Role Of Mechanical Ventilation Research Articles

Fire-induced flows for complex fire scenarios in a mechanically ventilated two-storey structure

This work deals with smoke propagation through a multi-compartment assembly in case of a fire event in a nuclear installation. The scientific issues are the understanding of flows involving two modes of propagation (vent and doorway), together with the role of mechanical ventilation and oxygen backflows to the fire. The study is based on the analysis of two scenarios reproduced experimentally at large scale and simulated numerically. The main outcomes concern the comparison of the flow at a doorway and at a vent, the consequence of the smoke propagation for thermal stratification and the combined effect of the fire heat release rate and mechanical ventilation. The results highlight the performance of computational fluid dynamics simulations in predicting these complex scenarios. Low-velocity flow zones are identified, enabling the structure of these flows and their amplitudes to be quantified. This information provides new insights to improve fire risk assessment in nuclear facilities.

The role of mechanical ventilation in primary graft dysfunction in the postoperative lung transplant recipient: A single center study and literature review.

BackgroundPrimary graft dysfunction (PGD) is still a major complication in patients undergoing lung transplantation (LTx). Much is unknown about the effect of postoperative mechanical ventilation on outcomes, with debate on the best approach to ventilation.Aim/PurposeThe goal of this study was to generate hypotheses on the association between postoperative mechanical ventilation settings and allograft size matching in PGD development.MethodThis is a retrospective study of LTx patients between September 2011 and September 2018 (n = 116). PGD was assessed according to the International Society of Heart and Lung Transplantation (ISHLT) criteria. Data were collected from medical records, including chest x‐ray assessments, blood gas analysis, mechanical ventilator parameters and spirometry.ResultsPositive end‐expiratory pressures (PEEP) of 5 cm H2O were correlated with lower rates of grade 3 PGD. Graft size was important as tidal volumes calculated according to the recipient yielded greater rates of PGD when low volumes were used, a correlation that was lost when donor metrics were used.ConclusionOur results highlight a need for greater investigation of the role donor characteristics play in determining post‐operative ventilation of a lung transplant recipient. The mechanical ventilation settings on postoperative LTx recipients may have an implication for the development of acute graft dysfunction. Severe PGD was associated with the use of a PEEP higher than 5 and lower tidal volumes and oversized lungs were associated with lower long‐term mortality. Lack of association between ventilatory settings and survival may point to the importance of other variables than ventilation in the development of PGD.

Covid-19 pneumonia: Timing of pneumomediastinum and pneumothorax in 11 patients

Purpose: As the pandemic continues, many complications, previously recognized as rare, are now being reported as more than frequent complications of Covid-19 pneumonia. Of those, pneumomediastinum and pneumothorax are gaining attention. Their mechanism of occurrence/trigger is not fully understood, but the timing at which they occur is unclear.Methods: This is a case series of 11 Covid-19 patients with pneumomediastinum; retrospectively, we shed light on some of the patients’ characteristics, the role of mechanical ventilation, and the timing of pneumomediastinum after initiation of mechanical ventilation.Results: We found that despite following the lung-protective strategy and despite keeping a plateau pressure at an acceptable range, most of our patients had an acute event around the same timing of mechanical ventilation.Conclusions: The similar timing raises questions about other risk factors that remain unknown. Timing and steroids can contribute to the higher incidence of these complications.

Adherence ability and serum resistance of different hospital clusters of Acinetobacter baumannii.

The role of mechanical ventilation and catheters in favouring Acinetobacter baumannii infections needs to be better understood. This study evaluated the adherence of 19 isolates of different hospital clusters of A. baumannii to abiotic surfaces and epithelial cells (HEp-2). Of the hydrophobic isolates, 80% adhered to polystyrene, indicating a close relationship between hydrophobicity and adherence. All isolates adhered to epithelial cells to different degrees, and 73·7% showed an aggregated pattern. Analysis of the serum resistance of catheter-tip isolates showed that all were resistant. These worrisome results showed that the high capacity of A. baumannii to adhere to surfaces and survive in human serum could hinder treatment and control of this pathogen.

Cardio-pulmonary-renal interactions in ICU patients. Role of mechanical ventilation, venous congestion and perfusion deficit on worsening of renal function: Insights from the MIMIC-III database.

Background Mechanical ventilation (MV) in ICU patients may impact hemodynamics and renal function. We aimed to describe the interactions of MV settings, hemodynamic parameters and worsening of renal function (WRF). Methods We included adult patients admitted for the first time in the ICU from the MIMIC-III database. Mean arterial blood pressure (mABP), central venous pressure (CVP) and positive end-expiratory pressure (PEEP) were collected and summarized as a time-weighted mean. The main outcome was WRF defined as acute kidney injury (AKI) occurrence or one-KDIGO stage worsening compared to the KDIGO stage the day before. We used a multinomial logistic regression at day 1 (ldmk-1) and day 2 (ldmk-2) according to a landmark-approach, with a two-days sliding perspective. Results 27,248/61,051 patients met the inclusion criteria (15,258 male (56.0%); 60.1% over 60 y). ICU and hospital mortality were 7.4 and 10.7%, respectively. MV was independently associated with WRF in the ldmrk-1 and -2 models (relative risk ratio [RRR] 8.15 [6.58;10.11] and 7.08 [3.97;12.61] at day-3 and 4, respectively). In MV patients, PEEP was associated with WRF in the ldmrk-1 and -2 models (RRR 1.36 [1.16, 1.6] and 1.17 [0.88, 1.56] by 1 cmH2O increase at day-3 and 4, respectively). Mean perfusion pressure decreased while central venous pressure increased over PEEP categories. In multivariable analysis, mABP, CVP and PEEP were independently associated with WRF. Conclusion In this large cohort of ICU patients, we observed a strong relationship between MV and WRF. PEEP was associated with WRF in MV patients. This association relied at least partly on renal venous congestion.

Alternative Ways of Cooling a Passive School Building in Order to Maintain Thermal Comfort in Summer

The heatwaves that have affected our civilization in recent years pose a serious threat to the environment as well as the proper functioning of our bodies. Schools are facilities with specific microclimatic requirements. Thermal conditions in educational buildings are decisive for the stimulation and efficiency of the learning process, as well as the interaction of students. Based on the measurements of thermal comfort carried out in the school building, with the energy standard of a passive building, it can be observed that in schools with very low energy consumption, the problem of interior overheating may occur in the summer months. In this paper, an attempt was made to search for alternative passive measures allowing for the required indoor microclimate conditions to be obtained. Such solutions are in line with the spirit of the European energy policy and sustainable development. A model of the school under study was created using the Design Builder simulation program. The role of mechanical ventilation and the possibility of night ventilation in reducing discomfort were examined. Consideration was given to the justification of using expensive heat pump installations with a ground heat exchanger to reduce overheating in summer. The application of the adaptive approach to the assessment of thermal conditions and the acceptance of limited overheating periods led to the conclusion that the analyzed building could function successfully without these additional installation elements. A proprietary tool for the analysis of microclimate conditions was proposed to estimate the hours of discomfort in a way that is objective and easy to calculate.

RESPIRATORY SUPPORT AT PREHOSPITAL STAGE OF EMERGENCY MEDICAL CARE: CURRENT STATUS, PROBLEMS AND PROSPECTS OF DEVELOPMENT

Patients with respiratory distress often seek emergency medical care and are frequently transported by emergency medical services (EMS). Some of them are in need of urgent respiratory support.EMSencounters with patients in respiratory distress and the role of mechanical ventilation (MV) in their treatment have not been well documented. The study objective was to characterize the epidemiology of prehospital respiratory distress and the impact of MV at subsequent patient outcomes. Some of the new trends in prehospital respiratory therapy have also been described.

Ventilator-induced diaphragmatic dysfunction: what have we learned?

The purpose of the review is to summarize and discuss recent research regarding the role of mechanical ventilation in producing weakness and atrophy of the diaphragm in critically ill patients, an entity termed ventilator-induced diaphragmatic dysfunction (VIDD). Severe weakness of the diaphragm is frequent in mechanically ventilated patients, in whom it contributes to poor outcomes including increased mortality. Significant progress has been made in identifying the molecular mechanisms responsible for VIDD in animal models, and there is accumulating evidence for occurrence of the same cellular processes in the diaphragms of human patients undergoing prolonged mechanical ventilation. Recent research is pointing the way to novel pharmacologic therapies as well as nonpharmacologic methods for preventing VIDD. The next major challenge in the field will be to move these findings from the bench to the bedside in critically ill patients.

Role of mechanical ventilation in the airborne transmission of infectious agents in buildings.

Infectious disease outbreaks and epidemics such as those due to SARS, influenza, measles, tuberculosis, and Middle East respiratory syndrome coronavirus have raised concern about the airborne transmission of pathogens in indoor environments. Significant gaps in knowledge still exist regarding the role of mechanical ventilation in airborne pathogen transmission. This review, prepared by a multidisciplinary group of researchers, focuses on summarizing the strengths and limitations of epidemiologic studies that specifically addressed the association of at least one heating, ventilating and/or air‐conditioning (HVAC) system‐related parameter with airborne disease transmission in buildings. The purpose of this literature review was to assess the quality and quantity of available data and to identify research needs. This review suggests that there is a need for well‐designed observational and intervention studies in buildings with better HVAC system characterization and measurements of both airborne exposures and disease outcomes. Studies should also be designed so that they may be used in future quantitative meta‐analyses.

Sleep Disturbances in Patients Admitted to a Step-Down Unit After ICU Discharge: the Role of Mechanical Ventilation

Severe sleep disruption is a well-documented problem in mechanically ventilated, critically ill patients during their time in the intensive care unit (ICU), but little attention has been paid to the period when these patients become clinically stable and are transferred to a step-down unit (SDU). We monitored the 24-h sleep pattern in 2 groups of patients, one on mechanical ventilation and the other breathing spontaneously, admitted to our SDU to assess the presence of sleep abnormalities and their association with mechanical ventilation. Twenty-two patients admitted to an SDU underwent 24-h polysomnography with monitoring of noise and light. One patient did not complete the study. At night, 10 patients showed reduced sleep efficiency, 6 had reduced percentage of REM sleep, and 3 had reduced percentage of slow wave sleep (SWS). Sleep amount and quality did not differ between patients breathing spontaneously and those on mechanical ventilation. Clinical severity (SAPS(II) score) was significantly correlated with daytime total sleep time and efficiency (r = 0.51 and 0.5, P < 0.05, respectively); higher pH was correlated with reduced sleep quantity and quality; and higher PaO(2) was correlated with increased SWS (r = 0.49; P = 0.02). Patients admitted to an SDU after discharge from an ICU still have a wide range of sleep abnormalities. These abnormalities are mainly associated with a high severity score and alkalosis. Mechanical ventilation does not appear to be a primary cause of sleep impairment.

Year in review 2010: Critical Care - respirology

In this review, 21 original papers published last year in the respirology and critical care sections of Critical Care are classified and analyzed in the following categories: mechanical ventilation, lung recruitment maneuvers, and weaning; the role of positive end-expiratory pressure in acute lung injury models; animal models of ventilator-induced lung injury; diaphragmatic dysfunction; the role of mechanical ventilation in heart-lung interaction; and miscellanea.

A case of bronchiolitis obliterans in a young child

Bronchiolitis obliterans (BO) is an infrequent chronic obstructive pulmonary disease that follows an insult to lower respiratory tract. BO following a severe lung infectious disease is the most common form reported in children. It implies a chronic necrotizing and ultimately fibrosing process affecting the small airways which results in progressive obliteration with resultant obstructive lung disease. The characteristic symptom-complex includes dyspnea, chronic cough, sputum production and wheezing. Although histopathology remains the gold standard for diagnosis, computed tomographic scan is of great help in diagnosis. Etiological role of mechanical ventilation has not yet been studied well. We report a case of BO in a three year old child occurring after an episode of lower respiratory tract infection requiring prolonged mechanical ventilation with subsequent development of ventilator-associated pneumonia. Our patient had a protracted clinical course with good response to corticosteroids.

Epidemiology, etiology, and diagnosis of hospital-acquired pneumonia and ventilator-associated pneumonia in Asian countries

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are significant public health issues in Asian countries, as they are worldwide. Mortality attributable to HAP and especially VAP can be very high. The present review aims to determine whether the incidence and prevalence of HAP and VAP are higher in Asian countries than in Western countries, whether the organisms causing these nosocomial infections differ etiologically, and whether they are more difficult to treat (ie, demonstrate greater resistance). The implementation of available guidelines can be best achieved through an understanding of local epidemiology, etiology, and resistance patterns, which can facilitate optimal treatment choices. The current review presents data on epidemiology, etiology, and diagnosis of HAP and VAP drawn from an expert panel of clinicians representing 10 Asian countries.

Mechanical Ventilation and Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome continues to be a high-mortality condition. The role of mechanical ventilation remains primarily a supportive modality. Recent research has elucidated the adverse impact of traditional ventilation strategies on development of the disease and, ultimately, mortality. The institution of low tidal volume ventilation has been the only intervention that has resulted in definitive improvement in survival. Animal and human investigations that culminated in the Acute Respiratory Distress Syndrome Network low tidal volume study are reviewed. Current controversies in the application of mechanical ventilation including the use of positive end-expiratory pressure, recruitment maneuvers, and high frequency oscillatory ventilation are also addressed.

Does extubation result in haemodynamic instability in patients following coronary artery bypass grafts?

Coronary heart disease and its management continue to be at the centre of Government health policy. The present political climate demands clinical effectiveness and best practice should be established, while maintaining the philosophy of cost-effectiveness and resource management. These directives have led practitioners to question the care of patients following coronary artery bypass surgery, in particular the role of mechanical ventilation and the subsequent act of extubation. A retrospective study of 89 patients who had coronary artery bypass grafts (emergency and elective) was undertaken, to establish if extubation had a significant effect on the haemodynamic status of patients with variable degrees of left ventricular function (19% with poor left ventricular function). The study found that extubation was achieved within a mean time of 4.97 hours following return from surgery. Extubation resulted in a significant increase in heart rate (P = 0.001), as well as a respiratory acidosis (pCO2: P = 0.000; pH: P = 0.000). However, the stability of the patient was not compromised, with neither mean arterial blood pressure (P = 0.825) nor oxygenation levels (P = 0.267) being significantly altered by extubation. On multivariate analysis, the act of extubation had no significant effect on any of the dependent variables. These results suggest that it is not extubation alone that has an impact on the haemodynamic stability of patients following coronary artery bypass grafts, but that this is indeed multifactorial. Therefore extubation is 'safe' practice for patients with varying degrees of left ventricular function following coronary artery bypass grafts. Limitations of the study are acknowledged.

Differential effects of halothane and thiopental on surfactant protein C messenger RNA in vivo and in vitro in rats.

Pulmonary surfactant is a complex mixture of proteins and phospholipids synthetized by alveolar type II cells. Volatile anesthetics have been shown to reduce surfactant phospholipid biosynthesis by rat alveolar type II cells. Surfactant-associated protein C (SP-C) is critical for the alveolar surfactant functions. Our goal was to evaluate the effects of halothane and thiopental on SP-C messenger RNA (mRNA) expression in vitro in rat alveolar type II cells and in vivo in mechanically ventilated rats. In vitro, freshly isolated alveolar type II cells were exposed to halothane during 4 h (1, 2, 4%) and 8 h (1%), and to thiopental during 4 h (10, 100 micrometer) and 8 h (100 micrometer). In vivo, rats were anesthetized with intraperitoneal thiopental or inhaled 1% halothane and mechanically ventilated for 4 or 8 h. SP-C mRNA expression was evaluated by ribonuclease protection assay. In vitro, 4-h exposure of alveolar type II cells to thiopental 10 and 100 micrometer increased their SP-C mRNA content to 145 and 197%, respectively, of the control values. In alveolar type II cells exposed for 4 h to halothane 1, 2, and 4%, the SP-C mRNA content increased dose-dependently to 160, 235, and 275%, respectively, of the control values. In vivo, in mechanically ventilated rats, 4 h of halothane anesthesia decreased the lung SP-C mRNA content to 53% of the value obtained in control (nonanesthetized, nonventilated) animals; thiopental anesthesia increased to 150% the lung SP-C mRNA content. These findings indicate that halothane and thiopental used at clinically relevant concentrations modulate the pulmonary SP-C mRNA content in rats. In vivo, the additive role of mechanical ventilation is suggested.

Role of Mechanical Ventilation During Ischemia on the Development of Reperfusion Injury of the Lung † 1746

Reperfusion injury is an important factor in the pathogenesis of necrotizing enterocolitis and hypoxic ischemic encephalopathy. Similar etiology has also been implicated in the development of lung injury seen in bronchopulmonary dysplasia. We used an isolated perfused rat lung model to study the effect of continuous mechanical ventilation during ischemia on the development of reperfusion injury. Sixteen Sprague-Dawely rats (wt 300-350 grams) were divided four groups, one control and three experimental groups. Lung preparations underwent 15 minutes of equilibration followed by 75 minutes of ischemia and 30 minutes of reperfusion (perfused with modified Krebs-Henseliet solution). Reperfusion injury was quantified by continuously monitoring the change in wet weight of the lung and by measuring the permeability to 125I labeled albumin at the end of reperfusion. Control lung preparations were continuously ventilated (20% O2) and perfused for 105 minutes. The experimental groups were ventilated with 20% O2 prior to ischemia and during reperfusion. These groups differed only in the ventilatory gas mixture used during ischemia. Group I, ventilated with 20%O2; Group II, ventilated with 100% N2; Group III, remained collapsed and unventilated. Results: Values are expressed as mean±SE, * denotes statistical significance (p<0.01). Lung preperations in Groups I and II remained isogravimeric and the albumin PS product was similar to control. Lung preparations in Group III (collapsed and unventilated) demonstrated injury as evidenced by a 1.5 fold increase in wet weight and 3 fold increase in albumin PS product. Conclusions: 1) Reperfusion injury causes an increase in vascular permeability, resulting in an increase in the wet weight of the lung. 2) Reperfusion injury occurs only when the lung is both ischemic and unventilated. 3) Continuous mechanical ventilation (irrespective of the gas mixture used) during ischemia protects against reperfusion injury. We speculate that this protection is as a result of maintaining alveolar stability during ischemia. Table

Oxyhemoglobin affinity in patients with chronic obstructive pulmonary disease and acute respiratory failure: role of mechanical ventilation.

Oxyhemoglobin affinity was assessed in 20 subjects with chronic obstructive pulmonary disease, all of whom experienced acute respiratory failure. PaCO2, pH, and 2,3-diphosphoglycerate (2,3-DPG) were measured 24 and 48 h after admission, and then during weaning (for the ten patients on mechanical ventilation) or on discharge (for the ten nonventilated patients). At 24 h, nonventilated patients had a lower pH (p less than .001) and 2,3-DPG concentration (p less than .05) and a higher PaCO2 (p less than .01) than ventilated patients; 48 h later only PaCO2 was higher (p less than .01) in the former, and there were no differences between the two groups in the final set of measurements. There was a persistent left shift in the oxyhemoglobin dissociation curve (P50 at pH 7.4) in both groups throughout the study period. In contrast, the in vivo P50 was significantly lower in ventilated patients only at 24 h (22.7 +/- 2.2 vs. 25.8 +/- 1.5 torr, respectively, p less than .005). Our results suggest that changes of in vivo P50 in ventilated patients are probably related to the Bohr effect induced by mechanical ventilation. The latter swiftly corrects severe respiratory acidosis, causing an intra-erythrocytic alkalotic pH and raising the levels of 2,3-DPG.