Chiara Adembri

Glycocalyx and sepsis-induced alterations in vascular permeability

Endothelial cells line the inner portion of the heart, blood vessels, and lymphatic vessels; a basal membrane of extracellular matrix lines the extraluminal side of endothelial cells. The apical side of endothelial cells is the site for the glycocalyx, which is a complex network of macromolecules, including cell-bound proteoglycans and sialoproteins. Sepsis-associated alterations of this structure may compromise endothelial permeability with associated interstitial fluid shift and generalized edema. Indeed, in sepsis, the glycocalyx acts as a target for inflammatory mediators and leukocytes, and its ubiquitous nature explains the damage of tissues that occurs distant from the original site of infection. Inflammatory-mediated injury to glycocalyx can be responsible for a number of specific clinical effects of sepsis, including acute kidney injury, respiratory failure, and hepatic dysfunction. Moreover, some markers of glycocalyx degradation, such as circulating levels of syndecan or selectins, may be used as markers of endothelial dysfunction and sepsis severity. Although a great deal of experimental evidence shows that alteration of glycocalyx is widely involved in endothelial damage caused by sepsis, therapeutic strategies aiming at preserving its integrity did not significantly improve the outcome of these patients.

Neuroprotective effects of propofol in models of cerebral ischemia: Inhibition of mitochondrial swelling as a possible mechanism

Background:Propofol (2,6-diisopropylphenol) has been shown to attenuate neuronal injury in a number of experimental conditions, but studies in models of cerebral ischemia have yielded conflicting results. Moreover, the mechanisms involved in its neuroprotective effects are yet unclear. Methods:The authors evaluated the neuroprotective effects of propofol in rat organotypic hippocampal slices exposed to oxygen-glucose deprivation, an in vitro model of cerebral ischemia. To investigate its possible mechanism of action, the authors then examined whether propofol could reduce Ca2+-induced rat brain mitochondrial swelling, an index of mitochondrial membrane permeability, as well as the mitochondrial swelling evoked by oxygen-glucose deprivation in CA1 pyramidal cells by transmission electron microscopy. Finally, they evaluated whether propofol could attenuate the infarct size and improve the neurobehavioral outcome in rats subjected to permanent middle cerebral artery occlusion in vivo. Results:When present in the incubation medium during oxygen-glucose deprivation and the subsequent 24 h recovery period, propofol (10–100 &mgr;m) attenuated CA1 injury in hippocampal slices in vitro. Ca2+-induced brain mitochondrial swelling was prevented by 30–100 &mgr;m propofol, and so were the ultrastructural mitochondrial changes in CA1 pyramidal cells exposed to oxygen-glucose deprivation. Twenty-four hours after permanent middle cerebral artery occlusion, propofol (100 mg/kg, intraperitoneal) reduced the infarct size by approximately 30% when administered immediately after and up to 30 min after the occlusion. Finally, propofol administered within 30 min after middle cerebral artery occlusion was unable to affect the global neurobehavioral score but significantly preserved spontaneous activity in ischemic rats. Conclusions:These results show that propofol, at clinically relevant concentrations, is neuroprotective in models of cerebral ischemia in vitro and in vivo and that it may act by preventing the increase in neuronal mitochondrial swelling.

Microalbuminuria as an early index of impairment of glomerular permeability in postoperative septic patients

Abstract Objective: To evaluate whether microalbuminuria increases in post-operative patients developing sepsis, and whether it is correlated to the sepsis severity score (SOFA) and the PaO2/FIO2 ratio. Design: Prospective study. Setting: University intensive care unit. Patient population: Fifty-five post-operative ASA II-III patients admitted to the ICU after major abdominal or vascular surgery. Interventions: None. Measurements and results: Urine collection and measurement of microalbuminuria and urinary creatinine on admission and again as soon as sepsis developed or at the end of the study (72 h after admission). Results are expressed as the microalbuminuria/creatinine ratio (MACR). The MACR significantly increased as soon as sepsis (defined according to the ACPP/SCCM Consensus Conference) appeared. The MACR positively correlated to the SOFA score, but had no relation to the PaO2/FIO2 ratio. Patients not developing sepsis did not show any increase in the MACR during the study period. Conclusions: Post-operative patients developing sepsis, unlike those with an uncomplicated post-operative evolution, showed an increase in glomerular permeability which was revealed by MACR. The increase in the MACR was positively correlated to the increase in SOFA score, while it had no relation to the PaO2/FIO2 ratio.

Pharmacokinetic Evaluation of Meropenem and Imipenem in Critically Ill Patients with Sepsis

ObjectiveTo evaluate and compare the pharmacokinetic profiles of imipenem and meropenem in a population of critically ill patients with sepsis to find possible differences that may help in selecting the most appropriate drug and/or dosage in order to optimise empiric antimicrobial therapy.Patients and methodsThis was a single-centre, randomised, nonblind study of the pharmacokinetics of both intravenous imipenem 1g and meropenem 1g in 20 patients admitted to an intensive care unit with sepsis in whom antimicrobial therapy was indicated on clinical grounds. Patients were divided into two groups: group I received intravenous imipenem 1g plus cilastatin 1g, and group II received intravenous meropenem 1g over 30 minutes. Peripheral blood samples were collected at 0, 0.5 (end of infusion), 0.75, 1, 1.5, 2, 3, 4, 6 and 8 hours after the first dose and were centrifuged for 10 minutes at 4°C. Urine samples were collected during the 8 hours after antimicrobial administration at 2-hour intervals: 0–2, 2–4, 4–6 and 6–8 hours. The total volume of urine was recorded; the serum and urine samples were immediately frozen and stored at −80°C until assayed. Pharmacokinetic analysis was carried out through computerised programs using the least-square regression method and a two-compartment open model. Statistical differences were evaluated by means of one-way ANOVA.ResultsThe following pharmacokinetic differences between the two drugs were observed: the imipenem mean peak serum concentration was significantly higher than for meropenem (90.1 ± 50.9 vs 46.6 ± 14.6 mg/L, p < 0.01); the area under the serum concentration-time curve was significantly higher for imipenem than for meropenem (216.5 ± 86.3 vs 99.5 ± 23.9 mg · h/L, p < 0.01), while the mean volume of distribution and mean total clearance were significantly higher for meropenem than for imipenem (25 ± 4.1 vs 17.4 ± 4.5L, p < 0.01 and 191 ± 52.2 vs 116.4 ± 42.3 mL/min, p < 0.01, respectively).ConclusionThe more favourable pharmacokinetic profile of imipenem compared with meropenem in critically ill patients with sepsis might balance the possibly greater potency demonstrated in vitro for meropenem against Gram-negative strains. Hence, the clinical efficacy of the two carbapenems depends mostly on their correct dosage.

Vitamin E protects human skeletal muscle from damage during surgical ischemia-reperfusion.

PURPOSE The biochemical and morphological alterations induced in lower limb skeletal muscle by ischemia-reperfusion (I-R) during aortic surgery and the effect of vitamin E pretreatment were investigated. METHODS Two groups of patients undergoing aortic aneurysm resection, one untreated and one treated with vitamin E, were examined. Quadricep muscle biopsies were taken after induction of anesthesia, at the end of ischemia, and after reperfusion. The malondialdehyde (MDA) content and morphology of biopsies were examined to assess peroxidative processes. RESULTS Ischemia did not induce an increase in MDA content but did increase neutrophil infiltration in muscle fibers of untreated patients. Reperfusion led to a significant increase in MDA content and to intermyofibrillar edema and mitochondrial swelling. The MDA content was not increased during ischemia and neutrophil infiltration was minimal in vitamin E treated patients. At reperfusion, the MDA content, the ultrastructural injuries and neutrophil infiltration were significantly reduced by the treatment. CONCLUSIONS Vitamin E is effective in reducing the oxidative muscle damage occurring after a period of I-R.

Low-dose hydrocortisone during severe sepsis: effects on microalbuminuria.

Objective:The aim of this study was to investigate the effect of low-dose hydrocortisone on glomerular permeability measured by the microalbuminuria to creatinine ratio (MACR) and on other markers of sepsis in severe septic patients. Design:Randomized prospective study. Setting:University intensive care unit. Patients:The study involved 40 patients with severe sepsis randomized into the hydrocortisone group (n = 20) and the standard therapy group (n = 20). Interventions:The hydrocortisone group received standard therapy plus a continuous infusion of hydrocortisone for 6 days, whereas the standard therapy group received only standard therapy. Measurements and Main Results:MACR, serum C-reactive protein, and procalcitonin concentrations were recorded every day from the day before the steroid therapy (T0) until the 6 days after (T1, T2, T3, T4, T5, and T6). Concentrations in the hydrocortisone group and the standard therapy group were compared using Mann-Whitney test at each time. We also compared with Wilcoxon signed rank test the values determined in each group at T0 with those at each subsequent time. Median MACR decreased from T0 to T6 in both patient groups; however, values were significantly lower in the hydrocortisone group from T3 through to T6. Median serum C-reactive protein also decreased from T0 in both patient groups, with significantly lower values in the hydrocortisone group from T3 through to T6. There were no significant differences in procalcitonin between groups compared with baseline values or at any individual time point. Conclusions:Low-dose hydrocortisone seems to reduce MACR and serum C-reactive protein but not procalcitonin in patients with severe sepsis. Further studies are needed to confirm these results and to understand the underlying molecular mechanisms.

Neutrophils as mediators of human skeletal muscle ischemia-reperfusion syndrome

Nine patients with aortic aneurysm undergoing arterial reconstruction with temporary aortic occlusion were studied. Since a typical condition of ischemia-reperfusion of the muscles of the lower limbs was created during this surgery, muscle biopsies from the right femoral quadriceps as well as blood samples from the homolateral saphenous vein were taken: (1) before clamping of the aorta, (2) just before declamping, and (3) 30 minutes after reperfusion. Light microscopy revealed a consistent granulocyte infiltration in the ischemic and reperfused skeletal muscle. Ultrastructural damage to the muscle fibers was seen during ischemia and became more severe upon reperfusion. The recruitment of granulocytes into the muscle tissue paralleled the activation of the blood complement system and an increase in circulating neutrophils. Although a spontaneous superoxide anion (O2-) generation from such granulocytes cannot be proved, upon stimulation with formyl-methionyl-leucyl-phenylalanine neutrophils showed a reduced ability in O2 free radical production at the end of ischemia and enhanced O2- generation at reperfusion as compared with the controls. All these findings indicate an active role of granulocytes in the genesis of reperfusion-induced tissue injuries.

Carbamylated erythropoietin is neuroprotective in an experimental model of traumatic brain injury.

Objective:The well-documented neuroprotective effects of recombinant human erythropoietin (rhEPO) are commonly associated with untoward erythrocyte-stimulating effects (polycythemia), with subsequent risk of thromboembolic complications. A carbamylated-rhEPO (CEPO) derivative, which is neuroprotective but lacks hematopoietic activity, has been recently developed. In this study, we evaluated the neuroprotective capability of CEPO in an in vitro model of cerebral trauma in which rhEPO was previously shown to reduce posttraumatic cell death. Design:Prospective, controlled experiment. Setting:Animal, basic science laboratory. Subjects:Wistar rats, 8 days old. Interventions:Organotypic hippocampal slices, obtained from rat brains, were subjected to a well-characterized model of mechanical injury followed by addition of 10 IU/mL rhEPO, 10–100 IU/mL CEPO, or vehicle (injured control) to the incubation medium at different times to assess the temporal window of therapeutic neuroprotection. Measurements and Main Results:Posttraumatic cell death was quantified at 12, 24, or 48 hrs after injury by measuring propidium iodide fluorescence in the selectively vulnerable CA1 hippocampal area. Posttraumatic injury, observed in injured, vehicle-treated hippocampal slices, was significantly attenuated by addition of either 10 IU/mL rhEPO or 10 IU/mL CEPO. The neuroprotective efficacy of 10 IU/mL rhEPO or CEPO remained intact even when administration was delayed 1 hr after trauma. Qualitative microscopy in semithin sections showed that both rhEPO and CEPO exerted a marked pyramidal neuron-sparing effect. Conclusion:Our study shows that 10 IU/mL CEPO exerts neuroprotective effects comparable with those of rhEPO in an in vitro model of mechanical cerebral trauma. Because CEPO lacks hematopoietic effects and seems to possess a prolonged therapeutic time window, this erythropoietin derivative may represent an exciting new pharmacologic tool in treating patients with mechanical injury to the brain.

Pharmacokinetic and Pharmacodynamic Parameters of Antimicrobials Potential for Providing Dosing Regimens that Are Less Vulnerable to Resistance

Whereas infections caused by multidrug-resistant micro-organisms are increasing worldwide, there are few new molecules, especially ones that are active against Gram-negative strains. There are extensive data showing that the administration of antimicrobials according to pharmacokinetic/pharmacodynamic parameters improves the possibility of a positive clinical outcome, particularly in severely ill patients. Evidence is growing that when pharmacokinetic/pharmacodynamic parameters are used to target not only clinical cure but also eradication, the spread of resistance will also be contained. The present paper summarizes the most relevant papers published in this field and provides some suggestions for dosing regimens that can be adopted in the clinical setting to limit the spread of resistance.

Cefazolin bolus and continuous administration for elective cardiac surgery: Improved pharmacokinetic and pharmacodynamic parameters

OBJECTIVE Cefazolin (1-2 g bolus at induction possibly repeated after cardiopulmonary bypass) remains the standard for antibiotic prophylaxis in cardiac surgery. Data indicate, however, that it is underdosed with this dosing schedule. A prospective, randomized study comparing intermittent versus loading dose plus continuous infusion for the same total dose of cefazolin was performed to assess which modality is pharmacokinetically and pharmacodynamically advantageous. METHODS Patients received 2 g cefazolin as a starting dose and then were divided into an intermittent group (receiving another 1 g at 3, 9, and 15 hours after the first dose) and a continuous group (continuous infusion started after the first dose, providing 1 g every 6 hours for 18 hours). Cefazolin levels were measured in blood and atria. RESULTS Mean total and calculated free trough concentrations in blood varied greatly among patients in the intermittent group and were lower than those in the continuous group (P < .05 at 15, 18 and 24 hours). For 9 of 10 (90%) patients in the continuous infusion group, the targeted pharmacokinetic and pharmacodynamic goal (time above minimal inhibitory concentration >90%) was achieved, whereas the goal was met for only 3 of 10 (30%) in the intermittent group (P < .05). The mean atrial tissue concentration was also higher with continuous infusion (P < .05). CONCLUSIONS Administration of cefazolin as bolus plus continuous infusion has pharmacokinetic and pharmacodynamic advantages relative to intermittent administration. It provides more stable serum levels, lower interpatient variability, and higher myocardial tissue penetration.