Positive End-expiratory Pressure Levels Research Articles

Impact of positive end-expiratory pressure on renal resistive index in mechanical ventilated patients.

Growing evidence shows the complex interaction between lung and kidney in critically ill patients. The renal resistive index (RRI) is a bedside measurement of the resistance of the renal blood flow and it is correlated with kidney injury. The positive end-expiratory pressure (PEEP) level could affect the resistance of renal blood flow, so we assumed that RRI could help to monitoring the changes in renal hemodynamics at different PEEP levels. Our hypothesis was that the RRI at ICU admission could predict the risk of acute kidney injury in mechanical ventilated critically ill patients. We performed a prospective study including 92 patients requiring mechanical ventilation for ≥ 48h. A RRI ≥ 0.70, was deemed as pathological. RRI was measured within 24h from ICU admission while applying 5,10 and 15 cmH2O of PEEP in random order (PEEP trial). Overall, RRI increased from 0.62 ± 0.09 at PEEP 5 to 0.66 ± 0.09 at PEEP 15 (p < 0.001). The mean RRI value during the PEEP trial was able to predict the occurrence of AKI with AUROC = 0.834 [95%CI 0.742-0.927]. Patients exhibiting a RRI ≥ 0.70 were 17/92(18%) at PEEP 5, 28/92(30%) at PEEP 10, 38/92(41%) at PEEP 15, respectively. Thirty-eight patients (41%) exhibited RRI ≥ 0.70 at least once during the PEEP trial. In these patients, AKI occurred in 55% of the cases, versus 13% remaining patients, p < 0.001. RRI seems able to predict the risk of AKI in mechanical ventilated patients; further, RRI values are influenced by the PEEP level applied. Clinical gov NCT03969914 Registered 31 May 2019.

Determination of optimal positive end-expiratory pressure using electrical impedance tomography in infants under general anesthesia: Comparison between supine and prone positions.

This study determined the optimal positive end-expiratory pressure levels in infants in supine and prone positions under general anesthesia using electrical impedance tomography (EIT). This prospective observational single-centre study included infants scheduled for surgery in the prone position. An electrical impedance tomography sensor was applied after inducing general anesthesia. The optimal positive end-expiratory pressure in the supine position was determined in a decremental trial based on EIT and compliance. Subsequently, the patient's position was changed to prone. Electrical impedance tomography parameters, including global inhomogeneity index, regional ventilation delay, opening pressure, the centre of ventilation, and pendelluft volume, were continuously obtained up to 1 h after prone positioning. The optimal positive end-expiratory pressure in the prone position was similarly determined. Data from 30 infants were analyzed. The mean value of electrical impedance tomography-based optimal positive end-expiratory pressure in the prone position was significantly higher than that in the supine position [10.9 (1.6) cmH2O and 6.1 (0.9) cmH2O, respectively (p < .001)]. Significant differences were observed between electrical impedance tomography- and compliance-based optimal positive end-expiratory pressure. Peak and mean airway, plateau, and driving pressures increased 1 h after prone positioning compared with those in the supine position. In addition, the centre of ventilation for balance in ventilation between the ventral and dorsal regions improved. The prone position required higher positive end-expiratory pressure than the supine position in mechanically ventilated infants under general anesthesia. EIT is a promising tool to find the optimal positive end-expiratory pressure, which needs to be individualized.

Effects of positive end-expiratory pressure on pulmonary perfusion distribution and intrapulmonary shunt during one-lung ventilation in pigs A randomized crossover study.

During one-lung ventilation (OLV), positive end-expiratory pressure (PEEP) can improve lung aeration, but might over-distend lung units and increase intrapulmonary shunt. We hypothesized that higher PEEP shifts pulmonary perfusion from the ventilated to the non-ventilated lung, resulting in a U-shaped relationship with intrapulmonary shunt during OLV. In nine anesthetized female pigs, a thoracotomy was performed and intravenous lipopolysaccharide infused to mimic the inflammatory response of thoracic surgery. Animals underwent OLV in supine position with PEEP of 0 cmH2O, 5 cmH2O, titrated to best respiratory system compliance, and 15 cmH2O (PEEP0, PEEP5, PEEPtitr, and PEEP15, respectively, 45 min each, Latin square sequence). Respiratory, hemodynamic, and gas exchange variables were measured. The distributions of perfusion and ventilation were determined by i.v. fluorescent microspheres and computed tomography, respectively. Compared to two lung ventilation, the driving pressure increased with OLV, irrespective of the PEEP level. During OLV, cardiac output was lower at PEEP15 (5.5 ± 1.5 l/min) than PEEP0 (7.6 ± 3 l/min) and PEEP5 (7.4 ± 2.9 l/min; P=0.004), while the intrapulmonary shunt was highest at PEEP0 (PEEP0: 48.1 ± 14.4 %; PEEP5: 42.4 ± 14.8 %; PEEPtitr: 37.8 ± 11.0 %; PEEP15: 39.0 ± 10.7 %; P=0.027). The relative perfusion of the ventilated lung did not differ among PEEP levels (PEEP0: 65.0 ± 10.6 %; PEEP5:68.7 ± 8.7 %; PEEPtitr: 68.2 ± 10.5 %; PEEP15: 58.4 ± 12.8%; P=0.096), but the centers of relative perfusion and ventilation in the ventilated lung shifted from ventral to dorsal, and from cranial to caudal zones with increasing PEEP. In this experimental model of thoracic surgery, higher PEEP during OLV did not shift the perfusion from the ventilated to the non-ventilated lung, thus not increasing intrapulmonary shunt. This study was registered and approved by the Landesdirektion Dresden, Germany (25-5131/496/33).

Effect of different positive end expiratory pressure levels on optic nerve sheath diameter in patients with or without midline shift who are undergoing supratentorial craniotomy

PurposeIn general, high levels of PEEP application is avoided in patients undergoing craniotomy to prevent a rise in ICP. But that approach would increase the risk of secondary brain injury especially in hypoxemic patients. Because the optic nerve sheath is distensible, a rise in ICP is associated with an increase in the optic nerve sheath diameter (ONSD). The cutoff value for elevated ICP assessed by ONSD is between 5.6 and 6.3 mm. We aimed to evaluate the effect of different PEEP levels on ONSD and compare the effect of different PEEP levels in patients with and without intracranial midline shift.MethodsThis prospective observational study was performed in aged 18–70 years, ASA I–III, 80 patients who were undergoing supratentorial craniotomy. After the induction of general anesthesia, the ONSD’s were measured by the linear transducer from 3 mm below the globe at PEEP values of 0–5–10 cmH2O. The ONSD were compered between patients with (n = 7) and without midline shift (n = 73) at different PEEP values.ResultsThe increases in ONSD due to increase in PEEP level were determined (p < 0.001). No difference was found in the comparison of ONSD between patients with and without midline shift in different PEEP values (p = 0.329, 0.535, 0.410 respectively). But application of 10 cmH2O PEEP in patients with a midline shift increased the mean ONSD value to 5.73 mm. This value is roughly 0.1 mm higher than the lower limit of the ONSD cutoff value.ConclusionsThe ONSD in adults undergoing supratentorial tumor craniotomy, PEEP values up to 5 cmH2O, appears not to be associated with an ICP increase; however, the ONSD exceeded the cutoff for increased ICP when a PEEP of 10 cmH2O was applied in patients with midline shift.

Exploring alveolar recruitability using positive end-expiratory pressure in mice overexpressing TGF-β1: a structure–function analysis

Pre-injured lungs are prone to injury progression in response to mechanical ventilation. Heterogeneous ventilation due to (micro)atelectases imparts injurious strains on open alveoli (known as volutrauma). Hence, recruitment of (micro)atelectases by positive end-expiratory pressure (PEEP) is necessary to interrupt this vicious circle of injury but needs to be balanced against acinar overdistension. In this study, the lung-protective potential of alveolar recruitment was investigated and balanced against overdistension in pre-injured lungs. Mice, treated with empty vector (AdCl) or adenoviral active TGF-β1 (AdTGF-β1) were subjected to lung mechanical measurements during descending PEEP ventilation from 12 to 0 cmH2O. At each PEEP level, recruitability tests consisting of two recruitment maneuvers followed by repetitive forced oscillation perturbations to determine tissue elastance (H) and damping (G) were performed. Finally, lungs were fixed by vascular perfusion at end-expiratory airway opening pressures (Pao) of 20, 10, 5 and 2 cmH2O after a recruitment maneuver, and processed for design-based stereology to quantify derecruitment and distension. H and G were significantly elevated in AdTGF-β1 compared to AdCl across PEEP levels. H was minimized at PEEP = 5–8 cmH2O and increased at lower and higher PEEP in both groups. These findings correlated with increasing septal wall folding (= derecruitment) and reduced density of alveolar number and surface area (= distension), respectively. In AdTGF-β1 exposed mice, 27% of alveoli remained derecruited at Pao = 20 cmH2O. A further decrease in Pao down to 2 cmH2O showed derecruitment of an additional 1.1 million alveoli (48%), which was linked with an increase in alveolar size heterogeneity at Pao = 2–5 cmH2O. In AdCl, decreased Pao resulted in septal folding with virtually no alveolar collapse. In essence, in healthy mice alveoli do not derecruit at low PEEP ventilation. The potential of alveolar recruitability in AdTGF-β1 exposed mice is high. H is optimized at PEEP 5–8 cmH2O. Lower PEEP folds and larger PEEP stretches septa which results in higher H and is more pronounced in AdTGF-β1 than in AdCl. The increased alveolar size heterogeneity at Pao = 5 cmH2O argues for the use of PEEP = 8 cmH2O for lung protective mechanical ventilation in this animal model.

Lung donor bronchoalveolar lavage positivity: Incidence, risk factors, and lung transplant recipients’ outcome

BackgroundInconsistent data exists regarding the risk factors for bronchoalveolar lavage (BAL) positivity in lung donors, the incidence of donor-derived infections (DDI), and the effect of BAL positivity on lung transplant (LuTx) recipients’ outcome. MethodsA retrospective analysis was conducted on consecutive LuTx at a single center from January 2016 to December 2022. Donors’ data, including characteristics, graft function and BAL samples were collected pre-procurement. Recipients underwent BAL before LuTx and about the 3rd, 7th and 14th day after LuTx. A DDI was defined as BAL positivity (bacterial growth ≥104 colony forming units) for identical bacterial species between donor and recipient. Recipients’ pre-operative characteristics, intra-operative management, and post-operative outcomes were assessed. Two recipient cohorts were identified based on lung colonization status before undergoing LuTx. ResultsOut of 188 LuTx procedures performed, 169 were analyzed. Thirty-six percent of donors’ BAL tested positive. Donors’ characteristics and graft function at procurement were not associated with BAL positivity. Fourteen DDI were detected accounting for 23% of recipients receiving a graft with a positive BAL. Only among uncolonized recipients, receiving a graft with positive BAL is associated with higher likelihood of requiring invasive ventilation at 72 hours after LuTx on higher positive end-expiratory pressure levels having lower PaO2/FiO2, prolonged duration of mechanical ventilation and longer ICU stay. No difference in hospital length of stay was observed. ConclusionsReceiving a graft with a positive BAL, which is poorly predicted by donors’ characteristics, carries the risk of developing a DDI and is associated to a worse early graft function among uncolonized recipients.

Decision day – A retrospective analysis of COVID-19 patients treated with high PEEP non-invasive ventilation

Background and objectives. This retrospective analysis investigates the effect of high levels of Positive End-Expiratory Pressure (PEEP) during Non-Invasive Ventilation (NIV) in patients with COVID 19 Acute Respiratory Distress Syndrome (ARDS). Materials and methods. In the University Hospital Center Zagreb from October 2021 to February 2022, the study analyzed data from 97 patients who received NIV for acute respiratory support during ICU stay. The effect of NIV on survival, the length of stay in the ICU as well as the duration of the support itself was investigated. Results. Results show that despite low mortality in patients with NIV support, mortality is quite high in patients who required intubation. There is also a divergence of the respiratory support level parameter after the 3rd day on NIV, which suggests that moment as pivotal for assessing the continuation of NIV support. Conclusions. The results show that high level PEEP is a viable option for starting respiratory support in ARDS, but also the importance of timely assessment to optimize patient outcomes.

Predicting Successful Weaning from Mechanical Ventilation by Reduction in Positive End-expiratory Pressure Level Using Machine Learning.

Weaning patients from mechanical ventilation (MV) is a critical and resource intensive process in the Intensive Care Unit (ICU) that impacts patient outcomes and healthcare expenses. Weaning methods vary widely among providers. Prolonged MV is associated with adverse events and higher healthcare expenses. Predicting weaning readiness is a non-trivial process in which the positive end-expiratory pressure (PEEP), a crucial component of MV, has potential to be indicative but has not yet been used as the target. We aimed to predict successful weaning from mechanical ventilation by targeting changes in the PEEP-level using a supervised machine learning model. This retrospective study included 12,153 mechanically ventilated patients from Medical Information Mart for Intensive Care (MIMIC-IV) and eICU collaborative research database (eICU-CRD). Two machine learning models (Extreme Gradient Boosting and Logistic Regression) were developed using a continuous PEEP reduction as target. The data is splitted into 80% as training set and 20% as test set. The model's predictive performance was reported using 95% confidence interval (CI), based on evaluation metrics such as area under the receiver operating characteristic (AUROC), area under the precision-recall curve (AUPRC), F1-Score, Recall, positive predictive value (PPV), and negative predictive value (NPV). The model's descriptive performance was reported as the variable ranking using SHAP (SHapley Additive exPlanations) algorithm. The best model achieved an AUROC of 0.84 (95% CI 0.83-0.85) and an AUPRC of 0.69 (95% CI 0.67-0.70) in predicting successful weaning based on the PEEP reduction. The model demonstrated a Recall of 0.85 (95% CI 0.84-0.86), F1-score of 0.86 (95% CI 0.85-0.87), PPV of 0.87 (95% CI 0.86-0.88), and NPV of 0.64 (95% CI 0.63-0.66). Most of the variables that SHAP algorithm ranked to be important correspond with clinical intuition, such as duration of MV, oxygen saturation (SaO2), PEEP, and Glasgow Coma Score (GCS) components. This study demonstrates the potential application of machine learning in predicting successful weaning from MV based on continuous PEEP reduction. The model's high PPV and moderate NPV suggest that it could be a useful tool to assist clinicians in making decisions regarding ventilator management.

Effects of positive end-expiratory pressure on regional cerebral oxygen saturation in elderly patients undergoing thoracic surgery during one-lung ventilation: a randomized crossover-controlled trial

BackgroundA significant reduction in regional cerebral oxygen saturation (rSO2) is commonly observed during one-lung ventilation (OLV), while positive end-expiratory pressure (PEEP) can improve oxygenation. We compared the effects of three different PEEP levels on rSO2, pulmonary oxygenation, and hemodynamics during OLV.MethodsForty-three elderly patients who underwent thoracoscopic lobectomy were randomly assigned to one of six PEEP combinations which used a crossover design of 3 levels of PEEP—0 cmH2O, 5 cmH2O, and 10 cmH2O. The primary endpoint was rSO2 in patients receiving OLV 20 min after adjusting the PEEP. The secondary outcomes included hemodynamic and respiratory variables.ResultsAfter exclusion, thirty-six patients (36.11% female; age range: 60–76 year) were assigned to six groups (n = 6 in each group). The rSO2 was highest at OLV(0) than at OLV(10) (difference, 2.889%; [95% CI, 0.573 to 5.204%]; p = 0.008). Arterial oxygen partial pressure (PaO2) was lowest at OLV(0) compared with OLV(5) (difference, -62.639 mmHg; [95% CI, -106.170 to -19.108 mmHg]; p = 0.005) or OLV(10) (difference, -73.389 mmHg; [95% CI, -117.852 to -28.925 mmHg]; p = 0.001), while peak airway pressure (Ppeak) was lower at OLV(0) (difference, -4.222 mmHg; [95% CI, -5.140 to -3.304 mmHg]; p < 0.001) and OLV(5) (difference, -3.139 mmHg; [95% CI, -4.110 to -2.167 mmHg]; p < 0.001) than at OLV(10).ConclusionsPEEP with 10 cmH2O makes rSO2 decrease compared with 0 cmH2O. Applying PEEP with 5 cmH2O during OLV in elderly patients can improve oxygenation and maintain high rSO2 levels, without significantly increasing peak airway pressure compared to not using PEEP.Trial registrationChinese Clinical Trial Registry ChiCTR2200060112 on 19 May 2022.

Maintaining moderate versus lower PEEP after cardiac surgery: a propensity-scored matched analysis

BackgroundSetting positive end-expiratory pressure (PEEP) at around 5 cm H2O in the early postoperative period seems a common practice for most patients. It remains unclear if the routine application of higher levels of PEEP confers any meaningful clinical benefit for cardiac surgical patients. The aim of this study was to compare moderate versus conventional lower PEEP on patient-centered outcomes in the intensive care unit (ICU).MethodsThis is a single-center retrospective study involving patients receiving cardiac surgery from June 2022 to May 2023. Propensity-score matching (PSM) was used to balance the baseline differences. Primary outcomes were the duration of mechanical ventilation and ICU length of stay. Secondary outcomes included PaO2/FiO2 ratio at 24 h and the need for prone positioning during ICU stay.ResultsA total of 334 patients were included in the study, 102 (31%) of them received moderate PEEP (≥ 7 cm H2O) for the major time in the early postoperative period (12 h). After PSM, 79 pairs of patients were matched with balanced baseline data. The results showed that there was marginal difference in the distribution of mechanical ventilation duration (p = 0.05) and the Moderate PEEP group had a higher extubation rate at the day of T-piece trial (65 [82.3%] vs 52 [65.8%], p = 0.029). Applying moderate PEEP was also associated with better oxygenation. No differences were found regarding ICU length of stay and patients requiring prone positioning between groups.ConclusionIn selective cardiac surgical patients, using moderate PEEP compared with conventional lower PEEP in the early postoperative period correlated to better oxygenation, which may have potential for earlier liberation of mechanical ventilation.

Positive end-expiratory pressure limits inspiratory effort through modulation of the effort-to-drive ratio: an experimental crossover study

BackgroundHow assisted spontaneous breathing should be used during acute respiratory distress syndrome is questioned. Recent evidence suggests that high positive end-expiratory pressure (PEEP) may limit the risk of patient self-inflicted lung injury (P-SILI). The aim of this study was to assess the effects of PEEP on esophageal pressure swings, inspiratory drive, and the neuromuscular efficiency of ventilation. We hypothesized that high PEEP would reduce esophageal pressure swings, regardless of inspiratory drive changes, by modulating the effort-to-drive ratio (EDR). This was tested retrospectively in an experimental animal crossover study. Anesthetized pigs (n = 15) were subjected to mild to moderate lung injury and different PEEP levels were applied, changing PEEP from 0 to 15 cmH2O and back to 0 cmH2O in steps of 3 cmH2O. Airway pressure, esophageal pressure (Pes), and electric activity of the diaphragm (Edi) were collected. The EDR was calculated as the tidal change in Pes divided by the tidal change in Edi. Statistical differences were tested using the Wilcoxon signed-rank test.ResultsInspiratory esophageal pressure swings decreased from − 4.2 ± 3.1 cmH2O to − 1.9 ± 1.5 cmH2O (p < 0.01), and the mean EDR fell from − 1.12 ± 1.05 cmH2O/µV to − 0.24 ± 0.20 (p < 0.01) as PEEP was increased from 0 to 15 cmH2O. The EDR was significantly correlated to the PEEP level (rs = 0.35, p < 0.01).ConclusionsHigher PEEP limits inspiratory effort by modulating the EDR of the respiratory system. These findings indicate that PEEP may be used in titration of the spontaneous impact on ventilation and in P-SILI risk reduction, potentially facilitating safe assisted spontaneous breathing. Similarly, ventilation may be shifted from highly spontaneous to predominantly controlled ventilation using PEEP. These findings need to be confirmed in clinical settings.

Phenotypes of esophageal pressure response to the change of positive end-expiratory pressure in patients with moderate acute respiratory distress syndrome.

Esophageal pressure (Pes) has been used as a surrogate of pleural pressure (Ppl) to titrate positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS) patients. The relationship between Pes and PEEP remains undetermined. A gastric tube with a balloon catheter was inserted to monitor Pes in moderate to severe ARDS patients who underwent invasive mechanical ventilation. To assess the end-expiratory Pes response (ΔPes) to PEEP changes (ΔPEEP), the PEEP level was decreased and increased subsequently (with an average change of 3 cmH2O). The patients underwent the following two series of PEEP adjustment: (I) from PEEP-3 cmH2O to PEEPbaseline; and (II) from PEEPbaseline to PEEP+3 cmH2O. The patients were classified as "PEEP-dependent type" if they had ΔPes ≥30% ΔPEEP and were otherwise classified as "PEEP-independent type" (ΔPes <30% ΔPEEP in any series). In total, 54 series of PEEP adjustments were performed in 18 ARDS patients. Of these patients, 12 were classified as PEEP-dependent type, and six were classified as PEEP-independent type. During the PEEP adjustment, end-expiratory Pes changed significantly in the PEEP-dependent patients, who had a Pes of 10.8 (7.9, 12.3), 12.5 (10.5, 14.9), and 14.5 (13.1, 18.3) cmH2O at PEEP-3 cmH2O, PEEPbaseline, and PEEP+3 cmH2O, respectively (median and quartiles; P<0.0001), while end-expiratory transpulmonary pressure (PL) was maintained at an optimal range [-0.1 (-0.7, 0.4), 0.1 (-0.6, 0.5), and 0.3 (-0.3, 0.7) cmH2O, respectively]. In the PEEP-independent patients, the Pes remained unchanged, with a Pes of 15.4 (11.4, 17.8), 15.5 (11.6, 17.8), and 15.4 (11.7, 18.30) cmH2O at each of the three PEEP levels, respectively. Meanwhile, end-expiratory PL significantly improved [from -5.5 (-8.5, -3.4) at PEEP-3 cmH2O to -2.5 (-5.0, -1.6) at PEEPbaseline to -0.5 (-1.8, 0.3) at PEEP+3 cmH2O; P<0.01]. Two types of Pes phenotypes were identified according to the ΔPes to ΔPEEP. The underlying mechanisms and implications for clinical practice require further exploration.

Effects on mechanical power of different devices used for inhaled sedation in a bench model of protective ventilation in ICU

BackgroundInhaled sedation during invasive mechanical ventilation in patients with acute respiratory distress syndrome (ARDS) has received increasing attention. However, inhaled sedation devices increase dead-space ventilation and an undesirable effect is the increase in minute ventilation needed to maintain CO2 removal. A consequence of raising minute ventilation is an increase in mechanical power (MP) that can promote lung injury. However, the effect of inhaled sedation devices on MP remains unknown.MethodsWe conducted a bench study to assess and compare the effects of three devices delivering inhaled sevoflurane currently available in ICU (AnaConDa-50 mL (ANA-50), AnaConDa-100 mL (ANA-100), and MIRUS) on MP by using a test lung model set with three compliances (20, 40, and 60 mL/cmH2O). We simulated lung-protective ventilation using a low tidal volume and two levels of positive end-expiratory pressure (5 and 15 cmH2O) under ambient temperature and dry conditions. Following the insertion of the devices, either the respiratory rate or tidal volume was increased in 15%-steps until end-tidal CO2 (EtCO2) returned to the baseline value. MP was calculated at baseline and after EtCO2 correction using a simplified equation.ResultsFollowing device insertion, the EtCO2 increase was significantly greater with MIRUS (+ 78 ± 13%) and ANA-100 (+ 100 ± 11%) than with ANA-50 (+ 49 ± 7%). After normalizing EtCO2 by adjusting minute ventilation, MP significantly increased by more than 50% with all inhaled sedation devices compared to controls. The lowest increase in MP was observed with ANA-50 (p < 0.05 versus ANA-100 and MIRUS). The Costa index, another parameter assessing the mechanical energy delivered to the lungs, calculated as driving pressure × 4 + respiratory rate, significantly increased by more than 20% in all experimental conditions. Additional experiments performed under body temperature, ambient pressure, and gas saturated with water vapor conditions, confirmed the main results with an increase in MP > 50% with all devices after normalizing EtCO2 by adjusting minute ventilation.ConclusionInhaled sedation devices substantially increased MP in this bench model of protective ventilation, which might limit their benefits in ARDS.

Value and Variability of Pulse Shape Indicator for Estimating Mean Arterial Pressure in the Radial and Femoral Arteries.

The form factor (FF) is a pulse shape indicator that corresponds to the fraction of pulse pressure added to diastolic blood pressure to estimate the time-averaged mean arterial pressure (MAP). Our invasive study assessed the FF value and variability at the radial and femoral artery levels and evaluated the recommended fixed FF value of 0.33. Hemodynamically stable patients were prospectively included in 2 intensive care units. FF was documented at baseline and during dynamic maneuvers. A total of 632 patients (64±16 years of age, 66% men, MAP=81±14 mm Hg) were included. Among them, 355 (56%) had a radial catheter and 277 (44%) had a femoral catheter. The FF was 0.34±0.06. In multiple linear regression, FF was influenced by biological sex (P<0.0001) and heart rate (P=0.04) but not by height, weight, or catheter location. The radial FF was 0.35±0.06, whereas the femoral FF was 0.34±0.05 (P=0.08). Both radial and femoral FF were higher in women than in men (P<0.05). When using the 0.33 FF value to estimate MAP, the error was -0.4±4.0 mm Hg and -0.1±2.9 mm Hg at the radial and femoral level, respectively, and the MAP estimate still demonstrated high accuracy and good precision even after changes in norepinephrine dose, increase in positive end-expiratory pressure level, fluid administration, or prone positioning (n=218). Despite higher FF in women and despite interindividual variability in FF, using a fixed FF value of 0.33 yielded accurate and precise estimations of MAP. This finding has potential implications for blood pressure monitoring devices and the study of pulse wave amplification.

Influence of Fractional Inspired Oxygen Tension on Lung Perfusion Distribution, Regional Ventilation, and Lung Volume during Mechanical Ventilation of Supine Healthy Swine.

Lower fractional inspired oxygen tension (Fio2) during general anesthesia can reduce lung atelectasis. The objectives are to evaluate the effect of two Fio2 (0.4 and 1) during low positive end-expiratory pressure (PEEP) ventilation over lung perfusion distribution, volume, and regional ventilation. These variables were evaluated at two PEEP levels and unilateral lung atelectasis. In this exploratory study, 10 healthy female piglets (32.3 ± 3.4 kg) underwent mechanical ventilation in two atelectasis models: (1) bilateral gravitational atelectasis (n = 6), induced by changes in PEEP and Fio2 in three combinations: high PEEP with low Fio2 (Fio2 = 0.4), zero PEEP (PEEP0) with low Fio2 (Fio2 = 0.4), and PEEP0 with high Fio2 (Fio2 = 1); and (2) unilateral atelectasis (n = 6), induced by left bronchial occlusion, with the left lung aerated (Fio2 = 0.21) and low aerated (Fio2 = 1; n = 5 for this step). Measurements were conducted after 10 min in each step, encompassing assessment of respiratory mechanics, oxygenation, and hemodynamics; lung ventilation and perfusion by electrical impedance tomography; and lung aeration and perfusion by computed tomography. During bilateral gravitational atelectasis, PEEP reduction increased atelectasis in dorsal regions, decreased respiratory compliance, and distributed lung ventilation to ventral regions with a parallel shift of perfusion to the same areas. With PEEP0, there were no differences between low and high Fio2 in respiratory compliance (23.9 ± 6.5 ml/cm H2O vs. 21.9 ± 5.0; P = 0.441), regional ventilation, and regional perfusion, despite higher lung collapse (18.6 ± 7.6% vs. 32.7 ± 14.5%; P = 0.045) with high Fio2. During unilateral lung atelectasis, the deaerated lung had a lower shunt (19.3 ± 3.6% vs. 25.3 ± 5.5%; P = 0.045) and lower computed tomography perfusion to the left lung (8.8 ± 1.8% vs. 23.8 ± 7.1%; P = 0.007). PEEP0 with low Fio2, compared with high Fio2, did not produce significant changes in respiratory system compliance, regional lung ventilation, and perfusion despite significantly lower lung collapse. After left bronchial occlusion, the shrinkage of the parenchyma with Fio2 = 1 enhanced hypoxic pulmonary vasoconstriction, reducing intrapulmonary shunt and perfusion of the nonventilated areas.

Bedside personalized methods based on electrical impedance tomography or respiratory mechanics to set PEEP in ARDS and recruitment-to-inflation ratio: a physiologic study

BackgroundVarious Positive End-Expiratory Pressure (PEEP) titration strategies have been proposed to optimize ventilation in patients with acute respiratory distress syndrome (ARDS). We aimed to compare PEEP titration strategies based on electrical impedance tomography (EIT) to methods derived from respiratory system mechanics with or without esophageal pressure measurements, in terms of PEEP levels and association with recruitability.MethodsNineteen patients with ARDS were enrolled. Recruitability was assessed by the estimated Recruitment-to-Inflation ratio (R/Iest) between PEEP 15 and 5 cmH2O. Then, a decremental PEEP trial from PEEP 20 to 5 cmH2O was performed. PEEP levels determined by the following strategies were studied: (1) plateau pressure 28–30 cmH2O (Express), (2) minimal positive expiratory transpulmonary pressure (Positive PLe), (3) center of ventilation closest to 0.5 (CoV) and (4) intersection of the EIT-based overdistension and lung collapse curves (Crossing Point). In addition, the PEEP levels determined by the Crossing Point strategy were assessed using different PEEP ranges during the decremental PEEP trial.ResultsExpress and CoV strategies led to higher PEEP levels than the Positive PLe and Crossing Point ones (17 [14–17], 20 [17–20], 8 [5–11], 10 [8–11] respectively, p < 0.001). For each strategy, there was no significant association between the optimal PEEP level and R/Iest (Crossing Point: r2 = 0.073, p = 0.263; CoV: r2 < 0.001, p = 0.941; Express: r2 < 0.001, p = 0.920; Positive PLe: r2 = 0.037, p = 0.461). The PEEP level obtained with the Crossing Point strategy was impacted by the PEEP range used during the decremental PEEP trial.ConclusionsCoV and Express strategies led to higher PEEP levels than the Crossing Point and Positive PLe strategies. Optimal PEEP levels proposed by these four methods were not associated with recruitability. Recruitability should be specifically assessed in ARDS patients to optimize PEEP titration.

Positive end-expiratory pressure and surfactant administration mode influence function in ex-vivo premature sheep lungs.

Respiratory distress syndrome often necessitates endotracheal surfactant administration in extremely preterm infants. Our study aimed to explore a multi-modal simulation tool for investigating treatment strategies in exvivo sheep lungs during spontaneous breathing. An electromechanical lung simulator (xPULM) mimicking spontaneous breathing was coupled with a non-aerated premature sheep lung, replicating a premature respiratory system. Changes in tidal volume for different positive end-expiratory pressure (PEEP) levels prior to and after either bolus or nebulised surfactant administration were compared. In two preterm sheep lungs, we observed a progressive decline in tidal volume with increasing PEEP levels prior to surfactant delivery from 0.30 ± 0.01 mL at zero PEEP to 0.04 ± 0.01 mL at 15 cmH2O PEEP. Our measurements showed that both bolus (p < 0.05) and nebulised (p < 0.05) surfactant administration resulted in a significant increase in tidal volume, with no significant difference (p = 0.71) between the two methods. The experimental setup demonstrated the feasibility of xPULM for investigating the effectiveness of different PEEP levels and modes of surfactant administration with respect to tidal volume in premature sheep lungs. The lack of adequate lung water resorption in our model warrants further investigations.

Pulmonary response prediction through personalized basis functions in a virtual patient model

Background and ObjectiveRecruitment maneuvers with subsequent positive-end-expiratory-pressure (PEEP) have proven effective in recruiting lung volume and preventing alveoli collapse. However, determining a safe, effective, and patient-specific PEEP is not standardized, and this more optimal PEEP level evolves with patient condition, requiring personalised monitoring and care approaches to maintain optimal ventilation settings. MethodsThis research examines 3 physiologically relevant basis function sets (exponential, parabolic, cumulative) to enable better prediction of elastance evolution for a virtual patient or digital twin model of MV lung mechanics, including novel elements to model and predict distension elastance. Prediction accuracy and robustness are validated against recruitment maneuver data from 18 volume-controlled ventilation (VCV) patients at 7 different baseline PEEP levels (0 to 12 cmH2O) and 14 pressure-controlled ventilation (PCV) patients at 4 different baseline PEEP levels (6 to 12 cmH2O), yielding 623 and 294 prediction cases, respectively. Predictions were made up to 12 cmH2O of added PEEP ahead, covering 6 × 2 cmH2O PEEP steps. ResultsThe 3 basis function sets yield median absolute peak inspiratory pressure (PIP) prediction error of 1.63 cmH2O for VCV patients, and median peak inspiratory volume (PIV) prediction error of 0.028 L for PCV patients. The exponential basis function set yields a better trade-off of overall performance across VCV and PCV prediction than parabolic and cumulative basis function sets from other studies. Comparing predicted and clinically measured distension prediction in VCV demonstrated consistent, robust high accuracy with R2 = 0.90–0.95. ConclusionsThe results demonstrate recruitment mechanics are best captured by an exponential basis function across different mechanical ventilation modes, matching physiological expectations, and accurately capture, for the first time, distension mechanics to within 5–10 % accuracy. Enabling the risk of lung injury to be predicted before changing ventilator settings. The overall outcomes significantly extend and more fully validate this digital twin or virtual mechanical ventilation patient model.

Effect of automated head-thorax elevation during chest compressions on lung ventilation: a model study

Our goal was to investigate the effects of head-thorax elevation (HUP) during chest compressions (CC) on lung ventilation. A prospective study was performed on seven human cadavers. Chest was automatically compressed-decompressed in flat position and during progressive HUP from 18 to 35°. Lung ventilation was measured with electrical impedance tomography. In each cadaver, 5 sequences were randomly performed: one without CC at positive end-expiratory pressure (PEEP) 0cmH2O, 3 s with CC at PEEP0, 5 or 10cmH2O and 1 with CC and an impedance threshold device at PEEP0cmH2O. The minimal-to-maximal change in impedance (VTEIT in arbitrary unit a.u.) and the minimal impedance in every breathing cycle (EELI) the) were compared between flat, 18°, and 35° in each sequence by a mixed-effects model. Values are expressed as median (1st–3rd quartiles). With CC, between flat, 18° and 35° VTEIT decreased at each level of PEEP. It was 12416a.u. (10,689; 14,442), 11,239 (7667; 13,292), and 6457 (4631; 9516), respectively, at PEEP0. The same was true with the impedance threshold device. EELI/VTEIT significantly decreased from − 0.30 (− 0.40; − 0.15) before to − 1.13 (− 1.70; − 0.61) after the CC (P = 0.009). With HUP lung ventilation decreased with CC as compared to flat position. CC are associated with decreased in EELI.

Impact of Positive End-Expiratory Pressure and FiO2 on Lung Mechanics and Intrapulmonary Shunt in Mechanically Ventilated Patients with ARDS Due to COVID-19 Pneumonia.

Purpose: This study aimed to investigate the effects of inspired oxygen fraction (FiO2) and positive end-expiratory pressure (PEEP) on gas exchange in mechanically ventilated patients with COVID-19. Methods: Two FiO2 (100%, 40%) were tested at 3 decreasing levels of PEEP (15, 10, and 5 cmH2O). At each FiO2 and PEEP, gas exchange, respiratory mechanics, hemodynamics, and the distribution of ventilation and perfusion were assessed with electrical impedance tomography. The impact of FiO2 on the intrapulmonary shunt (delta shunt) was analyzed as the difference between the calculated shunt at FiO2 100% (shunt) and venous admixture at FiO2 40% (venous admixture). Results: Fourteen patients were studied. Decreasing PEEP from 15 to 10 cmH2O did not change shunt (24 [21-28] vs 27 [24-29]%) or venous admixture (18 [15-26] vs 23 [18-34]%) while partial pressure of arterial oxygen (FiO2 100%) was higher at PEEP 15 (262 [198-338] vs 256 [147-315] mmHg; P < .05). Instead when PEEP was decreased from 10 to 5 cmH2O, shunt increased to 36 [30-39]% (P < .05) and venous admixture increased to 33 [30-43]% (P < .05) and partial pressure of arterial oxygen (100%) decreased to 109 [76-177] mmHg (P < .05). At PEEP 15, administration of 100% FiO2 resulted in a shunt greater than venous admixture at 40% FiO2, ((24 [21-28] vs 18 [15-26]%, P = .005), delta shunt 5.5% (2.3-8.8)). Compared to PEEP 10, PEEP of 5 and 15 cmH2O resulted in decreased global and pixel-level compliance. Cardiac output at FiO2 100% resulted higher at PEEP 5 (5.4 [4.4-6.5]) compared to PEEP 10 (4.8 [4.1-5.5], P < .05) and PEEP 15 cmH2O (4.7 [4.5-5.4], P < .05). Conclusion: In this study, PEEP of 15 cmH2O, despite resulting in the highest oxygenation, was associated with overdistension. PEEP of 5 cmH2O was associated with increased shunt and alveolar collapse. Administration of 100% FiO2 was associated with an increase in intrapulmonary shunt in the setting of high PEEP. Trial registration: NCT05132933.