Time-Controlled Adaptive Ventilation (TCAV): a personalized strategy for lung protection.

Acute respiratory distress syndrome (ARDS) alters the dynamics of lung inflation during mechanical ventilation. Repetitive alveolar collapse and expansion (RACE) predisposes the lung to ventilator-induced lung injury (VILI). Two broad approaches are currently used to minimize VILI: (1) low tidal volume (LVT) with low-moderate positive end-expiratory pressure (PEEP); and (2) open lung approach (OLA). The LVT approach attempts to protect already open lung tissue from overdistension, while simultaneously resting collapsed tissue by excluding it from the cycle of mechanical ventilation. By contrast, the OLA attempts to reinflate potentially recruitable lung, usually over a period of seconds to minutes using higher PEEP used to prevent progressive loss of end-expiratory lung volume (EELV) and RACE. However, even with these protective strategies, clinical studies have shown that ARDS-related mortality remains unacceptably high with a scarcity of effective interventions over the last two decades. One of the main limitations these varied interventions demonstrate to benefit is the observed clinical and pathologic heterogeneity in ARDS. We have developed an alternative ventilation strategy known as the Time Controlled Adaptive Ventilation (TCAV) method of applying the Airway Pressure Release Ventilation (APRV) mode, which takes advantage of the heterogeneous time- and pressure-dependent collapse and reopening of lung units. The TCAV method is a closed-loop system where the expiratory duration personalizes VT and EELV. Personalization of TCAV is informed and tuned with changes in respiratory system compliance (CRS) measured by the slope of the expiratory flow curve during passive exhalation. Two potentially beneficial features of TCAV are: (i) the expiratory duration is personalized to a given patient's lung physiology, which promotes alveolar stabilization by halting the progressive collapse of alveoli, thereby minimizing the time for the reopened lung to collapse again in the next expiration, and (ii) an extended inspiratory phase at a fixed inflation pressure after alveolar stabilization gradually reopens a small amount of tissue with each breath. Subsequently, densely collapsed regions are slowly ratcheted open over a period of hours, or even days. Thus, TCAV has the potential to minimize VILI, reducing ARDS-related morbidity and mortality.

Physiological and clinical effects of trunk inclination adjustment in patients with respiratory failure: a scoping review and narrative synthesis.

BACKGROUND: Adjusting trunk inclination from a semi-recumbent position to a supine-flat position or vice versa in patients with respiratory failure significantly affects numerous aspects of respiratory physiology including respiratory mechanics, oxygenation, end-expiratory lung volume, and ventilatory efficiency. Despite these observed effects, the current clinical evidence regarding this positioning manoeuvre is limited. This study undertakes a scoping review of patients with respiratory failure undergoing mechanical ventilation to assess the effect of trunk inclination on physiological lung parameters. METHODS: The PubMed, Cochrane, and Scopus databases were systematically searched from 2003 to 2023. INTERVENTIONS: Changes in trunk inclination. MEASUREMENTS: Four domains were evaluated in this study: 1) respiratory mechanics, 2) ventilation distribution, 3) oxygenation, and 4) ventilatory efficiency. RESULTS: After searching the three databases and removing duplicates, 220 studies were screened. Of these, 37 were assessed in detail, and 13 were included in the final analysis, comprising 274 patients. All selected studies were experimental, and assessed respiratory mechanics, ventilation distribution, oxygenation, and ventilatory efficiency, primarily within 60 min post postural change. CONCLUSION: In patients with acute respiratory failure, transitioning from a supine to a semi-recumbent position leads to decreased respiratory system compliance and increased airway driving pressure. Additionally, C-ARDS patients experienced an improvement in ventilatory efficiency, which resulted in lower PaCO2 levels. Improvements in oxygenation were observed in a few patients and only in those who exhibited an increase in EELV upon moving to a semi-recumbent position. Therefore, the trunk inclination angle must be accurately reported in patients with respiratory failure under mechanical ventilation.

Positive end-expiratory pressure in the pediatric intensive care unit.

Application of positive end-expiratory pressure (PEEP) targeted towards improving oxygenation is one of the components of the ventilatory management of pediatric acute respiratory distress syndrome (PARDS). Low end-expiratory airway pressures cause repetitive opening and closure of unstable alveoli, leading to surfactant dysfunction and parenchymal shear injury. Consequently, there is less lung volume available for tidal ventilation when there are atelectatic lung regions. This will increase lung strain in aerated lung areas to which the tidal volume is preferentially distributed. Pediatric critical care practitioners tend to use low levels of PEEP and inherently accept higher FiO2, but these practices may negatively affect patient outcome. The Pediatric Acute Lung Injury Consensus Conference (PALICC) suggests that PEEP should be titrated to oxygenation/oxygen delivery, hemodynamics, and compliance measured under static conditions as compared to other clinical parameters or any of these parameters in isolation in patients with PARDS, while limiting plateau pressure and/or driving pressure limits.

Association between driving pressure-guided ventilation and postoperative pulmonary complications in surgical patients: a meta-analysis with trial sequential analysis.

BACKGROUND: Prior studies have reported inconsistent results regarding the association between driving pressure-guided ventilation and postoperative pulmonary complications (PPCs). We aimed to investigate whether driving pressure-guided ventilation is associated with a lower risk of PPCs. METHODS: We systematically searched electronic databases for RCTs comparing driving pressure-guided ventilation with conventional protective ventilation in adult surgical patients. The primary outcome was a composite of PPCs. Secondary outcomes were pneumonia, atelectasis, and acute respiratory distress syndrome (ARDS). Meta-analysis and subgroup analysis were conducted to calculate risk ratios (RRs) with 95% confidence intervals (CI). Trial sequential analysis (TSA) was used to assess the conclusiveness of evidence. RESULTS: Thirteen RCTs with 3401 subjects were included. Driving pressure-guided ventilation was associated with a lower risk of PPCs (RR 0.70, 95% CI 0.56-0.87, P=0.001), as indicated by TSA. Subgroup analysis (P for interaction=0.04) found that the association was observed in non-cardiothoracic surgery (nine RCTs, 1038 subjects, RR 0.61, 95% CI 0.48-0.77, P< 0.0001), with TSA suggesting sufficient evidence and conclusive result; however, it did not reach significance in cardiothoracic surgery (four RCTs, 2363 subjects, RR 0.86, 95% CI 0.67-1.10, P=0.23), with TSA indicating insufficient evidence and inconclusive result. Similarly, a lower risk of pneumonia was found in non-cardiothoracic surgery but not in cardiothoracic surgery (P for interaction=0.046). No significant differences were found in atelectasis and ARDS between the two ventilation strategies. CONCLUSIONS: Driving pressure-guided ventilation was associated with a lower risk of postoperative pulmonary complications in non-cardiothoracic surgery but not in cardiothoracic surgery. SYSTEMATIC REVIEW PROTOCOL: INPLASY 202410068.

Novel Oxygenation and Saturation Indices for Mortality Prediction in COVID-19 ARDS Patients: The Impact of Driving Pressure and Mechanical Power.

Background: The oxygenation index (OI) and oxygen saturation index (OSI) are proven mortality predictors in pediatric and adult patients, traditionally using mean airway pressure (Pmean). We introduce novel indices, replacing Pmean with DP (ΔPinsp), MPdyn, and MPtot, assessing their potential for predicting COVID-19 acute respiratory distress syndrome (ARDS) mortality, comparing them to traditional indices. Methods: We studied 361 adult COVID-19 ARDS patients for 7 days, collecting ΔPinsp, MPdyn, and MPtot, OI-ΔPinsp, OI-MPdyn, OI-MPtot, OSI-ΔPinsp, OSI-MPdyn, and OSI-MPtot. We compared these in surviving and non-surviving patients over the first 7 intensive care unit (ICU) days using Mann-Whitney U test. Logistic regression receiver operating characteristic (ROC) analysis assessed AUC and CI values for ICU mortality on day three. We determined cut-off values using Youden's method and conducted multivariate Cox regression on parameter limits. Results: All indices showed significant differences between surviving and non-surviving patients on the third day of ICU care. The AUC values of OI-ΔPinsp were significantly higher than those of P/F and OI-Pmean (P values .0002 and <.0001, respectively). Similarly, AUC and CI values of OSI-ΔPinsp and OSI-MPdyn were significantly higher than those of SpO2/FiO2 and OSI-Pmean values (OSI-ΔPinsp: P < .0001, OSI-MPdyn: P values .047 and .028, respectively). OI-ΔPinsp, OSI-ΔPinsp, OI-MPdyn, OSI-MPdyn, OI-MPtot, and OSI-MPtot had AUC values of 0.72, 0.71, 0.69, 0.68, 0.66, and 0.64, respectively, with cut-off values associated with hazard ratios and P values of 7.06 (HR = 1.84, P = .002), 8.04 (HR = 2.00, P ≤ .0001), 7.12 (HR = 1.68, P = .001), 5.76 (HR = 1.70, P ≤ .0001), 10.43 (HR = 1.52, P = .006), and 10.68 (HR = 1.66, P = .001), respectively. Conclusions: Critical values of all indices were associated to higher ICU mortality rates and extended mechanical ventilation durations. The OI-ΔPinsp, OSI-ΔPinsp, and OSI-MPdyn indices displayed the strongest predictive capabilities for ICU mortality. These novel indices offer valuable insights for intensivists in the clinical management and decision-making process for ARDS patients.

Effect of incremental PEEP titration on postoperative pulmonary complications in patients undergoing emergency laparotomy: a randomized controlled trial.

Postoperative pulmonary complications (PPC) has a significant negative impact and are associated with increased length of hospital stay and cost of care. Emergency surgery is a well-established risk factor for PPC. Previous studies reported that personalized positive end-expiratory pressure (PEEP) might reduce postoperative atelectasis and postoperative pulmonary complications. N = 168 adult patients undergoing major emergency laparotomy under general anesthesia were recruited in this study. A minimum driving pressure based incremental PEEP titration was compared to a fixed PEEP of 5 cmH2O. The primary outcome was PPC up to postoperative day 7. The mean (standard deviation) of the recruited patients was 41.7(16.1)y, and 48.8% (82 of 168 patients) were female. The risk of PPC at postoperative day 7 was similar in both the study groups [Relative risk (RR) (95% Confidence interval, CI) 0.81 (0.58, 1.13); p = 0.25]. In addition, the incidence of intraoperative hypotension [p = 0.75], oxygen-free days at day 28 [p = 0.27], duration of postoperative hospital stay [p = 0.50], length of postoperative intensive care unit stay [p = 0.28], and in-hospital mortality [p = 0.38] were similar in two groups. Incidence of PPC was not reduced with the use of an individualized PEEP strategy based on lowest driving pressure. However, the incidence of hypotension and bradycardia was also not increased with titrated PEEP.Trial Registration: www.ctri.nic.in ; CTRI/2020/12/029765.

The impact of a lung-protective ventilation mode using transpulmonary driving pressure titrated positive end-expiratory pressure on the prognosis of patients with acute respiratory distress syndrome.

OBJECTIVE: This study aimed to assess the impact of a lung-protective ventilation strategy utilizing transpulmonary driving pressure titrated positive end-expiratory pressure (PEEP) on the prognosis [mechanical ventilation duration, hospital stay, 28-day mortality rate and incidence of ventilator-associated pneumonia (VAP), survival outcome] of patients with Acute Respiratory Distress Syndrome (ARDS). METHODS: A total of 105 ARDS patients were randomly assigned to either the control group (n = 51) or the study group (n = 53). The control group received PEEP titration based on tidal volume [A tidal volume of 6 mL/kg, flow rate of 30-60 L/min, frequency of 16-20 breaths/min, constant flow rate, inspiratory-to-expiratory ratio of 1:1 to 1:1.5, and a plateau pressure ≤ 30-35 cmH2O. PEEP was adjusted to maintain oxygen saturation (SaO2) at or above 90%, taking into account blood pressure], while the study group received PEEP titration based on transpulmonary driving pressure (Esophageal pressure was measured as a surrogate for pleural pressure using an esophageal pressure measurement catheter connected to the ventilator. Tidal volume and PEEP were adjusted based on the observed end-inspiratory and end-expiratory transpulmonary pressures, aiming to maintain a transpulmonary driving pressure below 15 cmH2O during mechanical ventilation. Adjustments were made 2-4 times per day). Statistical analysis and comparison were conducted on lung function indicators [oxygenation index (OI), arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2)] as well as other measures such as heart rate, mean arterial pressure, and central venous pressure in two groups of patients after 48 h of mechanical ventilation. The 28-day mortality rate, duration of mechanical ventilation, length of hospital stay, and ventilator-associated pneumonia (VAP) incidence were compared between the two groups. A 60-day follow-up was performed to record the survival status of the patients. RESULTS: In the control group, the mean age was (55.55 ± 10.51) years, with 33 females and 18 males. The pre-ICU hospital stay was (32.56 ± 9.89) hours. The mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was (19.08 ± 4.67), and the mean Murray Acute Lung Injury score was (4.31 ± 0.94). In the study group, the mean age was (57.33 ± 12.21) years, with 29 females and 25 males. The pre-ICU hospital stay was (33.42 ± 10.75) hours. The mean APACHE II score was (20.23 ± 5.00), and the mean Murray Acute Lung Injury score was (4.45 ± 0.88). They presented a homogeneous profile (all P > 0.05). Following intervention, significant improvements were observed in PaO2 and OI compared to pre-intervention values. The study group exhibited significantly higher PaO2 and OI compared to the control group, with statistically significant differences (all P < 0.05). After intervention, the study group exhibited a significant increase in PaCO2 (43.69 ± 6.71 mmHg) compared to pre-intervention levels (34.19 ± 5.39 mmHg). The study group's PaCO2 was higher than the control group (42.15 ± 7.25 mmHg), but the difference was not statistically significant (P > 0.05). There were no significant differences in hemodynamic indicators between the two groups post-intervention (all P > 0.05). The study group demonstrated significantly shorter mechanical ventilation duration and hospital stay, while 28-day mortality rate and incidence of ventilator-associated pneumonia (VAP) showed no significant differences. Kaplan-Meier survival analysis revealed a significantly better survival outcome in the study group at the 60-day follow-up (HR = 0.565, 95% CI: 0.320-0.999). CONCLUSION: Lung-protective mechanical ventilation using transpulmonary driving pressure titrated PEEP effectively improves lung function, reduces mechanical ventilation duration and hospital stay, and enhances survival outcomes in patients with ARDS. However, further study is needed to facilitate the wider adoption of this approach.

Prone-position decreases airway closure in a patient with ARDS undergoing venovenous extracorporeal membrane oxygenation.

PURPOSE: Airway closure is a interruption of communication between larger and smaller airways. The presence of airway closure during mechanical ventilation may lead to the overestimation of driving pressure (DP), introducing errors in the assessment of respiratory mechanics and in positive end-expiratory pressure (PEEP) setting on the ventilator. Patients with severe acute respiratory distress syndrome (ARDS) may exhibit the airway closure phenomenon, which can be easily diagnosed with a low-flow inflation. Prone positioning is a therapeutic manoeuver proven to reduce mortality in ARDS patients, and has been widely implemented also in patients requiring veno-venous extracorporeal membrane oxygenation (V-V ECMO). To date, the impact of prone positioning on changes in airway closure has not been described. METHODS: We present an image analysis of the pressure waveform during volume-controlled ventilation and low-flow inflations before and after prone positioning in an ARDS patient on VV ECMO. RESULTS: A high airway opening pressure level (23 cmH2O) was detected in the supine position during tidal ventilation. Airway closure was confirmed by using a low-flow inflation. Prone positioning significantly attenuated airway closure, with the airway opening pressure decreasing to 13 cmH2O. After re-supination, airway closure was lower as compared with supine position at baseline (17 cmH2O). CONCLUSION: Prone positioning reduced airway closure in an ARDS patient on VV ECMO support.

Predictive performance of the variation rate of the driving pressure on the outcome of invasive mechanical ventilation in patients with acute respiratory distress syndrome.

PURPOSE: To assess the value of the driving pressure variation rate (ΔP%) in predicting the outcome of weaning from invasive mechanical ventilation in patients with acute respiratory distress syndrome. METHODS: In this case-control study, a total of 35 patients with moderate-severe acute respiratory distress syndrome were admitted to the intensive care unit between January 2022 and December 2022 and received invasive mechanical ventilation for at least 48 h were enrolled. Patients were divided into successful weaning group and failed weaning group depending on whether they could be removed from ventilator support within 14 days. Outcome measures including driving pressure, PaO2:FiO2, and positive end-expiratory pressure, etc. were assessed every 24 h from day 0 to day 14 until successful weaning was achieved. The measurement data of non-normal distribution were presented as median (Q1, Q3), and the differences between groups were compared by Wilcoxon rank sum test. And categorical data use the Chi-square test or Fisher's exact test to compare. The predictive value of ΔP% in predicting the outcome of weaning from the ventilator was analyzed using receiver operating characteristic curves. RESULTS: Of the total 35 patients included in the study, 17 were successful vs. 18 failed in weaning from a ventilator after 14 days of mechanical ventilation. The cut-off values of the median ΔP% measured by Operator 1 vs. Operator 2 in the first 4 days were ≥ 4.17% and 4.55%, respectively (p < 0.001), with the area under curve of 0.804 (sensitivity of 88.2%, specificity of 64.7%) and 0.770 (sensitivity of 88.2%, specificity of 64.7%), respectively. There was a significant difference in mechanical ventilation duration between the successful weaning group and the failure weaning group (8 (6, 13) vs. 12 (7.5, 17.3), p = 0.043). The incidence of ventilator-associated pneumonia in the successful weaning group was significantly lower than in the failed weaning group (0.2‰ vs. 2.3‰, p = 0.001). There was a significant difference noted between these 2 groups in the 28-day mortality (11.8% vs. 66.7%, p = 0.003). CONCLUSION: The median ΔP% in the first 4 days of mechanical ventilation showed good predictive performance in predicting the outcome of weaning from mechanical ventilation within 14 days. Further study is needed to confirm this finding.

Changes in Driving Pressure vs Oxygenation as Predictor of Mortality in Moderate to Severe Acute Respiratory Distress Syndrome Patients Receiving Prone Position Ventilation.

Background: Prone position ventilation (PPV) causes improvement in oxygenation, nevertheless, mortality in severe acute respiratory distress syndrome (ARDS) remains high. The changes in the driving pressure (DP) and its role in predicting mortality in moderate to severe ARDS patients receiving PPV is unexplored. Methods: A prospective observational study, conducted between September 2020 and February 2023 on moderate-severe ARDS patients requiring PPV. The values of DP and oxygenation (ratio of partial pressure of arterial oxygen to fraction of inspired oxygen [PaO2/FiO2]) before, during, and after PPV were recorded. The aim was to compare the DP and oxygenation before, during and after PPV sessions among moderate- severe ARDS patients, and determine the best predictor of mortality. Results: Total of 52 patients were included; 28-day mortality was 57%. Among the survivors, DP prior to PPV as compared to post-PPV session reduced significantly, from 16.36 ± 2.57 cmH2O to 13.91 ± 1.74 cmH2O (p-value < 0.001), whereas DP did not reduce in the non-survivors (19.43 ± 3.16 to 19.70 ± 3.15 cmH2O (p-value = 0.318)]. Significant improvement in PaO2/FiO2 before PPV to post-PPV among both the survivors [92.75 [67.5-117.75]) to [205.50 (116.25-244.50)], (p-value < 0.001) and also among the non-survivors [87.90 (67.75-100.75)] to [112 (88.00-146.50)], (p-value < 0.001) was noted. Logistic regression analysis showed DP after PPV session as best predictor of mortality (p-value = 0.044) and its AUROC to predict mortality was 0.939, cut-off ≥16 cmH2O, 90% sensitivity, 82% specificity. The Kaplan-Meier curve of DP after PPV ≥16 cmH2O and <16 cmH2O was significant (Log-rank Mantel-Cox p-value < 0.001). Conclusion: Prone position ventilation-induced decrease in DP is prognostic marker of survival than the increase in PaO2/FiO2. There is a primacy of DP, rather than oxygenation, in predicting mortality in moderate-severe ARDS. Post-PPV session DP ≥16 cmH2O was an independent predictor of mortality. How to cite this article: Todur P, Nileshwar A, Chaudhuri S, Shanbhag V, Cherisma C. Changes in Driving Pressure vs Oxygenation as Predictor of Mortality in Moderate to Severe Acute Respiratory Distress Syndrome Patients Receiving Prone Position Ventilation. Indian J Crit Care Med 2024;28(2):134-140.

Oxygenation Index and Oxygen Saturation Index for Predicting Postoperative Outcome in Patients Undergoing Emergency Surgery: A Prospective Cohort Study.

Background: The OI was originally evaluated as a prognostic tool for acute hypoxemic respiratory failure in children and was an independent predictor for mortality in adult patients with acute respiratory distress syndrome (ARDS). Methods: Oxygenation index and OSI of 201 adult patients undergoing emergency surgery were evaluated at different time points. The primary objective of this study was to find the correlation between OI and OSI. The secondary objectives were to find the prognostic utility of OI and OSI for postoperative mechanical ventilation and mortality. Results: Significant statistical correlation was found between OI and OSI both at the beginning (r 2 = 0.61; p < 0.001) and immediately after surgery (r 2 = 0.47; p < 0.001). Oxygen saturation index at the beginning [area under the receiver operating characteristics curve (AUROC) (95% CI) 0.76 (0.62-0.89); best cutoff 3.9, sensitivity 64% and specificity 45%] and immediately after surgery [AUROC (95% CI) 0.82 (0.72-0.92); best cutoff 3.57, sensitivity 79%, and specificity 62%] were reasonable predictors of the requirement of invasive ventilatory support. Exploratory analysis reported that older age (p = 0.02), higher total leukocyte count (p = 0.002), higher arterial lactate (p = 0.02), and higher driving pressure (p < 0.001) were independently associated with hospital mortality. Conclusion: In adult patients undergoing emergency laparotomy under general anesthesia, OI and OSI were found to be correlated. Both metrics demonstrated reasonable accuracy in predicting the need for invasive ventilatory support beyond 24 hours and hospital mortality. How to cite this article: Thakuria R, Ernest EE, Chowdhury AR, Pangasa N, Kayina CA, Bhattacharjee S, et al. Oxygenation Index and Oxygen Saturation Index for Predicting Postoperative Outcome in Patients Undergoing Emergency Surgery: A Prospective Cohort Study. Indian J Crit Care Med 2024;28(7):645-649.

Mechanical power of ventilation and driving pressure: two undervalued parameters for pre extracorporeal membrane oxygenation ventilation and during daily management?

The current ARDS guidelines highly recommend lung protective ventilation which include plateau pressure (Pplat < 30 cm H2O), positive end expiratory pressure (PEEP > 5 cm H2O) and tidal volume (Vt of 6 ml/kg) of predicted body weight. In contrast, the ELSO guidelines suggest the evaluation of an indication of veno-venous extracorporeal membrane oxygenation (ECMO) due to hypoxemic or hypercapnic respiratory failure or as bridge to lung transplantation. Finally, these recommendations remain a wide range of scope of interpretation. However, particularly patients with moderate-severe to severe ARDS might benefit from strict adherence to lung protective ventilation strategies. Subsequently, we discuss whether extended physiological ventilation parameter analysis might be relevant for indication of ECMO support and can be implemented during the daily routine evaluation of ARDS patients. Particularly, this viewpoint focus on driving pressure and mechanical power.

Management of severe acute respiratory distress syndrome: a primer.

This narrative review explores the physiology and evidence-based management of patients with severe acute respiratory distress syndrome (ARDS) and refractory hypoxemia, with a focus on mechanical ventilation, adjunctive therapies, and veno-venous extracorporeal membrane oxygenation (V-V ECMO). Severe ARDS cases increased dramatically worldwide during the Covid-19 pandemic and carry a high mortality. The mainstay of treatment to improve survival and ventilator-free days is proning, conservative fluid management, and lung protective ventilation. Ventilator settings should be individualized when possible to improve patient-ventilator synchrony and reduce ventilator-induced lung injury (VILI). Positive end-expiratory pressure can be individualized by titrating to best respiratory system compliance, or by using advanced methods, such as electrical impedance tomography or esophageal manometry. Adjustments to mitigate high driving pressure and mechanical power, two possible drivers of VILI, may be further beneficial. In patients with refractory hypoxemia, salvage modes of ventilation such as high frequency oscillatory ventilation and airway pressure release ventilation are additional options that may be appropriate in select patients. Adjunctive therapies also may be applied judiciously, such as recruitment maneuvers, inhaled pulmonary vasodilators, neuromuscular blockers, or glucocorticoids, and may improve oxygenation, but do not clearly reduce mortality. In select, refractory cases, the addition of V-V ECMO improves gas exchange and modestly improves survival by allowing for lung rest. In addition to VILI, patients with severe ARDS are at risk for complications including acute cor pulmonale, physical debility, and neurocognitive deficits. Even among the most severe cases, ARDS is a heterogeneous disease, and future studies are needed to identify ARDS subgroups to individualize therapies and advance care.

Estimation of transpulmonary driving pressure during synchronized mechanical ventilation using a single lower assist maneuver (LAM) in rabbits: a comparison to measurements made with an esophageal balloon.

BACKGROUND: Mechanical ventilation is applied to unload the respiratory muscles, but knowledge about transpulmonary driving pressure (ΔPL) is important to minimize lung injury. We propose a method to estimate ΔPL during neurally synchronized assisted ventilation, with a simple intervention of lowering the assist for one breath ("lower assist maneuver", LAM). METHODS: In 24 rabbits breathing spontaneously with imposed loads, titrations of increasing assist were performed, with two neurally synchronized modes: neurally adjusted ventilatory assist (NAVA) and neurally triggered pressure support (NPS). Two single LAM breaths (not sequentially, but independently) were performed at each level of assist by acutely setting the assist to zero cm H2O (NPS) or NAVA level 0 cm H2O/uV (NAVA) for one breath. NPS and NAVA titrations were followed by titrations in controlled-modes (volume control, VC and pressure control, PC), under neuro-muscular blockade. Breaths from the NAVA/NPS titrations were matched (for flow and volume) to VC or PC. Throughout all runs, we measured diaphragm electrical activity (Edi) and esophageal pressure (PES). We measured ΔPL during the spontaneous modes (PL_PES) and controlled mechanical ventilation (CMV) modes (PL_CMV) with the esophageal balloon. From the LAMs, we derived an estimation of ΔPL ("PL_LAM") using a correction factor (ratio of volume during the LAM and volume during assist) and compared it to measured ΔPL during passive (VC or PC) and spontaneous breathing (NAVA or NPS). A requirement for the LAM was similar Edi to the assisted breath. RESULTS: All animals successfully underwent titrations and LAMs for NPS/NAVA. One thousand seven-hundred ninety-two (1792) breaths were matched to passive ventilation titrations (matched Vt, r = 0.99). PL_LAM demonstrated strong correlation with PL_CMV (r = 0.83), and PL_PES (r = 0.77). Bland-Altman analysis revealed little difference between the predicted PL_LAM and measured PL_CMV (Bias = 0.49 cm H2O and 1.96SD = 3.09 cm H2O). For PL_PES, the bias was 2.2 cm H2O and 1.96SD was 3.4 cm H2O. Analysis of Edi and PES at peak Edi showed progressively increasing uncoupling with increasing assist. CONCLUSION: During synchronized mechanical ventilation, a LAM breath allows for estimations of transpulmonary driving pressure, without measuring PES, and follows a mathematical transfer function to describe respiratory muscle unloading during synchronized assist.

Impact of ventilation strategies on pulmonary and cardiovascular complications in patients undergoing general anaesthesia for elective surgery: a systematic review and meta-analysis.

BACKGROUND: Many RCTs have evaluated the influence of intraoperative tidal volume (tV), PEEP, and driving pressure on the occurrence of postoperative pulmonary complications, cardiovascular complications, and mortality in adult patients. Our meta-analysis aimed to investigate the association between tV, PEEP, and driving pressure and the above-mentioned outcomes. METHODS: We conducted a systematic review and meta-analysis of RCTs from inception to May 19, 2022. The primary outcome was the incidence of postoperative pulmonary complications; the secondary outcomes were intraoperative cardiovascular complications and 30-day mortality. Primary and secondary outcomes were evaluated stratifying patients in the following groups: (1) low tV (LV, tV 6-8 ml kg-1 and PEEP ≥5 cm H2O) vs high tV (HV, tV >8 ml kg-1 and PEEP=0 cm H2O); (2) higher PEEP (HP, ≥6 cm H2O) vs lower PEEP (LP, <6 cm H2O); and (3) driving pressure-guided PEEP (DP) vs fixed PEEP (FP). RESULTS: We included 16 RCTs with a total sample size of 4993. The incidence of postoperative pulmonary complications was lower in patients treated with LV than with HV (OR=0.402, CI 0.280-0.577, P<0.001) and lower in DP than in FP group (OR=0.358, CI 0.187-0.684, P=0.002). Postoperative pulmonary complications did not differ between HP and LP groups; the incidence of intraoperative cardiovascular complications was higher in HP group (OR=1.385, CI 1.027-1.867, P=0.002). The 30-day mortality was not influenced by the ventilation strategy. CONCLUSIONS: Optimal intraoperative mechanical ventilation is unclear; however, our meta-analysis showed that low tidal volume and driving pressure-guided PEEP strategies were associated with a reduction in postoperative pulmonary complications.

Effect of driving pressure-guided positive end-expiratory pressure on postoperative pulmonary complications in patients undergoing laparoscopic or robotic surgery: a randomised controlled trial.

BACKGROUND: Individualised positive end-expiratory pressure (PEEP) improves respiratory mechanics. However, whether PEEP reduces postoperative pulmonary complications (PPCs) remains unclear. We investigated whether driving pressure-guided PEEP reduces PPCs after laparoscopic/robotic abdominal surgery. METHODS: This single-centre, randomised controlled trial enrolled patients at risk for PPCs undergoing laparoscopic or robotic lower abdominal surgery. The individualised group received driving pressure-guided PEEP, whereas the comparator group received 5 cm H2O fixed PEEP during surgery. Both groups received a tidal volume of 8 ml kg-1 ideal body weight. The primary outcome analysed per protocol was a composite of pulmonary complications (defined by pre-specified clinical and radiological criteria) within 7 postoperative days after surgery. RESULTS: Some 384 patients (median age: 67 yr [inter-quartile range: 61-73]; 66 [18%] female) were randomised. Mean (standard deviation) PEEP in patients randomised to individualised PEEP (n=178) was 13.6 cm H2O (2.1). Individualised PEEP resulted in lower mean driving pressures (14.7 cm H2O [2.6]), compared with 185 patients randomised to standard PEEP (18.4 cm H2O [3.2]; mean difference: -3.7 cm H2O [95% confidence interval (CI): -4.3 to -3.1 cm H2O]; P<0.001). There was no difference in the incidence of pulmonary complications between individualised (25/178 [14.0%]) vs standard PEEP (36/185 [19.5%]; risk ratio [95% CI], 0.72 [0.45-1.15]; P=0.215). Pulmonary complications as a result of desaturation were less frequent in patients randomised to individualised PEEP (8/178 [4.5%], compared with standard PEEP (30/185 [16.2%], risk ratio [95% CI], 0.28 [0.13-0.59]; P=0.001). CONCLUSIONS: Driving pressure-guided PEEP did not decrease the incidence of pulmonary complications within 7 days of laparoscopic or robotic lower abdominal surgery, although uncertainty remains given the lower than anticipated event rate for the primary outcome. CLINICAL TRIAL REGISTRATION: KCT0004888 (http://cris.nih.go.kr, registration date: April 6, 2020).

Driving pressure-guided ventilation and postoperative pulmonary complications in thoracic surgery: a multicentre randomised clinical trial.

BACKGROUND: Airway driving pressure, easily measured as plateau pressure minus PEEP, is a surrogate for alveolar stress and strain. However, the effect of its targeted reduction remains unclear. METHODS: In this multicentre trial, patients undergoing lung resection surgery were randomised to either a driving pressure group (n=650) receiving an alveolar recruitment/individualised PEEP to deliver the lowest driving pressure or to a conventional protective ventilation group (n=650) with fixed PEEP of 5 cm H2O. The primary outcome was a composite of pulmonary complications within 7 days postoperatively. RESULTS: The modified intention-to-treat analysis included 1170 patients (mean [standard deviation, sd]; age, 63 [10] yr; 47% female). The mean driving pressure was 7.1 cm H2O in the driving pressure group vs 9.2 cm H2O in the protective ventilation group (mean difference [95% confidence interval, CI]; -2.1 [-2.4 to -1.9] cm H2O; P<0.001). The incidence of pulmonary complications was not different between the two groups: driving pressure group (233/576, 40.5%) vs protective ventilation group (254/594, 42.8%) (risk difference -2.3%; 95% CI, -8.0% to 3.3%; P=0.42). Intraoperatively, lung compliance (mean [sd], 42.7 [12.4] vs 33.5 [11.1] ml cm H2O-1; P<0.001) and Pao2 (median [inter-quartile range], 21.5 [14.5 to 30.4] vs 19.5 [13.5 to 29.1] kPa; P=0.03) were higher and the need for rescue ventilation was less frequent (6.8% vs 10.8%; P=0.02) in the driving pressure group. CONCLUSIONS: In lung resection surgery, a driving pressure-guided ventilation improved pulmonary mechanics intraoperatively, but did not reduce the incidence of postoperative pulmonary complications compared with a conventional protective ventilation. CLINICAL TRIAL REGISTRATION: NCT04260451.

Do we have the 'power' to 'drive' down the incidence of pulmonary complications after thoracic surgery.

The concept, mechanisms, and physical and physiological determinants of ventilator-induced lung injury, as well as the influence of lung-protective ventilation strategies, are novel paradigms of modern intensive care and perioperative medicine. Driving pressure and mechanical power have emerged as meaningful and modifiable targets with specific relevance to thoracic anaesthesia and one-lung ventilation. The relationship between these factors and postoperative pulmonary complications remains complex because of the methodological design and outcome selection. Larger observational studies are required to better understand the characteristics of driving pressure and power in current practice of thoracic anaesthesia in order to design future trials in high-risk thoracic populations at risk of acute lung injury.

Neurally Adjusted Ventilatory Assist Versus Pressure Support Ventilation: A Comprehensive Review.

Mechanical ventilation serves as crucial life support for critically ill patients. Although it is life-saving prolonged ventilation carries risks and complications like barotrauma, Ventilator-associated pneumonia, sepsis, and many others. Optimizing patient-ventilator interactions and facilitating early weaning is necessary for improved intensive care unit (ICU) outcomes. Traditionally Pressure support ventilation (PSV) mode is widely used for weaning patients who are intubated and mechanically ventilated. Neurally adjusted ventilatory assist (NAVA) mode of the ventilator is an emerging ventilator mode that delivers pressure depending on the patient's respiratory drive, which in turn prevents over-inflation and improves the patient's ventilator interactions. Our article revises and compares the effectiveness of NAVA compared to PSV ventilation under different contexts. Overall we conclude that NAVA level of ventilation can be safely administered in a patient with acute respiratory failure, provided diaphragmatic paralysis is not considered. NAVA improves asynchrony index, wean-off time, and sleep quality and is associated with increased ventilator-free days. These results are based on small-scale studies with low power, and further studies are warranted in large-scale cohorts with more diverse populations to confirm these results.

Effect of intravenous vs. inhaled penehyclidine on respiratory mechanics in patients during one-lung ventilation for thoracoscopic surgery: a prospective, double-blind, randomised controlled trial.

BACKGROUND: Minimising postoperative pulmonary complications (PPCs) after thoracic surgery is of utmost importance. A major factor contributing to PPCs is the driving pressure, which is determined by the ratio of tidal volume to lung compliance. Inhalation and intravenous administration of penehyclidine can improve lung compliance during intraoperative mechanical ventilation. Therefore, our study aimed to compare the efficacy of inhaled vs. intravenous penehyclidine during one-lung ventilation (OLV) in mitigating driving pressure and mechanical power among patients undergoing thoracic surgery. METHODS: A double-blind, prospective, randomised study involving 176 patients scheduled for elective thoracic surgery was conducted. These patients were randomly divided into two groups, namely the penehyclidine inhalation group and the intravenous group before their surgery. Driving pressure was assessed at T1 (5 min after OLV), T2 (15 min after OLV), T3 (30 min after OLV), and T4 (45 min after OLV) in both groups. The primary outcome of this study was the composite measure of driving pressure during OLV. The area under the curve (AUC) of driving pressure from T1 to T4 was computed. Additionally, the secondary outcomes included mechanical power, lung compliance and the incidence of PPCs. RESULTS: All 167 participants, 83 from the intravenous group and 84 from the inhalation group, completed the trial. The AUC of driving pressure for the intravenous group was 39.50 ± 9.42, while the inhalation group showed a value of 41.50 ± 8.03 (P = 0.138). The incidence of PPCs within 7 days after surgery was 27.7% in the intravenous group and 23.8% in the inhalation group (P = 0.564). No significant differences were observed in any of the other secondary outcomes between the two groups (all P > 0.05). CONCLUSIONS: Our study found that among patients undergoing thoracoscopic surgery, no significant differences were observed in the driving pressure and mechanical power during OLV between those who received an intravenous injection of penehyclidine and those who inhaled it. Moreover, no significant difference was observed in the incidence of PPCs between the two groups.