Positive End-expiratory Pressure Levels Research Articles

Aeration strategy at birth does not impact carotid haemodynamics in preterm lambs

BackgroundThe impact of different respiratory strategies at birth on the preterm lung is well understood; however, concerns have been raised that lung recruitment may impede cerebral haemodynamics. This study aims to examine the effect of three different ventilation strategies on carotid blood flow, carotid artery oxygen content and carotid oxygen delivery.Methods124–127-day gestation apnoeic intubated preterm lambs studied as part of a larger programme primarily assessing lung injury were randomised to positive pressure ventilation with positive end-expiratory pressure (PEEP) 8 cmH2O (No-RM; n = 12), sustained inflation (SI; n = 15) or dynamic PEEP strategy (DynPEEP; maximum PEEP 14 or 20 cmH2O, n = 41) at birth, followed by 90 min of standardised ventilation. Haemodynamic data were continuously recorded, with intermittent arterial blood gas analysis.ResultsOverall carotid blood flow measures were comparable between strategies. Except for mean carotid blood flow that was significantly lower for the SI group compared to the No-RM and DynPEEP groups over the first 3 min (p < 0.0001, mixed effects model). Carotid oxygen content and oxygen delivery were similar between strategies. Maximum PEEP level did not alter cerebral haemodynamic measures.ConclusionsAlthough there were some short-term variations in cerebral haemodynamics between different PEEP strategies and SI, these were not sustained.ImpactDifferent pressure strategies to facilitate lung aeration at birth in preterm infants have been proposed. There is minimal information on the effect of lung recruitment on cerebral haemodynamics.This is the first study that compares the effect of sustained lung inflation and dynamic and static positive end-expiratory pressure on cerebral haemodynamics.We found that the different ventilation strategies did not alter carotid blood flow, carotid oxygen content or carotid oxygen delivery.This preclinical study provides some reassurance that respiratory strategies designed to focus on lung aeration at birth may not impact cerebral haemodynamics in preterm neonates.

Brain-Lung Crosstalk: Management of Concomitant Severe Acute Brain Injury and Acute Respiratory Distress Syndrome.

Purpose of ReviewTo summarize pathophysiology, key conflicts, and therapeutic approaches in managing concomitant severe acute brain injury (SABI) and acute respiratory distress syndrome (ARDS).Recent FindingsARDS is common in SABI and independently associated with worse outcomes in all SABI subtypes. Most landmark ARDS trials excluded patients with SABI, and evidence to guide decisions is limited in this population. Potential areas of conflict in the management of patients with both SABI and ARDS are (1) risk of intracranial pressure (ICP) elevation with high levels of positive end-expiratory pressure (PEEP), permissive hypercapnia due to lung protective ventilation (LPV), or prone ventilation; (2) balancing a conservative fluid management strategy with ensuring adequate cerebral perfusion, particularly in patients with symptomatic vasospasm or impaired cerebrovascular blood flow; and (3) uncertainty about the benefit and harm of corticosteroids in this population, with a mortality benefit in ARDS, increased mortality shown in TBI, and conflicting data in other SABI subtypes. Also, the widely adapted partial pressure of oxygen (PaO2) target of > 55 mmHg for ARDS may exacerbate secondary brain injury, and recent guidelines recommend higher goals of 80–120 mmHg in SABI. Distinct pathophysiology and trajectories among different SABI subtypes need to be considered.SummaryThe management of SABI with ARDS is highly complex, and conventional ARDS management strategies may result in increased ICP and decreased cerebral perfusion. A crucial aspect of concurrent management is to recognize the risk of secondary brain injury in the individual patient, monitor with vigilance, and adjust management during critical time windows. The care of these patients requires meticulous attention to oxygenation and ventilation, hemodynamics, temperature management, and the neurological exam. LPV and prone ventilation should be utilized, and supplemented with invasive ICP monitoring if there is concern for cerebral edema and increased ICP. PEEP titration should be deliberate, involving measures of hemodynamic, pulmonary, and brain physiology. Serial volume status assessments should be performed in SABI and ARDS, and fluid management should be individualized based on measures of brain perfusion, the neurological exam, and cardiopulmonary status. More research is needed to define risks and benefits in corticosteroids in this population.

Tidal Volume and Positive End-expiratory Pressure and Postoperative Hypoxemia during General Anesthesia: A Single-center Multiple Crossover Factorial Cluster Trial.

Intraoperative mechanical ventilation is a major component of general anesthesia. The extent to which various intraoperative tidal volumes and positive end-expiratory pressures (PEEP) effect on postoperative hypoxia and lung injury remains unclear. We hypothesized that adults having orthopedic surgery, ventilation using different tidal volumes and PEEP levels affect the oxygenation within first hour in the postoperative care unit. We conducted a two-by-two factorial crossover cluster trial at the Cleveland Clinic Main Campus. We enrolled patients having orthopedic surgery with general anesthesia who were assigned to factorial clusters with tidal volumes of 6 or 10 ml/kg of predicted body weight and to PEEP of 5 or 8 cm H2O in 1-week clusters. The primary outcome was the effect of tidal volume or PEEP on time-weighted average peripheral oxygen saturation measured by pulse oximetry divided by the fraction of inspired oxygen (Spo2/Fio2 ratio) during the initial postoperative hour. We enrolled 2,860 patients who had general anesthesia for orthopedic surgery from September 2018 through October 2020. The interaction between tidal volume and PEEP was not significant (P = 0.565). The mean ± SD time-weighted average of Spo2/Fio2 ratio was 353 ± 47 and not different in patients assigned to high and low tidal volume (estimated effect, 3.5%; 97.5% CI, -0.4% to 7.3%; P = 0.042), for those assigned to high and low PEEP (estimated effect, -0.2%; 97.5% CI, -4.0% to 3.6%; P = 0.906). We did not find significant difference in ward Spo2/Fio2 ratio, pulmonary complications, and duration of hospitalization among patients assigned to various tidal volumes and PEEP levels. Among adults having major orthopedic surgery, postoperative oxygenation is similar, with tidal volumes between 6 and 10 ml/kg and PEEP between 5 and 8 cm H2O. Our results suggest that any combination of tidal volumes between 6 and 10 ml/kg and PEEP between 5 versus 8 ml cm H2O can be used safely for orthopedic surgery.

Recruitable alveolar collapse and overdistension during laparoscopic gynecological surgery and mechanical ventilation: a prospective clinical study

BackgroundLaparoscopic surgery in Trendelenburg position may impede mechanical ventilation (MV) due to positioning and high intra-abdominal pressure. We sought to identify the positive end-expiratory pressure (PEEP) levels necessary to counteract atelectasis formation (“Open-Lung-PEEP”) and to provide an equal balance between overdistension and alveolar collapse (“Best-Compromise-PEEP”).MethodsIn 30 patients undergoing laparoscopic gynecological surgery, relative overdistension and alveolar collapse were assessed with electrical impedance tomography (EIT) during a decremental PEEP trial ranging from 20 to 4 cmH2O in supine position without capnoperitoneum and in Trendelenburg position with capnoperitoneum.ResultsIn supine position, the median Open-Lung-PEEP was 12 (8–14) cmH2O with 8.7 (4.7–15.5)% of overdistension and 1.7 (0.4–2.2)% of collapse. Best-Compromise-PEEP was 8 (6.5–10) cmH2O with 4.2 (2.4–7.2)% of overdistension and 5.1 (3.9–6.5)% of collapse. In Trendelenburg position with capnoperitoneum, Open-Lung-PEEP was 18 (18–20) cmH 2 O (p < 0.0001 vs supine position) with 1.8 (0.5–3.9)% of overdistension and 0 (0–1.2)% of collapse and Best-Compromise-PEEP was 18 (16–20) cmH2O (p < 0.0001 vs supine position) with 1.5 (0.7–3.0)% of overdistension and 0.2 (0–2.7)% of collapse. Open-Lung-PEEP and Best-Compromise-PEEP were positively correlated with body mass index during MV in supine position but not in Trendelenburg position.ConclusionThe PEEP levels required for preventing alveolar collapse and for balancing collapse and overdistension in Trendelenburg position with capnoperitoneum were significantly higher than those required for achieving the same goals in supine position without capnoperitoneum. Even with high PEEP levels, alveolar overdistension was negligible during MV in Trendelenburg position with capnoperitoneum.Trial registrationThis study was prospectively registered at German Clinical Trials registry (DRKS00016974).

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).

Induction of severe hypoxemia and low lung recruitability for the evaluation of therapeutic ventilation strategies: a translational model of combined surfactant-depletion and ventilator-induced lung injury

BackgroundModels of hypoxemic lung injury caused by lavage-induced pulmonary surfactant depletion are prone to prompt recovery of blood oxygenation following recruitment maneuvers and have limited translational validity. We hypothesized that addition of injurious ventilation following surfactant-depletion creates a model of the acute respiratory distress syndrome (ARDS) with persistently low recruitability and higher levels of titrated “best” positive end-expiratory pressure (PEEP) during protective ventilation.MethodsTwo types of porcine lung injury were induced by lung lavage and 3 h of either protective or injurious ventilation, followed by 3 h of protective ventilation (N = 6 per group). Recruitment maneuvers (RM) and decremental PEEP trials comparing oxygenation versus dynamic compliance were performed after lavage and at 3 h intervals of ventilation. Pulmonary gas exchange function, respiratory mechanics, and ventilator-derived parameters were assessed after each RM to map the course of injury severity and recruitability.ResultsLung lavage impaired respiratory system compliance (Crs) and produced arterial oxygen tensions (PaO2) of 84±13 and 80±15 (FIO2 = 1.0) with prompt increase after RM to 270–395 mmHg in both groups. After subsequent 3 h of either protective or injurious ventilation, PaO2/FIO2 was 104±26 vs. 154±123 and increased to 369±132 vs. 167±87 mmHg in response to RM, respectively. After additional 3 h of protective ventilation, PaO2/FIO2 was 120±15 vs. 128±37 and increased to 470±68 vs. 185±129 mmHg in response to RM, respectively. Subsequently, decremental PEEP titration revealed that Crs peaked at 36 ± 10 vs. 25 ± 5 ml/cm H2O with PEEP of 12 vs. 16 cmH2O, and PaO2/FIO2 peaked at 563 ± 83 vs. 334 ± 148 mm Hg with PEEP of 16 vs. 22 cmH2O in the protective vs. injurious ventilation groups, respectively. The large disparity of recruitability between groups was not reflected in the Crs nor the magnitude of mechanical power present after injurious ventilation, once protective ventilation was resumed.ConclusionAddition of transitory injurious ventilation after lung lavage causes prolonged acute lung injury with diffuse alveolar damage and low recruitability yielding high titrated PEEP levels. Mimicking lung mechanical and functional characteristics of ARDS, this porcine model rectifies the constraints of single-hit lavage models and may enhance the translation of experimental research on mechanical ventilation strategies.

Potential rebreathing of carbon dioxide during noninvasive ventilation provided by critical care ventilator

BackgroundCritical care ventilators are frequently used to provide noninvasive ventilation (NIV) support to critically ill patients. Questions remain regarding carbon dioxide (CO2) clearance while using a critical care ventilator and dual limb circuit with various patient interfaces. The purpose of this study is to determine the positive end expiratory pressure (PEEP) level required to effectively washout CO2 for full-face and oronasal masks when using a dual limb circuit.MethodThis randomized crossover trial was conducted at an academic medical center in the Midwest United States. After obtaining informed consent, eight healthy volunteers were placed on a 980 Puritan Bennett (Medtronic, Minneapolis, MN) ventilator operating in the NIV mode. All subjects performed 20 min of breathing on four levels of PEEP (0, 2, 4, and 5 cm H2O) and pressure support of 5 cm H2O. NIV settings were applied to four masks (two oronasal and two full-face masks) that were randomly selected with a 5-min washout period between each mask. The fraction of inspired carbon dioxide (FICO2) was sampled/monitored with a nasal cannula using a Capnostream 20p monitor (Medtronic, Minneapolis, MN) and reported as percentages. A Kruskal–Wallis test was used to reveal significant differences across PEEP levels. Pairwise comparisons of the groups were made using Mann–Whitney tests with a family-wise error correction.ResultsMedian (IQR) FICO2 was significantly lower 0.0% (0%–0.92%) at PEEP of 5 compared to 1.83% (0.66%–4.0%; p < 0.001) at PEEP of 0 or 1.0% (0.33%–2.66%; p = 0.002) at PEEP of 2. FICO2 was significantly lower 0.5% (0%–1.92%) at PEEP of 4 compared to PEEP of 0 (p = 0.001).ConclusionA PEEP level of at least 5 cm H2O associated with the reported leak was required to minimize the likelihood of CO2 rebreathing while using a critical care ventilator to provide NIV with a double limb circuit and full-face or oronasal masks.

Oxygenation versus driving pressure for determining the best positive end-expiratory pressure in acute respiratory distress syndrome

ObjectiveThe aim of this prospective longitudinal study was to compare driving pressure and absolute PaO2/FiO2 ratio in determining the best positive end-expiratory pressure (PEEP) level.Patients and methodsIn 122 patients with acute respiratory distress syndrome, PEEP was increased until plateau pressure reached 30 cmH2O at constant tidal volume, then decreased at 15-min intervals, to 15, 10, and 5 cmH2O. The best PEEP by PaO2/FiO2 ratio (PEEPO2) was defined as the highest PaO2/FiO2 ratio obtained, and the best PEEP by driving pressure (PEEPDP) as the lowest driving pressure. The difference between the best PEEP levels was compared to a non-inferiority margin of 1.5 cmH2O.Main resultsThe best mean PEEPO2 value was 11.9 ± 4.7 cmH2O compared to 10.6 ± 4.1 cmH2O for the best PEEPDP: mean difference = 1.3 cmH2O (95% confidence interval [95% CI], 0.4–2.3; one-tailed P value, 0.36). Only 46 PEEP levels were the same with the two methods (37.7%; 95% CI 29.6–46.5). PEEP level was ≥ 15 cmH2O in 61 (50%) patients with PEEPO2 and 39 (32%) patients with PEEPDP (P = 0.001).ConclusionDepending on the method chosen, the best PEEP level varies. The best PEEPDP level is lower than the best PEEPO2 level. Computing driving pressure is simple, faster and less invasive than measuring PaO2. However, our results do not demonstrate that one method deserves preference over the other in terms of patient outcome.Clinical trial number: #ACTRN12618000554268. Registered 13 April 2018.

Effects of PEEP on regional ventilation-perfusion mismatch in the acute respiratory distress syndrome

PurposeIn the acute respiratory distress syndrome (ARDS), decreasing Ventilation-Perfusion left( {{{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}}} right) mismatch might enhance lung protection. We investigated the regional effects of higher Positive End Expiratory Pressure (PEEP) on {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} mismatch and their correlation with recruitability. We aimed to verify whether PEEP improves regional {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} mismatch, and to study the underlying mechanisms.MethodsIn fifteen patients with moderate and severe ARDS, two PEEP levels (5 and 15 cmH2O) were applied in random order. {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} mismatch was assessed by Electrical Impedance Tomography at each PEEP. Percentage of ventilation and perfusion reaching different ranges of {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} ratios were analyzed in 3 gravitational lung regions, leading to precise assessment of their distribution throughout different {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} mismatch compartments. Recruitability between the two PEEP levels was measured by the recruitment-to-inflation ratio method.ResultsIn the non-dependent region, at higher PEEP, ventilation reaching the normal {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} compartment (p = 0.018) increased, while it decreased in the high {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} one (p = 0.023). In the middle region, at PEEP 15 cmH2O, ventilation and perfusion to the low {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} compartment decreased (p = 0.006 and p = 0.011) and perfusion to normal {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} increased (p = 0.003). In the dependent lung, the percentage of blood flowing through the non-ventilated compartment decreased (p = 0.041). Regional {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} mismatch improvement was correlated to lung recruitability and changes in regional tidal volume.ConclusionsIn patients with ARDS, higher PEEP optimizes the distribution of both ventilation (in the non-dependent areas) and perfusion (in the middle and dependent lung). Bedside measure of recruitability is associated with improved {{dot{V}} mathord{left/ {vphantom {{dot{V}} {dot{Q}}}} right. kern-nulldelimiterspace} {dot{Q}}} mismatch.

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.

Validation of lung sonography in the implementation of open lung strategy as a recruitment maneuver versus traditional sustained inflation in acute respiratory distress syndrome patients

Introduction Acute respiratory distress syndrome (ARDS) is a serious problem in critically ill patients with high mortality rates. Lung recruitment maneuvers (RM) are important in the treatment of ARDS with an aim to improve oxygenation. There are many approved methods for lung recruitment like the traditional sustained inflation technique and the stepladder positive end-expiratory pressure (PEEP) titration technique. The traditional methods to evaluate RM like computed tomography and pressure–volume curves showed some limitation and disadvantages. Thus, bedside ultrasonography (US) could be a safe bedside tool to evaluate lung aeration and the effectiveness of RM defining the optimum PEEP needed and preventing lung overdistension. Aim To evaluate the usefulness of lung US as a guide to follow up RM by PEEP titration technique in comparison to sustained inflation technique. Patients and methods In all, 40 ARDS patients were segregated into two groups: group 1 included 20 patients who were subjected to traditional sustained inflation RM and group 2 included 20 patients were subjected to sonar-guided lung recruitment. US scoring, PO2, PO2/FiO2, and lung compliance were used to evaluate the pulmonary recruitment end point defining the best PEEP. Results Lung compliance, PO2, and PO2/FiO2 were significantly increased after RM in both groups (P&lt;0.05); however, there was no statistically significant difference between the two groups. The best PEEP in group 1 and group 2 were 20.60±3.485 and 15.90±5.340, respectively, with a significant difference between the two groups (P=0.002). There was no statically significant difference between the two groups regarding complication, vent days and ICU days. Conclusion Bedside US can be very useful in the evaluation and management of mechanically ventilated patients in ICUs and to guide the RM in ARDS patients. There is no significant difference between the sustained inflation RM and the sonar-guided stepwise PEEP titration RM regarding oxygenation and compliance except for the level of PEEP reached, which is lower in the stepwise PEEP titration group giving less potentiality for complications.

Effect of Prone Positioning With Individualized Positive End-Expiratory Pressure in Acute Respiratory Distress Syndrome Using Electrical Impedance Tomography.

Background: Positive end-expiratory pressure (PEEP) optimization during prone positioning remains under debate in acute respiratory distress syndrome (ARDS). This study aimed to investigate the effect of prone position on the optimal PEEP guided by electrical impedance tomography (EIT). Methods: We conducted a retrospective analysis on nineteen ARDS patients in a single intensive care unit. All patients underwent PEEP titration guided by EIT in both supine and prone positions. EIT-derived parameters, including center of ventilation (CoV), regional ventilation delay (RVD), percentage of overdistension (OD) and collapse (CL) were calculated. Optimal PEEP was defined as the PEEP level with minimal sum of OD and CL. Patients were divided into two groups: 1) Lower Optimal PEEPPP (LOP), where optimal PEEP was lower in the prone than in the supine position, and 2) Not-Lower Optimal PEEPPP (NLOP), where optimal PEEP was not lower in the prone compared with the supine position. Results: Eleven patients were classified as LOP (9 [8-9] vs. 12 [10-15] cmH2O; PEEP in prone vs. supine). In the NLOP group, optimal PEEP increased after prone positioning in four patients and remained unchanged in the other four patients. Patients in the LOP group had a significantly higher body mass index (26 [25-28] vs. 22 [17-25] kg/m2; p = 0.009) and lower ICU mortality (0/11 vs. 4/8; p = 0.018) compared with the NLOP group. Besides, PaO2/FiO2 increased significantly during prone positioning in the LOP group (238 [170-291] vs. 186 [141-195] mmHg; p = 0.042). CoV and RVD were also significantly improved during prone positioning in LOP group. No such effects were found in the NLOP group. Conclusion: Broad variability in optimal PEEP between supine and prone position was observed in the studied ARDS patients. Not all patients showed decreased optimal PEEP during prone positioning. Patients with higher body mass index exhibited lower optimal PEEP in prone position, better oxygenation and ventilation homogeneity.

Risk Factors for Mortality in Mechanically Ventilated Patients with COVID-19 in a Mississippi Community Health System.

To evaluate differences between survivors versus nonsurvivors undergoing mechanical ventilation for coronavirus disease 2019 (COVID-19)-associated respiratory failure at two community medical centers. This was a multicenter, retrospective cohort analysis of all adult patients mechanically ventilated for COVID-19-associated respiratory failure in two community hospital intensive care units in southern Mississippi from March 15, 2020 through October 10, 2020. Among 56 patients requiring mechanical ventilation, the mortality rate was 75% (42/56). Expired patients were intubated later (2 vs 5 days, 95% confidence interval [CI] 6.314-0.8041, P = 0.0983), had lower PaO2:FiO2 ratios (65 vs 77.5 mm Hg, 95% CI 36.08-59.03, P = 0.6305), and tolerated lower levels of positive end-expiratory pressure (7.9 vs 12.6 cm H2O, 95% CI 0.1373-6.722, P = 0.0415) at the time of intubation. Our results suggest that earlier intubation may be associated with reduced mortality in patients with COVID-19-associated respiratory failure and should be further evaluated in the form of a randomized controlled trial.

Asymmetrical Lung Injury: Management and Outcome.

Among mechanically ventilated patients, asymmetrical lung injury is probably extremely frequent in the intensive care unit but the lack of standardized measurements does not allow to describe any prevalence among mechanically ventilated patients. Many past studies have focused only on unilateral injury and have mostly described the effect of lateral positioning. The good lung put downward might receive more perfusion while the sick lung placed upward receive more ventilation than supine. This usually results in better oxygenation but can also promote atelectasis in the healthy lung and no consensus has emerged on the clinical indication of this posture. Recently, electrical impedance tomography (EIT) has allowed for the first time to precisely describe the distribution of ventilation in each lung and to better study asymmetrical lung injury. At low positive-end-expiratory pressure (PEEP), a very heterogeneous ventilation exists between the two lungs and the initial increase in PEEP first helps to recruit the sick lung and protect the healthier lung. However, further increasing PEEP distends the less injured lung and must be avoided. The right level can be found using EIT and transpulmonary pressure. In addition, EIT can show that in the two lungs, airway closure is present but with very different airway opening pressures (AOPs) which cannot be identified on a global assessment. This may suggest a very different PEEP level than on a global assessment. Lastly, epidemiological studies suggest that in hypoxemic patients, the number of quadrants involved has a strong prognostic value. The number of quadrants is more important than the location of the unilateral or bilateral nature of the involvement for the prognosis, and hypoxemic patients with unilateral lung injury should probably be considered as requiring lung protective ventilation as classical acute respiratory distress syndrome.

Clinical Implications of Determining Individualized Positive End-Expiratory Pressure Using Electrical Impedance Tomography in Post-Cardiac Surgery Patients: A Prospective, Non-Randomized Interventional Study.

Optimal positive end-expiratory pressure (PEEP) can induce sustained lung function improvement. This prospective, non-randomized interventional study aimed to investigate the effect of individualized PEEP determined using electrical impedance tomography (EIT) in post-cardiac surgery patients (n = 35). Decremental PEEP trials were performed from 20 to 4 cmH2O in steps of 2 cmH2O, guided by EIT. PEEP levels preventing ventilation loss in dependent lung regions (PEEPONLINE) were set. Ventilation distributions and oxygenation before the PEEP trial, and 5 min and 1 h after the PEEPONLINE setting were examined. Furthermore, we analyzed the saved impedance data offline to determine the PEEP levels that provided the best compromise between overdistended and collapsed lung (PEEPODCL). Ventilation distributions of dependent regions increased at 5 min after the PEEPONLINE setting compared with those before the PEEP trial (mean ± standard deviation, 41.3 ± 8.5% vs. 49.1 ± 9.3%; p < 0.001), and were maintained at 1 h thereafter (48.7 ± 9.4%, p < 0.001). Oxygenation also showed sustained improvement. Rescue oxygen therapy (high-flow nasal cannula, noninvasive ventilation) after extubation was less frequent in patients with PEEPONLINE ≥ PEEPODCL than in those with PEEPONLINE < PEEPODCL (1/19 vs. 6/16; p = 0.018). EIT-guided individualized PEEP stabilized the improvement in ventilation distribution and oxygenation. Individual PEEP varies with EIT measures, and may differentially affect oxygenation after cardiac surgery.

Comparison of Global and Regional Compliance-Guided Positive End-Expiratory Pressure Titration on Regional Lung Ventilation in Moderate-to-Severe Pediatric Acute Respiratory Distress Syndrome.

PurposeTo investigate the difference in the positive end-expiratory pressure (PEEP) selected with chest electrical impedance tomography (EIT) and with global dynamic respiratory system compliance (Crs) in moderate-to-severe pediatric acute respiratory distress syndrome (pARDS).MethodsPatients with moderate-to-severe pARDS (PaO2/FiO2 < 200 mmHg) were retrospectively included. On the day of pARDS diagnosis, two PEEP levels were determined during the decremental PEEP titration for each individual using the best compliance (PEEPC) and EIT-based regional compliance (PEEPEIT) methods. The differences of global and regional compliance (for both gravity-dependent and non-dependent regions) under the two PEEP conditions were compared. In addition, the EIT-based global inhomogeneity index (GI), the center of ventilation (CoV), and standard deviation of regional delayed ventilation (RVDSD) were also calculated and compared.ResultsA total of 12 children with pARDS (5 with severe and 7 with moderate pARDS) were included. PEEPC and PEEPEIT were identical in 6 patients. In others, the differences were only ± 2 cm H2O (one PEEP step). There were no statistical differences in global compliance at PEEPC and PEEPEIT [28.7 (2.84–33.15) vs. 29.74 (2.84–33.47) ml/cm H2O median (IQR), p = 0.028 (the significant level after adjusted for multiple comparison was 0.017)]. Furthermore, no differences were found in regional compliances and other EIT-based parameters measuring spatial and temporal ventilation distributions.ConclusionAlthough EIT provided information on ventilation distribution, PEEP selected with the best Crs might be non-inferior to EIT-guided regional ventilation in moderate-to-severe pARDS. Further study with a large sample size is required to confirm the finding.

Cardiovascular and Gas Exchange Effects of Individualized Positive End-Expiratory Pressures in Cats Anesthetized With Isoflurane.

ObjectivesTo compare the effects of four levels of end-expiratory pressure [zero (ZEEP) and three levels of positive end-expiratory pressure (PEEP)] on the cardiovascular system and gas exchange of cats anesthetized with isoflurane and mechanically ventilated for 3 h with a tidal volume of 10 ml/kg.Study DesignProspective, randomized, controlled trial.AnimalsSix healthy male neutered purpose-bred cats.MethodsAnesthesia was induced with isoflurane and maintained at 1.3 minimum alveolar concentration. PEEP of maximal respiratory compliance (PEEPmaxCrs) was identified in a decremental PEEP titration, and cats were randomly ventilated for 3 h with one of the following end-expiratory pressures: ZEEP, PEEPmaxCrs minus 2 cmH2O (PEEPmaxCrs−2), PEEPmaxCrs, and PEEPmaxCrs plus 2 cmH2O (PEEPmaxCrs+2). Cardiovascular and gas exchange variables were recorded at 5, 30, 60, 120, and 180 min (T5 to T180, respectively) of ventilation and compared between and within ventilation treatments with mixed-model ANOVA followed by Dunnet's and Tukey's tests (normal distribution) or Friedman test followed by the Dunn's test (non-normal distribution). Significance to reject the null hypothesis was considered p < 0.05.ResultsMean arterial pressure (MAP—mmHg) was lower in PEEPmaxCrs+2 [63 (49–69); median (range)] when compared to ZEEP [71 (67–113)] at T5 and stroke index (ml/beat/kg) was lower in PEEPmaxCrs+2 (0.70 ± 0.20; mean ± SD) than in ZEEP (0.90 ± 0.20) at T60. Cardiac index, oxygen delivery index (DO2I), systemic vascular resistance index, and shunt fraction were not significantly different between treatments. The ratio between arterial partial pressure and inspired concentration of oxygen (PaO2/FIO2) was lower in ZEEP than in the PEEP treatments at various time points. At T180, DO2I was higher when compared to T5 in PEEPmaxCrs. Dopamine was required to maintain MAP higher than 60 mmHg in one cat during PEEPmaxCrs and in three cats during PEEPmaxCrs+2.ConclusionIn cats anesthetized with isoflurane and mechanically ventilated for 3 h, all levels of PEEP mildly improved gas exchange with no significant difference in DO2I when compared to ZEEP. The PEEP levels higher than PEEPmaxCrs−2 caused more cardiovascular depression, and dopamine was an effective treatment. A temporal increase in DO2I was observed in the cats ventilated with PEEPmaxCrs. The effects of these levels of PEEP on respiratory mechanics, ventilation-induced lung injury, as well as in obese and critically ill cats deserve future investigation for a better understanding of the clinical use of PEEP in this species.

Intraoperative protective mechanical ventilation in patients requiring emergency abdominal surgery: the multicentre prospective randomised IMPROVE-2 study protocol

IntroductionEmergency abdominal surgery is associated with a high risk of postoperative complications. One of the most serious is postoperative respiratory failure (PRF), with reported rates up to 20%–30% and attributable...

Variation of Left Ventricular Outflow Tract Velocity Time Integral at Different Positive End-Expiratory Pressure Levels Can Predict Fluid Responsiveness in Mechanically Ventilated Critically Ill Patients

To explore whether the variation of left ventricular outflow tract velocity time integral (LVOT VTI) between positive end-expiratory pressure (PEEP) 10 cmH2O and PEEP 0 cmH2O can predict fluid responsiveness in mechanically ventilated critically ill patients. An observational study. A tertiary hospital intensive care unit. A total of 79 critically ill patients who were on controlled mechanical ventilation. Transthoracic echocardiography was performed at different PEEP levels and was also performed before and after passive leg raising (PLR). The patients were classified as the fluid responders (n=45) and the fluid nonresponders (n=34) according to the LVOT VTI change after PLR (ΔVTIPLR). The difference of LVOT VTI between PEEP 10 cmH2O and PEEP 0 cmH2O (ΔVTIPEEP) was much higher in responders than in nonresponders (17.9% v 2.1%, p < 0.001). The ΔVTIPEEP and ΔVTIPLR were correlated among all patients (r=0.582, p < 0.001). The receiver operating characteristic curve analysis revealed that the ΔVTIPEEP was a good predictor of fluid responsiveness, with an area under the curve of 0.935 (95% confidence interval: 0.885-0.986, p < 0.001), and the optimal cutoff value was 10.5%. Variation of LVOT VTI between PEEP 10 cmH2O and PEEP 0 cmH2O can be used to predict fluid responsiveness in critically ill patients on controlled mechanical ventilation.

Respiratory-Cardiovascular Interactions During Mechanical Ventilation: Physiology and Clinical Implications.

Positive-pressure inspiration and positive end-expiratory pressure (PEEP) increase pleural, alveolar, lung transmural, and intra-abdominal pressure, which decrease right and left ventricular (RV; LV) preload and LV afterload and increase RV afterload. The magnitude and clinical significance of the resulting changes in ventricular function are determined by the delivered tidal volume, the total level of PEEP, the compliance of the lungs and chest wall, intravascular volume, baseline RV and LV function, and intra-abdominal pressure. In mechanically ventilated patients, the most important, adverse consequences of respiratory-cardiovascular interactions are a PEEP-induced reduction in cardiac output, systemic oxygen delivery, and blood pressure; RV dysfunction in patients with ARDS; and acute hemodynamic collapse in patients with pulmonary hypertension. On the other hand, the hemodynamic changes produced by respiratory-cardiovascular interactions can be beneficial when used to assess volume responsiveness in hypotensive patients and by reducing dyspnea and improving hypoxemia in patients with cardiogenic pulmonary edema. Thus, a thorough understanding of the physiological principles underlying respiratory-cardiovascular interactions is essential if critical care practitioners are to anticipate, recognize, manage, and utilize their hemodynamic effects. © 2022 American Physiological Society. Compr Physiol 12:1-24, 2022.