Mechanical power: meaning, uses and limitations

Ventilator-induced lung injury in rat models: are they all equal in the race?

Risk of ventilator-induced lung injury (VILI) is an inevitable and precarious accompaniment of ventilator treatment in critically ill patients worldwide. It can both instigate and aggravate acute respiratory distress syndrome (ARDS) where the only prevention or treatment so far has been empirical approach of what is considered to be lung protective ventilator settings in an attempt to shield the lung tissues against the mechanical stress that unavoidably follows ventilator treatment. The weakened state of the patients limits clinical drug research and pushes for drug discovery in animal models. Mice and rats are often the choice of small animal model, representing about 95% of all laboratory animal studies, as their physiology can mimic that which is found in humans. Mice have been a more popular choice for ventilator studies but due to technical issues, there is some advantage gained in using rats as they are substantially larger. Inducing VILI and ARDS in these models can prove challenging and often the acute nature of the injury used to produce similar tissue damage as in humans does not necessarily fully reflect clinical reality. The aim of this review was to analyse and summarize methods of recent publications in the field, describing what approaches have been utilized to simulate these conditions, possibly identifying a common track enabling comparison of results between studies. However, the study shows a high variety of methods employed by researchers causing comparisons of results difficult and perhaps implying that a more standardized approach should be used.

The effects of different prone ventilation strategies on mechanical power and respiratory mechanics in acute respiratory distress syndrome patients: a prospective, single-center observational study

Background

Acute respiratory distress syndrome (ARDS) is a common pathological condition among critically ill patients that often requires mechanical ventilation support. However, mechanical ventilation increases the risk of ventilator-induced lung injury (VILI). Different prone ventilation strategies may have varying effects on mechanical power (MP) and respiratory mechanics. This study aimed to compare the effects of prone ventilation and lateral-prone ventilation on MP and respiratory mechanics in ARDS patients to assess the relative risks of VILI associated with these strategies.

Methods

This prospective, single-center observational study employed a randomized trial. One hundred and twenty-two patients with moderate-to-severe ARDS admitted to the Department of Critical Care Medicine at Lishui Central Hospital between December 2021 and April 2024 were enrolled in this study. Patients were randomly assigned to receive either prone or lateral-prone ventilation strategies. The primary outcomes included MP, driving pressure (DP), static lung compliance (Cstat), airway resistance (Raw), the oxygenation index [i.e., the oxygen saturation to fraction of inspired oxygen (SpO2/FiO2) ratio], the mortality rate, and the duration of the mechanical ventilation. Statistical analyses were performed to compare the effects of the two ventilation strategies on the respiratory mechanics and clinical outcomes.

Results

The baseline characteristics of the patients, such as age, gender, and body mass index, were comparable between the two groups. No significant differences were found between the groups in terms of the Acute Physiology and Chronic Health Evaluation II (APACHE-II) score. No significant differences were observed in the SpO2/FiO2 ratio, mean arterial pressure (MAP), or Raw at different time points. However, MP differed significantly between the prone and lateral-prone groups. No significant differences were found between the two groups regarding heart rate (HR), MAP, and Cstat.

Conclusions

Compared to prone ventilation, lateral-prone ventilation significantly reduced MP in ARDS patients. The early adoption of lateral-prone ventilation may help mitigate the risk of VILI. This strategy holds clinical promise and warrants further validation and optimization.

Beyond pressure and volume: mechanical power levels in a cohort of intensive care unit patients

BACKGROUND

Several ventilator parameters can be used to evaluate gas exchange and mechanical properties of the respiratory system in acute respiratory failure patients. The calculation of mechanical power (MP), a critical parameter that summarizes the energy transferred from the ventilator to the patient's lungs, is not routinely made in these patients.

METHODS

This study analyzed the distribution of MP in a cohort of 70 patients requiring mechanical ventilation and investigated its association with clinical outcomes.

RESULTS

This study included 39 men and 31 women with a mean age of 57.7 ± 15.1 years. The mean MP index decreased significantly from 10.4 J/min ± 5.65 on day 2 of mechanical ventilation to 8.3 J/min ± 4.1 on day 4 (p = 0.045). The mean length of mechanical ventilation was 5.2 ±6.5days. Mechanical power measured on day 2 (r = 0.317, p = 0.052) and day 4 (r = 0.352, p = 0.030) positively correlated with the duration of mechanical ventilation. There were no differences in MP between survivors and non-survivors on both day 2 (p = 0.458) and day 4 (p = 0.373).

CONCLUSIONS

This study analyzed the distribution of MP levels in mechanically ventilated patients in an ICU. Mechanical power measured on days 2 and 4 of mechanical ventilation had a positive correlation with the duration of ventilation, but it was not a significant predictor of ICU mortality.

Mechanical Power to Predict Ventilator Liberation in Patients With a Tracheostomy

Background: Mechanical power (MP) is useful for predicting the outcomes of attempts to liberate patients from mechanical ventilation. MP is computed based on measured variables derived to determine the power in joules required to breathe while receiving mechanical ventilation. The main objectives of this study were to calculate a cutoff value of MP that would predict successful liberation and to determine the prediction rate of liberation success based on this cutoff value. Methods: This was a single-center retrospective study. Data from 110 tracheostomized subjects receiving mechanical ventilation were analyzed. We divided subjects into two groups based on ventilator liberation outcome. Confounding factors in subject background were adjusted using propensity score matching (PSM). Statistically significant differences in MP at tracheostomy and liberation success between liberation success and failure groups were examined. We calculated the MP cutoff value for successful liberation using the area under the curve of the receiver operating characteristic (ROC) and its corresponding prediction rate of liberation success. Results: The number of subjects in the successful liberation group was 79 and that of the failed liberation group was 31. The MP cutoff value and corresponding prediction rate for liberation success were 256.5 J/min (area under the curve-ROC = 0.839) and 92.2%, respectively. After PSM, the low MP group (n = 36), divided based on the MP cutoff value, had a significantly higher liberation success rate than the high MP group (n = 36), with an odds ratio of 19.95 (CI 3.95, 91.23, P < .001). Conclusion: MP at tracheostomy was a strong predictor of successful ventilator liberation, and the prediction rate of liberation success based on the MP cutoff value was shown to be very high. We recommend that patients with low MP be actively considered for liberation. In contrast, those with high MP should continue weaning while simultaneously making early transfer arrangements if liberation is unsuccessful.

Pressure Control Surrogate Formula for Estimating Mechanical Power in ARDS Is Associated With Mortality

Background: Mechanical power (MP) applied to the respiratory system (MPRS) is associated with ventilator-induced lung injury (VILI) and ARDS mortality. Absent automated ventilator MPRS measurements, the alternative is clinically unwieldy equations. However, simplified surrogate formulas are now available and accurately reflect values produced by airway pressure-volume curves. This retrospective, observational study examined whether the surrogate pressure -control equation alone could accurately assess mortality risk in subjects with ARDS managed almost exclusively with volume control (VC) ventilation. Methods: Nine hundred and forty-eight subjects were studied in whom invasive mechanical ventilation and implementation of ARDS Network ventilator protocols commenced ≤ 24 h after ARDS onset and who survived > 24 h. MPRS was calculated as 0.098 x breathing frequency x tidal volume x (PEEP + driving pressure). MPRS was assessed as a risk factor for hospital mortality and compared between non-survivors and survivors across Berlin definition classifications. In addition, mortality was compared across 4 MPRS thresholds associated with VILI or mortality (ie, 15, 20, 25, and 30 J/min). Results: MPRS was associated with increased mortality risk: odds ratio (95% CI) of 1.06 (1.04-1.07) J/min (P < .001). Median MPRS differentiated non-survivors from survivors in mild (24.7 J/min vs 18.5 J/min, respectively, P = .034), moderate (25.7 J/min vs 21.3 J/min, respectively, P < .001), and severe ARDS (28.7 J/min vs 23.5 J/min, respectively, P < .001). Across 4 MPRS thresholds, mortality increased from 23-29% when MPRS was ≤ threshold versus 38-51% when MPRS was > threshold (P < .001). In the > cohort, the odds ratio (95% CI) increased from 2.03 (1.34-3.12) to 2.51 (1.87-3.33). Conclusion: The pressure control surrogate formula is sufficiently accurate to assess mortality in ARDS, even when using VC ventilation. In our subjects when MPRS exceeds established cutoff values for VILI or mortality risk, we found mortality risk consistently increased by a factor of > 2.0.

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.

Mechanical ventilation energy analysis: Recruitment focuses injurious power in the ventilated lung

The progression of acute respiratory distress syndrome (ARDS) from its onset due to disease or trauma to either recovery or death is poorly understood. Currently, there are no generally accepted treatments aside from supportive care using mechanical ventilation. However, this can lead to ventilator-induced lung injury (VILI), which contributes to a 30 to 40% mortality rate. In this study, we develop and demonstrate a technique to quantify forms of energy transport and dissipation during mechanical ventilation to directly evaluate their relationship to VILI. A porcine ARDS model was used, with ventilation parameters independently controlling lung overdistension and alveolar/airway recruitment/derecruitment (RD). Hourly measurements of airflow, tracheal and esophageal pressures, respiratory system impedance, and oxygen transport were taken for six hours following lung injury to track energy transfer and lung function. The final degree of injury was assessed histologically. Total and dissipated energies were quantified from lung pressure-volume relationships and subdivided into contributions from airflow, tissue viscoelasticity, and RD. Only RD correlated with physiologic recovery. Despite accounting for a very small fraction (2 to 5%) of the total energy dissipation, RD is damaging because it occurs quickly over a very small area. We estimate power intensity of RD energy dissipation to be 100 W/m2, equivalent to 10% of the Sun's luminance at the Earth's surface. Minimizing repetitive RD events may thus be crucial for mitigating VILI.

Elucidating the causal relationship of mechanical power and lung injury: a dynamic approach to ventilator management

BACKGROUND

Mechanical power (MP) serves as a crucial predictive indicator for ventilator-induced lung injury and plays a pivotal role in tailoring the management of mechanical ventilation. However, its application across different diseases and stages remains nuanced.

METHODS

Using AmsterdamUMCdb, we conducted a retrospective study to analyze the causal relationship between MP and outcomes of invasive mechanical ventilation, specifically SpO2/FiO2 ratio (P/F) and ventilator-free days at day 28 (VFD28). We employed causal inferential analysis with backdoor linear regression and double machine learning, guided by directed acyclic graphs, to estimate the average treatment effect (ATE) in the whole population and conditional average treatment effect (CATE) in the individual cohort. Additionally, to enhance interpretability and identify MP thresholds, we conducted a simulation analysis.

RESULTS

In the study, we included 11,110 unique admissions into analysis, of which 58.3% (6391) were surgical admissions. We revealed a negative and significant causal effect of median MP on VFD28, with estimated ATEs of -0.135 (95% confidence interval [CI]: -0.15 to -0.121). The similar effect was not observed in Maximal MP and minimal MP. The effect of MP was more pronounced in the medical subgroup, with a CATE of -0.173 (95% CI: -0.197 to -0.143) determined through backdoor linear regression. Patients with cardio, respiratory, and infection diagnoses, who required long-term intubation, sustained higher impact on CATEs across various admission diagnoses. Our simulations showed that there is no single MP threshold that can be applied to all patients, as the optimal threshold varies depending on the patient's condition.

CONCLUSION

Our study underscores the importance of tailoring MP adjustments on an individualized basis in ventilator management. This approach opens up new avenues for personalized treatment strategies and provides fresh insights into the real-time impact of MP in diverse clinical scenarios. It highlights the significance of median MP while acknowledging the absence of universally applicable thresholds.

Ventilatory variables and computed tomography features in COVID-19 ARDS and non-COVID-19-related ARDS: a prospective observational cohort study

BACKGROUND

This study compared the ventilatory variables and computed tomography (CT) features of patients with coronavirus disease 2019 (COVID-19) versus those of patients with pulmonary non-COVID-19-related acute respiratory distress syndrome (ARDS) during the early phase of ARDS.

METHODS

This prospective, observational cohort study of ARDS patients in Taiwan was performed between February 2017 and June 2018 as well as between October 2020 and January 2024. Analysis was performed on clinical characteristics, including consecutive ventilatory variables during the first week after ARDS diagnosis. Analysis was also performed on CT scans obtained within one week after ARDS onset.

RESULTS

A total of 222 ARDS patients were divided into a COVID-19 ARDS group (n = 44; 19.8%) and a non-COVID-19 group (all pulmonary origin) (n = 178; 80.2%). No significant difference was observed between the two groups in terms of all-cause hospital mortality (38.6% versus 47.8%, p = 0.277). Pulmonary non-COVID-19 patients presented higher values for mechanical power (MP), MP normalized to predicted body weight (MP/PBW), MP normalized to compliance (MP/compliance), ventilatory ratio (VR), peak inspiratory pressure (Ppeak), and dynamic driving pressure (∆P) as well as lower dynamic compliance from day 1 to day 7 after ARDS onset. In both groups, non-survivors exceeded survivors and presented higher values for MP, MP/PBW, MP/compliance, VR, Ppeak, and dynamic ∆P with lower dynamic compliance from day 1 to day 7 after ARDS onset. The CT severity score for each of the five lung lobes and total CT scores were all significantly higher in the non-COVID-19 group (all p < 0.05). Multivariable logistic regression models revealed that Sequential Organ Failure Assessment (SOFA) score was independently associated with mortality in the COVID-19 group. In the non-COVID-19 group, body mass index, immunocompromised status, SOFA score, MP/PBW and total CT severity scores were independently associated with mortality.

CONCLUSIONS

In the early course of ARDS, physicians should be aware of the distinctions between COVID-19-related ARDS and non-COVID-19-related ARDS in terms of ventilatory variables and CT imaging presentations. It is also important to tailor the mechanical ventilation settings according to these distinct subsets of ARDS.

The association of ventilator mechanical power with weaning outcomes in intensive care unit patients: a narrative review

Background and Objective

Mechanical power (MP) provides an integrated index of the mechanical properties of the respiratory system during mechanical ventilation. Increased levels of MP may identify patients who will do poorly during weaning and extubation. This literature review investigated the use of MP as a predictor of weaning outcomes in intensive care unit (ICU) patients, including a focused comparison of patients with coronavirus disease 19 (COVID-19) infections and patients with other causes of respiratory failure.

Methods

A review of the literature using PubMed, Embase, MEDLINE, and Preprint identified 305 possible studies; after removal of duplicates, 219 studies were screened, and five papers were selected for analysis. A search updated in 2024 identified four additional papers to include in this review.

Key Content and Findings

These studies demonstrate that higher MP levels are associated with weaning failure in ICU patients and that adjustment of MP for lung-thorax compliance (LTC) improves the prediction of outcomes. One study analyzed outcomes in patients with COVID-19 infections and reported that despite having higher MPs, patients with COVID-19 had lower rates of weaning failures. This result suggests different respiratory mechanics in these patients that could complicate weaning decisions.

Conclusions

In summary, MP can predict weaning outcomes in patients with respiratory failure requiring mechanical ventilation. However, some patients with COVID-19 infection may have unusual respiratory mechanics that may influence these associations.

ARDS Ventilation, The Man Behind the Evolution

How to cite this article: Prayag S. ARDS Ventilation, The Man Behind the Evolution. Indian J Crit Care Med 2025;29(1):12-13.

Mechanical Power Is Associated With Mortality in Pressure-Controlled Ventilated Patients: A Dutch, Single-Center Cohort Study

IMPORTANCE

Mechanical power (MP) could serve as a valuable parameter in clinical practice to estimate the likelihood of adverse outcomes. However, the safety thresholds for MP in mechanical ventilation remain underexplored and contentious.

OBJECTIVES

This study aims to investigate the association between MP and hospital mortality across varying degrees of lung disease severity, classified by Pao2/Fio2 ratios.

DESIGN, SETTING, AND PARTICIPANTS

This is a retrospective cohort study using automatically extracted data. Patients admitted to the ICU of a tertiary referral hospital in The Netherlands between 2018 and 2024 and ventilated in pressure-controlled mode were included.

MAIN OUTCOMES AND MEASURES

Logistic regression, adjusted for age, sex, Acute Physiology and Chronic Health Evaluation-IV score, and Pao2/Fio2 ratio, was used to calculate the odds ratio (OR) for all-cause in-hospital mortality.

RESULTS

A total of 2184 patients were analyzed, with a mean age of 62.5 ± 13.8 years, of whom 1508 (70.2%) were male. The mean MP was highest in patients with the lowest Pao2/Fio2 ratios (21.5 ± 6.5 J/min) compared with those with the highest ratios (12.0 ± 3.8 J/min; p < 0.001). Adjusted analyses revealed that increased MP was associated with higher mortality (OR, 1.06; 95% CI, 1.03-1.09 per J/min increase). Similarly, MP normalized for body weight showed a stronger association with mortality (OR, 1.004; 95% CI, 1.002-1.006 per J/min/kg increase). An increase in mortality was seen when MP exceeded 16-18 J/min.

CONCLUSIONS AND RELEVANCE

Our findings demonstrate a significant association between MP and hospital mortality, even after adjusting for key confounders. Mortality increases notably when MP exceeds 16-18 J/min. Normalized MP presents an even stronger association with mortality. These results underscore the need for further research into ventilation strategies that consider MP adjustments.

Positive end-expiratory pressure management in patients with severe ARDS: implications of prone positioning and extracorporeal membrane oxygenation

The optimal strategy for positive end-expiratory pressure (PEEP) titration in the management of severe acute respiratory distress syndrome (ARDS) patients remains unclear. Current guidelines emphasize the importance of a careful risk-benefit assessment for PEEP titration in terms of cardiopulmonary function in these patients. Over the last few decades, the primary goal of PEEP usage has shifted from merely improving oxygenation to emphasizing lung protection, with a growing focus on the individual pattern of lung injury, lung and chest wall mechanics, and the hemodynamic consequences of PEEP. In moderate-to-severe ARDS patients, prone positioning (PP) is recommended as part of a lung protective ventilation strategy to reduce mortality. However, the physiologic changes in respiratory mechanics and hemodynamics during PP may require careful re-assessment of the ventilation strategy, including PEEP. For the most severe ARDS patients with refractory gas exchange impairment, where lung protective ventilation is not possible, veno-venous extracorporeal membrane oxygenation (V-V ECMO) facilitates gas exchange and allows for a "lung rest" strategy using "ultraprotective" ventilation. Consequently, the importance of lung recruitment to improve oxygenation and homogenize ventilation with adequate PEEP may differ in severe ARDS patients treated with V-V ECMO compared to those managed conservatively. This review discusses PEEP management in severe ARDS patients and the implications of management with PP or V-V ECMO with respect to respiratory mechanics and hemodynamic function.

Expert perspectives on ECCO2R for acute hypoxemic respiratory failure: consensus of a 2022 European roundtable meeting

BACKGROUND

By controlling hypercapnia, respiratory acidosis, and associated consequences, extracorporeal CO2 removal (ECCO2R) has the potential to facilitate ultra-protective lung ventilation (UPLV) strategies and to decrease injury from mechanical ventilation. We convened a meeting of European intensivists and nephrologists and used a modified Delphi process to provide updated insights into the role of ECCO2R in acute respiratory distress syndrome (ARDS) and to identify recommendations for a future randomized controlled trial.

RESULTS

The group agreed that lung protective ventilation and UPLV should have distinct definitions, with UPLV primarily defined by a tidal volume (VT) of 4-6 mL/kg predicted body weight with a driving pressure (ΔP) ≤ 14-15 cmH2O. Fourteen (93%) participants agreed that ECCO2R would be needed in the majority of patients to implement UPLV. Furthermore, 10 participants (majority, 63%) would select patients with PaO2:FiO2 > 100 mmHg (> 13.3 kPa) and 14 (consensus, 88%) would select patients with a ventilatory ratio of > 2.5-3. A minimum CO2 removal rate of 80 mL/min delivered by continuous renal support machines was suggested (11/14 participants, 79%) for this objective, using a short, double-lumen catheter inserted into the right internal jugular vein as the preferred vascular access. Of the participants, 14/15 (93%, consensus) stated that a new randomized trial of ECCO2R is needed in patients with ARDS. A ΔP of ≥ 14-15 cmH2O was suggested by 12/14 participants (86%) as the primary inclusion criterion.

CONCLUSIONS

ECCO2R may facilitate UPLV with lower volume and pressures provided by the ventilator, while controlling respiratory acidosis. Since recent European Society of Intensive Care Medicine guidelines on ARDS recommended against the use of ECCO2R for the treatment of ARDS outside of randomized controlled trials, new trials of ECCO2R are urgently needed, with a ΔP of ≥ 14-15 cmH2O suggested as the primary inclusion criterion.

The relationship between mechanical power normalized to dynamic lung compliance and weaning outcomes in mechanically ventilated patients

BACKGROUND

Prolonged mechanical ventilation is associated with an increased risk of mortality in these patients. However, there exists a significant clinical need for novel indicators that can complement traditional weaning evaluation methods and effectively guide ventilator weaning.

OBJECTIVES

To investigate the specific relationship between mechanical power normalized to dynamic lung compliance (Cdyn-MP) and weaning outcomes in patients on mechanical ventilation for more than 24 hours, as well as those who underwent a T-tube weaning strategy.

METHODS

A retrospective cohort study was conducted using the Medical Information Mart for Intensive Care-IV v1.0 database (MIMIC-IV v1.0). Patients who received invasive mechanical ventilation for more than 24 hours and underwent a T-tube ventilation strategy for weaning were enrolled. Patients were divided into two groups based on their weaning outcome: weaning success and failure. Ventilation parameter data were collected every 4 hours during the first 24 hours before the first spontaneous breathing trial (SBT).

RESULTS

Of all the 3,695 patients, 1,421 (38.5%) experienced weaning failure. Univariate logistic regression analysis revealed that the risk of weaning failure increased as the Cdyn-MP level rose (OR 1.34, 95% CI 1.31-1.38, P<0.001). After adjusting for age, body mass index, disease severity, and pre-weaning disease status, patients with high Cdyn-MP quartiles in the 4 hours prior to the SBT had a significantly greater risk of weaning failure than those with low Cdyn-MP quartiles (odds ratio 10.37, 95% CI 7.56-14.24). These findings were robust and consistent in both subgroup and sensitivity analyses.

CONCLUSION

The increased Cdyn-MP before SBT was independently associated with a higher risk of weaning failure in mechanically ventilated patients. Cdyn-MP has the potential to be a useful indicator for guiding the need for ventilator weaning and complementing traditional weaning evaluation methods.

Effect of automated versus conventional ventilation on mechanical power of ventilation-A randomized crossover clinical trial

INTRODUCTION

Mechanical power of ventilation, a summary parameter reflecting the energy transferred from the ventilator to the respiratory system, has associations with outcomes. INTELLiVENT-Adaptive Support Ventilation is an automated ventilation mode that changes ventilator settings according to algorithms that target a low work-and force of breathing. The study aims to compare mechanical power between automated ventilation by means of INTELLiVENT-Adaptive Support Ventilation and conventional ventilation in critically ill patients.

MATERIALS AND METHODS

International, multicenter, randomized crossover clinical trial in patients that were expected to need invasive ventilation > 24 hours. Patients were randomly assigned to start with a 3-hour period of automated ventilation or conventional ventilation after which the alternate ventilation mode was selected. The primary outcome was mechanical power in passive and active patients; secondary outcomes included key ventilator settings and ventilatory parameters that affect mechanical power.

RESULTS

A total of 96 patients were randomized. Median mechanical power was not different between automated and conventional ventilation (15.8 [11.5-21.0] versus 16.1 [10.9-22.6] J/min; mean difference -0.44 (95%-CI -1.17 to 0.29) J/min; P = 0.24). Subgroup analyses showed that mechanical power was lower with automated ventilation in passive patients, 16.9 [12.5-22.1] versus 19.0 [14.1-25.0] J/min; mean difference -1.76 (95%-CI -2.47 to -10.34J/min; P < 0.01), and not in active patients (14.6 [11.0-20.3] vs 14.1 [10.1-21.3] J/min; mean difference 0.81 (95%-CI -2.13 to 0.49) J/min; P = 0.23).

CONCLUSIONS

In this cohort of unselected critically ill invasively ventilated patients, automated ventilation by means of INTELLiVENT-Adaptive Support Ventilation did not reduce mechanical power. A reduction in mechanical power was only seen in passive patients.

STUDY REGISTRATION

Clinicaltrials.gov (study identifier NCT04827927), April 1, 2021.

URL OF TRIAL REGISTRY RECORD

https://clinicaltrials.gov/study/NCT04827927?term=intellipower&rank=1.

Effects of prone positioning on lung mechanical power components in patients with acute respiratory distress syndrome: a physiologic study

BACKGROUND

Prone positioning (PP) homogenizes ventilation distribution and may limit ventilator-induced lung injury (VILI) in patients with moderate to severe acute respiratory distress syndrome (ARDS). The static and dynamic components of ventilation that may cause VILI have been aggregated in mechanical power, considered a unifying driver of VILI. PP may affect mechanical power components differently due to changes in respiratory mechanics; however, the effects of PP on lung mechanical power components are unclear. This study aimed to compare the following parameters during supine positioning (SP) and PP: lung total elastic power and its components (elastic static power and elastic dynamic power) and these variables normalized to end-expiratory lung volume (EELV).

METHODS

This prospective physiologic study included 55 patients with moderate to severe ARDS. Lung total elastic power and its static and dynamic components were compared during SP and PP using an esophageal pressure-guided ventilation strategy. In SP, the esophageal pressure-guided ventilation strategy was further compared with an oxygenation-guided ventilation strategy defined as baseline SP. The primary endpoint was the effect of PP on lung total elastic power non-normalized and normalized to EELV. Secondary endpoints were the effects of PP and ventilation strategies on lung elastic static and dynamic power components non-normalized and normalized to EELV, respiratory mechanics, gas exchange, and hemodynamic parameters.

RESULTS

Lung total elastic power (median [interquartile range]) was lower during PP compared with SP (6.7 [4.9-10.6] versus 11.0 [6.6-14.8] J/min; P < 0.001) non-normalized and normalized to EELV (3.2 [2.1-5.0] versus 5.3 [3.3-7.5] J/min/L; P < 0.001). Comparing PP with SP, transpulmonary pressures and EELV did not significantly differ despite lower positive end-expiratory pressure and plateau airway pressure, thereby reducing non-normalized and normalized lung elastic static power in PP. PP improved gas exchange, cardiac output, and increased oxygen delivery compared with SP.

CONCLUSIONS

In patients with moderate to severe ARDS, PP reduced lung total elastic and elastic static power compared with SP regardless of EELV normalization because comparable transpulmonary pressures and EELV were achieved at lower airway pressures. This resulted in improved gas exchange, hemodynamics, and oxygen delivery.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00017449). Registered June 27, 2019. https://drks.de/search/en/trial/DRKS00017449.

Association of elastic power in mechanical ventilation with the severity of acute respiratory distress syndrome: a retrospective study

BACKGROUND

Mechanical power (MP) is the total energy released into the entire respiratory system per minute which mainly comprises three components: elastic static power, Elastic dynamic power and resistive power. However, the energy to overcome resistance to the gas flow is not the key factor in causing lung injury, but the elastic power (EP) which generates the baseline stretch of the lung fibers and overcomes respiratory system elastance may be closely related to the ARDS severity. Thus, this study aimed to investigate whether EP is superior to other ventilator variables for predicting the severity of lung injury in ARDS patients.

METHODS

We retrieved patient data from the Medical Information Mart for Intensive Care III (MIMIC-III) database. The retrieved data involved adults (≥ 18 years) diagnosed with ARDS and subjected to invasive mechanical ventilation for ≥ 48 h. We employed univariate and multivariate logistic regression analyses to investigate the correlation between EP and development of moderate-severe ARDS. Furthermore, we utilized restricted cubic spline models to assess whether there is a linear association between EP and incidence of moderate-severe ARDS. In addition, we employed a stratified linear regression model and likelihood ratio test in subgroups to identify potential modifications and interactions.

RESULTS

Moderate-severe ARDS occurred in 73.4% (296/403) of the patients analyzed. EP and MP were significantly associated with moderate-severe ARDS (odds ratio [OR] 1.21, 95% confidence interval [CI] 1.15-1.28, p < 0.001; and OR 1.15, 95%CI 1.11-1.20, p < 0.001; respectively), but EP showed a higher area-under-curve (95%CI 0.72-0.82, p < 0.001) than plateau pressure, driving pressure, and static lung compliance in predicting ARDS severity. The optimal cutoff value for EP was 14.6 J/min with a sensitivity of 75% and specificity of 66%. Quartile analysis revealed that the relationship between EP and ARDS severity remained robust and reliable in subgroup analysis.

CONCLUSION

EP is a good ventilator variable associated with ARDS severity and can be used for grading ARDS severity. Close monitoring of EP is advised in patients undergoing mechanical ventilation. Additional experimental trials are needed to investigate whether adjusting ventilator variables according to EP can yield significant improvements in clinical outcomes.

The effect of inspiratory rise time on mechanical power calculations in pressure control ventilation: dynamic approach

BACKGROUND

Mechanical power may serve as a valuable parameter for predicting ventilation-induced injury in mechanically ventilated patients. Over time, several equations have been developed to calculate power in both volume control ventilation (VCV) and pressure control ventilation (PCV). Among these equations, the linear model mechanical power equation (MPLM) closely approximates the reference method when applied in PCV. The dynamic mechanical power equation (MPdyn) computes power by utilizing the ventilatory work of breathing parameter (WOBv), which is automatically measured by the mechanical ventilator. In our study, conducted in patients with Covid-19 Acute Respiratory Distress Syndrome (C-ARDS), we calculated mechanical power using both the MPLM and MPdyn equations, employing different inspiratory rise times (Tslope) at intervals of 5%, ranging from 5 to 20% and compared the obtained results.

RESULTS

In our analysis, we used univariate linear regression at both I:E ratios of 1:2 and 1:1, considering all Tslope values. These analyses revealed that the MPdyn and MPLM equations exhibited strong correlations, with R2 values exceeding 0.96. Furthermore, our Bland-Altman analysis, which compared the power values derived from the MPdyn and MPLM equations for patient averages and all measurements, revealed a mean difference of -0.42 ± 0.41 J/min (equivalent to 2.6% ± 2.3%, p < 0.0001) and -0.39 ± 0.57 J/min (equivalent to 3.6% ± 3.5%, p < 0.0001), respectively. While there was a statistically significant difference between the equations in both absolute value and relative proportion, this difference was not considered clinically relevant. Additionally, we observed that each 5% increase in Tslope time corresponded to a decrease in mechanical power values by approximately 1 J/min.

CONCLUSIONS

The differences between mechanical power values calculated using the MPdyn and MPLM equations at various Tslope durations were determined to lack clinical significance. Consequently, for practical and continuous mechanical power estimation in Pressure-Controlled Ventilation (PCV) mode, the MPdyn equation presents itself as a viable option. It is important to note that as Tslope times increased, the calculated mechanical power exhibited a clinically relevant decrease.

Understanding the mechanisms of ventilator-induced lung injury using animal models

Mechanical ventilation is a life-saving therapy in several clinical situations, promoting gas exchange and providing rest to the respiratory muscles. However, mechanical ventilation may cause hemodynamic instability and pulmonary structural damage, which is known as ventilator-induced lung injury (VILI). The four main injury mechanisms associated with VILI are as follows: barotrauma/volutrauma caused by overstretching the lung tissues; atelectrauma, caused by repeated opening and closing of the alveoli resulting in shear stress; and biotrauma, the resulting biological response to tissue damage, which leads to lung and multi-organ failure. This narrative review elucidates the mechanisms underlying the pathogenesis, progression, and resolution of VILI and discusses the strategies that can mitigate VILI. Different static variables (peak, plateau, and driving pressures, positive end-expiratory pressure, and tidal volume) and dynamic variables (respiratory rate, airflow amplitude, and inspiratory time fraction) can contribute to VILI. Moreover, the potential for lung injury depends on tissue vulnerability, mechanical power (energy applied per unit of time), and the duration of that exposure. According to the current evidence based on models of acute respiratory distress syndrome and VILI, the following strategies are proposed to provide lung protection: keep the lungs partially collapsed (SaO2 > 88%), avoid opening and closing of collapsed alveoli, and gently ventilate aerated regions while keeping collapsed and consolidated areas at rest. Additional mechanisms, such as subject-ventilator asynchrony, cumulative power, and intensity, as well as the damaging threshold (stress-strain level at which tidal damage is initiated), are under experimental investigation and may enhance the understanding of VILI.

Mechanical ventilation in patients with acute respiratory distress syndrome: current status and future perspectives

INTRODUCTION

Although there has been extensive research on mechanical ventilation for acute respiratory distress syndrome (ARDS), treatment remains mainly supportive. Recent studies and new ventilatory modes have been proposed to manage patients with ARDS; however, the clinical impact of these strategies remains uncertain and not clearly supported by guidelines. The aim of this narrative review is to provide an overview and update on ventilatory management for patients with ARDS.

AREAS COVERED

This article reviews the literature regarding mechanical ventilation in ARDS. A comprehensive overview of the principal settings for the ventilator parameters involved is provided as well as a report on the differences between controlled and assisted ventilation. Additionally, new modes of assisted ventilation are presented and discussed. The evidence concerning rescue strategies, including recruitment maneuvers and extracorporeal membrane oxygenation support, is analyzed. PubMed, EBSCO, and the Cochrane Library were searched up until June 2023, for relevant literature.

EXPERT OPINION

Available evidence for mechanical ventilation in cases of ARDS suggests the use of a personalized mechanical ventilation strategy. Although promising, new modes of assisted mechanical ventilation are still under investigation and guidelines do not recommend rescue strategies as the standard of care. Further research on this topic is required.