes to evolving tissue damage and energetic impairment following traumatic brain injury (TBI). Calcium-mediated activation of calcineurin results in production of tissue-damaging nitric oxide and free oxygen radicals. Inhibition of calcineurin induced by the immunosuppressant tacrolimus (FK506) has been shown to reduce structural and functional damage after ischemia. The aims of the present study were to investigate time- and dose-dependent short-term antiedematous effects of tacrolimus following TBI.

Methods. A left temporoparietal contusion (controlled cortical impact injury [CCII]) was induced in 51 male Sprague—Dawley rats. Tacrolimus (1 or 3 mg/kg body weight) was administered by a single intraperitoneal injection at 5 minutes, 30 minutes, or 4 hours after CCII occurred. Control rats received physiological saline. Water contents of traumatized and nontraumatized hemispheres, as well as cerebrospinal fluid (CSF) levels of mediators reflecting tissue damage (the proinflammatory cytokines interleukin [IL]-6 and tumor necrosis factor [TNF]—α, the excitotoxin glutamate, and the adenosine triphosphate—degradation product hypoxanthine), were determined 24 hours after trauma.

Although CSF levels of IL-6 and TNFα were completely suppressed by tacrolimus at all time points and at both concentrations, CSF levels of glutamate and hypoxanthine, as well as edema formation, were only marginally influenced. Significant reduction of cerebral water content was confined to nontraumatized hemispheres. In addition, the higher dose of tacrolimus failed to exert significant antiedematous effects on traumatized hemispheres.

Conclusions. Under the present study design, the potency of tacrolimus in reducing edema formation following CCII seems limited. However, its immunosuppressive effects could be of value in influencing the posttraumatic inflammatory response known to aggravate tissue damage.

Effects of dopamine on posttraumatic cerebral blood flow, brain edema, and cerebrospinal fluid glutamate and hypoxanthine concentrations

OBJECTIVES

Dopamine is often used in the treatment of traumatic brain injury to maintain cerebral perfusion pressure. However, it remains unclear whether dopamine contributes to secondary brain injury caused by vasoconstriction and resulting diminished cerebral perfusion. The present study investigated the effects of dopamine in different concentrations on posttraumatic cortical cerebral blood flow (CBF), brain edema formation, and cerebrospinal fluid concentrations of glutamate and hypoxanthine.

DESIGN

Randomized, placebo-controlled trial.

SETTING

Animal laboratory.

SUBJECTS

Eighteen male Sprague-Dawley rats subjected to a focal cortical brain injury.

INTERVENTIONS

Four hours after controlled cortical impact, rats were randomized to receive physiologic saline solution (n = 6), 10-12 tig/kg/min dopamine (n = 6), or 40-50 microg/kg/min dopamine (n = 6), for 3 hrs. Cortical CBF was measured over both hemispheres by using laser-Doppler flowmetry before trauma and before, during, and after the infusion period. At 8 hrs after trauma, brains were removed to determine hemispheric swelling and water content. Cisternal cerebrospinal fluid was sampled to measure glutamate and hypoxanthine.

MEASUREMENTS AND MAIN RESULTS

After trauma, cortical CBF was significantly decreased by 46% within the vicinity of the cortical contusion in all rats. Infusion of saline and 10-12 ig/kg/min dopamine did not change mean arterial blood pressure (MABP) or cortical CBF. However, infusion of 40-50 microg/kg/min dopamine, which elevated MABP from 89 to 120 mm Hg, significantly increased posttraumatic CBF within and around the contusion by 35%. Over the nontraumatized hemisphere, CBF remained unchanged. Hemispheric swelling, water content, cerebrospinal fluid glutamate, and hypoxanthine levels were not affected by dopamine in the given dosages.

CONCLUSIONS

Under the present study design, there was no evidence for a dopamine-mediated vasoconstriction, because posttraumatic cortical CBF was increased by dopamine-induced elevation of MABP. However, the increase in CBF did not significantly affect edema formation or cerebrospinal fluid glutamate and hypoxanthine levels.

Riluzole reduces brain swelling and contusion volume in rats following controlled cortical impact injury

Modulation of the glutamatergic and excitotoxic pathway may attenuate secondary damage following traumatic brain injury by reducing presynaptic glutamate release and blocking sodium channels in their inactivated state. The aim of the present study was to investigate the neuroprotective potential of riluzole in traumatic brain-injured rats. A left temporoparietal contusion was induced in 70 male Sprague-Dawley rats (controlled cortical impact injury). Riluzole (8 mg/kg body weight) was given 30 min, and 6, 24, and 30 h after trauma, while control rats received physiological saline. Experiments were performed at two different degrees of trauma severity as defined by penetration depth of the impactor rod (1 vs. 1.5 mm) with the aim of investigating impact of severity of tissue damage on the neuroprotective potential of riluzole. At 48 h after trauma, brains were removed to determine hemispheric swelling and water content and to assess cortical contusion volume. Before brain removal cisternal cerebrospinal fluid (CSF) was collected in all rats to determine the effects of riluzole on substances associated with edema formation. For this, the excitatory transmitter glutamate, the volume-regulatory amino acid taurine, and the ATP-degradation product hypoxanthine were analyzed by high-performance liquid chromatography. Overall, the degree of tissue damage seems to influence the neuroprotective potential of riluzole. In rats with a less severe trauma (1-mm penetration depth), hemispheric swelling, cerebral water content of the traumatized hemisphere and cortical contusion volume were significantly reduced under riluzole compared to controls (p < 0.05). In rats with a more severe trauma (1.5-mm penetration depth), the neuroprotective effect of riluzole failed to reach statistical significance. Following trauma, CSF glutamate, taurine, and hypoxanthine levels were significantly increased compared to nontraumatized rats (p < 0.001). However, these neurochemical parameters as measured in cisternal CSF failed to reflect trauma-dependent increases in severity of tissue damage and did not reveal riluzole-mediated neuroprotection. Under the present study design, riluzole significantly reduced brain edema formation and contusion volume in rats subjected to a mild focal cortical contusion.

Thiopental in CSF and serum correlates with prolonged loss of cortical activity

Barbiturate coma is initiated in brain-injured patients whenever elevated intracranial pressure remains unresponsive to other therapeutical strategies. However, barbiturates alter cortical activity resulting in difficulties in clinical evaluation. Therefore, we investigated the impact of long-term thiopental administration on responsiveness to exteroceptive stimuli in relation to pharmacokinetics of thiopental in CSF and serum. Long-term infusion increases thiopental levels which remain elevated for 6 and 9 days in CSF and serum, respectively, after termination of its administration. Prolonged unresponsiveness to exteroceptive stimuli correlates with persisting thiopental in CSF and serum. Thus, quantitative analysis of thiopental in serum becomes indispensable in predicting the length of drug-induced neurological impairment and in avoiding misinterpretation of the neurological status.

Increased cerebrospinal fluid glutamate and taurine concentrations are associated with traumatic brain edema formation in rats

Glutamate-mediated excitotoxicity results in cell swelling and contributes to brain edema formation. Since increased extracellular taurine reflects glutamate-induced cell swelling in vitro, elevated CSF taurine could therefore unmask glutamate-mediated cytotoxic edema formation under in vivo conditions. For this, the temporal profile of brain edema and changes in cisternal CSF glutamate and taurine levels were determined in 28 rats following focal traumatic brain injury. Compared to six non-traumatized rats, CSF glutamate (4. 8+/-0.3 vs. 10+/-0.9 microM) and taurine levels (12+/-1.3 vs. 41+/-3 microM) were significantly increased at 8 h after trauma (P<0.001). Over time, CSF glutamate and taurine were significantly increased by 24 (glutamate: 38+/-4.4 microM) and 48 h (taurine: 51+/-4 microM), respectively. While CSF glutamate closely reflected changes in hemispheric water content, alterations in CSF taurine occurred diametrically to those seen for glutamate. Under the present study design, increased CSF taurine could reflect glutamate-induced cell swelling. In addition, neuronal release of taurine with its inhibitory and antiexcitotoxic functions could explain the observed diametric changes in CSF glutamate, CSF taurine, and hemispheric water content. Therefore, increasing taurine could be a therapeutic approach in attenuating post-traumatic glutamate-mediated cell damage.

Temporal profile of cerebrospinal fluid glutamate, interleukin-6, and tumor necrosis factor-alpha in relation to brain edema and contusion following controlled cortical impact injury in rats

Traumatic brain injury is associated with release of the excitotoxin glutamate and production of pro-inflammatory cytokines IL-6 and tumor necrosis factor-alpha (TNF-alpha). Following controlled cortical impact injury, cerebrospinal fluid (CSF) glutamate, IL-6, and TNF-alpha concentrations were measured to investigate their relationship to evolving tissue damage. Compared to non-traumatized rats CSF glutamate, IL-6 and TNF-alpha levels were significantly increased by 8 h after trauma (P<0.005). Parallel to increasing brain swelling and contusion CSF glutamate was significantly elevated over time, reaching highest levels by 48 h (33+/-4 microM) while IL-6 and TNF-alpha showed maximum values at 24 h after trauma (42+/-7 and 4.7+/-1 pg/ml) (P<0.005). The observed different temporal profile of CSF glutamate, IL-6, and TNF-alpha following focal traumatic brain injury could be of therapeutic importance.

Significant reduction in brain swelling by administration of nonpeptide kinin B2 receptor antagonist LF 16-0687Ms after controlled cortical impact injury in rats

OBJECT

Identification of new therapeutic agents aimed at attenuating posttraumatic brain edema formation remains an unresolved challenge. Among others, activation of bradykinin B2 receptors is known to mediate the formation of brain edema. The purpose of this study was to investigate the protective effect of the novel nonpeptide B2 receptor antagonist, LF 16-0687Ms, in brain-injured rats.

METHODS

Focal contusion was produced by controlled cortical impact injury. Five minutes after trauma, the rats received a single dose of no, low- (3 mg/kg body weight), or high- (30 mg/kg) dose LF 16-0687Ms. After 24 hours, the amount of brain swelling and hemispheric water content were determined. Low and high doses of LF 16-0687Ms significantly reduced brain swelling by 25% and 27%, respectively (p < 0.03). Hemispheric water content tended to be increased in the nontraumatized hemisphere. In a subsequent series of 10 rats, cisternal cerebrospinal fluid (CSF) samples were collected to determine whether changes in substances associated with edema formation could clarify why LF 16-0687Ms increases water content. For this, the volume regulator amino acid taurine, the excitatory transmitter glutamate, and the adenosine triphosphate degradation products hypoxanthine and xanthine were measured. In CSF, the levels of taurine, hypoxanthine, and xanthine were significantly decreased following a single administration of LF 16-0687Ms (p < 0.005); the level of glutamate, however, was double that found in control animals (p < 0.05).

CONCLUSIONS

Using the present study design, a single administration of LF 16-0687Ms successfully reduced posttraumatic brain swelling. The decreased levels of taurine, hypoxanthine, and xanthine may reflect reduced posttraumatic brain edema, whereas the increased level of glutamate could account for the elevated water content observed in the nontraumatized hemisphere.

Glutamate-containing parenteral nutrition doubles plasma glutamate: a risk factor in neurosurgical patients with blood-brain barrier damage?

OBJECTIVES

Animal studies have shown that the elevation of plasma glutamate levels increase cerebral edema formation whenever the blood-brain barrier is disturbed. Therefore, changes in plasma glutamate levels as influenced by the administration of a glutamate-containing amino acid solution were investigated in neurosurgical patients.

DESIGN

Prospective, descriptive study.

SETTING

Eight-bed neurosurgical intensive care unit in a university hospital.

PATIENTS

Twenty-three neurosurgical patients requiring parenteral nutrition.

INTERVENTIONS

Parenteral nutrition was begun 24 hrs after craniotomy. Patients receiving a glutamate-containing amino acid solution (3.75 g/L glutamate) were compared with patients infused with a glutamate-free solution.

MEASUREMENTS AND MAIN RESULTS

Arterial plasma and urine amino acids were analyzed using high-performance liquid chromatography. Administration of a glutamate-containing solution doubled plasma glutamate levels in neurosurgical patients (from 53.3 +/- 9.8 microM [preinfusion] to 98.5 +/- 18.7 microM [after 4 hrs of infusion]; p < 0.001), whereas no elevation was seen when infusing a glutamate-free solution (from 52.3 +/- 7.3 [1 hr of infusion] to 53.6 +/- 6.4 microM [4 hrs of infusion]). Upon terminating the glutamate-containing infusion, arterial plasma glutamate levels decreased immediately (from 120 +/- 13.2 microM to 81.2 +/- 19.5 microM). Glutamate as infused in excess appears to exceed a renal threshold and is eliminated renally.

CONCLUSIONS

As shown in animal models, administration of a glutamate-containing amino acid solution significantly increased plasma glutamate levels. Because such an increase in plasma glutamate levels could aggravate cerebral edema formation, glutamate-containing amino acid solutions cannot be recommended for patients with a disturbed blood-brain barrier.

Thiopental attenuates energetic impairment but fails to normalize cerebrospinal fluid glutamate in brain-injured patients

OBJECTIVES

Brain-injured patients are susceptible to secondary brain damage related to decreased cerebral perfusion pressure associated with edema formation and increased intracranial pressure (ICP). Whenever conventional therapy fails to reduce elevated ICP, barbiturate coma represents an additional intervention that may control ICP. In patients suffering from severe traumatic brain injury, cerebrospinal fluid levels of glutamate, hypoxanthine, and lactate were measured during barbiturate coma and correlated to electroencephalographic recordings and ICP.

DESIGN

Prospective, descriptive study.

SETTING

Ten-bed surgical intensive care unit in a university hospital.

PATIENTS

Twenty-one patients with severe traumatic brain injury (Glasgow Coma Scale score < or = 9); 11 required barbiturate coma because of refractory intracranial hypertension, and 10 were manageable with continuous administration of fentanyl and midazolam.

INTERVENTIONS

Thiopental was administered continuously for increased ICP within the first 24 hrs after trauma and adjusted to the burst-suppression pattern (four to six bursts per minute) on continuous electroencephalographic monitoring.

MEASUREMENTS AND MAIN RESULTS

Glutamate and hypoxanthine were analyzed using high-performance liquid chromatography, whereas lactate was measured enzymatically. Patients requiring thiopental presented with significantly higher ICP, glutamate, and hypoxanthine levels than patients receiving fentanyl and midazolam (p < .05). Within the first 24 hrs, thiopental significantly reduced cerebrospinal fluid glutamate and hypoxanthine levels in all patients, i.e., the burst-suppression pattern was successfully induced (p < .001). Interestingly, in five patients cerebrospinal fluid glutamate increased to initial values again despite unchanged neuronal activity. In these patients, ICP, hypoxanthine, and lactate remained significantly elevated compared with the six patients with steadily decreasing cerebrospinal fluid glutamate, hypoxanthine, lactate, and ICP values (p < .02).

CONCLUSIONS

Barbiturate coma does not unequivocally preserve energetic stability despite successful suppression of neuronal activity. Despite the use of barbiturate coma in patients with refractory intracranial hypertension, persistent release or impaired uptake of glutamate may be associated with continuous anaerobic metabolism, as shown by increases in cerebrospinal fluid hypoxanthine and lactate levels.

Glutamate and taurine are increased in ventricular cerebrospinal fluid of severely brain-injured patients

Glutamate contributes to secondary brain damage, resulting in cell swelling and brain edema. Under in vitro conditions, increased extracellular levels of the amino acid taurine reflect glutamate-induced osmotic cell swelling. In vivo, increases in cerebrospinal fluid (CSF) taurine could, therefore, unmask glutamate-mediated cytotoxic edema formation and possibly differentiate it from vasogenic edema. To test this hypothesis, ventricular CSF glutamate and taurine levels were measured in 28 severely brain-injured patients on days 1, 5, and 14 after trauma. Posttraumatic changes in CSF amino acids were investigated in regard to extent of tissue damage and alterations in brain edema as estimated by computerized tomography. On day 1, CSF glutamate and taurine levels were significantly increased in patients with subdural or epidural hematomas (8+/-0.8/71+/-12 microM), contusions (21+/-4.1/122+/-18 microM), and generalized brain edema (13+/-3.2/80+/-15 microM) compared to lumbar control CSF (1.3+/-0.1/12+/-1 microM; p < 0.001). CSF amino acids, however, did not reflect edema formation and resolution as estimated by computerized tomography. CSF taurine correlated positively with glutamate, eventually depicting glutamate-induced cell swelling. However, parallel neuronal release of taurine with its inhibitory function cannot be excluded. Thus, the sensitivity of taurine in unmasking cytotoxic edema formation is weakened by the inability in defining its origin and function under the conditions chosen in the present study. Overall, persisting pathologic ventricular CSF glutamate and taurine levels are highly suggestive of ongoing glial and neuronal impairment in humans following severe traumatic brain injury.

Thiopental and midazolam do not seem to impede metabolism of glutamate in brain-injured patients

Increased extracellular glutamate levels are related to glial and neuronal damage. Glutamate-mediated toxicity is limited by glial uptake and metabolic transformation of glutamate to glutamine and the energetic compounds alanine and lactate which are utilized by surrounding neurons. Under in vitro conditions, barbiturates have been shown to reduce glutamate uptake and its further metabolism, possibly impeding metabolic coupling between astrocytes and neurons. The aims were to investigate if under clinical conditions, the barbiturate thiopental reduces important detoxification of glutamate, resulting in lower CSF glutamine, alanine and lactate levels as opposed to patients receiving midazolam. During long-term administration of thiopental and midazolam, pathologically elevated ventricular CSF glutamate levels were associated with significantly increased glutamine and alanine levels up to 14 days after trauma. CSF lactate, however, remained normal. These data suggest that long-term administration of thiopental and midazolam under clinical conditions does not impede enzymatic activities responsible for detoxification and metabolism of glutamate.

Barbiturate coma may promote reversible bone marrow suppression in patients with severe isolated traumatic brain injury

OBJECTIVES

Barbiturate coma is employed in brain-injured patients whenever increases in intracranial pressure remain unresponsive to less aggressive therapeutic regimens. Barbiturate-mediated neuroprotection, however, is weakened by an increased infection rate related to barbiturate-induced immunosuppression. Co-administration of barbiturates with antibiotics known to induce bone marrow suppression could, in turn, potentiate barbiturate-mediated immunosuppression. Adverse drug reactions and interactions of thiopental with antibiotics in terms of leukopenia, infection rate, and bone marrow suppression were investigated.

METHODS

White blood cells were measured daily, tracheobronchial secretion and urine were examined for bacterial growth twice a week or if an infection was suspected.

RESULTS

A total of 52 patients with severe isolated head injury were consecutively investigated. Due to increased intracranial pressure (ICP), which did not respond to analgosedation, barbiturate coma was performed in 23 cases. The other 29 patients remained analgosedated. Leukocytes and neutrophils were reversibly and significantly decreased in all patients, mostly sustained under thiopental. The pulmonary infection rate due to gram-negative organisms was nearly doubled during barbiturate coma. Reversible agranulocytosis and bone marrow suppression attributed to antibiotics developed in six patients after thiopental administration. Mortality rate, however, was not increased by these adverse effects.

CONCLUSIONS

Barbiturate coma may cause reversible leukopenia and an increased infection rate. Long-term administration of thiopental may also promote reversible antibiotic-induced bone marrow suppression. The mechanisms and site of interaction between thiopental and antibiotics cannot be assessed by the present study and remain to be clarified. However, during and after barbiturate coma, close monitoring of leukocytes and infections and careful selection of antibiotics is required.

Soluble ICAM-1 in CSF coincides with the extent of cerebral damage in patients with severe traumatic brain injury

The intercellular adhesion molecule-1 (ICAM-1) expressed by endothelial cells is crucial in promoting adhesion and transmigration of circulating leukocytes across the blood-brain barrier (BBB). Migrated immunocompetent cells, in turn, release mediators that stimulate glial and endothelial cells to express ICAM-1 and release cytokines, possibly sustaining cerebral damage. Following activation, proteolytic cleavage of membrane-anchored ICAM-1 results in measurable levels of a soluble form, sICAM-1. The aims of this study were to investigate the changes of sICAM-1 levels in ventricular CSF and serum and to elucidate the influence of structural brain damage as estimated by computerized tomography (CT) as well as the extent of BBB dysfunction as calculated by the CSF/serum albumin ratio (QA) in patients with severe traumatic brain injury (TBI). All investigated parameters revealed two subgroups. Patients belonging to group A had sICAM-1 levels in CSF above normal range, presented marked cerebral damage and a disturbance of the BBB (range 0.6-24.7 ng/ml, n = 8). In contrast, patients belonging to group B had no elevation of sICAM-1 values in CSF (range 0.3-3.9 ng/ml, n = 5; p < 0.017) and showed minor cerebral damage with an intact BBB in most cases. In addition, overall analysis showed that sICAM-1 in CSF correlated with the extent of BBB damage as indicated by the QA (r = 0.76; p < 0.001). These results suggest that increased sICAM-1 levels in CSF might depict ongoing immunologic activation and that sICAM-1 correlates with the extent of tissue and BBB damage. The origin of soluble ICAM-1 in CSF and its pathophysiologic role after TBI remains to be clarified.

Neurotransmitters in cerebrospinal fluid reflect pathological activity

The excitatory transmitters glutamate and aspartate become toxic whenever their extracellular levels are increased because of neuronal, glial and endothelial impairment. Taurine, a volume-regulating amino acid, is released upon excitotoxin-induced cell swelling. Our aim was to investigate if glutamate and aspartate in cerebrospinal fluid (CSF) reveal neuropathology in neurological patients, and if taurine unmasks glutamate-mediated toxicity. Glutamate and aspartate are doubled in viral meningitis, acute multiple sclerosis (MS) and myelopathy compared with control subjects and patients with peripheral facial nerve palsy. These levels do not coincide with a disturbed blood-brain barrier, as estimated by the albumin ratio, are independent of their precursors (glutamine, asparagine) and are not associated with cell lysis. Taurine is significantly increased in meningitis, acute MS, and myelopathy, suggesting glutamate-mediated toxicity. Analysis of transmitters in lumbar CSF can be used to identify patients with cerebral and spinal pathology who might benefit from specific receptor-modulating agents.

Cerebrospinal fluid hypoxanthine, xanthine and uric acid levels may reflect glutamate-mediated excitotoxicity in different neurological diseases

Glutamate-mediated excitotoxicity is associated with adenosine triphosphate (ATP) degradation and generation of oxygen radicals. Hypoxanthine and lactate depict energetic impairment, while xanthine and uric acid reflect activity of radical producing xanthine oxidase. Cerebrospinal fluid (CSF) glutamate, hypoxanthine, lactate, xanthine, and uric acid were investigated in neurological patients. In multiple sclerosis, myelopathy, stroke, epilepsy and viral meningitis glutamate, hypoxanthine, xanthine, and uric acid are increased 2-3-fold compared to controls. Lactate is only elevated in meningitis. Normal lactate dehydrogenase (LDH) levels and absent correlation between the albumin ratio and neurochemical parameters exclude an artificial increase due to cell lysis and barrier damage. Absent correlation between neurochemical parameters within each patient group is most likely related to preserved glial and neuronal uptake mechanisms. CSF hypoxanthine, xanthine, and uric acid levels appear superior to lactate in reflecting glutamate-mediated excitotoxicity in neurological patients.

[Neurochemical changes and current pharmacological approaches in craniocerebral trauma]

In recent years, our knowledge concerning pathophysiological changes in brain metabolism after traumatic brain injury (TBI) has greatly expanded. This, in turn, has enabled the development of specific pharmacological strategies for the supplementary treatment of brain-injured patients with the aim of reducing secondary brain damage. The present article focuses on the pathophysiology of TBI and the possibilities for pharmacological intervention. While some of the substances reviewed and presently used in the treatment of TBI, others are under experimental and clinical evaluation at different stages.

Unspecific metabolic blood parameters as used in clinical routine may differentiate malignant from benign cerebral tumors

The investigation of rather insensitive metabolic parameters (protein, fibrinogen, blood urea nitrogen (BUN), blood glucose) reveals significant differences between tumor-bearing and tumor-free patients as well as benign and malignant neoplasms. Whereas metastases and glioblastomas (GBM) show significantly elevated BUN levels (21.9 +/- 1.7; 8 +/- 2.2 mg/dl) compared to benign tumors (meningioma WHO I, astrocytoma I, II) (16 +/- 0.9 mg/dl) and tumor-free matched controls (e.g. 13.9 +/- 1.4 mg/dl) only metastases depict higher glucose (141.7 +/- 11mg/dl) counts. Fibrinogen, significantly elevated in malignancy (395 +/- 25.2; 397.2 +/- 25.9 mg/dl) is without difference between meningioma, astrocytoma (253.2 +/- 16.6; 271.5 +/- 16.5 mg/dl) and controls (e.g. 270.1 +/- 10.8 mg/dl). Correlating BUN with total protein reveals a metabolic mismatch to nearly all tumor patients, regardless of dignity, as compared to tumor-free patients. Neuroendocrinoimmunological changes are the most likely reason for these overt as well as occult findings, making investigation of more sensitive metabolic parameters a rewarding task.