Assessment of pulmonary function in the early phase of ARDS in pediatric patients

Surfactant status assessment and personalized therapy for surfactant deficiency or dysfunction

Surfactant is a pivotal neonatal drug used both for respiratory distress syndrome due to surfactant deficiency and for more complex surfactant dysfunctions (such as in case of neonatal acute respiratory distress syndrome). Despite its importance, indications for surfactant therapy are often based on oversimplified criteria. Lung biology and modern monitoring provide several diagnostic tools to assess the patient surfactant status and they can be used for a personalized surfactant therapy. This is desirable to improve the efficacy of surfactant treatment and reduce associated costs and side effects. In this review we will discuss these diagnostic tools from a pathophysiological and multi-disciplinary perspective, focusing on the quantitative or qualitative surfactant assays, lung mechanics or aeration measurements, and gas exchange metrics. Their biological and technical characteristics are described with practical information for clinicians. Finally, available evidence-based data are reviewed, and the diagnostic accuracy of the different tools is compared. Lung ultrasound seems the most suitable tool for assessing the surfactant status, while some other promising tests require further research and/or development.

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.

Automated closed–loop FiO2 titration increases the percentage of time spent in optimal zones of oxygen saturation in pediatric patients–A randomized crossover clinical trial

Introduction

We aimed to compare automated ventilation with closed–loop control of the fraction of inspired oxygen (FiO₂) to automated ventilation with manual titrations of the FiO₂ with respect to time spent in predefined pulse oximetry (SpO₂) zones in pediatric critically ill patients.

Methods

This was a randomized crossover clinical trial comparing Adaptive Support Ventilation (ASV) 1.1 with use of a closed–loop FiO₂ system vs. ASV 1.1 with manual FiO₂ titrations. The primary endpoint was the percentage of time spent in optimal SpO₂ zones. Secondary endpoints included the percentage of time spent in acceptable, suboptimal and unacceptable SpO₂ zones, and the total number of FiO₂ changes per patient.

Results

We included 30 children with a median age of 21 (11–48) months; 12 (40%) children had pediatric ARDS. The percentage of time spent in optimal SpO₂ zones increased with use of the closed–loop FiO₂ controller vs. manual oxygen control [96.1 (93.7–98.6) vs. 78.4 (51.3–94.8); P < 0.001]. The percentage of time spent in acceptable, suboptimal and unacceptable zones decreased. Findings were similar with the use of closed-loop FiO₂ controller compared to manual titration in patients with ARDS [95.9 (81.6–98.8) vs. 78 (49.5–94.8) %; P = 0.027]. The total number of closed-loop FiO₂ changes per patient was 52 (11.8–67), vs. the number of manual changes 1 (0–2), (P < 0.001).

Conclusion

In this randomized crossover trial in pediatric critically ill patients under invasive ventilation with ASV, use of a closed–loop control of FiO₂ titration increased the percentage of time spent within in optimal SpO₂ zones, and increased the total number of FiO₂ changes per patient.

Clinical trial registration

ClinicalTrials.gov, identifier: NCT04568642.

Adherence to Lung-Protective Ventilation Principles in Pediatric Acute Respiratory Distress Syndrome: A Pediatric Acute Respiratory Distress Syndrome Incidence and Epidemiology Study

OBJECTIVES

To describe mechanical ventilation management and factors associated with nonadherence to lung-protective ventilation principles in pediatric acute respiratory distress syndrome.

DESIGN

A planned ancillary study to a prospective international observational study. Mechanical ventilation management (every 6 hr measurements) during pediatric acute respiratory distress syndrome days 0-3 was described and compared with Pediatric Acute Lung Injury Consensus Conference tidal volume recommendations (< 7 mL/kg in children with impaired respiratory system compliance, < 9 mL/kg in all other children) and the Acute Respiratory Distress Syndrome Network lower positive end-expiratory pressure/higher Fio2 grid recommendations.

SETTING

Seventy-one international PICUs.

PATIENTS

Children with pediatric acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Analyses included 422 children. On pediatric acute respiratory distress syndrome day 0, median tidal volume was 7.6 mL/kg (interquartile range, 6.3-8.9 mL/kg) and did not differ by pediatric acute respiratory distress syndrome severity. Plateau pressure was not recorded in 97% of measurements. Using delta pressure (peak inspiratory pressure - positive end-expiratory pressure), median tidal volume increased over quartiles of median delta pressure (p = 0.007). Median delta pressure was greater than or equal to 18 cm H2O for all pediatric acute respiratory distress syndrome severity levels. In severe pediatric acute respiratory distress syndrome, tidal volume was greater than or equal to 7 mL/kg 62% of the time, and positive end-expiratory pressure was lower than recommended by the positive end-expiratory pressure/Fio2 grid 70% of the time. In multivariable analysis, tidal volume nonadherence was more common with severe pediatric acute respiratory distress syndrome, fewer PICU admissions/yr, non-European PICUs, higher delta pressure, corticosteroid use, and pressure control mode. Adherence was associated with underweight stature and cuffed endotracheal tubes. In multivariable analysis, positive end-expiratory pressure/Fio2 grid nonadherence was more common with higher pediatric acute respiratory distress syndrome severity, ventilator decisions made primarily by the attending physician, pre-ICU cardiopulmonary resuscitation, underweight stature, and age less than 2 years. Adherence was associated with respiratory therapist involvement in ventilator management and longer time from pediatric acute respiratory distress syndrome diagnosis. Higher nonadherence to tidal volume and positive end-expiratory pressure recommendations were independently associated with higher mortality and longer duration of ventilation after adjustment for confounding variables. In stratified analyses, these associations were primarily influenced by children with severe pediatric acute respiratory distress syndrome.

CONCLUSIONS

Nonadherence to lung-protective ventilation principles is common in pediatric acute respiratory distress syndrome and may impact outcome. Modifiable factors exist that may improve adherence.

Randomized crossover trial to compare driving pressures in a closed-loop and a conventional mechanical ventilation mode in pediatric patients

INTRODUCTION

In mechanically ventilated patients, driving pressure (ΔP) represents the dynamic stress applied to the respiratory system and is related to ICU mortality. An evolution of the Adaptive Support Ventilation algorithm (ASV® 1.1) minimizes inspiratory pressure in addition to minimizing the work of breathing. We hypothesized that ASV 1.1 would result in lower ΔP than the ΔP measured in APV-CMV (controlled mandatory ventilation with adaptive pressure ventilation) mode with physician-tailored settings. The aim of this randomized crossover trial was therefore to compare ΔP in ASV 1.1 with ΔP in physician-tailored APV-CMV mode.

METHODS

Pediatric patients admitted to the PICU with heterogeneous-lung disease were enrolled if they were ventilated invasively with no detectable respiratory effort, hemodynamic instability, or significant airway leak around the endotracheal tube. We compared two 60-min periods of ventilation in APV-CMV and ASV 1.1, which were determined by randomization and separated by 30-min washout periods. Settings were adjusted to reach the same minute ventilation in both modes. ΔP was calculated as the difference between plateau pressure and total PEEP measured using end-inspiratory and end-expiratory occlusions, respectively.

RESULTS

There were 26 patients enrolled with a median age of 16 (9-25 [IQR]) months. The median ΔP for these patients was 10.4 (8.5-12.1 [IQR]) and 12.4 (10.5-15.3 [IQR]) cmH2O in the ASV 1.1 and APV-CMV periods, respectively (p < .001). The median tidal volume (VT) selected by the ASV 1.1 algorithm was 6.4 (5.1-7.3 [IQR]) ml/kg and RR was 41 (33 50 [IQR]) b/min, whereas the median of the same values for the APV-CMV period was 7.9 (6.8-8.3 [IQR]) ml/kg and 31 (26-41[IQR]) b/min, respectively. In both ASV 1.1 and APV-CMV modes, the highest ΔP was used to ventilate those patients with restrictive lung conditions at baseline.

CONCLUSION

In this randomized crossover trial, ΔP in ASV 1.1 was lower compared to ΔP in physician-tailored APV-CMV mode in pediatric patients with different lung conditions. The use of ASV 1.1 may therefore result in continued, safe ventilation in a heterogeneous pediatric patient group.

Invasive and noninvasive ventilation strategies for acute respiratory failure in children with coronavirus disease 2019

PURPOSE OF REVIEW

Severe Acute Respiratory Syndrome Coronavirus 2 presents as symptomatic coronavirus disease 2019 (COVID-19) disease in susceptible patients. Severe pediatric COVID-19 disease is rare, limiting potential data accumulation on associated respiratory failure in children. Pediatric intensivists and pulmonologists managing COVID-19 patients look to adult guidelines and pediatric-specific consensus statements to guide management. The purpose of this article is to review the current literature and recommended strategies for the escalation of noninvasive and invasive respiratory support for acute respiratory failure associated with COVID-19 disease in children.

RECENT FINDINGS

There are no prospective studies comparing COVID-19 treatment strategies in children. Adult and pediatric ventilation management interim guidance is based on evidence-based guidelines in non-COVID acute respiratory distress syndrome, with considerations of (1) noninvasive positive pressure ventilation versus high-flow nasal cannula and (2) high versus lower positive end expiratory pressure strategies related to lung compliance and potential lung recruitability.

SUMMARY

Management of acute respiratory failure from COVID-19 requires individualized titration of noninvasive and invasive ventilation modalities with consideration of preserved or compromised pulmonary compliance. Research regarding best practices in the management of pediatric severe COVID-19 with respiratory failure is lacking and is acutely needed as the pandemic surges and vaccination of the pediatric population will be delayed compared to adults.

Surfactant therapies for pediatric and neonatal ARDS: ESPNIC expert consensus opinion for future research steps

Pediatric (PARDS) and neonatal (NARDS) acute respiratory distress syndrome have different age-specific characteristics and definitions. Trials on surfactant for ARDS in children and neonates have been performed well before the PARDS and NARDS definitions and yielded conflicting results. This is mainly due to heterogeneity in study design reflecting historic lack of pathobiology knowledge. We reviewed the available clinical and preclinical data to create an expert consensus aiming to inform future research steps and advance the knowledge in this area. Eight trials investigated the use of surfactant for ARDS in children and ten in neonates, respectively. There were improvements in oxygenation (7/8 trials in children, 7/10 in neonates) and mortality (3/8 trials in children, 1/10 in neonates) improved. Trials were heterogeneous for patients' characteristics, surfactant type and administration strategy. Key pathobiological concepts were missed in study design. Consensus with strong agreement was reached on four statements: 1. There are sufficient preclinical and clinical data to support targeted research on surfactant therapies for PARDS and NARDS. Studies should be performed according to the currently available definitions and considering recent pathobiology knowledge. 2. PARDS and NARDS should be considered as syndromes and should be pre-clinically studied according to key characteristics, such as direct or indirect (primary or secondary) nature, clinical severity, infectious or non-infectious origin or patients' age. 3. Explanatory should be preferred over pragmatic design for future trials on PARDS and NARDS. 4. Different clinical outcomes need to be chosen for PARDS and NARDS, according to the trial phase and design, trigger type, severity class and/or surfactant treatment policy. We advocate for further well-designed preclinical and clinical studies to investigate the use of surfactant for PARDS and NARDS following these principles.

Minimal Change in Cardiac Index With Increasing PEEP in Pediatric Acute Respiratory Distress Syndrome

Objective: To determine if increasing positive end expiratory pressure (PEEP) leads to a change in cardiac index in children with Pediatric Acute Respiratory Distress Syndrome ranging from mild to severe. Design: Prospective interventional study. Setting: Multidisciplinary Pediatric Intensive Care Unit in a University teaching hospital. Patients: Fifteen intubated children (5 females, 10 males) with a median age of 72 months (IQR 11, 132) and a median weight of 19.3 kg (IQR 7.5, 53.6) with a severity of Pediatric Acute Respiratory Distress Syndrome that ranged from mild to severe with a median lung injury score of 2.3 (IQR 2.0, 2.7). Measurements: Cardiac index (CI) and stroke volume (SV) were measured on baseline ventilator settings and subsequently with a PEEP 4 cmH₂O higher than baseline. Change in CI and SV from baseline values was evaluated using Wilcoxon signed rank test. Results: A total of 19 paired measurements obtained. The median baseline PEEP was 8 cmH₂O (IQR 8, 10) Range 6-14 cmH₂O. There was no significant change in cardiac index or stroke volume with change in PEEP. Baseline median CI 4.4 L/min/m² (IQR 3.4, 4.8) and PEEP 4 higher median CI of 4.3 L/min/m² (IQR 3.6, 4.8), p = 0.65. Baseline median SV 26 ml (IQR 13, 44) and at PEEP 4 higher median SV 34 ml (IQR 12, 44) p = 0.63. Conclusion: There is no significant change in cardiac index or stroke volume with increasing PEEP by 4 cmH₂O in a population of children with mild to severe PARDS. Clinical Trial Registration: The study is registered on Clinical trails.gov under the Identifier: NCT02354365.

Does Size Matter When Calculating the "Correct" Tidal Volume for Pediatric Mechanical Ventilation?: A Hypothesis Based on FVC

BACKGROUND

Tidal volumes standardized to predicted body weight are recommended for adult mechanical ventilation, but children are frequently ventilated by using measured body weight. The goal of this study was to examine the difference in FVC (in milliliters per kilogram [mL/kg]) by using measured body weight compared with predicted body weight in children.

METHODS

This retrospective analysis included outpatient pulmonary function tests (PFTs) from two datasets. Dataset one included 6- to 19-year-old patients undergoing PFTs from the nationally representative Canadian Health Measures Survey. Dataset two included 6- to 20-year-old patients undergoing PFTs at a freestanding children's hospital. FVC mL/kg values were analyzed against BMI z scores to show changes in FVC vs BMI between measured and predicted weight.

RESULTS

Dataset one included 5,394 PFTs from the Canadian survey. FVC from measured weight decreased as the BMI z score group increased. The median FVC from measured weight was 81.4 mL/kg in the lowest BMI z score group and 51.7 mL/kg in the highest BMI z score group. FVC from predicted weight increased slightly with increasing BMI z score group. Dataset two included 8,472 patient PFTs from clinical measurement. A decline in median FVC from measured weight (from 69.4 to 37.6 mL/kg) as BMI z score group increased was also seen.

CONCLUSIONS

FVC differs significantly when standardizing to measured weight vs predicted weight. Obese children have lung volumes reflecting their predicted body weight from height. Children with low or normal BMI have lung volumes reflecting measured body weight. These findings suggest that targeting tidal volume by using the lower of measured and predicted body weights would be the most lung-protective strategy.

Variability in Usual Care Mechanical Ventilation for Pediatric Acute Respiratory Distress Syndrome: Time for a Decision Support Protocol?

OBJECTIVES

Although pediatric intensivists philosophically embrace lung protective ventilation for acute lung injury and acute respiratory distress syndrome, we hypothesized that ventilator management varies. We assessed ventilator management by evaluating changes to ventilator settings in response to blood gases, pulse oximetry, or end-tidal CO2. We also assessed the potential impact that a pediatric mechanical ventilation protocol adapted from National Heart Lung and Blood Institute acute respiratory distress syndrome network protocols could have on reducing variability by comparing actual changes in ventilator settings to those recommended by the protocol.

DESIGN

Prospective observational study.

SETTING

Eight tertiary care U.S. PICUs, October 2011 to April 2012.

PATIENTS

One hundred twenty patients (age range 17 d to 18 yr) with acute lung injury/acute respiratory distress syndrome.

MEASUREMENTS AND MAIN RESULTS

Two thousand hundred arterial and capillary blood gases, 3,964 oxygen saturation by pulse oximetry, and 2,757 end-tidal CO2 values were associated with 3,983 ventilator settings. Ventilation mode at study onset was pressure control 60%, volume control 19%, pressure-regulated volume control 18%, and high-frequency oscillatory ventilation 3%. Clinicians changed FIO2 by ±5 or ±10% increments every 8 hours. Positive end-expiratory pressure was limited at ~10 cm H2O as oxygenation worsened, lower than would have been recommended by the protocol. In the first 72 hours of mechanical ventilation, maximum tidal volume/kg using predicted versus actual body weight was 10.3 (8.5-12.9) (median [interquartile range]) versus 9.2 mL/kg (7.6-12.0) (p < 0.001). Intensivists made changes similar to protocol recommendations 29% of the time, opposite to the protocol's recommendation 12% of the time and no changes 56% of the time.

CONCLUSIONS

Ventilator management varies substantially in children with acute respiratory distress syndrome. Opportunities exist to minimize variability and potentially injurious ventilator settings by using a pediatric mechanical ventilation protocol offering adequately explicit instructions for given clinical situations. An accepted protocol could also reduce confounding by mechanical ventilation management in a clinical trial.

The Montreux definition of neonatal ARDS: biological and clinical background behind the description of a new entity

Acute respiratory distress syndrome (ARDS) is undefined in neonates, despite the long-standing existing formal recognition of ARDS syndrome in later life. We describe the Neonatal ARDS Project: an international, collaborative, multicentre, and multidisciplinary project which aimed to produce an ARDS consensus definition for neonates that is applicable from the perinatal period. The definition was created through discussions between five expert members of the European Society for Paediatric and Neonatal Intensive Care; four experts of the European Society for Paediatric Research; two independent experts from the USA and two from Australia. This Position Paper provides the first consensus definition for neonatal ARDS (called the Montreux definition). We also provide expert consensus that mechanisms causing ARDS in adults and older children-namely complex surfactant dysfunction, lung tissue inflammation, loss of lung volume, increased shunt, and diffuse alveolar damage-are also present in several critical neonatal respiratory disorders.

An Official American Thoracic Society/European Respiratory Society Workshop Report: Evaluation of Respiratory Mechanics and Function in the Pediatric and Neonatal Intensive Care Units

Ready access to physiologic measures, including respiratory mechanics, lung volumes, and ventilation/perfusion inhomogeneity, could optimize the clinical management of the critically ill pediatric or neonatal patient and minimize lung injury. There are many techniques for measuring respiratory function in infants and children but very limited information on the technical ease and applicability of these tests in the pediatric and neonatal intensive care unit (PICU, NICU) environments. This report summarizes the proceedings of a 2011 American Thoracic Society Workshop critically reviewing techniques available for ventilated and spontaneously breathing infants and children in the ICU. It outlines for each test how readily it is performed at the bedside and how it may impact patient management as well as indicating future areas of potential research collaboration. From expert panel discussions and literature reviews, we conclude that many of the techniques can aid in optimizing respiratory support in the PICU and NICU, quantifying the effect of therapeutic interventions, and guiding ventilator weaning and extubation. Most techniques now have commercially available equipment for the PICU and NICU, and many can generate continuous data points to help with ventilator weaning and other interventions. Technical and validation studies in the PICU and NICU are published for the majority of techniques; some have been used as outcome measures in clinical trials, but few have been assessed specifically for their ability to improve clinical outcomes. Although they show considerable promise, these techniques still require further study in the PICU and NICU together with increased availability of commercial equipment before wider incorporation into daily clinical practice.

Short-term effects of neuromuscular blockade on global and regional lung mechanics, oxygenation and ventilation in pediatric acute hypoxemic respiratory failure

Background

Neuromuscular blockade (NMB) has been shown to improve outcome in acute respiratory distress syndrome (ARDS) in adults, challenging maintaining spontaneous breathing when there is severe lung injury. We tested in a prospective physiological study the hypothesis that continuous administration of NMB agents in mechanically ventilated children with severe acute hypoxemic respiratory failure (AHRF) improves the oxygenation index without a redistribution of tidal volume V_T toward non-dependent lung zones.

Methods

Oxygenation index, PaO₂/FiO₂ ratio, lung mechanics (plateau pressure, mean airway pressure, respiratory system compliance and resistance), hemodynamics (heart rate, central venous and arterial blood pressures), oxygenation [oxygenation index (OI), PaO₂/FiO₂ and SpO₂/FiO₂], ventilation (physiological dead space-to-V_T ratio) and electrical impedance tomography measured changes in end-expiratory lung volume (EELV), and V_T distribution was measured before and 15 min after the start of continuous infusion of rocuronium 1 mg/kg. Patients were ventilated in a time-cycled, pressure-limited mode with pre-set V_T. All ventilator settings were not changed during the study.

Results

Twenty-two patients were studied (N = 18 met the criteria for pediatric ARDS). Median age (25–75 interquartile range) was 15 (7.8–77.5) weeks. Pulmonary pathology was present in 77.3%. The median lung injury score was 9 (8–10). The overall median CoV and regional lung filling characteristics were not affected by NMB, indicating no ventilation shift toward the non-dependent lung zones. Regional analysis showed a homogeneous time course of lung inflation during inspiration, indicating no tendency to atelectasis after the introduction of NMB. NMB decreased the mean airway pressure (p = 0.039) and OI (p = 0.039) in all patients. There were no significant changes in lung mechanics, hemodynamics and EELV. Subgroup analysis showed that OI decreased (p = 0.01) and PaO₂/FiO₂ increased (p = 0.02) in patients with moderate or severe PARDS.

Conclusions

NMB resulted in an improved oxygenation index in pediatric patients with AHRF. Distribution of V_T and regional lung filling characteristics were not affected.

Monitoring of children with pediatric acute respiratory distress syndrome: proceedings from the Pediatric Acute Lung Injury Consensus Conference

OBJECTIVE

To critically review the potential role of monitoring technologies in the management of pediatric acute respiratory distress syndrome, and specifically regarding monitoring of the general condition, respiratory system mechanics, severity scoring parameters, imaging, hemodynamic status, and specific weaning considerations.

DESIGN

Consensus conference of experts in pediatric acute lung injury.

METHODS

A panel of 27 experts met over the course of 2 years to develop a taxonomy to define pediatric acute respiratory distress syndrome and to make recommendations regarding treatment and research priorities. The monitoring subgroup comprised two experts. When published data were lacking a modified Delphi approach, emphasizing strong professional agreement was used.

RESULTS

The Pediatric Acute Lung Injury Consensus Conference experts developed and voted on a total of 151 recommendations addressing the topics related to pediatric acute respiratory distress syndrome, 21 of which related to monitoring of a child with pediatric acute respiratory distress syndrome. All 21 recommendations had agreement, with 19 (90%) reaching strong agreement.

CONCLUSIONS

The Consensus Conference developed pediatric-specific recommendations related to monitoring children with pediatric acute respiratory distress syndrome. These include interpreting monitored values such as tidal volume using predicted body weight, monitoring tidal volume at the end of the endotracheal tube in small children, and continuous monitoring of exhaled carbon dioxide in intubated children with pediatric acute respiratory distress syndrome, among others. These recommendations for monitoring in pediatric acute respiratory distress syndrome are intended to promote optimization and consistency of care for children with pediatric acute respiratory distress syndrome and identify areas of uncertainty requiring further investigation.

Pathobiology of acute respiratory distress syndrome

The unique characteristics of pulmonary circulation and alveolar-epithelial capillary-endothelial barrier allow for maintenance of the air-filled, fluid-free status of the alveoli essential for facilitating gas exchange, maintaining alveolar stability, and defending the lung against inhaled pathogens. The hallmark of pathophysiology in acute respiratory distress syndrome is the loss of the alveolar capillary permeability barrier and the presence of protein-rich edema fluid in the alveoli. This alteration in permeability and accumulation of fluid in the alveoli accompanies damage to the lung epithelium and vascular endothelium along with dysregulated inflammation and inappropriate activity of leukocytes and platelets. In addition, there is uncontrolled activation of coagulation along with suppression of fibrinolysis and loss of surfactant. These pathophysiological changes result in the clinical manifestations of acute respiratory distress syndrome, which include hypoxemia, radiographic opacities, decreased functional residual capacity, increased physiologic deadspace, and decreased lung compliance. Resolution of acute respiratory distress syndrome involves the migration of cells to the site of injury and re-establishment of the epithelium and endothelium with or without the development of fibrosis. Most of the data related to acute respiratory distress syndrome, however, originate from studies in adults or in mature animals with very few studies performed in children or juvenile animals. The lack of studies in children is particularly problematic because the lungs and immune system are still developing during childhood and consequently the pathophysiology of pediatric acute respiratory distress syndrome may differ in significant ways from that seen in acute respiratory distress syndrome in adults. This article describes what is known of the pathophysiologic processes of pediatric acute respiratory distress syndrome as we know it today while also presenting the much greater body of evidence on these processes as elucidated by adult and animal studies. It is also our expressed intent to generate enthusiasm for larger and more in-depth investigations of the mechanisms of disease and repair specific to children in the years to come.

Bronchiolitis

Everyone on the planet is exposed to respiratory syncytial virus (RSV) infection by the age of 2 years. Most infants admitted to the pediatric intensive care unit (PICU) for respiratory support during this infection are previously healthy, but their principal risk for needing PICU treatment is young age. That is, if you are born in October/November in the northern hemisphere, then your first winter exposure to RSV is likely to be when you are less than 4 months of age and vulnerable because of poor respiratory mechanical reserve (Alonso et al. 2007). However, if you are born in May/June, then you will be 7–8 months during your first winter exposure to RSV, much bigger and stronger and have more efficient thoracic and diaphragmatic mechanics. In the PICU, the main predictors of severe outcome in previously well infants appear to be young age, presence of apnea, and pulmonary consolidation on admission chest radiograph (Tasker et al. 2000; Lopez Guinea et al. 2007). Taken together, we can say that more severe RSV bronchiolitis in PICU practice is typically a problem of pulmonary consolidation, poor respiratory mechanics, and poor reserve, in the younger infant.

The Respiratory System

This chapter addresses upper airway physiology for the pediatric intensivist, focusing on functions that affect ventilation, with an emphasis on laryngeal physiology and control in breathing. Effective control of breathing ensures that the airway is protected, maintains volume homeostasis, and provides ventilation. Upper airway structures are effectors for all of these functions that affect the entire airway. Nasal functions include air conditioning and protective reflexes that can be exaggerated and involve circulatory changes. Oral cavity and pharyngeal patency enable airflow and feeding, but during sleep pharyngeal closure can result in apnea. Coordination of breathing with sucking and nutritive swallowing alters during development, while nonnutritive swallowing at all ages limits aspiration. Laryngeal functions in breathing include protection of the subglottic airway, active maintenance of its absolute volume, and control of tidal flow patterns. These are vital functions for normal lung growth in fetal life and during rapid adaptations to breathing challenges from birth through adulthood. Active central control of breathing focuses on the coordination of laryngeal and diaphragmatic activities, which adapts according to the integration of central and peripheral inputs. For the intensivist, knowledge of upper airway physiology can be applied to improve respiratory support. In a second part the mechanical properties of the respiratory system as a critical component of the chain of events that result in translation of the output of the respiratory rhythm generator to ventilation are described. A comprehensive understanding of respiratory mechanics is essential to the delivery of optimized and individualized mechanical ventilation. The basic elements of respiratory mechanics will be described and developmental changes in the airways, lungs, and chest wall that impact on measurement of respiratory mechanics with advancing postnatal age are reviewed. This will be follwowed by two sections, the first on respiratory mechanics in various neonatal pathologies and the second in pediatric pathologies. The latter can be classified in three categories. First, restrictive diseases may be of pulmonary origin, such as chronic interstitial lung diseases or acute lung injury/acute respiratory distress syndrome, which are usually associated with reduced lung compliance. Restrictive diseases may also be due to chest wall abnormalities such as obesity or scoliosis (idiopathic or secondary to neuromuscular diseases), which are associated with a reduction in chest wall compliance. Second, obstructive diseases are represented by asthma and wheezing disorders, cystic fibrosis, long term sequelae of neonatal lung disease and bronchiolitis obliterans following hematopoietic stem cell transplantation. Obstructive diseases are defined by a reduced FEV1/VC ratio. Third, neuromuscular diseases, mainly represented by DMD and SMA, are associated with a decrease in vital capacity linked to respiratory muscle weakness that is better detected by PImax, PEmax and SNIP measurements.

Clinical and biological role of secretory phospholipase A2 in acute respiratory distress syndrome infants

INTRODUCTION

Secretory phospholipase A2 is supposed to play a role in acute lung injury but no data are available for pediatric acute respiratory distress syndrome (ARDS). It is not clear which enzyme subtypes are secreted and what the relationships are between enzyme activity, biophysical and biochemical parameters, and clinical outcomes. We aimed to measure the enzyme and identify its subtypes and to study its biochemical and biophysical effect. The secondary aim was to correlate enzyme activity with clinical outcome.

METHODS

Bronchoalveolar lavage was performed in 24 infants with ARDS and 14 controls with no lung disease. Samples were assayed for secretory phospholipase A2 and molecules related to its activity and expression. Western blotting and captive bubble surfactometry were also performed. Clinical data were real time downloaded.

RESULTS

Tumor necrosis factor-α (814 (506-2,499) vs. 287 (111-1,315) pg/mL; P = 0.04), enzyme activity (430 (253-600) vs. 149 (61-387) IU/mL; P = 0.01), free fatty acids (4.3 (2.8-8.6) vs. 2 (0.8-4.6) mM; P = 0.026), and minimum surface tension (25.6 ± 6.1 vs. 18 ± 1.8 mN/m; P = 0.006) were higher in ARDS than in controls. Phospholipids are lower in ARDS than in controls (76.5 (54-100) vs. 1,094 (536-2,907) μg/mL; P = 0.0001). Three enzyme subtypes were identified (-IIA, -V, -X), although in lower quantities in controls; another subtype (-IB) was mainly detected in ARDS. Significant correlations exist between enzyme activity, free fatty acids (ρ = 0.823; P < 0.001), and surface tension (ρ = 0.55; P < 0.028). Correlations also exist with intensive care stay (ρ = 0.54; P = 0.001), PRISM-III24 (ρ = 0.79; P< 0.001), duration of ventilation (ρ = 0.53; P = 0.002), and oxygen therapy (ρ = 0.54; P = 0.001).

CONCLUSIONS

Secretory phospholipase A2 activity is raised in pediatric ARDS and constituted of four subtypes. Enzyme correlates with some inflammatory mediators, surface tension, and major clinical outcomes. Secretory phospholipase A2 may be a clinically relevant target in pediatric ARDS.

Epidemiological features and risk factor analysis of children with acute lung injury

BACKGROUND

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) represents a devastating complication observed in critical care medicine. The purpose of this study is to investigate the epidemiological aspects of ALI/ARDS in pediatric intensive care unit (PICU) and risk factors of mortality.

METHODS

Patients with ALI/ARDS in PICU of Beijing Children's Hospital, a tertiary medical center from November 1, 2005 to October 31, 2006 were included in this prospective study. We identified the risk factors for underlying diseases and mortality during a 3-month followup using multivariate logistic regression analysis.

RESULTS

In 562 critically ill patients admitted to PICU of Beijing Children's Hospital, there were 15 ALI-non ARDS patients and 29 ARDS patients, resulting in an incidence of 7.8% (44/562). The mortality rate of ARDS was 24.1% (7/29) and that of ALI/ARDS was 18.2% (8/44). At a 3-month follow-up, 12 patients died after being discharged from PICU and the total mortality rate was 45.5% (20/44). ALI/ARDS patients with pulmonary disease had better outcomes than those with extra-pulmonary involvements (P<0.05). Discharge against medical advice, low PaO(2)/FiO(2) during hospital stay and high PaCO2 on PICU admission were risk factors of mortality.

CONCLUSIONS

ARDS has a high mortality rate in PICU, especially in those with extra-pulmonary diseases. In addition to aggressive medical management of comorbidity, lung protection and avoidance of discharge against medical advice will decrease the mortality.

The pediatric multiple organ dysfunction syndrome

OBJECTIVES

To review the epidemiology of pediatric multiple organ dysfunction syndrome (MODS) and summarize current concepts regarding the pathophysiology of shock, organ dysfunction, and nosocomial infections in this population.

DATA SOURCE

A MEDLINE-based literature search using the keywords MODS and child, without any restriction to the idiom.

MAIN RESULTS

Critically ill children may frequently develop multisystemic manifestations during the course of severe infections, multiple trauma, surgery for congenital heart defects, or transplantations. Descriptive scores to estimate the severity of pediatric MODS have been validated. Young age and chronic health conditions have also been recognized as important contributors to the development of MODS. Unbalanced inflammatory processes and activation of coagulation may lead to the development of capillary leak and acute respiratory distress syndrome. Neuroendocrine and metabolic responses may result in insufficient adaptive immune response and the development of nosocomial infections, which may further threaten host homeostasis.

CONCLUSIONS

Over the last 20 yrs, there has been an increasing knowledge on the epidemiology of pediatric MODS and on the physiologic mechanisms involved in the genesis of organ dysfunction. Nevertheless, further studies are needed to more clearly evaluate what is the long-term outcome of pediatric MODS.

Ventilator assessment of respiratory mechanics in paediatric intensive care

Many modern "paediatric" mechanical ventilators have in-built features for estimation of respiratory mechanics which could be useful in the management of ventilated infants and children. The aim of this study was to determine if such measurements were reproducible and accurate. Ventilator (Draeger Evita 4) displayed compliance (Cvent) and resistance (Rvent) values were assessed and compared to the results of respiratory system mechanics (respiratory system compliance (Crs) and resistance (Rrs)) measurements obtained using a single breath occlusion technique. Seventeen children (median age 5.1; range 0.3 to 16 yrs) were studied on 24 occasions. The mean coefficients of variations for the techniques were similar (Cvent 13%; Crs 11%; Rvent 16%; Rrs 14%). The mean (SD) Crs (22.8 (12.3) ml/cmH2O) did not differ significantly from Cvent (22.1 (12.7) ml/cm H2O) but the mean Rrs 21.0 (12.7) cmH2O/l/s was significantly higher than the mean Rvent 32.0 (32.0) cmH2O/l/s (p = 0.03). Bland and Altman analysis demonstrated a mean difference of -10.94 cmH2O/l/s (SD 24.1) between Rrs and Rvent; the agreement between Rrs and Rvent decreased as Rrs increased (p = 0.008).

CONCLUSIONS

Ventilator assessment of compliance, but not resistance, using the Evita 4 is reproducible and reliable.

Pediatric acute lung injury

Among ventilated children, the incidence of acute lung injury (ALI) was 9%; of that latter group 80% developed the acute respiratory distress syndrome (ARDS). The population-based prevalence of pediatric ARDS was 5.5 cases/100.000 inhabitants. Underlying diseases in children were septic shock (34%), respiratory syncytial virus infections (16%), bacterial pneumonia (15%), near-drowning 9%, and others. Mortality ranged from 18% to 27% for ALI (including ALI-non ARDS and ARDS) and from 29% to 50% for ARDS. Mortality was only 3%-11% in children with ALI-non ARDS. As risk factors, oxygenation indices and multi-organ failure have been identified. New insights into the pathophysiology (for example the interplay between intraalveolar coagulation/fibrinolysis and inflammation and the genetic polymorphism for the angiotensin-converting enzyme) offer new therapeutic options. Lung protective mechanical ventilation with optimal lung recruitment is the mainstay of supportive therapy. New therapeutic modalities refer to corticosteroid and surfactant treatment. Well-designed follow up studies are needed.

Physiological consequences of early-life insult

The most commonly observed severe lung injuries in early life are the respiratory distress syndrome in premature infants and the acute respiratory distress syndrome in children. Both diseases are characterised by alveolar instability, fluid filled airspace and some degree of airway obstruction. In the acute phase, collapsed alveoli can be reopened with positive end-expiratory pressure and lung recruitment. New insight into the physiology of lung recruitment suggests that the shape of the pressure-volume curve is defined by the change in rate of alveolar opening and closing. Reduced lung volumes and severe ventilation maldistribution are found in the acute phase but may persist during childhood. Any severe lung injury in this early phase of life can cause significant structural and functional damage to the developing lung. Follow-up studies of children with chronic lung disease have shown that the functional abnormalities will improve but may still be present in later childhood.

Effect of forced deflation maneuvers upon measurements of respiratory mechanics in ventilated infants

OBJECTIVE

To determine the effect of forced deflation maneuvers on respiratory mechanics and to assess the reproducibility of such measurements in intubated infants with lung disease.

DESIGN AND SETTING

Prospective study in the pediatric intensive care unit of a university children's hospital.

PATIENTS

Ten clinically stable infants requiring mechanically assisted ventilation for acute pulmonary disease, mean age 5.9 months (1-18), mean weight 5.8 kg (3.2-13).

INTERVENTIONS

Two sets of measurements of compliance (Crs) and resistance (Rrs) were obtained at 20-min intervals both before and after +40/-40 cmH(2)O forced deflation maneuvers. Forced deflation measurements were repeated at the end of the study.

RESULTS

. Forced deflation caused a significant increase in Crs from 0.53+/-0.09 and 0.58+/-0.11 ml/cmH(2)O/kg to 0.71+/-0.11 and 0.68+/-0.11 ml/cmH(2)O/kg. Rrs measurements did not differ. The low coefficients of variation for repeated measures of the baseline measurements (Crs 4.2+/-0.5%, Rrs 7.1+/-0.8%, for forced vital capacity 8.6+/-2.5%, maximum expiratory flows at 25% vital capacity 16.0%+/-3.3%) confirmed the good reproducibility during stable conditions.

CONCLUSIONS

Inflation and deflation maneuvers affect subsequent measurements of respiratory system compliance but not measurements of maximum expiratory flow-volume relationships in intubated infants, probably through recruitment of lung volume. Careful interpretation and planning of the sequence of infant pulmonary function testing is necessary to reassure that changes are not related to short-term alterations in volume history.

Acute lung injury: pathophysiology, assessment and current therapy

Acute respiratory distress syndrome (ARDS) is a clinically defined entity describing the severity of diffuse alveolar injury caused by direct or indirect injury to the lung. Pathophysiology, clinical course and outcome of ARDS depend on the underlying cause, the severity of the disease and co-morbidities. Pulmonary function tests show restrictive lung disease, which is characterised by a reduction in lung compliance and functional residual capacity, resulting in marked ventilation-perfusion inequality. Current ventilator strategies aim to minimise ventilator-induced lung injury by targeting mechanical ventilation between the lower and upper inflection point of the pressure volume curve. This includes recruitment manoeuvres and the use of high PEEP to open the atelectatic lung and the use of permissive hypercapnia and the limitation of peak inspiratory pressure below 35 cm H2O to avoid overinflation. The clinical benefit of newer modes of ventilatory support such as inverse ratio ventilation, high frequency oscillatory ventilation, surfactant replacement, prone positioning and inhaled nitric oxide has yet to be determined in children.

Acute lung injury: outcomes and new therapies

Mortality rates in ARDS are improving, with several recent studies reporting mortality in the order of 20-40% rather than the early descriptions of this disease in which a mortality of 40-60% or higher was frequently cited. The ability to accurately predict outcomes plays an important role in the assessment of the impact of new therapies. Traditionally clinicians have relied on simple respiratory indices to assess mortality risk; however, the predictive ability of such indices, particularly early in the course of the disease, is somewhat limited. Adult data suggest that improved prediction not only of the outcome of established ARDS but also of the development of ARDS in at-risk patients may be obtained by measuring the concentrations of inflammatory mediators and/or surfactant-associated proteins in plasma or bronchoalveolar lavage samples. A bewildering array of therapies for ARDS is available; in many cases the benefits are uncertain. Treatments of proven value in adults include using PEEP beyond the lower inflection point of the pressure-volume curve and limiting tidal volumes to 6 ml/kg. Nitric oxide appears to offer no benefit to outcomes, although it does improve oxygenation in some patients. Surfactant is still undergoing assessment in randomised controlled trials; however, the use of aerosolised surfactant has been recently shown to be ineffective in adult patients with ARDS. Perfluorocarbon-assisted gas exchange (PAGE) or partial liquid ventilation is similarly still being assessed in randomised controlled trials in adults.

Dynamic respiratory system mechanics in infants during pressure and volume controlled ventilation

Dynamic respiratory system mechanics can be determined using multiple linear regression (MLR) analysis. There is no need for a particular ventilator setting or for a special ventilatory manoeuvre. The purpose of this study was to investigate whether or not different ventilator modes and the flow-dependent resistance of the endotracheal tube (ETT) influence the determination of resistance and compliance by MLR. Ten paediatric patients who were on controlled mechanical ventilation for various disorders were investigated. The ventilator modes were changed between pressure control (PC) and volume control (VC). Flow and airway pressure were measured and tracheal pressure was continuously calculated. Each mode was applied for 3 min, and 10 consecutive breaths at the end of each period were analysed. Respiratory mechanics were determined by MLR based on either airway pressure, thus including the resistance of the ETT, or tracheal pressure. Resistance was found to be slightly higher in PC than in VC. There was no effect on determination of compliance between the different modes. Elimination of the flow-dependent resistance of the ETT preserved the differences between the modes. The authors conclude that using multiple linear regression compliance is not affected by the actual ventilator mode, whereas resistance is.

Analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients

OBJECTIVE

Analysis of dynamic respiratory system mechanics is generally based on a resistance-compliance model in which nonlinearities of the respiratory mechanics indices are not considered. The recently developed SLICE method analyzing consecutive volume slices of the tidal volume was used for determination of non-linear volume-dependent respiratory system mechanics. Volume-dependent compliance C(Slice) and resistance R(Slice) were compared with C(MLR) and R(MLR) obtained by standard multiple linear regression analysis (MLR).

DESIGN

Prospective observational study.

SETTING

Pediatric intensive care unit in a university hospital.

PATIENTS

Fifteen pediatric patients, aged 24 days to 9.6 yrs, weighing 3-67.5 kg.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

With respect to their pulmonary status, the patients were grouped into three clinical groups: patients with no lung diseases, patients with restrictive lung diseases, and patients with obstructive lung diseases. All patients were mechanically ventilated via a cuffed endotracheal tube in the pressure-controlled mode. Flow and airway pressure were measured at the proximal end of the tube and tracheal pressure was continuously calculated. Respiratory mechanics were determined either with the SLICE method or, as reference, by using standard MLR. In most patients, the pressure-volume relationship was nonlinear, particularly in patients with restrictive and obstructive lung diseases. In the presence of considerable nonlinearity, the volume-dependent respiratory mechanics indices obtained by the SLICE method showed better agreement between recalculated and original pressure-volume loops compared with the MLR results. Furthermore, signs of overdistension of the patient's lung became obvious when using the SLICE method, whereas they were undetected by MLR.

CONCLUSIONS

The SLICE method is well suited for the analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients. The SLICE method may be used as a first step toward an adaptation of ventilator settings with respect to the actual mechanical status of the patient's respiratory system, and, to prevent pulmonary overdistension.

Infant lung function after inhaled nitric oxide therapy for persistent pulmonary hypertension of the newborn

Our objectives were to determine whether the use of inhaled nitric oxide (iNO) for severe persistent pulmonary hypertension of the newborn (PPHN) causes impaired lung function during infancy. We therefore performed a prospective study of lung function in 22 infants after neonatal intensive care unit (NICU) discharge who had been treated for severe persistent pulmonary hypertension of the newborn (PPHN) with (n = 15) or without (n = 7) iNO, and compared these findings in lung function to those of healthy control infants (n = 18). Five infants with interstitial lung disease (ILD) were included to assure that the pulmonary function tests (PFT) were sensitive enough to detect abnormalities of lung function in this age group. We measured passive respiratory mechanics and functional residual capacity (FRC) using a commercially available system. All data were expressed as means and standard deviation. Statistical analysis was performed by analysis of variance (ANOVA). A Bonferroni multiple comparisons test was used for variables that showed overall group differences. Twenty-two infants were studied during follow-up 4-12 months after NICU discharge. None of the infants were actuely ill, and only one infant was on 0.25 L of oxygen per minute at the time of study. We found no differences in lung function between the treatment groups (iNO + mechanical ventilation (MV), or MV alone), or between either treatment group and healthy control infants of the same age. We were able to detect significant differences in functional residual capacity adjusted for weight or height, and compliance of the respiratory system adjusted for weight or lung volume in the ILD infants compared to the healthy controls or infants who had PPHN, indicating that these PFTs were sensitive enough to determine abnormal lung function in this age group. We conclude that inhaled nitric oxide therapy for the treatment of severe PPHN does not alter lung function as determined by lung volume and passive respiratory mechanics measurements during early infancy.

Acute respiratory distress syndrome caused by respiratory syncytial virus

Acute respiratory distress syndrome (ARDS) complicating severe respiratory syncytial virus (RSV) infection has been described in only a few infants. In contrast to the low mortality rates usually associated with RSV infections (< 5%), mortality rates in the range of 40-70% have been reported in pediatric patients with ARDS. However, studies on patients with ARDS are usually lumped with respect to causation, and the disease course of RSV-induced ARDS has not been previously studied. We examined the pulmonary function abnormalities of 37 infants with RSV-induced respiratory failure who were admitted to our pediatric intensive care unit for assisted ventilation. Measurements included respiratory mechanics, maximum expiratory flow-volume curves, and lung volumes. These allowed the calculation of a Murray lung injury score (modified for pediatric use) in which radiographic findings, ventilator settings, lung compliance, and blood gas results were considered. We identified ten infants with severe restrictive lung disease who fulfilled the clinical criteria for classification as ARDS. All had lung injury scores above 2.5, compatible with a diagnosis of ARDS. Twenty-seven infants had obstructive patterns of lung function consistent with a clinical diagnosis of RSV bronchiolitis. The patients with RSV-induced ARDS were significantly younger, and had a longer time on assisted ventilation (P < 0.05) and a higher proportion of predisposing illnesses (P < 0.05, odds ratio = 6.67, two-tailed Fisher's exact test) when compared with the patients who had obstructive disease. Only one patient (who had immunodeficiency) died, and all others were successfully managed on conventional mechanical ventilation. We conclude that RSV-induced respiratory failure represents a relatively benign cause of ARDS in pediatric patients. Our observations support the notion of differentiating ARDS with respect to causation, especially when novel and experimental therapy is considered and mortality rates are analyzed.