Positive End-expiratory Pressure Research Articles

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).

Is EIT-guided positive end-expiratory pressure titration for optimizing PEEP in ARDS the white elephant in the room? A systematic review with meta-analysis and trial sequential analysis.

Electrical Impedance Tomography (EIT) is a novel real-time lung imaging technology for personalized ventilation adjustments, indicating promising results in animals and humans. The present study aimed to assess its clinical utility for improved ventilation and oxygenation compared to traditional protocols. Comprehensive electronic database screening was done until 30th November, 2023. Randomized controlled trials,controlled clinical trials, comparative cohort studies, and assessments of EIT-guided PEEP titration and conventional methods in adult ARDS patients regarding outcome, ventilatory parameters, and P/F ratio were included. Our search retrieved five controlled cohort studies and two RCTs with 515 patients and overall reduced risk of mortality [RR = 0.68; 95% CI: 0.49 to 0.95; I2 = 0%], better dynamic compliance [MD = 3.46; 95% CI: 1.59 to 5.34; I2 = 0%] with no significant difference in PaO2/FiO2 ratio [MD = 6.5; 95%CI -13.86 to 26.76; I2 = 74%]. The required information size except PaO2/FiO2 was achieved for a power of 95% based on the 50% reduction in risk of mortality, 10% improved compliance as the cumulative Z-score of the said outcomes crossed the alpha spending boundary and did not dip below the inner wedge of futility. EIT-guided individualized PEEP titration is a novel modality; further well-designed studies are needed to substantiate its utility.

Oxygenation and ventilation during prolonged experimental cardiopulmonary resuscitation with either continuous or 30:2 compression-to-ventilation ratios together with 10 cmH20 positive end-expiratory pressure

BackgroundIn refractory out-of-hospital cardiac arrest, the patient is commonly transported to hospital with mechanical continuous chest compressions (CCC). Limited data are available on the optimal ventilation strategy. Accordingly, we compared arterial oxygenation and haemodynamics during manual asynchronous continuous ventilation and compressions with a 30:2 compression-to-ventilation ratio together with the use of 10 cmH2O positive end-expiratory pressure (PEEP).MethodsIntubated and anaesthetized landrace pigs with electrically induced ventricular fibrillation were left untreated for 5 min (n = 31, weight ca. 55 kg), after which they were randomized to either the CCC group or the 30:2 group with the the LUCAS® 2 piston device and bag-valve ventilation with 100% oxygen targeting a tidal volume of 8 ml/kg with a PEEP of 10 cmH2O for 35 min. Arterial blood samples were analysed every 5 min, vital signs, near-infrared spectroscopy and electrical impedance tomography (EIT) were measured continuously, and post-mortem CT scans of the lungs were obtained.ResultsThe arterial blood values (median + interquartile range) at the 30-min time point were as follows: PaO2: 180 (86–302) mmHg for the 30:2 group; 70 (49–358) mmHg for the CCC group; PaCO2: 41 (29–53) mmHg for the 30:2 group; 44 (21–67) mmHg for the CCC group; and lactate: 12.8 (10.4–15.5) mmol/l for the 30:2 group; 14.7 (11.8–16.1) mmol/l for the CCC group. The differences were not statistically significant. In linear mixed models, there were no significant differences between the groups. The mean arterial pressures from the femoral artery, end-tidal CO2, distributions of ventilation from EIT and mean aeration of lung tissue in post-mortem CTs were similar between the groups. Eight pneumothoraces occurred in the CCC group and 2 in the 30:2 group, a statistically significant difference (p = 0.04).ConclusionsThe 30:2 and CCC protocols with a PEEP of 10 cmH2O resulted in similar gas exchange and vital sign outcomes in an experimental model of prolonged cardiac arrest with mechanical compressions, but the CCC protocol resulted in more post-mortem pneumothoraces.

Positive end-expiratory pressure and the incidence of postoperative pulmonary complications in patients undergoing general anaesthesia.

To evaluate the effect of intraoperative positive end-expiratory pressure and driving pressure on the development of postoperative pulmonary complications. The prospective study included 83 patients undergoing abdominal surgery and receiving general anaesthesia. Patients were divided into two groups: with low intraoperative positive end-expiratory pressure (0-2cm H2O) and with high intraoperative positive end-expiratory pressure (8-10cm H2O). The primary endpoint is the development of postoperative pulmonary complications during follow-up. The incidence of postoperative pulmonary complications in the group of low intraoperative positive end-expiratory pressure was 9.8%, while in the group of high positive end-expiratory pressure was 7.1% (p = 0.6), demonstrating that high positive end-expiratory pressure used during general anaesthesia does not affect the frequency of complications (odds ratio = 0.71, p = 0.6). In the multivariate analysis that controls for all confounders, driving pressure resulted in a significant and independent risk factor for complications. High intraoperative positive end-expiratory pressure does not affect the frequency of postoperative pulmonary complications. The increase in driving pressure is a risk factor for complications. Positive end-expiratory pressure is easily implemented, and its use does not result in significant economic costs.

Weaning strategies for children on home invasive mechanical ventilation.

Children who require home mechanical ventilation (HMV) with an artificial airway or invasive mechanical ventilation (HMV) have a possibility of successful weaning due to the potential of compensatory lung growth. Internationally accepted guidelines on how to wean from HMV in children is not available, we summarize the weaning strategies from the literature reviews combined with our 27-year experience in the Pediatric Home Respiratory Care program at the tertiary care center in Thailand. The readiness to wean is considered in patients with hemodynamic stability, having effective cough measured by maximal inspiratory pressure, requiring a fraction of inspired oxygen (FiO2) < 40%, positive end expiratory pressure <5 cmH2O, and acceptable arterial blood gases. The strategies of weaning is start weaning during the daytime while the child is awake and close monitoring is feasible. Disconnect time is gradually increased through naps and sleeping hours. Weaning from the conventional mechanical ventilator to Bilevel PAP or CPAP are optional. Factors affected the successful weaning are mainly the underlying diseases, complications, growth and development, caregivers, and resources. Weaning should be stopped during acute illness or increased work of breathing. The readiness for decannulation could be determined by using the speaking devices, tracheostomy capping, and measurement of end-expiratory pressure. Polysomnography and airway evaluation by bronchoscopy are recommended before decannulation.Weaning when the child is ready is crucial because living with HMV can be challenging and stressful. Failure to remove a tracheostomy when indicated can result in delayed speech, social problems as well as risk for infection.

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.

Comparative effects of variable versus conventional volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in thoracic surgery patients: A randomized controlled clinical trial

BackgroundMechanical ventilation with variable tidal volumes (V-VCV) has the potential to improve lung function during general anesthesia. We tested the hypothesis that V-VCV compared to conventional volume-controlled ventilation (C-VCV) would improve intraoperative arterial oxygenation and respiratory system mechanics in patients undergoing thoracic surgery under one-lung ventilation (OLV). MethodsPatients were randomized to V-VCV (n = 39) or C-VCV (n = 39). During OLV tidal volume of 5 mL/kg predicted body weight (PBW) was used. Both groups were ventilated with a positive end-expiratory pressure (PEEP) of 5 cm H2O, inspiration to expiration ratio (I:E) of 1:1 (during OLV) and 1:2 during two-lung ventilation, the respiratory rate (RR) titrated to arterial pH, inspiratory peak-pressure ≤ 40 cm H2O and an inspiratory oxygen fraction of 1.0. ResultsSeventy-five out of 78 Patients completed the trial and were analyzed (dropouts were excluded). The partial pressure of arterial oxygen (PaO2) 20 min after the start of OLV did not differ among groups (V-VCV: 25.8 ± 14.6 kPa vs C-VCV: 27.2 ± 15.3 kPa; mean difference [95% CI]: 1.3 [−8.2, 5.5], P = 0.700). Furthermore, intraoperative gas exchange, intraoperative adverse events, need for rescue maneuvers due to desaturation and hypercapnia, incidence of postoperative pulmonary and extra-pulmonary complications, and hospital free days at day 30 after surgery did not differ between groups. ConclusionsIn thoracic surgery patients under OLV, V-VCV did not improve oxygenation or respiratory system mechanics compared to C-VCV.Ethical Committee: EK 420092019.Trial registration: at the German Clinical Trials Register: DRKS00022202 (16.06.2020).

A Recruitment Maneuver After Apnea Testing Improves Oxygenation and Reduces Atelectasis in Organ Donors After Brain Death.

Hypoxemia is the main modifiable factor preventing lungs from being transplanted from organ donors after brain death. One major contributor to impaired oxygenation in patients with brain injury is atelectasis. Apnea testing, an integral component of brain death declaration, promotes atelectasis and can worsen hypoxemia. In this study, we tested whether performing a recruitment maneuver (RM) after apnea testing could mitigate hypoxemia and atelectasis. During the study period, an RM (positive end-expiratory pressure of 15cm H2O for 15s then 30cm H2O for 30s) was performed immediately after apnea testing. We measured partial pressure of oxygen, arterial (PaO2) before and after RM. The primary outcomes were oxygenation (PaO2 to fraction of inspired oxygen [FiO2] ratio) and the severity of radiographic atelectasis (proportion of lung without aeration on computed tomography scans after brain death, quantified using an image analysis algorithm) in those who became organ donors. Outcomes in RM patients were compared with control patients undergoing apnea testing without RM in the previous 2years. Recruitment maneuver was performed in 54 patients after apnea testing, with a median immediate increase in PaO2 of 63mm Hg (interquartile range 0-109, p = 0.07). Eighteen RM cases resulted in hypotension, but none were life-threatening. Of this cohort, 37 patients became organ donors, compared with 37 donors who had apnea testing without RM. The PaO2:FiO2 ratio was higher in the RM group (355 ± 129 vs. 288 ± 127, p = 0.03), and fewer had hypoxemia (PaO2:FiO2 ratio < 300mm Hg, 22% vs. 57%; p = 0.04) at the start of donor management. The RM group showed less radiographic atelectasis (median 6% vs. 13%, p = 0.045). Although there was no difference in lungs transplanted (35% vs. 24%, p = 0.44), both better oxygenation and less atelectasis were associated with a higher likelihood of lungs being transplanted. Recruitment maneuver after apnea testing reduces hypoxemia and atelectasis in organ donors after brain death. This effect may translate into more lungs being transplanted.

Obesity and anesthesia.

Surgical procedures on obese patients are dramatically increasing worldwide over the past few years. In this review, we discuss the physiopathology of predominantly respiratory system in obese patients, the importance of preoperative evaluation, preoxygenation and intraoperative positive end expiratory pressure (PEEP) titration to prevent pulmonary complications and the optimization of airway management and oxygenation to reduce or prevent postoperative respiratory complications. Many patients are coming to preoperative clinic with medication history of glucagon-like-peptide 1 agonists (GLP-1) agonists and it has raised many questions regarding Nil Per Os (NPO)/perioperative fasting guidelines due to delayed gastric emptying caused by these medications. American Society of Anesthesiologists (ASA) has come up with guiding document to help with such situations. Ambulatory surgery centers are doing more obesity cases in a safe manner which were deemed unsafe at one point. Quantitative train of four (TOF) monitoring, better neuromuscular reversal agents and gastric ultrasounds seemed to have made a significant impact in the care of obese patients in the perioperative period. Obese patients are at higher risk of perioperative complications, mainly associated with those related to the respiratory function. An appropriate preoperative evaluation, intraoperative management, and postoperative support and monitoring is essential to improve outcome and increase the safety of the surgical procedure.

Prediction and simulation of PEEP setting effects with machine learning models

ObjectiveTo establish a new machine learning-based method to adjust positive end-expiratory pressure (PEEP) using only already routinely measured data. DesignRetrospective observational study. SettingIntensive care unit (ICU). Patients or participants51811 mechanically ventilated patients in multiple ICUs in the USA (data from MIMIC-III and eICU databases). InterventionsNo interventions. Main variables of interestSuccess parameters of ventilation (arterial partial pressures of oxygen and carbon dioxide and respiratory system compliance) ResultsThe multi-tasking neural network model performed significantly best for all target tasks in the primary test set. The model predicts arterial partial pressures of oxygen and carbon dioxide and respiratory system compliance about 45 min into the future with mean absolute percentage errors of about 21.7%, 10.0% and 15.8%, respectively. The proposed use of the model was demonstrated in case scenarios, where we simulated possible effects of PEEP adjustments for individual cases. ConclusionsOur study implies that machine learning approach to PEEP titration is a promising new method which comes with no extra cost once the infrastructure is in place. Availability of databases with most recent ICU patient data is crucial for the refinement of prediction performance.

Effect of postoperative oxygen therapy regimen modification on oxygenation in patients with acute type A aortic dissection

ObjectiveIn this study, we investigated the effect of various oxygen therapy regimens on oxygenation in patients with acute type A aortic dissection (AAD). MethodsA quasi-randomized controlled trial was conducted, in which patients with AAD hospitalized for surgery from June to September 2021 were assigned to the control group (patients received conventional oxygen therapy after postoperative mechanical ventilation, weaning, and extubation) and those who were admitted from October to December 2021 were assigned to the observation group [patients underwent optimally adjusted therapy based on the treatment of the control group, which mainly included prioritized elevation of positive end-expiratory pressure (PEEP) and restricted use of the fraction of inspired oxygen (FiO2)].The postoperative oxygenation index, blood gas analysis, and duration of mechanical ventilation were compared between the two groups. ResultsThere were significant differences in oxygenation observed at 2 h postoperatively between the groups. 12, 24, and 72 h postoperatively, the oxygenation index varied significantly between the two groups. There were statistically significant differences in the time effects of the oxygenation index and PaO2 between the two groups, as well as significant differences in the length of stay in the intensive care unit. ConclusionFor the postoperative care of patients with AAD, it is suggested that the minimum FiO2 required for oxygenation of patients be maintained. In addition, it is possible to enhance PEEP as a priority when PaO2is low.

Gastric Insufflation with High Flow Nasal Oxygen Therapy in Adult Patients Admitted to Intensive Care Unit: An Observational Study.

With the provision of a small positive end-expiratory pressure (PEEP) effect, high-flow nasal oxygen (HFNO) therapy carries a risk of stomach distension. The present study was conducted to find out the air leak in the gastric antrum leading to gastric distension in adult patients with acute respiratory failure receiving HFNO therapy. Adult patients with early hypoxemic respiratory failure requiring HFNO therapy were enrolled in this trial. Before initiation of HFNO therapy, baseline gastric volume (GV) and the average number of peristaltic contractions over one minute were measured using ultrasound. Once the patient was stabilized on HFNO therapy, a 2nd, 3rd, and 4th ultrasound scans were acquired at 10, 20, and 30 minutes respectively. Vitals and blood gas values were recorded at the baseline and after 30 min of initiation of HFNO therapy. Patient comfort, duration of HFNO therapy, and outcome were also recorded. The GV at 10, 20, and 30 minutes were significantly larger (p < 0.001) compared to baseline. This increase in GV was associated with a significantly increased number of peristaltic contractions and had a significant positive correlation with the HFNO flow (r = 0.541; p < 0.001). The HFNO therapy was well tolerated by most of the patients and led to a significant improvement in the vitals and blood gas parameters at 30 minutes after initiation of HFNO therapy. In adult patients with hypoxemic respiratory failure, the use of HFNO therapy produces gas leaks into the stomach leading to increased gastric volume. The gastric distension increases the peristaltic contraction and higher flows result in more distension. Ramachandran A, Bhatia P, Mohammed S, Kamal M, Chhabra S, Paliwal B. Gastric Insufflation with High Flow Nasal Oxygen Therapy in Adult Patients Admitted to Intensive Care Unit: An Observational Study. Indian J Crit Care Med 2024;28(4):393-398.

Influence of intra-abdominal pressure on ventilatory mechanical power delivery and respiratory driving pressure during laparoscopic cholecystectomy: A prospective cohort study

Abstract Background and Aims: Pneumoperitoneum creation for laparoscopic surgery increases the intraabdominal pressure and causes alveolar atelectasis. We investigated the influence of an increase in intra-abdominal pressure (IAP) on ventilatory mechanical power (MP) delivery during pneumoperitoneum creation for laparoscopic cholecystectomy. Material and Methods: In a prospective cohort design, we enrolled 42 patients undergoing laparoscopic cholecystectomy. During pneumoperitoneum creation, the IAP was sequentially raised to three predefined IAP levels (8, 11 and 14 mmHg), keeping identical ventilatory settings (timepoints T1, T2, and T3). After that, positive end-expiratory pressure (PEEP) was sequentially raised from 5 to 8 to 11 cmH2O (timepoint T4 and T5). The primary outcome included ventilatory MP delivery at each timepoint. Other variables included respiratory driving pressure (DP), airway resistance (AR), and respiratory compliance (RC). Results: The MP increased linearly with a rise in IAP from T1 to T3 (r = 0.71, P &lt; 0.001); the MP increased by 0.19 per unit rise in IAP (effect size 0.90, P &lt; 0.001). A similar positive correlation was also observed between DP and IAP from T1 to T3 (r = 0.73, P &lt; 0.001); the DP increased by 0.72 per unit rise in IAP (effect size 0.89, P &lt; 0.001). The MP increased significantly on increasing PEEP from T3 to T5, while the DP decreased concomitantly (P &lt; 0.001). The AR increased significantly from T1 to T3, while RC decreased concomitantly; vice-versa was observed at T4 and T5 (P &lt; 0.001). Conclusions: The ventilatory MP delivery rises linearly with an increase in IAP. Targeting an IAP-guided MP level could be an attractive approach to minimize lung injury.

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.

Awake pronation with helmet CPAP in early COVID-19 ARDS patients: effects on respiratory effort and distribution of ventilation assessed by EIT.

Prone positioning with continuous positive airway pressure (CPAP) is widely used for respiratory support in awake patients with COVID-19-associated acute respiratory failure. We aimed to assess the respiratory mechanics and distribution of ventilation in COVID-19-associated ARDS treated by CPAP in awake prone position. We studied 16 awake COVID-19 patients with moderate-to-severe ARDS. The study protocol consisted of a randomized sequence of supine and prone position with imposed positive end-expiratory pressure (PEEP) of 5 and 10 cmH2O delivered by helmet CPAP. Respiratory mechanics and distribution of ventilation were assessed through esophageal pressure (PES) and electrical impedance tomography (EIT). At the end of each 20-min phase, arterial blood gas analysis was performed, and PES swing and EIT tracings were recorded for the calculation of the respiratory mechanics and regional ventilation. The patient's position had no significant effects on respiratory mechanics. EIT analysis did not detect differences among global indices of ventilation. A significant proportion of pixels in the sternal region of interest showed an increase in compliance from the supine to prone position and PaO2/FIO2 increased accordingly. The best improvement of both PaO2/FIO2 and sternal compliance was obtained in the prone position with PEEP 10 cmH2O. In the studied subjects, prone positioning during CPAP treatment raised oxygenation without improvement of "protective" ventilation or global ventilatory inhomogeneity indices. Prone positioning with higher PEEP significantly increased the compliance of sternal regions.

Reinforcement learning for intensive care medicine: actionable clinical insights from novel approaches to reward shaping and off-policy model evaluation

BackgroundReinforcement learning (RL) holds great promise for intensive care medicine given the abundant availability of data and frequent sequential decision-making. But despite the emergence of promising algorithms, RL driven bedside clinical decision support is still far from reality. Major challenges include trust and safety. To help address these issues, we introduce cross off-policy evaluation and policy restriction and show how detailed policy analysis may increase clinical interpretability. As an example, we apply these in the setting of RL to optimise ventilator settings in intubated covid-19 patients.MethodsWith data from the Dutch ICU Data Warehouse and using an exhaustive hyperparameter grid search, we identified an optimal set of Dueling Double-Deep Q Network RL models. The state space comprised ventilator, medication, and clinical data. The action space focused on positive end-expiratory pressure (peep) and fraction of inspired oxygen (FiO2) concentration. We used gas exchange indices as interim rewards, and mortality and state duration as final rewards. We designed a novel evaluation method called cross off-policy evaluation (OPE) to assess the efficacy of models under varying weightings between the interim and terminal reward components. In addition, we implemented policy restriction to prevent potentially hazardous model actions. We introduce delta-Q to compare physician versus policy action quality and in-depth policy inspection using visualisations.ResultsWe created trajectories for 1118 intensive care unit (ICU) admissions and trained 69,120 models using 8 model architectures with 128 hyperparameter combinations. For each model, policy restrictions were applied. In the first evaluation step, 17,182/138,240 policies had good performance, but cross-OPE revealed suboptimal performance for 44% of those by varying the reward function used for evaluation. Clinical policy inspection facilitated assessment of action decisions for individual patients, including identification of action space regions that may benefit most from optimisation.ConclusionCross-OPE can serve as a robust evaluation framework for safe RL model implementation by identifying policies with good generalisability. Policy restriction helps prevent potentially unsafe model recommendations. Finally, the novel delta-Q metric can be used to operationalise RL models in clinical practice. Our findings offer a promising pathway towards application of RL in intensive care medicine and beyond.

Determinants of acute kidney injury during high-power mechanical ventilation: secondary analysis from experimental data

BackgroundThe individual components of mechanical ventilation may have distinct effects on kidney perfusion and on the risk of developing acute kidney injury; we aimed to explore ventilatory predictors of acute kidney failure and the hemodynamic changes consequent to experimental high-power mechanical ventilation.MethodsSecondary analysis of two animal studies focused on the outcomes of different mechanical power settings, including 78 pigs mechanically ventilated with high mechanical power for 48 h. The animals were categorized in four groups in accordance with the RIFLE criteria for acute kidney injury (AKI), using the end-experimental creatinine: (1) NO AKI: no increase in creatinine; (2) RIFLE 1-Risk: increase of creatinine of > 50%; (3) RIFLE 2-Injury: two-fold increase of creatinine; (4) RIFLE 3-Failure: three-fold increase of creatinine;ResultsThe main ventilatory parameter associated with AKI was the positive end-expiratory pressure (PEEP) component of mechanical power. At 30 min from the initiation of high mechanical power ventilation, the heart rate and the pulmonary artery pressure progressively increased from group NO AKI to group RIFLE 3. At 48 h, the hemodynamic variables associated with AKI were the heart rate, cardiac output, mean perfusion pressure (the difference between mean arterial and central venous pressures) and central venous pressure. Linear regression and receiving operator characteristic analyses showed that PEEP-induced changes in mean perfusion pressure (mainly due to an increase in CVP) had the strongest association with AKI.ConclusionsIn an experimental setting of ventilation with high mechanical power, higher PEEP had the strongest association with AKI. The most likely physiological determinant of AKI was an increase of pleural pressure and CVP with reduced mean perfusion pressure. These changes resulted from PEEP per se and from increase in fluid administration to compensate for hemodynamic impairment consequent to high PEEP;

Predicting the Length of Mechanical Ventilation in Acute Respiratory Disease Syndrome Using Machine Learning: The PIONEER Study.

Background: The ability to predict a long duration of mechanical ventilation (MV) by clinicians is very limited. We assessed the value of machine learning (ML) for early prediction of the duration of MV > 14 days in patients with moderate-to-severe acute respiratory distress syndrome (ARDS). Methods: This is a development, testing, and external validation study using data from 1173 patients on MV ≥ 3 days with moderate-to-severe ARDS. We first developed and tested prediction models in 920 ARDS patients using relevant features captured at the time of moderate/severe ARDS diagnosis, at 24 h and 72 h after diagnosis with logistic regression, and Multilayer Perceptron, Support Vector Machine, and Random Forest ML techniques. For external validation, we used an independent cohort of 253 patients on MV ≥ 3 days with moderate/severe ARDS. Results: A total of 441 patients (48%) from the derivation cohort (n = 920) and 100 patients (40%) from the validation cohort (n = 253) were mechanically ventilated for >14 days [median 14 days (IQR 8-25) vs. 13 days (IQR 7-21), respectively]. The best early prediction model was obtained with data collected at 72 h after moderate/severe ARDS diagnosis. Multilayer Perceptron risk modeling identified major prognostic factors for the duration of MV > 14 days, including PaO2/FiO2, PaCO2, pH, and positive end-expiratory pressure. Predictions of the duration of MV > 14 days showed modest discrimination [AUC 0.71 (95%CI 0.65-0.76)]. Conclusions: Prolonged MV duration in moderate/severe ARDS patients remains difficult to predict early even with ML techniques such as Multilayer Perceptron and using data at 72 h of diagnosis. More research is needed to identify markers for predicting the length of MV. This study was registered on 14 August 2023 at ClinicalTrials.gov (NCT NCT05993377).

Effect of Different Extubation Strategies on Atelectasis in Older Adults after Major Abdominal Surgeries: A Prospective Randomised Controlled Trial.

Older patients are particularly vulnerable to age-related respiratory changes. This prospective randomized controlled trial studied the effects of high and low fractions of inspired oxygen (FiO2) with the recruitment maneuver (RM) during extubation on lung atelectasis post-operatively in older patients undergoing major abdominal surgery. We randomized a total of 132 patients aged >60 years who underwent both elective and emergency major abdominal surgeries and met the inclusion criteria into three groups (H, HR, and LR) using computer-generated block randomization. Group H received high FiO2 (1), Group HR received high FiO2 (1) with RM followed by a positive end-expiratory pressure of 5 cm H2O, and Group LR received low FiO2 (0.4) with RM followed by a positive end-expiratory pressure of 5 cm H2O 10 min before extubation. Oxygenation and atelectasis were measured using the arterial partial pressure of oxygen (PaO2)/FiO2 ratios and lung ultrasound score. Postoperative pulmonary complications were recorded up to 24 h postoperatively. The mean PaO2/FiO2 at 30 min post-extubation was significantly higher in Groups LR and HR compared to that in Group H (390.71 ± 29.55, 381.97 ± 24.97, and 355.37 ± 31.7, p <0.001). In the immediate postoperative period, the median lung ultrasound score was higher in Group H than that in Groups LR and HR (6 [5-7]), 3 [3-5], and 3.5 [2.25-4.75], p <0.001). The incidence of oxygen desaturation and oxygen requirements was higher in Group H during the postoperative period. The RM before extubation is beneficial in reducing atelectasis and postoperative pulmonary complications, irrespective of the FiO2 concentration used in older adults undergoing major abdominal surgeries.

Outcomes associated with ventilator-associated events (VAE), respiratory infections (VARI), pneumonia (VAP) and tracheobronchitis (VAT) in ventilated pediatric ICU patients: A multicentre prospective cohort study

ObjectivesAn objective categorization of respiratory infections based on outcomes is an unmet clinical need. Ventilator-associated pneumonia and tracheobronchitis remain used in clinical practice, whereas ventilator-associated events (VAE) are limited to surveillance purposes. Research methodology/designThis was a secondary analysis from a multicentre observational prospective cohort study. VAE were defined as a sustained increase in minimum Oxygen inspired fraction (FiO2) and/or Positive end-expiratory pressures (PEEP) of ≥ 0.2/2 cm H2O respectively, or an increase of 0.15 FiO2 + 1 cm H20 positive end-expiratory pressures for ≥ 1 calendar-day. Setting15 Paediatric Intensive Care Units. Main outcome measuresMechanical ventilation duration, intensive care and hospital length of stay; (LOS) and mortality. ResultsA cohort of 391 ventilated children with an age (median, [Interquartile Ranges]) of 1 year[0.2–5.3] and 7 days[5–10] of mechanical ventilation were included. Intensive care and hospital stays were 11 [7–19] and 21 [14–39] days, respectively. Mortality was 5.9 %. Fifty-eight ventilator-associated respiratory infections were documented among 57 patients: Seventeen (29.3 %) qualified as ventilator-associated pneumonia (VAP) and 41 (70.7 %) as ventilator-associated tracheobronchitis (VAT). Eight pneumonias and 16 tracheobronchitis (47 % vs 39 %,P = 0.571) required positive end-expiratory pressure or oxygen increases consistent with ventilator-associated criteria. Pneumonias did not significantly impact on outcomes when compared to tracheobronchitis. In contrast, infections (pneumonia or tracheobronchitis) following VAEs criteria were associated with > 6, 8 and 15 extra-days of ventilation (16 vs 9.5, P = 0.001), intensive care stay (23.5 vs 15; P = 0.004) and hospital stay (39 vs 24; P = 0.015), respectively. ConclusionWhen assessing ventilated children with respiratory infections, VAE apparently is associated with higher ventilator-dependency and LOS compared with pneumonia or tracheobronchitis. Implications for practiceIncorporating the modification of ventilatory settings for further categorization of the respiratory infections may facilitate therapeutic management among ventilated patients.