High-frequency oscillatory ventilation in pediatric respiratory failure: a multicenter experience

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.

Mechanical Ventilation in Pediatric and Neonatal Patients

Pediatric acute respiratory distress syndrome (PARDS) remains a significant cause of morbidity and mortality, with mortality rates as high as 50% in children with severe PARDS. Despite this, pediatric lung injury and mechanical ventilation has been poorly studied, with the majority of investigations being observational or retrospective and with only a few randomized controlled trials to guide intensivists. The most recent and universally accepted guidelines for pediatric lung injury are based on consensus opinion rather than objective data. Therefore, most neonatal and pediatric mechanical ventilation practices have been arbitrarily adapted from adult protocols, neglecting the differences in lung pathophysiology, response to injury, and co-morbidities among the three groups. Low tidal volume ventilation has been generally accepted for pediatric patients, even in the absence of supporting evidence. No target tidal volume range has consistently been associated with outcomes, and compliance with delivering specific tidal volume ranges has been poor. Similarly, optimal PEEP has not been well-studied, with a general acceptance of higher levels of F_iO₂ and less aggressive PEEP titration as compared with adults. Other modes of ventilation including airway pressure release ventilation and high frequency ventilation have not been studied in a systematic fashion and there is too little evidence to recommend supporting or refraining from their use. There have been no consistent outcomes among studies in determining optimal modes or methods of setting them. In this review, the studies performed to date on mechanical ventilation strategies in neonatal and pediatric populations will be analyzed. There may not be a single optimal mechanical ventilation approach, where the best method may simply be one that allows for a personalized approach with settings adapted to the individual patient and disease pathophysiology. The challenges and barriers to conducting well-powered and robust multi-institutional studies will also be addressed, as well as reconsidering outcome measures and study design.

Early Use of Adjunctive Therapies for Pediatric Acute Respiratory Distress Syndrome: A PARDIE Study

Rationale: Few data exist to guide early adjunctive therapy use in pediatric acute respiratory distress syndrome (PARDS).Objectives: To describe contemporary use of adjunctive therapies for early PARDS as a framework for future investigations.Methods: This was a preplanned substudy of a prospective, international, cross-sectional observational study of children with PARDS from 100 centers over 10 study weeks.Measurements and Main Results: We investigated six adjunctive therapies for PARDS: continuous neuromuscular blockade, corticosteroids, inhaled nitric oxide (iNO), prone positioning, high-frequency oscillatory ventilation (HFOV), and extracorporeal membrane oxygenation. Almost half (45%) of children with PARDS received at least one therapy. Variability was noted in the median starting oxygenation index of each therapy; corticosteroids started at the lowest oxygenation index (13.0; interquartile range, 7.6-22.0) and HFOV at the highest (25.7; interquartile range, 16.7-37.3). Continuous neuromuscular blockade was the most common, used in 31%, followed by iNO (13%), corticosteroids (10%), prone positioning (10%), HFOV (9%), and extracorporeal membrane oxygenation (3%). Steroids, iNO, and HFOV were associated with comorbidities. Prone positioning and HFOV were more common in middle-income countries and less frequently used in North America. The use of multiple ancillary therapies increased over the first 3 days of PARDS, but there was not an easily identifiable pattern of combination or order of use.Conclusions: The contemporary description of prevalence, combinations of therapies, and oxygenation threshold for which the therapies are applied is important for design of future studies. Region of the world, income, and comorbidities influence adjunctive therapy use and are important variables to include in PARDS investigations.

Outcomes of Severe PARDS on High-Frequency Oscillatory Ventilation - A Single Centre Experience

OBJECTIVE

To describe experience with high-frequency oscillatory ventilation (HFOV) in children with acute respiratory distress syndrome (ARDS) transitioned from conventional mechanical ventilation (CMV) due to refractory hypoxemia and to assess factors associated with survival and also compare outcomes of patients who were managed with early HFOV (within 24 h of intubation) vs. late HFOV.

METHODS

This retrospective, observational study was conducted in a tertiary care hospital's pediatric intensive care unit. Thirty-four children with pediatric acute respiratory distress syndrome (PARDS) managed with HFOV were included.

RESULTS

Of 34 children with PARDS managed with HFOV after failure of conventional ventilation to improve oxygenation, 8 survived. Improvement in the Oxygenation Index (OI) at 48 h of initiation of HFOV along with percent increase in PaO₂/FiO₂ (P/F ratio) at 24 h of HFOV were predictors of survival. The response to HFOV, based on OI and P/F ratio, between 24 and 48 h of ventilation identified potential survivors. Also, lower positive end-expiratory pressure (PEEP) on CMV and shorter duration of CMV before initiation of HFOV were associated with survival.

CONCLUSIONS

Survival in pediatric ARDS patients treated with HFOV could be predicted by using trends of OI - with survivors showing a more rapid decline in OI between 24 and 48 h of initiation compared to non-survivors.

High frequency oscillatory ventilation in a cohort of children with respiratory failure

OBJECTIVES

Our objective was to determine survival and variables associated with poor outcomes for patients requiring high frequency oscillatory ventilator (HFOV) support. We tested the ability of markers of oxygenation to predict outcome, specifically, the oxygenation index (OI), both prior to and after initiation of HFOV. We also aimed to examine the effect of immunocompromised condition (IC), and specifically stem cell transplant (SCT), on outcome.

DESIGN

A retrospective, observational study was performed at two pediatric intensive care units (ICU) and included patients treated with HFOV over a 5 year time period. Oxygenation index and PF ratios were calculated for all patients prior to and at 24 h of HFOV support.

RESULTS

Of the 134 patients meeting inclusion criteria, mortality was 42% with a higher rate of mortality (P < 0.001) for both immunocompromised (66%) and SCT patients (83%). Survivors had improved markers of oxygenation at 24 h as compared to non-survivors (P < 0.001). IC and SCT were the variables most closely associated with mortality. Survivors were placed on HFOV earlier than non-survivors. The OI at 24 h of HFOV support was the best predictor of mortality among markers of oxygenation.

CONCLUSIONS

In this cohort of patients, use of HFOV for pediatric respiratory failure demonstrated a mortality rate in keeping with published data. The presence of an immunocompromised condition was a risk factor for mortality in severe respiratory failure with SCT recipients having the lowest survival rate. The OI at 24 h was the best predictor of mortality, especially in immunocompromised and SCT patients.

High-Frequency Oscillatory Ventilation Use and Severe Pediatric ARDS in the Pediatric Hematopoietic Cell Transplant Recipient

INTRODUCTION

The effectiveness of high-frequency oscillatory ventilation (HFOV) in the pediatric hematopoietic cell transplant patient has not been established. We sought to identify current practice patterns of HFOV, investigate parameters during HFOV and their association with mortality, and compare the use of HFOV to conventional mechanical ventilation in severe pediatric ARDS.

METHODS

This is a retrospective analysis of a multi-center database of pediatric and young adult allogeneic hematopoietic cell transplant subjects requiring invasive mechanical ventilation for critical illness from 2009 through 2014. Twelve United States pediatric centers contributed data. Continuous variables were compared using a Wilcoxon rank-sum test or a Kruskal-Wallis analysis. For categorical variables, univariate analysis with logistic regression was performed.

RESULTS

The database contains 222 patients, of which 85 subjects were managed with HFOV. Of this HFOV cohort, the overall pediatric ICU survival was 23.5% (n = 20). HFOV survivors were transitioned to HFOV at a lower oxygenation index than nonsurvivors (25.6, interquartile range 21.1-36.8, vs 37.2, interquartile range 26.5-52.2, P = .046). Survivors were transitioned to HFOV earlier in the course of mechanical ventilation, (day 0 vs day 2, P = .002). No subject survived who was transitioned to HFOV after 1 week of invasive mechanical ventilation. We compared subjects with severe pediatric ARDS treated only with conventional mechanical ventilation versus early HFOV (within 2 d of invasive mechanical ventilation) versus late HFOV. There was a trend toward difference in survival (conventional mechanical ventilation 24%, early HFOV 30%, and late HFOV 9%, P = .08).

CONCLUSIONS

In this large database of pediatric allogeneic hematopoietic cell transplant subjects who had acute respiratory failure requiring invasive mechanical ventilation for critical illness with severe pediatric ARDS, early use of HFOV was associated with improved survival compared to late implementation of HFOV, and the subjects had outcomes similar to those treated only with conventional mechanical ventilation.

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.

Volume and Pressure Delivery During Pediatric High-Frequency Oscillatory Ventilation

OBJECTIVE

Identify variables independently associated with delivered tidal volume (VT) and measured mean airway pressure during high-frequency oscillatory ventilation across the range of pediatric endotracheal tube sizes.

DESIGN

In vitro study.

SETTING

Research laboratory.

INTERVENTIONS

An in vitro bench model of the intubated pediatric respiratory system during high-frequency oscillatory ventilation was used to obtain delivered VT and mean airway pressure (in the distal lung) for various endotracheal tube sizes. Measurements were taken at different combinations of ventilator set mean airway pressure (Paw), amplitude (ΔP), frequency, and test lung compliance. Multiple regression analysis was used to construct multivariable models predicting delivered VT and mean airway pressure.

MEASUREMENTS AND MAIN RESULTS

Variables independently associated with higher delivered VT for all endotracheal tube sizes include higher ΔP (p < 0.001), lower frequency (p < 0.001), and higher test lung compliance (p < 0.001). A multiplicative interaction between frequency and ΔP magnifies the delivered VT when ΔP is high and frequency is low (p < 0.001). Delivered mean airway pressure becomes lower than set Paw as ΔP increases (p < 0.001) and frequency increases (p < 0.05). Ventilator set Paw is the largest determinant of delivered mean airway pressure; however, increasing ΔP resulted in a lower delivered mean airway pressure. For example, in a 4.0 mm ID endotracheal tube, increasing ΔP by 10 cm H2O resulted in an average decrease of delivered mean airway pressure by 4.5%.

CONCLUSIONS

This is the first study to quantify the interaction between ΔP and frequency in delivered VT and the effect of ΔP and frequency on delivered mean airway pressure. These results demonstrate the need to measure or estimate VT and delivered pressures during high-frequency oscillatory ventilation and may be useful in determining optimal strategies for lung protective ventilation during high-frequency oscillatory ventilation.

Recent Advances in Pediatric Ventilatory Assistance

In this review on respiratory assistance, we aim to discuss the following recent advances: the optimization and customization of mechanical ventilation, the use of high-frequency oscillatory ventilation, and the role of noninvasive ventilation. The prevention of ventilator-induced lung injury and diaphragmatic dysfunction is now a key aspect in the management of mechanical ventilation, since these complications may lead to higher mortality and prolonged length of stay in intensive care units. Different physiological measurements, such as esophageal pressure, electrical activity of the diaphragm, and volumetric capnography, may be useful objective tools to help guide ventilator assistance. Companies that design medical devices including ventilators and respiratory monitoring platforms play a key role in knowledge application. The creation of a ventilation consortium that includes companies, clinicians, researchers, and stakeholders could be a solution to promote much-needed device development and knowledge implementation.

Extracorporeal Membrane Oxygenation for Pediatric Respiratory Failure: Risk Factors Associated With Center Volume and Mortality

OBJECTIVES

Recent analyses show higher mortality at low-volume centers providing extracorporeal membrane oxygenation. We sought to identify factors associated with center volume and mortality to explain survival differences and identify areas for improvement.

DESIGN

Retrospective cohort study.

SETTING

Patients admitted to children's hospitals in the Pediatric Health Information System database and supported with extracorporeal membrane oxygenation for respiratory failure from 2003 to 2014.

PATIENTS

A total of 5,303 patients aged 0-18 years old met inclusion criteria: 3,349 neonates and 1,954 children.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Low center volume was defined as less than 20, medium 20-49, and large greater than or equal to 50 cases per year. Center volume was also assessed as a continuous integer. Among neonates, clinical factors including intraventricular hemorrhage (relative risk, 1.4; 95% CI, 1.24-1.56) and acute renal failure (relative risk, 1.38; 95% CI, 1.20-1.60) were more common at low-volume compared to larger centers and were associated with in-hospital death. After adjustment for differences in demographic factors and primary pulmonary conditions, mild prematurity, acute renal failure, intraventricular hemorrhage, and receipt of dialysis remained independently associated with mortality, as did center volume measured as a continuous number. Among children, the risk of acute renal failure was almost 20% greater (relative risk, 1.18; 95% CI, 1.02-1.38) in small compared to large centers, but dialysis and bronchoscopy were used significantly less but were associated with mortality. After adjustment for differences in demographic factors and primary pulmonary conditions, acute renal failure, acute liver necrosis, acute pancreatitis, and receipt of bronchoscopy remained independently associated with mortality. Center volume measurement was not associated with mortality given these factors.

CONCLUSIONS

Among neonates, investigation for intraventricular hemorrhage prior to extracorporeal membrane oxygenation and preservation of renal function are important factors for improvement. Earlier initiation of extracorporeal membrane oxygenation and careful attention to preservation of organ function are important to improve survival for children.

Early High-Frequency Oscillatory Ventilation in Pediatric Acute Respiratory Failure. A Propensity Score Analysis

RATIONALE

The use of high-frequency oscillatory ventilation (HFOV) for acute respiratory failure in children is prevalent despite the lack of efficacy data.

OBJECTIVES

To compare the outcomes of patients with acute respiratory failure managed with HFOV within 24-48 hours of endotracheal intubation with those receiving conventional mechanical ventilation (CMV) and/or late HFOV.

METHODS

This is a secondary analysis of data from the RESTORE (Randomized Evaluation of Sedation Titration for Respiratory Failure) study, a prospective cluster randomized clinical trial conducted between 2009 and 2013 in 31 U.S. pediatric intensive care units. Propensity score analysis, including degree of hypoxia in the model, compared the duration of mechanical ventilation and mortality of patients treated with early HFOV matched with those treated with CMV/late HFOV.

MEASUREMENTS AND MAIN RESULTS

Among 2,449 subjects enrolled in RESTORE, 353 patients (14%) were ever supported on HFOV, of which 210 (59%) had HFOV initiated within 24-48 hours of intubation. The propensity score model predicting the probability of receiving early HFOV included 1,064 patients (181 early HFOV vs. 883 CMV/late HFOV) with significant hypoxia (oxygenation index ≥ 8). The degree of hypoxia was the most significant contributor to the propensity score model. After adjusting for risk category, early HFOV use was associated with a longer duration of mechanical ventilation (hazard ratio, 0.75; 95% confidence interval, 0.64-0.89; P = 0.001) but not with mortality (odds ratio, 1.28; 95% confidence interval, 0.92-1.79; P = 0.15) compared with CMV/late HFOV.

CONCLUSIONS

In adjusted models including important oxygenation variables, early HFOV was associated with a longer duration of mechanical ventilation. These analyses make supporting the current approach to HFOV less convincing.

Pediatric Acute Hypoxemic Respiratory Failure: Management of Oxygenation

Acute hypoxemic respiratory failure (AHRF) is one of the hallmarks of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), which are caused by an inflammatory process initiated by any of a number of potential systemic and/or pulmonary insults that result in heterogeneous disruption of the capillary-pithelial interface. In these critically sick patients, optimizing the management of oxygenation is crucial. Physicians managing pediatric patients with ALI or ARDS are faced with a complex array of options influencing oxygenation. Certain treatment strategies can influence clinical outcomes, such as a lung protective ventilation strategy that specifies a low tidal volume (6 mL/kg) and a plateau pressure limit (30 cm H2O). Other strategies such as different levels of positive end expiratory pressure, altered inspiration to expiration time ratios, recruitment maneuvers, prone positioning, and extraneous gases or drugs may also affect clinical outcomes. This article reviews state-of-the-art strategies on the management of oxygenation in acute hypoxemic respiratory failure in children.

Extracorporeal Life Support in Pediatric and Neonatal Critical Care: A Review

Extracorporeal life support (ECLS) is a modified form of cardiopulmonary bypass used to provide prolonged tissue oxygen delivery in patients with respiratory and/or cardiac failure. The first large-scale success of ECLS was achieved in the management of term newborns with respiratory failure. ECLS has become an accepted therapeutic modality for neonates, children, and adults who have failed conventional therapy and in whom cardiac and/or respiratory insufficiency is potentially reversible. The use of ECLS allows one to reduce other cardiopulmonary supports and apply a gentle ventilation strategy in a population of severely compromised critical care patients. ECLS has now been employed in more than 26,000 neonatal and pediatric patients with an overall survival rate of 68%. ECLS has evolved significantly over 25 years of clinical practice; patient selection for this complex and highly invasive therapy, as well as how ECLS is employed in different patient groups, is constantly changing. Generally, ECLS is used more liberally now than in the past. The number of patients requiring this support, however, is declining yearly, and those patients who receive ECLS compose a more severe subset of an intensive care population. This review provides an overview of the development of ECLS and the equipment and techniques employed. The use of ECLS for neonatal respiratory failure, pediatric respiratory failure, and cardiac support are outlined. Management of the ECLS patient is discussed in detail, and outcome of these patients is reviewed. Finally, current trends and future implications of ECLS in neonatal and pediatric critical care are addressed.

High-Frequency Oscillatory Ventilation in Pediatric Acute Lung Injury: A Multicenter International Experience

OBJECTIVE

We aim to describe current clinical practice, the past decade of experience and factors related to improved outcomes for pediatric patients receiving high-frequency oscillatory ventilation. We have also modeled predictive factors that could help stratify mortality risk and guide future high-frequency oscillatory ventilation practice.

DESIGN

Multicenter retrospective, observational questionnaire study.

SETTING

Seven PICUs.

PATIENTS

Demographic, disease factor, and ventilatory and outcome data were collected, and 328 patients from 2009 to 2010 were included in this analysis.

INTERVENTIONS

None.

MEASUREMENT AND MAIN RESULTS

Patients were classified into six cohorts based on underlying diagnosis. We used univariate analysis to identify factors associated with mortality risk and multivariate logistic regression to identify independent predictors of mortality risk. An oxygenation index greater than 35 and immunocompromise exhibited the greatest predictive power (p < 0.0001) for increased mortality risk, and respiratory syncytial virus was associated with lowest mortality risk (p = 0.003). Differences in mortality risk as a function of oxygenation index were highly dependent on primary underlying condition. A trend toward an increase in oscillator amplitude and frequency was observed when compared with historical data.

CONCLUSIONS

Given the number of centers and subjects included in the database, these findings provide a robust description of current practice regarding the use of high-frequency oscillatory ventilation for pediatric hypoxic respiratory failure. Patients with severe hypoxic respiratory failure and immunocompromise had the highest mortality risk, and those with respiratory syncytial virus had the lowest. A means of identifying the risk of 30-day mortality for subjects can be obtained by identifying the underlying disease and oxygenation index on conventional ventilation preceding the initiation of high-frequency oscillatory ventilation.

Relevant Outcomes in Pediatric Acute Respiratory Distress Syndrome Studies

Despite distinct epidemiology and outcomes, pediatric acute respiratory distress syndrome (PARDS) is often managed based on evidence extrapolated from treatment of adults. The impact of non-pulmonary processes on mortality as well as the lower mortality rate compared to adults with acute respiratory distress syndrome (ARDS) renders the utilization of short-term mortality as a primary outcome measure for interventional studies problematic. However, data regarding alternatives to mortality are profoundly understudied, and proposed alternatives, such as ventilator-free days, may be themselves subject to hidden biases. Given the neuropsychiatric and functional impairment in adult survivors of ARDS, characterization of these morbidities in children with PARDS is of paramount importance. The purpose of this review is to frame these challenges in the context of the existing pediatric literature, and using adult ARDS as a guide, suggest potential clinically relevant outcomes that deserve further investigation. The goal is to identify important areas of study in order to better define clinical practice and facilitate future interventional trials in PARDS.

Use of High-Frequency Ventilation in the Pediatric Intensive Care Unit

Objective To evaluate the clinical characteristics, ventilator settings, and gas exchange indices of patients placed on high-frequency percussive ventilation (HFPV) and high-frequency oscillatory ventilation (HFOV). Methods Retrospective observation of all consecutive patients aged 0 to 18 years with acute respiratory failure managed with high-frequency ventilation from the institution's introduction of HFPV on May 1, 2012, until July 10, 2013. Measurements and Main Results Twenty-seven patients underwent HFPV as a first mode of high-frequency ventilation and 16 patients underwent HFOV first. HFPV was used more frequently in patients with acute respiratory illnesses (p < 0.01), lower Pediatric Index of Mortality 2 scores (rank-sum p < 0.04), higher Spo ₂/Fio ₂ (SF) ratios (p < 0.01), and lower oxygen saturation indices (p < 0.01). HFPV patients showed increased SF ratios (p < 0.01) and decreased Paco ₂ levels (p = 0.02) 6 hours after initiation, and HFOV patients showed no significant differences. Peak inspiratory pressures (HFPV) and mean airway pressures (HFOV) remained at or below 30 cm H₂O at each time point. HFPV and HFOV patients had an average of 2.8 and 2.9 mode changes, respectively. Mortality was 15% in the HFPV group and 50% in the HFOV group. Conclusions HFPV is associated with rapid improvement in oxygenation and ventilation at acceptable airway pressures in patients with acute respiratory failure of various etiologies, primarily for those with difficulties of ventilation or secretion management. In our institution, HFOV appears to be initiated first in children with higher severity of illness.

Factors associated with interhospital transfer of children with respiratory failure from level II to level I pediatric intensive care units

PURPOSE

Of all sources of admission to level I pediatric intensive care units (PICUs), interhospital transfer admissions from level II PICUs carry the highest mortality and resource use burden. We sought to investigate factors associated with transfer of children with respiratory failure from level II to level I PICUs.

METHODS

A case-control study was conducted among children with respiratory failure admitted to 6 level II PICUs between January 1, 1997, and December 31, 2007, with frequency matching of 466 nontransferred children (controls) to 187 transferred children (cases).

RESULTS

Among 653 children, transferred children were younger and had more comorbidities. After multivariable analysis, transferred children were more likely to have comorbidities (odds ratio [OR], 2.02; 95% confidence interval [CI], 1.36-2.98) and receive escalated care including high-frequency ventilation (OR, 2.57; 95% CI, 1.04-6.37) and surfactant therapy (OR, 5.33; 95% CI, 1.35-21.0).

CONCLUSIONS

The study identified patient-level and process-of-care factors associated with transfer from level II to level I PICUs. These findings highlight the influence of escalated care on transfer decision making for critically ill children in respiratory failure.

Comorbidities and assessment of severity of pediatric acute respiratory distress syndrome: proceedings from the Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

To determine the impact of patient-specific and disease-related characteristics on the severity of illness and on outcome in pediatric patients with acute respiratory distress syndrome with the intent of guiding current medical practice and identifying important areas for future research.

DESIGN

Electronic searches of PubMed, EMBASE, Web of Science, Cochrane, and Scopus were conducted. References were reviewed for relevance and features included in the following section.

SETTINGS

Not applicable.

SUBJECTS

PICU patients with evidence of acute lung injury, acute hypoxemic respiratory failure, and acute respiratory distress syndrome.

INTERVENTIONS

Not applicable.

MEASUREMENTS AND MAIN RESULTS

The comorbidities associated with outcome in pediatric acute respiratory distress syndrome can be divided into 1) patient-specific factors and 2) factors inherent to the disease process. The primary comorbidity associated with poor outcome is preexisting congenital or acquired immunodeficiency. Severity of disease is often described by factors identifiable at admission to the ICU. Many measures that are predictive are influenced by the underlying disease process itself, but may also be influenced by nutritional status, chronic comorbidities, or underlying genetic predisposition. Of the measures available at the bedside, both PaO2/FIO2 ratio and oxygenation index are fairly consistent and robust predictors of disease severity and outcomes. Multiple organ system dysfunction is the single most important independent clinical risk factor for mortality in children at the onset of acute respiratory distress syndrome.

CONCLUSIONS

The assessment of oxygenation and ventilation indices simultaneously with genetic and biomarker measurements holds the most promise for improved risk stratification for pediatric acute respiratory distress syndrome patients in the very near future. The next phases of pediatric acute respiratory distress syndrome pathophysiology and outcomes research will be enhanced if 1) age group differences are examined, 2) standardized datasets with adequately explicit definitions are used, 3) data are obtained at standardized times after pediatric acute respiratory distress syndrome onset, and 4) nonpulmonary organ failure scores are created and implemented.

Extracorporeal support in children with pediatric acute respiratory distress syndrome: proceedings from the Pediatric Acute Lung Injury Consensus Conference

OBJECTIVE

Extracorporeal life support has undergone a revolution in the past several years with the advent of new, miniaturized equipment and success in supporting patients with a variety of illnesses. Most experience has come with the use of extracorporeal membrane oxygenation, a modified form of cardiopulmonary bypass that can support the heart, lungs, and circulation for days to months at a time. To describe the recommendations for the use of extracorporeal membrane oxygenation in children with pediatric acute respiratory distress syndrome based on a review of the literature and expert opinion.

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 extracorporeal support subgroup comprised two international 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, 11 of which related to extracorporeal support. All recommendations had agreement, with 10 recommendations (91%) achieving strong agreement. These recommendations included the utilization of extracorporeal support for reversible causes of pediatric acute respiratory distress syndrome, consideration of quality of life when making the decision to use extracorporeal support, and the use of the Extracorporeal Life Support Organization registry to report all extracorporeal support activity, among others.

CONCLUSIONS

Pediatric extracorporeal membrane oxygenation for pediatric acute respiratory distress syndrome could benefit from more specific data collection and collaboration of focused investigators to establish validated criteria for optimal application of extracorporeal membrane oxygenation and patient management protocols. Until that time, consensus opinion offers some insight into guidelines.

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

OBJECTIVE

To provide additional details and evidence behind the recommendations for outcomes assessment of patients with pediatric acute respiratory distress syndrome from the Pediatric Acute Lung Injury Consensus Conference.

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 outcomes subgroup comprised four 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, seven of which related to outcomes after pediatric acute respiratory distress syndrome. All seven recommendations had strong agreement. Children with acute respiratory distress syndrome continue to have a high mortality, specifically, in relation to certain comorbidities and etiologies related to pediatric acute respiratory distress syndrome. Comorbid conditions, such as an immunocompromised state, increase the risk of mortality even further. Likewise, certain etiologies, such as non-pulmonary sepsis, also place children at a higher risk of mortality. Significant long-term effects were reported in adult survivors of acute respiratory distress syndrome: diminished lung function and exercise tolerance, reduced quality of life, and diminished neurocognitive function. Little knowledge of long-term outcomes exists in children who survive pediatric acute respiratory distress syndrome. Characterization of the longer term consequences of pediatric acute respiratory distress syndrome in children is vital to help identify opportunities for improved therapeutic and rehabilitative strategies that will lessen the long-term burden of pediatric acute respiratory distress syndrome and improve the quality of life in children.

CONCLUSIONS

The Consensus Conference developed pediatric-specific recommendations for pediatric acute respiratory distress syndrome regarding outcome measures and future research priorities. These recommendations 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.

Clinical Use of Nonconventional Modes of Ventilator Support

High-frequency oscillatory ventilation (HFOV) is now a mainstay of respiratory care for the neonatal patient. In this chapter, we will define HFOV as those ventilators with a “true” active expiratory phase created by a piston or diaphragm. Jet ventilation and flow interrupters are discussed elsewhere in this book.

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.

High frequency oscillation and airway pressure release ventilation in pediatric respiratory failure

BACKGROUND

Airway pressure release ventilation (APRV) and high frequency oscillatory ventilation (HFOV) are frequently used in acute lung injury (ALI) refractory to conventional ventilation. Our aim was to describe our experience with APRV and HFOV in refractory pediatric ALI, and to identify factors associated with survival.

METHODS

We analyzed 104 patients with hypoxemia refractory to conventional ventilation transitioned to either APRV or HFOV. Demographics, oxygenation index (OI), and PaO2 /FiO2 (PF ratio) were recorded before transition to either mode of nonconventional ventilation (NCV) and for every 12 hr after transition.

RESULTS

Relative to APRV, patients on HFOV were younger and had more significant lung disease evidenced by higher OI (28.5 [18.6, 36.2] vs. 21.0 [15.5, 30.0], P = 0.008), lower PF ratios (73 [59,94] vs. 99 [76,131], P = 0.002), and more frequent use of inhaled nitric oxide. In univariate analysis, HFOV was associated with more frequent neuromuscular blockade. Forty-one of 104 patients died on NCV (39.4%). Survivors demonstrated improvement in OI 24 hr after transition to NCV, whereas non-survivors did not (12.9 [8.9, 20.9] vs. 28.1 [17.6, 37.1], P < 0.001). After controlling for immunocompromised status, number of vasopressors, and OI before transition, mode of NCV was not associated with mortality.

CONCLUSIONS

In a heterogeneous PICU population with hypoxemia refractory to conventional ventilation transitioned to NCV, improvement in oxygenation at 24 hr was associated with survival. Immunocompromised status, number of vasopressor infusions, and the OI before transition to NCV were independently associated with survival.

Improved oxygenation 24 hours after transition to airway pressure release ventilation or high-frequency oscillatory ventilation accurately discriminates survival in immunocompromised pediatric patients with acute respiratory distress syndrome*

OBJECTIVES

Children with an immunocompromised condition and requiring invasive mechanical ventilation have high risk of death. Such patients are commonly transitioned to rescue modes of nonconventional ventilation, including airway pressure release ventilation and high-frequency oscillatory ventilation, for acute respiratory distress syndrome refractory to conventional ventilation. Our aim was to describe our experience with airway pressure release ventilation and high-frequency oscillatory ventilation in children with an immunocompromised condition and acute respiratory distress syndrome refractory to conventional ventilation and to identify factors associated with survival.

DESIGN

Retrospective cohort study.

SETTING

Tertiary care, university-affiliated PICU.

PATIENTS

Sixty pediatric patients with an immunocompromised condition and acute respiratory distress syndrome refractory to conventional ventilation transitioned to either airway pressure release ventilation or high-frequency oscillatory ventilation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Demographic data, ventilator settings, arterial blood gases, oxygenation index, and PaO(2)/FIO(2) were recorded before transition to either mode of nonconventional ventilation and at predetermined intervals after transition for up to 5 days. Mortality in the entire cohort was 63% and did not differ between patients transitioned to airway pressure release ventilation and high-frequency oscillatory ventilation. For both airway pressure release ventilation and high-frequency oscillatory ventilation, improvements in oxygenation index and PaO(2)/FIO(2) at 24 hours expressed as a fraction of pretransition values (oxygenation index(24)/oxygenation index(pre) and PaO(2)/FIO(224)/PaO(2)/FIO(2pre)) reliably discriminated nonsurvivors from survivors, with receiver operating characteristic areas under the curves between 0.89 and 0.95 (p for all curves < 0.001). Sensitivity-specificity analysis suggested that less than 15% reduction in oxygenation index (90% sensitive, 75% specific) or less than 90% increase in PaO(2)/FIO(2) (80% sensitive, 94% specific) 24 hours after transition to airway pressure release ventilation were the optimal cutoffs to identify nonsurvivors. The comparable values 24 hours after transition to high-frequency oscillatory ventilation were less than 5% reduction in oxygenation index (100% sensitive, 83% specific) or less than 80% increase in PaO(2)/FIO(2) (91% sensitive, 89% specific) to identify nonsurvivors.

CONCLUSIONS

In this single-center retrospective study of pediatric patients with an immunocompromised condition and acute respiratory distress syndrome failing conventional ventilation transitioned to either airway pressure release ventilation or high-frequency oscillatory ventilation, improved oxygenation at 24 hours expressed as PaO(2)/FIO(224)/PaO(2)/FIO(2pre) or oxygenation index(24)/oxygenation indexpre reliably discriminates nonsurvivors from survivors. These findings should be prospectively verified.

Acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is commonly associated with severe sepsis. While the criteria for diagnosis have evolved since the first description in 1967, the characteristics of hypoxemia, tachypnea, rapidly progressing acute respiratory failure, and poor lung compliance continue. Scoring systems have been developed in an effort to quantify the severity of lung injury, with the most recent being the Berlin Definition. This system attempts to define acute lung injury (ALI) and ARDS with more precision in terms of timing of disease onset, severity of disease, and chest radiograph findings. The number of reported cases of ALI/ARDS per year is lower in pediatric patients vs. adults; however, mortality rates continue to be high. Sepsis-related ARDS has a generally higher disease severity and poorer recovery period from lung injury with an increased mortality rate. ARDS results from an initial insult (direct and/or indirect) which triggers a series of cell-mediated responses leading to damage to the capillary endothelium, alveolar epithelium, and impaired fluid removal from the alveolar space. There is, however, gradual resolution of hypoxemia, lung function, and radiographic abnormalities in survivors of ARDS. Management of ARDS is mainly supportive with specific mechanical ventilation strategies and goal-directed therapies. Prevention of ventilator-induced lung injury (VILI) has been demonstrated to have a positive impact on outcomes in patients with ARDS.

High-frequency oscillatory ventilation in children with acute respiratory distress syndrome: experience of a pediatric intensive care unit

OBJECTIVE

To describe the effects of high-frequency oscillatory ventilation (HFOV) as a rescue ventilatory support in pediatric patients with acute respiratory distress syndrome (ARDS).

METHODS

Twenty-five children (1 month < age < 17 years) admitted to a university hospital pediatric intensive care unit (ICU) with ARDS and submitted to HFOV for a minimum of 48 hours after failure of conventional mechanical ventilation were assessed.

RESULTS

Twenty eight days after the onset of ARDS, the mortality rate was 52% (13/25). Over the course of 48 hours, the use of HFOV reduced the oxygenation index [38 (31-50) vs. 17 (10-27)] and increased the ratio of partial arterial pressure O2 and fraction of inspired O2 [65 [44-80) vs. 152 (106-213)]. Arterial CO2 partial pressure [54 (45-74) vs. 48 (39-58) mmHg] remained unchanged. The mean airway pressure ranged between 23 and 29 cmH2O. HFOV did not compromise hemodynamics, and a reduction in heart rate was observed (141±32 vs. 119±22 beats/min), whereas mean arterial pressure (66±20 vs. 71±17 mmHg) and inotropic score [44 (17-130) vs. 20 (16-75)] remained stable during this period. No survivors were dependent on oxygen.

CONCLUSION

HFOV improves oxygenation in pediatric patients with ARDS and severe hypoxemia refractory to conventional ventilatory support.

Advances in monitoring and management of pediatric acute lung injury

This article focuses on the respiratory management and monitoring of pediatric acute lung injury (ALI) as a specific cause for respiratory failure. Definitive, randomized, controlled trials in pediatrics to guide optimal ventilatory management are few. The only adjunct therapy that has been proved to improve clinical outcome is low tidal volume ventilation, but only in adult patients. Careful monitoring of the patient's respiratory status with airway graphic analysis and capnography can be helpful. Definitive data are needed in the pediatric population to assist in the care of infants, children, and adolescents with ALI to improve survival and functional outcome.

Factors associated with mortality in pediatric patients requiring extracorporeal life support for severe pneumonia

OBJECTIVES

In children with respiratory failure secondary to pneumonia, extracorporeal life support can be lifesaving. Our goal was to identify variables associated with mortality in children with pneumonia requiring extracorporeal life support.

DESIGN

Data query and abstraction from a multicenter, international registry of extracorporeal life support, the Extracorporeal Life Support Organization Registry.

SETTING

Extracorporeal Life Support Organization registry data from 1985 to 2010.

PATIENTS

Patients ≤ 18 yr of age who received extracorporeal life support for respiratory failure secondary to pneumonia.

INTERVENTIONS

None.

MEASUREMENTS AND OUTCOMES

Clinical variables, year of extracorporeal life support, and extracorporeal life support center location were collected. The primary outcome was survival at hospital discharge. Results are reported as predictive margins, which allow estimation of standardized mortality rates and differences for risk factors.

RESULTS

One thousand four hundred eighty-nine children were included. The median (interquartile range) age and duration of extracorporeal life support were 5.7 months (2.5-21.5) and 11 days (7-18). Arterial cannulation was performed in 65% of patients. Mortality was 39%. There was no relationship between mortality and age or pathogen. Duration of extracorporeal life support had a biphasic relationship on mortality; mortality decreased 1.3% per day on extracorporeal life support until 14 days and then increased by 1.8% per day thereafter. Other independent predictors of mortality (p < 0.05) were pre-extracorporeal life support factors including duration of mechanical ventilation, peak inspiratory pressure, arterial oxygen saturation, pH, cardiac arrest, need for an arterial cannula, decade of extracorporeal life support, international extracorporeal life support center, and decrease in FIO2 over the first 24 hrs on extracorporeal life support.

CONCLUSIONS

In children with severe pneumonia receiving extracorporeal life support, prognostic factors associated with increased risk of death included extracorporeal life support treatment exceeding 14 days, arterial cannulation, longer duration of mechanical ventilation, and decreased ability to wean ventilator FIO2 over the first 24 hrs on extracorporeal life support. Analysis of the Extracorporeal Life Support Organization registry can identify prognostic variables, which may influence medical decision making, resource utilization, and family counseling.

High-frequency oscillatory ventilation in children: a 10-year experience

OBJECTIVES

The aim of the study was to describe the experience with high-frequency oscillatory ventilation (HFOV) in a Portuguese Pediatric Critical Care Unit, and to evaluate whether HFOV allowed improvement in oxygenation and ventilation.

METHODS

This was a retrospective observational cohort study of children ventilated by HFOV between January, 2002 and December, 2011. The following parameters were recorded: demographic and clinical data, and blood gases and ventilatory parameters during the first 48 hours of HFOV.

RESULTS

80 children were included, with a median age of 1.5 months (min: one week; max: 36 months). Pneumonia (n=50; 62.5%) and bronchiolitis (n=18; 22.5%) were the main diagnoses. Approximately 40% (n=32) of the patients developed acute respiratory distress syndrome (ARDS). Conventional mechanical ventilation was used in 68 (85%) of patients prior to HFOV. All patients who started HFOV had hypoxemia, and 56 (70%) also presented persistent hypercapnia. Two hours after starting HFOV, a significant improvement in SatO2/FiO2 ratio (128±0.63 vs. 163±0.72; p<0.001) that was sustained up to 24 hours of HFOV and a decrease in FiO2 were observed. Since the beginning of HFOV, the mean PCO2 significantly decreased (87±33 vs. 66±25; p<0.001), and the pH significantly improved (7.21±0.17 vs. 7.32±0.15; p<0.001). Overall survival was 83.8%.

CONCLUSIONS

HFOV enabled an improvement in hypercapnia and oxygenation. It is a safe option for the treatment of ARDS and severe small airway diseases.

Nontraditional modes of mechanical ventilation: progress or distraction?

As technology continues to develop, a wide range of novel and nontraditional modes of mechanical ventilation have become available for the management of critically ill patients. Proportional assist ventilation, neurally adjusted ventilatory assist and adaptive support ventilation are three novel modes of ventilation, which attempt to optimize patient-ventilator synchrony. Improved interactions between patient and ventilator may be important in improving clinical outcomes. Another important priority for mechanically ventilated patients is lung protection, and nontraditional modes of ventilation that may be implemented to minimize ventilator-associated lung injury include airway pressure release ventilation and high-frequency ventilation. Novel and nontraditional modes of ventilation may represent important tools in the critical care environment; however, continued investigation is needed to determine the overall impact of these various approaches on outcomes for mechanically ventilated patients.

High-frequency oscillatory ventilation in pediatric acute hypoxemic respiratory failure: disease-specific morbidity survival analysis

Background

Multiple ventilatory strategies for acute hypoxemic respiratory failure (AHRF) in children have been advocated, including high-frequency oscillatory ventilation (HFOV). Despite the frequent deployment of HFOV, randomized controlled trials remain elusive and currently there are no pediatric trials looking at its use. Our longitudinal study analyzed the predictive clinical outcome of HFOV in pediatric AHRF given disease-specific morbidity.

Methods

A retrospective 8-year review on pediatric intensive care unit admissions with AHRF ventilated by HFOV was performed. Primary outcomes included survival, morbidity, length of stay (LOS), and factors associated with survival or mortality.

Results

A total of 102 patients underwent HFOV with a 66 % overall survival rate. Survivors had a greater LOS than nonsurvivors (p = 0.001). Mortality odds ratio (OR) for patients without bronchiolitis was 8.19 (CI = 1.02, 65.43), and without pneumonia it was 3.07 (CI = 1.12, 8.39). A lower oxygenation index (OI) after HFOV commencement and at subsequent time points analyzed predicted survival. After 24 h, mortality was associated with an OI > 35 [OR = 31.11 (CI = 3.25, 297.98)]. Sepsis-related mortality was associated with a higher baseline FiO₂ (0.88 vs. 0.65), higher OI (42 vs. 22), and augmented metabolic acidosis (pH of 7.25 vs. 7.32) evaluated 4 h on HFOV (p < 0.05).

Conclusion

High-frequency oscillatory ventilation may be safely utilized. It has a 66 % overall survival rate in pediatric AHRF of various etiologies. Patients with morbidity limited to the respiratory system and optimized oxygenation indices are most likely to survive on HFOV.

Oxygenation index predicts mortality in pediatric stem cell transplant recipients requiring mechanical ventilation

The mortality in the ICU for pediatric HSCT recipients remains high. Early pulmonary complications continue to be an obstacle to the survival. We hypothesize OI is a predictor for mortality in critically ill pediatric HSCT recipients. Retrospective review of pediatric HSCT recipients between 2002 and 2010 who required intensive care during the same hospital admission as their transplant. Twenty-eight patients accounted for 31 ICU admissions. Twenty-six (84%) admissions required mechanical ventilation. Ten (38%) mechanically ventilated admissions were placed on HFOV. Mortality of those mechanically ventilated was 70%. An OI ≥ 20 at any point during ventilation was associated with 94% mortality, while an OI ≥ 25 had 100% mortality. There was a significant association between maximum OI at any point during mechanical ventilation and ICU mortality, with the odds of dying increasing by 13% for each unit increase of max OI (OR = 1.13, 95% CI = 1.01-1.26, p = 0.03). An OI of 20 had a sensitivity of 0.89 and specificity of 0.83 for predicting mortality. OI has a strong association with ICU mortality among pediatric stem cell recipients.

Inhaled prostacyclin and high-frequency oscillatory ventilation in a premature infant with respiratory syncytial virus-associated respiratory failure

In a 29-day-old premature infant with respiratory syncytial virus (RSV) pneumonia, we have shown an additive effect of high-frequency oscillatory ventilation (HFOV) and continuous inhalation of prostacyclin (iPGI(2)) with improvement of ventilation and oxygenation. The addition of continuous inhaled iPGI(2) to HFOV was beneficial in the treatment of hypoxemic respiratory failure owing to RSV-associated pneumonia. The improvement in alveolar recruitment by increasing lung expansion by HFOV along with less ventilation-perfusion mismatch by iPGI(2) appears to be responsible for the synergistic effect and favorable clinical outcome. We conclude that the combined therapy of HFOV and continuous inhaled iPGI(2) may be considered in RSV-associated hypoxemic respiratory failure in pediatric patients.

Bias flow does not affect ventilation during high-frequency oscillatory ventilation in a pediatric animal model of acute lung injury

OBJECTIVE

During high-frequency oscillatory ventilation, bias flow is the continuous flow of gas responsible for replenishing oxygen and removing CO(2) from the patient circuit. Bias flow is usually set at 20 L/min, but many patients require neuromuscular blockade at this flow rate. The need for neuromuscular blockade may be eliminated by increasing the bias flow rate, but CO(2) retention is a potential concern. We hypothesize that in a swine model of acute lung injury, increased bias flow rates will not affect CO(2) elimination.

DESIGN

Prospective, randomized, experimental study.

SETTING

Research laboratory at a university medical center.

SUBJECTS

Sixteen juvenile swine.

INTERVENTIONS

Sixteen juvenile swine (12-16.5 kg) were studied using a saline lavage model of acute lung injury. During high-frequency oscillatory ventilation, each animal was ventilated with bias flows of 10, 20, 30, and 40 L/min in random sequence. For ten animals, power was set at a constant level to maintain PaCO(2) 50-60 mm Hg, and amplitude was allowed to vary. For the remaining six animals, amplitude was kept constant to maintain PaCO(2) within the same range, while power was adjusted as needed with changes in bias flow. Linear regression was used for data analysis.

MEASUREMENTS AND MAIN RESULTS

Median overall PaCO(2) was 53 mm Hg (range: 31-81 mm Hg). Controlling for both power and amplitude, there was no statistically significant change in PaCO(2) as bias flow varied from 10 to 40 L/min.

CONCLUSIONS

Changes in bias flow during high-frequency oscillatory ventilation did not affect ventilation. Further clinical investigation is ongoing in infants and children with acute lung injury being managed with high-frequency oscillatory ventilation to assess the impact of alterations of bias flow on gas exchange, cardiopulmonary parameters, sedation requirements, and other clinical outcomes.

The use of high frequency oscillatory ventilation in a pediatric oncology intensive care unit

BACKGROUND

High frequency oscillatory ventilation (HFOV) has been successfully used in the management of acute respiratory distress syndrome (ARDS) in children. The aim of our study is to determine its effectiveness in pediatric patients with cancer or post hematopoietic stem cell transplantation (HSCT) diagnosed with ARDS.

PROCEDURE

A retrospective case review, in a pediatric intensive care unit (PICU) in a tertiary-care oncology center in Amman, Jordan. Patients included were children with cancer and/or receiving allogeneic HSCT who were diagnosed with ARDS and placed on HFOV from January 2007 to February 2009.

RESULTS

Data from 12 pediatric oncology patients on HFOV were analyzed for demographics, oncological diagnosis, PRISM III scores, ventilator settings before switching to HFOV and 24 hours after switching, complications, and outcomes. Alveolar-arterial oxygen (A-a) gradient and oxygen index (OI) were calculated, and pressure of arterial CO(2) (PaCO(2) ) was measured before and 24 hours after switching. Endpoints were successful extubation and discharge, or death while intubated. After 24 hours on HFOV, the A-a gradient decreased significantly in all patients (from a median of 564-267 torr; P=0.001). OI decreased in all but two patients who died (median 17); PaCO(2) decrease was not significant. Five patients died (two of them post-HSCT) and the 7 (58%) survivors were weaned from HFOV (median, 9 days) and discharged.

CONCLUSIONS

HFOV improves gas exchange and is useful in managing critically ill children with cancer and post-HSCT patients who develop ARDS.

Resolution of organ functional scores to predict the outcome in adult acute respiratory distress syndrome patients receiving high-frequency oscillatory ventilation

BACKGROUND

High-frequency oscillatory ventilation (HFOV) may be used as a rescue therapy for adults with acute respiratory distress syndrome who have failed conventional ventilation (CV). We undertook a prospective study to investigate the determinants of mortality and the sequential evolution of organ failures in HFOV-treated adult acute respiratory distress syndrome patients.

METHODS

The indication for HFOV was severe oxygenation failure (PaO2/FiO2 <120 mm Hg) while receiving aggressive CV support (defined by either PaO2 ≤65 mm Hg with FiO2 ≥0.6 when positive end-expiratory pressures >10 cmH2O or plateau airway pressure ≥35 cm H2O). Demographic, clinical, and physiologic data were collected prospectively (May 2007-July 2009). Organ System Failure (OSF), Sequential Organ Failure Assessment (SOFA), and Multiple Organ Dysfunction (MOD) scores were recorded during and after HFOV application. Additional outcome measures included HFOV successful weaning rate, cause of failure, complications, survival rate, and cause of death.

RESULTS

The intensive care unit mortality rate was 62% (21 of 34). Survivors had a significantly shorter CV time before HFOV than nonsurvivors (32.8 hours ± 16.7 hours vs. 47.9 hours ± 26.2 hours, p = 0.049). Survivors had significantly lower baseline lung injury scores, OSF, SOFA, and MOD scores than nonsurvivors. After HFOV, the OSF, SOFA, and MOD scores were significantly decreased for survivors, particularly from day 3 onward.

CONCLUSIONS

Survivors had early improvements in OSF scores after HFOV application. Organ failure system scoring may be used for deciding on HFOV initiation and for evaluating the effects of HFOV.

Pediatric acute respiratory failure: areas of debate in the pediatric critical care setting

Pediatric intensive care units across the world care for large numbers of mechanically ventilated infants and children on a daily basis, yet management of these patients is far from standardized. This lack of standardization may be a necessity in certain situations given variation between underlying disease processes, pathophysiology, response to therapy and available resources. However, there are many situations in which similar patients are managed differently across pediatric intensive care units simply because there are a shortage of available data to guide the management of these critically ill infants and children. Thus, a large fraction of pediatric critical care involves a combination of institutional preference, individual experience, opinion and extrapolation of adult data.

In vitro performance comparison of the Sensormedics 3100A and B high-frequency oscillatory ventilators

OBJECTIVE

The Sensormedics 3100A and 3100B are widely used to provide high-frequency oscillatory ventilation in clinical practice. Infants and children <35 kg are typically oscillated with the 3100A and >35 kg with the 3100B. This study compares the effect of ventilator and patient parameters on delivered tidal volume during high-frequency oscillatory ventilation of a test lung with these devices.

DESIGN

Laboratory-based study.

SUBJECTS

Test lung and Sensormedics 3100A and 3100B high-frequency oscillators.

INTERVENTIONS

A previously validated hot-wire flowmeter (Florian) was placed in series with either a 3100A (n = 3) or 3100B (n = 3) ventilator and a Michigan test lung. Tidal volumes were measured over a range of mean airway pressure, inspiratory:expiratory ratio, frequency, pressure amplitude, and endotracheal tube internal diameter.

MEASUREMENTS AND MAIN RESULTS

The 3100A and 3100B delivered similar tidal volumes across a range of ventilator parameters for an inspiratory:expiratory ratio of 1:1, differing by <10%. However, at an inspiratory:expiratory ratio of 1:2, there was a statistically significant decrease in tidal volume for the 3100B compared with the 3100A at lower frequencies, which was partially mitigated by increasing pressure amplitude. The difference in the generated pressure and flow waveforms may account for the observed tidal volume differences between the high-frequency oscillatory ventilation models. Delivered tidal volume was highly dependent on endotracheal tube size.

CONCLUSIONS

Multiple variables contribute to the delivered tidal volume during high-frequency oscillatory ventilation, including ventilator model selection and endotracheal tube size. It is possible that real-time, clinical monitoring of delivered tidal volume during high-frequency oscillatory ventilation would allow better titration and maximize performance of these ventilators in caring for critically ill patients.

Extracorporeal membrane oxygenation for pediatric respiratory failure: Survival and predictors of mortality. Crit Care Med. 2011;39:364-370. [PMID: 20959787 DOI: 10.1097/ccm.0b013e3181fb7b35]

OBJECTIVE

The last multicentered analysis of extracorporeal membrane oxygenation in pediatric acute respiratory failure was completed in 1993. We reviewed recent international data to evaluate survival and predictors of mortality.

DESIGN

Retrospective case series review.

SETTING

The Extracorporeal Life Support Organization Registry, which includes data voluntarily submitted from over 115 centers worldwide, was queried. The work was completed at the Division of Pediatric Critical Care, Department of Pediatrics, Primary Children's Medical Center, University of Utah, Salt Lake City, UT.

SUBJECTS

Patients aged 1 month to 18 yrs supported with extracorporeal membrane oxygenation for acute respiratory failure from 1993 to 2007.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

There were 3,213 children studied. Overall survival remained relatively unchanged over time at 57%. Considerable variability in survival was found based on pulmonary diagnosis, ranging from 83% for status asthmaticus to 39% for pertussis. Comorbidities significantly decreased survival to 33% for those with renal failure (n = 329), 16% with liver failure (n = 51), and 5% with hematopoietic stem cell transplantation (n = 22). The proportion of patients with comorbidities increased from 19% during 1993 to 47% in 2007. Clinical factors associated with mortality included precannulation ventilatory support longer than 2 wks and lower precannulation blood pH.

CONCLUSIONS

Although the survival of pediatric patients with acute respiratory failure treated with extracorporeal membrane oxygenation has not changed, this treatment is currently offered to increasingly medically complex patients. Mechanical ventilation in excess of 2 wks before the initiation of extracorporeal membrane oxygenation is associated with decreased survival.

Acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a common diagnosis among children admitted to pediatric intensive care units. This heterogeneous disorder has numerous pulmonary and non-pulmonary causes and is associated with a significant risk of mortality. Many supportive therapies exist for ARDS. SEARCH: Literature search was performed by using the key words ARDS and related topics on the Pubmed search engine maintained by the National Heart, Lung, Blood Institute. Pediatric randomized controlled trials that have been published in the last 10 years were included. Emphasis was placed on pediatric literature, although sentinel adult studies have been included. Most of the evidence presented is of levels I and II.

RESULTS

Low tidal volume is the only strategy that has consistently improved outcome in ARDS. A tidal volume of ≤ 6 mL/kg predicted body weight should be used. Ventilator induced lung injury may result in systemic effects with multi-system organ failure, and all efforts should be made to minimize this. Positive end-expiratory pressure should be used to judiciously maintain lung recruitment. There is insufficient evidence to routinely use high frequency ventilation, prone positioning, or inhaled nitric oxide. Calfactant therapy is promising and may be considered in children with direct lung injury and ARDS. Current literature does not support routine use of corticosteroids for non-resolving ARDS.