A simple method to estimate flow restriction for dual ventilation of dissimilar patients: The BathRC model.

BACKGROUND: With large numbers of COVID-19 patients requiring mechanical ventilation and ventilators possibly being in short supply, in extremis two patients may have to share one ventilator. Careful matching of patient ventilation requirements is necessary. However, good matching is difficult to achieve as lung characteristics can have a wide range and may vary over time. Adding flow restriction to the flow path between ventilator and patient gives the opportunity to control the airway pressure and hence flow and volume individually for each patient. This study aimed to create and validate a simple model for calculating required flow restriction. METHODS AND FINDINGS: We created a simple linear resistance-compliance model, termed the BathRC model, of the ventilator tubing system and lung allowing direct calculation of the relationships between pressures, volumes, and required flow restriction. Experimental measurements were made for parameter determination and validation using a clinical ventilator connected to two test lungs. For validation, differing amounts of restriction were introduced into the ventilator circuit. The BathRC model was able to predict tidal lung volumes with a mean error of 4% (min:1.2%, max:9.3%). CONCLUSION: We present a simple model validated model that can be used to estimate required flow restriction for dual patient ventilation. The BathRC model is freely available; this tool is provided to demonstrate that flow restriction can be readily estimated. Models and data are available at DOI 10.15125/BATH-00816.

Structural characterization of 1-deoxy-D-xylulose 5-phosphate Reductoisomerase from Vibrio vulnificus.

Vibrio vulnificus, a gram-negative bacterium, is the leading cause of seafood-borne illnesses and mortality in the United States. Previous studies have identified metabolites 2-C-methylerythritol 4-phosphate (MEP) as being essential for V. vulnificus growth and function. It was shown that 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Dxr) is a critical enzyme in the viability of V. vulnificus, and many other bacteria, as it catalyzes the rearrangement of 1-deoxy-D-xylulose-5-phosphate (Dxp) to 2-C-methylerythritol 4-phosphate (MEP) within the MEP pathway, found in plants and bacteria. The MEP pathway produces the isoprenoids, isopentenyl diphosphate and dimethylallyl pyrophosphate. In this study, we produced and structurally characterized V. vulnificus Dxr. The enzyme forms a dimeric assembly and contains a metal ion in the active site. Protein produced in Escherichia coli co-purifies with Mg2+ ions, however the Mg2+ cations may be substituted with Mn2+, as both of these metals may be utilized by Dxrs. These findings will provide a basis for the design of Dxr inhibitors that may find application as antimicrobial compounds.

Circle (CO2 reabsorbing) breathing systems: Human applications.

Artificial breathing systems to help humans survive extreme environments are used over a range of ambient pressures, using various gases of different volumetric concentrations. These activities include anaesthesia and intensive care activity, high-altitude mountaineering, firefighting, aerospace extravehicular space activity and underwater diving operations. A circle breathing system is one in which the exhaled carbon dioxide is absorbed by an alkali substance and the remaining unused gases are recirculated, usually for the sake of economy and environment. This allows the flow of the fresh gas to be considerably reduced, thereby saving on fresh-gas supply. Circle systems are often used in the circumstances cited above, although not always at low fresh-gas flows. The circle system used in anaesthesia and intensive care has the least engineering demands made on it, although it is used on patients who are highly vulnerable; it usually provides a mixture of air and oxygen, and perhaps a breathable anaesthetic gas, all at sea-level pressure. Mountaineering and firefighting applications involve an extreme earthbound environment, with the user undergoing extreme physical work. The astronaut's spacesuit and life support system contains a high-flow circle system, the breathing gases themselves pressurising the suit as well as providing respiratory life support and thermal comfort; the gas provided is pure oxygen at about a third of sea-level atmosphere. There are numerous varieties of breathing systems for diving, including a circle system, often for clandestine naval activity; the gases used are a combination of oxygen, nitrogen and helium, to minimise the possibility of decompression sickness, nitrogen narcosis and oxygen toxicity and must be provided at a varying pressure and concentration appropriate to depth.

Gas flow between coaxial tubes: impedance to gas flow in an endotracheal tube increases with a catheter within.

The insertion of a suction catheter or a bronchoscope down an endotracheal tube increases the resistance to gas flow down the tube. The extent to which this occurs depends on the relative diameters of the endotracheal tube and the coaxially introduced catheter. This study utilises a laboratory model to quantify this effect, using a steady flow down an annulus between two tubes whose long axes lie co-axially. Two diameters of an endotracheal tube were modelled to represent flow down adult and neonatal endotracheal tubes; these were of internal diameter (d(o)) 6.3 mm and 3.2 mm, and of length (L) 555 mm. A steady flow of air was generated to pass through the model 'endotracheal' tube. Flowrates were calculated to give Re of approximately 5000 for the larger endotracheal tube, and of approximately 1300 for the smaller. These values correspond to clinically appropriate flowrates in adult and neonatal patients, respectively. The pressure drop deltaPo down the endotracheal tube was measured initially without any obstruction, using a calibrated pressure transducer. Catheters of diameter (d(i)) 0.8 mm, 1.6 mm, and 3.2 mm were introduced into the larger diameter endotracheal tube, while catheters of 0.8 mm and 1.6 mm were introduced into the smaller one, and flow was restored to its original value. The pressure drops deltaP down the endotracheal tubes were measured with the catheters introduced a length 'x' into the tube, to x = L/2 and to x = L. Results are compared with a theoretical calculation on the basis of laminar flow for concentric tubes. If a sampling tube or suction catheter is used down the length of an infant's endotracheal tube, the results show that for most values of do/di, there is a significant rise in deltaP/deltaPo. Where a flexible bronchoscope is used down an endotracheal tube or a telescope down a rigid bronchoscope, the value of deltaP/deltaP(o) may also increase unacceptably where d(o)/d(i) is low. The results show that for equal d(o)/d(i), and equal values of x, deltaP/deltaPo are lower for higher values of Re than for lower; and that for lower values of Re there is a more rapid increase in deltaP/deltaPo as x increases, than for higher Re, especially at low values of d(o)/d(i). This result quantifiably confirms clinical experience; that care must be taken in introducing a catheter down a neonatal endotracheal tube. Deviation of these results from the theoretical calculation is less for the smaller Reynolds numbers and smaller values of d(o)/d(i), because under these conditions the flow is more likely to be laminar, with a greater degree of concentricity.

The effect of prehospital time related variables on mortality following severe thoracic trauma.

OBJECTIVES: The aims of this study is firstly to analyse the impact of prehospital time related variables on mortality, in a specific subset of HEMS patients and secondly to demonstrate any interactions between time related variables and factors taking place in the prehospital setting. METHODS: Retrospective analysis of 688 consecutive London HEMS transfers with severe thoracic trauma and mean injury severity score (ISS) of 35, during a 9-year period (1994-2002). We have analysed the effect of the following time related variables on mortality: activation time, arrival on scene time (AoS), stay on scene time (SoS), total time (ToT), rush-hour time (RhT) and leisure-hour time (LhT). We have also investigated the interaction of the above mentioned variables with observations and interventions taken place on scene and at accident and emergency department (A&E) following adjustment for type and severity of injury. For statistical analysis the time variables were grouped into quintiles. RESULTS: Six hundred eighty eight victims (510 males) with mean age of 38.5 ± 17.5 had total survival rate of 59.6%. The mean AoS and SoS were 11.6 ± 5.8 min and 36.6 ± 16.8 min, respectively. ToT>65 min, as in quintiles III, IV and V with mean ToT of 65.3 min, 74.9 min and 102.7 min respectively, had an influence on mortality with calculated adjusted OR of 1.37 (95%CI=0.47-3.94), 3.36 (95%CI = 1.22-9.23) and 1.43 (95%CI = 0.52-3.92) respectively with concomitant adjustment for type of injury, severity of injury, age, physiological variables on scene and on scene emergency thoracotomy (ET). ET on scene was an independent predictor for mortality (OR 3.94, 95%CI = 1.03-15.06). SoS of more than 34 min can lead to harmful changes on patients' pathophysiological status. ISS has no significant effect on AoS or SoS. RhT and LhT have no significant effect on mortality and they did not influence the AoS and SoS. CONCLUSION: This study suggests that time related variables have a complex and heterogeneous effect on mortality. Thoracic trauma victims usually have high ISS, in such population, ToT <65 min may be associated with lower possibility of death. Neither AoS nor SoS was influenced by time of incident or severity of injury.

Whole-body predictors of wrist shot accuracy in ice hockey: a kinematic analysis.

The purpose of this study was to identify joint angular kinematics that corresponds to shooting accuracy in the stationary ice hockey wrist shot. Twenty-four subjects participated in this study, each performing 10 successful shots on four shooting targets. An eight-camera infra-red motion capture system (240 Hz), along with passive reflective markers, was used to record motion of the joints, hockey stick, and puck throughout the performance of the wrist shot. A multiple regression analysis was carried out to examine whole-body kinematic variables with accuracy scores as the dependent variable. Significant accuracy predictors were identified in the lower limbs, torso and upper limbs. Interpretation of the kinematics suggests that characteristics such as a better stability of the base of support, momentum cancellation, proper trunk orientation and a more dynamic control of the lead arm throughout the wrist shot movement are presented as predictors for the accuracy outcome. These findings are substantial as they not only provide a framework for further analysis of motor control strategies using tools for accurate projection of objects, but more tangibly they may provide a comprehensive evidence-based guide to coaches and athletes for planned training to improve performance.

Emergency thoracotomy in the pre-hospital setting: a procedure requiring clarification.

OBJECTIVE: The aim of this study is to investigate the influence of Emergency Thoracotomy (ET) on mortality in a group of patients suffering from severe thoracic trauma requiring Helicopter Emergency Medical Service (HEMS) transfer to hospital. This is not clearly defined especially when thoracotomy takes place in the pre-hospital setting. METHODS: A retrospective review of 670 consecutive patients with severe thoracic trauma, transferred to The Royal London Hospital by HEMS between November 1994 and December 2002. ET (on scene, in the Accident and Emergency (A&E) department or in the operating theatre) was performed in 53 patients (7.7%). Both univariate and multivariate analyses were performed to evaluate ET as an independent predictor of mortality. RESULTS: There were 510 males and 160 females with a mean Injury Severity Score (ISS) of 35.12+/-17.5. Univariate analysis identified ET to be a predictor of mortality (OR=0.15, 95% CI=0.07-0.30). However, with multivariate analysis, ET was not found to be an independent predictor of mortality (OR=1.93, 95% CI=0.61-6.1). The independent predictors of mortality identified were: age>60 years (OR 5.57, 95% CI 2.19-14.16), Glasgow Coma Score <8 at the scene (OR=7.4, 95% CI=3.15-17.46), ISS>25 (OR 5.3, 95% CI=1.64-17.11), need for intubation at the scene (OR=2.80, 95% CI=1.022-7.69), oxygen saturation in A&E (<89%) (OR=2.39, 95% CI=1.13-5.05), haemothorax (OR=3.30, 95% CI=1.53-7.13) and bilateral injury (OR=3.1, 95% CI=1.51-6.61). CONCLUSIONS: Our study has shown that when confounding variables are accounted for, ET is not a predictor of mortality following severe chest trauma. This implies that in a well-selected group of patients it may be a significant and life-saving procedure.

Prospective validity of measuring angina severity with Canadian Cardiovascular Society class: The ACRE study.

BACKGROUND: Although the prevalence of angina remains high, the importance of grading angina severity is unclear. OBJECTIVES: To determine the extent to which angina severity is associated with angiographic findings, and the rate of revascularization, mortality and nonfatal myocardial infarction. METHODS: Prospective, population-based study with a 2.5-year follow-up of 2849 consecutive patients with angina undergoing coronary angiography at Barts and the London NHS Trust, London, United Kingdom, in the Appropriateness of Coronary Revascularisation (ACRE) study. Angina severity was assessed with the Canadian Cardiovascular Society (CCS) classification, ranging from class I (mild) to IV (severe). Outcome measures were revascularization rates, and all-cause mortality and nonfatal myocardial infarction. RESULTS: In age-adjusted analyses, a higher CCS class was linearly associated (P<0.001) with a higher number of diseased vessels and impaired left ventricular function. When adjusting for age, sex, smoking, history of hypertension, diabetes, number of diseased vessels, left ventricular function, use of acetylsalicylic acid, beta-blockers or statins, and revascularization status (for death and nonfatal myocardial infarction), a higher CCS class was linearly associated with higher coronary angioplasty (P<0.001) and bypass graft (P=0.03) rates, and lower all-cause mortality and nonfatal myocardial infarction (P<0.001; CCS IV versus I: hazard ratio 2.44, 95% CI 1.46 to 4.09). CONCLUSION: CCS class was linearly associated with angiographic findings, revascularization rates, mortality and nonfatal myocardial infarction. These findings support the importance of a four-level grading of symptom severity among angina patients.

Role of transvalvular gradient in outcome from valve replacement for aortic stenosis.

BACKGROUND: Despite limitations the transvalvular gradient (TVG) still is commonly used in aortic stenosis when patients are referred for aortic valve replacement. We wished to ascertain if it had a role in predicting outcome from valve replacement rather than as an indicator of severity, specifically investigating if the TVG affected renal dysfunction, hospital stay, and medium-term survival after valve replacement. METHODS: Six hundred and twenty-three consecutive patients who had aortic valve replacement were identified and 211 of these patients were isolated as first time replacement for aortic stenosis that formed the final study group, and were followed up for up to 48 months. Variables significant (p < 0.05) on univariate analysis were included in the logistic regression multivariate analysis (renal dysfunction, prolonged hospital stay) or Cox proportional hazard regression model (medium-term mortality). RESULTS: A significant association was present between TVG and age (p = 0.001). Multivariate analysis demonstrated angina greater than or equal to grade 3 Canadian Cardiovascular Society (CCS 3; p = 0.014) and having nonelective surgery (p < 0.001) to be independent predictors of renal dysfunction. Angina greater than or equal to CCS 3 (p = 0.013) was the only independent predictor of prolonged hospital stay. Independent predictors of medium-term mortality on multivariate analysis were age (p = 0.043) and having a size 19 valve prosthesis (p = 0.015). CONCLUSIONS: The TVG is inadequate as an independent predictor of the degree of aortic stenosis and outcome from aortic valve replacement in aortic stenosis. In contrast, the TVG may be a useful screening tool for detecting aortic stenosis in targeted elderly populations.

Patients' views of the consent process for adult cardiac surgery: questionnaire survey.

OBJECTIVE: Consent for surgical procedures has assumed increasing importance in surgical practice in recent days especially following the public inquiry into paediatric cardiac surgery deaths at Bristol in the UK. This study examines patient perceptions and recollections following surgical consent as currently practised in a UK cardiac unit. METHODS: One hundred consecutive patients who underwent cardiac surgery in a London teaching hospital from January to February 2003 were studied. Patients completed questionnaires a day before their discharge from the hospital. RESULTS: The majority of patients (89/100) responded that the information given at consent had been adequate or more than adequate. The time spent on the consent process was thought to be adequate by 91 patients. Eleven patients felt the consent had been insensitive. Several patients (38/100) felt use of booklets in preference to verbal explanations would be less intimidating. For most patients (94/100) the operation and postoperative course met their expectations; although 12 patients experienced untold complications, only five felt that they should have been informed of the possibility of the complication. Although most patients were informed of the risk of death during consent, at time of discharge 43 had forgotten the figure that had been quoted. Regarding the influence of media and publicity, 19 patients said that media had influenced their expectations of the consent process, 59 would have liked to see hospital league tables while 26 would have liked to know the mortality figures for their surgeon prior to giving consent. CONCLUSIONS: Our study shows that patients undergoing cardiac surgery are largely satisfied with our improved consent procedures in the post-Bristol era. Use of booklets may be a useful adjunct to verbal consent as currently practised.

Ethnic differences in invasive management of coronary disease: prospective cohort study of patients undergoing angiography.

OBJECTIVES: To compare rates of revascularisation in south Asian and white patients undergoing coronary angiography in relation to the appropriateness of revascularisation and clinical outcome. DESIGN: Prospective cohort study of patients with two and a half years' follow up; appropriateness of revascularisation rated by nine experts with no knowledge of ethnicity of patient. SETTING: Tertiary cardiac centre in London with referral from five contiguous health authorities. PARTICIPANTS: Consecutive patients (502 south Asian, 2974 white) undergoing coronary angiography in the appropriateness of coronary revascularisation study (ACRE). MAIN OUTCOME MEASURES: Coronary revascularisation, non-fatal myocardial infarction, mortality. RESULTS: There was no difference between south Asian and white patients in the proportions deemed appropriate for revascularisation (72% (361) v 68% (2022)) or in the proportions for whom the physician's intended management was revascularisation (39% (196) v 41% (1218)). Among patients appropriate for revascularisation, age adjusted rates of coronary angioplasty (hazard ratio 0.69, 95% confidence interval 0.47 to 1.00, P=0.058) and coronary artery bypass grafting (0.74, 0.58 to 0.91, P=0.007) were lower in south Asian than in white patients. These differences were smaller but still present after adjustment for socioeconomic status and after restriction of analysis to those patients for whom the intended management was revascularisation. There were no differences in mortality and non-fatal myocardial infarction between south Asian and white patients (1.07, 0.78 to 1.47). CONCLUSION: Among patients deemed appropriate for coronary artery bypass grafting, south Asian patients are less likely than white patients to receive it. This difference is not explained by physician bias.

The effect of completeness of revascularization on event-free survival at one year in the ARTS trial.

OBJECTIVES: We sought to assess the relationship between completeness of revascularization and adverse events at one year in the ARTS (Arterial Revascularization Therapies Study) trial. BACKGROUND: There is uncertainty to what extent degree of completeness of revascularization, using up-to-date techniques, influences medium-term outcome. METHODS: After consensus between surgeon and cardiologist regarding the potential for equivalence in the completeness of revascularization, 1,205 patients with multivessel disease were randomly assigned to either bypass surgery or stent implantation. All baseline and procedural angiograms and surgical case-record forms were centrally assessed for completeness of revascularization. RESULTS: Of 1,205 patients randomized, 1,172 underwent the assigned treatment. Complete data for review were available in 1,143 patients (97.5%). Complete revascularization was achieved in 84.1% of the surgically treated patients and 70.5% of the angioplasty patients (p < 0.001). After one year, the stented angioplasty patients with incomplete revascularization showed a significantly lower event-free survival than stented patients with complete revascularization (i.e., freedom from death, myocardial infarction, cerebrovascular accident and repeat revascularization) (69.4% vs. 76.6%; p < 0.05). This difference was due to a higher incidence of subsequent bypass procedures (10.0% vs. 2.0%; p < 0.05). Conversely, at one year, bypass surgery patients with incomplete revascularization showed only a marginally lower event-free survival rate than those with complete revascularization (87.8% vs. 89.9%). CONCLUSIONS: Complete revascularization was more frequently accomplished by bypass surgery than by stent implantation. One year after bypass, there was no significant difference in event-free survival between surgically treated patients with complete revascularization and those with incomplete revascularization, but patients randomized to stenting with incomplete revascularization had a greater need for subsequent bypass surgery.