Pressure-controlled Mode Research Articles

Simulating Floating Head Pressure Control With Artificial Intelligence

In this work, we model with artificial intelligence techniques one of the most used solutions for energy saving in the field of refrigeration. This solution, called floating head pressure control, allows for the optimum pressure condensation depending on the working environment, thus increasing the overall efficiency of the plant. Usually, these mechanisms are controlled by algorithms that are stored in the control memory of the chillers. Under certain environmental conditions, the optimal temperature and condensation pressure fluctuate with the environmental temperature. Thus, the absorbed electricity depends on the working parameters fixed by the control system of the chiller. Results in energy savings in these terms could grow as the external temperature decreases. The problem addressed in this work regards standard floating head pressure control (FHPC) systems that do not combine working environmental factors with the conditions of the machine and historical data because they are implemented adopting static models. We provide evidence about the potential of machine learning models in predicting the velocity of fans in order to adjust their load based on environmental factors and the conditions of the machine. A good setting of fan velocity will result in lower energy consumption. To do that we analyzed and implemented machine learning algorithms to provide instruments that support the operation of the chiller, enabling the floating head pressure control mode in the control system of the machine, during its process. We performed an empirical evaluation on both synthetic and real data to assess the quality of our proposal. Synthetic data are produced by an industrial software that simulates the behavior of chillers, while real-world data is collected from a commercial chiller. The results show that machine learning approaches are able to approximate real data getting errors that are 5 times smaller than the errors committed by the system that is now adopted. All the source code as well as the datasets will be made available online after the review process.

Inclusive modelling and parameter estimation of a steam power plant using an LMI‐based unknown input reconstruction algorithm

A comprehensive dynamic model of a steam power plant, including turbine, governor, and boiler models, is proposed in this paper. The whole turbine-boiler control strategies inter alia turbine following, boiler following, coordinated control, and sliding pressure control modes are also taken into account in the modelling procedure, making the integrated model adaptable for all the steam units. A novel multi-stage algorithm is asserted in the other part of the paper to estimate the obtained model parameters using input-output data from operational tests. Regarding the fact that the mechanical power as the turbine output and one of the synchronous generator (SG) inputs cannot be measured directly, an efficacious unknown input reconstruction (UIR) method is employed in this paper to determine the mechanical power from SG measured signals. The UIR observer in this method is obtained by solving a linear matrix inequality (LMI). Other parameters are identified by applying a Genetic Algorithm (GA) to the measurement data. Finally, the acquired model and parameters are validated by employing the recorded data from several tests, and the results are discussed.

Effect of Trendelenburg position during prone ventilation in fifteen COVID-19 patients. Observational study

Background Prone position ventilation has shown to improve oxygenation and mortality in severe ARDS. The data of prone position ventilation during severe ARDS secondary to COVID-19 have shown similar benefit in oxygenation and mortality. Usually, patient placed in prone position are placed flat or in reverse Trendelenburg positioning to decrease risk of aspiration and abdominal girth compressing the chest. To date, no studies are available to compare the effects of positioning the bed in different angles during the prone position ventilation. Methods An observational study in fifteen patients with severe ARDS secondary to COVID-19 who were placed in the prone position for the first time. All the patients were sedated and chemically paralyzed with no spontaneous effort. All patients were ventilated with the pressure-controlled mode with set PEEP according to the pressure-volume curves. Five patients had esophageal balloon manometry to estimate pleural pressures and trans-pulmonary pressures. Patients were initially placed in reverse Trendelenburg position and later in Trendelenburg position. Tidal volume and respiratory compliance were observed for 30 minutes after bed positioning has been achieved. Tidal volume and total respiratory compliance in both Trendelenburg and reverse Trendelenburg position were compared. Ventilator settings were not changed during the observation. No patients were suspected of increased intra-cranial or intra-ocular pressures. T-test was done to compare the values. Results Tidal volume significantly increased by 80.26 ± 23.4 ml/breath (95% CI 37.7 - 122.9) from 391.3 ± 52.7 to 471.6 ± 60.9 (20.5%) P 0.001. The respiratory system compliance significantly increased by 4.9 ml/cmH2O (95% CI 1.4 - 8.4) from 34.6 ± 4.7 to 39.5 ± 4.6 (14%) P 0.001. Of the five patients with esophageal balloon, the lung compliance significantly increased by 16.7 ml/cmH2O (95% CI 12.8 – 20.6) from 66.6 ± 1.7 to 83.3 ± 3.3 (25%) P 0.001. The chest wall compliance had small but non-significant increase by 1.5 ml/cmH2O (95% CI -1.3 – 4.3) from 65 ± 1.4 to 66.5 ± 2.3 (2%) P 0.085. Conclusion In this study, statistically significant increase in tidal volume, lung and respiratory system compliance were observed in patients placed in the Trendelenburg position during prone position ventilation. The results reflect the effect of body positioning during prone position ventilation. These effects may be the reflection of altered ventilation distribution throughout the lungs and change in pleural pressure as well as trans-pulmonary pressure during body positioning. More studies need to be done to confirm and examine this phenomenon. Precautions should be taken as this maneuver can increase the intra-cranial and intra-ocular pressures. Keywords: COVID-19, Trendelenburg, Reverse Trendelenburg, ARDS

Application of remote "Internet+" interactive mode in the management of patients with hypertension during normalized epidemic prevention and control of COVID-19

Objective: To explore the effect of remote "Internet+" interactive management strategy on blood pressure control in patients with hypertension during normalized epidemic prevention and control of COVID-19. Methods: This is a randomized controlled study. A total of 394 patients with hypertension who were treated in Chinese People's Liberation Army General Hospital from October 2019 to December 2020 were randomly divided into experimental group (197 cases) and control group (197 cases). The experimental group adopted remote "Internet+" interaction mode to carry out remote blood pressure intervention, and the control group received traditional blood pressure control mode, and the intervention time was 6 months. Evaluation indicators included blood pressure level, blood pressure lowering speed, time to target blood pressure, blood pressure measurement times, communication times with doctors, medication compliance, blood pressure measurement compliance and disease awareness after 6 months of intervention. The evaluation indexes of the two groups were compared, and the bivariate Pearson correlation analysis was used to explore the relationship between the speed of blood pressure reduction and the times of blood pressure measurement and doctor communication in all patients. Results: A total of 394 patients with hypertension were included in this study, including 209 males, aged (67.6±2.8) years old. After 6 months of intervention, the systolic and diastolic blood pressure of the two groups were both lower than the baseline blood pressure before intervention (both P<0.05), the systolic blood pressure ((125.7±11.7) mmHg (1 mmHg=0.133 kPa) vs. (132.6±12.9) mmHg, P<0.001) and diastolic blood pressure ((72.4±10.7) mmHg vs. (79.8±11.6) mmHg, P<0.001) in the experimental group were lower than those in the control group. The blood pressure reduction speed of the experimental group was faster than that of the control group ((18.63±1.59) mmHg/d vs. (13.26±2.85) mmHg/d, P<0.001), and the time to reach the target blood pressure in the experimental group was shorter than that in the control group ((23.69±2.93) d vs. (47.12±5.81) d, P<0.001). Compared with the control group, the blood pressure measurement times ((0.98±0.13) times/d vs. (0.20±0.40) times/d, P<0.05) and the number of communications with doctors ((0.97±0.16) times/week vs. (0.12±0.32) times/week, P<0.05) were significantly higher in the experimental group. Correlation analysis showed that the speed of blood pressure reduction was positively correlated with the number of blood pressure measurements (r=0.419, P<0.01) and the number of communications with doctors (r=0.857, P<0.01). The proportion of standardized medication (93.91% (185/197) vs. 51.78% (102/197), P<0.001), timely measurement (97.46% (192/197) vs. 47.21% (93/197), P<0.001) and high-degree disease awareness (94.42% (186/197) vs. 49.24% (97/197), P<0.001) were significantly higher in the experimental group than those in the control group. Conclusions: The remote "Internet+" interactive management strategy can effectively improve patients' blood pressure control. The doctor-patient interaction can improve medication compliance and measurement compliance of patients, and help shorten the time to reach the target blood pressure.

Testing and comparison of a thermodynamic vent system operating in different modes in a liquid nitrogen tank

• A multifunctional system was established for cryogen storage technology evaluation. • Four different pressure control modes were compared on the same testing system. • A new parameter was proposed for evaluating contribution factors to pressurization. • Ullage heating is more effective to self-pressurization than liquid evaporation. • Active TVS vents more fluid for depressurization than passive TVS does. Thermodynamic vent system (TVS) has been considered as a promising method for pressure control in cryogenic propellant tanks in microgravity environment. TVS could be operated in different modes, namely, the mixing-venting (MV) mode, the mixing-only (MO) mode, the mixing-only followed by mixing-venting (MOMV) mode, and the passive venting (PV) mode. An experimental investigation on the effect of operation mode on the TVS performance was conducted by using liquid nitrogen as the liquid oxygen simulant on a testing facility named Multi-functional Cryogenic Test System. Results of those four operating modes tests were compared regarding the ullage cooling effect, liquid temperature, pressure control capability, and mass loss. It was found that with the help of spraying, the MV mode and the MO mode cooled the ullage more effectively than the PV mode did. However, the PV mode is more effective in suppressing the increase of the liquid temperature. A non-dimensional parameter η has been proposed for comparison between the ullage heating and the liquid evaporation contribution to the pressurization in cryogenic fluid storage tanks. For the mixing-venting mode, the ullage heating is the main force that pressurizes the tank when the liquid is subcooled, while when the liquid is saturated, the evaporation takes over the role. Moreover, the MOMV mode performs the best in reducing mass loss within 0–1500 min. The results will be useful to make a control strategy for the operation of pressure control in on-orbit cryogenic tanks through thermodynamic venting method.

Empirical evidence for safety of mechanical ventilation during simulated cardiopulmonary resuscitation on a physical model.

Cardiac arrest is a critical event requiring adequate and timely response in order to increase a patient's chance of survival. In patients mechanically ventilated with advanced airways, cardiopulmonary resuscitation (CPR) maneuver may be simplified by keeping the ventilator on. This work assessed the response of an intensive care mechanical ventilator to CPR using a patient manikin ventilated in three conventional modes. Volume-controlled (VCV), pressure-controlled (PCV) and pressure regulated volume-controlled (PRVC) ventilation were applied in a thorax physical model, with or without chest compressions. The mechanical ventilator was set with inspiratory time of 1.0 s, ventilation rate of 10 breaths/min, positive end-expiratory pressure of 0 cmH2O, FiO2 of 1.0, target tidal volume of 600 mL and trigger level of -20 cmH2O. Airway opening pressure and ventilatory flow signals were continuously recorded. Chest compression resulted in increased airway peak pressure in all ventilation modes (p < 0.001), especially with VCV (137% in VCV, 83% in PCV, 80% in PRVC). However, these pressures were limited to levels similar to release valves in manual resuscitators (~60 cmH2O). In pressure-controlled modes tidal/min volumes decreased (PRVC = 11%, p = 0.027 and PCV = 12%, p < 0.001), while still within the variability observed during bag-valve-mask ventilation. During VCV, variation in tidal/min volumes were not significant (p = 0.140). Respiratory rate did not change with chest compression. Volume and pressure ventilation modes responded differently to chest compressions. Yet, variation in delivered volume and the measured peak pressures were within the reported for the standard bag-valve-mask system.

Comparison of BPAP S/T and Average Volume-Assured Pressure Support Modes for Hypercapnic Respiratory Failure in the Emergency Department: A Randomized Controlled Trial.

Background: There is limited research into the utility of average volume-assured pressure support (AVAPS), a volume-assured pressure-controlled mode, especially in patients with hypercapnic respiratory failure. Aims: This study aimed at a randomized comparison of AVAPS and bilevel positive airway pressure spontaneous/timed (BPAP S/T) modes in non-invasive mechanical ventilation (NIMV) application with hypercapnic respiratory failure patients in the emergency department (ED).Study Design: Randomized controlled study.Methods: In this prospective randomized controlled study, 80 patients admitted to ED with hypercapnic respiratory failure requiring NIMV were randomly assigned to AVAPS or S/T groups using the sealed envelope method (33 patients in the S/T group, 47 patients in the AVAPS group). Data of arterial blood gas (ABG), vital parameters, Glasgow Coma Score (GCS), additional treatment needs, and clinical outcomes were evaluated, and the treatment success rates of both groups were compared. Results: A total of 80 patients, 33 in the S/T and 47 in the AVAPS group, were analyzed in the study. The pH values improved in the AVAPS group compared to the baseline (0.07 [0.04-0.10] vs 0.03 [0.00-0.11]). PaCO2 (partial pressure of carbon dioxide) excretion was faster in the AVAPS group than in the S/T group in the first hour (10.20 mmHg [6.20-19.20] vs. 4.75 ([-] 0.83-16.88)). The comparison of blood gas measurements showed no significant differences between the groups regarding the changes in PaCO2 and pH values over time (P = .141 and P = .271, respectively). During the ED follow-up, 3 (6.4%) patients in the AVAPS group and 5 (15.2%) patients in the S/T group needed intubation [Relative risk: 0.42 (95% CI: 0.11 to 1.64), P = .21].Conclusion: In this study, improvements in blood gas parameters in the AVAPS group were faster compared to the S/T group; however, we did not find any significant difference between the groups in terms of clinical parameters. The AVAPS mode is as effective and safe as BPAP S/T in treating patients with hypercapnic respiratory failure in the ED.

Effect of pressure-controlled ventilation-volume guaranteed mode combined with individualized positive end-expiratory pressure on respiratory mechanics, oxygenation and lung injury in patients undergoing laparoscopic surgery in Trendelenburg position

The study aimed to investigate the efficacy of PCV-VG combined with individual PEEP during laparoscopic surgery in the Trendelenburg position. 120 patients were randomly divided into four groups: VF group (VCV plus 5cmH2O PEEP), PF group (PCV-VG plus 5cmH2O PEEP), VI group (VCV plus individual PEEP), and PI group (PCV-VG plus individual PEEP). Pmean, Ppeak, Cdyn, PaO2/FiO2, VD/VT, A-aDO2 and Qs/Qt were recorded at T1 (15 min after the induction of anesthesia), T2 (60 min after pneumoperitoneum), and T3 (5 min at the end of anesthesia). The CC16 and IL-6 were measured at T1 and T3. Our results showed that the Pmean was increased in VI and PI group, and the Ppeak was lower in PI group at T2. At T2 and T3, the Cdyn of PI group was higher than that in other groups, and PaO2/FiO2 was increased in PI group compared with VF and VI group. At T2 and T3, A-aDO2 of PI and PF group was reduced than that in other groups. The Qs/Qt was decreased in PI group compared with VF and VI group at T2 and T3. At T2, VD/VT in PI group was decreased than other groups. At T3, the concentration of CC16 in PI group was lower compared with other groups, and IL-6 level of PI group was decreased than that in VF and VI group. In conclusion, the patients who underwent laparoscopic surgery, PCV-VG combined with individual PEEP produced favorable lung mechanics and oxygenation, and thus reducing inflammatory response and lung injury.Clinical Trial registry: chictr.org. identifier: ChiCTR-2100044928

Comparison of the effects of volume-controlled ventilation and pressure-controlled ventilation modes on hemodynamics, respiratory mechanics and blood gas parameters in patients undergoing laparoscopic cholecystectomy

Background: This study aimed to compare the changes induced by VCV and PCV modes in hemodynamics, respiration (airway pressures, gas exchange parameters) and metabolism (acid-base balance) in patients undergoing laparoscopic cholecystectomy.Methods: Patients were divided into two randomised groups as volume-controlled ventilation (VCV) group (VC) and pressure-controlled ventilation (PCV) group (PC). The following parameters were recorded at 3 different time points: T1: in supine position 10 minutes after induction of anaesthesia, T2: 15 minutes after CO2 insufflation in inverted Trendelenburg position (head 30 degrees up), T3: 10 minutes after CO2 desufflation. HR, SpO2, SAP (systolic arterial pressure), DAP (diastolic arterial pressure), MAP (mean arterial pressure), PetCO2 (end-tidal carbon dioxide pressure), Ppeak, Pplateau, Pmean, Vt (tidal volume) and compliance with the available data, the cases in both groups Vd, Vd/Vt ratios and P(A-a)O2 were calculated. Arterial blood gas parameters (pH, PaO2, PaCO2, SaO2, P(a-et)CO2) values were recorded.Results: It was found that Ppeak and Pplateau values were significantly higher in the VC group (p&lt;0.05). It was found that compliance was significantly higher in the PC group (p&lt;0.05) (p&lt;0.01). In the postoperative period, it was found that PaO2 values were significantly higher in the PC group compared to the VC group (p&lt;0.05). It was found that the P(A-a)O2 values of the PC group were significantly higher than those of the VC group during the desufflation phase (p&lt;0.05).Conclusions: We think that PCV mode can be a good alternative for the prevention and correction of physiopathological changes due to laparoscopic surgery.

Regulation response of pilot-operated diaphragm type pressure-reducing valves: laboratory testing and impact on the performance of pressure control modes in water distribution systems

Pressure control is recognized as an efficient measure for reducing leaks from water distribution systems. We have evaluated the effectiveness of various pressure control modes by means of pilot-operated diaphragm type pressure-reducing valves (PRVs), taking into account the sensitivity of the valves to various settings. First, the response of a PRV to consecutive pressure settings variations was experimentally evaluated in the hydraulic simulation laboratory of National Institute for Scientific Research. These experiments revealed that the studied valve only reacts when variation in the pressure setting corresponds to at least a 1/6 turn of the pilot valve. Second, an actual case study from Quebec City, Canada, was simulated to evaluate the impact of the PRV response on three pressure control modes: fixed control, time-based control, and real-time control (RTC). The results show that RTC of pressure leads to reductions in leakage rate for the studied network but that the PRV operational constraints limit the expected performance of RTC.

Effects of Lung Injury on Regional Aeration and Expiratory Time Constants: Insights From Four-Dimensional Computed Tomography Image Registration.

Rationale: Intratidal changes in regional lung aeration, as assessed with dynamic four-dimensional computed tomography (CT; 4DCT), may indicate the processes of recruitment and derecruitment, thus portending atelectrauma during mechanical ventilation. In this study, we characterized the time constants associated with deaeration during the expiratory phase of pressure-controlled ventilation in pigs before and after acute lung injury using respiratory-gated 4DCT and image registration.Methods: Eleven pigs were mechanically ventilated in pressure-controlled mode under baseline conditions and following an oleic acid model of acute lung injury. Dynamic 4DCT scans were acquired without interrupting ventilation. Automated segmentation of lung parenchyma was obtained by a convolutional neural network. Respiratory structures were aligned using 4D image registration. Exponential regression was performed on the time-varying CT density in each aligned voxel during exhalation, resulting in regional estimates of intratidal aeration change and deaeration time constants. Regressions were also performed for regional and total exhaled gas volume changes.Results: Normally and poorly aerated lung regions demonstrated the largest median intratidal aeration changes during exhalation, compared to minimal changes within hyper- and non-aerated regions. Following lung injury, median time constants throughout normally aerated regions within each subject were greater than respective values for poorly aerated regions. However, parametric response mapping revealed an association between larger intratidal aeration changes and slower time constants. Lower aeration and faster time constants were observed for the dependent lung regions in the supine position. Regional gas volume changes exhibited faster time constants compared to regional density time constants, as well as better correspondence to total exhaled volume time constants.Conclusion: Mechanical time constants based on exhaled gas volume underestimate regional aeration time constants. After lung injury, poorly aerated regions experience larger intratidal changes in aeration over shorter time scales compared to normally aerated regions. However, the largest intratidal aeration changes occur over the longest time scales within poorly aerated regions. These dynamic 4DCT imaging data provide supporting evidence for the susceptibility of poorly aerated regions to ventilator-induced lung injury, and for the functional benefits of short exhalation times during mechanical ventilation of injured lungs.

Safety and efficacy evaluation of the automatic stepwise recruitment maneuver in the neonatal population: An in vivo interventional study. Can anesthesiologists safely perform automatic lung recruitment maneuvers in neonates?

A new software has recently been incorporated in almost all new anesthesia machines to enable automatic lung recruitment maneuvers. To date, no studies have assessed the safety and efficacy of these automatic software programs in the neonatal population. We aimed to evaluate the safety and efficacy of the lung recruitment maneuver performed using the automatic stepwise recruitment maneuver software of the FLOW-i 4.3 Anesthesia System® in a healthy and live neonatal model. Eight male newborn piglets were included in the study. The lung recruitment maneuver was performed in pressure-controlled ventilation with a constant driving pressure (15cmH2 O) in a stepwise increasing positive end-expiratory pressure (PEEP) model. The target peak inspiratory pressure (PIP) was 30cmH2 O and PEEP was 15cmH2 O. The maneuver lasted for 39seconds. The hemodynamic variables were monitored using the PICCO® system. The following respiratory parameters were monitored: oxygen saturation, fraction of inspired oxygen, partial pressure of oxygen and carbon dioxide in the arterial blood, end-tidal carbon dioxide pressure, PIP, plateau pressure, PEEP, static compliance (Cstat ), and dynamic compliance (Cdyn ). Safety was evaluated by assessing the accuracy of the software, need for not interrupting the maneuver, hemodynamic stability, and absence of adverse respiratory events with the lung recruitment maneuver. Efficacy was evaluated by improvement in Cstat and Cdyn after performing the lung recruitment maneuver. All lung recruitment maneuvers were safely performed as scheduled without any interruptions. No pneumothorax or other side effects were observed. Hemodynamic stability was maintained during the lung recruitment maneuver. We observed an improvement of 33% in Cdyn and 24% in Cstat after the maneuver. The automatic stepwise recruitment maneuver software of the FLOW-i 4.3 Anesthesia System® is safe and efficacious in a healthy neonatal model. We did not observe any adverse respiratory or hemodynamic events during the implementation of the lung recruitment maneuver in the pressure-controlled ventilation mode using a stepwise increasing PEEP (30/15cmH2 O) approach.

Design and simulation of mechanical ventilators.

During this period of COVID-19 pandemic, the lack of medical equipment (like ventilators) leads to complications arising in the medical field. A low-cost ventilator seems to be an alternative substitute to fill the lacking. This paper presents a numerical analysis for predicting the delivered parameters of a low-cost mechanical ventilator. Based on several manufactured mechanical ventilators, two proposed designs are investigated in this study. Fluid-structure interaction (FSI) analysis is used for solving any problems with the first design, and computational fluid dynamic (CFD) analysis with moving boundary is used for solving any issues with the second design. For this purpose, ANSYS Workbench platform is used to solve the set of equations. The results showed that the Ambu-bag-based mechanical ventilator exhibited difficulties in controlling ventilation variables, which certainly will cause serious health problems such as barotrauma. The mechanical ventilator based on piston-cylinder is more satisfactory with regards to delivered parameters to the patient. The ways to obtain pressure control mode (PCM) and volume control mode (VCM) are identified. Finally, the ventilator output is highly affected by inlet flow, length of the cylinder, and piston diameter.

862 Volume-Assured Pressure Support improves outcomes in a patient with Congenital Central Hypoventilation Syndrome

IntroductionCongenital Central Hypoventilation Syndrome (CCHS) is a condition caused by a mutation of the PHOX2B gene and an incidence of 1 in 50,000 live births. Clinically the condition is characterized by autonomic nervous system dysfunction, the most prominent feature of which is the failure of respiratory homeostasis during sleep. In patients severely affected, life-long ventilatory support is required. This might start as early as the newborn period. Subsequent adjustments are required due to their growth and development. The role of Volume-Assured Pressure Support (VAPS) ventilation in treatment of CCHS was only described in a couple reports before.Report of case(s)A 17-year-old female patient born at term and diagnosed with CCHS at birth at our center with a PHOX2B mutation confirmed. Her daytime ventilatory support was weaned at age 18 months and the tracheostomy was removed at age 10 years old. She relocated to another state, was lost to follow-up, and returned this year for adjustments of her ventilator whose settings had not been adjusted for several years. She was on a Trilogy 100 ventilator, in pressure-controlled mode with settings of EPAP 5, IPAP 20, and a rate of 22/min without supplemental oxygen. Her measured weight is 69kg, body mass index (BMI) 27. The patient complained of difficulty breathing while on those settings and reported decreased desire to use the machine. The patient was empirically switched to VAPS due to titration availability limitations during the COVID-19 pandemic. Initial AVAPS settings were: EPAP 4–7, PS 3–12, breath rate 16/min, TV 350mL. Upon implementing the changes, the patient reported improved comfort and increased usage. Average minute ventilation decreased from 10.5 to 5.8 L/min, patient triggered breaths increased from 1.1% to 12.3%, average breaths per minute decreased from 22.0/min to 16.2/min, the average peak flow 31.8 to 26.2L/min, tidal volume decreased from 463 to 355mL.ConclusionAVAPS ventilation can be successfully used in managing patients with CCHS, and it might be superior to pressure-controlled mode in certain cases, improving patient comfort and compliance.Support (if any)Department of Internal Medicine, University of New Mexico School of Medicine, Albuquerque, NM.

Adherence to Lung-Protective Ventilation Principles in Pediatric Acute Respiratory Distress Syndrome: A Pediatric Acute Respiratory Distress Syndrome Incidence and Epidemiology Study.

To describe mechanical ventilation management and factors associated with nonadherence to lung-protective ventilation principles in pediatric acute respiratory distress syndrome. A planned ancillary study to a prospective international observational study. Mechanical ventilation management (every 6 hr measurements) during pediatric acute respiratory distress syndrome days 0-3 was described and compared with Pediatric Acute Lung Injury Consensus Conference tidal volume recommendations (< 7 mL/kg in children with impaired respiratory system compliance, < 9 mL/kg in all other children) and the Acute Respiratory Distress Syndrome Network lower positive end-expiratory pressure/higher Fio2 grid recommendations. Seventy-one international PICUs. Children with pediatric acute respiratory distress syndrome. None. Analyses included 422 children. On pediatric acute respiratory distress syndrome day 0, median tidal volume was 7.6 mL/kg (interquartile range, 6.3-8.9 mL/kg) and did not differ by pediatric acute respiratory distress syndrome severity. Plateau pressure was not recorded in 97% of measurements. Using delta pressure (peak inspiratory pressure - positive end-expiratory pressure), median tidal volume increased over quartiles of median delta pressure (p = 0.007). Median delta pressure was greater than or equal to 18 cm H2O for all pediatric acute respiratory distress syndrome severity levels. In severe pediatric acute respiratory distress syndrome, tidal volume was greater than or equal to 7 mL/kg 62% of the time, and positive end-expiratory pressure was lower than recommended by the positive end-expiratory pressure/Fio2 grid 70% of the time. In multivariable analysis, tidal volume nonadherence was more common with severe pediatric acute respiratory distress syndrome, fewer PICU admissions/yr, non-European PICUs, higher delta pressure, corticosteroid use, and pressure control mode. Adherence was associated with underweight stature and cuffed endotracheal tubes. In multivariable analysis, positive end-expiratory pressure/Fio2 grid nonadherence was more common with higher pediatric acute respiratory distress syndrome severity, ventilator decisions made primarily by the attending physician, pre-ICU cardiopulmonary resuscitation, underweight stature, and age less than 2 years. Adherence was associated with respiratory therapist involvement in ventilator management and longer time from pediatric acute respiratory distress syndrome diagnosis. Higher nonadherence to tidal volume and positive end-expiratory pressure recommendations were independently associated with higher mortality and longer duration of ventilation after adjustment for confounding variables. In stratified analyses, these associations were primarily influenced by children with severe pediatric acute respiratory distress syndrome. Nonadherence to lung-protective ventilation principles is common in pediatric acute respiratory distress syndrome and may impact outcome. Modifiable factors exist that may improve adherence.

Mortality Rate in Mechanically Ventilated Neonates: A Developing Country Experience

Background: Although a great improvement has been achieved in the outcome of sick neonates with the effectivewidespread introduction of mechanical ventilation in neonatal intensive care units, a significant proportion of highfatality is still detected among such patients. This study was conducted to identify the complications, outcome, andcauses of death among a sample of critically ill Egyptian neonates subjected to mechanical ventilation using pressurecontrolledmode. Methods: The statistical population of this study were prospectively enrolled in the current study and consisted of 240 eligible patients fulfilling the study inclusion criteria. Those with multiple congenital malformations or post-surgical cases were excluded from the study. The data regarding medical record, clinical examination, indication for mechanicalventilation, complications related to mechanical ventilation, and outcome were collected, recorded, and analyzed. Results: The incidence of complications related to mechanical ventilation was obtained at 104 (43.3%), and VAP observedan increase (20%). Furthermore, the complications related to disease patterns were reported to be 56.7% and 22.5% forsepsis and septic shock. It has been revealed that 124 (51.7%) of the studied neonates had favorable outcomes; however,the remaining 116 (48.3%) of the subjects passed away with a significant increase in the incidence of VAP (P=0.013). Itwas reported that smaller gestational age and lower birth weight were the most significant risk factors. Conclusion: In Egypt; as a developing country, the mortality rate among critically ill neonates undergoing mechanicalventilation with pressure-controlled mode was significantly high, approaching 48.3%, with VAP being the mostcommon cause of death.

Comparison of Volume-Guaranteed or -Targeted, Pressure-Controlled Ventilation with Volume-Controlled Ventilation during Elective Surgery: A Systematic Review and Meta-Analysis.

For perioperative mechanical ventilation under general anesthesia, modern respirators aim at combining the benefits of pressure-controlled ventilation (PCV) and volume-controlled ventilation (VCV) in modes typically named “volume-guaranteed” or “volume-targeted” pressure-controlled ventilation (PCV-VG). This systematic review and meta-analysis tested the hypothesis that PCV-VG modes of ventilation could be beneficial in terms of improved airway pressures (Ppeak, Pplateau, Pmean), dynamic compliance (Cdyn), or arterial blood gases (PaO2, PaCO2) in adults undergoing elective surgery under general anesthesia. Three major medical electronic databases were searched with predefined search strategies and publications were systematically evaluated according to the Cochrane Review Methods. Continuous variables were tested for mean differences using the inverse variance method and 95% confidence intervals (CI) were calculated. Based on the assumption that intervention effects across studies were not identical, a random effects model was chosen. Assessment for heterogeneity was performed with the χ2 test and the I2 statistic. As primary endpoints, Ppeak, Pplateau, Pmean, Cdyn, PaO2, and PaCO2 were evaluated. Of the 725 publications identified, 17 finally met eligibility criteria, with a total of 929 patients recruited. Under supine two-lung ventilation, PCV-VG resulted in significantly reduced Ppeak (15 studies) and Pplateau (9 studies) as well as higher Cdyn (9 studies), compared with VCV [random effects models; Ppeak: CI −3.26 to −1.47; p < 0.001; I2 = 82%; Pplateau: −3.12 to −0.12; p = 0.03; I2 = 90%; Cdyn: CI 3.42 to 8.65; p < 0.001; I2 = 90%]. For one-lung ventilation (8 studies), PCV-VG allowed for significantly lower Ppeak and higher PaO2 compared with VCV. In Trendelenburg position (5 studies), this effect was significant for Ppeak only. This systematic review and meta-analysis demonstrates that volume-targeting, pressure-controlled ventilation modes may provide benefits with respect to the improved airway dynamics in two- and one-lung ventilation, and improved oxygenation in one-lung ventilation in adults undergoing elective surgery.

Body position and the effectiveness of mask ventilation in anaesthetised paralysed obese patients: A randomised cross-over study.

Airway management is more challenging in the obese. Compared with the supine position, the sitting position can decrease the collapsibility of the upper airway and improve respiratory mechanics. The aim of this study was to evaluate the 25° semisitting position on the effectiveness of mask ventilation in anaesthetised paralysed obese patients. A randomised, cross-over study. Medical centre managed by a university tertiary hospital. Thirty-eight obese adults scheduled for general anaesthesia. After anaesthesia and paralysis, two-handed mask ventilation was performed in the supine and 25° semi-sitting positions with a cross-over, in a randomised order. During mask ventilation, mechanical ventilation was delivered with a pressure-controlled mode with a peak inspiratory pressure of 15 cmH2O, a respiratory rate of 15 bpm, and no positive end-expiratory pressure. Ventilatory outcomes were based upon lean body weight. Exhaled tidal volume (ml kg-1), respiratory minute volume (ml kg-1 min-1), and the occurrence of inadequate ventilation, defined as an exhaled tidal volume less than 4 ml kg-1, or absence of end-tidal CO2 recording. Exhaled tidal volume (mean ± SD) in the 25° semi-sitting position was higher than in the supine position, 9.3 ± 2.7 vs. 7.6 ± 2.4 ml kg-1; P less than 0.001. Respiratory minute volume was improved in the 25° semisitting position compared with that in the supine position, 139.6 ± 40.7 vs. 113.4 ± 35.7 ml kg-1 min-1; P less than 0.001. The 25° semisitting position improved mask ventilation compared with the supine position in anaesthetised paralysed obese patients. ClinicalTrials.gov (NCT03996161).

Simultaneous ventilation in the Covid-19 pandemic. A bench study

COVID-19 pandemic sets the healthcare system to a shortage of ventilators. We aimed at assessing tidal volume (VT) delivery and air recirculation during expiration when one ventilator is divided into 2 test-lungs. The study was performed in a research laboratory in a medical ICU of a University hospital. An ICU (V500) and a lower-level ventilator (Elisée 350) were attached to two test-lungs (QuickLung) through a dedicated flow-splitter. A 50 mL/cmH2O Compliance (C) and 5 cmH2O/L/s Resistance (R) were set in both A and B test-lungs (A C50R5 / B C50R5, step1), A C50-R20 / B C20-R20 (step 2), A C20-R20 / B C10-R20 (step 3), and A C50-R20 / B C20-R5 (step 4). Each ventilator was set in volume and pressure control mode to deliver 800mL VT. We assessed VT from a pneumotachograph placed immediately before each lung, pendelluft air, and expiratory resistance (circuit and valve). Values are median (1st-3rd quartiles) and compared between ventilators by non-parametric tests. Between Elisée 350 and V500 in volume control VT in A/B test- lungs were 381/387 vs. 412/433 mL in step 1, 501/270 vs. 492/370 mL in step 2, 509/237 vs. 496/332 mL in step 3, and 496/281 vs. 480/329 mL in step 4. In pressure control the corresponding values were 373/336 vs. 430/414 mL, 416/185 vs. 322/234 mL, 193/108 vs. 176/ 92 mL and 422/201 vs. 481/329mL, respectively (P<0.001 between ventilators at each step for each volume). Pendelluft air volume ranged between 0.7 to 37.8 ml and negatively correlated with expiratory resistance in steps 2 and 3. The lower-level ventilator performed closely to the ICU ventilator. In the clinical setting, these findings suggest that, due to dependence of VT to C, pressure control should be preferred to maintain adequate VT at least in one patient when C and/or R changes abruptly and monitoring of VT should be done carefully. Increasing expiratory resistance should reduce pendelluft volume.

Model-based Patient Matching for in-parallel Multiplexing Mechanical Ventilation Support.

Surges of COVID-19 infections could lead to insufficient supply of mechanical ventilators, and rationing of needed care. Multiplexing mechanical ventilators (co-MV) to serve multiple patients is a potential temporary solution. However, if patients are ventilated in parallel ventilation, there is currently no means to match ventilation requirements or patients, with no guidelines to date for co-MV. This research uses patient-specific clinically validated respiratory mechanics models to propose a method for patient matching and mechanical ventilator settings for two-patient co-MV under pressure control mode. The proposed method can simulate and estimate the resultant tidal volume of different combinations of co-ventilated patients. With both patients fulfilling the specified constraint under similar ventilation settings, the actual mechanical ventilator settings for co-MV are determined. This method allows clinicians to analyze in silico co-MV before clinical implementation.