Positive End-expiratory Pressure Set Research Articles

Short time effects of compliance guided flow-controlled ventilation versus standard of care pressure-controlled ventilation: a prospective porcine trial.

Flow-controlled ventilation (FCV) represents a novel ventilation method, which guarantees a continuous gas flow during inspiration and expiration. Long term comparison to volume- and pressure-controlled ventilation (PCV) after five- and ten hours have shown improved gas exchange parameters and lung tissue aeration. Aim of this porcine trial was to compare gas exchange parameters and lung tissue aeration in short time application of FCV compared to PCV to determine effects which will most probably pertain in short lasting procedures under general anesthesia. After induction of general anesthesia nine pigs were randomly ventilated either with compliance guided FCV settings or standard of PCV with compliance titrated positive end-expiratory pressure and peak pressure set to achieve a tidal volume of 7 mL/kg. Subsequently an arterial blood gas sample was obtained, and a computed tomography scan was performed. Afterwards, each animal was extubated and on the following day the same protocol was performed again with the alternative ventilation method. Primary analysis of 18 datasets from nine animals (with paired comparison) revealed a significantly improved oxygenation with FCV compared to control (paO<inf>2</inf> 118 vs. 109, 95% CI 2 to 16 mm Hg; P=0.042). The required respiratory minute volume was significantly lower with FCV (7.4 vs. 10.8, 95% CI -4.0 to -2.9 L/min; P<0.001) to achieve similar levels of normocapnia. However, lung tissue aeration did not significantly differ between ventilation methods. In this short-term ventilation comparison FCV improved gas exchange parameters without differences in lung tissue aeration compared to PCV.

Electric impedance tomography-guided PEEP titration reduces mechanical power in ARDS: a randomized crossover pilot trial

BackgroundIn patients with acute respiratory distress syndrome undergoing mechanical ventilation, positive end-expiratory pressure (PEEP) can lead to recruitment or overdistension. Current strategies utilized for PEEP titration do not permit the distinction. Electric impedance tomography (EIT) detects and quantifies the presence of both collapse and overdistension. We investigated whether using EIT-guided PEEP titration leads to decreased mechanical power compared to high-PEEP/FiO2 tables.MethodsA single-center, randomized crossover pilot trial comparing EIT-guided PEEP selection versus PEEP selection using the High-PEEP/FiO2 table in patients with moderate–severe acute respiratory distress syndrome. The primary outcome was the change in mechanical power after each PEEP selection strategy. Secondary outcomes included changes in the 4 × driving pressure + respiratory rate (4 ΔP, + RR index) index, driving pressure, plateau pressure, PaO2/FiO2 ratio, and static compliance.ResultsEIT was consistently associated with a decrease in mechanical power compared to PEEP/FiO2 tables (mean difference − 4.36 J/min, 95% CI − 6.7, − 1.95, p = 0.002) and led to lower values in the 4ΔP + RR index (− 11.42 J/min, 95% CI − 19.01, − 3.82, p = 0.007) mainly driven by a decrease in the elastic–dynamic power (− 1.61 J/min, − 2.99, − 0.22, p = 0.027). The elastic–static and resistive powers were unchanged. Similarly, EIT led to a statistically significant change in set PEEP (− 2 cmH2O, p = 0.046), driving pressure, (− 2.92 cmH2O, p = 0.003), peak pressure (− 6.25 cmH2O, p = 0.003), plateau pressure (− 4.53 cmH2O, p = 0.006), and static respiratory system compliance (+ 7.93 ml/cmH2O, p = 0.008).ConclusionsIn patients with moderate–severe acute respiratory distress syndrome, EIT-guided PEEP titration reduces mechanical power mainly through a reduction in elastic–dynamic power.Trial registration This trial was prospectively registered on Clinicaltrials.gov (NCT 03793842) on January 4th, 2019.

Relationship between lung ultrasound and electrical impedance tomography as regional assessment tools during PEEP titration in acute respiratory distress syndrome caused by multi-lobar pneumonia: a pilot study.

Acute respiratory distress syndrome (ARDS) caused by multilobar pneumonia (MLP) is markedly different from typical ARDS in pathology, imaging characteristics, and lung mechanics. Regional lung assessment is required. We aimed to analyze the relationship between two regional assessment tools, lung ultrasound (LUS) and electrical impedance tomography (EIT) during positive end-expiratory pressure (PEEP) titration, and determine an appropriate PEEP level. We conducted a prospective study of patients with ARDS caused by MLP with PaO2/FiO2 < 150mmHg. All subjects were equipped with two EIT belts connected with a single EIT machine to measure upper and lower hemithorax impedance change alternatingly at each PEEP level. LUS score was simultaneously determined in chest wall regions corresponding to the EIT regions during PEEP titration. We acquired EIT and LUS data in eight regions of interest at seven PEEP levels in 12 subjects. Therefore, 672 pairs of data were obtained for analysis. There were significant relationships between LUS score and tidal impedance variation and pixel compliance (Cpix). The Spearman's rho between LUS score vs. tidal impedance variation and LUS score vs. the Cpix were -0.142, P < 0.001, and -0.195, P < 0.001, respectively. The relationship between the LUS score and Cpix remained the same at every PEEP level but did not reach statistical significance. The individual's mean expected PEEP by LUS was similar to the EIT [10.33(± 1.67) vs. 10.33(± 1.44) cm H2O, P = 0.15]. Regarding the MLP, the LUS scores were associated with EIT parameters, and LUS scores might proof helpful for finding individual PEEP settings in MLP.

Model-based Identification of Work of Breathing in CPAP Ventilation of Adults

The increasing burden of chronic respiratory disease to healthcare systems results in limited capacity to effectively treat patients. People with respiratory diseases, especially when exacerbated by muscular decruitment in sleep, are commonly prescribed a form of positive airway pressure (PAP) device to provide airway support. PAP is set to provide a clinically set PEEP (positive end expiratory pressure). The best method of setting PEEP, to maintain open airways without causing barotrauma, is still debated. Therefore, the efficacy of PAP is largely determined by clinical judgment at infrequent and expensive appointments with a respiratory specialist. Improving PEEP setting, requires improved understanding of, and ability to model, patient-specific pulmonary mechanics in relation to PAP. Investigation of subject work of breathing (WOB) contributions and their interaction with PAP has potential to inform control of PEEP to optimise the efficiency of patient effort. Imposed WOB increased with PEEP as the imposed resistance from CPAP circuitry increased. Subject lung elastance also increased with PEEP from a median of 4.98 to 8.31 cmH2O/L. Increases in imposed WOB and lung elastance account for the increase in subject muscular WOB (from 2.23, to 2.88, to 3.97 cmH2OL/L). Initial results from asthma subjects in the trial show a decrease in median subject WOB from ZEEP to 4cmH2O, which is not seen in non-asthmatics.

Time constant to determine PEEP levels in mechanically ventilated COVID-19 ARDS: a feasibility study

BackgroundWe hypothesized that the measured expiratory time constant (TauE) could be a bedside parameter for the evaluation of positive end-expiratory pressure (PEEP) settings in mechanically ventilated COVID-19 patients during pressure-controlled ventilation (PCV).MethodsA prospective study was conducted including consecutively admitted adults (n = 16) with COVID-19-related ARDS requiring mechanical ventilation. A PEEP titration using PCV with a fixed driving pressure of 14 cmH2O was performed and TauE recorded at each PEEP level (0 to 18 cmH2O) in prone (n = 29) or supine (n = 24) positions. The PEEP setting with the highest TauE (TauEMAX) was considered to represent the best tradeoff between recruitment and overdistention.ResultsTwo groups of patterns were observed in the TauE plots: recruitable (R) (75%) and nonrecruitable (NR) (25%). In the R group, the optimal PEEP and PEEP ranges were 8 ± 3 cmH2O and 6–10 cmH2O for the prone position and 9 ± 3 cmH2O and 7–12 cmH2O for the supine position. In the NR group, the optimal PEEP and PEEP ranges were 4 ± 4 cmH2O and 1–8 cmH2O for the prone position and 5 ± 3 cmH2O and 1–7 cmH2O for the supine position, respectively. The R group showed significantly higher optimal PEEP (p < 0.004) and PEEP ranges (p < 0.001) than the NR group. Forty-five percent of measurements resulted in the most optimal PEEP being significantly different between the positions (p < 0.01). Moderate positive correlation has been found between TauE vs CRS at all PEEP levels (r2 = 0.43, p < 0.001).ConclusionsTauE may be a novel method to assess PEEP levels. There was wide variation in patient responses to PEEP, which indicates the need for personalized evaluation.

PEEP titration by EIT strategies for patients with ARDS: A systematic review and meta-analysis

ObjectiveTo determine which method of Positive End-expiratory Pressure (PEEP) titration is more useful, and to establish an evidence base for the clinical impact of Electrical Impedance Tomography (EIT) based individual PEEP setting which appears to be a promising method to optimize PEEP in Acute Respiratory Distress Syndrome (ARDS) patients. DesignA systematic review and meta-analysis. Setting4 databases (PUBMED, EMBASE, Web Of Science, and the Cochrane Library) from 1980 to December 2020 were performed. ParticipantsRandomized clinical trials patients with ARDS. Main variablesPaO2/FiO2-ratio and respiratory system compliance. IntervensionThe quality of the studies was assessed with the Cochrane risk and bias tool. Results8 trials, including a total of 222 participants, were eligible for analysis. Meta-analysis demonstrates a significantly EIT-based individual PEEP setting for patients receiving higher PaO2/FiO2 ratio as compared to other PEEP titration strategies [5 trials, 202 patients, SMD 0.636, (95% CI 0.364−0.908)]. EIT-drived PEEP titration strategy did not significantly increase respiratory system compliance when compared to other peep titration strategies, [7 trials, 202 patients, SMD −0.085, (95% CI −0.342 to 0.172)]. ConclusionsThe benefits of PEEP titration with EIT on clinical outcomes of ARDS in placebo-controlled trials probably result from the visible regional ventilation of EIT. These findings offer clinicians and stakeholders a comprehensive assessment and high-quality evidence for the safety and efficacy of the EIT-based individual PEEP setting as a superior option for patients who undergo ARDS.

Position of different nebulizer types for aerosol delivery in an adult model of mechanical ventilation.

BackgroundThe optimal positions of different types of nebulizer for aerosol delivery remain unclear.MethodsThree ICU ventilators employing three types of nebulizer were separately connected to a simulated lung to simulate nebulization during invasive ventilation. Assist/control-pressure control (A/C-PC) mode was utilized, with inspiratory pressure (Pi) set to 12 cmH2O and positive end expiratory pressure (PEEP) set to 5 cmH2O, and with a target Vt of 500 ml. The bias flow of all the ventilators was set to 2 L/min. The three nebulizers were the continuous jet nebulizer (c-JN), the inspiratory synchronized jet nebulizer (i-JN), and the vibrating mesh nebulizer (VMN). The five nebulizer positions were as follows: at the Y-piece (position 1) and 15 cm from the Y-piece (position 2) between the endotracheal tube and the Y-piece, at the Y-piece (position 3) and 15 cm from the Y-piece (position 4) in the inspiratory limb; and at the humidifier inlet (position 5). Aerosols were collected with a disposable filter placed at the simulated lung outlet (n = 3) and were measured by UV spectrophotometry (276 nm). The measurements were compared under different experimental conditions.ResultsThe aerosol delivery of c-JN, i-JN, and VMN was 5.33 ± 0.49~11.12 ± 0.36%, 7.73 ± 0.76~13.75 ± 0.46% and 11.13 ± 56–30.2 ± 1.63%, respectively. The higher aerosol delivery: for c-JN~Positions 2 (10.95 ± 0.15%), fori-JN~Positions 1 or 2 (12.91 ± 0.88% or 13.45 ± 0.42%), for VMN~Positions 4(29.03 ± 1.08%); the lower aerosol delivery: for c-JN~Positions 1, 3 or 5, fori-JN~Positions 4 or 5, for VMN~Positions 5.The highest aerosol delivery:For c-JN at Position 2 (10.95 ± .15%), for i-JN at Position 1 or 2 (12.91 ± .88% or 13.45 ± .42%), for VMN at Positions 4 (29. 03 ± 1.08%); the lower aerosol delivery: for c-JN at Positions 1, 3 or 5, for i-JN at Positions 4 or 5, for VMN at Positions 5. The highest aerosol deliveryof c-JN was lower than that of i-JN while the VMN was the highest (all P < .05). However, no differences were observed between the highest aerosol delivery with c-JN and the lowest aerosol delivery with i-JN. Similar results were found between the lowest aerosol delivery with VMN and the highest aerosol delivery with c-JN /i-JN in the Avea ventilator. There were no differences in the highest aerosol delivery of each nebulizer among the different ventilators (all p > 0.05).ConclusionDuring adult mechanical ventilation, the type and position of nebulizer influences aerosol delivery efficiency, with no differences between ventilators.

Anesthesiology

The effect of intraoperative positive end-expiratory pressure (PEEP) and tidal volume settings on postoperative oxygenation and respiratory complications is unclear. In this issue of ANESTHESIOLOGY, Turan et al. tested whether ventilation using different tidal volumes and PEEP levels affects postoperative oxygenation for adult patients undergoing orthopedic surgery. In an accompanying editorial, Musch and Vidal Melo examine the current challenges and potential applications of intraoperative protective mechanical ventilation. Cover illustration: A. Johnson, Vivo Visuals Studio

PEEP-FiO2 table versus EIT to titrate PEEP in mechanically ventilated patients with COVID-19-related ARDS

RationaleIt is unknown how to titrate positive end-expiratory pressure (PEEP) in patients with COVID-19-related acute respiratory distress syndrome (ARDS). Guidelines recommend the one-size-fits-all PEEP-FiO2 table. In this retrospective cohort study, an electrical impedance tomography (EIT)-guided PEEP trial was used to titrate PEEP.ObjectivesTo compare baseline PEEP according to the high PEEP-FiO2 table and personalized PEEP following an EIT-guided PEEP trial.MethodsWe performed an EIT-guided decremental PEEP trial in patients with moderate-to-severe COVID-19-related ARDS upon intensive care unit admission. PEEP was set at the lowest PEEP above the intersection of curves representing relative alveolar overdistention and collapse. Baseline PEEP was compared with PEEP set according to EIT. We identified patients in whom the EIT-guided PEEP trial resulted in a decrease or increase in PEEP of ≥ 2 cmH2O.Measurements and main resultsWe performed a PEEP trial in 75 patients. In 23 (31%) patients, PEEP was decreased ≥ 2 cmH2O, and in 24 (32%) patients, PEEP was increased ≥ 2 cmH2O. Patients in whom PEEP was decreased had improved respiratory mechanics and more overdistention in the non-dependent lung region at higher PEEP levels. These patients also had a lower BMI, longer time between onset of symptoms and intubation, and higher incidence of pulmonary embolism. Oxygenation improved in patients in whom PEEP was increased.ConclusionsAn EIT-guided PEEP trial resulted in a relevant change in PEEP in 63% of patients. These results support the hypothesis that PEEP should be personalized in patients with ARDS.

High efficiency particulate air filters and heat & moisture exchanger filters increase positive end-expiratory pressure in helmet continuous positive airway pressure: A bench-top study

BackgroundHelmet continuous positive airway pressure (CPAP) has been widely used during the COVID-19 pandemic. Specific filters (i.e. High Efficiency Particulate Air filter: HEPA; Heat & Moisture Exchanger Filter: HMEF) were used to prevent Sars-CoV2 environmental dispersion and were connected to the CPAP helmet. However, HEPA and HMEF filters may act as resistors to expiratory gas flow and increase the levels of pressure within the hood. MethodsIn a bench-top study, we investigated the levels of airway pressure generated by different HEPA and HMEF filters connected to the CPAP helmet in the absence of a Positive End Expiratory Pressure (PEEP) valve and with two levels of PEEP (5 and 10 cmH2O). All steps were performed using 3 increasing levels of gas flow (60, 80, 100 L/min). ResultsThe use of 8 different commercially available filters significantly increased the pressure within the hood of the CPAP helmet with or without the use of PEEP valves. On average, the increase of pressure above the set PEEP ranged from 3 cmH2O to 10 cmH2O across gas flow rates of 60 to 100 L/min. The measure of airway pressure was highly correlated between the laboratory pressure transducer and the Helmet manometer. Bias with 95% Confidence Interval of Bias between the devices was 0.7 (-2.06; 0.66) cmH2O. ConclusionsThe use of HEPA and HMEF filters placed before the PEEP valve at the expiratory port of the CPAP helmet significantly increase the levels of airway pressure compared to the set level of PEEP. The manometer can detect accurately the airway pressure in the presence of HEPA and HMEF filters in the helmet CPAP and its use should considered.

COMPLIANCE-GUIDED FLOW CONTROLLED VENTILATION VS PRESSURE-CONTROLLED VENTILATION IN AN EXPERIMENTAL MODEL OF OLEIC ACID-INDUCED ARDS

TYPE: Abstract TOPIC: Critical Care PURPOSE: Aim of this study was to investigate efficiency of gas exchange and impact on circulation of individualized flow controlled ventilation (FCV) compared to pressure controlled ventilation (PCV) in a porcine model of oleic acid induced acute respiratory distress syndrome (ARDS). METHODS: In lung healthy pigs ARDS was induced by intravenous application of oleic acid until moderate to severe ARDS at a stable Horowitz index of 80-120 (paO2 / FiO2) was reached over a period of 30 minutes. Ventilation was either performed with individualized FCV established by compliance-guided pressure settings or PCV with compliance-guided titration of positive end-expiratory pressure and peak pressure set to achieve a tidal volume of 6 ml/kg over a period of 2 hours. RESULTS: The FCV group (n=8) showed significantly improved oxygenation (149.2 vs. 110.4 Horowitz index, p=0.027) and CO2 removal (paCO2 54.4 vs. 67.9 mmHg, p=0.006) at a significantly lower respiratory minute volume (8.4 vs. 11.9 l/min, p=0.005) compared to the PCV group (n=8). Additionally, in FCV hemodynamic stabilisation without an increase of cardiac index (4.5 vs. 8.6 l/min/m2, p<0.001) and a significant reduction of catecholamine support (norepinephrine 0.26 vs. 0.86 μg/kg/min, p=0.037) during 2 hours of ventilation was found. CONCLUSIONS: In this oleic acid induced porcine ARDS model individualized FCV significantly improved gas exchange and hemodynamic stability compared to best clinical practice PCV. CLINICAL IMPLICATIONS: FCV may represent a promising ventilation mode to improve outcome in ARDS patients but further clinical studies are warranted to safely implement FCV in routine patient care. DISCLOSURE: Support was provided from institutional and department sources, as well as research funding provided by Ventinova Medical B.V. to cover animal costs. KEYWORD: ARDS

Retrospective Review of Transpulmonary Pressure Guided Positive End-Expiratory Pressure Titration for Mechanical Ventilation in Class II and III Obesity.

OBJECTIVES:Acute respiratory distress syndrome is treated by utilizing a lung protective ventilation strategy. Obesity presents with additional physiologic considerations, and optimizing ventilator settings may be limited with traditional means. Transpulmonary pressure (PL) obtained via esophageal manometry may be more beneficial to titrating positive end-expiratory pressure (PEEP) in this population. We sought to determine the feasibility and impact of implementation of a protocol for use of esophageal balloon to set PEEP in obese patients in a community ICU.DESIGN:Retrospective cohort study of obese (body mass index [BMI] ≥ 35 kg/m2) patients undergoing individualized PEEP titration with esophageal manometry. Data were extracted from electronic health record, and Wilcoxon signed rank test was performed to determine whether there were differences in the ventilatory parameters over time.SETTING:Intensive care unit in a community based hospital system in Newark, Delaware.PATIENTS:Twenty-nine mechanically ventilated adult patients with a median BMI of 45.8 kg/m2 with acute respiratory distress syndrome (ARDS).INTERVENTION:Individualized titration of PEEP via esophageal catheter obtained transpulmonary pressures.MEASUREMENTS AND MAIN RESULTS:Outcomes measured include PEEP, oxygenation, and driving pressure (DP) before and after esophageal manometry at 4 and 24 hr. Clinical outcomes including adverse events (pneumothorax and pneumomediastinum), increased vasopressor use, rescue therapies (inhaled pulmonary vasodilators, extracorporeal membrane oxygenation, and new prone position), continuous renal replacement therapy, and tracheostomy were also analyzed. Four hours after PEEP titration, median PEEP increased from 12 to 20 cm H2O (p < 0.0001) with a corresponding decrease in median DP from 15 to 13 cm H2O (p = 0.002). Subsequently, oxygenation improved as median Fio2 decreased from 0.8 to 0.6 (p < 0.0001), and median oxygen saturation/Fio2 (S/F) ratio improved from 120 to 165 (p < 0.0001). One patient developed pneumomediastinum. No pneumothoraces were identified. Improvements in oxygenation continued to be seen at 24 hr, compared with the prior 4 hr mark, Fio2 (0.6–0.45; p < 0.004), and S/F ratio (165–211.11; p < 0.001). Seven patients required an increase in vasopressor support after 4 hours. Norepinephrine and epinephrine were increased by 0.05 (± 0.04) µg/kg/min and 0.02 (± 0.01) µg/kg/min on average, respectively.CONCLUSIONS:PL-guided PEEP titration in obese patients can be used to safely titrate PEEP and decrease DP, resulting in improved oxygenation.

Positive end-expiratory pressure setting based on transpulmonary pressure during robot-assisted laparoscopic prostatectomy: an observational intervention study

BackgroundIn robot-assisted laparoscopic prostatectomy (RALP), concerns include the formation of atelectasis and reduced functional residual capacity. The present study aimed to examine the feasibility of positive end-expiratory pressure (PEEP) setting based on transpulmonary pressure (Ptp) as well as the effects of incremental PEEP on respiratory mechanics, blood gases, cerebral oxygenation (rSO2), and hemodynamics.MethodsFourteen male patients who were scheduled to receive RALP were recruited. Patients received mechanical ventilation (tidal volume of 6 mL kg−1) and were placed in Trendelenburg position with positive-pressure capnoperitoneum. PEEP levels were increased from 0 to 15 cmH2O (5 cmH2O per increase) every 30 min. PEEP levels were assessed where end-expiratory Ptp levels of ≥0 cmH2O were achieved (PtpEEP0). Airway pressure, esophageal pressure, cardiac index, and blood gas and rSO2 values were measured after 30 min at each PEEP step and respiratory mechanics were calculated.ResultsWith increasing PEEP levels from 0 to 15 cmH2O or PtpEEP0, the values of PaO2 and respiratory system compliance increased, and the values of driving pressure decreased. The median PEEP level associated with PtpEEP0 was 15 cmH2O. Respiratory system compliance values were higher at PtpEEP0 than those at PEEP5 (P = 0.02). Driving pressure was significantly lower at PtpEEP0 than at PEEP5 (P = 0.0036). The cardiac index remained unchanged, and the values of rSO2 were higher at PtpEEP0 than at PEEP0 (right; P = 0.0019, left; P = 0.036).ConclusionsPEEP setting determined by transpulmonary pressure can help achieve higher respiratory system compliance values and lower driving pressure without disturbing hemodynamic parameters.

Initiation of a Lung Protective Ventilation Strategy in the Emergency Department: Does an Emergency Department-Based ICU Make a Difference?

BACKGROUND:Lung protective ventilation (LPV) is a key component in the management of acute respiratory distress syndrome and other acute respiratory pathology. Initiation of LPV in the emergency department (ED) is associated with improved patient-centered and system outcomes, but adherence to LPV among ED patients is low. The impact of an ED-based ICU (ED-ICU) on LPV adherence is not known.METHODS:This single-center, retrospective, cohort study analyzed rates of adherence to a multifaceted LPV strategy pre- and post-implementation of an ED-ICU. LPV strategy components included low tidal volume ventilation, avoidance of severe hyperoxia and high plateau pressures, and positive end-expiratory pressure settings in alignment with best-evidence recommendations. The primary outcome was adherence to the LPV strategy at time of ED departure.RESULTS AND CONCLUSIONS:A total of 561 ED visits were included in the analysis, of which 60.0% received some portion of their emergency care in the ED-ICU. Adherence to the LPV strategy was statistically significantly higher in the ED-ICU cohort compared with the pre-ED-ICU cohort (65.8% vs 41.4%; p < 0.001) and non-ED-ICU cohort (65.8% vs 43.1%; p < 0.001). Among the ED-ICU cohort, 92.8% of patients received low tidal volume ventilation. Care in the ED-ICU was also associated with shorter ICU and hospital length of stay. These findings suggest improved patient and resource utilization outcomes for mechanically ventilated ED patients receiving care in an ED-ICU.

Maximizing Oxygen Delivery in Portable Ventilators.

Military transport of critically ill/injured patients requires judicious use of resources. Maintaining oxygen (O2) supplies for mechanically ventilated is crucial. O2 cylinders are difficult to transport due to the size and weight and add the risk of fire in an aircraft. The proposed solution is the use of a portable oxygen concentrator (POC) to supply O2 for mechanical ventilation. As long as power is available, a POC can provide an endless supply of O2. Anecdotal evidence suggests that as little as 3 L/min of O2 could manage as many as 2/3 of the mechanically ventilated military aeromedical transport patients. We evaluated two each of the AutoMedx SAVe II, Hamilton T1, Zoll 731, and Ventec VOCSN portable ventilators over a range of settings paired with 1 and 2 Caire SAROS POCs at ground level and simulated altitudes of 8,000 feet, 16,000 feet, and 22,000 feet. The Ventec VOCSN has the capability of utilizing an internal O2 concentrator that uses pulsed dose technology, which was also evaluated. Each ventilator was attached to a Michigan Instruments Training Test Lung. Output from the POC was bled into each ventilator via the mechanism provided with each device. A Fleisch pneumotach was used to measure delivered tidal volume (VT), and a fast-response O2 analyzer was used to measure FiO2 within the simulated lung. Ventilator parameters and FiO2 were continuously measured and recorded at each altitude. One-way analysis of variance was used to determine statistically significant differences (P < .05) in FiO2 between ventilators and among the same ventilator model at each testing condition. Delivered FiO2 varied widely between ventilator models and between devices of the same model with some testing conditions. Differences in FiO2 between ventilators at a majority (98.5%) of testing conditions were statistically significant (P < .05) but not all were clinically important. The Zoll 731 delivered the highest and most consistent FiO2 over all ventilator/POC settings at all altitudes. Differences in FiO2 at a given ventilator/POC setting from ground level to 22,000 feet were not clinically important (<5%) with this device. The VOCSN utilizing the integrated internal O2 concentrator delivered the lowest FiO2 across all ventilator/POC settings and altitudes. Due to the inability of the SAVe II to operate at the minute ventilation and positive end expiratory pressure (PEEP) settings required by the testing protocol, the device was only tested at one ventilator setting. The Hamilton T1 failed to operate appropriately at the highest VT/PEEP setting at 16,000 feet and all but one ventilator setting at 22,000 feet. The delivered FiO2 was not included in the analysis for those ventilator settings. The highest delivered FiO2 was 0.85 ± 0.05 at the 250 mL VT setting using 2 POCs (P < .0001) at ground level with the Zoll 731. Oxygen delivery utilizing POCs is dependent upon multiple factors including ventilator operating characteristics, ventilator settings, altitude, and the use of pulsed dose or continuous flow O2. Careful patient selection would be paramount to provide safe mechanical ventilation using this method of O2 delivery.

Individualized positive end-expiratory pressure guided by end-expiratory lung volume in early acute respiratory distress syndrome: study protocol for the multicenter, randomized IPERPEEP trial

BackgroundIn acute respiratory distress syndrome (ARDS), response to positive end-expiratory pressure (PEEP) is variable according to different degrees of lung recruitability. The search for a tool to individualize PEEP based on patients’ individual response is warranted.End-expiratory lung volume (EELV) assessment by nitrogen washin-washout aids bedside estimation of PEEP-induced alveolar recruitment and may therefore help titrate PEEP on patient’s individual recruitability.We designed a randomized trial to test whether an individualized PEEP setting protocol driven by EELV measurement may improve a composite clinical outcome in patients with moderate-to-severe ARDS (IPERPEEP trial).MethodsIPERPEEP is an open-label, multicenter, randomized trial that will be conducted in 10 intensive care units in Italy and will enroll 132 ARDS patients showing PaO2/FiO2 ratio ≤ 150 mmHg within 24 h from endotracheal intubation while on mechanical ventilation with PEEP 5 cmH2O.To standardize lung volumes at study initiation, all patients will undergo mechanical ventilation with tidal volume of 6 ml/kg of predicted body weight and PEEP set to obtain a plateau pressure within 28 and 30 cmH2O for 30 min (EXPRESS PEEP).Afterwards, a 5-step decremental PEEP trial will be conducted (EXPRESS PEEP to PEEP 5 cmH2O), and EELV will be measured at each step. Recruitment-to-inflation ratio will be calculated for each PEEP range from EELV difference. Patients will be then randomized to receive mechanical ventilation with PEEP set according to the optimal recruitment observed in the PEEP trial (IPERPEEP arm) trial or to achieve a plateau pressure of 28–30 cmH2O (control arm, EXPRESS strategy). In both groups, tidal volume size, use of prone positioning and neuromuscular blocking agents, and weaning from PEEP and from mechanical ventilation will be standardized.The primary endpoint of the study is a composite clinical outcome incorporating in-ICU mortality, 60-day ventilator-free days, and serum interleukin-6 concentration over the course of the initial 72 h of treatment.DiscussionThe IPERPEEP study is a randomized trial powered to elucidate whether an individualized PEEP setting protocol based on bedside assessment of lung recruitability can improve a composite clinical outcome during moderate-to-severe ARDS.Trial registrationClinicalTrials.govNCT04012073. Registered 9 July 2019.

Airway Closure and Expiratory Flow Limitation in Acute Respiratory Distress Syndrome.

Acute respiratory distress syndrome (ARDS) is mostly characterized by the loss of aerated lung volume associated with an increase in lung tissue and intense and complex lung inflammation. ARDS has long been associated with the histological pattern of diffuse alveolar damage (DAD). However, DAD is not the unique pathological figure in ARDS and it can also be observed in settings other than ARDS. In the coronavirus disease 2019 (COVID-19) related ARDS, the impairment of lung microvasculature has been pointed out. The airways, and of notice the small peripheral airways, may contribute to the loss of aeration observed in ARDS. High-resolution lung imaging techniques found that in specific experimental conditions small airway closure was a reality. Furthermore, low-volume ventilator-induced lung injury, also called as atelectrauma, should involve the airways. Atelectrauma is one of the basic tenet subtending the use of positive end-expiratory pressure (PEEP) set at the ventilator in ARDS. Recent data revisited the role of airways in humans with ARDS and provided findings consistent with the expiratory flow limitation and airway closure in a substantial number of patients with ARDS. We discussed the pattern of airway opening pressure disclosed in the inspiratory volume-pressure curves in COVID-19 and in non-COVID-19 related ARDS. In addition, we discussed the functional interplay between airway opening pressure and expiratory flow limitation displayed in the flow-volume curves. We discussed the individualization of the PEEP setting based on these findings.

Right Ventricular Function in Acute Respiratory Distress Syndrome: Impact on Outcome, Respiratory Strategy and Use of Veno-Venous Extracorporeal Membrane Oxygenation.

Acute respiratory distress syndrome (ARDS) is characterized by protein-rich alveolar edema, reduced lung compliance and severe hypoxemia. Despite some evidence of improvements in mortality over recent decades, ARDS remains a major public health problem with 30% 28-day mortality in recent cohorts. Pulmonary vascular dysfunction is one of the pivot points of the pathophysiology of ARDS, resulting in a certain degree of pulmonary hypertension, higher levels of which are associated with morbidity and mortality. Pulmonary hypertension develops as a result of endothelial dysfunction, pulmonary vascular occlusion, increased vascular tone, extrinsic vessel occlusion, and vascular remodeling. This increase in right ventricular (RV) afterload causes uncoupling between the pulmonary circulation and RV function. Without any contractile reserve, the right ventricle has no adaptive reserve mechanism other than dilatation, which is responsible for left ventricular compression, leading to circulatory failure and worsening of oxygen delivery. This state, also called severe acute cor pulmonale (ACP), is responsible for excess mortality. Strategies designed to protect the pulmonary circulation and the right ventricle in ARDS should be the cornerstones of the care and support of patients with the severest disease, in order to improve prognosis, pending stronger evidence. Acute cor pulmonale is associated with higher driving pressure (≥18 cmH2O), hypercapnia (PaCO2 ≥ 48 mmHg), and hypoxemia (PaO2/FiO2 < 150 mmHg). RV protection should focus on these three preventable factors identified in the last decade. Prone positioning, the setting of positive end-expiratory pressure, and inhaled nitric oxide (INO) can also unload the right ventricle, restore better coupling between the right ventricle and the pulmonary circulation, and correct circulatory failure. When all these strategies are insufficient, extracorporeal membrane oxygenation (ECMO), which improves decarboxylation and oxygenation and enables ultra-protective ventilation by decreasing driving pressure, should be discussed in seeking better control of RV afterload. This review reports the pathophysiology of pulmonary hypertension in ARDS, describes right heart function, and proposes an RV protective approach, ranging from ventilatory settings and prone positioning to INO and selection of patients potentially eligible for veno-venous extracorporeal membrane oxygenation (VV ECMO).

Reproducible determination of transpulmonary pressures

Oesophageal pressures, as measured in an oesophageal balloon catheter, are a validated substitute for pleural pressures.Transpulmonary pressures, indispensable to improve our understanding of ventilatory physiology, are therefore typically calculated as the difference between airway and oesophageal pressures.The oesophageal pressure signal, however, features a superimposed oscillation due to cardiac motion, not representative for pleural pressure. Additionally, oesophageal contractions or surgical manipulation can alter the signal. In practice, transpulmonary pressures are therefore manually determined from the pressure-time graphic by visual inspection of the waves and averaging a limited number of samples.We suggest an approach to extract the end-expiratory transpulmonary pressure from the raw monitoring data.•Our approach reproducibly determines end-expiratory transpulmonary pressures at a given level of set positive end-expiratory pressure at the ventilator.•Our approach ignores surgical disturbance and cardiac oscillations in the oesophageal pressure signal.

Positive end-expiratory pressure individualization guided by continuous end-expiratory lung volume monitoring during laparoscopic surgery.

To determine whether end-expiratory lung volume measured with volumetric capnography (EELVCO2) can individualize positive end-expiratory pressure (PEEP) setting during laparoscopic surgery. We studied patients undergoing laparoscopic surgery subjected to Fowler (F-group; n = 20) or Trendelenburg (T-group; n = 20) positions. EELVCO2 was measured at 0° supine (baseline), during capnoperitoneum (CP) at 0° supine, during CP with Fowler (head up + 20°) or Trendelenburg (head down - 30°) positions and after CP back to 0° supine. PEEP was adjusted to preserve baseline EELVCO2 during and after CP. Baseline EELVCO2 was statistically similar to predicted FRC in both groups. At supine and CP, EELVCO2 decreased from baseline values in F-group [median and IQR 2079 (768) to 1545 (725) mL; p = 0.0001] and in T-group [2164 (789) to 1870 (940) mL; p = 0.0001]. Change in body position maintained EELVCO2 unchanged in both groups. PEEP adjustments from 5.6 (1.1) to 10.0 (2.5) cmH2O in the F-group (p = 0.0001) and from 5.6 (0.9) to 10.0 (2.6) cmH2O in T-group (p = 0.0001) were necessary to reach baseline EELVCO2 values. EELVCO2 increased close to baseline with PEEP in the F-group [1984 (600) mL; p = 0.073] and in the T-group [2175 (703) mL; p = 0.167]. After capnoperitoneum and back to 0° supine, PEEP needed to maintain EELVCO2 was similar to baseline PEEP in F-group [5.9 (1.8) cmH2O; p = 0.179] but slightly higher in the T-group [6.5 (2.2) cmH2O; p = 0.006]. Those new PEEP values gave EELVCO2 similar to baseline in the F-group [2039 (980) mL; p = 0.370] and in the T-group [2150 (715) mL; p = 0.881]. Breath-by-breath noninvasive EELVCO2 detected changes in lung volume induced by capnoperitoneum and body position and was useful to individualize the level of PEEP during laparoscopy.Trial registry: Clinicaltrials.gov NCT03693352. Protocol started 1st October 2018.