Increase In Positive End-expiratory Pressure Research Articles

Manifestations of toxic pulmonary edema during respiratory support in an experiment

BACKGROUND: Currently, respiratory support is successfully used to treat pulmonary edema of non-toxic origin. The manifestations of pulmonary edema of non-toxic origin and toxic pulmonary edema have similar features, so respiratory support can be effective in treating the latter. AIM: To describe the manifestations of toxic pulmonary edema in rabbits and demonstrate the effectiveness of artificial pulmonary ventilation with support of positive end-expiratory pressure (PEEP) in case of severe intoxication with thermal destruction products of fluoroplastic-4. MATERIALS AND METHODS: Three rabbits were used in the study: rabbit N 1 (control), rabbit N 2 (intoxication) and rabbit N 3 (treatment). Rabbits N 2 and 3 were subjected to severe intoxication with thermal destruction products of fluoroplastic-4 (1,5 HLC50, 15 min). For treatment, rabbit N 3 (treatment), an hour after exposure, underwent mechanical ventilation with PEEP (pressure-controlled mode; oxygen fraction — 0,3; starting PEEP — 5 cm H2O, tidal volume — 20–25 ml). At various times, chest radiography was performed, oxygenation index, hemoglobin saturation (SaO2), and partial pressure of carbon dioxide in exhaled air (PetCO2) were determined. Posthumously, pathological changes in lung tissue, pulmonary coefficient were determined, and histological examination was performed. RESULTS: Exposure of rabbit N 2 (intoxication) to the thermal destruction products of fluoroplastic-4 led to the sequential formation of the interstitial and alveolar phases of toxic pulmonary edema, which contributed to its death 13 hours after exposure. As SaO2 decreased and PetCO2 increased (3 and 5 hours after exposure), in rabbit N 3 (treatment), during respiratory support, PEEP was increased twice by 2 cm H2O (maintaining a given respiratory volume), which led to the normalization of the studied parameters. On the 7th day after exposure, the condition of rabbit N 3 (treatment) did not differ from the condition of rabbit N 1 (control); no pathological changes in the respiratory system were detected. CONCLUSION: Carrying out mechanical ventilation with PEEP, started an hour after exposure (with a stepwise increase in PEEP as the condition worsens), is effective for correcting toxic pulmonary edema in rabbits caused by severe intoxication with the thermal destruction products of fluoroplastic-4.

Incremental Application of Positive End-Expiratory Pressure for the Evaluation of Atelectasis During RP-EBUS and Bronchoscopy (I-APPEAR).

CT-to-body divergence-described as the difference between preprocedural CT scans and intraprocedural lung architecture-is a significant barrier to improving diagnostic yield during navigational bronchoscopy. A major proposed contributor to CT-to-body divergence is the development of atelectasis, which can confound visualization of peripheral lung lesions via radial probe endobronchial ultrasound (RP-EBUS). High positive end-expiratory pressure (PEEP) ventilatory strategies have been used to decrease atelectasis, allowing the lesion to re-APPEAR on intraprocedure imaging. However, standardized PEEP levels may not be appropriate for all patients due to hemodynamic and ventilatory impacts. We performed a multicenter, prospective observational study in which patients were imaged with RP-EBUS under general anesthesia to determine if subsegmental atelectasis would resolve as incremental increases in PEEP were applied. Resolution of atelectasis was based on the transition from a non-aerated pattern to an aerated appearance on RP-EBUS. RP-EBUS images were reviewed by 3 experienced operators to determine correlation. Forty-three patients underwent RP-EBUS examination following navigational bronchoscopy. Thirty-seven patients underwent incremental PEEP application and subsequent RP-EBUS imaging. Atelectasis was determined to have resolved in 33 patients (88.2%) following increased PEEP. The intraclass correlation coefficient between reviewers was 0.76. A recruitment maneuver was performed in 7 (16.3%) patients after atelectasis persisted at maximal PEEP. Atelectasis was not identified in the examined subsegments in 6 (10.8%) patients despite zero PEEP. RP-EBUS is an effective tool to monitor what pressure atelectasis within a lung segment has resolved with increasing levels of PEEP.

PEEP trial and effect on hemodynamic in cardiogenic shock

Abstract Funding Acknowledgements None. Introduction Congestion is a paramount pathophysiological driver in patients with cardiogenic shock. Almost half of patients admitted due to cardiogenic shock undertake mechanical ventilation although ventilatory parameter, and their potential hemodynamic effect on the hemodynamic and congestion profile are often neglected. Purpose We sought to evaluate the hemodynamic effect of positive end-expiratory pressure (PEEP) titration on patients admitted to intensive care unit for CS. Methods We perform PEEP titration trial on patients undertaking mechanical ventilation for respiratory failure related to CS. The trial consisted in 3 steps of PEEP increase from 5 to 15 cmH2O. For each step arterial saturation, right atrial -RAP- and systemic blood pressure along with heart rate and respiratory mechanics (tidal volume-TV-, dynamic lung compliance- CLdyn, driving- Δ- and plateau pressure- Ppl) were measured. All the measures were taken at end-expiration; RAP trace was analyzed and systolic, mean and diastolic component collected. The final PEEP was decided based on the best matching between saturation, CLdyn and TV. Descriptive and repeated measures with Bonferroni correction were applied as statistical analysis (IBM SPSS 29). Results Twelve patients were included (10 male, 66 ± 7 years old; 8 acute myocardial infarction and 4 acute heart failure). At baseline the mean RAP was 8.44 (± 2.32) ; SBP 106 (IQR 92-112), HR 94 (IQR 88 - 102) Δ and Ppl pressures respectively 7.42 (± 0.79) and 12.08 (± 0.79, ),VT 427(± 65.42) and CLdyn 58.3 (± 7.1). The right atrial pressure (RAP) differed between AMI and AHDF (8.25 ± 2.25 vs 20.25 ± 1.5; p < 0.001), so HR did (113 ± 3.4 versus 96 ± 3.2 betas per minutes; p 0.015). RAP varied consistently during the PEEP trial (either sRAP, dRAP and mRAP- Table and Figure 1). The TV changed signficnatly between the 1st and 3rd step (p 0.004) and the CLdyn varied consistently throughout the 3 steps of the PEEP trial (p <0.001). A significant difference were observed according to aetiology in RAP (AMI Vs ADHF, eman difference 2.4 versus 4.3 mmHg) and in CLdyn (AMI Vs ADHF mean difference 12.31 vs 8 .65, p < 0.01) but not in the other parameters evaluated (p > 0.05). Conclusion This is the first, small, study evaluating the effect of positive pressure ventilation in CS patients according to etiologies. As previously demonstrated PEEP influences the right side hemodynamic by increasing the RAP, although resulting in better CLdyn. The extent of the effect of PEEP increased may be dependent on the underlying aetiology of CS. Considering that the sample size is extremely limited, these results advocate a wider validation. However, the positive pressures induced by the ventilation in patient with CS should be taken in consideration when the comprehensive evaluation of hemodynamic to define congestion profile and phenotype are performed.Table 1.Hemodynamic parametersGraph PEEP vs RAP

Modelling lung diffusion-perfusion limitation in mechanically ventilated SARS-CoV-2 patients.

This is the first study to describe the daytime evolution of respiratory parameters in mechanically ventilated COVID-19 patients. The data base refers to patients hospitalised in the intensive care unit (ICU) at Arequipa Hospital (Peru, 2335m) in 2021. In both survivors (S) and non-survivors (NS) patients, a remarkable decrease in respiratory compliance was observed, revealing a proportional decrease in inflatable alveolar units. The S and NS patients were all hyperventilated and their SatO2 was maintained at >90%. However, while S remained normocapnic, NS developed progressive hypercapnia. We compared the efficiency of O2 uptake and CO2 removal in the air blood barrier relying on a model allowing to partition between diffusion and perfusion limitations to gas exchange. The decrease in O2 uptake was interpreted as diffusion limitation, while the impairment in CO2 removal was modelled by progressive perfusion limitation. The latter correlated with the increase in positive end-expiratory pressure (PEEP) and plateau pressure (Pplat), leading to capillary compression, increased blood velocity, and considerable shortening of the air-blood contact time.

The effect of increased positive end expiratory pressure on brain tissue oxygenation and intracranial pressure in acute brain injury patients

Cerebral hypoxia is an important cause of secondary brain injury. Improving systemic oxygenation may increase brain tissue oxygenation (PbtO2). The effects of increased positive end-expiratory pressure (PEEP) on PbtO2 and intracranial pressure (ICP) needs to be further elucidated. This is a single center retrospective cohort study (2016–2021) conducted in a 34-bed Department of Intensive Care unit. All patients with acute brain injury under mechanical ventilation who were monitored with intracranial pressure and brain tissue oxygenation (PbtO2) catheters and underwent at least one PEEP increment were included in the study. Primary outcome was the rate of PbtO2 responders (increase in PbtO2 > 20% of baseline) after PEEP increase. ΔPEEP was defined as the difference between PEEP at 1 h and PEEP at baseline; similarly ΔPbtO2 was defined as the difference between PbtO2 at 1 h after PEEP incrementation and PbtO2 at baseline. We included 112 patients who underwent 295 episodes of PEEP increase. Overall, the median PEEP increased form 6 (IQR 5–8) to 10 (IQR 8–12) cmH2O (p = 0.001), the median PbtO2 increased from 21 (IQR 16–29) mmHg to 23 (IQR 18–30) mmHg (p = 0.001), while ICP remained unchanged [from 12 (7–18) mmHg to 12 (7–17) mmHg; p = 0.42]. Of 163 episode of PEEP increments with concomitant PbtO2 monitoring, 34 (21%) were PbtO2 responders. A lower baseline PbtO2 (OR 0.83 [0.73–0.96)]) was associated with the probability of being responder. ICP increased in 142/295 episodes of PEEP increments (58%); no baseline variable was able to identify this response. In PbtO2 responders there was a moderate positive correlation between ΔPbtO2 and ΔPEEP (r = 0.459 [95% CI 0.133–0.696]. The response in PbtO2 and ICP to PEEP elevations in brain injury patients is highly variable. Lower PbtO2 values at baseline could predict a significant increase in brain oxygenation after PEEP increase.

Tidal Volume, Positive End-expiratory Pressure, and Postoperative Hypoxemia: Reply.

Suleiman et al.1 assert that driving pressure and mechanical power (because of increased respiratory rate in low tidal volume groups) may be more important determinants of perioperative lung injury and postoperative pulmonary complications than tidal volume and positive end-expiratory pressure (PEEP). We used a factorial cluster design to assign 2,860 patients to four combinations of tidal volume and PEEP. There were no differences in oxygenation during recovery or in pulmonary complications among the groups. We therefore concluded that any combinations of tidal volume between 6 and 10 ml/kg and PEEP between 5 and 8 cm H2O are comparably safe in relatively healthy patients having general anesthesia for orthopedic surgery.2As expected, both driving pressure and mechanical power differed among our four treatment groups (table 1). For example, mechanical power increased approximately 1.2 J/min with each increase in tidal volume and/or PEEP, ranging from 10.7 to 14.4 J/min with the biggest intergroup difference being 1.3 J/min. Driving pressure increased 2 to 3 cm H2O with higher tidal volume (table 1).Mechanical power is affected by tidal volume and respiratory rate. We therefore evaluated mechanical power as a predictor of our primary outcome, the oxygen saturation measured by pulse oximetry to fraction of inspired oxygen (Spo2/Fio2) ratio. The relationship was significant, with each Joule per minute increase in mechanical power being associated with –2.12 (95% CI, –2.49 to –1.74; P < 0.0001) reduction in Spo2/Fio2 ratio, an amount that is not remotely clinically meaningful.At least in healthy lungs, postoperative oxygenation and complications are similar at any combination of tidal volume 6 to 10 ml/kg and PEEP of 5 to 8 cm H20, which is roughly twice as high as the threshold for a change in intraoperative mechanical power that is associated with increased risk for postoperative respiratory failure.3Dr. Gama de Abreu received consultation fees from Ambu (Ballerup, Denmark), Lungpacer (Vancouver, Canda) and Medtronic (Lisbon, Portugal). The other authors declare no competing interests.

Effects of positive end-expiratory pressure on cerebral hemodynamics in acute brain injury patients.

Background: Cerebral autoregulation is the mechanism that allows to maintain the stability of cerebral blood flow despite changes in cerebral perfusion pressure. Maneuvers which increase intrathoracic pressure, such as the application of positive end-expiratory pressure (PEEP), have been always challenged in brain injured patients for the risk of increasing intracranial pressure (ICP) and altering autoregulation. The primary aim of this study is to assess the effect of PEEP increase (from 5 to 15cmH2O) on cerebral autoregulation. Secondary aims include the effect of PEEP increase on ICP and cerebral oxygenation. Material and Methods: Prospective, observational study including adult mechanically ventilated patients with acute brain injury requiring invasive ICP monitoring and undergoing multimodal neuromonitoring including ICP, cerebral perfusion pressure (CPP) and cerebral oxygenation parameters obtained with near-infrared spectroscopy (NIRS), and an index which expresses cerebral autoregulation (PRx). Additionally, values of arterial blood gases were analyzed at PEEP of 5 and 15cmH2O. Results are expressed as median (interquartile range). Results: Twenty-five patients were included in this study. The median age was 65years (46-73). PEEP increase from 5 to 15cmH2O did not lead to worsened autoregulation (PRx, from 0.17 (-0.003-0.28) to 0.18 (0.01-0.24), p = 0.83). Although ICP and CPP changed significantly (ICP: 11.11 (6.73-15.63) to 13.43 (6.8-16.87) mm Hg, p = 0.003, and CPP: 72.94 (59.19-84) to 66.22 (58.91-78.41) mm Hg, p = 0.004), these parameters did not reach clinically relevant levels. No significant changes in relevant cerebral oxygenation parameters were observed. Conclusion: Slow and gradual increases of PEEP did not alter cerebral autoregulation, ICP, CPP and cerebral oxygenation to levels triggering clinical interventions in acute brain injury patients.

Releasing high positive end-expiratory pressure to a low level generates a pronounced increase in particle flow from the airways

ObjectivesDetecting particle flow from the airways by a non-invasive analyzing technique might serve as an additional tool to monitor mechanical ventilation. In the present study, we used a customized particles in exhaled air (PExA) technique, which is an optical particle counter for the monitoring of particle flow in exhaled air. We studied particle flow while increasing and releasing positive end-expiratory pressure (PEEP). The aim of this study was to investigate the impact of different levels of PEEP on particle flow in exhaled air in an experimental setting. We hypothesized that gradually increasing PEEP will reduce the particle flow from the airways and releasing PEEP from a high level to a low level will result in increased particle flow.MethodsFive fully anesthetized domestic pigs received a gradual increase of PEEP from 5 cmH2O to a maximum of 25 cmH2O during volume-controlled ventilation. The particle count along with vital parameters and ventilator settings were collected continuously and measurements were taken after every increase in PEEP. The particle sizes measured were between 0.41 µm and 4.55 µm.ResultsA significant increase in particle count was seen going from all levels of PEEP to release of PEEP. At a PEEP level of 15 cmH2O, there was a median particle count of 282 (154–710) compared to release of PEEP to a level of 5 cmH2O which led to a median particle count of 3754 (2437–10,606) (p < 0.009). A decrease in blood pressure was seen from baseline to all levels of PEEP and significantly so at a PEEP level of 20 cmH2O.ConclusionsIn the present study, a significant increase in particle count was seen on releasing PEEP back to baseline compared to all levels of PEEP, while no changes were seen when gradually increasing PEEP. These findings further explore the significance of changes in particle flow and their part in pathophysiological processes within the lung.

The effect of positive end-expiratory pressure on intracranial pressure in obese and non-obese severe brain injury patients: a retrospective observational study

BackgroundThe effect of positive end-expiratory pressure (PEEP) on intracranial pressure (ICP) had never been studied in obese patients with severe brain injury (SBI). The main aim was to evaluate the effect of PEEP on ICP in SBI patients with mechanical ventilation according to obesity status.MethodsSBI patients admitted to the ICU with mechanical ventilation between 2014 and 2015 were included. Demographic, hemodynamic, arterial blood gas, and ventilator data at the time of the paired PEEP and ICP observations were recorded and compared between obese (body mass index ≥ 30 kg/m2) and non-obese SBI patients. Generalized estimating equation (GEE) model was used to assess the relationship between PEEP and ICP in obese and non-obese SBI patients, respectively.ResultsSix hundred twenty-seven SBI patients were included, 407 (65%) non-obese and 220 (35%) obese patients. A total of 30,415 paired PEEP and ICP observations were recorded in these patients, 19,566 (64.3%) for non-obese and 10,849 (35.7%) for obese. In the multivariable analysis, a statistically significant relationship between PEEP and ICP was found in obese SBI patients, but not in non-obese ones. For every cmH2O increase in PEEP, there was a 0.19 mmHg increase in ICP (95% CI [0.05, 0.33], P = 0.007) and a 0.15 mmHg decrease in CPP (95% CI [-0.29, -0.01], P = 0.036) in obese SBI patients after adjusting for confounders.ConclusionsThe results suggested that, contrary to non-obese SBI patients, the application of PEEP may produce an increase in ICP in obese SBI patients. However, the effect was modest and may be clinically inconsequential.

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.

Capnodynamic monitoring of lung volume and blood flow in response to increased positive end-expiratory pressure in moderate to severe COVID-19 pneumonia: an observational study

BackgroundThe optimal level of positive end-expiratory pressure (PEEP) during mechanical ventilation for COVID-19 pneumonia remains debated and should ideally be guided by responses in both lung volume and perfusion. Capnodynamic monitoring allows both end-expiratory lung volume ({text{EELV}}_{{{text{CO}}_{2} }}) and effective pulmonary blood flow (EPBF) to be determined at the bedside with ongoing ventilation.MethodsPatients with COVID-19-related moderate to severe respiratory failure underwent capnodynamic monitoring of {text{EELV}}_{{{text{CO}}_{2} }} and EPBF during a step increase in PEEP by 50% above the baseline (PEEPlow to PEEPhigh). The primary outcome was a > 20 mm Hg increase in arterial oxygen tension to inspired fraction of oxygen (P/F) ratio to define responders versus non-responders. Secondary outcomes included changes in physiological dead space and correlations with independently determined recruited lung volume and the recruitment-to-inflation ratio at an instantaneous, single breath decrease in PEEP. Mixed factor ANOVA for group mean differences and correlations by Pearson’s correlation coefficient are reported including their 95% confidence intervals.ResultsOf 27 patients studied, 15 responders increased the P/F ratio by 55 [24–86] mm Hg compared to 12 non-responders (p < 0.01) as PEEPlow (11 ± 2.7 cm H2O) was increased to PEEPhigh (18 ± 3.0 cm H2O). The {text{EELV}}_{{{text{CO}}_{2} }} was 461 [82–839] ml less in responders at PEEPlow (p = 0.02) but not statistically different between groups at PEEPhigh. Responders increased both {text{EELV}}_{{{text{CO}}_{2} }} and EPBF at PEEPhigh (r = 0.56 [0.18–0.83], p = 0.03). In contrast, non-responders demonstrated a negative correlation (r = − 0.65 [− 0.12 to − 0.89], p = 0.02) with increased lung volume associated with decreased pulmonary perfusion. Decreased (− 0.06 [− 0.02 to − 0.09] %, p < 0.01) dead space was observed in responders. The change in {text{EELV}}_{{{text{CO}}_{2} }} correlated with both the recruited lung volume (r = 0.85 [0.69–0.93], p < 0.01) and the recruitment-to-inflation ratio (r = 0.87 [0.74–0.94], p < 0.01).ConclusionsIn mechanically ventilated patients with moderate to severe COVID-19 respiratory failure, improved oxygenation in response to increased PEEP was associated with increased end-expiratory lung volume and pulmonary perfusion. The change in end-expiratory lung volume was positively correlated with the lung volume recruited and the recruitment-to-inflation ratio. This study demonstrates the feasibility of capnodynamic monitoring to assess physiological responses to PEEP at the bedside to facilitate an individualised setting of PEEP.Trial registration: NCT05082168 (18th October 2021).

Potential for the lung recruitment and the risk of lung overdistension during 21\xa0days of mechanical ventilation in patients with\xa0 COVID-19 after noninvasive ventilation failure: the COVID-VENT observational trial

BackgroundData on the lung respiratory mechanics and gas exchange in the time course of COVID-19-associated respiratory failure is limited. This study aimed to explore respiratory mechanics and gas exchange, the lung recruitability and risk of overdistension during the time course of mechanical ventilation.MethodsThis was a prospective observational study in critically ill mechanically ventilated patients (n = 116) with COVID-19 admitted into Intensive Care Units of Sechenov University. The primary endpoints were: «optimum» positive end-expiratory pressure (PEEP) level balanced between the lowest driving pressure and the highest SpO2 and number of patients with recruitable lung on Days 1 and 7 of mechanical ventilation. We measured driving pressure at different levels of PEEP (14, 12, 10 and 8 cmH2O) with preset tidal volume, and with the increase of tidal volume by 100 ml and 200 ml at preset PEEP level, and calculated static respiratory system compliance (CRS), PaO2/FiO2, alveolar dead space and ventilatory ratio on Days 1, 3, 5, 7, 10, 14 and 21.ResultsThe «optimum» PEEP levels on Day 1 were 11.0 (10.0–12.8) cmH2O and 10.0 (9.0–12.0) cmH2O on Day 7. Positive response to recruitment was observed on Day 1 in 27.6% and on Day 7 in 9.2% of patients. PEEP increase from 10 to 14 cmH2O and VT increase by 100 and 200 ml led to a significant decrease in CRS from Day 1 to Day 14 (p < 0.05). Ventilatory ratio was 2.2 (1.7–2,7) in non-survivors and in 1.9 (1.6–2.6) survivors on Day 1 and decreased on Day 7 in survivors only (p < 0.01). PaO2/FiO2 was 105.5 (76.2–141.7) mmHg in non-survivors on Day 1 and 136.6 (106.7–160.8) in survivors (p = 0.002). In survivors, PaO2/FiO2 rose on Day 3 (p = 0.008) and then between Days 7 and 10 (p = 0.046).ConclusionLung recruitability was low in COVID-19 and decreased during the course of the disease, but lung overdistension occurred at «intermediate» PEEP and VT levels. In survivors gas exchange improvements after Day 7 mismatched CRS.Trial registrationClinicalTrials.gov, NCT04445961. Registered 24 June 2020—Retrospectively registered.

Influence of the end inspiratory pause on respiratory mechanics and tidal gas distribution of surgical patients ventilated under a tailored open lung approach strategy: A randomised, crossover trial

BackgroundThe effect of modifying the end inspiratory pause (EIP) on respiratory mechanics and gas distribution of surgical patients ventilated with an open lung approach (OLA) has not been addressed before. MethodsProspective, randomised, crossover study carried out in a tertiary hospital. Subjects were assigned to receive an initial EIP of 10% or 30% of the total inspiratory time. We compared standard ventilation [time 0: tidal volume (VT) 7 mL × kg−1, respiratory rate (RR) 13, inspiratory:expiratory (I:E) rate 1:2, positive end-expiratory pressure (PEEP) 5 cm H2O and EIP 10% and 30% for groups 1 and 2, respectively) with tailored OLA (similar parameters except for a tailored PEEP after a stepwise recruitment manoeuvre), followed by a crossover assignment sequence between groups (times 2–4). ResultsWe included 32 adult subjects undergoing major surgery. Tailored OLA strategy was associated with a significant increase in PEEP, plateau pressure (Pplat), PaO2, and compliance of the respiratory system (CRS) with a significant decrease in driving pressure (Pdriv) and PaCO2, and a more homogeneous gas distribution in both groups. A significantly lower PEEP (p < 0.001), Pdriv (5 [5–6] versus 6.5 [6–8] cmH2O; p < 0.001) and mean airway pressure (Pmean; p < 0.001) together with a higher CRS (77 [67−87] versus 58 [52−70] ml*cmH2O−1; p < 0.001) were observed when an EIP of 30% was applied as compared to an EIP of 10%. ConclusionThe use of a tailored OLA strategy combined with a longer EIP is associated with a higher CRS, and a lower Pdriv, Pmean and PEEP. Additional studies are necessary to assess if the improved ventilatory conditions observed with a longer EIP are associated with better patients’ outcomes.Trial registration at clinicaltrials.gov with identifier: NCT03568786.

Lung Ultrasound and Electrical Impedance Tomography During Ventilator-Induced Lung Injury.

Lung damage during mechanical ventilation involves lung volume and alveolar water content, and lung ultrasound (LUS) and electrical impedance tomography changes are related to these variables. We investigated whether these techniques may detect any signal modification during the development of ventilator-induced lung injury (VILI). Experimental animal study. Experimental Department of a University Hospital. Forty-two female pigs (24.2 ± 2.0 kg). The animals were randomized into three groups (n = 14): high tidal volume (TV) (mean TV, 803.0 ± 121.7 mL), high respiratory rate (RR) (mean RR, 40.3 ± 1.1 beats/min), and high positive-end-expiratory pressure (PEEP) (mean PEEP, 24.0 ± 1.1 cm H2O). The study lasted 48 hours. At baseline and at 30 minutes, and subsequently every 6 hours, we recorded extravascular lung water, end-expiratory lung volume, lung strain, respiratory mechanics, hemodynamics, and gas exchange. At the same time-point, end-expiratory impedance was recorded relatively to the baseline. LUS was assessed every 12 hours in 12 fields, each scoring from 0 (presence of A-lines) to 3 (consolidation). In a multiple regression model, the ratio between extravascular lung water and end-expiratory lung volume was significantly associated with the LUS total score (p < 0.002; adjusted R2, 0.21). The variables independently associated with the end-expiratory difference in lung impedance were lung strain (p < 0.001; adjusted R2, 0.18) and extravascular lung water (p < 0.001; adjusted R2, 0.11). Data suggest as follows. First, what determines the LUS score is the ratio between water and gas and not water alone. Therefore, caution is needed when an improvement of LUS score follows a variation of the lung gas content, as after a PEEP increase. Second, what determines the end-expiratory difference in lung impedance is the strain level that may disrupt the intercellular junction, therefore altering lung impedance. In addition, the increase in extravascular lung water during VILI development contributed to the observed decrease in impedance.

A more gradual positive end-expiratory pressure increase reduces lung damage and improves cardiac function in experimental acute respiratory distress syndrome.

Increases in positive end-expiratory pressure (PEEP) or recruitment maneuvers may increase stress in lung parenchyma, extracellular matrix, and lung vessels; however, adaptative responses may occur. We evaluated the effects of PEEP on lung damage and cardiac function when increased abruptly, gradually, or more gradually in experimental mild/moderate acute respiratory distress syndrome (ARDS) induced by Escherichia coli lipopolysaccharide intratracheally. After 24 h, Wistar rats (n = 48) were randomly assigned to four mechanical ventilation strategies according to PEEP levels: 1) 3 cmH2O for 2 h (control); 2) 3 cmH2O for 1 h followed by an abrupt increase to 9 cmH2O for 1 h (no adaptation time); 3) 3 cmH2O for 30 min followed by a gradual increase to 9 cmH2O over 30 min then kept constant for 1 h (shorter adaptation time); and 4) more gradual increase in PEEP from 3 cmH2O to 9 cmH2O over 1 h and kept constant thereafter (longer adaptation time). At the end of the experiment, oxygenation improved in the shorter and longer adaptation time groups compared with the no-adaptation and control groups. Diffuse alveolar damage and expressions of interleukin-6, club cell protein-16, vascular cell adhesion molecule-1, amphiregulin, decorin, and syndecan were higher in no adaptation time compared with other groups. Pulmonary arterial pressure was lower in longer adaptation time than in no adaptation (P = 0.002) and shorter adaptation time (P = 0.025) groups. In this model, gradually increasing PEEP limited lung damage and release of biomarkers associated with lung epithelial/endothelial cell and extracellular matrix damage, as well as the PEEP-associated increase in pulmonary arterial pressure.NEW & NOTEWORTHY In a rat model of Escherichia coli lipopolysaccharide-induced mild/moderate acute respiratory distress syndrome, a gradual PEEP increase (shorter adaptation time) effectively mitigated histological lung injury and biomarker release associated with lung inflammation, damage to epithelial cells, endothelial cells, and the extracellular matrix compared with an abrupt increase in PEEP. A more gradual PEEP increase (longer adaptation time) decreased lung damage, pulmonary vessel compression, and pulmonary arterial pressure.

Transoesophageal Ultrasound Assessment of Lung Aeration in Patients With Acute Respiratory Distress Syndrome.

Introduction: The effect of positive end-expiratory pressure (PEEP) depends closely on the potential for lung recruitment. Bedside assessment of lung recruitability is crucial for personalized lung-protective mechanical ventilation in acute respiratory distress syndrome (ARDS) patients.Methods: We developed a transoesophageal lung ultrasound (TE-LUS) method in which a quantitative (computer-assisted) grayscale determination served as a guide to PEEP-induced lung recruitment. The method is based on the following hypothesis: when the PEEP increases, inflation of the recruited alveoli leads to significant changes in the air/water ratio. Normally ventilated areas are hypoechoic because the ultrasound waves are weakly reflected while poorly aerated areas or non-aerated areas are hyperechoic. We calculated the TE-LUS re-aeration score (RAS) as the ratio of the mean gray scale level at low PEEP to that value at high PEEP for the lower and upper lobes. A RAS > 1 indicated an increase in ventilated area. We used this new method to detect changes in ventilation in patients with a low (<0.5) vs. high (≥0.5) recruitment-to-inflation (R/I) ratio (i.e., the ratio between the recruited lung compliance and the respiratory system compliance at low PEEP).Results: We included 30 patients with moderate-to-severe ARDS. In patients with a high R/I ratio, the TE-LUS RAS was significantly higher in the lower lobes than in the upper lobes (1.20 [1.12–1.63] vs. 1.05 [0.89–1.38]; p = 0.05). Likewise, the TE-LUS RAS in the lower lobes was significantly higher in the high R/I group than in the low R/I group (1.20 [1.12–1.63] vs. 1.07 [1.00–1.20]; p = 0.04).Conclusion: The increase in PEEP induces a substantial gain in the ventilation detected by TE-LUS of poorly or non-aerated lower lobes (dependent lung regions), especially in patients with a high R/I ratio.

Effect of positive end-expiratory pressure on additional passive ventilation generated by CPR compressions in a porcine model

BackgroundCompressions given during cardiopulmonary resuscitation generate small, ineffective passive ventilations through oscillating waves. Positive end-expiratory pressure increases the volume of these passive ventilations; however, its effect on passive ventilation is unknown. Our objective was to determine if increasing positive end-expiratory pressure during cardiopulmonary resuscitation increases passive ventilation generated by compressions to a clinically significant point. This study was conducted on 13 Landrace-Yorkshire pigs. After inducing cardiac arrest with bupivacaine, cardiopulmonary resuscitation was performed with a LUCAS 3.1. During cardiopulmonary resuscitation, pigs were ventilated at a positive end-expiratory pressure of 0, 5, 10, 15, 20 cmH2O (randomly determined) for 9 min. Using the NM3 respiratory monitoring device, expired minute ventilation and volumetric capnography were measured. Arterial blood gas was obtained for each positive end-expiratory pressure level to compare the effects of positive end-expiratory pressure on carbon dioxide.ResultsIncreasing positive end-expiratory pressure from 0 to 20 cmH2O increased the mean (SEM) expired minute ventilation from 6.33 (0.04) to 7.33 (0.04) mL/min. With the 5-cmH2O incremental increases in positive end-expiratory pressure from 0 to 20 cmH2O, volumetric capnography increased from a mean (SEM) of 94.19 (0.78) to 115.18 (0.8) mL/min, except for 15 cmH2O, which showed greater carbon dioxide exhalation with volumetric capnography compared with 20 cmH2O. PCO2 declined significantly as positive end-expiratory pressure was increased from 0 to 20 cmH2O.ConclusionsWhen increasing positive end-expiratory pressure from 0 to 20, the contribution to overall ventilation from gas oscillations generated by the compressions became more significant, and may even lead to hypocapnia, especially when using positive end-expiratory pressures between 15 and 20.

Indications for and Utility of Tracheal Aspirate Cultures for the Diagnosis of VAI

Background: Tracheal aspirate bacterial cultures are routinely collected in mechanically ventilated children for the evaluation of ventilator-associated infections (VAIs). However, frequent bacterial colonization of endotracheal and tracheostomy tubes contribute to the marginal performance characteristics of the test for diagnosing VAI. Published literature characterizing drivers of culture collection and the predictive value of positive cultures are limited. Methods: This single-center, retrospective cohort study included children admitted to the pediatric intensive care unit who were receiving mechanical ventilation for at least 48 hours and had 1 or more semiquantitative tracheal aspirate cultures collected between September 1, 2019, and August 31, 2020. Indications for culture collection were determined through medical record review and included fever, hypothermia, tracheal secretion changes, radiographic pneumonia, increased oxygen requirement, and/or increased positive end-expiratory pressure (PEEP). A positive culture was defined as moderate or heavy growth of a noncommensal bacterial organism. A purulent Gram stain was defined as detection of moderate or many white blood cells. Diagnosis of VAI was based on treating-clinician documentation and was ascertained through medical record review. Logistic regression accounting for clustering by patient was performed to estimate the association between indications for culture collection and (1) culture positivity, (2) purulent Gram stain, and (3) diagnosis of VAI. Results: In total, 625 tracheal aspirate cultures were performed in 261 unique patients. Common indications for culture collection included isolated fever or hypothermia (n = 124, 20%), fever with an increase in oxygen requirement or PEEP (n = 71, 11%), isolated increase in oxygen requirement or PEEP (n = 67, 11%), or isolated secretion change (n = 54, 9%) (Figure 1). Overall, 230 cultures (37%) were positive and 218 (35%) Gram stains were purulent. There were no associations between culture indications and a positive culture. Presence of isolated fever was negatively associated with a purulent Gram stain (odds ratio [OR], 0.49; 95% CI, 0.30–0.81; P = .005); otherwise, there were no associations between indication and purulent Gram stain. Finally, in a multivariable model, odds of VAI diagnosis increased with both the number of indications for culture collection and purulent Gram stain, but not with positive culture (Figure 2). Conclusions: Number and type of clinical signs were not associated with tracheal aspirate culture positivity or purulence on Gram stain, but they were associated with a clinical diagnosis of VAI. These findings suggest that positive tracheal aspirate cultures may not aid clinicians in the diagnosis of VAI, and they highlight the opportunity for improved diagnostic stewardship.Funding: NoDisclosures: None

Knobmanship: Dialing Up Understanding of VAE Triggers

Background: Mechanical ventilation is a lifesaving therapy for critically ill patients. Hospitals perform surveillance for the NHSN for ventilator-associated events (VAE) by monitoring mechanically ventilated patients for metrics that are generally thought to be objective and preventable and that lead to poor patient outcomes. The VAE definition is met in a stepwise manner; initially, a ventilator-associated condition (VAC) is triggered with an increase in positive end-expiratory pressure (PEEP, &gt;3 cm H2O) or fraction of inspired oxygen (FIO2, 0.20 or 20 points) after a period of stability or improvement on the ventilator. We believe that many reported VAEs could be avoided by provider and respiratory therapy attention to “knobmanship.” We define knobmanship as knowledge of the VAE definition and trigger points combined with appropriate clinical care for mechanically ventilated patients while avoiding unnecessary triggering of the VAE definition by avoiding small unneeded changes in PEEP or FIO2. Methods: We performed a chart review of 283 patients who had a reported VAE to the NHSN between January 1, 2019, and December 31, 2020. We collected data including type of VAE, VAE triggering criteria, and clinical course. Results: Of the 283 VAEs, 59 were triggered by a PEEP increase from 5 to 8 with stable or decreasing FIO2. Of the 59 VAEs, 33 were VACs, 18 were infection-related ventilator- associated complications (IVACs), and 8 were possible ventilator-associated pneumonia (PVAP). Most of these transient changes in PEEP were deemed clinically unnecessary. A 21% reduction of VAEs reported to the NSHN over the 2-year review period could have been avoided by knobmanship. Conclusions: The VAE definition may often be triggered by provider bias to the ventilator settings rather than what the patient’s clinical-condition requires. Attention to knobmanship may result in substantial decrease in reported VAE.Funding: NoDisclosures: None

Lung Ultrasonography in the Monitoring of Intraoperative Recruitment Maneuvers

Introduction: Postoperative respiratory failure is a serious problem in patients who undergo general anesthesia. Approximately 90% of mechanically ventilated patients during the surgery may develop atelectasis that leads to perioperative complications. Aim: The aim of this study is to determine whether it is possible to optimize recruitment maneuvers with the use of chest ultrasonography, thus limiting the risk of respiratory complications in patients who undergo general anesthesia. Methodology: The method of incremental increases in positive end-expiratory pressure (PEEP) values with simultaneous continuous ultrasound assessments was employed in mechanically ventilated patients. Results: The study group comprised 100 patients. The employed method allowed for atelectasis reduction in 91.9% of patients. The PEEP necessary to reverse areas of atelectasis averaged 17cmH2O, with an average peak pressure of 29cmH2O. The average PEEP that prevented repeat atelectasis was 9cmH2O. A significant improvement in lung compliance and saturation was obtained. Conclusions: Ultrasound-guided recruitment maneuvers facilitate the patient-based adjustment of the process. Consequently, the reduction in ventilation pressures necessary to aerate intraoperative atelectasis is possible, with the simultaneous reduction in the risk of procedure-related complications.