Central vein catheter-related thrombosis in intensive care patients: incidence, risks factors, and relationship with catheter-related sepsis

OBJECTIVE

To evaluate the incidence and risk factors for catheter-related central vein thrombosis in ICU patients.

DESIGN

Observational prospective multicenter study.

SETTING

An 8-bed surgical ICU, a 10-bed surgical cardiovascular ICU, and a 10-bed medical-surgical ICU.

PATIENTS

During an 18-month period, 265 internaljugular or subclavian catheters were included. Veins were explored by duplex scanning performed just before or < 24 h after catheter removal. Suspected risk factors of catheter-related central vein thrombosis were recorded.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Fifty-seven catheters were excluded from the analysis. Therefore 208 catheters were analyzed. Mean age of patients was 64+/-15 years, simplified acute physiologic score was 12+/-5, organ system failure score at insertion was 1+/-1, and mean duration of catheterization was 9+/-5 days. A catheter-related internal jugular or subclavian vein thrombosis occurred in 33% of the cases (42% [95% confidence interval (CI), 34 to 49%] and 10% [95% CI, 3 to 18%], respectively). Thrombosis was limited in 8%, large in 22%, and occlusive in 3% of the cases. Internal jugular route (relative risk [RR], 4.13; 95% CI, 1.72 to 9.95), therapeutic heparinization (RR 0.47; 95% CI, 0.23 to 0.99), and age >64 years (RR, 2.44; 95% CI, 2.05 to 3.19) were independently associated with catheter-related thrombosis. Moreover, the risk of catheter-related sepsis was 2.62-fold higher when thrombosis occurred (p=0.011).

CONCLUSIONS

Catheter-related central vein thrombosis is a frequent complication of central venous catheterization in ICU patients and is closely associated with catheter-related sepsis.

Outcomes of primary and catheter-related bacteremia. A cohort and case-control study in critically ill patients

We studied a cohort of 2201 patients hospitalized in 15 French intensive care units (ICUs) for > or = 48 h during a 4-mo period to assess the incidence and outcomes of primary and definite catheter-related bloodstream (CRB) or secondary nosocomial bloodstream infection (NBSI). Variables associated with ICU death and duration of stay were determined by logistic regression, and attributable mortality and length of stay (LOS) from a nested matched case-control (96 pairs) study, stratified on the source of bacteremia. Bacteremia occurred in 5% (95% CI 4.1-6%) of patients with > or = 48 h ICU stay. Primary, CRB, and secondary NBSI accounted for 29%, 26%, and 45% of the 111 episodes, respectively. NBSI was associated with a markedly increased risk of death (OR = 4.6; 95% CI 2.9-7.1) and an attributable mortality of 35% (95% CI, 28%-47%). In the case-control study, the excess mortality was 20% (p = 0.03) in patients with primary bacteremia and CRB, and 55% (p < 0.001) for secondary bacteremia; in patients with CRB only, the excess mortality was 11.5%. The median excess ICU LOS in survivors of NBSI was 9.5 d, and was similar, irrespective of its source. The risk of mortality associated with primary and catheter-related bacteremia appears much lower than that of secondary bacteremia, but is sizable, and the excess LOS incurred by the various categories of bacteremia is comparable. Differentiating catheter-related bacteremia from both primary and other secondary bacteremia appears warranted in studies conducted in critically ill patients.

Variations in extracellular levels of dopamine, noradrenaline, glutamate, and aspartate across the sleep--wake cycle in the medial prefrontal cortex and nucleus accumbens of freely moving rats

We used intracerebral microdialysis coupled with electrophysiologic recordings to determine relative changes in the concentrations of several neurotransmitters in the medial prefrontal cortex and nucleus accumbens of freely moving rats during waking, slow-wave sleep, and rapid eye movement (REM) sleep. The concentrations of noradrenaline, dopamine, glutamate, and aspartate in 2-min dialysate samples were analyzed by capillary electrophoresis combined with laser-induced fluorescence detection. Changes in glutamate and aspartate concentrations were found only in the nucleus accumbens, in which a decrease was obtained during both slow-wave sleep and REM sleep compared to waking. A progressive reduction in the release of noradrenaline was observed from waking to REM sleep in both structures. In contrast, dopamine concentrations were higher during waking and REM sleep compared to that during slow-wave sleep. The latter results demonstrate that contrary to the findings of earlier electrophysiologic studies carried out on ventral tegmental area dopaminergic neurons, changes in the release of dopamine in projection areas occur across the sleep-wake cycle. The elevated levels of dopamine during waking and REM sleep in the medial prefrontal cortex and the nucleus accumbens could result from changes during these two states in afferent modulation at the level of cell bodies or at the level of dopaminergic terminals.

Mortality of nosocomial pneumonia in ventilated patients: influence of diagnostic tools

The overmortality induced by nosocomial infections, especially pneumonia in ventilated patients (VNP), is still a matter of controversy because it is difficult to know precisely the respective effects of VNP per se and both the underlying illness and the severity of the disease that indicates ICU stay. During a 3-yr period, for each patient mechanically ventilated for more than 48 h we recorded underlying illness, reason for mechanical ventilation, clinical and therapeutic data collected during the first 48 h of ventilation, and death in the ICU. Patients with suspicion of VNP (S-VNP) according to clinical, radiologic, and biologic criteria underwent bronchoscopy with protected specimen brush (PSB) and bronchoalveolar lavage culture (BAL-C). VNP was confirmed (C-VNP) if PSB > or = 10(3) cfu/ml and/or BAL-C > or = 10(4) cfu/ml. Prognostic multivariate analysis was performed introducing S-VNP and C-VNP as time-dependent covariates. Of the 387 studied patients, 112 S-VNP and 56 C-VNP were observed with overall mortality of 43% (168 patients). MacCabe, APACHE II score, shock, use of sedatives and absence of enteral nutrition were additively associated with an increased mortality as well as C-VNP (relative risk [RR]: 1.8, p = 0.007). Nevertheless, when S-VNP and C-VNP were simultaneously introduced in the Cox model, only S-VNP remained associated with increased mortality. In patients suspected of VNP, confirmation of VNP using PSB and/or BAL-C adds no prognostic information. Whether this could be explained by the lack of sensitivity of protected distal samples or the severity of underlying conditions of S-VNP patients is still an open issue. A multivariate analysis based on follow-up data during the ICU course of ventilated patients will be initiated in the near future.

Separate areas of rat medulla oblongata with populations of serotonin- and adrenaline-containing neurons alter blood pressure after L-glutamate stimulation

Separate populations of serotonin- and adrenaline-containing neurons exist in the ventrolateral medulla oblongata and project to the intermediolateral cell column of the spinal cord. The medullary serotonin nuclei appear to constitute a heterogeneous group with diverse effects on arterial pressure. Microinjections of sodium glutamate (which excites cell bodies but not axons of passage) made in the area of the ventrolateral serotonin cells evokes an increase in arterial pressure which is abolished by prior 5,7-dihydroxytryptamine (5,7-DHT) treatment. In contrast, glutamate microinjection in the area of the serotonin-containing cell bodies in the midline of the medulla evokes falls in arterial pressure and these responses are attenuated by pretreatment with 5,7-DHT. Glutamate microinjection made in the ventrolateral medulla in the area of the adrenaline-containing cells, evokes increases in arterial pressure which are not altered by 5,7-DHT pretreatment. After ablation of the area of the adrenaline-containing cells by electrolytic lesion, the pressor function of the ventrolateral serotonin-containing cells is still observed. These results suggest that although the serotonin-containing neurons of the ventrolateral medulla are closely aligned with the ventrolateral adrenaline area, the serotonin cell groups and the cells of the adrenaline area exert their pressor actions independently.

Capillary zone electrophoresis with laser-induced fluorescence detection for the determination of nanomolar concentrations of noradrenaline and dopamine: application to brain microdialysate analysis

Determination of catecholamines by capillary zone electrophoresis with laser-induced fluorescence detection was performed on low-concentration samples, which were derivatized with naphthalene-2,3-dicarboxaldehyde to give highly fluorescent compounds. When the borate concentration in the derivatization medium was decreased from 130 to 13 mM, sensitivity for noradrenaline (NA) and dopamine (DA) was greatly enhanced while resolution between these two compounds decreased. A 50 mM borate concentration in derivatization medium was chosen since it provided maximal resolution between NA and DA, together with a high separation efficiency (3.1 million theoretical plates per meter for DA). The injection of 2.4 nL of a NA and DA solution derivatized at 10(-9) M produced peaks with signal-to-noise ratio of 8:1 and 3:1, respectively, corresponding to 1.8 amol of each catecholamine. The calibration curves were linear when NA and DA solutions were derivatized at concentrations ranging from 10(-6) to 10(-9) M. This method was used to determine NA in brain extracellular fluid: a peak corresponding to a basal level of 5 x 10(-9) M endogeneous NA was observed in microdialysates from the medial frontal cortex of the rat, and its nature was confirmed by both electrophoretic and pharmacological validations.

Unrelated course of subthalamic nucleus and globus pallidus neuronal activities across vigilance states in the rat

The pallido-subthalamic pathway powerfully controls the output of the basal ganglia circuitry and has been implicated in movement disorders observed in Parkinson's disease (PD). To investigate the normal functioning of this pathway across the sleep-wake cycle, single-unit activities of subthalamic nucleus (STN) and globus pallidus (GP) neurons were examined, together with cortical electroencephalogram and nuchal muscular activity, in non-anaesthetized head-restrained rats. STN neurons shifted from a random discharge in wakefulness (W) to a bursting pattern in slow wave sleep (SWS), without any change in their mean firing rate. This burst discharge occurred in the 1-2 Hz range, but was not correlated with cortical slow wave activity. In contrast, GP neurons, with a mean firing rate higher in W than in SWS, exhibited a relatively regular discharge whatever the state of vigilance. During paradoxical sleep, both STN and GP neurons increased markedly their mean firing rate relative to W and SWS. Our results are not in agreement with the classical 'direct/indirect' model of the basal ganglia organization, as an inverse relationship between STN and GP activities is not observed under normal physiological conditions. Actually, because the STN discharge pattern appears dependent on coincident cortical activity, this nucleus can hardly be viewed as a relay along the indirect pathway, but might rather be considered as an input stage conveying corticothalamic information to the basal ganglia.

A randomized cross-over comparison of the hemodynamic response to intermittent hemodialysis and continuous hemofiltration in ICU patients with acute renal failure

OBJECTIVE

To compare the hemodynamic response of ICU patients with acute renal failure of a 24-h continuous arteriovenous hemofiltration (CAVH) and that of patients with a 4-h intermittent hemodialysis (HD).

DESIGN

Cross-over randomized clinical trial. The two periods to be compared were a 24-h CAVH and the 24-h encompassing a 4-h HD. These two periods were separated by a 24-h wash-out period.

SETTING

Ten bed medicosurgical ICU of a tertiary care center in Paris, France.

PATIENTS

Inclusion criterion was the requirement of replacement therapy for acute renal failure in patients already submitted to mechanical ventilation.

INTERVENTIONS

CAVH was performed with Ringers' lactate used for restitution and infused before the hemofilter. The ultrafiltrate output was maintained at around 15 ml/min. HD was performed with a bicarbonate-buffered dialysate.

MEAN OUTCOME MEASURES

Mean arterial pressure (MAP), use of adrenergic drugs, and change in body weight during each period.

RESULTS

Twenty-seven consecutive patients were included, 15 CAVH-HD and 12HD-CAVH. CAVH and HD allowed the same metabolic efficacy. No hemodynamic parameter (MAP, amount of adrenergic drugs, change in body weight) differed between the two methods.

CONCLUSIONS

CAVH is equivalent to HD in terms of MAP and the use of vasopressive drugs and fluids. Establishing the superiority of CAVH would require carefully controlled studies assessing either outcome or changes in tissue oxygenation.

Effect of previous antimicrobial therapy on the accuracy of the main procedures used to diagnose nosocomial pneumonia in patients who are using ventilation

We evaluated the effect of antibiotic treatment received before the suspicion of pneumonia on the diagnostic yield of protected specimen brush (PSB), direct examination (BAL D) and culture (BAL C) of lavage fluid on consecutive mechanically ventilated patients with suspected nosocomial pneumonia. Bronchoscopy was always performed before any treatment for suspected pneumonia. One hundred and sixty-one patients with suspected pneumonia underwent PSB and BAL before any institution or change in antibiotic therapy (AB). Sixty-five patients received AB for an earlier septic episode (ON AB group) and 96 patients did not (OFF AB group). All but two strains recovered were highly resistant to previous AB. Sensitivity and specificity of each test were not different between the ON AB and OFF AB groups as well as the percentage of complete agreement between the 3 procedures, 74 and 67% respectively. We conclude that previous AB received to treat an earlier septic episode unrelated to suspected pneumonia do not affect the diagnostic yield of PSB and BAL.

Enhanced temporal resolution for the microdialysis monitoring of catecholamines and excitatory amino acids using capillary electrophoresis with laser-induced fluorescence detection. Analytical developments and in vitro validations

This paper reports the development of a method based on capillary electrophoresis with laser-induced fluorescence detection for the simultaneous determination of catecholamines and excitatory amino acids on submicroliter microdialysis samples, with short analysis times (3 min or less), high sensitivity (nanomolar range, i.e., attomoles detected) and high separation efficiency (up to 1.10(6) theoretical plates). A continuous flow derivatization of small volumes of microdialysate (500 nl) using naphthalene-2,3-dicarboxaldehyde as derivatizing reagent is described. Thereafter, two subsequent off-line analyses are performed on each of the 30-s dialysates to determine catecholamines and amino acids. The performances of the present method are demonstrated in vitro by monitoring rapid fluctuations in the concentration of catecholamines and amino acids in the external microdialysis medium.

Campylobacter fetus bloodstream infection: risk factors and clinical features

In this paper, we report 21 cases of Campylobacter fetus bloodstream infection observed in our institution over a 9-year period. The median age of the patients was 78 years. Most of them (62%) had a significant underlying disease, such as diabetes, immunodeficiency or cardiovascular disease. The main clinical features were fever with (62% of cases) or without (38%) extra-intestinal symptoms. These included mycotic aneurysm of the abdominal aorta (24%) and cellulitis (19%). Antibiotic treatment was mainly based on amoxicilline-clavulanate (57%) or imipenem (21%), for a median duration of 28 days. A favourable outcome was observed in 72% of cases. Death directly attributable to infection was observed for three patients, due to the rupture of an infected aneurysm or relapsing bloodstream infection with septic shock. All patients initially treated with imipenem had a favourable outcome. This report adds evidence that C. fetus bloodstream infection should be suspected in elderly patients with fever, immunodeficiency and cardiovascular damages. Imipenem seems to be the most active drug, especially in severe cases.

Time-course variations in tyrosine hydroxylase activity in the rat locus coeruleus after electrolytic destruction of the nuclei raphe dorsalis or raphe centralis

Time-course variations in tyrosine hydroxylase activity were measured in the locus coeruleus of the albino rat after electrolytic coagulation of either the nucleus raphe dorsalis or the nucleus raphe centralis. Highly significant increases were measured at 4 days after lesioning of the raphe dorsalis (30.33%) and the raphe centralis (81.55%) compared with control values, whereas the activity in groups A9 and A10 was unchanged at this time-point. In conjunction with other experimental evidences, an hypothesis is proposed that the catecholaminergic neurons located in the locus coeruleus are directly and/or indirectly controlled by the serotonin-containing neurons located in the anterior raphe system nuclei.

Determination of reference values for serotonin concentration in platelets of healthy newborns, children, adults, and elderly subjects by HPLC with electrochemical detection

We adapted a high-performance liquid chromatographic method with electrochemical detection (Clin Chim Acta 1984;139:1-12) to the determination of platelet serotonin. We used this method to determine platelet serotonin reference values in a healthy population, measuring platelet serotonin concentration in the following subjects: 31 newborns (16 girls, 15 boys); 41 children (11 girls, 30 boys), ages 20 months to 15 years; 56 adults (26 women, 30 men), ages 20 to 58 years; and 20 elderly subjects (16 women, four men), ages 65 to 94 years. There was no significant difference in platelet serotonin concentration between sexes in each age group. However, significant changes (P less than 0.001) were observed between the newborns (mean +/- SD: 1.67 +/- 0.74 nmol/10(9) platelets) and the children (4.09 +/- 1.04) or the adults (3.81 +/- 0.87). Moreover, the platelet serotonin concentration in the elderly subjects (2.57 +/- 1.12) was significantly (P less than 0.001) lower than in the adults and children and significantly higher (P less than 0.01) than in the newborns. Such age-related differences must be taken into consideration when data from neurological or psychiatric patients and control subjects are compared.

In vivo monitoring of extracellular noradrenaline and glutamate from rat brain cortex with 2-min microdialysis sampling using capillary electrophoresis with laser-induced fluorescence detection

The measurement of neurotransmitters by capillary electrophoresis (CE) has emerged as a reliable and sensitive method for microdialysis sample analysis. This paper describes a method which employs laser-induced fluorescence detection (LIFD) of catecholamines and excitatory amino acid derivatives formed after reaction with naphthalene-2,3-dicarboxaldehyde. On-line derivatization of very small volumes of microdialysis samples (500 nl) is developed before two off-line analyses (total run time of less than 10 min) are performed to detect derivatives of catecholamines and excitatory amino acids formed in each sample. High microdialysis temporal resolution is reached (2-min fractions) for the simultaneous monitoring of noradrenaline (NA) and glutamate concentrations from rat brain cortex microdialysates. The system performance is evaluated and pharmacological characterization of the determination of NA in cortical dialysates by CE-LIFD is reported.

Distribution of alpha-1 and alpha-2 binding sites in the rat locus coeruleus

Precise anatomical distribution of alpha-1 and alpha-2 adrenergic binding sites has been investigated in the rat locus coeruleus (LC) using quantitative radioautography of brain sections incubated with 3H-prazosin or 3H-idazoxan. Distribution patterns of 3H-prazosin (alpha-1 sites) and 3H-idazoxan (alpha-2 sites) were heterogeneous and different along a postero-anterior axis in the LC. Comparison between distribution of alpha-2 binding sites and noradrenergic (NA) cellular density suggests that at least a fraction of these sites might be localized on NA perikarya or dendrites in this structure. Quantitative estimations of the binding parameters along this postero-anterior axis in the LC have revealed that the heterogeneous distributions of alpha-1 and alpha-2 binding sites are due not only to variations in the maximal densities of sites but also to variations in the affinities of these sites for their respective ligand.

Early increase in phenylethanolamine-N-methyltransferase activity in a new strain of spontaneously hypertensive rats

By repeated inbreeding, 2 strains of spontaneously hypertensive and normotensive rats have been simultaneously selected. The activities of tyrosine hydroxylase and phenylethanolamine-N-methyltransferase were determined in various central catecholaminergic nuclei (C1, C2, A6 and A9) and in two peripheral tissues (adrenal glands and superior cervical ganglion). These assays were performed on rats belonging to the normotensive or the hypertensive strain at 3 ages which characterize the development of hypertension (5, 9 and 21 weeks). Except for a decrease in the C1 region of 9-week-old rats, no significant change in tyrosine hydroxylase activity occurred in central or peripheral structures of the spontaneously hypertensive rats when compared to the normotensive rats. In contrast, the activity of the phenylethanolamine-N-methyltransferase (PNMT), was increased in the C2 adrenergic group of the medulla oblongata in young spontaneously hypertensive rats: +43% (P less than 0.001) at 5 weeks of age and +32% (P less than 0.001) in 9-week-old rats. However, there was no significant difference between the 21-week-old rats. No modification of the PNMT activity was found in the C1 adrenergic group of the medulla oblongata. PNMT activity was increased significantly in the adrenal glands of 5-week-old hypertensive rats (+22%, P less than 0.001). By 9 weeks, the difference in PNMT activity in the adrenals was no longer significant. Thus, in young rats of the hypertensive strain, there was an increase in the capacity to synthetize adrenaline in the C2 area of the medulla oblongata and in the adrenal glands. While the enzymatic change present in the adrenals seems to be specific to this new strain of hypertensive rats, the elevation of PNMT activity in a specific region of the medulla oblongata (C2 group) is a characteristic common to at least two independently derived strains of genetically hypertensive rats.

Toward brain imaging of serotonin 5-HT1A autoreceptor internalization

Enhancing cerebral serotonin (5-hydroxytryptamine, 5-HT) neurotransmission is a common property of antidepressant treatments and the basis for their efficacy. 5-HT1A receptors located on the cell body and dendrites of 5-HT neurons (autoreceptors) play a key role in this regard. Because they normally mediate an inhibition of neuronal firing, their desensitization is a prerequisite to the delayed enhancement of 5-HT neurotransmission upon treatment with monoamine oxidase (MAOI) inhibitors or specific serotonin reuptake inhibitors (SSRI). Using beta-sensitive microprobes in vivo, we measured a significant decrease (-30%) in binding sites for the 5-HT1A PET radioligand [18F]MPPF associated with an equivalent reduction (-34%) in the cell surface density of 5-HT1A receptor immunoreactivity (internalization), in the nucleus raphe dorsalis (autoreceptors), but not hippocampus (heteroreceptors), of rats given a single dose of the specific 5-HT1A receptor agonist, 8-OH-DPAT (0.5 mg/kg, iv). This effect was completely blocked by pretreatment with the selective 5-HT1A antagonist WAY 100635. Having ruled out that this decreased density of [18F]MPPF binding in the nucleus raphe dorsalis of 8-OH-DPAT-treated rats resulted from a local blood flow effect, we obtained autoradiographic evidence indicating that the total amount of specific binding of [18F]MPPF in tissue sections was unaffected by the 8-OH-DPAT treatment in either NRD or hippocampus. It was therefore concluded that the internalization of 5-HT1A autoreceptors accounted for the decreased binding in vivo of [18F]MPPF in the nucleus raphe dorsalis of rats treated with 8-OH-DPAT. Thus, PET imaging might provide a mean to measure 5-HT1A receptor internalization in human brain and thus assess responsiveness to antidepressant treatment.

In vivo temporal sequence of rat striatal glutamate, aspartate and dopamine efflux during apomorphine, nomifensine, NMDA and PDC in situ administration

In vivo microdialysis was used to investigate the interactions between dopamine (DA), glutamate (Glu) and aspartate (Asp) in anaesthetised-rat striatum. The combination of brain microdialysis and capillary electrophoresis with laser-induced fluorescence detection (CE-LIFD) allows the simultaneous monitoring of the efflux of these neurotransmitters up to every 10 s. DA and Glu reuptake inhibitors, nomifensine and L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) and, dopaminergic and glutamatergic receptor agonists, apomorphine and NMDA respectively, were administered by reverse dialysis. Reverse dialysis of 20 micro M nomifensine induced a rapid and marked increase (+3200% at 5 min) in extracellular DA, while a decrease in Glu and Asp (-11 and -25%, respectively) was observed simultaneously. Reverse dialysis of 10 micro M apomorphine led to progressive changes: -63% decrease in DA and +25% Glu increase at 36 min. Reverse dialysis of 1 mM NMDA induced a simultaneous increase in DA, Glu and Asp which peaked at +2 min (+840%, +40% and +150%, respectively). Surprisingly, a second increase in Glu was observed 5 min after the end of NMDA perfusion. Reverse dialysis of PDC (1 mM and 10 mM) induced a rapid increase in Glu and Asp levels, while DA increased with a 26-s delay. These findings indicate that, in the striatum, endogenous DA and Glu may act in opposition to regulate each other's efflux. These results have been obtained due to unique features offered by microdialysis coupled with CE-LIFD.

Differential effects of neurotensin on dopamine release in the caudal and rostral nucleus accumbens: a combined in vivo electrochemical and electrophysiological study

The time-course of variations in extracellular dopamine concentration following local pressure ejection of 10(-7) to 10(-3) M neurotensin into the ventral tegmental area of the rat was determined in the minute range in the nucleus accumbens by means of differential normal pulse voltammetry associated with carbon fibre electrodes. The effects of neurotensin ejection into the ventral tegmental area were further investigated on the firing activity of the corresponding dopaminergic neurons. The lowest concentration of neurotensin (10(-7) M) enhanced the extracellular dopamine concentration throughout the nucleus accumbens and stimulated the discharge activity of ventral tegmental area dopaminergic neurons. The two highest concentrations of neurotensin (10(-5) M and 10(-3) M) evoked two patterns of responses on the extracellular dopamine concentration and on the discharge activity of dopaminergic neurons. The extracellular dopamine concentration was increased above basal levels in the caudal part of the nucleus accumbens. In the rostral part, the evoked changes exhibited a multiphasic time-course characterized by a decreasing phase below baseline. The firing rate of dopaminergic neurons was either increased or decreased, depending on the neuron being tested. In fact, neurotensin ejection was always followed by an exacerbation of bursting activity, the resulting effect on the mean firing rate being related to the duration of the interburst intervals. Indeed, short interburst intervals permitted an increase in mean firing rate whereas long interburst intervals, indicative of excessive depolarization, led to a decrease in mean firing rate. These results suggest that variations in extracellular dopamine concentration evoked by neurotensin administration into the ventral tegmental area are the result of neurotensin-evoked changes in dopaminergic activity. Moreover, the differential effects evoked by high concentrations of neurotensin could be attributable to two subpopulations of ventral tegmental area dopaminergic neurons which could project differentially to the caudal and the rostral parts of the nucleus accumbens.

Extracorporeal carbon dioxide removal technique improves oxygenation without causing overinflation

Extracorporeal CO2 removal combined with low frequency positive pressure ventilation (ECCO2R-LFPPV) improves gas exchange and decreases peak pressures, respiratory rates, and tidal volumes in animals and in humans. Recent evidence suggests that pulmonary barotrauma results from lung overinflation rather than from high pressures. This study was to test the hypothesis whether ECCO2R-LFPPV could improve gas exchange without causing lung overinflation, despite the use of higher levels of PEEP, when compared with conventional mechanical ventilation. Eleven patients with severe adult respiratory distress syndrome (ARDS) who failed to respond to different modes of mechanical ventilation were treated with ECCO2R-LFPPV. Risk of pulmonary barotrauma was evaluated by static pressure-volume (P-V) curves and dynamic changes in volumes monitored by respiratory inductive plethysmography (Respitrace). ECCO2R-LFPPV PaO2/FIO2 increased from 79 +/- 21 to 207 +/- 108 (p = 0.003). Risk of barotrauma, as shown by the shape of the P-V curve, was present in all patients receiving mechanical ventilation even though most of them were treated with permissive hypoventilation. By contrast, no evidence of persistent lung overinflation could be detected by either static P-V curves or dynamic measurements in nine of 11 patients who were treated by ECCO2R-LFPPV. The two remaining patients had severe airway obstruction because of bleeding, and they remained ventilated with persistent risk of barotrauma. We conclude that ECCO2R-LFPPV improves gas exchange without causing lung overinflation in a majority of patients with ARDS.

Coupling on-line brain microdialysis, precolumn derivatization and capillary electrophoresis for routine minute sampling of O-phosphoethanolamine and excitatory amino acids

In previous papers, we described the analysis of excitatory amino acids (EAAs) and catecholamines in microdialysis samples using capillary electrophoresis with laser-induced fluorescence detection (CE-LIFD). In the present paper, we report that an automated analysis of such samples can be easily achieved by on-line coupling of the microdialysis probe with a continuous flow derivatization system and a commercially available CE-LIFD apparatus. Because of the short analysis time (less than 2 min) and high separation efficiency (100-200,000 theoretical plates), high temporal resolution of microdialysis (minute range) is preserved as compared to off-line systems, while both EAAs and O-phosphoethanolamine (PEA) can be simultaneously detected. This new method has been applied to the measurement of these compounds in microdialysis samples from hippocampal slice cultures and striatum of anesthetized rats. Extracellular concentrations of EAAs, but not PEA, increased during perfusion of a solution containing high K+ or a glutamate uptake inhibitor. However, after in vitro ischemia on hippocampal slices, both EAAs and PEA concentrations increased, but with different temporal patterns.