Multiphysics analysis of chip and resonator designs for increased damage threshold of external cavity high-power laser diodes.

We present a detailed analysis of multiphysics simulation results to evaluate the threshold for catastrophic optical damage (COD) of high-power laser diodes under misaligned external optical feedback. Three different chip designs are investigated: the non-injecting mirror concept, the non-absorbing mirror concept and the introduction of an additional energy barrier within the waveguide near the front facet. Furthermore, a modification of the external resonator that promises a lower sensitivity towards misalignments is considered. The dependence of the COD threshold on the additional design parameters (bandgap change, modification length, focal length) and the impact of the different approaches on electro-optical efficiency as well as beam quality are analyzed. Compared to the initial design, the different chip design concepts promise an increase of the achievable output power by 8%, 27% and 27% respectively, whereas the modified resonator fully prevents feedback-induced failure.

Continuous vs Intermittent Meropenem Administration in Critically Ill Patients With Sepsis: The MERCY Randomized Clinical Trial.

Importance: Meropenem is a widely prescribed ß-lactam antibiotic. Meropenem exhibits maximum pharmacodynamic efficacy when given by continuous infusion to deliver constant drug levels above the minimal inhibitory concentration. Compared with intermittent administration, continuous administration of meropenem may improve clinical outcomes. Objective: To determine whether continuous administration of meropenem reduces a composite of mortality and emergence of pandrug-resistant or extensively drug-resistant bacteria compared with intermittent administration in critically ill patients with sepsis. Design, Setting, and Participants: A double-blind, randomized clinical trial enrolling critically ill patients with sepsis or septic shock who had been prescribed meropenem by their treating clinicians at 31 intensive care units of 26 hospitals in 4 countries (Croatia, Italy, Kazakhstan, and Russia). Patients were enrolled between June 5, 2018, and August 9, 2022, and the final 90-day follow-up was completed in November 2022. Interventions: Patients were randomized to receive an equal dose of the antibiotic meropenem by either continuous administration (n = 303) or intermittent administration (n = 304). Main Outcomes and Measures: The primary outcome was a composite of all-cause mortality and emergence of pandrug-resistant or extensively drug-resistant bacteria at day 28. There were 4 secondary outcomes, including days alive and free from antibiotics at day 28, days alive and free from the intensive care unit at day 28, and all-cause mortality at day 90. Seizures, allergic reactions, and mortality were recorded as adverse events. Results: All 607 patients (mean age, 64 [SD, 15] years; 203 were women [33%]) were included in the measurement of the 28-day primary outcome and completed the 90-day mortality follow-up. The majority (369 patients, 61%) had septic shock. The median time from hospital admission to randomization was 9 days (IQR, 3-17 days) and the median duration of meropenem therapy was 11 days (IQR, 6-17 days). Only 1 crossover event was recorded. The primary outcome occurred in 142 patients (47%) in the continuous administration group and in 149 patients (49%) in the intermittent administration group (relative risk, 0.96 [95% CI, 0.81-1.13], P = .60). Of the 4 secondary outcomes, none was statistically significant. No adverse events of seizures or allergic reactions related to the study drug were reported. At 90 days, mortality was 42% both in the continuous administration group (127 of 303 patients) and in the intermittent administration group (127 of 304 patients). Conclusions and Relevance: In critically ill patients with sepsis, compared with intermittent administration, the continuous administration of meropenem did not improve the composite outcome of mortality and emergence of pandrug-resistant or extensively drug-resistant bacteria at day 28. Trial Registration: ClinicalTrials.gov Identifier: NCT03452839.

Plasma volume contraction reduces atrial natriuretic peptide after four days of hypobaric hypoxia exposure.

We investigated whether low arterial oxygen tension ([Formula: see text]) or hypoxia-induced plasma volume (PV) contraction, which reduces central blood volume (BV) and atrial distension, explain reduction in circulating atrial natriuretic peptide (ANP) after prolonged hypoxic exposure. Ten healthy males were exposed for 4 days to hypobaric hypoxia corresponding to an altitude of 3,500 m. PV changes were determined by carbon monoxide rebreathing. Venous plasma concentrations of midregional proANP (MR-proANP) were measured before and at the end of the exposure. At the latter time point, the measurement was repeated after 1) restoration of [Formula: see text] by breathing a hyperoxic gas mixture for 30 min and 2) restoration of BV by fluid infusion. Correspondingly, left ventricular end-diastolic volume (LVEDV), left atrial area (LAA), and right atrial area (RAA) were determined by ultrasound before exposure and both before and after fluid infusion at the end of the exposure. Hypoxic exposure reduced MR-proANP from 37.9 ± 18.5 to 24.5 ± 10.3 pmol/L (P = 0.034), LVEDV from 107.4 ± 33.5 to 91.6 ± 26.3 mL (P = 0.005), LAA from 15.8 ± 4.9 to 13.3 ± 4.2 cm2 (P = 0.007), and RAA from 16.2 ± 3.1 to 14.3 ± 3.5 cm2 (P = 0.001). Hyperoxic breathing did not affect MR-proANP (24.8 ± 12.3 pmol/L, P = 0.890). Conversely, fluid infusion restored LVEDV, LAA, and RAA to near-baseline values (108.0 ± 29.3 mL, 17.2 ± 5.7 cm2, and 17.2 ± 3.1 cm2, respectively, P > 0.05 vs. baseline) and increased MR-proANP to 29.5 ± 13.3 pmol/L (P = 0.010 vs. preinfusion and P = 0.182 vs. baseline). These findings support that ANP reduction in hypoxia is at least partially attributed to plasma volume contraction, whereas reduced [Formula: see text] does not seem to contribute.

GPU-accelerated wave-optical model for external-cavity diode lasers.

The spatial distribution of the optical feedback field in an external-cavity diode laser (ECDL) is an important parameter influencing its lifetime and filamentation. From a modeling point of view, the evaluation of the full diffraction integral is required to calculate the propagation of light through thick lenses such as fast axis collimation lenses or beam transformation systems used for high-power diode lasers. In this Letter, we illustrate an algorithm for the accelerated computation of the Rayleigh-Sommerfeld diffraction integral on a graphics processing unit. We further show a validation of the results by measurements on an ECDL.

Endothelial function and shear stress in hypobaric hypoxia: time course and impact of plasma volume expansion in men.

High-altitude exposure typically reduces endothelial function, and this is modulated by hemoconcentration resulting from plasma volume contraction. However, the specific impact of hypobaric hypoxia independent of external factors (e.g., cold, varying altitudes, exercise, diet, and dehydration) on endothelial function is unknown. We examined the temporal changes in blood viscosity, shear stress, and endothelial function and the impact of plasma volume expansion (PVX) during exposure to hypobaric hypoxia while controlling for external factors. Eleven healthy men (25 ± 4 yr, mean ± SD) completed two 4-day chamber visits [normoxia (NX) and hypobaric hypoxia (HH; equivalent altitude, 3,500 m)] in a crossover design. Endothelial function was assessed via flow-mediated dilation in response to transient (reactive hyperemia; RH-FMD) and sustained (progressive handgrip exercise; SS-FMD) increases in shear stress before entering and after 1, 6, 12, 48, and 96 h in the chamber. During HH, endothelial function was also measured on the last day after PVX to preexposure levels (1,140 ± 320 mL balanced crystalloid solution). Blood viscosity and arterial shear stress increased on the first day during HH compared with NX and remained elevated at 48 and 96 h (P < 0.005). RH-FMD did not differ during HH compared with NX and was unaffected by PVX despite reductions in blood viscosity (P < 0.05). The stimulus-response slope of increases in shear stress to vasodilation during SS-FMD was preserved in HH and increased by 44 ± 73% following PVX (P = 0.023). These findings suggest that endothelial function is maintained in HH when other stressors are absent and that PVX improves endothelial function in a shear-stress stimulus-specific manner.NEW & NOTEWORTHY Using a normoxic crossover study design, we examined the impact of hypobaric hypoxia (4 days; altitude equivalent, 3,500 m) and hemoconcentration on blood viscosity, shear stress, and endothelial function. Blood viscosity increased during the hypoxic exposure and was accompanied by elevated resting and exercising arterial shear stress. Flow-mediated dilation stimulated by reactive hyperemia and handgrip exercise was preserved throughout the hypoxic exposure. Plasma volume expansion reversed the hypoxia-associated hemoconcentration and selectively increased handgrip exercise flow-mediated dilation.

Venous Pooling in Suspension Syndrome Assessed with Ultrasound.

INTRODUCTION: Suspension syndrome describes a potentially life-threatening event during passive suspension on a rope. The pathophysiological mechanism is not fully understood; however, the most widespread hypothesis assumes blood pools in the lower extremities, prompting a reduction in cardiac preload and cardiac output and leading to tissue hypoperfusion, loss of consciousness, and death. The aim of this study was to assess venous pooling by ultrasound in simulated suspension syndrome using human subjects. METHODS: In this trial, 20 healthy volunteers were suspended in a sit harness for a maximum of 60 min with and without preceding exercise. Venous pooling was assessed by measuring the diameter of the superficial femoral vein (SFV) with ultrasound at baseline in supine and standing positions as well as during and after suspension. RESULTS: SFV diameter increased and blood flow became progressively sluggish. In 30% of the tests, near syncope occurred. However, SFV diameter did not differ between subjects with and without near syncope. CONCLUSIONS: Free hanging in a harness leads to rapid venous pooling in the lower limbs. The most important measure to prevent suspension syndrome might be constant movement of the legs.

Hypothermic Cardiac Arrest With Full Neurologic Recovery After Approximately Nine Hours of Cardiopulmonary Resuscitation: Management and Possible Complications.

We describe full neurologic recovery from accidental hypothermia with cardiac arrest despite the longest reported duration of mechanical cardiopulmonary resuscitation (CPR) and extracorporeal life support (8 hours, 42 minutes). Clinical data and blood samples were obtained from emergency medical services (EMS) and the intensive care department. A 31-year-old man experienced a witnessed hypothermic cardiac arrest with a core temperature of 26°C (78.8°F) during a summer thunderstorm; he received mechanical CPR for 3 hours and 42 minutes, followed by 5 hours of extracorporeal life support. The use of a standard operating procedure that integrates a technical mountain rescue performed by EMS, optimizes prolonged CPR to the hub hospital, and enables prompt placement of extracorporeal life support is described and discussed. Three months postaccident, the patient had recovered completely (Cerebral Performance Category score of 1) and resumed normal daily life. Neurologically intact survival from hypothermic cardiac arrest is common, suggesting that aggressive resuscitation measures are warranted. There is a need for the establishment of a clear standard operating procedure and multiteam education and training to further optimize the patient survival chain from on-site triage and treatment to inhospital extracorporeal life support and postresuscitation care.

Correction to: Suspension syndrome: a potentially fatal vagally mediated circulatory collapse-an experimental randomized crossover trial.

The original version of this article unfortunately contained a mistake. Information was missing in the acknowledgements section. The correct information is given below.

Suspension syndrome: a potentially fatal vagally mediated circulatory collapse-an experimental randomized crossover trial.

PURPOSE: Suspension syndrome describes a potentially life-threatening event during passive suspension on a rope. The pathophysiological mechanism is not fully understood and optimal treatment unknown. We aimed to elucidate the pathophysiology and to give treatment recommendations. METHODS: In this experimental, randomized crossover trial, 20 healthy volunteers were suspended in a sit harness for a maximum of 60 min, with and without prior climbing. Venous pooling was assessed by measuring the diameter of the superficial femoral vein (SFV), lower leg tissue oxygenation (StO2) and by determining localized bioelectrical impedance. Hemodynamic response was assessed by measuring heart rate, blood pressure, stroke volume, and left ventricular diameters. Signs and symptoms of pre-syncope were recorded. RESULTS: Twelve (30%) out of 40 tests were prematurely terminated due to pre-syncopal symptoms (mean 44.7 min, minimum 13.4, maximum 59.7). SFV diameter increased, StO2 and the capacitive resistance of the cells decreased indicating venous pooling. Heart rate and blood pressure did not change in participants without pre-syncope. In contrast, in participants experiencing pre-syncope, heart rate and blood pressure dropped immediately before the event. All symptoms dissolved and values returned to normal within 5 min with participants in a supine position. CONCLUSIONS: Sudden pre-syncope during passive suspension in a harness was observed in 30% of the tests. Blood pools in the veins of the lower legs; however, a vagal mechanism finally leads to loss of consciousness. Time to pre-syncope is unpredictable and persons suspended on a rope should be rescued and put into a supine position as soon as possible.

Pre-operative evaluation of adults undergoing elective noncardiac surgery: Updated guideline from the European Society of Anaesthesiology.

: The purpose of this update of the European Society of Anaesthesiology (ESA) guidelines on the pre-operative evaluation of the adult undergoing noncardiac surgery is to present recommendations based on the available relevant clinical evidence. Well performed randomised studies on the topic are limited and therefore many recommendations rely to a large extent on expert opinion and may need to be adapted specifically to the healthcare systems of individual countries. This article aims to provide an overview of current knowledge on the subject with an assessment of the quality of the evidence in order to allow anaesthesiologists all over Europe to integrate - wherever possible - this knowledge into daily patient care. The Guidelines Committee of the ESA formed a task force comprising members of the previous task force, members of ESA scientific subcommittees and an open call for volunteers was made to all individual active members of the ESA and national societies. Electronic databases were searched from July 2010 (end of the literature search of the previous ESA guidelines on pre-operative evaluation) to May 2016 without language restrictions. A total of 34 066 abtracts were screened from which 2536 were included for further analysis. Relevant systematic reviews with meta-analyses, randomised controlled trials, cohort studies, case-control studies and cross-sectional surveys were selected. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was used to assess the level of evidence and to grade recommendations. The final draft guideline was posted on the ESA website for 4 weeks and the link was sent to all ESA members, individual or national (thus including most European national anaesthesia societies). Comments were collated and the guidelines amended as appropriate. When the final draft was complete, the Guidelines Committee and ESA Board ratified the guidelines.

Thin-film filter wavelength-stabilized, grating combined, high-brightness kW-class direct diode laser.

We report on kW-class dense wavelength beam combining of a laser diode module consisting of ten broad-area laser diode bars by using a novel multi-laser cavity approach based on a thin-film filter (TFF) as a dispersive optical element. The wavelength-stabilized output of the TFF cavity is beam combined upon a -1st order transmission grating. Hereby, a cylindrical telescope is used for linear dispersion-matching between the TFF and the combiner grating. On the basis of simulations of the resulting beam quality deterioration, we are able to optimize the cavity and the combiner setup for optimal beam quality preservation. We demonstrate a highly efficient direct diode laser with 1.1-kW output power and a symmetrical beam parameter product of about 6mm × mrad (95 % power content) in both beam axis.

[Emergency medicine at the limit: shock-, analgesic therapy and airway management in difficult terrain]. / Notfallmedizin im alpinen Gelände - Schock-, Schmerztherapie und Atemwegssicherung.

Rescue operations in mountain and remote areas pose special challenges for the rescue team and often differ substantially from rescue missions in the urban environment. Given the growing sports and leisure activities in mountains, incidence of alpine emergencies is expected to rise further. The following article describes the treatment of haemorrhagic shock, analgesic therapy and airway management in mountain rescue.

Prevalence of airway patency and air pocket in critically buried avalanche victims - a scoping review.

INTRODUCTION: Survival of critically buried avalanche victims is directly dependent on the patency of the airway and the victims' ability to breathe. While guidelines and avalanche research have consistently emphasized on the importance of airway patency, there is a notable lack of evidence regarding its prevalence. OBJECTIVE: The aim of this review is to provide insight into the prevalence of airway patency and air pocket in critically buried avalanche victims. METHODS: A scoping review was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline extension for scoping reviews. MEDLINE and Cochrane databases, as well as additional manual searching was performed to identify literature reporting data on airway patency and the presence of an air pocket in critically buried avalanche victims. After eliminating duplicates, we screened abstracts and main texts to identify eligible studies. RESULTS: Of 4,109 studies identified 154 were eligible for further screening. Twenty-four publications and three additional data sources with a total number of 566 cases were included in this review. The proportion of short-term (< 35 min) to long-term burial (≥ 35 min) in the analysed studies was 19% and 66%, respectively. The burial duration remained unknown in 12% of cases. The prevalence of airway patency in critically buried avalanche victims was 41% while that of airway obstruction was 12%, with an overall rate of reporting as low as 50%. An air pocket was present in 19% of cases, absent in 46% and unknown in 35% of the cases. CONCLUSION: The present study found that in critically buried avalanche victims patent airways were more than three times more prevalent than obstructed, with the airway status reported only in half of the cases. This high rate of airway patency supports the ongoing development and the effectiveness of avalanche rescue systems which oppose asphyxiation in critically buried avalanche victims. Further effort should be done to improve the documentation of airway patency and the presence of an air pocket in avalanche victims and to identify factors affecting the rate of airway obstruction.

Critically buried avalanche victims can develop severe hypothermia in less than 60 min.

BACKGROUND: A major challenge in the management of avalanche victims in cardiac arrest is differentiating hypothermic from non-hypothermic cardiac arrest, as management and prognosis differ. Duration of burial with a cutoff of 60 min is currently recommended by the resuscitation guidelines as a parameter to aid in this differentiation However, the fastest cooling rate under the snow reported so far is 9.4 °C per hour, suggesting that it would take 45 min to cool below 30 °C, which is the temperature threshold below which a hypothermic cardiac arrest can occur. CASE PRESENTATION: We describe a case with a cooling rate of 14 °C per hour, assessed on site with an oesophageal temperature probe. This is by far the most rapid cooling rate after critical avalanche burial reported in the literature and further challenges the recommended 60 min threshold for triage decisions. The patient was transported under continuous mechanical CPR to an ECLS facility and rewarmed with VA-ECMO, although his HOPE score was 3% only. After three days he developed brain death and became an organ donor. CONCLUSIONS: With this case we would like to underline three important aspects: first, whenever possible, core body temperature should be used instead of burial duration to make triage decisions. Second, the HOPE score, which is not well validated for avalanche victims, had a good discriminatory ability in our case. Third, although extracorporeal rewarming was futile for the patient, he donated his organs. Thus, even if the probability of survival of a hypothermic avalanche patient is low based on the HOPE score, ECLS should not be withheld by default and the possibility of organ donation should be considered.

Surgical masks and filtering facepiece class 2 respirators (FFP2) have no major physiological effects at rest and during moderate exercise at 3000-m altitude: a randomised controlled trial.

BACKGROUND: During the COVID-19 pandemic, the use of face masks has been recommended or enforced in several situations; however, their effects on physiological parameters and cognitive performance at high altitude are unknown. METHODS: Eight healthy participants (four females) rested and exercised (cycling, 1 W/kg) while wearing no mask, a surgical mask or a filtering facepiece class 2 respirator (FFP2), both in normoxia and hypobaric hypoxia corresponding to an altitude of 3000 m. Arterialised oxygen saturation (SaO2), partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2), heart and respiratory rate, pulse oximetry (SpO2), cerebral oxygenation, visual analogue scales for dyspnoea and mask's discomfort were systematically investigated. Resting cognitive performance and exercising tympanic temperature were also assessed. RESULTS: Mask use had a significant effect on PaCO2 (overall +1.2 ± 1.7 mmHg). There was no effect of mask use on all other investigated parameters except for dyspnoea and discomfort, which were highest with FFP2. Both masks were associated with a similar non-significant decrease in SaO2 during exercise in normoxia (-0.5 ± 0.4%) and, especially, in hypobaric hypoxia (-1.8 ± 1.5%), with similar trends for PaO2 and SpO2. CONCLUSIONS: Although mask use was associated with higher rates of dyspnoea, it had no clinically relevant impact on gas exchange at 3000 m at rest and during moderate exercise, and no detectable effect on resting cognitive performance. Wearing a surgical mask or an FFP2 can be considered safe for healthy people living, working or spending their leisure time in mountains, high-altitude cities or other hypobaric environments (e.g. aircrafts) up to an altitude of 3000 m.

Suspension syndrome: a scoping review and recommendations from the International Commission for Mountain Emergency Medicine (ICAR MEDCOM).

BACKGROUND: Suspension syndrome describes a multifactorial cardio-circulatory collapse during passive hanging on a rope or in a harness system in a vertical or near-vertical position. The pathophysiology is still debated controversially. AIMS: The International Commission for Mountain Emergency Medicine (ICAR MedCom) performed a scoping review to identify all articles with original epidemiological and medical data to understand the pathophysiology of suspension syndrome and develop updated recommendations for the definition, prevention, and management of suspension syndrome. METHODS: A literature search was performed in PubMed, Embase, Web of Science and the Cochrane library. The bibliographies of the eligible articles for this review were additionally screened. RESULTS: The online literature search yielded 210 articles, scanning of the references yielded another 30 articles. Finally, 23 articles were included into this work. CONCLUSIONS: Suspension Syndrome is a rare entity. A neurocardiogenic reflex may lead to bradycardia, arterial hypotension, loss of consciousness and cardiac arrest. Concomitant causes, such as pain from being suspended, traumatic injuries and accidental hypothermia may contribute to the development of the Suspension Syndrome. Preventive factors include using a well-fitting sit harness, which does not cause discomfort while being suspended, and activating the muscle pump of the legs. Expediting help to extricate the suspended person is key. In a peri-arrest situation, the person should be positioned supine and standard advanced life support should be initiated immediately. Reversible causes of cardiac arrest caused or aggravated by suspension syndrome, e.g., hyperkalaemia, pulmonary embolism, hypoxia, and hypothermia, should be considered. In the hospital, blood and further exams should assess organ injuries caused by suspension syndrome.