Evangelia Douka

Crack identification in beams using wavelet analysis

In this paper a simple method for crack identification in beam structures based on wavelet analysis is presented. The fundamental vibration mode of a cracked cantilever beam is analyzed using continuous wavelet transform and both the location and size of the crack are estimated. The position of the crack is located by the sudden change in the spatial variation of the transformed response. To estimate the size of the crack, an intensity factor is defined which relates the size of the crack to the coefficients of the wavelet transform. An intensity factor law is established which allows accurate prediction of crack size. The viability of the proposed method is investigated both analytically and experimentally in case of a cantilever beam containing a transverse surface crack. In the light of the results obtained, the advantages and limitations of the proposed method as well as suggestions for future work are presented and discussed.

Crack identification in plates using wavelet analysis

In this paper, a method for crack identification in plates based on wavelet analysis is presented. The case of an all-over part-through crack parallel to one edge of the plate is considered. The vibration modes of the plate are analyzed using the continuous wavelet transform and both the location and depth of the crack are estimated. The position of the crack is determined by the sudden change in the spatial variation of the transformed displacement response. To estimate the depth of the crack, an intensity factor is defined which relates the depth of the crack to the coefficients of the wavelet transform. An intensity factor law is established which allows accurate prediction of crack depth. The viability of the proposed approach is demonstrated using simulation examples. In view of the obtained results, the advantages and limitations of the proposed approach as well as suggestions for future work are presented and discussed.

Historical perspective of the word “sepsis”

Sir: In their article “Organ dysfunction during sepsis”, Singh and Evans [1] mentioned that the word “sepsis” is derived from the Greek word sepsin, which means ‘to make putrid’. The correct word is sepsis [σηψις], which is the original Greek word for the “decomposition of animal or vegetable organic matter in the presence of bacteria”. We meet the word for the first time in Homer’s poems, where Sepsis is a derivative of the verb form sepo [σηπω], which means “I rot”. The term sepsis is also found in the Corpus Hippocraticum exchangeably with the word sepidon [σηπεδών] (“the decay of webs”): Epidemic. B. 2,2, Prorret. I. 99. Aristoteles, Plutarch and Galen use the word sepsis [σηψις] in the same meaning as Hippocrates. The word “sepsis” has thus persisted for 2,700 years with more or less unchanged meaning. References

Pseudomonas aeruginosa Susceptible Only to Colistin in Intensive Care Unit Patients

BACKGROUND Gram-negative bacilli, including multi-drug-resistant (MDR) Pseudomonas aeruginosa, are responsible for severe intensive care unit (ICU)-acquired infections, mainly pneumonia and bacteremia. The aim of this study was to determine the incidence of MDR strains of Pseudomonas in patients undergoing cardiac surgery, to elucidate the effectiveness of treating these patients with colistin, and to assess the safety of the drug. METHODS A prospective study was conducted among 1,452 patients who underwent surgery for a variety of cardiac lesions over a one-year period, and who spent a portion of the recovery period in the surgical ICU. Their case histories were analyzed to identify infectious complications. Diagnosis of infection was based on clinical data, and the pathogen was tested with respect to its susceptibility to colistin (polymyxin E). The clinical response to the antibiotic was evaluated. RESULTS Over the 12-month period, among 115 infected patients, 15 were affected by strains of P. aeruginosa. In 10 patients, this pathogen proved resistant to all potentially active antibiotics except colistin. All of the affected patients were being ventilated mechanically, and eight of them presented with ventilator-associated pneumonia (VAP), whereas one patient suffered a deep incisional surgical site infection and bacteremia and the remaining patient had a superficial infection of a lower-extremity vein graft donor site. The MDR pathogen was introduced to the hospital by three patients transferred from three institutions. All patients were treated with intravenous colistin. In cases of VAP, aerosolized colistin was added. Deterioration of renal function occurred in three patients (30%), all of whom had a history of renal insufficiency. Cure or clinical improvement was observed in seven patients (70%), whereas four patients, including one who improved initially, developed sepsis and died with multiple organ dysfunction syndrome (mortality rate 40%). CONCLUSIONS The increasing prevalence of MDR P. aeruginosa in ICU patients has rekindled interest in polymyxins, which had been abandoned because of toxic side effects. Colistin retained significant in vitro activity against this virulent organism, had an acceptable safety profile, and should be considered as a treatment option in critically ill patients with infection caused by MDR gram-negative bacilli. Aerosolized colistin may merit further consideration as a therapeutic intervention for patients with refractory pulmonary infections.

Methicillin-resistant Staphylococcus aureus preventing strategy in cardiac surgery

OBJECTIVES The aim of this survey was to elucidate the efficacy of methicillin-resistant Staphylococcus aureus (MRSA) preventing strategy in our institution by investigating the incidence and evaluating the morbidity and mortality associated with this multi-resistant virulent organism. METHODS A prospective observational cohort among patients submitted to cardiovascular surgical procedures was conducted from 1 January 1997 to 31 December 2005. Preventing strategy included active screening programs by nasal swabs for all patients admitted from other hospitals or being at risk for developing infectious complications. Carriers or infected patients remained isolated and were treated promptly. Furthermore, all newly employed health care workers were screened for MRSA and carriers were treated with mupirocin until the eradication of the pathogen. RESULTS Throughout the 9-year study period 826 infectious complications were registered among 15,270 cardiac surgical patients. Total infection rate was 5.4%. MRSA was identified in 86 patients; 56 patients proved carriers and 30 infected. The MRSA associated infection rate was 0.2%. During this period of time mean ICU stay was 1.7 days and ICU mortality rate was 2.9%. MRSA infected patients presented a mean ICU stay of 46.5 days and a mortality rate of 30%. In ten patients, MRSA was detected in tracheal secretions, in four patients in swabs taken from donor site infection and in four patients from superficial sternal surgical wound. In ten patients the pathogen was isolated from cultures of the surgical site drainage and the diagnosis of post-sternotomy mediastinitis was confirmed. The remaining two patients were defined as having severe sepsis; MRSA was documented in central venous catheter tips and blood cultures. CONCLUSIONS The prompt determination, isolation and appropriate treatment of MRSA patients admitted from other institutions combined with the detection and elimination of carriers among new health care workers and patients at high risk of developing infectious complications prevented further spread of the pathogen.

Preventing strategy of multidrug-resistant Acinetobacter baumanii susceptible only to colistin in cardiac surgical intensive care units.

OBJECTIVE The study aimed to determine the incidence and mortality of multidrug-resistant Acinetobacter baumannii in cardiac surgery, to elucidate the effectiveness of colistin treatment and to identify if the additional measures to the recommended procedures were able to control the dissemination of the pathogen. METHODS A prospective observational cohort was conducted among cardiac surgical patients from 1 September 2005 to 31 December 2006. We reviewed the prophylactic measures of the surgical intensive care unit and implemented a two scale multiple program. Scale I included classical infection control measures, while Scale II referred to the geographic isolation of multidrug-resistant Acinetobacter baumannii patients and environmental intense surveillance. RESULTS Among 151 out of 1935 infected patients 20 were colonized and infected by strains of multidrug-resistant A. baumannii susceptible only to colistin. Seventeen patients presented respiratory tract infection, one patient suffered deep surgical site infection and two patients catheter related infection. Transmission of the pathogen occurred via two patients transferred from two other institutions. They were all treated with colistin. Cure or clinical improvement was observed only in four patients (20%). Scale I measures were implemented for the whole 16-month period while scale II for two separate periods of 3 weeks. Environmental specimens (n>350) proved negative. CONCLUSIONS The increasing prevalence of multidrug-resistant A. baumannii in surgical intensive care unit patients creates demand on strict screening and contact precautions. Following this infection control strategy we were able to achieve intermittent eradication of the pathogen during a 16-month period with continuous function of the intensive care unit. Despite the significant in vitro activity of colistin against multidrug-resistant Acinetobacter baumannii the results were discouraging.

Longitudinal Assessment of Adrenal Function in the Early and Prolonged Phases of Critical Illness in Septic Patients: Relations to Cytokine Levels and Outcome

CONTEXT Adrenal dysfunction remains a controversial issue in critical care. The long-stay intensive care unit (ICU) population may be at increased risk of adrenal insufficiency. OBJECTIVE We aimed to determine whether adrenal dysfunction develops during the course of sepsis. DESIGN This is a prospective observational longitudinal study. SETTING The study was conducted in the ICU of a secondary/tertiary care hospital. PATIENTS We studied 51 consecutive mechanically ventilated patients with sepsis. INTERVENTION We measured cortisol, ACTH, cortisol-binding globulin, cytokines, and cortisol 30 minutes after 1 μg ACTH(1-24), upon sepsis diagnosis and every 3 to 4 days, until Day 30 or until recovery or death. MAIN OUTCOME MEASURES We looked for changes in baseline and stimulated cortisol levels and its relationship to ACTH levels, sepsis severity or survival. RESULTS Baseline and stimulated cortisol levels did not vary significantly. Septic patients with shock had higher baseline (20 ± 6 vs 17 ± 5 μg/dL, P = .03) and stimulated cortisol levels (26 ± 5 vs 23 ± 6 μg/dL, P = .04), compared with those without shock. On Day 1, ACTH levels could not predict cortisol levels (R(2) = 0.06, P = .08). ACTH levels increased significantly after Day 10 and, at this time point, they related to cortisol levels (R(2) = 0.35, P < .001). Development of septic shock, or resolution from it, was not associated with changes in baseline, stimulated cortisol levels, or the cortisol increment. There was much inpatient variability in the diagnosis of adrenal dysfunction at different time points. CONCLUSIONS Total cortisol levels relate both to the severity and outcome of sepsis and remain fairly unchanged during the course of illness. Initially, cortisol levels are largely ACTH independent, whereas ACTH increases and correlates with cortisol levels later on. Adrenal dysfunction does not seem to be a major problem during the prolonged phase of sepsis. Although not significant, the variation in cortisol levels may be such that classification of patients varies, questioning the utility of arbitrary cut-offs to define adrenal dysfunction in septic patients.

Combination of Renal Biomarkers Predicts Acute Kidney Injury in Critically Ill Adults

Objective: Most studies so far have focused on the performance of individual biomarkers to detect early acute kidney injury (AKI) in the adult intensive care unit (ICU) patients; however, they have not determined the predictive ability of their combinations. The aim of this study was to compare the predictive abilities of plasma neutrophil gelatinase-associated lipocalin (pNGAL), urine neutrophil gelatinase-associated lipocalin (uNGAL), plasma cystatin C (pCysC), serum creatinine (sCr), and their combinations in detecting AKI in an adult general ICU population. Methods: A total of 100 consecutive ICU patients were included in the analysis. AKI was defined according to RIFLE criteria. Biomarker predictive abilities were evaluated by area under the curve (AUC), net reclassification improvement (NRI), and integrated discrimination improvement (IDI). Results: AKI occurred in 36% of patients 7 days post-admission. All three novel biomarkers as well as sCr had moderate predictive abilities for AKI occurrence. The most efficient combinations (pNGAL + sCr and pNGAL + uNGAL + sCr) were selected to participate in the subsequent analyses. Both combinations, when added to a reference clinical model, increased its AUC significantly (0.858, p = 0.04). Their NRI (0.78, p = 0.0002) was equal to that of pNGAL, but higher than that of the other three biomarkers, whereas their IDI was higher than that of any individual biomarker (0.23, p = 0.0001). Both combinations had better specificities, positive likelihood ratios, and positive predictive values than those of any individual biomarker. Conclusion: The biomarker combinations had better predictive characteristics compared with those of each biomarker alone.

Epidemiology, risk factors for and outcome of candidaemia among non-neutropenic patients in a Greek intensive care unit.

To determine the epidemiology, risk factors for and outcome of candidaemia in critically ill patients, a matched case–control study was performed in a 25‐bed intensive care unit (ICU) from August 2004 to January 2006. Candidaemia occurred in 33 patients; each patient was matched to four controls according to admission illness severity, diagnostic category and length of ICU stay. Candida non‐albicans species predominated (67.7%). The presence of acute respiratory distress syndrome (ARDS) was the only independent risk factor for candidaemia development (OR, 2.93; 95% CI 1.09–7.81, P = 0.032). Mortality was 60.6% among patients with candidaemia and 22% among controls (P < 0.001). The presence of candidaemia (OR, 9.37; 95% CI 3.48–25.26, P < 0.001) and the illness severity on admission (acute physiologic and chronic health evaluation II score, OR, 1.17; 95% CI 1.12–1.24, P < 0.001) were independently associated with mortality. Among candidaemic patients, risk factors for mortality were the severity of organ dysfunction (sequential organ failure assessment score, OR, 1.57; 95% CI 1.00–2.46, P = 0.05) and a low serum albumin level (OR, 0.74; 95% CI 0.59–0.94, P = 0.012) both of them occurred on candidaemia onset. We conclude that in critically ill patients matched for illness severity and length of ICU stay, the only independent risk factor for candidaemia was the presence of ARDS. Mortality was independently associated with acquisition of candidaemia and with the illness severity at candidaemia onset.

High-dose tigecycline-associated alterations in coagulation parameters in critically ill patients with severe infections

We read with great interest in a recent issue of the International ournal of Antimicrobial Agents the report by Molina-Manso et al. n the in vitro susceptibility to nine antibiotics of staphylococci solates recovered from orthopaedic infections [1]. All antibiotics ested are commonly used in the treatment of prosthetic joint infecions (PJIs). The authors revealed that none of the antibiotics proved to be otally effective against biofilms with regard to minimum biofilm radication concentration (MBEC) data, even with concentrations ighly above the minimum inhibitory concentration (MIC) of the solates. These results were obtained with the static Calgary Biofilm evice (CBD) method, which allows determination of the MBEC, hich is the concentration of antibiotic killing nearly 100% of bacteia in a biofilm. Unfortunately, this method does not detect the ctual number of bacteria in the biofilm used as an inoculum in BEC tests. As inoculum size and (extended) incubation time (24 h) nfluence the results of susceptibility test challenge, MBEC values ould be mistaken [2]. Despite these drawbacks, and although this method needs wellrained technicians, these data are interesting especially because he authors reported and confirmed the best activity of rifampicin even if the results were poor with this system), the pivotal antibitic used to eradicate staphylococci PJIs. None of the antibiotics as effective in eradicating the biofilm but, at 24 h, with this ystem rifampicin remains a key antibiotic against Gram-positive athogens [3]. In this study, Molina-Manso et al. could not identify ny difference in antibiofilm activity. We agree with the authors hat all of the strains tested were able to form biofilms on the CBD egs but in their conditions. According to our experience, whatever the system used to detect iofilm or adherence abilities with the BioFilm Ring Test, Staphyococcus aureus clinical isolates involved in hip and knee PJIs can roduce biofilm. Nevertheless, the comparison remains delicate ecause this last method investigates the first step of adhesion in he biofilm cycle life [4]. In contrast, the CBD method as well as he Christensen or resazurin methods are considered as endpoint ethods. Thus, we need to keep in mind that technical conditions, specially the medium used, pH, oxygenation, ionic concentrations nd glucose concentration, could lead to huge variations in biofilm etermination that do not mimic real life. Therefore, these MBEC esults should be interpreted with caution according to the limits nd performance of the method used [4]. Second, we were surprised to find a slight activity of tigecyline, a bacteriostatic antibiotic. According to personal data and the iterature, with time–kill curve and biofilm studies, tigecycline conrmed its bacteriostatic activity. Moreover, with an in vitro MBEC etermination method using microcalorimetry [5], we systematially did not observe any efficacy against an early or mature biofilm ut only a delay in the time of growth. It would have been interestng to compare the MIC and minimum bactericidal concentration n logarithmic and stationary phase with the MBEC determination btained with this system. Antimicrobial Agents 45 (2015) 84–95