A review of the UK and British Channel Islands practical tidal stream energy resource.

This review provides a critical, multi-faceted assessment of the practical contribution tidal stream energy can make to the UK and British Channel Islands future energy mix. Evidence is presented that broadly supports the latest national-scale practical resource estimate, of 34 TWh/year, equivalent to 11% of the UK's current annual electricity demand. The size of the practical resource depends in part on the economic competitiveness of projects. In the UK, 124 MW of prospective tidal stream capacity is currently eligible to bid for subsidy support (MeyGen 1C, 80 MW; PTEC, 30 MW; and Morlais, 14 MW). It is estimated that the installation of this 124 MW would serve to drive down the levelized cost of energy (LCoE), through learning, from its current level of around 240 £ / MWh to below 150 £ / MWh , based on a mid-range technology learning rate of 17%. Doing so would make tidal stream cost competitive with technologies such as combined cycle gas turbines, biomass and anaerobic digestion. Installing this 124 MW by 2031 would put tidal stream on a trajectory to install the estimated 11.5 GW needed to generate 34 TWh/year by 2050. The cyclic, predictable nature of tidal stream power shows potential to provide additional, whole-system cost benefits. These include reductions in balancing expenditure that are not considered in conventional LCoE estimates. The practical resource is also dependent on environmental constraints. To date, no collisions between animals and turbines have been detected, and only small changes in habitat have been measured. The impacts of large arrays on stratification and predator-prey interaction are projected to be an order of magnitude less than those from climate change, highlighting opportunities for risk retirement. Ongoing field measurements will be important as arrays scale up, given the uncertainty in some environmental and ecological impact models. Based on the findings presented in this review, we recommend that an updated national-scale practical resource study is undertaken that implements high-fidelity, site-specific modelling, with improved model validation from the wide range of field measurements that are now available from the major sites. Quantifying the sensitivity of the practical resource to constraints will be important to establish opportunities for constraint retirement. Quantification of whole-system benefits is necessary to fully understand the value of tidal stream in the energy system.

Impact of large volume paracentesis on respiratory parameters including transpulmonary pressure and on transpulmonary thermodilution derived hemodynamics: A prospective study.

INTRODUCTION: Appropriate mechanical ventilation and prevention of alveolar collaps is mainly dependent on transpulmonary pressure TPP. TPP is assessed by measurement of esophageal pressure EP, largely influenced by pleural and intraabdominal pressure IAP. Consecutively, TPP-guided ventilation might be particularly useful in patients with high IAP. This study investigates the impact of large volume paracentesis LVP on TPP, EP, IAP as well as on hemodynamic and respiratory function in patients with liver cirrhosis and tense ascites. MATERIAL AND METHODS: We analysed 23 LVP-procedures in 11 cirrhotic patients ventilated with the AVEA Viasys respirator (CareFusion, USA) which is capable to measure EP via an esophageal tube. RESULTS: LVP of a mean volume of 4826±1276 mL of ascites resulted in marked increases in inspiratory (17.9±8.9 vs. 5.4±13.3 cmH2O; p<0.001) as well as expiratory TPP (-3.0±4.7 vs. -15.9±10.9 cmH2O; p<0.001; primary endpoint). In parallel, the inspiratory (2.4±8.7 vs. 14.1±14.5 cmH2O; p<0.001) and expiratory EP (12.4±6.0 vs. 24.9±11.3 cmH2O; p<0.001) significantly decreased. The effects were most pronounced for the release of the first 500 mL of ascites. LVP evoked substantial decreases in IAP and central venous pressure CVP. By contrast, mean arterial pressure, cardiac index, global end-diastolic volume index, extravascular lung water index and systemic vascular resistance index did not change. Among the respiratory parameters we observed an increase in paO2/FiO2 (247.7±60.9 vs. 208.3±46.8 mmHg; p<0.001) and a decrease in Oxygenation Index OI (4.8±2.0 vs. 5.8±3.1 cmH2O/mmHg; p = 0.002). Tidal volume (510±100 vs. 452±113 mL; p = 0.008) and dynamic respiratory system compliance Cdyn (46.8±15.9 vs. 35.1±14.6 mL/cmH20; p<0.001) increased, whereas paCO2 (47.3±10.7 vs. 51.2±12.3mmHg; p = 0.046) and the respiratory rate decreased (17.1±7.3 vs. 19.6±7.8 min-1; p = 0.010). CONCLUSIONS: In mechanically ventilated patients with decompensated cirrhosis, intraabdominal hypertension resulted in a substantially decreased TPP despite PEEP-setting according to the ARDSNet. In these patients LVP markedly increased TPP and improved respiratory function in parallel with a decline of EP. Furthermore, LVP induced a decrease in IAP and CVP, while other hemodynamic parameters did not change.

Predictors of the accuracy of pulse-contour cardiac index and suggestion of a calibration-index: a prospective evaluation and validation study.

BACKGROUND: Cardiac Index (CI) is a key-parameter of hemodynamic monitoring. Indicator-dilution is considered as gold standard and can be obtained by pulmonary arterial catheter or transpulmonary thermodilution (TPTD; CItd). Furthermore, CI can be estimated by Pulse-Contour-Analysis (PCA) using arterial wave-form analysis (CIpc). Obviously, adjustment of CIpc to CItd initially improves the accuracy of CIpc. Despite uncertainty after which time accuracy of CIpc might be inappropriate, recalibration by TPTD is suggested after a maximum of 8 h. We hypothesized that accuracy of CIpc might not only depend on time to last TPTD, but also on changes of the arterial wave curve detectable by PCA itself. Therefore, we tried to prospectively characterize predictors of accuracy and precision of CIpc (primary outcome). In addition to "time to last TPTD" we evaluated potential predictors detectable solely by pulse-contour-analysis. Finally, the study aimed to develop a pulse-contour-derived "calibration-index" suggesting recalibration and to validate these results in an independent collective. METHODS: In 28 intensive-care-patients with PiCCO-monitoring (Pulsion Medical-Systems, Germany) 56 datasets were recorded. CIpc-values at baseline and after intervals of 1 h, 2 h, 4 h, 6 h and 8 h were compared to CItd derived from immediately subsequent TPTD. Results from this evaluation-collective were validated in an independent validation-collective (49 patients, 67 datasets). RESULTS: Mean bias values CItd-CIpc after different intervals ranged between -0.248 and 0.112 L/min/m(2). Percentage-error after different intervals to last TPTD ranged between 18.6% (evaluation, 2 h-interval) and 40.3% (validation, 6 h-interval). In the merged data, percentage-error was below 30% after 1 h, 2 h, 4 h and 8 h, and exceeded 30% only after 6 h. "Time to last calibration" was neither associated to accuracy nor to precision of CIpc in any uni- or multivariate analysis. By contrast, the height of CIpc and particularly changes in CIpc compared to last thermodilution-derived CItd(base) univariately and independently predicted the bias CItd-CIpc in both collectives. Relative changes of CIpc compared to CItd(base) exceeding thresholds derived from the evaluation-collective (-11.6% < CIpc-CItd(base)/CItd(base) < 7.4%) were confirmed as significant predictors of a bias |CItd-CIpc| ≥ 20% in the validation-collective. CONCLUSION: Recalibration triggered by changes of CIpc compared to CItd(base) derived from last calibration should be preferred to fixed intervals.

Pharmacokinetics of chewed vs. swallowed raltegravir in a patient with AIDS and MAI infection: some new conflicting data.

BACKGROUND: While HIV, AIDS and atypical Mycobacterium infections are closely linked, the use of Integrase-Inhibitor based cART, notably raltegravir-based regimens is more widespread. RAL should be double-dosed to 800 mg semi-daily in situation of rifampicin co-medication, because RAL is more rapidly metabolized due to rifampicin-induced Uridine-5'-diphosph- gluronosyl-transferase (UGT1A1). Recently, it was speculated that chewed RAL might lead to increased absorption, which might compensate the inductive effect of rifampicin-rapid metabolized RAL, as part of cost-saving effects in countries with high-tuberculosis prevalence and less economic power. METHODS: We report measurement of raltegravir pharmacokinetics in a 34-year AIDS-patient suffering from disseminated Mycobacterium avium infection with necessity of parenteral rifampicin treatment. RAL levels were measured with HPLC (internal standard: carbamazepine, LLQ 11 ng/ml, validation with Valistat 2.0 program (Arvecon, Germany)). For statistical analysis, a two-sided Wilcoxon signed rank test for paired samples was used. RESULTS: High intra-personal variability in raltegravir serum levels was seen. Comparable Cmax concentrations were found for 800 mg chewed and swallowed RAL, as well as for 400 mg chewed and swallowed RAL. While Cmax seems to be more dependent from overall RAL dosing than from swallowed or chewed tablets, increased AUC12 is clearly linked to higher RAL dosages per administration. Anyway, chewed raltegravir showed a rapid decrease in serum levels. CONCLUSIONS: We found no evidence that chewed 400 mg semi-daily raltegravir in rifampicin co-medication leads to optimized pharmacokinetics. There is need for more data from randomized trials for further recommendations.

Fungal "colonisation" is associated with increased mortality in medical intensive care unit patients with liver cirrhosis.

OBJECTIVES: Patients with liver cirrhosis are at increased risk for fungal infections. However, distinction of fungal colonisation (FC) and invasive mycoses is difficult. Aim of this study was to analyse the impact of FC on mortality of cirrhotic ICU-patients. METHODS: Retrospective mortality analysis of a prospectively maintained database on 120 cirrhotic patients with and without FC. Comparison to 120 noncirrhotic controls matched for APACHE-II (24.9 ± 3.7 vs. 25.0 ± 2.6; p = 0.263). RESULTS: About 69/120 (58%) of patients with cirrhosis had FC. These patients had significantly higher APACHE-II score and mortality compared to cirrhotic patients without FC (27 ± 3 vs. 23 ± 4, p < 0.001; 78 vs. 35%, p < 0.001). In multivariate analysis, FC was independently (p = 0.047) associated to mortality. Mortality of noncirrhotic patients with FC (14/31; 45.2%) was not different to noncirrhotic controls without FC [28/89 (31.2%; p = 0.168)]. Similarly, in multivariate analysis of noncirrhotics, APACHE-II (p < 0.001), but not FC, was independently associated to mortality. Multiple regression analysis of all 240 cirrhotic and noncirrhotic patients demonstrated that APACHE-II (p < 0.001), cirrhosis (p = 0.001) and FC (p = 0.049) were independently associated with mortality. CONCLUSION: Fungal "colonisation" is independently associated to mortality in cirrhotic ICU-patients. Early antimycotic therapy should be considered in critically ill cirrhotic patients with FC.

Effects of paracentesis on hemodynamic parameters and respiratory function in critically ill patients.

BACKGROUND: Ascites is a major and common complication of liver cirrhosis. Large or refractory ascites frequently necessitates paracentesis. The aim of our study was to investigate the effects of paracentesis on hemodynamic and respiratory parameters in critically ill patients. METHODS: Observational study comparing hemodynamic and respiratory parameters before and after paracentesis in 50 critically ill patients with advanced hemodynamic monitoring. 28/50 (56%) required mechanical ventilation.Descriptive statistics are presented as mean ± standard deviation for normally distributed data and median, range, and interquartile range (IQR) for non-normally distributed data. Comparisons of hemodynamic and respiratory parameters before and after paracentesis were performed by Wilcoxon signed-rank tests. Bivariate relations were assessed by Spearman's correlation coefficient and univariate regression analyses. RESULTS: Median amount of ascites removed was 5.99 L (IQR, 3.33-7.68 L). There were no statistically significant changes in hemodynamic parameters except a decrease in mean arterial pressure (-7 mm Hg; p = 0.041) and in systemic vascular resistance index (-116 dyne·sec/cm5/m2; p = 0.016) when measured 2 hours after paracentesis. In all patients, oxygenation ratio (PaO2/FiO2; median, 220 mmHg; IQR, 161-329 mmHg) increased significantly when measured immediately (+58 mmHg; p = 0.001), 2 hours (+9 mmHg; p = 0.004), and 6 hours (+6 mmHg); p = 0.050) after paracentesis. In mechanically ventilated patients, lung injury score (cumulative points without x-ray; median, 6; IQR, 4-7) significantly improved immediately (5; IQR, 4-6; p < 0.001), 2 hours (5; IQR, 4-7; p = 0.003), and 6 hours (6; IQR 4-6; p = 0.012) after paracentesis. CONCLUSION: Paracentesis in critically ill patients is safe regarding circulatory function and is related to immediate and sustained improvement of respiratory function.

Continuous intravenous administration of vancomycin in medical intensive care unit patients.

PURPOSE: The aim of this study was to evaluate continuous vancomycin infusion (contV) in intensive care unit patients. MATERIALS AND METHODS: A retrospective study in 164 patients treated with contV was conducted. They were compared with 75 patients treated with intermittent vancomycin infusion. RESULTS: The median duration of vancomycin therapy in the contV group was 6 (5%-95% percentile range, 2-21) days. The median daily vancomycin dose in the contV group was 960 (526-1723) mg, resulting in a median serum vancomycin plateau concentration of 19.8 (9.8-29.4) mg/L (target: 15-25 mg/L). The contV administration regime was sufficient regarding achievement of the target serum vancomycin concentration. However, in the contV group, serum vancomycin levels were frequently in a subtherapeutic range on treatment days 1 (44%), 2 (29%), and 3 (23%). In the contV group, serum vancomycin concentration determinations per treatment day were performed significantly less often compared with the intermittent vancomycin infusion group (0.38 [0.15-0.75] vs 0.43 [0.22-1.00], P = .041). CONCLUSIONS: In medical intensive care unit patients, contV is sufficient to achieve target serum vancomycin concentrations. Because contV frequently resulted in subtherapeutic drug levels on the first days of therapy, a higher loading or starting dose might be necessary.

Continuous venovenous hemodialysis with regional citrate anticoagulation in patients with liver failure: a prospective observational study.

INTRODUCTION: Liver failure patients might be at risk for citrate accumulation during continuous venovenous hemodialysis (CVVHD) with regional citrate anticoagulation. The aim of this study was to investigate the predictive capability of baseline liver function parameters regarding citrate accumulation, expressed as an increase in the calcium total/calcium ionized (Ca(tot)/Ca(ion)) ratio ≥ 2.5, and to describe the feasibility of citrate CVVHD in liver failure patients. METHODS: We conducted a prospective observational study in medical ICU patients treated in a German university hospital. We performed 43 CVVHD runs using citrate for regional anticoagulation in 28 critically ill patients with decompensated liver cirrhosis or acute liver failure (maximum of two CVVHD runs per patient). Liver function was characterized before CVVHD using laboratory parameters, calculation of Child-Pugh and Model of End-stage Liver Disease scores, and determination of the plasma disappearance rate of indocyanine green. In addition to blood gas analysis, we measured total calcium and citrate in serum at baseline and after definitive time points for each CVVHD run. RESULTS: Accumulation of citrate in serum correlated with an increase in the Ca(tot)/Ca(ion) ratio. Although the critical upper threshold of Ca(tot)/Ca(ion) ratio ≥ 2.5 was exceeded 10 times in seven different CVVHD runs, equalization of initial metabolic acidosis was possible without major disturbances of acid-base and electrolyte status. Standard laboratory liver function parameters showed poor predictive capabilities regarding citrate accumulation in terms of an elevated Ca(tot)/Ca(ion) ratio ≥ 2.5. In contrast, serum lactate ≥ 3.4 mmol/l and prothrombin time ≤ 26% predicted an increase in the Ca(tot)/Ca(ion) ratio ≥ 2.5 with high sensitivity (86% for both lactate and prothrombin time) and specificity (86% for lactate, 92% for prothrombin time). CONCLUSIONS: Despite substantial accumulation of citrate in serum, CVVHD with regional citrate anticoagulation seems feasible in patients with severely impaired liver function. Citrate accumulation in serum is reflected by an increase in the Ca(tot)/Ca(ion) ratio. To identify patients at risk for citrate accumulation in terms of a Ca(tot)/Ca(ion) ratio ≥ 2.5, baseline serum lactate (threshold ≥ 3.4 mmol/l) and prothrombin time (threshold ≤ 26%) may be useful for risk prediction in daily clinical practice. Careful monitoring of electrolytes and acid-base status is mandatory to ensure patient safety.

Prediction of extubation failure in medical intensive care unit patients.

PURPOSE: The purpose of this study was to evaluate prediction factors for extubation failure (need for reintubation within 48 hours) in medical intensive care unit patients. MATERIALS AND METHODS: Sixty-one patients extubated after mechanical ventilation for more than 48 hours were included in the study. A retrospective analysis of medical records and a prospectively maintained database on respiratory parameters was conducted. RESULTS: Low serum anion gap (P = .001), low serum anion gap corrected for serum albumin (P = .010), and low arterial partial pressure of oxygen (Pao(2))/fraction of inspired oxygen (Fio(2)) ratio (P = .032) were significantly associated with extubation failure. Binary logistic regression analysis revealed low uncorrected and corrected serum anion gap (P = .006 and P = .025, respectively; odds ratio, 0.59 for both) and low Pao(2)/Fio(2) ratio (P = .038; odds ratio, 0.99) as risk factors for extubation failure. Regarding extubation failure, receiver operating characteristic curve (ROC) analysis demonstrated good predictive capabilities of serum anion gap (ROC area under the curve, 0.835; P = .004; cutoff, 7.7 mEq/L; sensitivity, 70.4%; specificity, 85.7%) and corrected serum anion gap (ROC area under the curve, 0.808; P = .009; cutoff, 8.8 mEq/L; sensitivity, 87.5%; specificity, 71.4%). A significantly higher risk for extubation failure was observed in patients with serum anion gap 5.2 mEq/L or less (relative risk, 8.8; 95% confidence interval, 2.4-32.4; P = .004) and corrected serum anion gap 8.6 mEq/L or less (relative risk, 10.0; 95% confidence interval, 2.2-44.9; P = .004). CONCLUSIONS: Low preextubation serum anion gap values and low preextubation Pao(2)/Fio(2) ratio might help to predict extubation failure in medical intensive care unit patients.

Advanced hemodynamic monitoring before and after transjugular intrahepatic portosystemic shunt: implications for selection of patients--a prospective study.

PURPOSE: To investigate immediate and short-term effects of transjugular intrahepatic portosystemic shunt (TIPS) on cardiocirculatory, hepatic, and renal function and characterize predictors for TIPS outcome in terms of organ function after TIPS. MATERIALS AND METHODS: This prospective study was approved by the ethics committee at a university hospital and was conducted in a medical intensive care unit. Informed consent was obtained. Twenty patients with indication for TIPS were enrolled. Monitoring of hemodynamic and hepatic function (transpulmonary thermodilution, indocyanine green plasma disappearance rate [ICG-PDR]) was performed. Biochemical markers of organ function were obtained. Statistical analysis (Wilcoxon test, Spearman correlation, multivariate linear regression analysis, receiver operating characteristic [ROC] analysis) was performed. RESULTS: After TIPS, central venous pressure (median, 11 vs 15 cm H(2)O; P < .001), cardiac index (3.4 vs 3.8 L/min/m(2); P = .001), and global end-diastolic volume index (GEDVI) (726 vs 775 mL/m(2); P = .003) increased significantly. Portosystemic pressure gradient (28 vs 11 cm H(2)O; P < .001) and systemic vascular resistance index (1610 vs 1384 dyn · sec · cm(-5) · m(2); P = .015) decreased significantly. Creatinine (1.1 vs 1.1 mg/dL; P = .008) and blood urea nitrogen (BUN) (27 vs 21 mg/dL; P = .006) decreased significantly. Bilirubin (1.8 vs 2.2 mg/dL; P = .032) and international normalized ratio (1.4 vs 1.5; P = .022) increased significantly. ICG-PDR significantly deteriorated after TIPS (P = .006). Higher baseline creatinine was independently associated with a decrease in creatinine after TIPS (R = 0.816, P < .001). ROC analysis identified baseline BUN (P = .026, area under ROC curve [AUC] = 0.818), cystatin C (P = .033, AUC = 0.805), and creatinine (P = .052, AUC = 0.779) as predictors of a decrease in creatinine of 0.5 mg/dL or greater and/or 25% or greater. An increase in bilirubin of 1 mg/dL or greater 1 week after TIPS was significantly associated with high baseline BUN (P = .007, AUC = 0.893) and high central venous pressure (P = .040, AUC = 0.800). Lower baseline alanine aminotransferase (P = .002, AUC = 1.000) and cardiac power index · GEDVI (P = .005, AUC = 0.960) predicted favorable TIPS outcome (creatinine decrease of ≥ 0.2 mg/dL without model for end-stage liver disease score increase of more than one point). CONCLUSION: Patients with renal insufficiency, compensated hepatocellular function, decreased cardiac preload, and decreased cardiac performance benefit most from TIPS.

Auditory evoked potentials compared with bispectral index for monitoring of midazolam and propofol sedation during colonoscopy.

OBJECTIVES: The purpose of this study was to evaluate and compare Bispectral index (BIS) and A-line auditory evoked potential index (AAI) for monitoring depth of low-dose midazolam and propofol sedation during colonoscopy. METHODS: A total of 115 consecutive patients (ASA I-IV), receiving low-dose midazolam and propofol sedation for colonoscopy, were evaluated. BIS and AAI levels, Observer's Assessment of Alertness/Sedation (OAA/S) scores, blood pressure, heart rate, oxygen saturation, as well as the presence or absence of eyelash reflex, patient reaction to an external noxious stimulus and to procedure-related pain were recorded every 1-3 min by a single trained observer. RESULTS: There was a positive correlation between BIS and OAA/S scores (correlation coefficient=0.77) and to a lesser extent AAI and OAA/S scores (correlation coefficient=0.47). BIS and AAI showed significant differences between subsequent levels of sedation (P<0.001). The clustered receiver operating characteristic curve estimate of BIS for the detection of deep sedation was significantly better than that of AAI (P<0.001). Regarding the presence or absence of eyelash reflex and patient reaction to an external noxious stimulus and to procedure-related pain, significant different levels were found for BIS as well as AAI, respectively. Only small changes were observed in hemodynamic variables and oxygen saturation. Overall, our data suggest target BIS levels of slightly above 73 for moderate sedation (defined as OAA/S scores 2 and 3). CONCLUSIONS: BIS and AAI correlated with the level of sedation. Hemodynamic variables were poor indicators of the hypnotic-anesthetic status of the patient. BIS discriminated best between moderate and deep sedation and could complement clinical observation for guidance of moderate sedation.

Validation of the X-Vision ERCP Training System and technical challenges during early training of sphincterotomy.

BACKGROUND & AIMS: A new fluoroscopy-free training system for endoscopic retrograde cholangiopancreatography (ERCP) with different model subtypes recently was developed. This study aimed to establish construct validity by investigating whether the X-Vision ERCP Training System could distinguish experienced endoscopists from beginners and to reveal characteristic mistakes during sphincterotomy. METHODS: Six staff gastroenterologists that practice ERCP, 10 trainees that perform esophagogastroduodenoscopy and colonoscopy, and 12 residents without endoscopic experience each sequentially attempted 4 different models, simulating selective cannulation of the pancreatic or bile duct, intubation of differently arranged rubber papillas, stent placement, and sphincterotomy of a biopapilla. Performance parameters were recorded and participants' expectations were compared before and after training to determine whether the simulator was a credible tool for ERCP training. Staff gastroenterologists graded the realism and utility of the simulation. The quality of sphincterotomy was assessed by an expert endoscopist. RESULTS: Participants with ERCP experience had significantly shorter procedure times compared with those with intermediate (P < .001) or no endoscopic experience (P < .001). Total and single credibility scores significantly increased after simulator practice. The faculty found the X-Vision ERCP Training System to be realistic and useful for training. In the less-experienced groups, common mistakes made during sphincterotomy included inadequate positioning of the duodenoscope, traumatic intubation of the papilla, and continued cutting despite insufficient endoscopic view. CONCLUSIONS: The X-Vision ERCP Training System distinguished subjects with different levels of experience and was regarded as realistic and useful for ERCP training. Common mistakes during sphincterotomy could be assessed objectively.