Respiratory entrainment related reverse triggering in mechanically ventilated children.

BACKGROUND: The underlying pathophysiological pathways how reverse triggering is being caused are not fully understood. Respiratory entrainment may be one of these mechanisms, but both terms are used interchangeably. We sought to characterize reverse triggering and the relationship with respiratory entrainment among mechanically ventilated children with and without acute lung injury. METHODS: We performed a secondary phyiology analysis of two previously published data sets of invasively mechanically ventilated children < 18 years with and without lung injury mechanically ventilated in a continuous or intermittent mandatory ventilation mode. Ventilator waveforms, electrical activity of the diaphragm measured with surface electromyography and oesophageal tracings were analyzed for entrained and non-entrained reverse triggered breaths. RESULTS: In total 102 measurements (3110 min) from 67 patients (median age 4.9 [1.8 ; 19,1] months) were analyzed. Entrained RT was identified in 12 (12%) and non-entrained RT in 39 (38%) recordings. Breathing variability for entrained RT breaths was lower compared to non-entrained RT breaths. We did not observe breath stacking during entrained RT. Double triggering often occurred during non-entrained RT and led to an increased tidal volume. Patients with respiratory entrainment related RT had a shorter duration of MV and length of PICU stay. CONCLUSIONS: Reverse triggering is not one entity but a clinical spectrum with different mechanisms and consequences. TRIAL REGISTRATION: Not applicable.

Evaluation of Optimal Esophageal Catheter Balloon Inflation Volume in Mechanically Ventilated Children.

BACKGROUND: Accuracy of esophageal pressure measured by an air-filled esophageal balloon catheter is dependent on balloon filling volume. However, this has been understudied in mechanically ventilated children. We sought to study the optimal filling volume in children receiving ventilation by using previously reported calibration methods. Secondary objectives included to examine the difference in pressure measurements at individualized optimal filling volume versus a standardized inflation volume and to study if a static hold during calibration is required to identify the optimal filling volume. METHODS: An incremental inflation calibration procedure was performed in children receiving ventilation, <18 y, instrumented with commercially available catheters (6 or 8 French) who were not breathing spontaneously. The balloon was manually inflated by 0.2 to 1.6 mL (6 French) or 2.6 mL (8 French). Esophageal pressure (Pes) and airway pressure tracings were recorded during the procedure. Data were analyzed offline by using 2 methods: visual determination of filling range with the calculation of the highest difference between expiratory and inspiratory Pes and determination of a correctly filled balloon by calculating the esophageal elastance. RESULTS: We enrolled 40 subjects with median (interquartile range [IQR]) age 6.8 (2-25) months. The optimal filling volume ranged from 0.2 to 1.2 mL (median [IQR] 0.6 [0.2-1.0] mL) in the subjects with a 6 French catheter and 0.2-2.0 mL (median [IQR] 0.7 [0.5-1.2] mL) for 8 French catheters. Inflating the balloon with 0.6 mL (median computed from the whole cohort) gave an absolute difference in transpulmonary pressure that ranged from -4 to 7 cm H2O compared with the personalized volume. Pes calculated over 5 consecutives breaths differed with a maximum of 1 cm H2O compared to Pes calculated during a single inspiratory hold. The esophageal elastance was correlated with weight, age, and sex. CONCLUSIONS: The optimal balloon inflation volume was highly variable, which indicated the need for an individual calibration procedure. Pes was not overestimated when an inspiratory hold was not applied.

Surface electromyography to quantify neuro-respiratory drive and neuro-mechanical coupling in mechanically ventilated children.

BACKGROUND: The patient's neuro-respiratory drive, measured as electrical activity of the diaphragm (EAdi), quantifies the mechanical load on the respiratory muscles. It correlates with respiratory effort but requires a dedicated esophageal catheter. Transcutaneous (surface) monitoring of respiratory muscle electromyographic (sEMG) signals may be considered a suitable alternative to EAdi because of its non-invasive character, with the additional benefit that it allows for simultaneously monitoring of other respiratory muscles. We therefore sought to study the neuro-respiratory drive and timing of inspiratory muscles using sEMG in a cohort of children enrolled in a pediatric ventilation liberation trial. The neuro-mechanical coupling, relating the pressure generated by the inspiratory muscles to the sEMG signals of these muscles, was also calculated. METHODS: This is a secondary analysis of data from a randomized cross-over trial in ventilated patients aged < 5 years. sEMG recordings of the diaphragm and parasternal intercostal muscles (ICM), esophageal pressure tracings and ventilator scalars were simultaneously recorded during continuous spontaneous ventilation and pressure controlled-intermittent mandatory ventilation, and at three levels of pressure support. Neuro-respiratory drive, timing of diaphragm and ICM relative to the mechanical ventilator's inspiration and neuro-mechanical coupling were quantified. RESULTS: Twenty-nine patients were included (median age: 5.9 months). In response to decreasing pressure support, both amplitude of sEMG (diaphragm: p = 0.001 and ICM: p = 0.002) and neuro-mechanical efficiency indices increased (diaphragm: p = 0.05 and ICM: p < 0.001). Poor correlations between neuro-respiratory drive and respiratory effort were found, with R2: 0.088 [0.021-0.152]. CONCLUSIONS: sEMG allows for the quantification of the electrical activity of the diaphragm and ICM in mechanically ventilated children. Both neuro-respiratory drive and neuro-mechanical efficiency increased in response to lower inspiratory assistance. There was poor correlation between neuro-respiratory drive and respiratory effort. TRIAL REGISTRATION: ClinicalTrials.gov ID NCT05254691. Registered 24 February 2022, registered retrospectively.

Understanding clinical and biological heterogeneity to advance precision medicine in paediatric acute respiratory distress syndrome.

Paediatric acute respiratory distress syndrome (PARDS) is a heterogeneous clinical syndrome that is associated with high rates of mortality and long-term morbidity. Factors that distinguish PARDS from adult acute respiratory distress syndrome (ARDS) include changes in developmental stage and lung maturation with age, precipitating factors, and comorbidities. No specific treatment is available for PARDS and management is largely supportive, but methods to identify patients who would benefit from specific ventilation strategies or ancillary treatments, such as prone positioning, are needed. Understanding of the clinical and biological heterogeneity of PARDS, and of differences in clinical features and clinical course, pathobiology, response to treatment, and outcomes between PARDS and adult ARDS, will be key to the development of novel preventive and therapeutic strategies and a precision medicine approach to care. Studies in which clinical, biomarker, and transcriptomic data, as well as informatics, are used to unpack the biological and phenotypic heterogeneity of PARDS, and implementation of methods to better identify patients with PARDS, including methods to rapidly identify subphenotypes and endotypes at the point of care, will drive progress on the path to precision medicine.

Effect of pediatric ventilation weaning technique on work of breathing.

BACKGROUND: Ventilator liberation is one of the most challenging aspects in patients with respiratory failure. Most patients are weaned through a transition from full to partial respiratory support, whereas some advocate using a continuous spontaneous ventilation (CSV). However, there is little scientific evidence supporting the practice of pediatric ventilator liberation, including the timing of onset of and the approach to weaning mode. We sought to explore differences in patient effort between a pressure controlled continuous mode of ventilation (PC-CMV) [in this cohort PC assist/control (PC-A/C)] with a reduced ventilator rate and CSV, and to study changes in patient effort with decreasing PS. METHODS: In this prospective physiology cross-over study, we randomized children < 5 years to first PC-A/C with a 25% reduction in ventilator rate, or CSV (continuous positive airway pressure [CPAP] + PS). Patients were then crossed over to the other arm. Patient effort was measured by calculating inspiratory work of breathing (WOB) using the Campbell diagram (WOBCampbell), and by pressure-rate-product (PRP) and pressure-time-product (PTP). Respiratory inductance plethysmography (RIP) was used to calculate the phase angle. Measurements were obtained at baseline, during PC-A/C and CPAP + PS, and during decreasing set PS (maximum -6 cmH2O). RESULTS: Thirty-six subjects with a median age of 4.4 (IQR 1.5-11.9) months and median ventilation time of 4.9 (IQR 3.4-7.0) days were included. Nearly all patients (94.4%) were admitted with primary respiratory failure. WOBCampbell during baseline [0.67 (IQR 0.38-1.07) Joules/L] did not differ between CSV [0.49 (IQR 0.17-0.83) Joules/L] or PC-A/C [0.47 (IQR 0.17-1.15) Joules/L]. Neither PRP, PTP, ∆Pes nor phase angle was different between the two ventilator modes. Reducing pressure support resulted in a statistically significant increase in patient effort, albeit that these differences were clinically negligible. CONCLUSIONS: Patient effort during pediatric ventilation liberation was not increased when patients were in a CSV mode of ventilation compared to a ventilator mode with a ventilator back-up rate. Reducing the level of PS did not lead to clinically relevant increases in patient effort. These data may aid in a better approach to pediatric ventilation liberation. Trial registration clinicaltrials.gov NCT05254691. Registered 24 February 2022.

Clinical Challenges in Pediatric Ventilation Liberation: A Meta-Narrative Review.

OBJECTIVES: To map the evidence for ventilation liberation practices in pediatric respiratory failure using the Realist And MEta-narrative Evidence Syntheses: Evolving Standards publication standards. DATA SOURCES: CINAHL, MEDLINE, COCHRANE, and EMBASE. Trial registers included the following: ClinicalTrials.gov, European Union clinical trials register, International Standardized Randomized Controlled Trial Number register. STUDY SELECTION: Abstracts were screened followed by review of full text. Articles published in English language incorporating a heterogeneous population of both infants and older children were assessed. DATA EXTRACTION: None. DATA SYNTHESIS: Weaning can be considered as the process by which positive pressure is decreased and the patient becomes increasingly responsible for generating the energy necessary for effective gas exchange. With the growing use of noninvasive respiratory support, extubation can lie in the middle of the weaning process if some additional positive pressure is used after extubation, while for some extubation may constitute the end of weaning. Testing for extubation readiness is a key component of the weaning process as it allows the critical care practitioner to assess the capability and endurance of the patient's respiratory system to resume unassisted ventilation. Spontaneous breathing trials (SBTs) are often seen as extubation readiness testing (ERT), but the SBT is used to determine if the patient can maintain adequate spontaneous ventilation with minimal ventilatory support, whereas ERT implies the patient is ready for extubation. CONCLUSIONS: Current literature suggests using a structured approach that includes a daily assessment of patient's readiness to extubate may reduce total ventilation time. Increasing evidence indicates that such daily assessments needs to include SBTs without added pressure support. Measures of elevated load as well as measures of impaired respiratory muscle capacity are independently associated with extubation failure in children, indicating that these should also be assessed as part of ERT.

Driving Pressure Is Associated With Outcome in Pediatric Acute Respiratory Failure.

OBJECTIVES: Driving pressure (ratio of tidal volume over respiratory system compliance) is associated with mortality in acute respiratory distress syndrome. We sought to evaluate if such association could be identified in critically ill children. DESIGN: We studied the association between driving pressure on day 1 of mechanical ventilation and ventilator-free days at day 28 through secondary analyses of prospectively collected physiology data. SETTING: Medical-surgical university hospital PICU. PATIENTS: Children younger than 18 years (stratified by Pediatric Mechanical Ventilation Consensus Conference clinical phenotype definitions) without evidence of spontaneous respiration. INTERVENTIONS: Inspiratory hold maneuvers. MEASUREMENTS AND MAIN RESULTS: Data of 222 patients with median age 11 months (2-51 mo) were analyzed. Sixty-five patients (29.3%) met Pediatric Mechanical Ventilation Consensus Conference criteria for restrictive and 78 patients (35.1%) for mixed lung disease, and 10.4% of all patients had acute respiratory distress syndrome. Driving pressure calculated by the ratio of tidal volume over respiratory system compliance for the whole cohort was 16 cm H2O (12-21 cm H2O) and correlated with the static airway pressure gradient (plateau pressure minus positive end-expiratory pressure) (Spearman correlation coefficient = 0.797; p < 0.001). Bland-Altman analysis showed that the dynamic pressure gradient (peak inspiratory pressure minus positive end-expiratory pressure) overestimated driving pressure (levels of agreement -2.295 to 7.268). Rematching the cohort through a double stratification procedure (obtaining subgroups of patients with matched mean levels for one variable but different mean levels for another ranking variable) showed a reduction in ventilator-free days at day 28 with increasing driving pressure in patients ventilated for a direct pulmonary indication. Competing risk regression analysis showed that increasing driving pressure remained independently associated with increased time to extubation (p < 0.001) after adjusting for Pediatric Risk of Mortality III 24-hour score, presence of direct pulmonary indication jury, and oxygenation index. CONCLUSIONS: Higher driving pressure was independently associated with increased time to extubation in mechanically ventilated children. Dynamic assessments of driving pressure should be cautiously interpreted.

Performance of acute respiratory distress syndrome definitions in a high acuity paediatric intensive care unit.

BACKGROUND: For years, paediatric critical care practitioners used the adult American European Consensus Conference (AECC) and revised Berlin Definition (BD) for acute respiratory distress syndrome (ARDS) to study the epidemiology of paediatric ARDS (PARDS). In 2015, the paediatric specific definition, Paediatric Acute Lung Injury Consensus Conference (PALICC) was developed. The use of non-invasive metrics of oxygenation to stratify disease severity were introduced in this definition, although this potentially may lead to a confounding effect of disease severity since it is more common to place indwelling arterial lines in sicker patients. We tested the hypothesis that PALICC outperforms AECC/BD in our high acuity PICU, which employs a liberal use of indwelling arterial lines and high-frequency oscillatory ventilation (HFOV). METHODS: We retrospectively collected data from children < 18 years mechanically ventilated for at least 24 h in our tertiary care, university-affiliated paediatric intensive care unit. The primary endpoint was the difference in the number of PARDS cases between AECC/BD and PALICC. Secondary endpoints included mortality and ventilator free days. Performance was assessed by the area under the receiver operating characteristics curve (AUC-ROC). RESULTS: Data from 909 out of 2433 patients was eligible for analysis. AECC/BD identified 35 (1.4%) patients (mortality 25.7%), whereas PALICC identified 135 (5.5%) patients (mortality 14.1%). All but two patients meeting AECC/Berlin criteria were also identified by PALICC. Almost half of the cohort (45.2%) had mild, 33.3% moderate and 21.5% severe PALICC PARDS at onset. Highest mortality rates were seen in patients with AECC acute lung injury (ALI)/mild Berlin and severe PALICC PARDS. The AUC-ROC for Berlin was the highest 24 h (0.392 [0.124-0.659]) after onset. PALICC showed the highest AUC-ROC at the same moment however higher than Berlin (0.531 [0.345-0.716]). Mortality rates were significantly increased in patients with bilateral consolidations (9.3% unilateral vs 26.3% bilateral, p = 0.025). CONCLUSIONS: PALICC identified more new cases PARDS than the AECC/Berlin definition. However, both PALICC and Berlin performed poorly in terms of mortality risk stratification. The presence of bilateral consolidations was associated with a higher mortality rate. Our findings may be considered in future modifications of the PALICC criteria.

Trends in Pediatric Patient-Ventilator Asynchrony During Invasive Mechanical Ventilation.

OBJECTIVES: To explore the level and time course of patient-ventilator asynchrony in mechanically ventilated children and the effects on duration of mechanical ventilation, PICU stay, and Comfort Behavior Score as indicator for patient comfort. DESIGN: Secondary analysis of physiology data from mechanically ventilated children. SETTING: Mixed medical-surgical tertiary PICU in a university hospital. PATIENTS: Mechanically ventilated children 0-18 years old were eligible for inclusion. Excluded were patients who were unable to initiate and maintain spontaneous breathing from any cause. MEASUREMENTS AND MAIN RESULTS: Twenty-nine patients were studied with a total duration of 109 days. Twenty-two study days (20%) were excluded because patients were on neuromuscular blockade or high-frequency oscillatory ventilation, yielding 87 days (80%) for analysis. Patient-ventilator asynchrony was detected through analysis of daily recorded ventilator airway pressure, flow, and volume versus time scalars. Approximately one of every three breaths was asynchronous. The percentage of asynchronous breaths significantly increased over time, with the highest prevalence on the day of extubation. There was no correlation with the Comfort Behavior score. The percentage of asynchronous breaths during the first 24 hours was inversely correlated with the duration of mechanical ventilation. Patients with severe patient-ventilator asynchrony (asynchrony index > 10% or > 75th percentile of the calculated asynchrony index) did not have a prolonged duration of ventilation. CONCLUSIONS: The level of patient-ventilator asynchrony increased over time was not related to patient discomfort and inversely related to the duration of mechanical ventilation.

Additional work of breathing from trigger errors in mechanically ventilated children.

BACKGROUND: Patient-ventilator asynchrony is associated with increased morbidity and mortality. A direct causative relationship between Patient-ventilator asynchrony and adverse clinical outcome have yet to be demonstrated. It is hypothesized that during trigger errors excessive pleural pressure swings are generated, contributing to increased work-of-breathing and self-inflicted lung injury. The objective of this study was to determine the additional work-of-breathing and pleural pressure swings caused by trigger errors in mechanically ventilated children. METHODS: Prospective observational study in a tertiary paediatric intensive care unit in an university hospital. Patients ventilated > 24 h and < 18 years old were studied. Patients underwent a 5-min recording of the ventilator flow-time, pressure-time and oesophageal pressure-time scalar. Pressure-time-product calculations were made as a proxy for work-of-breathing. Oesophageal pressure swings, as a surrogate for pleural pressure swings, during trigger errors were determined. RESULTS: Nine-hundred-and-fifty-nine trigger errors in 28 patients were identified. The additional work-of-breathing caused by trigger errors showed great variability among patients. The more asynchronous breaths were present the higher the work-of-breathing of these breaths. A higher spontaneous breath rate led to a lower amount of trigger errors. Patient-ventilator asynchrony was not associated with prolonged duration of mechanical ventilation or paediatric intensive care stay. CONCLUSIONS: The additional work-of-breathing caused by trigger errors in ventilated children can take up to 30-40% of the total work-of-breathing. Trigger errors were less common in patients breathing spontaneously and those able to generate higher pressure-time-product and pressure swings. TRIAL REGISTRATION: Not applicable.

Energy transmission in mechanically ventilated children: a translational study.

BACKGROUND: Recurrent delivery of tidal mechanical energy (ME) inflicts ventilator-induced lung injury (VILI) when stress and strain exceed the limits of tissue tolerance. Mechanical power (MP) is the mathematical description of the ME delivered to the respiratory system over time. It is unknown how ME relates to underlying lung pathology and outcome in mechanically ventilated children. We therefore tested the hypothesis that ME per breath with tidal volume (Vt) normalized to bodyweight correlates with underlying lung pathology and to study the effect of resistance on the ME dissipated to the lung. METHODS: We analyzed routinely collected demographic, physiological, and laboratory data from deeply sedated and/or paralyzed children < 18 years with and without lung injury. Patients were stratified into respiratory system mechanic subgroups according to the Pediatric Mechanical Ventilation Consensus Conference (PEMVECC) definition. The association between MP, ME, lung pathology, and duration of mechanical ventilation as a primary outcome measure was analyzed adjusting for confounding variables and effect modifiers. The effect of endotracheal tube diameter (ETT) and airway resistance on energy dissipation to the lung was analyzed in a bench model with different lung compliance settings. RESULTS: Data of 312 patients with a median age of 7.8 (1.7-44.2) months was analyzed. Age (p <  0.001), RR p <  0.001), and Vt <  0.001) were independently associated with MPrs. ME but not MP correlated significantly (p <  0.001) better with lung pathology. Competing risk regression analysis adjusting for PRISM III 24 h score and PEMVECC stratification showed that ME on day 1 or day 2 of MV but not MP was independently associated with the duration of mechanical ventilation. About 33% of all energy generated by the ventilator was transferred to the lung and highly dependent on lung compliance and airway resistance but not on endotracheal tube size (ETT) during pressure control (PC) ventilation. CONCLUSIONS: ME better related to underlying lung pathology and patient outcome than MP. The delivery of generated energy to the lung was not dependent on ETT size during PC ventilation. Further studies are needed to identify injurious MErs thresholds in ventilated children.

Spontaneous Breathing and Imposed Work During Pediatric Mechanical Ventilation: A Bench Study.

OBJECTIVES: To calculate imposed work of breathing during simulated spontaneous breathing at a given tidal volume across the range of normal length or shortened pediatric endotracheal tube sizes and endotracheal tubes with an intraluminal catheter in situ. DESIGN: In vitro study. SETTING: Research laboratory. INTERVENTIONS: A bench model (normal compliance, no airway resistance) simulating sinusoid flow spontaneous breathing used to calculate imposed work of breathing for various endotracheal tube sizes (3.0-7.5 mm). Imposed work of breathing was calculated by integrating inspiratory tidal volume over the end-expiratory difference between the positive end-expiratory pressure and the tracheal pressure. Measurements were taken at different combinations of set spontaneous tidal volume (2.5, 5.0, 7.5, and 10 mL/kg), age-appropriate inspiratory times, length of endotracheal tube, and presence of intraluminal catheter. MEASUREMENTS AND MAIN RESULTS: Overall median imposed work of breathing (Joules/L) was not significantly different between the four age groups: 0.047 Joules/L (interquartile range, 0.020-0.074 Joules/L) for newborns, 0.077 Joules/L (interquartile range, 0.032-0.127 Joules/L) for infants, 0.109 Joules/L (interquartile range, 0.0399-0.193 Joules/L) for small children, and 0.077 Joules/L (interquartile range, 0.032-0.132 Joules/L) for adolescents. Shortening the endotracheal tubes resulted in a significant difference in reduction in overall imposed work of breathing, but the absolute reduction was most notable in small children (0.030 Joules/L) and the least effect in neonates (0.016 Joules/L). Overall imposed work of breathing increased in each age group when an intraluminal catheter was in situ: 91.09% increase in imposed work of breathing in neonates to 0.168 Joules/L, 84.98% in infants to 0.142 Joules/L, 81.98% in small children to 0.219 Joules/L, and 55.45% in adolescents to 0.140 Joules/L. CONCLUSIONS: Calculated imposed work of breathing were not different across the range of endotracheal tube sizes. The low imposed work of breathing values found in this study might be appreciated as clinically irrelevant. Our findings add to the change in reasoning that it is appropriate to perform spontaneous breathing trials without pressure support. Nonetheless, our findings on the measured imposed work of breathing values need to be confirmed in a clinical study.

Effect of Endotracheal Tube Size, Respiratory System Mechanics, and Ventilator Settings on Driving Pressure.

OBJECTIVES: We sought to investigate factors that affect the difference between the peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions (resistive pressure) during pressure controlled ventilation across a range of endotracheal tube sizes, respiratory mechanics, and ventilator settings. DESIGN: In vitro study. SETTING: Research laboratory. PATIENTS: None. INTERVENTIONS: An in vitro bench model of the intubated respiratory system during pressure controlled ventilation was used to obtain the difference between peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions across a range of endotracheal tubes sizes (3.0-8.0 mm). Measurements were taken at combinations of pressure above positive end-expiratory pressure (10, 15, and 20 cm H2O), airway resistance (no, low, high), respiratory system compliance (ranging from normal to extremely severe), and inspiratory time at constant positive end-expiratory pressure (5 cm H2O). Multiple regression analysis was used to construct models predicting resistive pressure stratified by endotracheal tube size. MEASUREMENTS AND MAIN RESULTS: On univariate regression analysis, respiratory system compliance (ß -1.5; 95% CI, -1.7 to -1.4; p < 0.001), respiratory system resistance (ß 1.7; 95% CI, 1.5-2.0; p < 0.001), pressure above positive end-expiratory pressure (ß 1.7; 95% CI, 1.4-2.0; p < 0.001), and inspiratory time (ß -0.7; 95% CI, -1.0 to -0.4; p < 0.001) were associated with resistive pressure. Multiple linear regression analysis showed the independent association between increasing respiratory system compliance, increasing airway resistance, increasing pressure above positive end-expiratory pressure, and decreasing inspiratory time and resistive pressure across all endotracheal tube sizes. Inspiratory time was the strongest variable associated with a proportional increase in resistive pressure. The contribution of airway resistance became more prominent with increasing endotracheal tube size. CONCLUSIONS: Peak inspiratory pressures measured during pressure controlled ventilation overestimated plateau pressure irrespective of endotracheal tube size, especially with decreased inspiratory time or increased airway resistance.

Ventilator-induced lung injury in children: a reality?

Mechanical ventilation (MV) is inextricably linked to the care of critically ill patients admitted to the paediatric intensive care unit (PICU). Even today, little evidence supports best MV practices for life-threatening acute respiratory failure in children. However, careful attention must be paid because this life-saving technique induces pulmonary inflammation that aggravates pre-existing lung injury, a concept that is known as ventilator-induced lung injury (VILI). The delivery of too large tidal volumes (Vt) (i.e., volutrauma) and repetitive opening and closure of alveoli (i.e., atelectrauma) are two key mechanisms underlying VILI. Despite the knowledge of these mechanisms, the clinical relevance of VILI in critically ill children is poorly understood as almost all of our knowledge has been obtained from studies in adults or experimental studies mimicking the adult critical care situation. This leaves the question if VILI is relevant in the paediatric context. In fact, limited paediatric experimental data showed that the use of large, supraphysiologic Vt resulted in less inflammation and injury in paediatric animal models compared to adult models. Furthermore, the association between large Vt and adverse outcome has not been confirmed and the issue of setting positive end-expiratory pressure (PEEP) to prevent atelectrauma has hardly been studied in paediatric clinical studies. Hence, even today, the question whether or not there VILI is relevant in pediatric critical remains to be answered. Consequently, how MV is used remains thus based on institutional preferences, personal beliefs and clinical data extrapolated from adults. This signifies the need for clinical and experimental studies in order to better understand the use and effects of MV in paediatric patients with or without lung injury.

The effect of pressure support on imposed work of breathing during paediatric extubation readiness testing.

BACKGROUND: Paediatric critical care practitioners often make use of pressure support (PS) to overcome the perceived imposed work of breathing (WOBimp) during an extubation readiness test (ERT). However, no paediatric data are available that shows the necessity of adding of pressure support during such tests. We sought to measure the WOBimp during an ERT with and without added pressure support and to study its clinical correlate. This was a prospective study in spontaneously breathing ventilated children < 18 years undergoing ERT. Using tracheal manometry, WOBimp was calculated by integrating the difference between positive end-expiratory pressure (PEEP) and tracheal pressure (Ptrach) over the measured expiratory tidal volume (VTe) under two paired conditions: continuous positive airway pressure (CPAP) with and without PS. Patients with post-extubation upper airway obstruction were excluded. RESULTS: A total of 112 patients were studied. Median PS during the ERT was 10 cmH2O. WOBimp was significantly higher without PS (median 0.27, IQR 0.20-0.50 J/L) than with added PS (median 0.00, IQR 0.00-0.11 J/L). Although there were statistically significant changes in spontaneous breath rate [32 (23-42) vs. 37 (27-46) breaths/min, p < 0.001] and higher ET-CO2 [5.90 (5.38-6.65) vs. 6.23 (5.55-6.94) kPa, p < 0.001] and expiratory Vt decreased [7.72 (6.66-8.97) vs. 7.08 (5.82-8.08) mL/kg, p < 0.001] in the absence of PS, these changes appeared clinically irrelevant since the Comfort B score remained unaffected [12 (10-13) vs. 12 (10-13), P = 0.987]. Multivariable analysis showed that changes in WOBimp occurred independent of endotracheal tube size. CONCLUSIONS: Withholding PS during ERT does not lead to clinically relevant increases in WOBimp, irrespective of endotracheal tube size.

Transcutaneous electromyographic respiratory muscle recordings to quantify patient-ventilator interaction in mechanically ventilated children.

BACKGROUND: To explore the feasibility of transcutaneous electromyographic respiratory muscle recordings to automatically quantify the synchronicity of patient-ventilator interaction in the pediatric intensive care unit. METHODS: Prospective observational study in a tertiary paediatric intensive care unit in an university hospital. Spontaneous breathing mechanically ventilated children < 18 years of age were eligible for inclusion. Patients underwent a 5-min continuous recording of ventilator pressure waveforms and transcutaneous electromyographic signal of the diaphragm. To evaluate patient-ventilator interaction, the obtained neural inspiration and ventilator pressurization timings were used to calculate trigger and cycle-off errors of each breath. Calculated errors were displayed in the dEMG-phase scale. RESULTS: Data of 23 patients were used for analysis. Based on the dEMG-phase scale, the median rates of synchronous, dyssynchronous and asynchronous breaths as classified by the automated analysis were 12.2% (1.9-33.8), 47.5% (36.3-63.1), and 28.9% (6.6-49.0). CONCLUSIONS: The dEMG-phase scale quantifying patient-ventilator breath synchronicity was demonstrated to be feasible and a reliable scale for mechanically ventilated children, reflected by high intra-class correlation coefficients. As this non-invasive tool is not restricted to a type of ventilator, it could easily be clinical implemented in the ventilated pediatric population. However; correlation studies between the EMG signal measured by surface EMG and esophageal catheters have to be performed.

Patient-Ventilator Asynchrony During Assisted Ventilation in Children.

OBJECTIVE: To describe the frequency and type of patient-ventilator asynchrony in mechanically ventilated children by analyzing ventilator flow and pressure signals. DESIGN: Prospective observational study. SETTING: Tertiary PICU in a university hospital. PATIENTS: Mechanically ventilated children between 0 and 18 years old and who were able to initiate and maintain spontaneous breathing were eligible for inclusion. Patients with congenital or acquired neuromuscular disorders, those with congenital or acquired central nervous system disorders, and those who were unable to initiate and maintain spontaneous breathing from any other cause were excluded. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: All patients were ventilated in a time-cycled, pressure-limited mode with flow triggering set at 1.0 L/min by using the Evita XL (Dräger, Lubeck, Germany). Patient-ventilator asynchrony was identified by a random 30-minute continuous recording and an offline analysis of the flow and pressure signals. Patient-ventilator asynchrony was categorized and labeled into four different groups: 1) trigger asynchrony (i.e., insensitive trigger, double triggering, autotriggering, or trigger delay), 2) flow asynchrony, 3) termination asynchrony (i.e., delayed or premature termination), and 4) expiratory asynchrony. Flow and pressure signals were recorded in 45 patients for 30 minutes. A total number of 57,651 breaths were analyzed. Patient-ventilator asynchrony occurred in 19,175 breaths (33%), and it was seen in every patient. Ineffective triggering was the most predominant type of asynchrony (68%), followed by delayed termination (19%), double triggering (4%), and premature termination (3%). Patient-ventilator asynchrony significantly increased with lower levels of peak inspiratory pressure, positive end-expiratory pressure, and set frequency. CONCLUSIONS: Patient-ventilator asynchrony is extremely common in mechanically ventilated children, and the predominant cause is ineffective triggering.