Associations of dynamic driving pressure and mechanical power with postoperative pulmonary complications-posthoc analysis of two randomised clinical trials in open abdominal surgery

Flow-controlled versus pressure-controlled ventilation in thoracic surgery with one-lung ventilation - A randomized controlled trial

STUDY OBJECTIVE

Comparison of flow-controlled ventilation (FCV) to standard of pressure-controlled ventilation (PCV) in thoracic surgery procedures requiring one-lung ventilation.

DESIGN

Prospective, non-blinded, randomized, controlled trial.

SETTING

Operating theater at a university hospital, Austria.

PATIENTS

Patients scheduled for elective, thoracic surgery.

INTERVENTIONS

Participants received ventilation randomly either with FCV or PCV per-protocol for the duration of anesthesia.

MEASUREMENTS

The primary endpoint was oxygenation assessed by paO2 / FiO2 ratio 30 min after the start of OLV. Secondary endpoints included the required minute volume for CO2 removal, applied mechanical power and incidence of postoperative pulmonary complications.

MAIN RESULTS

A total of 46 patients were enrolled and 43 included in the primary analysis. The primary endpoint paO2 / FiO2 ratio was significantly higher in the FCV group (n = 21) compared to the control group (PCV n = 22) (187 vs 136 mmHg, MD 39 (95 % CI 1 to 75); p = 0.047). The required respiratory minute volume to obtain comparable mild hypercapnia during OLV was significantly lower in FCV (3.0 vs 4.5 l/min, MD -1.3 (95 % CI -1.9 to -0.8); p < 0.001). The applied mechanical power was also significantly lower (3.5 versus 7.6 J/min, MD -3.8 (95 % CI -5.3 to -2.7); p < 0.001).

CONCLUSIONS

In this single-center randomized controlled trial, flow-controlled ventilation improved gas exchange parameters in terms of oxygenation and carbon dioxide removal during one-lung ventilation in patients undergoing thoracic surgery and reduced the mechanical impact of artificial ventilation.

Mechanical power of ventilation and survival in critically ill obese patients

BACKGROUND

Obesity complicates mechanical ventilation due to altered respiratory mechanics, raising the risk of ventilator-induced lung injury (VILI). Mechanical power (MP) quantifies the energy transferred from the ventilator to the lungs per unit time, incorporating factors such as tidal volume, airway pressures, respiratory rate, and PEEP. The role of mechanical power as a predictor of outcomes in critically obese patients remains uncertain.

METHODS

This retrospective cohort study analyzed data from the MIMIC-IV database, including 1860 obese patients (BMI ≥ 30 kg/m2) on mechanical ventilation for at least 48 h. Mechanical power was calculated over the first and second 24-h intervals, with time-weighted averages considered. Logistic regression, propensity score matching, and inverse probability of treatment weighting were employed to assess the relationships between mechanical power and hospital mortality.

RESULTS

A total of 1860 patients were included in the final analysis, of whom 539 (29.0 %) experienced in-hospital mortality. The median mechanical power during the second 24 h of ventilation was 15.50 J/min [10.54, 21.45], while the time-weighted average mechanical power was 16.12 J/min [11.75, 20.94]. No significant association was found between mechanical power during the second 24 h of ventilation and hospital mortality (OR 0.99, 95 % CI 0.97-1.00). However, time-weighted average mechanical power was associated with hospital length of stay (OR 0.98, 95 % CI 0.96-1.00). Additionally, the duration of mechanical ventilation emerged as a significant predictor of hospital mortality, whereas mechanical power alone did not significantly impact ICU or 28-day mortality.

CONCLUSIONS

Mechanical power did not predict hospital mortality in critically ill obese patients, suggesting the need for tailored ventilatory strategies focusing on both mechanical power and exposure duration.

Predicting postoperative pulmonary infection in elderly patients undergoing major surgery: a study based on logistic regression and machine learning models

BACKGROUND

Postoperative pulmonary infection (POI) is strongly associated with a poor prognosis and has a high incidence in elderly patients undergoing major surgery. Machine learning (ML) algorithms are increasingly being used in medicine, but the predictive role of logistic regression (LR) and ML algorithms for POI in high-risk populations remains unclear.

METHODS

We conducted a retrospective cohort study of older adults undergoing major surgery over a period of six years. The included patients were randomly divided into training and validation sets at a ratio of 7:3. The features selected by the least absolute shrinkage and selection operator regression algorithm were used as the input variables of the ML and LR models. The random forest of multiple interpretable methods was used to interpret the ML models.

RESULTS

Of the 9481 older adults in our study, 951 developed POI. Among the different algorithms, LR performed the best with an AUC of 0.80, whereas the decision tree performed the worst with an AUC of 0.75. Furthermore, the LR model outperformed the other ML models in terms of accuracy (88.22%), specificity (90.29%), precision (44.42%), and F1 score (54.25%). Despite employing four interpretable methods for RF analysis, there existed a certain degree of inconsistency in the results. Finally, to facilitate clinical application, we established a web-friendly version of the nomogram based on the LR algorithm; In addition, patients were divided into three significantly distinct risk intervals in predicting POI.

CONCLUSIONS

Compared with popular ML algorithms, LR was more effective at predicting POI in older patients undergoing major surgery. The constructed nomogram could identify high-risk elderly patients and facilitate perioperative management planning.

TRIAL REGISTRATION

The study was retrospectively registered (NCT06491459).

Mechanical power is not associated with mortality in COVID-19 mechanically ventilated patients

BACKGROUND

The relative contribution of the different components of mechanical power to mortality is a subject of debate and has not been studied in COVID-19. The aim of this study is to evaluate both the total and the relative impact of each of the components of mechanical power on mortality in a well-characterized cohort of patients with COVID-19-induced acute respiratory failure undergoing invasive mechanical ventilation. This is a secondary analysis of the CIBERESUCICOVID project, a multicenter observational cohort study including fifty Spanish intensive care units that included COVID-19 mechanically ventilated patients between February 2020 and December 2021. We examined the association between mechanical power and its components (elastic static, elastic dynamic, total elastic and resistive power) with 90-day mortality after adjusting for confounders in seven hundred ninety-nine patients with COVID-19-induced respiratory failure undergoing invasive mechanical ventilation.

RESULTS

At the initiation of mechanical ventilation, the PaO2/FiO2 ratio was 106 (78; 150), ventilatory ratio was 1.69 (1.40; 2.05), and respiratory system compliance was 35.7 (29.2; 44.5) ml/cmH2O. Mechanical power at the initiation of mechanical ventilation was 24.3 (18.9; 29.6) J/min, showing no significant changes after three days. In multivariable regression analyses, mechanical power and its components were not associated with 90-day mortality at the start of mechanical ventilation. After three days, total elastic and elastic static power were associated with higher 90-day mortality, but this relationship was also found for positive end-expiratory pressure.

CONCLUSIONS

Neither mechanical power nor its components were independently associated with mortality in COVID-19-induced acute respiratory failure at the start of MV. Nevertheless, after three days, static elastic power and total elastic power were associated with lower odds of survival. Positive end-expiratory pressure and plateau pressure, however, captured this risk in a similar manner.

Understanding ventilator-induced lung injury: The role of mechanical power

Mechanical ventilation stands as a life-saving intervention in the management of respiratory failure. However, it carries the risk of ventilator-induced lung injury. Despite the adoption of lung-protective ventilation strategies, including lower tidal volumes and pressure limitations, mortality rates remain high, leaving room for innovative approaches. The concept of mechanical power has emerged as a comprehensive metric encompassing key ventilator parameters associated with the genesis of ventilator-induced lung injury, including volume, pressure, flow, resistance, and respiratory rate. While numerous animal and human studies have linked mechanical power and ventilator-induced lung injury, its practical implementation at the bedside is hindered by calculation challenges, lack of equation consensus, and the absence of an optimal threshold. To overcome the constraints of measuring static respiratory parameters, dynamic mechanical power is proposed for all patients, regardless of their ventilation mode. However, establishing a causal relationship is crucial for its potential implementation, and requires further research. The objective of this review is to explore the role of mechanical power in ventilator-induced lung injury, its association with patient outcomes, and the challenges and potential benefits of implementing a ventilation strategy based on mechanical power.

Correlations between primary tumour location, biomarkers of inflammation and lung injury, and postoperative pulmonary complications in patients underwent laparoscopic colorectomy: a propensity score matched analysis of 300 patients

Introduction

The impact of distinct primary colorectal cancer (CRC) sites on lung injury and complications remains largely unexplored, despite the palpable differences in surgical positions, procedures, and the resulting mechanically induced respiratory pressures at each site.

Materials and methods

This study employed a forwards-looking approach utilising the propensity score matching (PSM) method; 300 patients with pathological CRC after laparoscopic surgery from April 2019 to May 2023 were enrolled. Two categories were bifurcated based on their surgical locations: the rectosigmoid colon (RSC) group and the descending/ascending colon (DAC) group, with a 2:1 ratio. The occurrence of postoperative pulmonary complications (PPCs) within a 30-day postoperative period was meticulously evaluated. Additionally, assessments have been performed for plasma biomarkers of immune response dynamics and lung injury (plasma soluble advanced glycation end-product receptor [sRAGE], angiopoietin-2 [ANG-2], interleukin-1β/6 [IL-1β/IL-6]) and other parameters.

Results

Although the increase in postoperative lung epithelial damage, as indicated by the plasma sRAGE levels, was significant in the RSC group (DAC vs. RSC; 1029.6 [576.8-1365.2] vs. 1271.6 [896.3-1587.6]; odds ratio=0.999; 95% CI: 0.998 to 1.000; P=0.007), a significantly increased percentage of PPCs was observed in the DAC group (DAC vs. RSC; hazard ratio=1.669; 95% CI, 1.141 to 2.439; P=0.008). A univariate Cox proportional hazards model revealed that sRAGE, ANG-2, IL-1β, and IL-6 levels were not correlated with the incidence of time-to-PPCs across the two cohorts (P>0.05). Propensity score-weighted Cox regression and causal mediation analysis further demonstrated that the DAC site directly affected the incidence of PPCs, regardless of the other baseline confounders and clinical covariates related to the tumour site and PPCs.

Conclusion

The primary site of CRC is an independent predictor of the development of PPCs. Despite the steep Trendelenburg position of the RSC group inciting more pulmonary stress, inflammation and lung epithelial injury, as indicated by higher sRAGE, it demonstrated a lower PPCs occurrence relative to its DAC counterpart, with a slightly inclined or reversed Trendelenburg position. None of the plasma biomarkers of inflammation or lung injury indicated sufficient prognostic value for PPCs.

Association of mechanical power and postoperative pulmonary complications among young children undergoing video-assisted thoracic surgery: A retrospective study

BACKGROUND

Previous studies have discussed the correlation between mechanical power (MP) and lung injury. However, evidence regarding the relationship between MP and postoperative pulmonary complications (PPCs) in children remains limited, specifically during one-lung ventilation (OLV).

OBJECTIVES

Propensity score matching was employed to generate low MP and high MP groups to verify the relationship between MP and PPCs. Multivariable logistic regression was performed to identify risk factors of PPCs in young children undergoing video-assisted thoracic surgery (VATS).

DESIGN

A retrospective study.

SETTING

Single-site tertiary children's hospital.

PATIENTS

Children aged ≤2 years who underwent VATS between January 2018 and February 2023.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The incidence of PPCs.

RESULTS

Overall, 581 (median age, 6 months [interquartile range: 5-9.24 months]) children were enrolled. The median [interquartile range] MP during OLV were 2.17 [1.84 to 2.64) J min-1. One hundred and nine (18.76%) children developed PPCs. MP decreased modestly during the study period (2.63 to 1.99 J min-1; P < 0.0001). In the propensity score matched cohort for MP (221 matched pairs), MP (median MP 2.63 vs. 1.84 J min-1) was not associated with a reduction in PPCs (adjusted odds ratio, 1.43; 95% CI, 0.87 to 2.37; P = 0.16). In the propensity score matched cohort for dynamic components of MP (139 matched pairs), dynamic components (mean 2.848 vs. 4.162 J min-1) was not associated with a reduction in PPCs (adjusted odds ratio, 1.62; 95% CI, 0.85 to 3.10; P  = 0.15).The multiple logistic analysis revealed PPCs within 7 days of surgery were associated with male gender, OLV duration >90 min, less surgeon's experience and lower positive end-expiratory pressure (PEEP) value.

CONCLUSIONS

MP and dynamic components were not associated with PPCs in young children undergoing VATS, whereas PPCs were associated with male gender, OLV duration >90 min, less surgeon's experience and lower PEEP value.

TRIAL REGISTRATION

ChiCTR2300074649.

Protective mechanical ventilation in critically ill patients after surgery

PURPOSE OF REVIEW

This review aims to provide an updated overview of lung protective strategies in critically ill patients after surgery, focusing on the utility of postoperative open-lung ventilation during the transition from the operating room to the intensive care unit.

RECENT FINDINGS

Mechanically ventilated patients after surgery represent a challenge in the intensive care unit. Different protective strategies have been proposed to minimize the risk of ventilator-induced lung injury (VILI) and facilitate adequate weaning from mechanical ventilation. Fast-track extubation protocols, increasingly standard in the care of critically ill patients postsurgery, have demonstrated improvements in recovery and reductions in acute lung injury, primarily based on retrospective studies. Open-lung ventilation strategies, such as individualization of positive-end expiratory pressure based on driving pressure and postoperative noninvasive ventilation support with high-flow nasal cannula, are becoming standard of care in high-risk surgical patients after major abdominal or thoracic surgeries.

SUMMARY

Mechanical ventilation in surgical patients should adhere to lung protective strategies (i.e., individualizing positive end expiratory pressure and prioritize alveolar recruitment) during the transition from the operating room to the intensive care unit.

The association between intraoperative low driving pressure ventilation and perioperative healthcare-associated costs: A retrospective multicenter cohort study

STUDY OBJECTIVE

A low dynamic driving pressure during mechanical ventilation for general anesthesia has been associated with a lower risk of postoperative respiratory complications (PRC), a key driver of healthcare costs. It is, however, unclear whether maintaining low driving pressure is clinically relevant to measure and contain costs. We hypothesized that a lower dynamic driving pressure is associated with lower costs.

DESIGN

Multicenter retrospective cohort study.

SETTING

Two academic healthcare networks in New York and Massachusetts, USA.

PATIENTS

46,715 adult surgical patients undergoing general anesthesia for non-ambulatory (inpatient and same-day admission) surgery between 2016 and 2021.

INTERVENTIONS

The primary exposure was the median intraoperative dynamic driving pressure.

MEASUREMENTS

The primary outcome was direct perioperative healthcare-associated costs, which were matched with data from the Healthcare Cost and Utilization Project-National Inpatient Sample (HCUP-NIS) to report absolute differences in total costs in United States Dollars (US$). We assessed effect modification by patients' baseline risk of PRC (score for prediction of postoperative respiratory complications [SPORC] ≥ 7) and effect mediation by rates of PRC (including post-extubation saturation < 90%, re-intubation or non-invasive ventilation within 7 days) and other major complications.

MAIN RESULTS

The median intraoperative dynamic driving pressure was 17.2cmH2O (IQR 14.0-21.3cmH2O). In adjusted analyses, every 5cmH2O reduction in dynamic driving pressure was associated with a decrease of -0.7% in direct perioperative healthcare-associated costs (95%CI -1.3 to -0.1%; p = 0.020). When a dynamic driving pressure below 15cmH2O was maintained, -US$340 lower total perioperative healthcare-associated costs were observed (95%CI -US$546 to -US$132; p = 0.001). This association was limited to patients at high baseline risk of PRC (n = 4059; -US$1755;97.5%CI -US$2495 to -US$986; p < 0.001), where lower risks of PRC and other major complications mediated 10.7% and 7.2% of this association (p < 0.001 and p = 0.015, respectively).

CONCLUSIONS

Intraoperative mechanical ventilation targeting low dynamic driving pressures could be a relevant measure to reduce perioperative healthcare-associated costs in high-risk patients.

Impact of mechanical power on ICU mortality in ventilated critically ill patients: a retrospective study with continuous real-life data

BACKGROUND

Over the past decade, numerous studies on potential factors contributing to ventilation-induced lung injury have been carried out. Mechanical power has been pointed out as the parameter that encloses all ventilation-induced lung injury-contributing factors. However, studies conducted to date provide data regarding mechanical power during the early hours of mechanical ventilation that may not accurately reflect the impact of power throughout the period of mechanical ventilatory support on intensive care unit mortality.

METHODS

Retrospective observational study conducted at a single center in Spain. Patients admitted to the intensive care unit, > o = 18 years of age, and ventilated for over 24 h were included. We extracted the mechanical power values throughout the entire mechanical ventilation in controlled modes period from the clinical information system every 2 min. First, we calculate the cutoff-point for mechanical power beyond which there was a greater change in the probability of death. After, the sum of time values above the safe cut-off point was calculated to obtain the value in hours. We analyzed if the number of hours the patient was under ventilation with a mechanical power above the safe threshold was associated with intensive care unit mortality, invasive mechanical ventilation days, and intensive care unit length of stay. We repeated the analysis in different subgroups based on the degree of hypoxemia and in patients with SARS CoV-2 pneumonia.

RESULTS

The cut-off point of mechanical power at with there is a higher increase in intensive care unit mortality was 18 J/min. The greater the number of hours patients were under mechanical power > 18 J/min the higher the intensive care unit mortality in all the study population, in patients with SARS CoV-2 pneumonia and in mild to moderate hypoxemic respiratory failure. The risk of death in the intensive care unit increases 0.1% for each hour with mechanical power exceeding 18 J/min. The number of hours with mechanical power > 18 J/min also affected the days of invasive mechanical ventilation and intensive care unit length of stay.

CONCLUSIONS

The number of hours with mechanical power > 18 J/min is associated with mortality in the intensive care unit in critically ill patients. Continuous monitoring of mechanical power in controlled modes using an automated clinical information system could alert the clinician to this risk.

Mechanical power during robotic-assisted laparoscopic prostatectomy: an observational study

BACKGROUND

Robotic-assisted laparoscopic radical prostatectomy (RALP) requires pneumoperitoneum and steep Trendelenburg position. Our aim was to investigate the influence of the combination of pneumoperitoneum and Trendelenburg position on mechanical power and its components during RALP.

METHODS

Sixty-one prospectively enrolled patients scheduled for RALP were studied in supine position before surgery, during pneumoperitoneum and Trendelenburg position and in supine position after surgery at constant ventilatory setting. In a subgroup of 17 patients the response to increasing positive end-expiratory pressure (PEEP) from 5 to 10 cmH2O was studied.

RESULTS

The application of pneumoperitoneum and Trendelenburg position increased the total mechanical power (13.8 [11.6 - 15.5] vs 9.2 [7.5 - 11.7] J/min, p < 0.001) and its elastic and resistive components compared to supine position before surgery. In supine position after surgery the total mechanical power and its elastic component decreased but remained higher compared to supine position before surgery. Increasing PEEP from 5 to 10 cmH2O within each timepoint significantly increased the total mechanical power (supine position before surgery: 9.8 [8.4 - 10.4] vs 12.1 [11.4 - 14.2] J/min, p < 0.001; pneumoperitoneum and Trendelenburg position: 13.8 [12.2 - 14.3] vs 15.5 [15.0 - 16.7] J/min, p < 0.001; supine position after surgery: 10.2 [9.4 - 10.7] vs 12.7 [12.0 - 13.6] J/min, p < 0.001), without affecting respiratory system elastance.

CONCLUSION

Mechanical power in healthy patients undergoing RALP significantly increased both during the pneumoperitoneum and Trendelenburg position and in supine position after surgery. PEEP always increased mechanical power without ameliorating the respiratory system elastance.

Intraoperative Ventilation/Perfusion Mismatch and Postoperative Pulmonary Complications after Major Noncardiac Surgery: A Prospective Cohort Study

BACKGROUND

Postoperative pulmonary complications can increase hospital length of stay, postoperative morbidity, and mortality. Although many factors can increase the risk of postoperative pulmonary complications, it is not known whether intraoperative ventilation/perfusion (V/Q) mismatch can be associated with an increased risk of postoperative pulmonary complications after major noncardiac surgery.

METHODS

This study enrolled patients undergoing general anesthesia for noncardiac surgery and evaluated intraoperative V/Q distribution using the automatic lung parameter estimator technique. The assessment was done after anesthesia induction, after 1 h from surgery start, and at the end of surgery. Demographic and procedural information were collected, and intraoperative ventilatory and hemodynamic parameters were measured at each timepoint. Patients were followed up for 7 days after surgery and assessed daily for postoperative pulmonary complication occurrence.

RESULTS

The study enrolled 101 patients with a median age of 71 [62 to 77] years, a body mass index of 25 [22.4 to 27.9] kg/m2, and a preoperative Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score of 41 [34 to 47]. Of these patients, 29 (29%) developed postoperative pulmonary complications, mainly acute respiratory failure (23%) and pleural effusion (11%). Patients with and without postoperative pulmonary complications did not differ in levels of shunt at T1 (postoperative pulmonary complications: 22.4% [10.4 to 35.9%] vs. no postoperative pulmonary complications:19.3% [9.4 to 24.1%]; P = 0.18) or during the protocol, whereas significantly different levels of high V/Q ratio were found during surgery (postoperative pulmonary complications: 13 [11 to 15] mmHg vs. no postoperative pulmonary complications: 10 [8 to 13.5] mmHg; P = 0.007) and before extubation (postoperative pulmonary complications: 13 [11 to 14] mmHg vs. no postoperative pulmonary complications: 10 [8 to 12] mmHg; P = 0.006). After adjusting for age, ARISCAT, body mass index, smoking, fluid balance, anesthesia type, laparoscopic procedure and surgery duration, high V/Q ratio before extubation was independently associated with the development of postoperative pulmonary complications (odds ratio, 1.147; 95% CI, 1.021 to 1.289; P = 0.02). The sensitivity analysis showed an E-value of 1.35 (CI, 1.11).

CONCLUSIONS

In patients with intermediate or high risk of postoperative pulmonary complications undergoing major noncardiac surgery, intraoperative V/Q mismatch is associated with the development of postoperative pulmonary complications. Increased high V/Q ratio before extubation is independently associated with the occurrence of postoperative pulmonary complications in the first 7 days after surgery.

EDITOR’S PERSPECTIVE

Driving pressure: A useful tool for reducing postoperative pulmonary complications

The operating room is a unique environment where surgery exposes patients to non-physiological changes that can compromise lung mechanics. Therefore, raising clinicians' awareness of the potential risk of ventilator-induced lung injury (VILI) is mandatory. Driving pressure is a useful tool for reducing lung complications in patients with acute respiratory distress syndrome and those undergoing elective surgery. Driving pressure has been most extensively studied in the context of single-lung ventilation during thoracic surgery. However, the awareness of association of VILI risk and patient positioning (prone, beach-chair, park-bench) and type of surgery must be raised.

Advancing ICU patient care with a Real-Time predictive model for mechanical Power to mitigate VILI

BACKGROUND

Invasive Mechanical Ventilation (IMV) in Intensive Care Units (ICU) significantly increases the risk of Ventilator-Induced Lung Injury (VILI), necessitating careful management of mechanical power (MP). This study aims to develop a real-time predictive model of MP utilizing Artificial Intelligence to mitigate VILI.

METHODOLOGY

A retrospective observational study was conducted, extracting patient data from Clinical Information Systems from 2018 to 2022. Patients over 18 years old with more than 6 h of IMV were selected. Continuous data on IMV variables, laboratory data, monitoring, procedures, demographic data, type of admission, reason for admission, and APACHE II at admission were extracted. The variables with the highest correlation to MP were used for prediction and IMV data was grouped in 15-minute intervals using the mean. A mixed neural network model was developed to forecast MP 15 min in advance, using IMV data from 6 h before the prediction and current patient status. The model's ability to predict future MP was analyzed and compared to a baseline model predicting the future value of MP as equal to the current value.

RESULTS

The cohort consisted of 1967 patients after applying inclusion criteria, with a median age of 63 years and 66.9 % male. The deep learning model achieved a mean squared error of 2.79 in the test set, indicating a 20 % improvement over the baseline model. It demonstrated high accuracy (94 %) in predicting whether MP would exceed a critical threshold of 18 J/min, which correlates with increased mortality. The integration of this model into a web platform allows clinicians real-time access to MP predictions, facilitating timely adjustments to ventilation settings.

CONCLUSIONS

The study successfully developed and integrated in clinical practice a predictive model for MP. This model will assist clinicians allowing for the adjustment of ventilatory parameters before lung damage occurs.

Epidemiology, ventilation management and outcomes of COVID-19 ARDS patients versus patients with ARDS due to pneumonia in the Pre-COVID era

BACKGROUND

Ventilation management may differ between COVID-19 ARDS (COVID-ARDS) patients and patients with pre-COVID ARDS (CLASSIC-ARDS); it is uncertain whether associations of ventilation management with outcomes for CLASSIC-ARDS also exist in COVID-ARDS.

METHODS

Individual patient data analysis of COVID-ARDS and CLASSIC-ARDS patients in six observational studies of ventilation, four in the COVID-19 pandemic and two pre-pandemic. Descriptive statistics were used to compare epidemiology and ventilation characteristics. The primary endpoint were key ventilation parameters; other outcomes included mortality and ventilator-free days and alive (VFD-60) at day 60.

RESULTS

This analysis included 6702 COVID-ARDS patients and 1415 CLASSIC-ARDS patients. COVID-ARDS patients received lower median VT (6.6 [6.0 to 7.4] vs 7.3 [6.4 to 8.5] ml/kg PBW; p < 0.001) and higher median PEEP (12.0 [10.0 to 14.0] vs 8.0 [6.0 to 10.0] cm H2O; p < 0.001), at lower median ΔP (13.0 [10.0 to 15.0] vs 16.0 [IQR 12.0 to 20.0] cm H2O; p < 0.001) and higher median Crs (33.5 [26.6 to 42.1] vs 28.1 [21.6 to 38.4] mL/cm H2O; p < 0.001). Following multivariable adjustment, higher ΔP had an independent association with higher 60-day mortality and less VFD-60 in both groups. Higher PEEP had an association with less VFD-60, but only in COVID-ARDS patients.

CONCLUSIONS

Our findings show important differences in key ventilation parameters and associations thereof with outcomes between COVID-ARDS and CLASSIC-ARDS.

TRIAL REGISTRATION

Clinicaltrials.gov (identifier NCT05650957), December 14, 2022.

Effect of the prone position on mechanical power in elective surgical patients under general anesthesia: A prospective observational study

OBJECTIVES

To evaluate how the prone position influences mechanical power (MP) during elective surgical procedures.

METHODS

In this prospective study carried out at Karadeniz Ereğli Government Hospital, Zonguldak, Turkey, from January 2024 to February 2024, 76 patients under general anesthesia were evaluated at different time points during the surgical procedure. Hemodynamic, laboratory, and mechanical ventilation data were also recorded.

RESULTS

The MP increased in the prone position at the beginning of surgery. Transitioning to the supine position at the end of surgery led to a decrease in MP. At the end of surgery, the mean MP in supine and prone positions was found to be higher compared to those measured in the first hour of surgery. Mechanical power and body mass index (BMI) exhibited a significant positive correlation.

CONCLUSION

Position changes influence MP. Returning to the prone position increases MP. An increase in BMI is associated with an increase in MP.ANZCTR Reg. No.: ACTRN12623001281684.

Utilising intraoperative respiratory dynamic features for developing and validating an explainable machine learning model for postoperative pulmonary complications

BACKGROUND

Timely detection of modifiable risk factors for postoperative pulmonary complications (PPCs) could inform ventilation strategies that attenuate lung injury. We sought to develop, validate, and internally test machine learning models that use intraoperative respiratory features to predict PPCs.

METHODS

We analysed perioperative data from a cohort comprising patients aged 65 yr and older at an academic medical centre from 2019 to 2023. Two linear and four nonlinear learning models were developed and compared with the current gold-standard risk assessment tool ARISCAT (Assess Respiratory Risk in Surgical Patients in Catalonia Tool). The Shapley additive explanation of artificial intelligence was utilised to interpret feature importance and interactions.

RESULTS

Perioperative data were obtained from 10 284 patients who underwent 10 484 operations (mean age [range] 71 [65-98] yr; 42% female). An optimised XGBoost model that used preoperative variables and intraoperative respiratory variables had area under the receiver operating characteristic curves (AUROCs) of 0.878 (0.866-0.891) and 0.881 (0.879-0.883) in the validation and prospective cohorts, respectively. These models outperformed ARISCAT (AUROC: 0.496-0.533). The intraoperative dynamic features of respiratory dynamic system compliance, mechanical power, and driving pressure were identified as key modifiable contributors to PPCs. A simplified model based on XGBoost including 20 variables generated an AUROC of 0.864 (0.852-0.875) in an internal testing cohort. This has been developed into a web-based tool for further external validation (https://aorm.wchscu.cn/).

CONCLUSIONS

These findings suggest that real-time identification of surgical patients' risk of postoperative pulmonary complications could help personalise intraoperative ventilatory strategies and reduce postoperative pulmonary complications.

Association between mechanical power during one-lung ventilation and pulmonary complications after thoracoscopic lung resection surgery: a prospective observational study

BACKGROUND

The role of mechanical power on pulmonary outcomes after thoracic surgery with one-lung ventilation was unclear. We investigated the association between mechanical power and postoperative pulmonary complications in patients undergoing thoracoscopic lung resection surgery.

METHODS

In this single-center, prospective observational study, 622 patients scheduled for thoracoscopic lung resection surgery were included. Volume control mode with lung protective ventilation strategies were implemented in all participants. The primary endpoint was a composite of postoperative pulmonary complications during hospital stay. Multivariable logistic regression models were used to evaluate the association between mechanical power and outcomes.

RESULTS

The incidence of pulmonary complications after surgery during hospital stay was 24.6% (150 of 609 patients). The multivariable analysis showed that there was no link between mechanical power and postoperative pulmonary complications.

CONCLUSIONS

In patients undergoing thoracoscopic lung resection with standardized lung-protective ventilation, no association was found between mechanical power and postoperative pulmonary complications.

TRIAL REGISTRATION

Trial registration number: ChiCTR2200058528, date of registration: April 10, 2022.

Association of Mechanical Energy and Power with Postoperative Pulmonary Complications in Lung Resection Surgery: A Post Hoc Analysis of Randomized Clinical Trial Data

BACKGROUND

Mechanical power (MP), the rate of mechanical energy (ME) delivery, is a recently introduced unifying ventilator parameter consisting of tidal volume, airway pressures, and respiratory rates, which predicts pulmonary complications in several clinical contexts. However, ME has not been previously studied in the perioperative context, and neither parameter has been studied in the context of thoracic surgery utilizing one-lung ventilation.

METHODS

The relationships between ME variables and postoperative pulmonary complications were evaluated in this post hoc analysis of data from a multicenter randomized clinical trial of lung resection surgery conducted between 2020 and 2021 (n = 1,170). Time-weighted average MP and ME (the area under the MP time curve) were obtained for individual patients. The primary analysis was the association of time-weighted average MP and ME with pulmonary complications within 7 postoperative days. Multivariable logistic regression was performed to examine the relationships between energy variables and the primary outcome.

RESULTS

In 1,055 patients analyzed, pulmonary complications occurred in 41% (431 of 1,055). The median (interquartile ranges) ME and time-weighted average MP in patients who developed postoperative pulmonary complications versus those who did not were 1,146 (811 to 1,530) J versus 924 (730 to 1,240) J (P < 0.001), and 6.9 (5.5 to 8.7) J/min versus 6.7 (5.2 to 8.5) J/min (P = 0.091), respectively. ME was independently associated with postoperative pulmonary complications (ORadjusted, 1.44 [95% CI, 1.16 to 1.80]; P = 0.001). However, the association between time-weighted average MP and postoperative pulmonary complications was time-dependent, and time-weighted average MP was significantly associated with postoperative pulmonary complications in cases utilizing longer periods of mechanical ventilation (210 min or greater; ORadjusted, 1.46 [95% CI, 1.11 to 1.93]; P = 0.007). Normalization of ME and time-weighted average MP either to predicted body weight or to respiratory system compliance did not alter these associations.

CONCLUSIONS

ME and, in cases requiring longer periods of mechanical ventilation, MP were independently associated with postoperative pulmonary complications in thoracic surgery.

EDITOR’S PERSPECTIVE

Individualised flow-controlled ventilation reduces applied mechanical power and improves ventilation efficiency in a porcine intra-abdominal hypertension model

BACKGROUND

Aim of this study was to evaluate feasibility and effects of individualised flow-controlled ventilation (FCV), based on compliance guided pressure settings, compared to standard of pressure-controlled ventilation (PCV) in a porcine intra-abdominal hypertension (IAH) model. The primary aim of this study was to investigate oxygenation. Secondary aims were to assess respiratory and metabolic variables and lung tissue aeration.

METHODS

Pigs were randomly assigned to FCV (n = 9) and PCV (n = 9). IAH was induced by insufflation of air into the abdomen to induce IAH grades ranging from 0 to 3. At each IAH grade FCV was undertaken using compliance guided pressure settings, or PCV (n = 9) was undertaken with the positive end-expiratory pressure titrated for maximum compliance and the peak pressure set to achieve a tidal volume of 7 ml/kg. Gas exchange, ventilator settings and derived formulas were recorded at two timepoints for each grade of IAH. Lung aeration was assessed by a computed tomography scan at IAH grade 3.

RESULTS

All 18 pigs (median weight 54 kg [IQR 51-67]) completed the observation period of 4 h. Oxygenation was comparable at each IAH grade, but a significantly lower minute volume was required to secure normocapnia in FCV at all IAH grades (7.6 vs. 14.4, MD - 6.8 (95% CI - 8.5 to - 5.2) l/min; p < 0.001). There was also a significant reduction of applied mechanical power being most evident at IAH grade 3 (25.9 vs. 57.6, MD - 31.7 (95% CI - 39.7 to - 23.7) J/min; p < 0.001). Analysis of Hounsfield unit distribution of the computed tomography scans revealed a significant reduction in non- (5 vs. 8, MD - 3 (95% CI - 6 to 0) %; p = 0.032) and poorly-aerated lung tissue (7 vs. 15, MD - 6 (95% CI - 13 to - 3) %, p = 0.002) for FCV. Concomitantly, normally-aerated lung tissue was significantly increased (84 vs. 76, MD 8 (95% CI 2 to 15) %; p = 0.011).

CONCLUSIONS

Individualised FCV showed similar oxygenation but required a significantly lower minute volume for CO2-removal, which led to a remarkable reduction of applied mechanical power. Additionally, there was a shift from non- and poorly-aerated lung tissue to normally-aerated lung tissue in FCV compared to PCV.

Magnitude and time to peak oxygenation effect of prone positioning in ventilated adults with COVID-19 related acute hypoxemic respiratory failure

BACKGROUND

Prone positioning may improve oxygenation in acute hypoxemic respiratory failure and was widely adopted in COVID-19 patients. However, the magnitude and timing of its peak oxygenation effect remain uncertain with the optimum dosage unknown. Therefore, we aimed to investigate the magnitude of the peak effect of prone positioning on the PaO2 :FiO2 ratio during prone and secondly, the time to peak oxygenation.

METHODS

Multi-centre, observational study of invasively ventilated adults with acute hypoxemic respiratory failure secondary to COVID-19 treated with prone positioning. Baseline characteristics, prone positioning and patient outcome data were collected. All arterial blood gas (ABG) data during supine, prone and after return to supine position were analysed. The magnitude of peak PaO2 :FiO2 ratio effect and time to peak PaO2 :FIO2 ratio effect was measured.

RESULTS

We studied 220 patients (mean age 54 years) and 548 prone episodes. Prone positioning was applied for a mean (±SD) 3 (±2) times and 16 (±3) hours per episode. Pre-proning PaO2 :FIO2 ratio was 137 (±49) for all prone episodes. During the first episode. the mean PaO2 :FIO2 ratio increased from 125 to a peak of 196 (p < .001). Peak effect was achieved during the first episode, after 9 (±5) hours in prone position and maintained until return to supine position.

CONCLUSIONS

In ventilated adults with COVID-19 acute hypoxemic respiratory failure, peak PaO2 :FIO2 ratio effect occurred during the first prone positioning episode and after 9 h. Subsequent episodes also improved oxygenation but with diminished effect on PaO2 :FIO2 ratio. This information can help guide the number and duration of prone positioning episodes.

Respiratory mechanics and mechanical power during low vs. high positive end-expiratory pressure in obese surgical patients - A sub-study of the PROBESE randomized controlled trial

STUDY OBJECTIVE

We aimed to characterize intra-operative mechanical ventilation with low or high positive end-expiratory pressure (PEEP) and recruitment manoeuvres (RM) regarding intra-tidal recruitment/derecruitment and overdistension using non-linear respiratory mechanics, and mechanical power in obese surgical patients enrolled in the PROBESE trial.

DESIGN

Prospective, two-centre substudy of the international, multicentre, two-arm, randomized-controlled PROBESE trial.

SETTING

Operating rooms of two European University Hospitals.

PATIENTS

Forty-eight adult obese patients undergoing abdominal surgery.

INTERVENTIONS

Intra-operative protective ventilation with either PEEP of 12 cmH2O and repeated RM (HighPEEP+RM) or 4 cmH2O without RM (LowPEEP).

MEASUREMENTS

The index of intra-tidal recruitment/de-recruitment and overdistension (%E2) as well as airway pressure, tidal volume (VT), respiratory rate (RR), resistance, elastance, and mechanical power (MP) were calculated from respiratory signals recorded after anesthesia induction, 1 h thereafter, and end of surgery (EOS).

MAIN RESULTS

Twenty-four patients were analyzed in each group. PEEP was higher (mean ± SD, 11.7 ± 0.4 vs. 3.7 ± 0.6 cmH2O, P < 0.001) and driving pressure lower (12.8 ± 3.5 vs. 21.7 ± 6.8 cmH2O, P < 0.001) during HighPEEP+RM than LowPEEP, while VT and RR did not differ significantly (7.3 ± 0.6 vs. 7.4 ± 0.8 ml∙kg-1, P = 0.835; and 14.6 ± 2.5 vs. 15.7 ± 2.0 min-1, P = 0.150, respectively). %E2 was higher in HighPEEP+RM than in LowPEEP following induction (-3.1 ± 7.2 vs. -12.4 ± 10.2%; P < 0.001) and subsequent timepoints. Total resistance and elastance (13.3 ± 3.8 vs. 17.7 ± 6.8 cmH2O∙l∙s-2, P = 0.009; and 15.7 ± 5.5 vs. 28.5 ± 8.4 cmH2O∙l, P < 0.001, respectively) were lower during HighPEEP+RM than LowPEEP. Additionally, MP was lower in HighPEEP+RM than LowPEEP group (5.0 ± 2.2 vs. 10.4 ± 4.7 J∙min-1, P < 0.001).

CONCLUSIONS

In this sub-cohort of PROBESE, intra-operative ventilation with high PEEP and RM reduced intra-tidal recruitment/de-recruitment as well as driving pressure, elastance, resistance, and mechanical power, as compared with low PEEP.

TRIAL REGISTRATION

The PROBESE study was registered at www.

CLINICALTRIALS

gov, identifier: NCT02148692 (submission for registration on May 23, 2014).

Flow-controlled versus pressure-controlled ventilation in cardiac surgery with cardiopulmonary bypass - A single-center, prospective, randomized, controlled trial

STUDY OBJECTIVE

Multifactorial comparison of flow-controlled ventilation (FCV) to standard of pressure-controlled ventilation (PCV) in terms of oxygenation in cardiac surgery patients after chest closure.

DESIGN

Prospective, non-blinded, randomized, controlled trial.

SETTING

Operating theatre at an university hospital, Austria.

PATIENTS

Patients scheduled for elective, open, on-pump, cardiac surgery.

INTERVENTIONS

Participants were randomized to either individualized FCV (compliance guided end-expiratory and peak pressure setting) or control of PCV (compliance guided end-expiratory pressure setting and tidal volume of 6-8 ml/kg) for the duration of surgery.

MEASUREMENTS

The primary outcome measure was oxygenation (PaO2/FiO2) 15 min after intraoperative chest closure. Secondary endpoints included CO2-removal assessed as required minute volume to achieve normocapnia and lung tissue aeration assessed by Hounsfield unit distribution in postoperative computed tomography scans.

MAIN RESULTS

Between April 2020 and April 2021 56 patients were enrolled and 50 included in the primary analysis (mean age 70 years, 38 (76%) men). Oxygenation, assessed by PaO2/FiO2, was significantly higher in the FCV group (n = 24) compared to the control group (PCV, n = 26) (356 vs. 309, median difference (MD) 46 (95% CI 3 to 90) mmHg; p = 0.038). Additionally, the minute volume required to obtain normocapnia was significantly lower in the FCV group (4.0 vs. 6.1, MD -2.0 (95% CI -2.5 to -1.5) l/min; p < 0.001) and correlated with a significantly lower exposure to mechanical power (5.1 vs. 9.8, MD -5.1 (95% CI -6.2 to -4.0) J/min; p < 0.001). Evaluation of lung tissue aeration revealed a significantly reduced amount of non-aerated lung tissue in FCV compared to PCV (5 vs. 7, MD -3 (95% CI -4 to -1) %; p < 0.001).

CONCLUSIONS

In patients undergoing on-pump, cardiac surgery individualized FCV significantly improved oxygenation and lung tissue aeration compared to PCV. In addition, carbon dioxide removal was accomplished at a lower minute volume leading to reduced applied mechanical power.

Effects of individualised positive end-expiratory pressure titration on respiratory and haemodynamic parameters during the Trendelenburg position with pneumoperitoneum: A randomised crossover physiologic trial

BACKGROUND

The Trendelenburg position with pneumoperitoneum during surgery promotes dorsobasal atelectasis formation, which impairs respiratory mechanics and increases lung stress and strain. Positive end-expiratory pressure (PEEP) can reduce pulmonary inhomogeneities and preserve end-expiratory lung volume (EELV), resulting in decreased inspiratory strain and improved gas-exchange. The optimal intraoperative PEEP strategy is unclear.

OBJECTIVES

To compare the effects of individualised PEEP titration strategies on set PEEP levels and resulting transpulmonary pressures, respiratory mechanics, gas-exchange and haemodynamics during Trendelenburg position with pneumoperitoneum.

DESIGN

Prospective, randomised, crossover single-centre physiologic trial.

SETTING

University hospital.

PATIENTS

Thirty-six patients receiving robot-assisted laparoscopic radical prostatectomy.

INTERVENTIONS

Randomised sequence of three different PEEP strategies: standard PEEP level of 5 cmH 2 O (PEEP 5 ), PEEP titration targeting a minimal driving pressure (PEEP ΔP ) and oesophageal pressure-guided PEEP titration (PEEP Poeso ) targeting an end-expiratory transpulmonary pressure ( PTP ) of 0 cmH 2 O.

MAIN OUTCOME MEASURES

The primary endpoint was the PEEP level when set according to PEEP ΔP and PEEP Poeso compared with PEEP of 5 cmH 2 O. Secondary endpoints were respiratory mechanics, lung volumes, gas-exchange and haemodynamic parameters.

RESULTS

PEEP levels differed between PEEP ΔP , PEEP Poeso and PEEP5 (18.0 [16.0 to 18.0] vs. 20.0 [18.0 to 24.0]vs. 5.0 [5.0 to 5.0] cmH 2 O; P  < 0.001 each). End-expiratory PTP and lung volume were lower in PEEP ΔP compared with PEEP Poeso ( P  = 0.014 and P  < 0.001, respectively), but driving pressure, lung stress, as well as respiratory system and dynamic elastic power were minimised using PEEP ΔP ( P  < 0.001 each). PEEP ΔP and PEEP Poeso improved gas-exchange, but PEEP Poeso resulted in lower cardiac output compared with PEEP 5 and PEEP ΔP .

CONCLUSION

PEEP ΔP ameliorated the effects of Trendelenburg position with pneumoperitoneum during surgery on end-expiratory PTP and lung volume, decreased driving pressure and dynamic elastic power, as well as improved gas-exchange while preserving cardiac output.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00028559, date of registration 2022/04/27). https://drks.de/search/en/trial/DRKS00028559.

Impact of Lower Tidal Volumes During One-Lung Ventilation: A 2022 Update of the Meta-analysis of Randomized Controlled Trials

OBJECTIVES

To clarify the influence of lower tidal volume (4-7 mL/kg) compared with higher tidal volume (8-15 mL/kg) during one-lung ventilation (OLV) on gas exchange and postoperative clinical outcome.

DESIGN

Meta-analysis of randomized trials.

SETTING

Thoracic surgery.

PARTICIPANTS

Patients receiving OLV.

INTERVENTIONS

Lower tidal volume during OLV.

MEASUREMENTS AND MAIN RESULTS

Primary outcome was PaO2-to-the oxygen fraction (PaO2/FIO2) ratio at the end of the surgery, after the reinstitution of two-lung ventilation. Secondary endpoints included perioperative changes in PaO2/FIO2 ratio and carbon dioxide (PaCO2) tension, airway pressure, the incidence of postoperative pulmonary complications, arrhythmia, and length of hospital stay. Seventeen randomized controlled trials (1,463 patients) were selected. Overall analysis showed that the use of low tidal volume during OLV was associated with a significantly higher PaO2/FIO2 ratio 15 minutes after the start of OLV and at the end of surgery (mean difference 33.7 mmHg [p = 0.02] and mean difference 18.59 mmHg [p < 0.001], respectively). The low tidal volume also was associated with higher PaCO2 values 15 minutes and 60 minutes after the start of OLV and with lower airway pressure, which was maintained during two-lung ventilation after surgery. Moreover, the application of lower tidal volume was associated with fewer postoperative pulmonary complications (odds ratio 0.50; p < 0.001) and arrhythmias (odds ratio 0.58; p = 0.009), with no difference in length of hospital stay.

CONCLUSIONS

The use of lower tidal volume, a component of protective OLV, increases the PaO2/FIO2 ratio, reduces the incidence of postoperative pulmonary complications, and should be considered strongly in daily practice.

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.

Individualized Positive End-expiratory Pressure Titration Strategies in Superobese Patients Undergoing Laparoscopic Surgery: Prospective and Nonrandomized Crossover Study

BACKGROUND

Superobesity and laparoscopic surgery promote negative end-expiratory transpulmonary pressure that causes atelectasis formation and impaired respiratory mechanics. The authors hypothesized that end-expiratory transpulmonary pressure differs between fixed and individualized positive end-expiratory pressure (PEEP) strategies and mediates their effects on respiratory mechanics, end-expiratory lung volume, gas exchange, and hemodynamic parameters in superobese patients.

METHODS

In this prospective, nonrandomized crossover study including 40 superobese patients (body mass index 57.3 ± 6.4 kg/m2) undergoing laparoscopic bariatric surgery, PEEP was set according to (1) a fixed level of 8 cm H2O (PEEPEmpirical), (2) the highest respiratory system compliance (PEEPCompliance), or (3) an end-expiratory transpulmonary pressure targeting 0 cm H2O (PEEPTranspul) at different surgical positioning. The primary endpoint was end-expiratory transpulmonary pressure at different surgical positioning; secondary endpoints were respiratory mechanics, end-expiratory lung volume, gas exchange, and hemodynamic parameters.

RESULTS

Individualized PEEPCompliance compared to fixed PEEPEmpirical resulted in higher PEEP (supine, 17.2 ± 2.4 vs. 8.0 ± 0.0 cm H2O; supine with pneumoperitoneum, 21.5 ± 2.5 vs. 8.0 ± 0.0 cm H2O; and beach chair with pneumoperitoneum; 15.8 ± 2.5 vs. 8.0 ± 0.0 cm H2O; P < 0.001 each) and less negative end-expiratory transpulmonary pressure (supine, -2.9 ± 2.0 vs. -10.6 ± 2.6 cm H2O; supine with pneumoperitoneum, -2.9 ± 2.0 vs. -14.1 ± 3.7 cm H2O; and beach chair with pneumoperitoneum, -2.8 ± 2.2 vs. -9.2 ± 3.7 cm H2O; P < 0.001 each). Titrated PEEP, end-expiratory transpulmonary pressure, and lung volume were lower with PEEPCompliance compared to PEEPTranspul (P < 0.001 each). Respiratory system and transpulmonary driving pressure and mechanical power normalized to respiratory system compliance were reduced using PEEPCompliance compared to PEEPTranspul.

CONCLUSIONS

In superobese patients undergoing laparoscopic surgery, individualized PEEPCompliance may provide a feasible compromise regarding end-expiratory transpulmonary pressures compared to PEEPEmpirical and PEEPTranspul, because PEEPCompliance with slightly negative end-expiratory transpulmonary pressures improved respiratory mechanics, lung volumes, and oxygenation while preserving cardiac output.

EDITOR’S PERSPECTIVE

Effects of obesity, pneumoperitoneum, and body position on mechanical power of intraoperative ventilation: an observational study

Mechanical power can describe the complex interaction between the respiratory system and the ventilator and may predict lung injury or pulmonary complications, but the power associated with injury of healthy human lungs is unknown. Body habitus and surgical conditions may alter mechanical power but the effects have not been measured. In a secondary analysis of an observational study of obesity and lung mechanics during robotic laparoscopic surgery, we comprehensively quantified the static elastic, dynamic elastic, and resistive energies comprising mechanical power of ventilation. We stratified by body mass index (BMI) and examined power at four surgical stages: level after intubation, with pneumoperitoneum, in Trendelenburg, and level after releasing the pneumoperitoneum. Esophageal manometry was used to estimate transpulmonary pressures. Mechanical power of ventilation and its bioenergetic components increased over BMI categories. Respiratory system and lung power were nearly doubled in subjects with class 3 obesity compared with lean at all stages. Power dissipated into the respiratory system was increased with class 2 or 3 obesity compared with lean. Increased power of ventilation was associated with decreasing transpulmonary pressures. Body habitus is a prime determinant of increased intraoperative mechanical power. Obesity and surgical conditions increase the energies dissipated into the respiratory system during ventilation. The observed elevations in power may be related to tidal recruitment or atelectasis, and point to specific energetic features of mechanical ventilation of patients with obesity that may be controlled with individualized ventilator settings.NEW & NOTEWORTHY Mechanical power describes the complex interaction between a patient's lungs and the ventilator and may be useful in predicting lung injury. However, its behavior in obesity and during dynamic surgical conditions is not understood. We comprehensively quantified ventilation bioenergetics and effects of body habitus and common surgical conditions. These data show body habitus is a prime determinant of intraoperative mechanical power and provide quantitative context for future translation toward a useful perioperative prognostic measurement.

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.