Mechanical power in pediatric acute respiratory distress syndrome: a PARDIE study

Mechanical power made simple: validating a simplified calculation of mechanical power in preterm lungs

BACKGROUND

The incidence of chronic lung disease is increasing, suggesting a need to explore novel ways to understand ventilator induced lung injury (VILI) in preterm infants. Mechanical power (MP) is a unifying measure of energy transferred to the respiratory system and a proposed determinant of VILI. The gold-standard method for calculating MP (geometric method) is not feasible in the clinical setting. This has prompted the derivation of simplified equations for calculating MP.

OBJECTIVE

To validate the agreement between a simplified calculation of MP (MPSimple) and the true MP calculated using the geometric method (MPRef).

METHODS

MPSimple and MPRef was calculated in mechanically ventilated preterm lambs (n = 71) and the agreement between both measures was determined using intraclass correlation coefficients (ICC), linear regression, and Bland-Altman analysis.

RESULTS

A strong linear relationship (adjusted R2 = 0.98), and excellent agreement (ICC = 0.99, 95% CI = 0.98-0.99) between MPSimple and MPRef was demonstrated. Bland-Altman analysis demonstrated a negligible positive bias (mean difference = 0.131 J/min·kg). The 95% limits of agreement were -0.06 to 0.32 J/min·kg.

CONCLUSIONS

In a controlled setting, there was excellent agreement between MPSimple and gold-standard calculations. MPSimple should be validated and explored in preterm neonates to assess the cause-effect relationship with VILI and neonatal outcomes.

IMPACT STATEMENT

Mechanical power (MP) unifies the individual components of ventilator induced lung injury (VILI) and provides an estimate of total energy transferred to the respiratory system during mechanical ventilation. As gold-standard calculations of mechanical power at the bedside are not feasible, alternative simplified equations have been proposed. In this study, MP calculated using a simplified equation had excellent agreement with true MP in mechanically ventilated preterm lambs. These results lay foundations to explore the role of MP in neonatal VILI and determine its relationship with short and long term respiratory outcomes.

Mechanical power and normalized mechanical power in pediatric acute respiratory distress syndrome

Background

Mechanical power (MP) refers to the energy transmitted over time to the respiratory system and serves as a unifying determinant of ventilator-induced lung injury. MP normalization is required to account for developmental changes in children. We sought to examine the relationship between mechanical energy (MEBW), MP normalized to body weight (MPBW), and MP normalized to respiratory compliance (MPCRS) concerning the severity and outcomes of pediatric acute respiratory distress syndrome (pARDS).

Method

In this retrospective study, children aged 1 month to 18 years diagnosed with pARDS who underwent pressure-control ventilation for at least 24 h between January 2017 and September 2020 were enrolled. We calculated MP using Becher's equation. Multivariable logistic regression analysis adjusted for age, pediatric organ dysfunction score, and oxygenation index (OI) was performed to determine the independent association of MP and its derivatives 24 h after diagnosing pARDS with 28-day mortality. The association was also studied for 28 ventilator-free days (VFD-28) and the severity of pARDS in terms of OI.

Results

Out of 246 admitted with pARDS, 185 were eligible, with an overall mortality of 43.7%. Non-survivors exhibited higher severity of illness, as evidenced by higher values of MP, MPBW, and MEBW. Multivariable logistic regression analysis showed that only MEBW but not MP, MPBW, or MPCRS at 24 h was independently associated with mortality [adjusted OR: 1.072 (1.002-1.147), p = 0.044]. However, after adjusting for the type of pARDS, MEBW was not independently associated with mortality [adjusted OR: 1.061 (0.992-1.136), p = 0.085]. After adjusting for malnutrition, only MP at 24 h was found to be independently associated. Only MPCRS at 1-4 and 24 h but not MP, MPBW, or MEBW at 24 h of diagnosing pARDS was significantly correlated with VFD-28.

Conclusions

Normalization of MP is better related to outcomes and severity of pARDS than non-normalized MP. Malnutrition can be a significant confounding factor in resource-limited settings.

Association between mechanical ventilation parameters and mortality in children with respiratory failure on ECMO: a systematic review and meta-analysis

Background

In refractory respiratory failure (RF), extracorporeal membrane oxygenation (ECMO) is a salvage therapy that seeks to reduce lung injury induced by mechanical ventilation. The parameters of optimal mechanical ventilation in children during ECMO are not known. Pulmonary ventilatory management during this therapy may impact mortality. The objective of this study was to evaluate the association between ventilatory parameters in children during ECMO therapy and in-hospital mortality.

Methods

A systematic search of PubMed/MEDLINE, Embase, Cochrane, and Google Scholar from January 2013 until May 2022 (PROSPERO 450744), including studies in children with ECMO-supported RF assessing mechanical ventilation parameters, was conducted. Risk of bias was assessed using the Newcastle-Ottawa scale; heterogeneity, with absence <25% and high >75%, was assessed using I2. Sensitivity and subgroup analyses using the Mantel-Haenszel random-effects model were performed to explore the impact of methodological quality on effect size.

Results

Six studies were included. The median age was 3.4 years (IQR: 3.2-4.2). Survival in the 28-day studies was 69%. Mechanical ventilation parameters associated with higher mortality were a very low tidal volume ventilation (<4 ml/kg; OR: 4.70; 95% CI: 2.91-7.59; p < 0.01; I2: 38%), high plateau pressure (mean Dif: -0.70 95% CI: -0.18, -0.22; p < 0.01), and high driving pressure (mean Dif: -0.96 95% CI: -1.83, -0.09: p = 0.03). The inspired fraction of oxygen (p = 0.09) and end-expiratory pressure (p = 0.69) were not associated with higher mortality. Patients who survived had less multiple organ failure (p < 0.01).

Conclusion

The mechanical ventilation variables associated with higher mortality in children with ECMO-supported respiratory failure are high plateau pressures, high driving pressure and very low tidal volume ventilation. No association between mortality and other parameters of the mechanical ventilator, such as the inspired fraction of oxygen or end-expiratory pressure, was found.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023450744, PROSPERO 2023 (CRD42023450744).

Mechanical ventilation during pediatric extracorporeal life support

PURPOSE OF REVIEW

To discuss the role of ventilator induced lung injury (VILI) and patient self-inflicted lung injury in ventilated children supported on extracorporeal membrane oxygenation (ECMO).

RECENT FINDINGS

While extracorporeal life support is used routinely used every day around the globe to support neonatal, pediatric, and adult patients with refractory cardiac and/or respiratory failure, the optimal approach to mechanical ventilation, especially for those with acute respiratory distress syndrome (ARDS), remains unknown and controversial. Given the lack of definitive data in this population, one must rely on available evidence in those with ARDS not supported with ECMO and extrapolate adult observations. Ventilatory management should include, as a minimum standard, limiting inspiratory and driving pressures, providing a sufficient level of positive end-expiratory pressure, and setting a low rate to reduce mechanical power. Allowing for spontaneous breathing and use of pulmonary specific ancillary treatment modalities must be individualized, while balancing the risk and benefits. Future studies delineating the best strategies for optimizing MV during pediatric extracorporeal life support are much needed.

SUMMARY

Future investigations will hopefully provide the needed evidence and better understanding of the overall goal of reducing mechanical ventilation intensity to decrease risk for VILI and promote lung recovery for those supported with ECMO.

Endotracheal tube, by the venturi effect, reduces the efficacy of increasing inlet pressure in improving pendelluft

In mechanically ventilated severe acute respiratory distress syndrome patients, spontaneous inspiratory effort generates more negative pressure in the dorsal lung than in the ventral lung. The airflow caused by this pressure difference is called pendelluft, which is a possible mechanisms of patient self-inflicted lung injury. This study aimed to use computer simulation to understand how the endotracheal tube and insufficient ventilatory support contribute to pendelluft. We established two models. In the invasive model, an endotracheal tube was connected to the tracheobronchial tree with 34 outlets grouped into six locations: the right and left upper, lower, and middle lobes. In the non-invasive model, the upper airway, including the glottis, was connected to the tracheobronchial tree. To recreate the inspiratory effort of acute respiratory distress syndrome patients, the lower lobe pressure was set at -13 cmH2O, while the upper and middle lobe pressure was set at -6.4 cmH2O. The inlet pressure was set from 10 to 30 cmH2O to recreate ventilatory support. Using the finite volume method, the total flow rates through each model and toward each lobe were calculated. The invasive model had half the total flow rate of the non-invasive model (1.92 L/s versus 3.73 L/s under 10 cmH2O, respectively). More pendelluft (gas flow into the model from the outlets) was observed in the invasive model than in the non-invasive model. The inlet pressure increase from 10 to 30 cmH2O decreased pendelluft by 11% and 29% in the invasive and non-invasive models, respectively. In the invasive model, a faster jet flowed from the tip of the endotracheal tube toward the lower lobes, consequently entraining gas from the upper and middle lobes. Increasing ventilatory support intensifies the jet from the endotracheal tube, causing a venturi effect at the bifurcation in the tracheobronchial tree. Clinically acceptable ventilatory support cannot completely prevent pendelluft.

The Impact of Mechanical Energy Assessment on Mechanical Ventilation: A Comprehensive Review and Practical Application

Mechanical ventilation (MV) provides basic organ support for patients who have acute hypoxemic respiratory failure, with acute respiratory distress syndrome as the most severe form. The use of excessive ventilation forces can exacerbate the lung condition and lead to ventilator-induced lung injury (VILI); mechanical energy (ME) or power can characterize such forces applied during MV. The ME metric combines all MV parameters affecting the respiratory system (ie, lungs, chest, and airways) into a single value. Besides evaluating the overall ME, this parameter can be also related to patient-specific characteristics, such as lung compliance or patient weight, which can further improve the value of ME for characterizing the aggressiveness of lung ventilation. High ME is associated with poor outcomes and could be used as a prognostic parameter and indicator of the risk of VILI. ME is rarely determined in everyday practice because the calculations are complicated and based on multiple equations. Although low ME does not conclusively prevent the possibility of VILI (eg, due to the lung inhomogeneity and preexisting damage), individualization of MV settings considering ME appears to improve outcomes. This article aims to review the roles of bedside assessment of mechanical power, its relevance in mechanical ventilation, and its associations with treatment outcomes. In addition, we discuss methods for ME determination, aiming to propose the most suitable method for bedside application of the ME concept in everyday practice.

Plateau Pressure and Driving Pressure in Volume- and Pressure-Controlled Ventilation: Comparison of Frictional and Viscoelastic Resistive Components in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

To examine frictional, viscoelastic, and elastic resistive components, as well threshold pressures, during volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) in pediatric patients with acute respiratory distress syndrome (ARDS).

DESIGN

Prospective cohort study.

SETTING

Seven-bed PICU, Hospital El Carmen de Maipú, Chile.

PATIENTS

Eighteen mechanically ventilated patients less than or equal to 15 years old undergoing neuromuscular blockade as part of management for ARDS.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients were in VCV mode during measurement of pulmonary mechanics, including: the first pressure drop (P1) upon reaching zero flow during the inspiratory hold, peak inspiratory pressure (PIP), plateau pressure (P PLAT ), and total positive end-expiratory pressure (tPEEP). We calculated the components of the working pressure, as defined by the following: frictional resistive = PIP-P1; viscoelastic resistive = P1-P PLAT ; purely elastic = driving pressure (ΔP) = P PLAT -tPEEP; and threshold = intrinsic PEEP. The procedures and calculations were repeated on PCV, keeping the same tidal volume and inspiratory time. Measurements in VCV were considered the gold standard. We performed Spearman correlation and Bland-Altman analysis. The median (interquartile range [IQR]) for patient age was 5 months (2-17 mo). Tidal volume was 5.7 mL/kg (5.3-6.1 mL/kg), PIP cm H 2 O 26 (23-27 cm H 2 O), P1 23 cm H 2 O (21-26 cm H 2 O), P PLAT 19 cm H 2 O (17-22 cm H 2 O), tPEEP 9 cm H 2 O (8-9 cm H 2 O), and ΔP 11 cm H 2 O (9-13 cm H 2 O) in VCV mode at baseline. There was a robust correlation (rho > 0.8) and agreement between frictional resistive, elastic, and threshold components of working pressure in both modes but not for the viscoelastic resistive component. The purely frictional resistive component was negligible. Median peak inspiratory flow with decelerating-flow was 21 (IQR, 15-26) and squared-shaped flow was 7 L/min (IQR, 6-10 L/min) ( p < 0.001).

CONCLUSIONS

P PLAT , ΔP, and tPEEP can guide clinical decisions independent of the ventilatory mode. The modest purely frictional resistive component emphasizes the relevance of maintaining the same safety limits, regardless of the selected ventilatory mode. Therefore, peak inspiratory flow should be studied as a mechanism of ventilator-induced lung injury in pediatric ARDS.

Mechanical Power Is Associated With Mortality in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

Mechanical power (MP) transferred from the ventilator to the lungs has been proposed as a summary variable that may impact mortality in children with acute respiratory distress syndrome (ARDS). To date, no study has shown an association between higher MP and mortality in children with ARDS.

DESIGN

Secondary analysis of a prospective observational study.

SETTING

Single-center, tertiary, academic PICU.

PATIENTS

Five hundred forty-six intubated children with ARDS enrolled between January 2013 and December 2019 receiving pressure-controlled ventilation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Higher MP was associated with increased mortality (adjusted hazard ratio [HR] 1.34 per 1 sd increase, 95% CI 1.08-1.65; p = 0.007). When assessing the contribution of individual components of MP, only positive end-expiratory pressure (PEEP) was associated with mortality (HR 1.32; p = 0.007), whereas tidal volume, respiratory rate, and driving pressure (ΔP = [peak inspiratory pressure (PIP)-PEEP]) were not. Finally, we tested whether there remained an association when specific terms were removed from the MP equation by calculating MP from static strain (remove ΔP), MP from dynamic strain (remove PEEP), and mechanical energy (remove respiratory rate). MP from static strain (HR 1.44; p < 0.001), MP from dynamic strain (HR 1.25; p = 0.042), and mechanical energy (HR 1.29; p = 0.009) were all associated with mortality. MP was associated with ventilator-free days only when using MP normalized to predicted body weight, but not when using measured weight.

CONCLUSIONS

Higher MP was associated with mortality in pediatric ARDS, and PEEP appears to be the component most consistently driving this association. As higher PEEP is used in sicker patients, the association between MP and mortality may reflect a marker of illness severity rather than MP itself being causal for mortality. However, our results support future trials testing different levels of PEEP in children with ARDS as a potential means to improve outcome.

Invasive Ventilatory Support in Patients With Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVE

To provide evidence for the Second Pediatric Acute Lung Injury Consensus Conference updated recommendations and consensus statements for clinical practice and future research on invasive mechanical ventilation support of patients with pediatric acute respiratory distress syndrome (PARDS).

DATA SOURCES

MEDLINE (Ovid), Embase (Elsevier), and CINAHL Complete (EBSCOhost).

STUDY SELECTION

We included clinical studies of critically ill patients undergoing invasive mechanical ventilation for PARDS, January 2013 to April 2022. In addition, meta-analyses and systematic reviews focused on the adult acute respiratory distress syndrome population were included to explore new relevant concepts (e.g., mechanical power, driving pressure, etc.) still underrepresented in the contemporary pediatric literature.

DATA EXTRACTION

Title/abstract review, full text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development and Evaluation approach was used to identify and summarize relevant evidence and develop recommendations, good practice statements and research statements. We identified 26 pediatric studies for inclusion and 36 meta-analyses or systematic reviews in adults. We generated 12 recommendations, two research statements, and five good practice statements related to modes of ventilation, tidal volume, ventilation pressures, lung-protective ventilation bundles, driving pressure, mechanical power, recruitment maneuvers, prone positioning, and high-frequency ventilation. Only one recommendation, related to use of positive end-expiratory pressure, is classified as strong, with moderate certainty of evidence.

CONCLUSIONS

Limited pediatric data exist to make definitive recommendations for the management of invasive mechanical ventilation for patients with PARDS. Ongoing research is needed to better understand how to guide best practices and improve outcomes for patients with PARDS requiring invasive mechanical ventilation.

Pathobiology, Severity, and Risk Stratification of Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

To review the literature for studies published in children on the pathobiology, severity, and risk stratification of pediatric acute respiratory distress syndrome (PARDS) with the intent of guiding current medical practice and identifying important areas for future research related to severity and risk stratification.

DATA SOURCES

Electronic searches of PubMed and Embase were conducted from 2013 to March 2022 by using a combination of medical subject heading terms and text words to capture the pathobiology, severity, and comorbidities of PARDS.

STUDY SELECTION

We included studies of critically ill patients with PARDS that related to the severity and risk stratification of PARDS using characteristics other than the oxygenation defect. Studies using animal models, adult only, and studies with 10 or fewer children were excluded from our review.

DATA EXTRACTION

Title/abstract review, full-text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development, and Evaluation approach was used to identify and summarize relevant evidence and develop recommendations for clinical practice. There were 192 studies identified for full-text extraction to address the relevant Patient/Intervention/Comparator/Outcome questions. One clinical recommendation was generated related to the use of dead space fraction for risk stratification. In addition, six research statements were generated about the impact of age on acute respiratory distress syndrome pathobiology and outcomes, addressing PARDS heterogeneity using biomarkers to identify subphenotypes and endotypes, and use of standardized ventilator, physiologic, and nonpulmonary organ failure measurements for future research.

CONCLUSIONS

Based on an extensive literature review, we propose clinical management and research recommendations related to characterization and risk stratification of PARDS severity.

Monitoring in Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

Monitoring is essential to assess changes in the lung condition, to identify heart-lung interactions, and to personalize and improve respiratory support and adjuvant therapies in pediatric acute respiratory distress syndrome (PARDS). The objective of this article is to report the rationale of the revised recommendations/statements on monitoring from the Second Pediatric Acute Lung Injury Consensus Conference (PALICC-2).

DATA SOURCES

MEDLINE (Ovid), Embase (Elsevier), and CINAHL Complete (EBSCOhost).

STUDY SELECTION

We included studies focused on respiratory or cardiovascular monitoring of children less than 18 years old with a diagnosis of PARDS. We excluded studies focused on neonates.

DATA EXTRACTION

Title/abstract review, full-text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development and Evaluation approach was used to identify and summarize evidence and develop recommendations. We identified 342 studies for full-text review. Seventeen good practice statements were generated related to respiratory and cardiovascular monitoring. Four research statements were generated related to respiratory mechanics and imaging monitoring, hemodynamics monitoring, and extubation readiness monitoring.

CONCLUSIONS

PALICC-2 monitoring good practice and research statements were developed to improve the care of patients with PARDS and were based on new knowledge generated in recent years in patients with PARDS, specifically in topics of general monitoring, respiratory system mechanics, gas exchange, weaning considerations, lung imaging, and hemodynamic monitoring.

The Physiological Basis of High-Frequency Oscillatory Ventilation and Current Evidence in Adults and Children: A Narrative Review

High-frequency oscillatory ventilation (HFOV) is a type of invasive mechanical ventilation that employs supra-physiologic respiratory rates and low tidal volumes (V_T) that approximate the anatomic deadspace. During HFOV, mean airway pressure is set and gas is then displaced towards and away from the patient through a piston. Carbon dioxide (CO₂) is cleared based on the power (amplitude) setting and frequency, with lower frequencies resulting in higher V_T and CO₂ clearance. Airway pressure amplitude is significantly attenuated throughout the respiratory system and mechanical strain and stress on the alveoli are theoretically minimized. HFOV has been purported as a form of lung protective ventilation that minimizes volutrauma, atelectrauma, and biotrauma. Following two large randomized controlled trials showing no benefit and harm, respectively, HFOV has largely been abandoned in adults with ARDS. A multi-center clinical trial in children is ongoing. This article aims to review the physiologic rationale for the use of HFOV in patients with acute respiratory failure, summarize relevant bench and animal models, and discuss the potential use of HFOV as a primary and rescue mode in adults and children with severe respiratory failure.

Ventilation-Induced Lung Injury (VILI) in Neonates: Evidence-Based Concepts and Lung-Protective Strategies

Supportive care with mechanical ventilation continues to be an essential strategy for managing severe neonatal respiratory failure; however, it is well known to cause and accentuate neonatal lung injury. The pathogenesis of ventilator-induced lung injury (VILI) is multifactorial and complex, resulting predominantly from interactions between ventilator-related factors and patient-related factors. Importantly, VILI is a significant risk factor for developing bronchopulmonary dysplasia (BPD), the most common chronic respiratory morbidity of preterm infants that lacks specific therapies, causes life-long morbidities, and imposes psychosocial and economic burdens. Studies of older children and adults suggest that understanding how and why VILI occurs is essential to developing strategies for mitigating VILI and its consequences. This article reviews the preclinical and clinical evidence on the pathogenesis and pathophysiology of VILI in neonates. We also highlight the evidence behind various lung-protective strategies to guide clinicians in preventing and attenuating VILI and, by extension, BPD in neonates. Further, we provide a snapshot of future directions that may help minimize neonatal VILI.