Hybrid optimization algorithm for enhanced performance and security of counter-flow shell and tube heat exchangers

A shell and tube heat exchanger (STHE) for heat recovery applications was studied to discover the intricacies of its optimization. To optimize performance, a hybrid optimization methodology was developed by combining the Neural Fitting Tool (NFTool), Particle Swarm Optimization (PSO), and Grey Relational Analysis (GRE). STHE heat exchangers were analyzed systematically using the Taguchi method to analyze the critical elements related to a particular response. To clarify the complex relationship between the heat exchanger efficiency and operational parameters, grey relational grades (GRGs) are first computed. A forecast of the grey relation coefficients was then conducted using NFTool to provide more insight into the complex dynamics. An optimized parameter with a grey coefficient was created after applying PSO analysis, resulting in a higher grey coefficient and improved performance of the heat exchanger. A major and far-reaching application of this study was based on heat recovery. A detailed comparison was conducted between the estimated values and the experimental results as a result of the hybrid optimization algorithm. In the current study, the results demonstrate that the proposed counter-flow shell and tube strategy is effective for optimizing performance.

Adaptive designs in critical care trials: a simulation study

BACKGROUND

Adaptive clinical trials are growing in popularity as they are more flexible, efficient and ethical than traditional fixed designs. However, notwithstanding their increased use in assessing treatments for COVID-19, their use in critical care trials remains limited. A better understanding of the relative benefits of various adaptive designs may increase their use and interpretation.

METHODS

Using two large critical care trials (ADRENAL.

CLINICALTRIALS

gov number, NCT01448109. Updated 12-12-2017; NICE-SUGAR.

CLINICALTRIALS

gov number, NCT00220987. Updated 01-29-2009), we assessed the performance of three frequentist and two bayesian adaptive approaches. We retrospectively re-analysed the trials with one, two, four, and nine equally spaced interims. Using the original hypotheses, we conducted 10,000 simulations to derive error rates, probabilities of making an early correct and incorrect decision, expected sample size and treatment effect estimates under the null scenario (no treatment effect) and alternative scenario (a positive treatment effect). We used a logistic regression model with 90-day mortality as the outcome and the treatment arm as the covariate. The null hypothesis was tested using a two-sided significance level (α) at 0.05.

RESULTS

Across all approaches, increasing the number of interims led to a decreased expected sample size. Under the null scenario, group sequential approaches provided good control of the type-I error rate; however, the type I error rate inflation was an issue for the Bayesian approaches. The Bayesian Predictive Probability and O'Brien-Fleming approaches showed the highest probability of correctly stopping the trials (around 95%). Under the alternative scenario, the Bayesian approaches showed the highest overall probability of correctly stopping the ADRENAL trial for efficacy (around 91%), whereas the Haybittle-Peto approach achieved the greatest power for the NICE-SUGAR trial. Treatment effect estimates became increasingly underestimated as the number of interims increased.

CONCLUSIONS

This study confirms the right adaptive design can reach the same conclusion as a fixed design with a much-reduced sample size. The efficiency gain associated with an increased number of interims is highly relevant to late-phase critical care trials with large sample sizes and short follow-up times. Systematically exploring adaptive methods at the trial design stage will aid the choice of the most appropriate method.

Future Predictions of Precipitation and Discharge Using CMIP5 Models in the Western Ghats Region, India

Climate change is expected to exacerbate the hydrological cycle globally and have a significant impact on water resources. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report states that observed and projected increases in both temperature and precipitation variability are the main reasons for projected climate change impacts on natural water resources. The examination of meteorological variables of the region, especially when agriculture is rainfall dependent, is very essential to formulate feasible adaptation strategies. As a result, using CORDEX-SA (Coordinated Regional Downscaling Experiment-South Asia) rainfall data (2021 to 2050), trend analysis was used to examine variations in rainfall data in the Kokkarne catchment of the Seetha river basin. Regression analysis was used to identify the season-wise rainfall trend. Annual, Summer, Monsoon, and Winter rainfall have depicted increasing trends with a rate of 2.46, 1.21, 2.77, and 0.009 mm per year respectively. The post-monsoon rainfall has projected a declining trend with a rate of -1.54 mm per year. Hence it is recommended that the designed strategies in the agricultural sector have to take the increasing, decreasing, and erratic nature of the trend of rainfall into consideration. Further considering the use of a Multi-Model Ensemble (MME) is reducing the SD and CV of rainfall data by 862 mm and 48.5% respectively. 87% of annual rainfall is contributed by monsoon season only with a Standard deviation of 424.4 mm and CV of 12%.

An Assessment of Future Predictions of Rainfall Using GCM Projections in the Western Ghats Region of India

The present study has been taken up to quantify the possible impacts of climate change on the climate variables using the outputs of the global climate model dataset over the Sagar and Kokkarne catchments. The baseline period considered is 30 years (1991-2020), and the daily rainfall dataset is used. The rainfall dataset for the future period is derived from five selected GCMs (Global Circulation Model) datasets under the (Representative Concentration Pathway) RCP 4.5 scenario for the period (2021-2050). The mean, standard deviation, and coefficient of variation of yearly rainfall are determined to check the rainfall variability using statistical analysis. The ensemble rainfall mean values of the five GCMs suggest that the uncertainty in the projected results is reduced by considering the cluster of GCMs. The minimum rainfall for the future period has shown an increasing trend (42.3 % 10.5 %) whereas maximum rainfall has shown decreasing trend (52.44 %, 15.28 %) for Sagar and Kokkarne catchments respectively. The future predicted results show that the percentage change in Ensemble mean annual rainfall for the period 2021-2050 with reference to rainfall data of the baseline period (1991-2020) is depicting an increasing trend of 2.52 % and 4.12 % for Sagar and Kokkarne catchments respectively. Monsoon arrival is earlier in the Kokkarne catchment as compared to the Sagar catchment. The highest positive percentage change in mean annual rainfall of 24.89 %, 10.25 % is projected by MPI-ESM-LR GCM, and the Highest negative percentage change in mean annual rainfall of -28.49 %, -9.19 % is projected by ACCESS1.0 GCM for Sagar and Kokkarne catchments respectively. This analysis will provide useful information for water resources planning engineers, research scientists, and farmers to assess the water availability in the region and create storage if essential.

Fuzzy Rank Based Parallel Online Feature Selection Method using Multiple Sliding Windows

Nowadays, in real-world applications, the dimensions of data are generated dynamically, and the traditional batch feature selection methods are not suitable for streaming data. So, online streaming feature selection methods gained more attention but the existing methods had demerits like low classification accuracy, fails to avoid redundant and irrelevant features, and a higher number of features selected. In this paper, we propose a parallel online feature selection method using multiple sliding-windows and fuzzy fast-mRMR feature selection analysis, which is used for selecting minimum redundant and maximum relevant features, and also overcomes the drawbacks of existing online streaming feature selection methods. To increase the performance speed of the proposed method parallel processing is used. To evaluate the performance of the proposed online feature selection method k-NN, SVM, and Decision Tree Classifiers are used and compared against the state-of-the-art online feature selection methods. Evaluation metrics like Accuracy, Precision, Recall, F1-Score are used on benchmark datasets for performance analysis. From the experimental analysis, it is proved that the proposed method has achieved more than 95% accuracy for most of the datasets and performs well over other existing online streaming feature selection methods and also, overcomes the drawbacks of the existing methods.

A fuzzy gaussian rank aggregation ensemble feature selection method for microarray data

In Microarray Data, it is complicated to achieve more classification accuracy due to the presence of high dimensions, irrelevant and noisy data. And also It had more gene expression data and fewer samples. To increase the classification accuracy and the processing speed of the model, an optimal number of features need to extract, this can be achieved by applying the feature selection method. In this paper, we propose a hybrid ensemble feature selection method. The proposed method has two phases, filter and wrapper phase in filter phase ensemble technique is used for aggregating the feature ranks of the Relief, minimum redundancy Maximum Relevance (mRMR), and Feature Correlation (FC) filter feature selection methods. This paper uses the Fuzzy Gaussian membership function ordering for aggregating the ranks. In wrapper phase, Improved Binary Particle Swarm Optimization (IBPSO) is used for selecting the optimal features, and the RBF Kernel-based Support Vector Machine (SVM) classifier is used as an evaluator. The performance of the proposed model are compared with state of art feature selection methods using five benchmark datasets. For evaluation various performance metrics such as Accuracy, Recall, Precision, and F1-Score are used. Furthermore, the experimental results show that the performance of the proposed method outperforms the other feature selection methods.

Vitamin D status and supplementation in adult patients receiving extracorporeal membrane oxygenation

The prevalence of vitamin D deficiency in critical illness is known to be high and associated with adverse clinical outcomes. Patients receiving extracorporeal membrane oxygenation (ECMO) may be at increased risk of vitamin D deficiency due to high severity of acute illness. Challenges with drug dosing in ECMO patients are recognised due to increased volume of distribution and drug absorption to circuit components. To describe the prevalence of vitamin D deficiency in ECMO patients and the effect of intramuscular dosing of cholecalciferol on levels of vitamin D metabolites, and to compare these data with intensive care unit (ICU) patients not receiving ECMO, two prospective studies were performed sequentially: an observational study of 100 consecutive ICU patients and an interventional study assessing effects of intramuscular cholecalciferol in 50 ICU patients. The subgroup of patients who required ECMO support in each of these studies was analysed and compared to patients who did not receive ECMO. Twenty-four ECMO patients, 12 from the observational study and 12 from the interventional study (who received intramuscular cholecalciferol) were studied-21/24 (88%) ECMO patients were vitamin D deficient at baseline compared to 65/126 (52%) of non-ECMO patients (<i>P</i>=0.006). Of the 12 ECMO patients who received cholecalciferol, six patients (50%) achieved correction of deficiency compared to 36/38 (95%) non-ECMO patients (<i>P</i>=0.001). The prevalence of vitamin D deficiency is higher in ECMO patients compared to other critically ill adults. Correction of deficiency with single dose cholecalciferol is not reliable; higher or repeated doses should be considered to correct deficiency.

Evaluation of Random Plasma Cortisol and the Low Dose Corticotropin Test as Indicators of Adrenal Secretory Capacity in Critically Ill Patients: A Prospective Study

It is unclear whether a random plasma cortisol measurement and the corticotropin (ACTH) test adequately reflect glucocorticoid secretory capacity in critical illness. This study aimed to determine whether these tests provide information representative of the 24 hour period.

Plasma cortisol was measured hourly for 24 hours in 21 critically ill septic patients followed by a corticotropin test with 1 μg dose administered intravenously. Serum and urine were analysed for ACTH and free cortisol respectively. Marked hourly variability in plasma cortisol was evident (coefficient of variation 8–30%) with no demonstrable circadian rhythm. The individual mean plasma cortisol concentrations ranged from 286±59 nmol/l to 796± 83 nmol/l. The 24 hour mean plasma cortisol was strongly correlated with both random plasma cortisol (r2 0.9, P<0.0001) and the cortisol response to corticotropin (r2 0.72, P<0.001). Only nine percent of patients increased their plasma cortisol by 250 nmol/l after corticotropin (euadrenal response). However, 35% of non-responders had spontaneous hourly rises >250 nmol/l thus highlighting the limitations of a single point corticotropin test. Urinary free cortisol was elevated (865±937 nmol) in both corticotropin responders and non-responders suggesting elevated plasma free cortisol. No significant relationship was demonstrable between plasma cortisol and ACTH.

We conclude that although random cortisol measurements and the low dose corticotropin tests reliably reflect the 24 hour mean cortisol in critical illness, they do not take into account the pulsatile nature of cortisol secretion. Consequently, there is the potential for erroneous conclusions about adrenal function based on a single measurement. We suggest that caution be exercised when drawing conclusions on the adequacy of adrenal function based on a single random plasma cortisol or the corticotropin test.

Serum Procalcitonin and C-reactive Protein as Markers of Sepsis and Outcome in Patients with Neurotrauma and Subarachnoid Haemorrhage

This prospective study evaluated serum procalcitonin (PCT) and C-reactive protein (CRP) as markers for systemic inflammatory response syndrome (SIRS)/sepsis and mortality in patients with traumatic brain injury and subarachnoid haemorrhage. Sixty-two patients were followed for 7 days. Serum PCT and CRP were measured on days 0, 1, 4, 5, 6 and 7.

Seventy-seven per cent of patients with traumatic brain injury and 83% with subarachnoid haemorrhage developed SIRS or sepsis (P=0.75). Baseline PCT and CRP were elevated in 35% and 55% of patients respectively (P=0.03). There was a statistically non-significant step-wise increase in serum PCT levels from no SIRS (0.4±0.6 ng/ml) to SIRS (3.05±9.3 ng/ml) to sepsis (5.5±12.5 ng/ml). A similar trend was noted in baseline PCT in patients with mild (0.06±0.9 ng/ml), moderate (0.8±0.7 ng/ml) and severe head injury (1.2±1.9 ng/ml). Such a gradation was not observed with serum CRP. There was a non-significant trend towards baseline PCT being a better marker of hospital mortality compared with baseline CRP (ROC-AUC 0.56 vs 0.31 respectively). This is the first prospective study to document the high incidence of SIRS in neurosurgical patients. In our study, serum PCT appeared to correlate with severity of traumatic brain injury and mortality. However, it could not reliably distinguish between SIRS and sepsis in this cohort. This is in part because baseline PCT elevation seemed to correlate with severity of injury. Only a small proportion of patients developed sepsis, thus necessitating a larger sample size to demonstrate the diagnostic usefulness of serum PCT as a marker of sepsis. Further clinical trials with larger sample sizes are required to confirm any potential role of PCT as a sepsis and outcome indicator in patients with head injuries or subarachnoid haemorrhage.

A controller based on Optimal Type-2 Fuzzy Logic: systematic design, optimization and real-time implementation

A computationally-efficient systematic procedure to design an Optimal Type-2 Fuzzy Logic Controller (OT2FLC) is proposed. The main scheme is to optimize the gains of the controller using Particle Swarm Optimization (PSO), then optimize only two parameters per type-2 membership function using Genetic Algorithm (GA). The proposed OT2FLC was implemented in real-time to control the position of a DC servomotor, which is part of a robotic arm. The performance judgments were carried out based on the Integral Absolute Error (IAE), as well as the computational cost. Various type-2 defuzzification methods were investigated in real-time. A comparative analysis with an Optimal Type-1 Fuzzy Logic Controller (OT1FLC) and a PI controller, demonstrated OT2FLC׳s superiority; which is evident in handling uncertainty and imprecision induced in the system by means of noise and disturbances.

Prospective memory in the ICU: the effect of visual cues on task execution in a representative simulation

Despite the potential dangers of clinical tasks being forgotten, few researchers have investigated prospective memory (PM) - the ability to remember to execute future tasks - in health-care contexts. Visual cues help people remember to execute intentions at the appropriate moment. Using an intensive care unit simulator, we investigated whether nurses' memory for future tasks improves when visual cues are present, and how nurses manage PM demands. Twenty-four nurses participated in a 40-minute scenario simulating the start of a morning shift. The scenario included eight PM tasks. The presence or absence of a visually conspicuous cue for each task was manipulated. The presence of a visual cue improved recall compared to no cue (64% vs. 50%, p = 0.03 one-tailed, η(p)(2) = 0.15). Nurses used deliberate reminders to manage their PM demands. PM in critical care might be supported by increasing the visibility of cues related to tasks.

PRACTITIONER SUMMARY

Nurses must remember to execute multiple future tasks to ensure patient safety. We investigated the effect of visual cues on nurses' ability to remember future tasks. Experimental manipulation of cues in a representative intensive care unit simulation indicated that visual cues increase the likelihood that future tasks are executed.

Gastric teratoma in an infant: a rare case report and discussion

Gastric teratoma is a rare tumor, accounting for less than 1 % of all teratomas in infants & children. To date, only about 102 cases have been reported in the literature. A 10 month old infant was brought with a history of upper abdominal mass which was otherwise asymptomatic. On evaluation it was diagnosed as gastric teratoma. On laparotomy the mass was found to be originating from lesser curvature of stomach. Mass was excised and histopathologically it was a mature cystic teratoma. No recurrence after 18 months of follow-up.

Surface water quality evaluation and modeling of Ghataprabha River, Karnataka, India

Belgaum city is a developmental hub of Karnataka State in India. In the recent time, the Government of Karnataka has planned to set up many processing industries in the vicinity of Belgaum to meet the growing needs of the region and to ease out the pressure on the already existing industrial hubs in Karnataka State. Ghataprabha, a tributary of river Krishna, is one of the major sources of water supply to Belgaum city and adjoining areas. During the last decade, a lot of anthropogenic activities such as unplanned agricultural activities are ongoing in many parts of the catchment. Therefore, people of Belgaum are more concerned about the quality of water in Ghataprabha river. Considering the significance of water quality of the river, surface water samples were collected during Pre- and Post-monsoon season from selected locations and analyzed for both physical and chemical constituents in the laboratory. The results indicate that the chemical parameters such as bicarbonates, sulphates, chlorides, sodium, potassium, calcium and magnesium are within the permissible limits. QUAL2E model was applied to assess the impact of point and non-point sources of pollution on the river water quality. Results show that the water quality conditions are highly acceptable all along the river stretch. Further, the variation of DO-BOD(5) with river discharge was also estimated. Also, a significant variations in DO (decrease in DO) with the increase in river flow was observed. However, at the downstream end, considerable improvement in DO was noticed which is attributed to the damming effect of the reservoir.

FRACTAL CHARACTERIZATION OF BPN WEIGHTS EVOLUTION

Training methodology of the Back Propagation Network (BPN) is well documented. One aspect of BPN that requires investigation is whether or not the BPN would get trained for a given training data set and architecture. In this paper the behavior of the BPN is analyzed during its training phase considering convergent and divergent training data sets. Evolution of the weights during the training phase was monitored for the purpose of analysis. The evolution of weights was plotted as return map and was characterized by means of fractal dimension. This fractal dimensional analysis of the weight evolution trajectories is used to provide a new insight to understand the behavior of BPN and dynamics in the evolution of weights.

A prospective comparison between written examination and either simulation-based or oral viva examination of intensive care trainees' procedural skills

We compared results of written assessment of intensive care trainees' procedural skills with results obtained from one of two live assessment formats for the purposes of assessing the concurrent validity of the different test methods. Forty-five Australasian senior trainees in intensive care medicine completed a written test relating to a procedural skill, as well as either a simulation format or oral viva assessment on the same procedural skill. We analysed correlation between written exam results and results obtained from simulation format or oral viva assessment. For those who completed the simulation format examination, we also maintained a narrative of actions and identified critical errors. There was limited correlation between written exam results and live (simulation or viva) procedure station results (r = 0.31). Correlation with written exam results was very low for simulation format assessments (r = 0.08) but moderate for oral viva format assessment (r = 0.58). Participants who passed a written exam based on management of a blocked tracheostomy scenario performed a number of dangerous errors when managing a simulated patient in that scenario. The lack of correlation between exam formats supports multi-modal assessment, as currently it is not known which format best represents workplace performance. Correlation between written and oral viva results may indicate redundancy between those test formats, whereas limited correlation between simulation and written exams may support the use of both formats as part of an integrated assessment strategy. We hypothesise that identification of critical candidate errors in a simulation format exam that were not exposed in a written exam may indicate better predictive validity for simulation format examination of procedural skills.

Distractions and Interruptions in the Intensive Care Unit: A Field Observation and a Simulator Experiment

Distractions and interruptions are frequently mentioned as sources of errors in healthcare research, and laboratory research has shown that they can disrupt cognition. However, the current evidence that distractions and interruptions cause patient harm is mixed. In two studies in an intensive care unit, we investigated whether and when distractions and interruptions might lead nurses to forget critical care tasks. Study 1 was an observational study using a mobile eye tracker. It investigated which properties of an interruption influence resumption times and how nurses manage distractions and interruptions. Study 2 was a controlled experiment in a full-scale patient simulator. It investigated whether reminders improve nurses' ability to remember routine tasks when multitasking and resume interrupted routine tasks. We discuss theoretical and practical implications of the studies.

Relative adrenal insufficiency in the intensive care population; background and critical appraisal of the evidence

Dysfunction of the hypothalamo-pituitary adrenal axis has become a central feature in descriptions of the pathophysiology of sepsis. However; despite hundreds of published articles including literature reviews and consensus statements, controversy still exists regarding the fundamental nature of the disorder and its relevance to clinical management. Often referred to as 'relative adrenal insufficiency', a recent consensus conference has proposed the alternate term 'critical illness related corticosteroid insufficiency' and suggested diagnostic criteria of a delta serum cortisol of less than 9 microg/l after adrenocorticotrophic hormone administration or a random total cortisol of under 10 microg/l. This review attempts to establish a critical reappraisal of the evidence for the existence of relative adrenal insufficiency/critical illness related corticosteroid insufficiency in patients with sepsis and examines the background, controversies and possibilities for future research into the condition.

A comparison of transcutaneous Doppler corrected flow time, b-type natriuretic peptide and central venous pressure as predictors of fluid responsiveness in septic shock: a preliminary evaluation

Aortic corrected flow time (FTc) is easily measured by Doppler techniques. Recent data using transoesophageal Doppler suggest that it may predict fluid responsiveness in critical care. This use of FTc has not previously been evaluated in septic shock, nor have any studies incorporated transcutaneously measured FTc. Furthermore, no comparison has been made between FTc, plasma B-type natriuretic peptide concentration (BNP) or central venous pressure. The aim of this preliminary study was to compare FTc, BNP and central venous pressure as predictors of fluid responsiveness in septic shock patients without cardiac dysrhythmia. This was a prospective study of 10 consecutive adult septic shock patients (in sinus rhythm; 60% mechanically ventilated) treated with intravenous fluid challenge (4% albumin 250 ml over 15 minutes) in a mixed medical/ surgical tertiary intensive care unit. Mean + SD Acute Physiological and Chronic Health Evaluation II score was 21.8 +/- 12.7. Haemodynamic assessment incorporating transcutaneous aortic Doppler (USCOM) occurred before and five minutes after fluid challenge. Concurrent with initial assessment, blood samples were collected for BNP assay (ADIVA Centaur). Four patients demonstrated an increase in stroke volume > or = 15% (responders). Percent change in stroke volume strongly correlated with baseline FTc (r = -0.81, P = 0.004) but not BNP (r = -0.3, P = 0.4) or central venous pressure (r = -0.4, P = 0.2). Baseline FTc < 350 ms discriminated responders from non-responders (P = 0.047). Our data support FTc as a better predictor of fluid responsiveness than either BNP or central venous pressure in septic shock. Transcutaneous aortic Doppler FTc offers promise as a simple, completely non-invasive predictor of fluid responsiveness and should be evaluated further

Evidence-based evolution of the high stakes postgraduate intensive care examination in Australia and New Zealand

The fellowship examination for intensive care medicine in Australia and New Zealand, first held in 1979, has undergone four major periods of development and change since inception. These periods are characterised as: 1. 1979 to 1996--initiation and establishment of the exam as a relevant and comprehensive assessment process for a new specialty. 2. 1997 to 2001--revision to increase breadth of coverage, increase reliability for a growing number of candidates and ensure that each candidate received the same exam: Expansion: to incorporate assessment of CanMEDS skills (including communication, procedures and professional qualities). Lengthening: to increase the number of exposures, to ensure reliability. Quarantining of candidates: to allow the provision of a similar exam for each candidate. 3. 2002 to 2006--increasing emphasis on examiner training, standard setting and increasing feedback to candidates to improve the educational experience and guide exam preparation. Blueprinting of questions to maintain validity. 4. 2008 onwards--logistic revision to ensure feasibility for a rapidly growing number of candidates and refinement to apply modem standard setting and quality control. The exam has been regarded as a 'tough but fair' assessment in its 30 years of existence and the committee overseeing its development has aimed to continually review the process to maintain those qualities as well as reliability, validity and feasibility. The increasing number of candidates has allowed accumulation of usable statistics but has tested the feasibility of running such a labour intensive exam. To date, there have been 800 presentations to the exam with 498 successful candidates.

Equivalent Metabolic Acidosis with Four Colloids and Saline on Ex Vivo Haemodilution

Colloid infusions can cause metabolic acidosis. Mechanisms and relative severity with different colloids are incompletely understood. We compared haemodilution acid-base effects of 4% albumin, 3.5% polygeline, 4% succinylated gelatin (all weak acid colloids, strong ion difference 12 mEq/l, 17.6 mEq/l and 34 mEq/l respectively), 6% hetastarch (non-weak acid colloid, strong ion difference zero) and 0.9% saline (crystalloid, strong ion difference zero). Gelatin weak acid properties were tracked via the strong ion gap.

Four-step ex vivo dilutions of pre-oxygenated human venous blood were performed to a final [Hb] near 50% baseline. With each fluid, base excess fell to approximately −13 mEq/l. Base excess/[Hb] relationships across dilution were linear and direct (R2 ≥0.96), slopes and intercepts closely resembling saline. Baseline strong ion gap was −0.3 (2.1) mEq/l. Post-dilution increases occurred in three groups: small with saline, hetastarch and albumin (to 3.5 (02) mEq/l, 4.3 (0.3) mEq/l, 3.3 (1.4) mEq/l respectively), intermediate with polygeline (to 12.2 (0.9) mEq/l) and greatest with succinylated gelatin (to 20.8 (1.4) mEq/l).

We conclude that, despite colloid weak acid activity ranging from zero (hydroxyethyl starch) to greater than that of albumin with both gelatin preparations, ex vivo dilution causes a metabolic acidosis of identical severity to saline in each case. This uniformity reflects modifications to the albumin and gelatin saline vehicles, in part aimed at pH correction. By proportionally increasing the strong ion difference, these modifications counter deviations from pure saline effects caused by colloid weak acid activity. Extrapolation in vivo requires further investigation.

Changes in serum procalcitonin and C-reactive protein following antimicrobial therapy as a guide to antibiotic duration in the critically ill: a prospective evaluation

Serial procalcitonin is reported to be useful to titrate duration of antibiotic therapy in the non critically ill patient with pneumonia. The aim of this study was to examine the relationship between antibiotic therapy and serial serum procalcitonin concentrations in a cohort of critically ill septic patients and examine for any differences between culture positive (CP) and culture negative (CN) sepsis. Seventy-five critically ill patients with suspected sepsis were enrolled in this prospective observational study. Serial procalcitonin and C-reactive protein assays were measured on days one, three, five, seven, 10 and 14. The mean duration of antibiotic therapy was similar in the two groups (10.4 +/- 5.1 (CP) vs. 8.4 +/- 5.1 (CN) days, P = 0.09). Serum procalcitonin concentrations were significantly higher at baseline in the CP than the CN group (14.9 +/- 22.9 vs. 6.8 +/- 21.5 ng/ml, P = 0.04). During the study period, serum concentrations of procalcitonin and C-reactive protein declined in both groups. Serum procalcitonin consistently remained higher in the CP group (P < 0.05) and did not return to normal values. In the CN group, procalcitonin concentrations fell below 0.5 only on day 10. There was no significant difference in C-reactive protein profile between the two groups. Four patients in the CP group (11%) had relapse of sepsis. The mean procalcitonins in the relapsed subgroup were lower than those in the remission subgroup (P = 0.02). Therapy for proven or presumed infections was associated with declining serum procalcitonin and C-reactive protein in critically ill septic patients. The marked variability and overlap in plasma profile of these markers between CP and CN sepsis makes it difficult to define a nadir plasma concentration at which one can recommend discontinuation of antibiotic therapy.

Acid-base effects of a bicarbonate-balanced priming fluid during cardiopulmonary bypass: comparison with Plasma-Lyte 148. A randomised single-blinded study

Fluid-induced metabolic acidosis can be harmful and can complicate cardiopulmonary bypass. In an attempt to prevent this disturbance, we designed a bicarbonate-based crystalloid circuit prime balanced on physico-chemical principles with a strong ion difference of 24 mEq/l and compared its acid-base effects with those of Plasma-Lyte 148, a multiple electrolyte replacement solution containing acetate plus gluconate totalling 50 mEq/l. Twenty patients with normal acid-base status undergoing elective cardiac surgery were randomised 1:1 to a 2 litre prime of either bicarbonate-balanced fluid or Plasma-Lyte 148. With the trial fluid, metabolic acid-base status was normal following bypass initiation (standard base excess 0.1 (1.3) mEq/l, mean, SD), whereas Plasma-Lyte 148 produced a slight metabolic acidosis (standard base excess -2.2 (2.1) mEq/l). Estimated group difference after baseline adjustment was 3.6 mEq/l (95% confidence interval 2.1 to 5.1 mEq/l, P=0.0001). By late bypass, mean standard base excess in both groups was normal (0.8 (2.2) mEq/l vs. -0.8 (1.3) mEq/l, P=0.5). Strong ion gap values were unaltered with the trial fluid, but with Plasma-Lyte 148 increased significantly on bypass initiation (15.2 (2.5) mEq/l vs. 2.5 (1.5) mEq/l, P < 0.0001), remaining elevated in late bypass (8.4 (3.4) mEq/l vs. 5.8 (2.4) mEq/l, P < 0.05). We conclude that a bicarbonate-based crystalloid with a strong ion difference of 24 mEq/l is balanced for cardiopulmonary bypass in patients with normal acid-base status, whereas Plasma-Lyte 148 triggers a surge of unmeasured anions, persisting throughout bypass. These are likely to be gluconate and/or acetate. Whether surges of exogenous anions during bypass can be harmful requires further study.

A clinician's guide to predicting fluid responsiveness in critical illness: applied physiology and research methodology

Intravenous fluid administration is often used in critical care with the goal of improving haemodynamics and consequently tissue perfusion and oxygen delivery. While inotropic and vasoactive drugs are often necessary to correct haemodynamic instability, resuscitation usually begins with fluid therapy. As fluid challenge can result in clinical deterioration, the ability to predict haemodynamic response is desirable. In this way it might be possible to avoid unnecessary volume replacement in critically ill patients. Cardiac preload is a concept that accounts for the relationship between ventricular filling and stroke volume. It has been challenging to apply this concept to clinical practice. For this reason, the study of fluid responsiveness is of increasing research and clinical interest. The clinical application of predicting fluid responsiveness requires an understanding of relevant physiological principles. Furthermore, an improved understanding of these principles should assist the clinician in appraising published data, which has been characterised by significant methodological differences. This review aims to assist the clinician by detailing the physiological principles that underlie the prediction of fluid responsiveness in the critically ill. In addition, the potential importance of methodological differences in the cutrent literature will be considered.

Stability of the strong ion gap versus the anion gap over extremes of PCO2 and pH

The strong ion gap (SIG) is under evaluation as a scanning tool for unmeasured ions. SIG is calculated by subtracting [buffer base], which is ([A-]+[HCO3-), from the apparent strong ion difference, which is ([Na+]+[K+]+[Ca++]+[Mg++]-[Cl-]-[L-lactate]). A- is the negative charge on albumin and phosphate. We compared the pH stability of the SIG with that of the anion gap (AG). In normal and hypoalbuminaemic hyperlactaemic blood, PCO2 was reduced stepwise in vitro from >200 mmHg to <20 mmHg, with serial blood gas and electrolyte analyses, and [albumin] and [phosphate] measurement on completion. Respective [haemoglobin], [albumin], [phosphate] and [lactate] in normal blood were 156 (0.9) g/l, 44 (2) g/l, 1.14 (0.06) mmol/l and 1.7 (0.8) mEq/l, and in hypoalbuminaemic blood 116 (0.9) g/l, 24 (2) g/l, 0.78 (0.06) mmol/l and 8.5 (0.5) mEq/l. pH increased from < 6.85 to > 7.55, causing significant falls in [Na+] and elevations in [Cl-]. Initial and final SIG values did not differ, showing no correlation with pH. Mean SIG was 0.5 +/- 1.5 mEq/l. AG values were directly correlated with pH (normal: R2 = 0.51, hypoalbuminaemic: R2 = 0.65). Final AG values significantly exceeded initial values (normal blood: 15.9 (1.7) mEq/l versus 8.9 (1.8) mEq/l, P < 0.01; hypoalbuminaemic blood: 16.5 (0.8) mEq/l versus 11.8 (2.0) mEq/l, P < 0.05). We conclude that, unlike the AG, the SIG is not affected by severe respiratory acidosis and alkalosis, enhancing its utility in acid-base disturbances.

Acid-base and bio-energetics during balanced versus unbalanced normovolaemic haemodilution

Fluids balanced to avoid acid-base disturbances may be preferable to saline, which causes metabolic acidosis in high volume. We evaluated acid-base and bio-energetic effects of haemodilution with a crystalloid balanced on physical chemical principles, versus crystalloids causing metabolic acidosis or metabolic alkalosis. Anaesthetised, mechanically ventilated Sprague-Dawley rats (n=32, allocated to four groups) underwent six exchanges of 9 ml crystalloid for 3 ml blood. Exchange was with one of three crystalloids with strong ion difference (SID) values of 0, 24 (balanced) and 40 mEq/l. Controls did not undergo haemodilution. Mean haemoglobin concentration fell to approximately 50 g/l after haemodilution. With SID 24 mEq/l fluid, metabolic acid-base remained unchanged. Dilution with SID 0 mEq/l and 40 mEq/l fluids caused a progressive metabolic acidosis and alkalosis respectively. Standard base excess (SBE) and haemoglobin concentration were directly correlated in the SID 0 mEq/l group (R2 = 0.61), indirectly correlated in the SBE 40 mEq/l group (R2 = 0.48) and showed no correlation in the SID 24 mEq/l group (R2 = 0.003). There were no significant differences between final ileal values of CO2 gap, nucleotides concentration, energy charge, or luminal lactate concentration. SID 40 mEq/l crystalloid dilution caused a significant rise in subcutaneous lactate. In this group mean kidney ATP concentration was significantly less than controls and renal energy charge significantly lower than SID 0 mEq/l and control groups. We conclude that a crystalloid SID of 24 mEq/l provides balanced haemodilution. Bio-energetic perturbations with higher SID haemodilution may be more severe and need further investigation.

B-type natriuretic peptide concentrations and myocardial dysfunction in critical illness

B-type natriuretic peptide (BNP) is the first biomarker of proven value in screening for left ventricular dysfunction. The availability of point-of-care testing has escalated clinical interest and the resultant research is defining a role for BNP in the investigation and treatment of critically ill patients. This review was undertaken with the aim of collecting and assimilating current evidence regarding the use of BNP assay in the evaluation of myocardial dysfunction in critically ill humans. The information is presented in a format based upon organ system and disease category. BNP assay has been studied in a spectrum of clinical conditions ranging from acute dyspnoea to subarachnoid haemorrhage. Its role in diagnosis, assessment of disease severity, risk stratification and prognostic evaluation of cardiac dysfunction appears promising, but requires further elaboration. The heterogeneity of the critically ill population appears to warrant a range of cut-off values. Research addressing progressive changes in BNP concentration is hindered by infrequent assay and appears unlikely to reflect the critically ill patient's rapidly changing haemodynamics. Multi-marker strategies may prove valuable in prognostication and evaluation of therapy in a greater variety of illnesses. Scant data exist regarding the use of BNP assay to alter therapy or outcome. It appears that BNP assay offers complementary information to conventional approaches for the evaluation of cardiac dysfunction. Continued research should augment the validity of BNP assay in the evaluation of myocardial function in patients with life-threatening illness.

Active-site properties of Phrixotrix railroad worm green and red bioluminescence-eliciting luciferases

The luciferases of the railroad worm Phrixotrix (Coleoptera: Phengodidae) are the only beetle luciferases that naturally produce true red bioluminescence. Previously, we cloned the green- (PxGR) and red-emitting (PxRE) luciferases of railroad worms Phrixotrix viviani and P. hirtus[OLE1]. These luciferases were expressed and purified, and their active-site properties were determined. The red-emitting PxRE luciferase displays flash-like kinetics, whereas PxGR luciferase displays slow-type kinetics. The substrate affinities and catalytic efficiency of PxRE luciferase are also higher than those of PxGR luciferase. Fluorescence studies with 8-anilino-1-naphthalene sulfonic acid and 6-p-toluidino-2-naphthalene sulfonic acid showed that the PxRE luciferase luciferin-binding site is more polar than that of PxGR luciferase, and it is sensitive to guanidine. Mutagenesis and modelling studies suggest that several invariant residues in the putative luciferin-binding site of PxRE luciferase cannot interact with excited oxyluciferin. These results suggest that one portion of the luciferin-binding site of the red-emitting luciferase is tighter than that of PxGR luciferase, whereas the other portion could be more open and polar.

Uneven evolutionary rates of bradykinin B1 and B2 receptors in vertebrate lineages

Bradykinin acts through two receptor subtypes in mammals and generates a variety of responses including pain, inflammation and hypotension. The evolutionary history of the bradykinin system has been unclear due to shortage of information outside mammals. We describe here two receptor subtypes and the bradykinin precursor in three species of bony fish (the zebrafish Danio rerio, the Japanese pufferfish Takifugu rubripes, and the green spotted pufferfish Tetraodon nigroviridis) and chicken and analyze the relationships to mammals by a combination of phylogeny, conserved synteny and exon-intron organization. All of these species have two receptor genes located close to each other in a tandem formation, with the B2 gene 5' to the B1 gene, in chromosomal regions displaying conserved synteny between the species (albeit conservation of synteny in zebrafish is still unclear due to poor genome assembly). The evolutionary rate differs between the two genes as well as between lineages leading to differing pharmacological properties for both B1 and B2 across vertebrate classes. Also the bradykinin precursor gene was identified in all of these species in a chromosome region with conserved synteny. The tissue distribution of mRNA in T. rubripes is similar for B1 and B2, suggesting more similar regulation for the two genes than in mammals. In conclusion, the receptor tandem duplication predates the divergence of ray-finned fish and tetrapods and no additional duplicates of the receptors or bradykinin seem to have survived the ray-finned fish tetraploidization.

The imaginary line method is not reliable for identification of prosthetic heart valves on AP chest radiographs

OBJECTIVE

To examine the utility of four criteria for distinguishing aortic from mitral valve prostheses on supine anteroposterior (AP) chest x rays in critically ill patients.

MATERIALS AND METHODS

Two reviewers independently examined the post operative chest X-rays (CXR) of all patients undergoing either an aortic or mitral valve replacement over a 32 month period, in a blinded fashion. They applied four criteria to each film. For each criterion a sensitivity and specificity of differentiating the valve positions correctly was calculated for each reviewer, as well as a kappa statistic for inter-observer agreement between the two reviewers.

RESULTS

Two hundred and twenty seven CXR's were evaluated by each of the reviewers. There were 174 aortic and 53 mitral valve replacements. There was a high level of inter-observer agreement for all four criteria applied (kappa values 0.785 to 0.966). Criterion one (imaginary line method) could be applied by both reviewers to less than 50% of CXR's, and when applied was specific but not sensitive. The other three criteria could be applied by both reviewers to approximately 80% of films. Criterion 2 (orientation method) was sensitive but not specific. Criteria 3 (valve orifice method) and 4 (perceived direction of blood flow method) were both highly sensitive and specific and are therefore the best methods.

CONCLUSIONS

The well known imaginary line method is of limited value when identifying prosthetic valve positions on supine AP CXR's. We advocate the use of the "valve orifice" method or the "perceived direction of blood flow" method to gain valuable information regarding the presence and position of prosthetic heart valves.