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BACKGROUND: There is uncertainty about how much positive end-expiratory pressure (PEEP) should be used in patients with acute respiratory distress syndrome (ARDS) due to coronavirus disease 2019 (COVID-19).OBJECTIVE: To investigate whether a higher PEEP strategy is superior to a lower PEEP strategy regarding the number of ventilator-free days (VFDs).DESIGN: Multicentre observational study conducted from 1 March to 1 June 2020.SETTING AND PATIENTS: Twenty-two ICUs in The Netherlands and 933 invasively ventilated COVID-19 ARDS patients.INTERVENTIONS: Patients were categorised retrospectively as having received invasive ventilation with higher (n=259) or lower PEEP (n=674), based on the high and low PEEP/FIO2 tables of the ARDS Network, and using ventilator settings and parameters in the first hour of invasive ventilation, and every 8 h thereafter at fixed time points during the first four calendar days. We also used propensity score matching to control for observed confounding factors that might influence outcomes.MAIN OUTCOMES AND MEASURES: The primary outcome was the number of VFDs. Secondary outcomes included distant organ failures including acute kidney injury (AKI) and use of renal replacement therapy (RRT), and mortality.RESULTS: In the unmatched cohort, the higher PEEP strategy had no association with the median [IQR] number of VFDs (2.0 [0.0 to 15.0] vs. 0.0 [0.0 to 16.0] days). The median (95% confidence interval) difference was 0.21 (-3.34 to 3.78) days, P = 0.905. In the matched cohort, the higher PEEP group had an association with a lower median number of VFDs (0.0 [0.0 to 14.0] vs. 6.0 [0.0 to 17.0] days) a median difference of -4.65 (-8.92 to -0.39) days, P = 0.032. The higher PEEP strategy had associations with higher incidence of AKI (in the matched cohort) and more use of RRT (in the unmatched and matched cohorts). The higher PEEP strategy had no association with mortality.CONCLUSION: In COVID-19 ARDS, use of higher PEEP may be associated with a lower number of VFDs, and may increase the incidence of AKI and need for RRT.TRIAL REGISTRATION: Practice of VENTilation in COVID-19 is registered at ClinicalTrials.gov, NCT04346342.

Purpose The positive end-expiratory pressure (PEEP) level with best respiratory system compliance (Crs) is frequently used for PEEP selection in acute respiratory distress syndrome (ARDS) patients. On occasion, two similar best Crs (where the difference between the Crs of two PEEP levels is 2O) may be identified during decremental PEEP titration. Selecting PEEP under such conditions is challenging. The aim of this study was to provide supplementary rationale for PEEP selection by assessing the global and regional ventilation distributions between two PEEP levels in this situation. Methods Eight ARDS cases with similar best Crs at two different PEEP levels were analyzed using examination-specific electrical impedance tomography (EIT) measures and airway stress index (SIaw). Five Crs were measured at PEEP values of 25 cm H2O (PEEP25), 20 cm H2O (PEEP20), 15 cm H2O (PEEPH), 11 cm H2O (PEEPI), and 7 cm H2O (PEEPL). The higher PEEP value of the two PEEPs with similar best Crs was designated as PEEPupper, while the lower designated as PEEPlower. Results PEEPH and PEEPI shared the best Crs in two cases, while similar Crs was found at PEEPI and PEEPL in the remaining six cases. SIaw was higher with PEEPupper as compared to PEEPlower (1.06 ± 0.10 versus 0.99 ± 0.09, p = 0.05). Proportion of lung hyperdistension was significantly higher with PEEPupper than PEEPlower (7.0 ± 5.1% versus 0.3 ± 0.5%, p = 0.0002). In contrast, proportion of recruitable lung collapse was higher with PEEPlower than PEEPupper (18.6 ± 4.4% versus 5.9 ± 3.7%, p lower than PEEPupper (34.4 ± 19.3% versus 16.0 ± 9.1%, p = 0.046). The intratidal gas distribution (ITV) index was also significantly higher at PEEPlower than PEEPupper (2.6 ± 1.3 versus 1.8 ± 0.7, p = 0.042). Conclusions PEEPupper is a rational selection in ARDS cases with two similar best Crs. EIT provides additional information for the selection of PEEP in such circumstances.

Air leak syndrome manifesting as pneumomediastinum (PM), pneumothorax (PNX) or subcutaneous emphysema (SCE) has been reported in COVID-19 patients with increasing frequency and with varying outcomes. We report a series of eight cases of PM or SCE from 1 April to May 31, 2021, among COVID-19 patients admitted in our ICU. All the patients had severe hypoxemia (PaO2/FiO2 ratio ?100) and were on noninvasive ventilation when the air leak was detected except one. PM/SCE was observed mostly on the 3 to 5 day after instituting positive pressure ventilation. High respiratory drive with mean tidal volumes in the range of 6 to 10ml/kg predicted body weight was observed in these patients. Mean inspiratory pressure (Pressure support + positive end expiratory pressure) and mean positive end expiratory pressure delivered by the ventilator ranged between 11 to 21 and 5 to 12 cm HO respectively. Outcomes varied with four deaths, four patients requiring intubation, two patients requiring chest drainage and four patients showing overall improvement out of the total eight patients with air leak. Key Messages: 1.Air leak syndrome is not rare in COVID-19 with reported incidence of 10-14%; 2. Spontaneous noninvasive ventilation in patients with high respiratory drive and large fluctuations in tidal volumes seems to be a risk factor for air leak in patients with severe lung involvement; 3. A conservative approach without intercostal drainage seems to be acceptable in the absence of pneumothorax; 4. Prognosis is varied depending on the underlying disease and not always catastrophic. Keywords: Air leak, Pneumomediastinum, COVID­19, Pneumothorax, Subcutaneous emphysema, Noninvasive, Spontaneous ventilation

BACKGROUND: The novel coronavirus-associated ARDS (COVID-19 ARDS) often requires invasive mechanical ventilation. A spectrum of atypical ARDS with different phenotypes (high vs low static compliance) has been hypothesized in COVID-19. METHODS: We conducted a retrospective analysis to identify respiratory mechanics in COVID-19 ARDS. Berlin definition was used to categorize severity of ARDS. Correlational analysis using t test, chi-square test, ANOVA test, and Pearson correlation was used to identify relationship between subject variables and respiratory mechanics. The primary outcome was duration of mechanical ventilation. Secondary outcomes were correlation between fluid status, C- reactive protein, PEEP, and D-dimer with respiratory and ventilatory parameters. RESULTS: Median age in our cohort was 60.5 y with predominantly male subjects. Up to 53% subjects were classified as severe ARDS (median P aO 2 /F IO 2 = 86) with predominantly low static compliance (median Cst- 25.5 mL/cm H2O). The overall mortality in our cohort was 61%. The total duration of mechanical ventilation was 35 d in survivors and 14 d in nonsurvivors. High PEEP (r = 0.45, P 2,000 ng/dL (P = .009) correlated with significant increase in physiologic dead space without significant correlation with P aO 2 /F IO 2 . Higher net fluid balance was inversely related to static compliance (r = −0.24, P = .045), and elevation in C- reactive protein was inversely related to P aO 2 /F IO 2 (r = −0.32, P = .02). CONCLUSIONS: In our cohort of mechanically ventilated COVID-19 ARDS subjects, high PEEP and D-dimer were associated with increase in physiologic dead space without significant effect on oxygenation, raising the question of potential microvascular dysfunction.

Background Personalizing mechanical ventilation requires the development of reliable bedside monitoring techniques. The multiple-breaths nitrogen washin–washout (MBNW) technique is currently available to measure end-expiratory lung volume (EELVMBNW), but the precision of the technique may be poor, with percentage errors ranging from 28 to 57%. The primary aim of the study was to evaluate the reliability of a novel MBNW bedside system using fast mainstream sensors to assess EELV in an experimental acute respiratory distress syndrome (ARDS) model, using computed tomography (CT) as the gold standard. The secondary aims of the study were: (1) to evaluate trending ability of the novel system to assess EELV; (2) to evaluate the reliability of estimated alveolar recruitment induced by positive end-expiratory pressure (PEEP) changes computed from EELVMBNW, using CT as the gold standard. Results Seven pigs were studied in 6 experimental conditions: at baseline, after experimental ARDS and during a decremental PEEP trial at PEEP 16, 12, 6 and 2 cmH2O. EELV was computed at each PEEP step by both the MBNW technique (EELVMBNW) and CT (EELVCT). Repeatability was assessed by performing replicate measurements. Alveolar recruitment between two consecutive PEEP levels after lung injury was measured with CT (VrecCT), and computed from EELV measurements (VrecMBNW) as ΔEELV minus the product of ΔPEEP by static compliance. EELVMBNW and EELVCT were significantly correlated (R2 = 0.97). An acceptable non-constant bias between methods was identified, slightly decreasing toward more negative values as EELV increased. The conversion equation between EELVMBNW and EELVCT was: EELVMBNW = 0.92 × EELVCT + 36. The 95% prediction interval of the bias amounted to ± 86 mL and the percentage error between both methods amounted to 13.7%. The median least significant change between repeated measurements amounted to 8% [CI95%: 4–10%]. EELVMBNW adequately tracked EELVCT changes over time (concordance rate amounting to 100% [CI95%: 87%–100%] and angular bias amounting to − 2° ± 10°). VrecMBNW and VrecCT were significantly correlated (R2 = 0.92). A non-constant bias between methods was identified, slightly increasing toward more positive values as Vrec increased. Conclusions We report a new bedside MBNW technique that reliably assesses EELV in an experimental ARDS model with high precision and excellent trending ability.

The objective: to compare efficacy and safety of Intellivent-ASV® with conventional ventilation modes during weaning in the patients after cardiac surgery.Subjects and methods. In this randomized controlled trial, 40 adult patients were ventilated with conventional ventilation modes and 40 with Intellivent-ASV after uncomplicated cardiac surgery. Eight physicians were involved in the study.Care of both groups was standardized, except for the modes of postoperative ventilation.We compared:- The physician’s workload, through accounting number of manual ventilator settings and time they spent near the ventilator in every group,- Duration of tracheal intubation in ICU,- Evaluation of ventilation safety by considering driving pressure, mechanical power, positive end expiratory pressure, and tidal volume level,- The frequency of adverse events, postoperative complications, and lethality.Results. There were significant differences in the duration of respiratory support in ICU: 226 ± 31 min (Intellivent Group) vs 271 ± 78 min (Control Group) (p = 0.0013).In Intellivent Group, the number of manual ventilator settings and time spent by physicians near the ventilator before tracheal extubation were significantly lower: 0 vs 4 (2–6), and 35 (25–53) sec vs 164 ± 69 sec respectively (p < 0.001 in both cases).Intellivent-ASV provided significantly more protective ventilation through reduction in the driving pressure, tidal volume, FiO2 and PEEP levels but no difference was noted between paO2/FiO2 ratio. ∆P and Vt were significantly lower in Intellivent Group – ∆P on mechanical ventilation was 6 (5–7) cm H2O vs 7.25 (6.5–9.5) cm H2O (p < 0.001); Vt on mechanical ventilation was 6 (5.2–7) vs 7 (6–9.5) ml/kg/PBW (p = 0.000003). PEEP and FiO2 levels were also significantly lower in Intellivent Group, PEEP on mechanical ventilation was 5 (5–7.5) cm H2O vs 7 (5–11.5) cm H2O and FiO2 level was 26 (22–30) % vs 34 (30–40) %.There were no significant differences between the groups in frequency of adverse events and duration of ICU and hospital stay.Conclusion. Application of Intellivent-ASV mode after uncomplicated cardiac surgery provides more protective mechanical ventilation and reduces the physician’s workload without compromising the quality of respiratory support and safety of patients.

Background We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) to assess the association of higher positive end-expiratory pressure (PEEP), as opposed to lower PEEP, with hospital mortality in adult intensive care unit (ICU) patients undergoing invasive mechanical ventilation for reasons other than acute respiratory distress syndrome (ARDS). Methods We performed an electronic search of MEDLINE, EMBASE, Scopus, Cochrane Central Register of Controlled Trials, CINAHL, and Web of Science from inception until June 16, 2021 with no language restrictions. In addition, a research-in-progress database and grey literature were searched. Results We identified 22 RCTs (2225 patients) comparing higher PEEP (1007 patients) with lower PEEP (991 patients). No statistically significant association between higher PEEP and hospital mortality was observed (risk ratio 1.02, 95% confidence interval 0.89–1.16; I2 = 0%, p = 0.62; low certainty of evidence). Among secondary outcomes, higher PEEP was associated with better oxygenation, higher respiratory system compliance, and lower risk of hypoxemia and ARDS occurrence. Furthermore, barotrauma, hypotension, duration of ventilation, lengths of stay, and ICU mortality were similar between the two groups. Conclusions In our meta-analysis of RCTs, higher PEEP, compared with lower PEEP, was not associated with mortality in patients without ARDS receiving invasive mechanical ventilation. Further large high-quality RCTs are required to confirm these findings.

Introduction High flow nasal cannula (HFNC) is a noninvasive ventilation (NIV) system that has demonstrated promise in the emergency department (ED) setting. Objective This narrative review evaluates the utility of HFNC in adult patients with acute hypoxemic respiratory failure in the ED setting. Discussion HFNC provides warm (37 °C), humidified (100% relative humidity) oxygen at high flows with a reliable fraction of inspired oxygen (FiO2). HFNC can improve oxygenation, reduce airway resistance, provide humidified flow that can flush anatomical dead space, and provide a low amount of positive end expiratory pressure. Recent literature has demonstrated efficacy in acute hypoxemic respiratory failure, including pneumonia, acute respiratory distress syndrome (ARDS), coronavirus disease 2019 (COVID-19), interstitial lung disease, immunocompromised states, the peri-intubation state, and palliative care, with reduced need for intubation, length of stay, and mortality in some of these conditions. Individual patient factors play an important role in infection control risks with respect to the use of HFNC in patients with COVID-19. Appropriate personal protective equipment, adherence to hand hygiene, surgical mask placement over the HFNC device, and environmental controls promoting adequate room ventilation are the foundation for protecting healthcare personnel. Frequent reassessment of the patient placed on HFNC is necessary; those with severe end organ dysfunction, thoracoabdominal asynchrony, significantly increased respiratory rate, poor oxygenation despite HFNC, and tachycardia are at increased risk of HFNC failure and need for further intervention. Conclusions HFNC demonstrates promise in several conditions requiring respiratory support. Further randomized trials are needed in the ED setting.

Pneumothorax and persistent air leak (PAL) are documented complications of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. Patients that fall in this category are often poor candidates for invasive thoracic surgical intervention. Endobronchial valves offer an effective and less invasive treatment option and can successfully treat PAL and support the weaning of patients with SARS-CoV-2 pneumonia off ventilation.

Background Acute kidney injury (AKI) in Covid-19 patients admitted to the intensive care unit (ICU) is common, and its severity may be associated with unfavorable outcomes. Severe Covid-19 fulfills the diagnostic criteria for acute respiratory distress syndrome (ARDS); however, it is unclear whether there is any relationship between ventilatory management and AKI development in Covid-19 ICU patients. Purpose To describe the clinical course and outcomes of Covid-19 ICU patients, focusing on ventilatory management and factors associated with AKI development. Methods Single-center, retrospective observational study, which assessed AKI incidence in Covid-19 ICU patients divided by positive end expiratory pressure (PEEP) tertiles, with median levels of 9.6 (low), 12.0 (medium), and 14.7 cmH2O (high-PEEP). Results Overall mortality was 51.5%. AKI (KDIGO stage 2 or 3) occurred in 38% of 101 patients. Among the AKI patients, 19 (53%) required continuous renal replacement therapy (CRRT). In AKI patients, mortality was significantly higher versus non-AKI (81% vs. 33%, p Conclusion The use of high PEEP in Covid-19 ICU patients is associated with a fivefold higher risk of AKI, leading to higher mortality. The cause and effect relationship needs further analysis. Graphic abstract

Rationale: The physiological basis of lung protection and the impact of positive end-expiratory pressure (PEEP) during pronation in acute respiratory distress syndrome are not fully elucidated. Obj...

BACKGROUND: Obesity may increase the risk of respiratory failure after cardiothoracic surgery. A recruitment maneuver followed by PEEP might decrease the risk of respiratory failure in obese subjects. We hypothesized that the routine use after heart surgery of a recruitment maneuver followed by high or low PEEP level would decrease the frequency of respiratory failure in obese subjects. METHODS: In a pragmatic, randomized controlled trial, we assigned obese subjects (ie, with body mass index [BMI] ≥ 30 kg/m(2)) in the immediate postoperative period of cardiothoracic surgery to either volume control ventilation with 5 cm H(2)O of PEEP (control group) or a recruitment maneuver followed by 5 or 10 cm H(2)O of PEEP in the intervention arms (RM5 and RM10 groups, respectively). The primary outcome was the proportion of subjects with postextubation respiratory failure, defined as the need for re-intubation, bi-level positive airway pressure, or high-flow nasal cannula within the first 48 h. RESULTS: The study included 192 subjects: 65 in the control group (BMI 33.5 ± 3.2 kg/m(2)), 66 in the RM5 group (BMI 34.5 ± 3.2 kg/m(2), and 61 in RM10 group (BMI 33.8 ± 4.8 kg/m(2)). Postextubation respiratory failure occurred in 14 subjects in the control group (21.5% [95% CI 13.3–35.3]), 21 subjects in the RM5 group (31.8% [95% CI 21.2–44.6]), and 9 subjects in the RM10 group (14.7% [95% CI 7.4–26.7]) (P = .07). The recruitment maneuver was stopped prematurely due to severe hypotension in 8 (12.1%) RM5 subjects and in 4 (6.6%) RM10 subjects (P = .28). There were no significant differences between the 3 groups for the frequencies of atelectasis, pneumonia, and death in the ICU. CONCLUSIONS: The routine use after heart surgery of a recruitment maneuver followed by 5 or 10 cm H(2)O of PEEP did not decrease the frequency of respiratory failure in obese subjects. A recruitment maneuver followed by 5 cm H(2)O of PEEP is inappropriate.

Background Postoperative pulmonary complications are common after cardiac surgery and have been related to lung collapse during cardiopulmonary bypass (CPB). No consensus exists regarding the effects of maintaining mechanical ventilation during CPB to decrease these complications. Research Question To determine whether maintaining low-tidal ventilation (3 mL/kg 5 times/min, with positive end expiratory pressure of 5 cm H2O) during CPB (ventilation strategy) was superior to a resting-lung strategy with no ventilation (no ventilation strategy) regarding postoperative pulmonary complications, including mortality. Study Design and Methods In a randomized controlled trial, patients undergoing cardiac surgery at a single center from May 2017 through August 2019 were randomized to the ventilation or no ventilation strategy during CPB (1:1 ratio). Apart from the CPB phase, perioperative ventilation procedures were standardized. Results The study included 1,501 patients (mean age, 68.8 ± 10.3 years; 1,152 (76.7%) men; mean EuroSCORE II, 2.3 ± 2.7). Seven hundred fifty-six patients were in the ventilation strategy group, and no differences existed in baseline characteristics and types of procedures between the two groups. An intention-to-treat analysis yielded no significant difference between the ventilation and no ventilation groups regarding incidence of the primary composite outcome combining death, early respiratory failure, ventilation support beyond day 2, and reintubation, with 112 of 756 patients (14.8%) in the ventilation group vs 133 of 745 patients (17.9%) in the no ventilation group (OR, 0.80; 95% CI, 0.61-1.05; P = .11). Strict per-protocol analyses of 1,338 patients (89.1%) with equally distributed preoperative characteristics yielded similar results (OR, 0.81; 95% CI, 0.60-1.09; P = .16). Post hoc analysis of the subgroup who underwent isolated coronary artery bypass graft procedures (n = 725) showed that the ventilation strategy was superior to the no ventilation strategy regarding the primary outcome (OR, 0.56; 95% CI, 0.37-0.84; P = .005). Interpretation Among patients undergoing cardiac surgery with CPB, continuation of low tidal volume ventilation was not superior to no ventilation during CPB with respect to postoperative complications, including death, early respiratory failure, ventilation support beyond day 2, and reintubation. Trial Registry ClinicalTrials.gov ; No.: NCT03098524; URL: www.clinicaltrials.gov

ZusammenfassungDie Beatmungstherapie kann offenbar nicht nur bei Patienten mit akutem Lungenversagen einen Einfluss auf den Krankheitsverlauf haben. Lungenprotektive Beatmungskonzepte werden daher auch für die Narkosebeatmung propagiert. Dieser Beitrag diskutiert verschiedene Aspekte der Beatmungstherapie in Narkose und berücksichtigt dabei auch die zunehmende Verbreitung von Adipositas bei erwachsenen Patienten.

Rationale: Asymmetrical lung injury is a frequent clinical presentation. Regional distribution of Vt and positive end-expiratory pressure (PEEP) could result in hyperinflation of the less-injured l...

PURPOSE OF REVIEW: Severe Acute Respiratory Syndrome Coronavirus 2 presents as symptomatic coronavirus disease 2019 (COVID-19) disease in susceptible patients. Severe pediatric COVID-19 disease is rare, limiting potential data accumulation on associated respiratory failure in children. Pediatric intensivists and pulmonologists managing COVID-19 patients look to adult guidelines and pediatric-specific consensus statements to guide management. The purpose of this article is to review the current literature and recommended strategies for the escalation of noninvasive and invasive respiratory support for acute respiratory failure associated with COVID-19 disease in children. RECENT FINDINGS: There are no prospective studies comparing COVID-19 treatment strategies in children. Adult and pediatric ventilation management interim guidance is based on evidence-based guidelines in non-COVID acute respiratory distress syndrome, with considerations of (1) noninvasive positive pressure ventilation versus high-flow nasal cannula and (2) high versus lower positive end expiratory pressure strategies related to lung compliance and potential lung recruitability. SUMMARY: Management of acute respiratory failure from COVID-19 requires individualized titration of noninvasive and invasive ventilation modalities with consideration of preserved or compromised pulmonary compliance. Research regarding best practices in the management of pediatric severe COVID-19 with respiratory failure is lacking and is acutely needed as the pandemic surges and vaccination of the pediatric population will be delayed compared to adults.

Objectives Patients on venoarterial extracorporeal membrane oxygenation have many risk factors for pulmonary complications in addition to their heart failure. Optimal positive end-expiratory pressure is unknown in these patients. The aim was to evaluate the ability of electrical impedance tomography to help the physician to select the optimal positive end-expiratory pressure in venoarterial extracorporeal membrane oxygenation treated and mechanically ventilated patients during a positive end-expiratory pressure trial. Design Observational prospective monocentric. Setting University hospital. Patients Patients (n = 23) older than 18 years old, on mechanical ventilation and venoarterial extracorporeal membrane oxygenation. Interventions A decreasing positive end-expiratory pressure trial (20-5 cm H2O) in increments of 5 cm H2O was performed and monitored by a collection of clinical parameters, ventilatory and ultrasonographic (cardiac and pulmonary) to define an optimal positive end-expiratory pressure according to respiratory criteria (optimal positive end-expiratory pressure selected by physician with respiratory parameters), and then adjusted according to hemodynamic and cardiac tolerances (optimal positive end-expiratory pressure selected by physician with respiratory, hemodynamic, and echocardiographic parameters). At the same time, electrical impedance tomography data (regional distribution of ventilation, compliance, and overdistension collapse) were recorded and analyzed retrospectively to define the optimal positive end-expiratory pressure. Measurements and main results The median of this optimal positive end-expiratory pressure was 10 cm H2O in our population. Electrical impedance tomography showed that increasing positive end-expiratory pressure promoted overdistention of ventral lung, maximum at positive end-expiratory pressure 20 cm H20 (34% [interquartile range, 24.5-40]). Decreasing positive end-expiratory pressure resulted in collapse of dorsal lung (29% [interquartile range, 21-45.8]). The optimal positive end-expiratory pressure selected by physician with respiratory parameters was not different from the positive end-expiratory pressure chosen by the electrical impedance tomography. However, there is a negative impact of a high level of intrathoracic pressure on hemodynamic and cardiac tolerances. Conclusions Our results support that electrical impedance tomography appears predictive to define optimal positive end-expiratory pressure on venoarterial extracorporeal membrane oxygenation , aided by echocardiography to optimize hemodynamic assessment and management.

Background Anesthetic management of patients with obesity undergoing laparoscopic abdominal surgeries requires careful plan for intraoperative mechanical ventilation aiming to avoid lung atelectasis and/or overdistention. There are conflicting data on the optimum positive end expiratory pressure (PEEP) during these surgeries. We hypothesized that lung ultrasound could be used for PEEP titration during laparoscopic surgery. Objective The purpose of this study is to evaluate the effectiveness of intraoperative individualized lung ultrasound-guided PEEP in obese patients undergoing laparoscopic bariatric surgery on intraoperative partial arterial oxygen tension (PaO2) and early postoperative pulmonary complications. Methods A randomized controlled trial included 40 adult patients with body mass index (BMI) > 35 kg/m2 undergoing laparoscopic bariatric surgery. Patients were randomized into: control group (n = 20) who received PEEP 4 cm.H2 O and ultrasound-guided group (n = 20) who received individualized lung ultrasound stepwise PEEP. All patients received volume-controlled ventilation with a tidal volume of 6 mL/kg of ideal weight and a fraction of inspired oxygen of .5. The primary outcome was the difference in partial arterial oxygen tension (PaO2) between the control group and the ultrasound-guided group. The secondary outcomes included the incidence of early postoperative pulmonary atelectasis, respiratory failure, bronchospasm, hypoxia or pneumothorax. Settings General surgery operating theatre at Cairo University hospitals. Results Ultrasound-guided group showed higher PO2 after PEEP optimization and postoperatively compared with control group (P = .005, and P = .01 respectively). Also, ultrasound-guided group showed no postoperative complications compared with control group that had 5 cases who developed postoperative pulmonary complications in the form of hypoxia and basal collapse in the first 24 hour postoperatively chest x ray (0% versus 25%, P = .047). Conclusion In patients with obesity undergoing laparoscopic bariatric surgery, the use of lung ultrasound individualized stepwise PEEP approach improved oxygenation, compliance and reduced the incidence of postoperative pulmonary atelectasis and hypoxia without causing hemodynamic instability.

Invasive mechanical ventilation is often initiated in the ED, and mechanically ventilated patients may be kept in the ED for hours before ICU transfer. Although lung-protective ventilation is beneficial, particularly in ARDS, it remains uncertain how often lung-protective tidal volumes are used in the ED, and whether lung-protective ventilation in this setting impacts patient outcomes.What is the association between the use of lung-protective ventilation in the ED and outcomes among invasively ventilated patients?A retrospective analysis (2011-2017) of a prospective registry from eight EDs enrolling consecutive adult patients (≥ 18 years) who received invasive mechanical ventilation in the ED was performed. Lung-protective ventilation was defined by use of tidal volumes ≤ 8 mL/kg predicted body weight. The primary outcome was hospital mortality. Secondary outcomes included development of ARDS, hospital length of stay, and total hospital costs.The study included 4,174 patients, of whom 2,437 (58.4%) received lung-protective ventilation in the ED. Use of lung-protective ventilation was associated with decreased odds of hospital death (adjusted OR [aOR], 0.91; 95% CI, 0.84-0.96) and development of ARDS (aOR, 0.87; 95% CI, 0.81-0.92). Patients who received lung-protective ventilation in the ED had shorter median duration of mechanical ventilation (4 vs 5 days; P 0.01), shorter median hospital length of stay (11 vs 14 days; P .001), and reduced total hospital costs (Can$44,348 vs Can$52,484 [US$34,153 vs US$40,418]; P = .03) compared with patients who received higher tidal volumes.Use of lung-protective ventilation in the ED was associated with important patient- and system-centered outcomes, including lower hospital mortality, decreased incidence of ARDS, lower hospital length of stay, and decreased total costs. Protocol development promoting the regular use of lung-protective ventilation in the ED may be of value.

Optimizing the positive end-expiratory pressure remains challenging for any clinician treating a patient with acute respiratory distress syndrome. This paper presents an approach to automate a PEEP titration maneuver and identify the best PEEP according to maximal compliance. The respiratory system was modeled by a single-compartment model, and parameters were estimated using multiple linear regression. A classifier identified the best PEEP using the scaled relative change in compliance between PEEP levels based on empirical data from previous manual PEEP titrations. An experimental system allows the in vivo testing of the automated PEEP titration, including additional safety measures. The complete system was tested in a single animal experiment and correctly identified the best PEEP. The introduced system is a step closer towards an automated, standardized PEEP optimization and closed-loop control of mechanical ventilation.

Introduction This study was conducted to assess fluid responsiveness in critically ill patients to avoid various complications of fluid overload. Material and methods This study was done in an ICU of a tertiary care hospital after approval from the institute ethical committee over 18 months. A total of 54 consenting adult patients were included in the study. Patients were hemodynamically unstable requiring mechanical ventilation, had acute circulatory failure, or those with at least one clinical sign of inadequate tissue perfusion. All patients were ventilated using tidal volume of 6-8 mL/kg, RR-12-15/minutes, positive end expiratory pressure (PEEP)-5 cm of water, and plateau pressure was kept below 30 cm water. They were sedated throughout the study. The arterial line and the central venous catheter were placed and connected to Vigileo-FloTrac transducer (Edward Lifesciences). Patients were classified into responder and nonresponder groups on the basis of the cardiac index (CI) after fluid challenge of 10 mL/kg of normal saline over 30 minutes. Pulse pressure variation (PPV), stroke volume variation (SVV), and systolic pressure variation (SPV) were assessed and compared at baseline, 30 minutes, and 60 minutes. Results In our study we found that PPV and SVV were significantly lower among responders than nonresponders at 30 minutes and insignificant at 60 minutes. Stroke volume variation was 10.28 ± 1.76 in the responder compared to 12.28 ± 4.42 (p = 0.02) at 30 minutes and PPV was 15.28 ± 6.94 in responders while it was 20.03 ± 4.35 in nonresponders (p = 0.01). We found SPV was insignificant at all time periods among both groups. Conclusion We can conclude that initial assessment for fluid responsiveness in critically ill mechanically ventilated patients should be based on PPV and SVV to prevent complications of fluid overload and their consequences. How to cite this article Kumar N, Malviya D, Nath SS, Rastogi S, Upadhyay V. Comparison of the Efficacy of Different Arterial Waveform-derived Variables (Pulse Pressure Variation, Stroke Volume Variation, Systolic Pressure Variation) for Fluid Responsiveness in Hemodynamically Unstable Mechanically Ventilated Critically Ill Patients. Indian J Crit Care Med 2021;25(1):48-53.

Introduction. The optic nerve is surrounded by layers of meninges and cerebrospinal fluid, which is why intracranial pressure affects the optic nerve sheath. Noninvasive measurement of the optic nerve sheath diameter is simple, accurate, repeatable and with minimal side effects. Effects of positive end-expiratory pressure on intracranial pressure. The application of positive end-expiratory pressure plays a significant role in improving gas exchange, but it leads to an increase in intrathoracic and central venous pressure, cerebral blood volume, reduces arterial and cerebral perfusion pressure and thus futher increases intracranial pressure. The effect of positive end-expiratory pressure depends on basal intracranial pressure and respiratory system compliance. Effects of carbon dioxide on intracranial pressure. Hypercapnia leads to cerebral vasodilatation and increases cerebral blood flow and intracranial pressure. Hypocapnia reduces intracranial pressure, but its prolonged effect may lead to cerebral ischemia. Effects of body position on intracranial pressure. Body position affects intracranial pressure, primarily by affecting cerebral venous drainage. Conclusion. Body position, application of positive end-expiratory pressure, and changes in carbon dioxide can affect intracranial pressure, which is why its monitoring is of importance. Numerous studies show that their effects on intracranial pressure can be easily monitored by ultrasound assessment of optic nerve sheath diameter.

Airway closure is a physiological phenomenon in which the distal airways are obstructed when the airway pressure drops below the airway opening pressure. We assessed this phenomenon in 27 patients with coronavirus disease 2019-related acute respiratory distress syndrome. Twelve (44%) patients had an airway opening pressure above 5 cmH2O. The median airway opening pressure was 8 cmH2O (interquartile range, 7–10), with a maximum value of 17 cmH2O. Three patients had a baseline positive end-expiratory pressure lower than the airway opening pressure.

Optic nerve sheath diameter (ONSD) sonography is a reliable method for evaluation of intracranial pressure, yet there is a lack of reliable normal values. In the study described here, we established normal ONSD values in three different age groups and both sexes. One hundred eighty-seven volunteers without central nervous system disease were enrolled in this prospective study. ONSD measurements were taken in volunteers in the supine and upright positions and after application of positive end-expiratory pressure (PEEP). Normal ONSD values were 4.9-5.3 mm (patient age range: 20-85), with significant differences between men and women (p0.001). ONSD values increased with age (∆ = 0.34 mm, p0.001). There were no differences compared with the upright position but application of PEEP led to significantly increased ONSD values (∆ = 0.21 mm, p = 0.008). ONSD values increased with age, correlated well with the width of the third ventricle, were significantly lower in the female cohort and quickly responded to PEEP, especially in women.

Purpose Ultra-protective ventilation with low tidal volume is used in severe acute respiratory distress syndrome (ARDS) patients under extracorporeal membrane oxygenation (ECMO). However, the optimal positive end-expiratory pressure (PEEP) is unknown. The aim of our study was to assess electrical impedance tomography's (EIT) ability to choose the best PEEP for these patients. Materials and methods A recruitment maneuver and after a decremental PEEP trial from 20 to 5 cmH20 were monitored by EIT, with lung images divided into four ventral-to-dorsal horizontal regions of interest. For each patient, three EIT-based PEEP were defined: PEEP ODCLmin (lowest pressure with the least EIT-based collapse lung [CL] and overdistension [OD]), PEEP ODCL15 (lowest pressure able to limit EIT-based collapse to less than or equal to 15% with the least overdistension) and PEEP Comp (PEEP with the highest EIT-based compliance). Results High PEEP levels were significantly associated with more overdistension while decreasing PEEP led to more collapsed zones. PEEP ODCL15 and PEEP Comp were in complete agreement with the reference Pulmonary PEEP (chosen according to usual respiratory clinical and ultrasound criteria), PEEP ODCLmin was in average agreement with the Pulmonary PEEP. Conclusion EIT may be a useful real-time monitoring technique to optimize the PEEP level in severe ARDS patients under ECMO. Take-home message Ultra-protective ventilation with low tidal volume is used in severe acute respiratory distress syndrome patients under extracorporeal membrane oxygenation (ECMO), but the optimal positive end-expiratory pressure is unknown. This trial shows that electrical impedance tomography may be an interesting non-invasive bedside tool to provide real-time monitoring of PEEP impact in severe ARDS patients under ECMO. The Pulmovista® electrical impedance tomography was provided by Drager (Lubeck, Germany) during the study period. Drager had no role in the study design, collection, analysis and interpretation of the data, writing the article, or the decision to submit the article for publication.

Purpose In patients with acute respiratory distress syndrome (ARDS), lung recruitment could be maximised with the use of recruitment manoeuvres (RM) or applying a positive end-expiratory pressure (PEEP) higher than what is necessary to maintain minimal adequate oxygenation. We aimed to determine whether ventilation strategies using higher PEEP and/or RMs could decrease mortality in patients with ARDS. Methods We searched MEDLINE, EMBASE and CENTRAL from 1996 to December 2019, included randomized controlled trials comparing ventilation with higher PEEP and/or RMs to strategies with lower PEEP and no RMs in patients with ARDS. We computed pooled estimates with a DerSimonian-Laird mixed-effects model, assessing mortality and incidence of barotrauma, population characteristics, physiologic variables and ventilator settings. We performed a trial sequential analysis (TSA) and a meta-regression. Results Excluding two studies that used tidal volume (VT) reduction as co-intervention, we included 3870 patients from 10 trials using higher PEEP alone (n = 3), combined with RMs (n = 6) or RMs alone (n = 1). We did not observe differences in mortality (relative risk, RR 0.96, 95% confidence interval, CI [0.84–1.09], p = 0.50) nor in incidence of barotrauma (RR 1.22, 95% CI [0.93–1.61], p = 0.16). In the meta-regression, the PEEP difference between intervention and control group at day 1 and the use of RMs were not associated with increased risk of barotrauma. The TSA reached the required information size for mortality (n = 2928), and the z-line surpassed the futility boundary. Conclusions At low VT, the routine use of higher PEEP and/or RMs did not reduce mortality in unselected patients with ARDS. Trial registration PROSPERO CRD42017082035.

OBJECTIVES Our goal was to evaluate the prevalence of and risk factors for pneumothorax in patients with invasive mechanical ventilation in the intensive care unit (ICU) diagnosed with coronavirus disease 2019 pneumonia. METHODS The prevalence of pneumothorax was retrospectively reviewed in 107 patients diagnosed with coronavirus disease 2019 pneumonia and treated in an ICU in Turkey between 11 March 2020 and 30 April 2020. RESULTS The patients were aged 19–92 years; 37 (34.6%) were women. Pneumothorax developed in 8 (7.5%) of the intubated patients. Four (50%) of the patients with pneumothorax and 68 (68.7%) of those without it died. In the univariable logistic regression analysis of the presence of comorbid diseases (P = 0.91), positive end-expiratory pressure (P = 0.18), compliance (P = 0.93), peak pressure (P = 0.41) and the Horowitz index (P = 0.13) did not show statistically significant effects in increasing the risk of pneumothorax. CONCLUSIONS There was no significant increase or decrease in the risk of pneumothorax in patients treated with invasive mechanical ventilation after the diagnosis of coronavirus disease 2019-related pneumonia/acute respiratory distress syndrome. However, consideration of the risk of pneumothorax in these individuals may have the potential to improve the prognoses in such settings., Severe acute respiratory syndrome coronavirus 2 is associated with high rates of transmission and death [1].

New findings What is the central question of this study? The study aimed to establish a novel model to study the chronic obstructive pulmonary disease (COPD)-related cardiopulmonary effects of dynamic hyperinflation in healthy subjects. What is the main finding and its importance? A model of expiratory resistance breathing (ERB) was established in which dynamic hyperinflation was induced in healthy subjects, expressed both by lung volumes and intrathoracic pressures. ERB outperformed existing methods and represents an efficacious model to study cardiopulmonary mechanics of dynamic hyperinflation without potentially confounding factors as present in COPD. Abstract Dynamic hyperinflation (DH) determines symptoms and prognosis of chronic obstructive pulmonary disease (COPD). The induction of DH is used to study cardiopulmonary mechanics in healthy subjects without COPD-related confounders like inflammation, hypoxic vasoconstriction and rarefication of pulmonary vasculature. Metronome-paced tachypnoea (MPT) has proven effective in inducing DH in healthy subjects, but does not account for airflow limitation. We aimed to establish a novel model incorporating airflow limitation by combining tachypnoea with an expiratory airway stenosis. We investigated this expiratory resistance breathing (ERB) model in 14 healthy subjects using different stenosis diameters to assess a dose-response relationship. Via cross-over design, we compared ERB to MPT in a random sequence. DH was quantified by inspiratory capacity (IC, litres) and intrinsic positive end-expiratory pressure (PEEPi, cmH2 O). ERB induced a stepwise decreasing IC (means (95% CI): tidal breathing: 3.66 (3.45-3.88), ERB 3 mm: 3.33 (1.75-4.91), 2 mm: 2.05 (0.76-3.34), 1.5 mm: 0.73 (0.12-1.58) litres) and increasing PEEPi (tidal breathing: 0.70 (0.50-0.80), ERB 3 mm: 11.1 (7.0-15.2), 2 mm: 22.3 (17.1-27.6), 1.5 mm: 33.4 (3.40-63) cmH2 O). All three MPT patterns increased PEEPi, but to a far lesser extent than ERB. No adverse events during ERB were noted. In conclusion, ERB was proven to be a safe and efficacious model for the induction of DH and might be used for the investigation of cardiopulmonary interaction in healthy subjects.

A male neonate born at 24 2/7 weeks’ gestation is transferred to our facility at 81 days of age to receive bilateral diode laser photocoagulation therapy for high-risk retinopathy of prematurity. The infant is requiring a high amount of ventilator support secondary to diffuse, persistent pulmonary interstitial emphysema and bronchopulmonary dysplasia (BPD). The infant’s chest radiograph on admission to our facility is shown in Fig 1. Figure 1. Chest radiograph demonstrates a lobular hyperlucent lesion overlying the superior mediastinum and right medial thorax as well as diffuse coarsened lung markings consistent with chronic lung disease of prematurity. At the time, this lucent lesion was suspected to be a pneumatocele. ### Prenatal and Birth Histories ### Summary of Initial Hospital Course In the NICU, the infant required 2 additional doses of surfactant at 16 and 24 hours of age with high ventilator settings. In the first few months of age, he was switched between high-frequency oscillatory ventilation and conventional ventilation multiple times because of intermittent periods of inadequate ventilation and oxygenation. On the 6th day of age, he required antibiotic therapy for methicillin-sensitive Staphylococcus …

Objectives Different techniques exist to select personalized positive end-expiratory pressure in patients affected by the acute respiratory distress syndrome. The positive end-expiratory transpulmonary pressure strategy aims to counteract dorsal lung collapse, whereas electrical impedance tomography could guide positive end-expiratory pressure selection based on optimal homogeneity of ventilation distribution. We compared the physiologic effects of positive end-expiratory pressure guided by electrical impedance tomography versus transpulmonary pressure in patients affected by acute respiratory distress syndrome. Design Cross-over prospective physiologic study. Setting Two academic ICUs. Patients Twenty ICU patients affected by acute respiratory distress syndrome undergoing mechanical ventilation. Intervention Patients monitored by an esophageal catheter and a 32-electrode electrical impedance tomography monitor underwent two positive end-expiratory pressure titration trials by randomized cross-over design to find the level of positive end-expiratory pressure associated with: 1) positive end-expiratory transpulmonary pressure (PEEPPL) and 2) proportion of poorly or nonventilated lung units (Silent Spaces) less than or equal to 15% (PEEPEIT). Each positive end-expiratory pressure level was maintained for 20 minutes, and afterward, lung mechanics, gas exchange, and electrical impedance tomography data were collected. Measurements and main results PEEPEIT and PEEPPL differed in all patients, and there was no correlation between the levels identified by the two methods (Rs = 0.25; p = 0.29). PEEPEIT determined a more homogeneous distribution of ventilation with a lower percentage of dependent Silent Spaces (p = 0.02), whereas PEEPPL was characterized by lower airway-but not transpulmonary-driving pressure (p = 0.04). PEEPEIT was significantly higher than PEEPPL in subjects with extrapulmonary acute respiratory distress syndrome (p = 0.006), whereas the opposite was true for pulmonary acute respiratory distress syndrome (p = 0.03). Conclusions Personalized positive end-expiratory pressure levels selected by electrical impedance tomography- and transpulmonary pressure-based methods are not correlated at the individual patient level. PEEPPL is associated with lower dynamic stress, whereas PEEPEIT may help to optimize lung recruitment and homogeneity of ventilation. The underlying etiology of acute respiratory distress syndrome could deeply influence results from each method.

Acute respiratory failure is the most common indication for admission to critical care. Appropriate management requires: early recognition and identification of precipitating factors; understanding of the pathophysiology and a systematic approach to assessing disease severity. Finally, if necessary, respiratory support can be non-invasive or invasive mechanical ventilation, and adjunctive therapies, including the timely use of extracorporeal respiratory support.

Tidal expiratory flow limitation (EFL), which may herald airway closure (AC), is a mechanism of loss of aeration in ARDS. In this prospective, short-term, two-center study, we measured static and dynamic chest wall (Est,cw and Edyn,cw) and lung (Est,L and Edyn,L) elastance with esophageal pressure, EFL, and AC at 5 cmH(2)O positive end-expiratory pressure (PEEP) in intubated, sedated, and paralyzed ARDS patients. For EFL determination, we used the atmospheric method and a new device allowing comparison of tidal flow during expiration to PEEP and to atmosphere. AC was validated when airway opening pressure (AOP) assessed from volume-pressure curve was found greater than PEEP by at least 1 cmH(2)O. EFL was defined whenever flow did not increase between exhalation to PEEP and to atmosphere over all or part of expiration. Elastance values were expressed as percentage of normal predicted values (%N). Among the 25 patients included, eight had EFL (32%) and 13 AOP (52%). Between patients with and without EFL Edyn,cw [median (1st to 3rd quartiles)] was 70 (16-127) and 102 (70-142) %N (P = 0.32) and Edyn,L338 (332-763) and 224 (160-275) %N (P \textless 0.001). The corresponding values for Est,cw and Est,L were 70 (56-88) and 85 (64-103) %N (P = 0.35) and 248 (206-348) and 170 (144-195) (P = 0.02), respectively. Dynamic E(L) had an area receiver operating characteristic curve of 0.88 [95% confidence intervals 0.83-0.92] for EFL and 0.74[0.68-0.79] for AOP. Higher Edyn,L was accurate to predict EFL in ARDS patients; AC can occur independently of EFL, and both should be assessed concurrently in ARDS patients.NEW & NOTEWORTHY Expiratory flow limitation (EFL) and airway closure (AC) were observed in 32% and 52%, respectively, of 25 patients with ARDS investigated during mechanical ventilation in supine position with a positive end-expiratory pressure of 5 cmH(2)O. The performance of dynamic lung elastance to detect expiratory flow limitation was good and better than that to detect airway closure. The vast majority of patients with EFL also had AC; however, AC can occur in the absence of EFL.

Protective ventilation is a prevailing ventilatory strategy these days and is comprised of small tidal volume, limited inspiratory pressure, and application of positive end-expiratory pressure (PEEP). However, several retrospective studies recently suggested that tidal volume, inspiratory pressure, and PEEP are not related to patient outcomes, or only related when they influence the driving pressure. Therefore, this review introduces the concept of driving pressure and looks into the possibility of driving pressure-guided ventilation as a new ventilatory strategy, especially in thoracic surgery where postoperative pulmonary complications are common, and thus, lung protection is of utmost importance.

Patients with moderate to severe acute respiratory distress syndrome (ARDS) benefit from prone positioning. Although the accuracy of esophageal pressure (Pes) to estimate regional pleural pressure (Ppl) has previously been assessed in the supine position, such data are not available in the prone position in ARDS. In six anesthetized, paralyzed, and mechanically ventilated female pigs, we measured Pes and Ppl into dorsal and ventral parts of the right pleural cavity. Airway pressure (Paw) and flow were measured at the airway opening. Severe ARDS [arterial partial pressure of oxygen ([Formula: see text])/fraction of inspired oxygen ([Formula: see text]) < 100 mmHg at positive end-expiratory pressure (PEEP) of 5 cmH2O] was induced by surfactant depletion. In supine and prone positions assigned in a random order, PEEP was set to 20, 15, 10, and 5 cmH2O and static end-expiratory chest wall pressures were measured from Pes (PEEPtot,es) and dorsal (PEEPtot,PplD) and ventral (PEEPtot,PplV) Ppl. The magnitude of the difference between PEEPtot,es and PEEPtot,PplD was similar in each position [-3.6 cmH2O in supine vs. -3.8 cmH2O in prone at PEEP 20 cmH2O (PEEP 20)]. The difference between PEEPtot,es and PEEPtot,PplV became narrower in the prone position (-8.3 cmH2O supine vs. -3.0 cmH2O prone at PEEP 20). PEEPtot,PplV was overestimated by Pes in the prone position at higher pressures. The median (1st-3rd quartiles) dorsal-to-ventral Ppl gradient was 4.4 (2.4-6.8) cmH2O in the supine position and -1.5 (-3.5 to +1.1) cmH2O in the prone position (P < 0.0001) and marginally influenced by PEEP (P = 0.058). Prone position narrowed end-expiratory dorsal-to-ventral Ppl vertical gradient, likely because of a more even distribution of mechanical forces over the chest wall.NEW & NOTEWORTHY In a porcine model of acute respiratory distress syndrome, we found that static end-expiratory esophageal pressure did not change significantly in prone position compared with supine position at any positive end-expiratory pressure (PEEP) tested between 5 and 20 cmH2O. Prone position was associated with an increased ventral pleural pressure and reduced end-expiratory dorsal-to-ventral pleural pressure (Ppl) vertical gradient, likely due to a more even distribution of mechanical forces over the chest wall.

With the emergence of COVID-19 we are confronted with a new clinical picture of acute respiratory distress syndrome in the intensive care unit. In the majority of patients, the respiratory mechanics are very different from the “normal” ARDS patient. We measured transpulmonary pressure and dead space ventilation to assess the effects of high and low PEEP levels on lung compliance and ventilation-perfusion mismatching. Advanced respiratory mechanics were assessed in 14 patients. Compared to ARDS patients, lung compliance was relatively high (61 ± 5 mL/cmH2O). COVID-19 patients had high dead space ventilation and gas exchange impairment (Bohr 52 ± 3%; Enghoff modification 67 ± 2%; ventilatory ratio 2.24 ± 0.23). we show that higher PEEP levels decrease lung compliance and in most cases increase dead space ventilation, indicating that high PEEP levels probably cause hyperinflation in patients with COVID-19. We suggest using prone position for an extended period of time, and apply lower PEEP levels as much as possible.

Objective Critical care therapy after cardiac surgery includes interventions to aid pulmonary and cardiac function. The aim of this study was to investigate the effect of such interventions on right ventricular function (RVF). Design This was a prospective intervention study. Setting This study was conducted at a single tertiary university hospital. Participants Thirty elective coronary artery bypass graft (CABG) patients were studied in the intensive care unit (ICU) following CABG surgery. Interventions The following interventions were investigated: Trendelenburg position; positive end-expiratory pressure (PEEP) 0, 5, and 10 cmH2O; increased oxygen fraction; and AAI, DDD, and VVI pacing. Measurements and Main Results Transesophageal echocardiography and a pulmonary artery catheter were used to assess hemodynamics and RVF. Transesophageal echocardiography measures included right ventricular (RV) fractional area change, RV ejection fraction, RV stroke volume (SV), and RV global longitudinal strain (RV-GLS). Trendelenburg increased global echocardiographic measures of RVF as well as cardiac output (CO) 0.44 L/min (95% CI: 0.21-0.67). Increasing PEEP from 0 to 10 reduced SV and consequently CO by 0.41 L/min. Pulmonary vascular resistance was not changed by increasing PEEP. AAI or DDD pacing (15 beats above baseline) increased CO 0.35 L/min (95% CI 0.07-0.63). In contrast VVI pacing decreased CO by 24% (1.2 L/min [95% CI 0.9-1.6]). Applying 100% O2 did not affect hemodynamics, but RV-GLS was improved −4.4% (95% CI: −6.9 to −1.9). Conclusion In patients with normal RVF undergoing CABG, several routine interventions in the ICU affect RVF, in particular PEEP and VVI pacing, which induces clinically important reductions in stroke volume.

BackgroundExcessive tidal volume, respiratory rate, and positive end-expiratory pressure (PEEP) are all potential causes of ventilator-induced lung injury, and all contribute to a single variable: the mechanical power. The authors aimed to determine whether high tidal volume or high respiratory rate or high PEEP at iso-mechanical power produce similar or different ventilator-induced lung injury.MethodsThree ventilatory strategies—high tidal volume (twice baseline functional residual capacity), high respiratory rate (40 bpm), and high PEEP (25 cm H2O)—were each applied at two levels of mechanical power (15 and 30 J/min) for 48 h in six groups of seven healthy female piglets (weight: 24.2 ± 2.0 kg, mean ± SD).ResultsAt iso-mechanical power, the high tidal volume groups immediately and sharply increased plateau, driving pressure, stress, and strain, which all further deteriorated with time. In high respiratory rate groups, they changed minimally at the beginning, but steadily increased during the 48 h. In contrast, after a sudden huge increase, they decreased with time in the high PEEP groups. End-experiment specific lung elastance was 6.5 ± 1.7 cm H2O in high tidal volume groups, 10.1 ± 3.9 cm H2O in high respiratory rate groups, and 4.5 ± 0.9 cm H2O in high PEEP groups. Functional residual capacity decreased and extravascular lung water increased similarly in these three categories. Lung weight, wet-to-dry ratio, and histologic scores were similar, regardless of ventilatory strategies and power levels. However, the alveolar edema score was higher in the low power groups. High PEEP had the greatest impact on hemodynamics, leading to increased need for fluids. Adverse events (early mortality and pneumothorax) also occurred more frequently in the high PEEP groups.ConclusionsDifferent ventilatory strategies, delivered at iso-power, led to similar anatomical lung injury. The different systemic consequences of high PEEP underline that ventilator-induced lung injury must be evaluated in the context of the whole body.Editor’s PerspectiveWhat We Already Know about This TopicWhat This Article Tells Us That Is New

Bronchopulmonary dysplasia (BPD) is an acquired, developmental chronic lung disease that is a consequence of premature birth. In the most severe form of the disease, infants may require prolonged periods of positive pressure ventilation. BPD is a heterogeneous disease with lung mechanics that differ from those in respiratory distress syndrome; strategies to manage the respiratory support in infants with severe BPD should take this into consideration. When caring for these infants, practitioners need to shift from the acute care ventilation strategies that use frequent blood gases and support adjustments designed to minimize exposure to positive pressure. Infants with severe BPD benefit from a chronic care model that uses less frequent ventilator adjustments and provides the level of positive support that will achieve the longer-term goal of ongoing lung growth and repair.

Background In acute respiratory failure elevated intraabdominal pressure aggravates lung collapse, tidal recruitment, and ventilation inhomogeneity. Low positive end-expiratory pressure (PEEP) may promote lung collapse and intrapulmonary shunting, whereas high PEEP may increase dead space by inspiratory overdistension. The authors hypothesized that an electrical impedance tomography–guided PEEP approach minimizing tidal recruitment improves regional ventilation and perfusion matching when compared to a table-based low PEEP/no recruitment and an oxygenation-guided high PEEP/full recruitment strategy in a hybrid model of lung injury and elevated intraabdominal pressure. Methods In 15 pigs with oleic acid–induced lung injury intraabdominal pressure was increased by intraabdominal saline infusion. PEEP was set in randomized order: (1) guided by a PEEP/inspired oxygen fraction table, without recruitment maneuver; (2) minimizing tidal recruitment guided by electrical impedance tomography after a recruitment maneuver; and (3) maximizing oxygenation after a recruitment maneuver. Single photon emission computed tomography was used to analyze regional ventilation, perfusion, and aeration. Primary outcome measures were differences in PEEP levels and regional ventilation/perfusion matching. Results Resulting PEEP levels were different (mean ± SD) with (1) table PEEP: 11 ± 3 cm H2O; (2) minimal tidal recruitment PEEP: 22 ± 3 cm H2O; and (3) maximal oxygenation PEEP: 25 ± 4 cm H2O; P < 0.001. Table PEEP without recruitment maneuver caused highest lung collapse (28 ± 11% vs. 5 ± 5% vs. 4 ± 4%; P < 0.001), shunt perfusion (3.2 ± 0.8 l/min vs. 1.0 ± 0.8 l/min vs. 0.7 ± 0.6 l/min; P < 0.001) and dead space ventilation (2.9 ± 1.0 l/min vs. 1.5 ± 0.7 l/min vs. 1.7 ± 0.8 l/min; P < 0.001). Although resulting in different PEEP levels, minimal tidal recruitment and maximal oxygenation PEEP, both following a recruitment maneuver, had similar effects on regional ventilation/perfusion matching. Conclusions When compared to table PEEP without a recruitment maneuver, both minimal tidal recruitment PEEP and maximal oxygenation PEEP following a recruitment maneuver decreased shunting and dead space ventilation, and the effects of minimal tidal recruitment PEEP and maximal oxygenation PEEP were comparable. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Introduction Oscillatory positive expiratory pressure (OPEP) devices facilitate secretion clearance by generating positive end expiratory pressure. However, different device designs may produce different levels of expiratory pressure with the same expiratory flow rate. We bench tested four devices to determine the relationship between expiratory flow and expiratory pressure in each. Methods A bench model was created to test the gas flow rates required by different OPEP devices to generate target expiratory pressure. Four different devices were tested: Acapella® (DH Green, Smiths Medical), AerobiKa® (Monaghan Medical Corporation), VibraPEP® (Curaplex), and vPEP™ (D R Burton Healthcare). Each OPEP device was tested to determine the expiratory flow needed to generate expiratory pressure thresholds considered appropriate for OPEP therapy. Results The expiratory flow required to generate the same expiratory pressure thresholds varied considerably among devices. Valved OPEP devices such as the VibraPEP required less flow than mechanical devices such as the vPEP, Aerobika, and Acapella. Discussion In this bench test of OPEP devices, we found considerable variability in expiratory flow requirements needed to generate an expiratory pressure of >10 cm H2O. Our finding suggests that smaller patients or those with limited expiratory airflow due to diseases such as COPD, obesity, chronic congestive heart failure, and restrictive lung disease may have better results when matched to OPEP devices requiring less expiratory airflow.

Mechanical ventilation (MV) is core intensive care unit (ICU) therapy during the Covid-19 pandemic. Optimising MV care to a specific patient with respiratory failure is difficult due to inter- and intra- patient variability in lung mechanics and condition. The ability to accurately predict patient-specific lung response to a change in MV settings would enable semi -automated care and significantly improve the efficiency of MV monitoring and care. It has particular emphasis when considering MV care required to treat Covid-19 patients, who require longer MV care, where patient-specific care can reduce the time on MV required. This study develops a nonlinear smooth hysteresis loop model (HLM) able to capture the essential lung dynamics in a patient-specific fashion from measured ventilator data, particularly for changes of compliance and infection points of the pressure-volume loop. The automated (no human input) hysteresis loop analysis (HLA) method is applied to identify HLM model parameters, enabling automated digital cloning to create a virtual patient model to accurately predict lung response at a specified positive end expiratory pressure (PEEP) level, as well as in response to the changes of PEEP. The performance of this automated digital cloning approach is assessed using clinical data from 4 patients and 8 recruitment maneuver (RM) arms. Validation results show the HLM-based hysteresis loops identified using HLA match clinical pressure volume loops very well with root-mean-square (RMS) errors less than 2% for all 8 data sets over 4 patients, validating the accuracy of the developed HLM in capturing the essential lung physiology and respiratory behaviours at different patient conditions. More importantly, the patient-specific digital clones at lower PEEP levels accurately predict lung response at higher PEEP levels with predicted peak inspiratory pressure (PIP) errors less than 2% in average. In addition, the resulted additional lung volume Vfrc obtained with PEEP changes are predicted with average absolute difference of 0.025L. The overall results validate the versatility and potential of the developed HLM for delineating changes of nonlinear lung dynamics, and its capability to create a predictive virtual patient with use of HLA for future treatment personalization and optimisation in MV therapy. Copyright (C) 2020 The Authors.

In this review we discuss the mechanisms of cardio-pulmonary interaction during spontaneous respiration and mechanical lung ventilation. We noted the interrelations between the changes of the intrathoracic pressure, venous return and cardiac output; the changes of the intrathoracic pressure and pulmonary hemodynamics; the values of the intrathoracic pressure and right and left ventricular myocardial contractility; the changing of respiratory phases and heart rate; the changes of respiratory muscles contraction and circulatory system. The phasic changes of the venous flow (it increases during respiration and decreases during expiration) are caused by the changes of both the intrathoracic and transdiaphragmatic pressures. However, the sucking thoracic effect is practically absent to the mean values of the venous return. During phasic respiratory changes the shifts of the venous return and pulmonary artery flow are opposite to the changes of the cardiac output and arterial pressure as a result of the changes of capacitance and resistance of the pulmonary vessels. In case of positive end expiratory pressure ventilation the changes of the cardiac output are dependent from the interrelations of the venous return, right ventricular myocardial contractility, pulmonary veins outflow and left ventricular myocardial contractility. The reflectory neurogenic influences on the heart and vessels from the pulmonary and respiratory muscles receptors are important during the cardio-pulmonary interaction.

Respiratory failure patients in the intensive care unit (ICU) require mechanical ventilation (MV) to support breathing and tissue oxygenation. Optimizing MV care is problematic. Significant patient variability confounds optimal MV settings and increase the risk of lung damage due to excessive pressure or volume delivery, which in turn can increase length of stay and cost, as well as mortality. Model-based care using in silico virtual patients can significantly affect ICU care, personalizing delivery and optimising care. This research presents a virtual patient model for pressure-controlled MV, an increasingly common mode of MV delivery, based on prior work applied to volume-controlled MV. This change necessitates predictions of flow and thus volume, instead of pressure, as the unspecified variable. A model is developed and validated using clinical data from five patients (N=5) during a series of PEEP (positive end expiratory pressure) changes in a recruitment maneuver (RM), creating a total of 242 predictions. Peak inspiratory volume, a measure of risk of lung damage, errors were 56 [26 95]mL (10.6 [5.3 19.1]%) for predictions of PEEP changes from 2-16cmH2O. Model fitting errors were all lower than 5%. Accurate predictions validate the model, and its potential to both personalise and optimise care. Copyright (C) 2020 The Authors.

Mechanical ventilation (MV) is a core treatment for patients suffering from respiratory disease and failure. However, MV settings are not standardized due to significant inter- and intra- patient variability in response to care, leading to variability in outcome. There is thus a need to personalize MV settings. This research significantly extends a single compartment lung mechanics model with physiologically relevant basis functions, and uses it to identify patient-specific lung mechanics and predict response to changes in MV settings. Nonlinear evolution of pulmonary elastance over positive end expiratory pressure (PEEP) is modelled by a newly proposed, physiologically relevant and simplified compensatory function to enable prediction of pulmonary response for both volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV), and identified as patient-specific using each patient’s data at a baseline PEEP. Predictions at higher PEEP levels test the validity of the proposed models based on errors in predicted peak inspiratory pressure (PIP) in two VCV trials and volume (PIV) in one PCV trial. A total of 210 prediction cases over 36 patients (22 VCV; 14 PCV) yielded absolute predicted PIP errors within 1.0 cmH2O (2.3%) and 3.3 cmH2O (7.3%) for 90% cases in VCV, while predicted PIV errors are within 0.073 L (16.8%) for 85% cases in PCV. In conclusion, a novel deterministic virtual patient model is presented, able to offer accurate prediction of pulmonary response across a wide range of PEEP changes for the two main MV modes used clinically, enabling predictive decision support in real-time to safely personalize and optimize care.

Ventilatory support, while life saving, can also cause or aggravate lung injury through several mechanisms which are encompassed within ventilator-associated lung injury (VALI). The important realizationin the acute respiratory distress syndrome that the “baby” lung resided in non-dependent areas led to the conceptualization of “lung rest” to reduce stress and strain to exposed alveolar units. We discuss concepts and mechanisms within VALI that ultimately induce maladaptive lung responses, as well as, current and future management strategies to detect and mitigate VALI at the bedside.

BackgroundThe acute respiratory distress syndrome (ARDS) has high morbidity and mortality. Positive end-expiratory pressure (PEEP) is commonly used in patients with ARDS but the best method to select the optimal PEEP level and reduce all-cause mortality is unclear. The primary objective of this network meta-analysis is to summarize the available evidence and to compare the effect of different PEEP selection strategies on all-cause mortality in adult patients with ARDS.MethodsWe will search MEDLINE, Cochrane Central Register of Controlled Trials, PubMed, EMBASE, and LILACS from inception onwards for randomized controlled trials assessing the effect of PEEP selection strategies in adult patients with moderate to severe ARDS. We will exclude studies that did not use a lung-protective ventilation approach as part of the comparator or intervention strategy. The primary outcome will be all-cause mortality (at the longest available follow-up and up to 90 days). Secondary outcomes will include barotrauma, ventilator-free days, intensive care unit and hospital length of stay, and changes in oxygenation. Two reviewers will independently screen all citations, full-text articles, and extract study-data. We will assess the risk of bias for each of the outcomes using version 2 of the Cochrane risk of bias tool for randomized controlled trials. If feasible, Bayesian network meta-analyses will be conducted to obtain pooled estimates of all potential head-to-head comparisons. We will report pairwise and network meta-analysis treatment effect estimates as risk ratios and risk differences, together with the associated 95% credible intervals. We will assess certainty in effect estimates using GRADE methodology.DiscussionThe present study will inform clinical decision-making for adult patients with ARDS and will improve our understanding of the limitations of the available literature assessing PEEP selection strategies. Finally, this information may also inform the design of future randomized trials, including the selection of interventions, comparators, and predictive enrichment strategies.Trial registrationPROSPERO 2020CRD42020193302.