Controlled Mechanical Ventilation in Critically Ill Patients and the Potential Role of Venous Bagging in Acute Kidney Injury.

A very low incidence of acute kidney injury (AKI) has been observed in COVID-19 patients purposefully treated with early pressure support ventilation (PSV) compared to those receiving mainly controlled ventilation. The prevention of subdiaphragmatic venous congestion through limited fluid intake and the lowering of intrathoracic pressure is a possible and attractive explanation for this observed phenomenon. Both venous congestion, or "venous bagging", and a positive fluid balance correlate with the occurrence of AKI. The impact of PSV on venous return, in addition to the effects of limiting intravenous fluids, may, at least in part, explain this even more clearly when there is no primary kidney disease or the presence of nephrotoxins. Optimizing the patient-ventilator interaction in PSV is challenging, in part because of the need for the ongoing titration of sedatives and opioids. The known benefits include improved ventilation/perfusion matching and reduced ventilator time. Furthermore, conservative fluid management positively influences cognitive and psychiatric morbidities in ICU patients and survivors. Here, it is hypothesized that cranial lymphatic congestion in relation to a more positive intrathoracic pressure, i.e., in patients predominantly treated with controlled mechanical ventilation (CMV), is a contributing risk factor for ICU delirium. No studies have addressed the question of how PSV can limit AKI, nor are there studies providing high-level evidence relating controlled mechanical ventilation to AKI. For this perspective article, we discuss studies in the literature demonstrating the effects of venous congestion leading to AKI. We aim to shed light on early PSV as a preventive measure, especially for the development of AKI and ICU delirium and emphasize the need for further research in this domain.

The Use of Bi-Nasal Prongs for Delivery of Non-Invasive Ventilation to Foals.

Non-invasive ventilation (NIV) is a method of providing respiratory support without the need for airway intubation. The current study was undertaken to assess tolerance to bi-nasal prongs and NIV in healthy, standing, lightly sedated foals. Bi-nasal prongs were well tolerated by foals, remaining in place for the allocated five minutes in four of six unsedated foals and, subsequently, in five of six lightly sedated foals. All foals tolerated NIV through bi-nasal prongs, although increasing airway pressures were associated with increases in inspiratory volume, duration of inspiration and air leakage in most foals. These changes preceded discontinuation/intolerance of NIV on the basis of behaviour changes consistent with discomfort. Increased circuit leakage was associated with reduced return of expired air to the ventilator and increasing disparity between inspiratory and expiratory times and tidal volumes. The study results suggest that bi-nasal prongs might be suitable for NIV but that design or fitting requires further optimization and that behaviour and ventilator variables should be monitored to assess patient tolerance of the procedure.

Nocturnal Pressure Controlled Ventilation Improves Sleep Efficiency in Patients Receiving Mechanical Ventilation.

BACKGROUND: Patients receiving mechanical ventilation commonly experience sleep fragmentation. The present meta-analysis compared the effects of pressure controlled ventilation (PCV) and pressure support ventilation (PSV) on sleep quality. METHODS: We conducted a search of the PubMed, Embase, and Cochrane Library databases for studies published before November 2023. In this meta-analysis, individual effect sizes were standardized, and the pooled effect size was determined by using random-effects models. The primary outcome was sleep efficiency. The secondary outcomes were wakefulness, percentages of REM (rapid eye movement) sleep and stages 3 and 4 non-REM sleep, the fragmentation index, and the incidence of apneic events. RESULTS: This meta-analysis examined 4 trials that involved 67 subjects. Sleep efficiency was significantly higher in the PCV group than in the PSV group (mean difference 15.57%, 95% CI 8.54%-22.59%). Wakefulness was significantly lower in the PCV group than in the PSV group (mean difference -18.67%, 95% CI -30.29% to -7.04%). The percentage of REM sleep was significantly higher in the PCV group than in the PSV group (mean difference 2.32%, 95% CI 0.20%-4.45%). Among the subjects with a tendency to develop sleep apnea, the fragmentation index was significantly lower in those receiving PCV than PSV (mean difference -40.00%, 95% CI -51.12% to -28.88%). The incidence of apneic events was significantly lower in the PCV group than in the PSV group (risk ratio 0.06, 95% CI 0.01-0.45). CONCLUSIONS: Compared with PSV, PCV may improve sleep quality in patients receiving nocturnal mechanical ventilation.

Successful Versus Failed Transition From Controlled Ventilation to Pressure Support Ventilation in COVID-19 Patients: A Retrospective Cohort Study.

OBJECTIVES: In patients with COVID-19 respiratory failure, controlled mechanical ventilation (CMV) is often necessary during the acute phases of the disease. Weaning from CMV to pressure support ventilation (PSV) is a key objective when the patient's respiratory functions improve. Limited evidence exists regarding the factors predicting a successful transition to PSV and its impact on patient outcomes. DESIGN: Retrospective observational cohort study. SETTING: Twenty-four Italian ICUs from February 2020 to May 2020. PATIENTS: Mechanically ventilated ICU patients with COVID-19-induced respiratory failure. INTERVENTION: The transition period from CMV to PSV was evaluated. We defined it as "failure of assisted breathing" if the patient returned to CMV within the first 72 hours. MEASUREMENTS AND MAIN RESULTS: Of 1260 ICU patients screened, 514 were included. Three hundred fifty-seven patients successfully made the transition to PSV, while 157 failed. Pao2/Fio2 ratio before the transition emerged as an independent predictor of a successful shift (odds ratio 1.00; 95% CI, 0.99-1.00; p = 0.003). Patients in the success group displayed a better trend in Pao2/Fio2, Paco2, plateau and peak pressure, and pH level. Subjects in the failure group exhibited higher ICU mortality (hazard ratio 2.08; 95% CI, 1.42-3.06; p < 0.001), an extended ICU length of stay (successful vs. failure 21 ± 14 vs. 27 ± 17 d; p < 0.001) and a longer duration of mechanical ventilation (19 ± 18 vs. 24 ± 17 d, p = 0.04). CONCLUSIONS: Our study emphasizes that the Pao2/Fio2 ratio was the sole independent factor associated with a failed transition from CMV to PSV. The unsuccessful transition was associated with worse outcomes.

Individual response in patient's effort and driving pressure to variations in assistance during pressure support ventilation.

BACKGROUND: During Pressure Support Ventilation (PSV) an inspiratory hold allows to measure plateau pressure (Pplat), driving pressure (∆P), respiratory system compliance (Crs) and pressure-muscle-index (PMI), an index of inspiratory effort. This study aims [1] to assess systematically how patient's effort (estimated with PMI), ∆P and tidal volume (Vt) change in response to variations in PSV and [2] to confirm the robustness of Crs measurement during PSV. METHODS: 18 patients recovering from acute respiratory failure and ventilated by PSV were cross-randomized to four steps of assistance above (+ 3 and + 6 cmH2O) and below (-3 and -6 cmH2O) clinically set PS. Inspiratory and expiratory holds were performed to measure Pplat, PMI, ∆P, Vt, Crs, P0.1 and occluded inspiratory airway pressure (Pocc). Electromyography of respiratory muscles was monitored noninvasively from body surface (sEMG). RESULTS: As PSV was decreased, Pplat (from 20.5 ± 3.3 cmH2O to 16.7 ± 2.9, P < 0.001) and ∆P (from 12.5 ± 2.3 to 8.6 ± 2.3 cmH2O, P < 0.001) decreased much less than peak airway pressure did (from 21.7 ± 3.8 to 9.7 ± 3.8 cmH2O, P < 0.001), given the progressive increase of patient's effort (PMI from -1.2 ± 2.3 to 6.4 ± 3.2 cmH2O) in line with sEMG of the diaphragm (r = 0.614; P < 0.001). As ∆P increased linearly with Vt, Crs did not change through steps (P = 0.119). CONCLUSION: Patients react to a decrease in PSV by increasing inspiratory effort-as estimated by PMI-keeping Vt and ∆P on a desired value, therefore, limiting the clinician's ability to modulate them. PMI appears a valuable index to assess the point of ventilatory overassistance when patients lose control over Vt like in a pressure-control mode. The measurement of Crs in PSV is constant-likely suggesting reliability-independently from the level of assistance and patient's effort.

Pendelluft in hypoxemic patients resuming spontaneous breathing: proportional modes versus pressure support ventilation.

BACKGROUND: Internal redistribution of gas, referred to as pendelluft, is a new potential mechanism of effort-dependent lung injury. Neurally-adjusted ventilatory assist (NAVA) and proportional assist ventilation (PAV +) follow the patient's respiratory effort and improve synchrony compared with pressure support ventilation (PSV). Whether these modes could prevent the development of pendelluft compared with PSV is unknown. We aimed to compare pendelluft magnitude during PAV + and NAVA versus PSV in patients with resolving acute respiratory distress syndrome (ARDS). METHODS: Patients received either NAVA, PAV + , or PSV in a crossover trial for 20-min using comparable assistance levels after controlled ventilation (> 72 h). We assessed pendelluft (the percentage of lost volume from the non-dependent lung region displaced to the dependent region during inspiration), drive (as the delta esophageal swing of the first 100 ms [ΔPes 100 ms]) and inspiratory effort (as the esophageal pressure-time product per minute [PTPmin]). We performed repeated measures analysis with post-hoc tests and mixed-effects models. RESULTS: Twenty patients mechanically ventilated for 9 [5-14] days were monitored. Despite matching for a similar tidal volume, respiratory drive and inspiratory effort were slightly higher with NAVA and PAV + compared with PSV (ΔPes 100 ms of -2.8 [-3.8--1.9] cm H2O, -3.6 [-3.9--2.4] cm H2O and -2.1 [-2.5--1.1] cm H2O, respectively, p < 0.001 for both comparisons; PTPmin of 155 [118-209] cm H2O s/min, 197 [145-269] cm H2O s/min, and 134 [93-169] cm H2O s/min, respectively, p < 0.001 for both comparisons). Pendelluft magnitude was higher in NAVA (12 ± 7%) and PAV + (13 ± 7%) compared with PSV (8 ± 6%), p < 0.001. Pendelluft magnitude was strongly associated with respiratory drive (ß = -2.771, p-value < 0.001) and inspiratory effort (ß = 0.026, p < 0.001), independent of the ventilatory mode. A higher magnitude of pendelluft in proportional modes compared with PSV existed after adjusting for PTPmin (ß = 2.606, p = 0.010 for NAVA, and ß = 3.360, p = 0.004 for PAV +), and only for PAV + when adjusted for respiratory drive (ß = 2.643, p = 0.009 for PAV +). CONCLUSIONS: Pendelluft magnitude is associated with respiratory drive and inspiratory effort. Proportional modes do not prevent its occurrence in resolving ARDS compared with PSV.

Neurally Adjusted Ventilatory Assist Versus Pressure Support Ventilation: A Comprehensive Review.

Mechanical ventilation serves as crucial life support for critically ill patients. Although it is life-saving prolonged ventilation carries risks and complications like barotrauma, Ventilator-associated pneumonia, sepsis, and many others. Optimizing patient-ventilator interactions and facilitating early weaning is necessary for improved intensive care unit (ICU) outcomes. Traditionally Pressure support ventilation (PSV) mode is widely used for weaning patients who are intubated and mechanically ventilated. Neurally adjusted ventilatory assist (NAVA) mode of the ventilator is an emerging ventilator mode that delivers pressure depending on the patient's respiratory drive, which in turn prevents over-inflation and improves the patient's ventilator interactions. Our article revises and compares the effectiveness of NAVA compared to PSV ventilation under different contexts. Overall we conclude that NAVA level of ventilation can be safely administered in a patient with acute respiratory failure, provided diaphragmatic paralysis is not considered. NAVA improves asynchrony index, wean-off time, and sleep quality and is associated with increased ventilator-free days. These results are based on small-scale studies with low power, and further studies are warranted in large-scale cohorts with more diverse populations to confirm these results.

Development of a non-invasive ventilator for emergency and beyond.

The SARS-CoV-2 pandemic led to the development and implementation of emergency ventilators owing to the shortage of ventilators globally. Using invasive ventilators for patient intubation has medical experts concerned about increasing mortality. Early intervention with oxygen and respiratory therapy reduces the need for intubation, increases survival rates, and reduces the stress of critical care ventilators in hospitals. This study explores the capabilities of an easy-to-build and accessible non-invasive ventilator during an emergency and the practical implementation of the ventilator beyond the scope of the emergency. The proposed system consists of a high-pressure turbine integrated with a microcontroller and pressure and flow sensors assembled in a portable design. The non-invasive pressure support system is tested with a single-chamber high-precision lung simulator capable of simulating multiple lung diseases. The system is operated in a spontaneous pressure support mode as a Bi-level Ventilator for varying degrees of pressure level and lung conditions. The proposed study implements two most commonly adapted non-invasive patient circuits, i.e., single passive limb leak circuit and single limb active circuit. Both circuits are tested with and without leakage compensation. Two clinically accepted ventilation modes, i.e., pressure support and volume-assured pressure support ventilation, are presented. The results demonstrate the feasibility of using this type of device for non-invasive respiratory support and highlight the need for further testing to assess its safety and effectiveness in various clinical settings.

The role of dexmedetomidine in ARDS: an approach to non-intensive care sedation.

Introduction: Severe COVID-19 is a life-threatening condition characterized by complications such as interstitial pneumonia, hypoxic respiratory failure, and acute respiratory distress syndrome (ARDS). Non-pharmacological intervention with mechanical ventilation plays a key role in treating COVID-19-related ARDS but is influenced by a high risk of failure in more severe patients. Dexmedetomidine is a new generation highly selective α2-adrenergic receptor (α2-AR) agonist that provides sedative effects with preservation of respiratory function. The aim of this study is to assess how dexmedetomidine influences gas exchange during non-invasive ventilation (NIV) and high-flow nasal cannula (HFNC) in moderate to severe ARDS caused by COVID-19 in a non-intensive care setting. Methods: This is a single center retrospective cohort study. We included patients who showed moderate to severe respiratory distress. All included subjects had indication to NIV and were suitable for a non-intensive setting of care. A total of 170 patients were included, divided in a control group (n = 71) and a treatment group (DEX group, n = 99). Results: A total of 170 patients were hospitalized for moderate to severe ARDS and COVID-19. The median age was 71 years, 29% females. The median Charlson comorbidity index (CCI) was 2.5. Obesity affected 21% of the study population. The median pO2/FiO2 was 82 mmHg before treatment. After treatment, the increase of pO2/FiO2 ratio was clinically and statistically significant in the DEX group compared to the controls (125 mmHg [97-152] versus 94 mmHg [75-122]; ***p < 0.0001). A significative reduction of NIV duration was observed in DEX group (10 [7-16] days vs. 13 [10-17] days; *p < 0.02). Twenty four patients required IMV in control group (n = 71) and 16 patients in DEX group (n = 99) with a reduction of endotracheal intubation of 62% (OR 0.38; **p < 0.008). A higher incidence of sinus bradycardia was observed in the DEX group. Conclusion: Dexmedetomidine provides a "calm and arousal" status which allows spontaneous ventilation in awake patients treated with NIV and HFNC. The adjunctive therapy with dexmedetomidine is associated with a higher pO2/FiO2, lower duration of NIV, and a lower risk of NIV failure. A higher incidence of sinus bradycardia needs to be considered.

Reverse Triggered Breath during Pressure Support Ventilation and Neurally Adjusted Ventilatory Assist at Increasing Propofol Infusion.

BACKGROUND: Reverse triggered breath (RTB) has been extensively described during assisted-controlled modes of ventilation. We aimed to assess whether RTB occurs during Pressure Support Ventilation (PSV) and Neurally Adjusted Ventilatory Assist (NAVA) at varying depths of propofol sedation. METHODS: This is a retrospective analysis of a prospective crossover randomized controlled trial conducted in an Intensive Care Unit (ICU) of a university hospital. Fourteen intubated patients for acute respiratory failure received six trials of 25 minutes randomly applying PSV and NAVA at three different propofol infusions: awake, light, and deep sedation. We assessed the occurrence of RTBs at each protocol step. The incidence level of RTBs was determined through the RTB index, which was calculated by dividing RTBs by the total number of breaths triggered and not triggered. RESULTS: RTBs occurred during both PSV and NAVA. The RTB index was greater during PSV than during NAVA at mild (1.5 [0.0; 5.3]% vs. 0.6 [0.0; 1.1]%) and deep (5.9 [0.7; 9.0]% vs. 1.7 [0.9; 3.5]%) sedation. CONCLUSIONS: RTB occurs in patients undergoing assisted mechanical ventilation. The level of propofol sedation and the mode of ventilation may influence the incidence of RTBs.

An investigation on the respiratory mechanics of mechanically ventilated patients during spontaneous breathing trials with enhanced low-level pressure support ventilation.

INTRODUCTION: Low-level pressure support ventilation (PSV) is most commonly adopted in spontaneous breathing trials (SBTs), and some have proposed setting the positive end-expiratory pressure (PEEP) to 0 cmH2 O in order to shorten the observation time of SBTs. This study aims to investigate the effects of two PSV protocols on the patients' respiratory mechanics. MATERIAL AND METHOD: A prospective randomized self-controlled crossover design was adopted in this study, which involved enrolling 30 difficult-to-wean patients who were admitted to the intensive care unit of the First Affiliated Hospital of Guangzhou Medical University between July 2019 and September 2021. Patients were subjected to the S group (pressure support: 8 cmH2 O, PEEP: 5 cmH2 O) and S1 group (PS: 8 cmH2 O, PEEP: 0 cmH2 O) for 30 min in a random order, and respiratory mechanics indices were dynamically monitored via a four-lumen multi-functional catheter with an integrated gastric tube. Among the 30 enrolled patients, 27 were successfully weaned. RESULT: The S group showed higher airway pressure (Paw), intragastric pressure (Pga) and airway pressure-time product (PTP) than the S1 group. The S group also showed a shorter inspiratory trigger delay, (93.80 ± 47.85) versus (137.33 ± 85.66) ms (P = 0.004); and fewer abnormal triggers, (0.97 ± 2.65) versus (2.67 ± 4.48) (P = 0.042) compared with the S1 group. Stratification based on the causes of mechanical ventilation revealed that under the S1 protocol, patients with chronic obstructive pulmonary disease (COPD) had a longer inspiratory trigger delay compared to both post-thoracic surgery (PTS) patients and patients with acute respiratory distress syndrome. Despite providing greater respiratory support, S group led to significant reductions in inspiratory trigger delay and less abnormal triggers compared to S1 group, especially among patients with chronic obstructive pulmonary disease. CONCLUSION: These findings suggest that the zero PEEP group was more likely to induce a higher number of patient-ventilator asynchronies in difficult-to-wean patients.

Effects of 2 modes of positive pressure ventilation on respiratory mechanics and gas exchange in foals.

BACKGROUND: Continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) can improve respiratory mechanics and gas exchange, but different airway pressures have not been compared in foals. HYPOTHESIS/OBJECTIVES: Assess the effect of different airway pressures during CPAP and PSV have on respiratory function in healthy foals with pharmacologically induced respiratory insufficiency. We hypothesized that increased airway pressures would improve respiratory mechanics and increased positive end-expiratory pressure (PEEP) would be associated with hypercapnia. ANIMALS: Six healthy foals from a university teaching herd. METHODS: A prospective, 2-phase, 2-treatment, randomized cross-over study design was used to evaluate sequential interventions in sedated foals using 2 protocols (CPAP and PSV). Outcome measures included arterial blood gases, spirometry, volumetric capnography, lung volume and aeration assessed using computed tomography (CT). RESULTS: Sedation and dorsal recumbency were associated with significant reductions in arterial oxygen pressure (PaO2 ), respiratory rate, and tidal volume. Continuous positive airway pressure was associated with improved PaO2 , without concurrent hypercapnia. Volumetric capnography identified improved ventilation:perfusion (V/Q) matching and increased carbon dioxide elimination during ventilation, and spirometry identified decreased respiratory rate and increased tidal volume. Peak inspiratory pressure was moderately associated with PaO2 and lung volume. Improved pulmonary aeration was evident in CT images, and lung volume was increased, particularly during CPAP. CONCLUSIONS AND CLINICAL IMPORTANCE: Both CPAP and PSV improved lung mechanics and gas exchange in healthy foals with induced respiratory insufficiency.

Impact of Preemptive Postoperative Pressure Support Ventilation and Physiotherapy on Postoperative Pulmonary Complications after Major Cervicofacial Cancer Surgery: A before and after Study.

Introduction: Complex cervicofacial cancer surgery with free flap reconstruction is known to have a high incidence of postoperative pulmonary complications (PPCs). We hypothesized that by implementing an optimized respiratory protocol, including preemptive postoperative pressure support ventilation, physiotherapy, and critical respiratory support and follow-up, we could decrease the incidence of PPCs. Patients and methods: We evaluated the incidence of PPCs over two periods in two groups of patients having a routine or optimized postoperative respiratory protocol: 156 adult patients undergoing major cervicofacial cancer surgery were assessed; 91 were in Group 1 (routine) and 65 were in Group 2 (optimized). In Group 1, no ventilatory support sessions were performed. The incidence of pulmonary complications in both groups was compared using a multivariate analysis. Mortality was also compared until one year postoperatively. Results: In Group 2 with an optimized protocol, the mean number of ventilatory support sessions was 3.7 ± 1 (minimum 2, maximum 6). The incidence of respiratory complications, which was 34% in Group 1 (routine), was reduced by 59% OR = 0.41 (0.16; 0.95), p = 0.043) to 21% for the optimized Group 2. No difference in mortality was found. Conclusions: The present retrospective study showed that using an optimized preemptive respiratory pressure support ventilation combined with physiotherapy after a major cervicofacial surgery could possibly help reduce the incidence of pulmonary complications. Prospective studies are needed to verify these findings.

Evaluation of the accuracy of established patient inspiratory effort estimation methods during mechanical support ventilation.

There is a clinical need for monitoring inspiratory effort to prevent lung- and diaphragm injury in patients who receive supportive mechanical ventilation in an Intensive Care Unit. Different pressure-based techniques are available to estimate this inspiratory effort at the bedside, but the accuracy of their effort estimation is uncertain since they are all based on a simplified linear model of the respiratory system, which omits gas compressibility of air, and the viscoelasticity and nonlinearities of the respiratory system. The aim of this in-silico study was to provide an overview of the pressure-based estimation techniques and to evaluate their accuracy using a more sophisticated model of the respiratory system and ventilator. The influence of the following parameters on the accuracy of the pressure-based estimation techniques was evaluated using the in-silico model: 1) the patient's respiratory mechanics 2) PEEP and the inspiratory pressure of the ventilator 3) gas compressibility of air 4) viscoelasticity of the respiratory system 5) the strength of the inspiratory effort. The best-performing technique in terms of accuracy was the whole breath occlusion. The average error and maximum error were the lowest for all patient archetypes. We found that the error was related to the expansion of gas in the breathing set and lungs and respiratory compliance. However, concerns exist that other factors not included in the model, such as a changed muscle-force relation during an occlusion, might influence the true accuracy. The estimation techniques based on the esophageal pressure showed an error related to the viscoelastic element in the model which leads to a higher error than the occlusion. The error of the esophageal pressure-based techniques is therefore highly dependent on the pathology of the patient and the settings of the ventilator and might change over time while a patient recovers or becomes more ill.

The effectiveness of pressure support ventilation and T-piece in differing duration among weaning patients: A systematic review and network meta-analysis.

BACKGROUND: A spontaneous breathing trial (SBT) is recommended to help patients to liberate themselves from mechanical ventilation as soon as possible in the ICU. The respiratory workload in SBT, which depends on being with or without respiratory support and a specific time, is more accurate to reflect how much support the weaning patients need compared with only considering SBT technologies. AIM: To compare and rank the effectiveness of different respiratory workloads during SBT via differing technologies (Pressure Support Ventilation and T-piece) and differing duration (30 and 120 min) in SBTs. STUDY DESIGN: A comprehensive literature search was performed in six English electronic databases to identify eligible randomized controlled trials (RCTs) published before September 2020. The pooled risk ratio (RR) with 95% confidence interval (CI) was calculated by Markov chain Monte Carlo methods. A Bayesian network meta-analysis was conducted using "gemtc" version 0.8.2 of R software. Each intervention's ranking possibilities were calculated using the surface under the cumulative ranking analysis (SUCRA). RESULTS: A total of nine RCTs including 3115 participants were eligible for this network meta-analysis involving four different commonly used SBT strategies and four outcomes. The only statistically significant difference was between Pressure Support Ventilation (PSV) 30 min and T-piece 120 min in the outcome of the rate of success in SBTs (RR = 0.91; 95% CI, 0.84-0.98). The cumulative rank probability showed that the rate of success in SBT from best to worst was PSV 30 min, PSV 120 min, T-piece 30 min and T-piece 120 min. PSV 30 min and PSV 120 min are more likely to have a higher rate of extubation (SUCRA values of 82.5% for 30 min PSV, 70.7% for 120 min PSV, 36.4% for T-piece 30 min, 10.4% for T-piece 120). Meanwhile, T-piece 120 min (SUCRA, 62.9%) and PSV 120 min (SUCRA, 60.9%) may result in lower reintubation rates, followed by T-piece 30 min (SUCRA, 41.8%) and PSV 30 min (SUCRA, 34.4%). CONCLUSIONS AND RELEVANCE TO CLINICAL PRACTICE: In comprehensive consideration of four outcomes, regarding SBT strategies, 30-min PSV was superior in simple-to-wean patients. Besides, 120-min T-piece and 120-min PSV are more likely to achieve a lower reintubation rate. Thus, the impact of duration is more significant among patients who have a high risk of reintubation. It is still unclear whether the SBTs affect the outcome of mortality; further studies may need to explore the underlying mechanism.

Modeling the therapy system of noninvasive pressure support ventilation with the respiratory patient in COPD and ARDS.

The noninvasive pressure support ventilation (NPSV) has been one of mechanical ventilation widely applied for the respiratory patients in chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), etc. To investigate and develop the technologies in NPSV conveniently and in low-cost, in this article, a therapy system model of NPSV was designed with developing the mathematical submodels of NPSV respirator and respiratory patient in COPD and ARDS. By simulating the respirator, breath circuit, mask and respiratory patients, a MATLAB-based virtual experimental platform was developed for virtual ventilations. And in order to test the authenticity and practicability of the therapy system model of NPSV, a lot of ASL5000-based physical experiments were carried out for comparative analysis with the simulated outputs: pressures, flows and volumes. The statistical conclusions demonstrate that the simulated results are consist with the results from the physical experiments (TTEST P > 0.39). The experimental results tell that the therapy system model of NPSV is effective and workable. The developed therapy system model of NPSV will be beneficial for clinician and researcher to explore the therapeutic methods and some potential measures in NPSV for saving the respiratory patient's health and life.

Mixed-integer quadratic programming approach for noninvasive estimation of respiratory effort profile during pressure support ventilation.

Information about respiratory mechanics such as resistance, elastance, and muscular pressure is important to mitigate ventilator-induced lung injury. Particularly during pressure support ventilation, the available options to quantify breathing effort and calculate respiratory system mechanics are often invasive or complex. We herein propose a robust and flexible estimation of respiratory effort better than current methods. We developed a method for non-invasively estimating breathing effort using only flow and pressure signals. Mixed-integer quadratic programming (MIQP) was employed, and the binary variables were the switching moments of the respiratory effort waveform. Mathematical constraints, based on ventilation physiology, were set for some variables to restrict feasible solutions. Simulated and patient data were used to verify our method, and the results were compared to an established estimation methodology. Our algorithm successfully estimated the respiratory effort, resistance, and elastance of the respiratory system, resulting in more robust performance and faster solver times than a previously proposed algorithm that used quadratic programming (QP) techniques. In a numerical simulation benchmark, the worst-case errors for resistance and elastance were 25% and 23% for QP versus <0.1% and <0.1% for MIQP, whose solver times were 4.7 s and 0.5 s, respectively. This approach can estimate several breathing effort profiles and identify the respiratory system's mechanical properties in invasively ventilated critically ill patients.

A Novel Mask with Selective Ports for Inflow and Outflow Reduces CO2 Rebreathing during Non-Invasive Ventilation: A Physiological Study in Healthy Volunteers.

BACKGROUND: CO2 rebreathing is one of the risks associated with noninvasive ventilation (NIV), possibly contributing to failure. In a bench study, we showed that a novel mask design, with separate limbs for inflow and outflow gases, significantly reduced CO2 rebreathing in different ventilation settings. OBJECTIVES: The study aimed to test whether a new mask design could 1) reduce CO2 rebreathing in healthy volunteers during NIV (phase 1) and 2) reduce minute ventilation (phase 2). MATERIALS AND METHODS: Healthy volunteers were randomly assigned to NIV using two masks in a crossover design: a traditional single-limb mask for inflow and outflow gases and a mask with two separated limbs. In phase 1, six ventilation settings were tested for each mask: CPAP (PEEP 5 cmH2O) and pressure support ventilation (PSV, PS Level 5 cmH2O) using a mechanical ventilator with a bias flow of 8 or 20 L/min; free-flow CPAP (PEEP 5 cmH2O) with 60 or 90 L/min of gas flow. A nasal cannula was inserted in one nostril of the volunteers and connected to a CO2 gas analyzer to measure CO2 during the respiratory cycle. In phase 2, volunteers underwent a prolonged time of ventilation in CPAP 90 L/min and PSV with 20 L/min of bias flow. During free-flow CPAP, electrical impedance tomography was used to record the change in impedance during tidal breathing and then estimate tidal volume. RESULTS: Ten healthy adults were enrolled in phase 1, and 8 volunteers in phase 2. CO2 during inspiration was significantly lower in each setting with the two-limb versus the one-limb mask (p < 0.001). The maximum CO2 reduction was observed in the continuous-flow CPAP settings. EtCO2 was lower with the two-limb mask compared to the one-limb mask (p < 0.001). However, no difference in minute ventilation was observed between the two masks. CONCLUSION: The new mask design with two ports for inhaled and exhaled gases reduced the amount of CO2 rebreathing in all tested ventilation settings. The CO2 rebreathing reduction did not decrease minute ventilation in healthy volunteers.

Integrating electrical impedance tomography and transpulmonary pressure monitoring to personalize PEEP in hypoxemic patients undergoing pressure support ventilation.

Monitoring with electrical impedance tomography (EIT) during a decremental PEEP trial has been used to identify the PEEP that yields the optimal balance of pulmonary overdistension and collapse. This method is based on pixel-level changes in respiratory system compliance and depends on fixed or measured airway driving pressure. We developed a novel approach to quantify overdistension and collapse during pressure support ventilation (PSV) by integrating transpulmonary pressure and EIT monitoring and performed pilot tests in three hypoxemic patients. We report that our experimental approach is feasible and capable of identifying a PEEP that balances overdistension and collapse in intubated hypoxemic patients undergoing PSV.

Effects of different fluid management on lung and kidney during pressure-controlled and pressure-support ventilation in experimental acute lung injury.

Optimal fluid management is critical during mechanical ventilation to mitigate lung damage. Under normovolemia and protective ventilation, pulmonary tensile stress during pressure-support ventilation (PSV) results in comparable lung protection to compressive stress during pressure-controlled ventilation (PCV) in experimental acute lung injury (ALI). It is not yet known whether tensile stress can lead to comparable protection to compressive stress in ALI under a liberal fluid strategy (LF). A conservative fluid strategy (CF) was compared with LF during PSV and PCV on lungs and kidneys in an established model of ALI. Twenty-eight male Wistar rats received endotoxin intratracheally. After 24 h, they were treated with CF (minimum volume of Ringer's lactate to maintain normovolemia and mean arterial pressure ≥70 mmHg) or LF (~4 times higher than CF) combined with PSV or PCV (VT  = 6 ml/kg, PEEP = 3 cmH2 O) for 1 h. Nonventilated animals (n = 4) were used for molecular biology analyses. CF-PSV compared with LF-PSV: (1) decreased the diffuse alveolar damage score (10 [7.8-12] vs. 25 [23-31.5], p = 0.006), mainly due to edema in axial and alveolar parenchyma; (2) increased birefringence for occludin and claudin-4 in lung tissue and expression of zonula-occludens-1 and metalloproteinase-9 in lung. LF compared with CF reduced neutrophil gelatinase-associated lipocalin and interleukin-6 expression in the kidneys in PSV and PCV. In conclusion, CF compared with LF combined with PSV yielded less lung epithelial cell damage in the current model of ALI. However, LF compared with CF resulted in less kidney injury markers, regardless of the ventilatory strategy.