Lung behavior during a staircase high-frequency oscillatory ventilation recruitment maneuver.

BACKGROUND: Lung volume optimization maneuvers (LVOM) are necessary to make physiologic use of high-frequency oscillatory ventilation (HFOV), but lung behavior during such maneuvers has not been studied to determine lung volume changes after initiation of HFOV, to quantify recruitment versus derecruitment during the LVOM and to calculate the time to stabilization after a pressure change. METHODS: We performed a secondary analysis of prospectively collected data in subjects < 18 years on HFOV. Uncalibrated respiratory inductance plethysmography (RIP) tracings were used to quantify lung recruitment and derecruitment during the LVOM inflation and deflation. The time constant was calculated according to the Niemann model. RESULTS: RIP data of 51 subjects (median age 3.5 [1.7-13.3] months) with moderate-to-severe pediatric acute respiratory distress syndrome (PARDS) in 85.4% were analyzed. Lung recruitment and derecruitment occurred during the LVOM inflation phase upon start of HFOV and between and within pressure changes. At 90% of maximum inflation pressure, lung derecruitment already started during the deflation phase. Time to stable lung volume (time constant) could only be calculated in 26.2% of all pressure changes during the inflation and in 21.4% during the deflation phase, independent of continuous distending pressure (CDP). Inability to calculate the time constant was due to lack of stabilization of the RIP signal or no change in any direction. CONCLUSIONS: Significant heterogeneity in lung behavior during a staircase incremental-decremental LVOM occurred, underscoring the need for higher initial inflation pressures when transitioning from conventional mechanical ventilation (CMV) and a longer time between pressure changes to allow for equilibration.

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.

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.

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.

Global and Regional Tidal Volume Distribution in Spontaneously Breathing Mechanically Ventilated Children.

BACKGROUND: Allowing the ventilated adult patient to breathe spontaneously may improve tidal volume (VT) distribution toward the dependent lung regions, reduce shunt fraction, and decrease dead space. It has not been studied if these effects under various levels of ventilatory support also occur in children. We sought to explore the effect of level of ventilatory support on VT distribution and end-expiratory lung volume (EELV) in spontaneously breathing ventilated children in the recovery phase of their acute respiratory failure. METHODS: This is a secondary analysis of data from a prospective clinical trial comparing 2 different ventilator modes during weaning in mechanically ventilated children < 5 y: CPAP + pressure support ventilation (PSV) and pressure control (PC)/intermittent mandatory ventilation (IMV) + PSV with the mandatory breath rate set at 25% of baseline. Using electrical impedance tomography (EIT), we assessed VT distribution by calculating the center of ventilation. Polynomial functions of the second degree were plotted to evaluate regional lung filling characteristics. Changes in end-expiratory impedance were calculated to assess changes in EELV. Baseline measurements were compared with measurements during CPAP/PSV, PC/IMV + PSV, and during a downward titration of the level of pressure support. RESULTS: Thirty-five subjects with a median age 4.5 (2.1-12.9) months and a median ventilation time of 4.9 (3.3-6.9) d were studied. The overall median coefficient of variation was 50.1% and not different between CPAP/PSV or PC/synchronized IMV + PSV. Regional filling characteristics of the lung identified a homogeneous VT distribution under all study conditions. Downtapering of the level of PSV resulted in a significant shift of the coefficient of variation toward the dependent lung regions. CONCLUSIONS: Our data showed that allowing ventilated children in the recovery phase of respiratory failure to breathe spontaneously in a continuous spontaneous ventilation mode did not negatively affect VT distribution or EELV.

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.

Physiologic responses to a staircase lung volume optimization maneuver in pediatric high-frequency oscillatory ventilation.

BACKGROUND: Titration of the continuous distending pressure during a staircase incremental-decremental pressure lung volume optimization maneuver in children on high-frequency oscillatory ventilation is traditionally driven by oxygenation and hemodynamic responses, although validity of these metrics has not been confirmed. METHODS: Respiratory inductance plethysmography values were used construct pressure-volume loops during the lung volume optimization maneuver. The maneuver outcome was evaluated by three independent investigators and labeled positive if there was an increase in respiratory inductance plethysmography values at the end of the incremental phase. Metrics for oxygenation (SpO2, FiO2), proximal pressure amplitude, tidal volume and transcutaneous measured pCO2 (ptcCO2) obtained during the incremental phase were compared between outcome maneuvers labeled positive and negative to calculate sensitivity, specificity, and the area under the receiver operating characteristic curve. Ventilation efficacy was assessed during and after the maneuver by measuring arterial pH and PaCO2. Hemodynamic responses during and after the maneuver were quantified by analyzing heart rate, mean arterial blood pressure and arterial lactate. RESULTS: 41/54 patients (75.9%) had a positive maneuver albeit that changes in respiratory inductance plethysmography values were very heterogeneous. During the incremental phase of the maneuver, metrics for oxygenation and tidal volume showed good sensitivity (> 80%) but poor sensitivity. The sensitivity of the SpO2/FiO2 ratio increased to 92.7% one hour after the maneuver. The proximal pressure amplitude showed poor sensitivity during the maneuver, whereas tidal volume showed good sensitivity but poor specificity. PaCO2 decreased and pH increased in patients with a positive and negative maneuver outcome. No new barotrauma or hemodynamic instability (increase in age-adjusted heart rate, decrease in age-adjusted mean arterial blood pressure or lactate > 2.0 mmol/L) occurred as a result of the maneuver. CONCLUSIONS: Absence of improvements in oxygenation during a lung volume optimization maneuver did not indicate that there were no increases in lung volume quantified using respiratory inductance plethysmography. Increases in SpO2/FiO2 one hour after the maneuver may suggest ongoing lung volume recruitment. Ventilation was not impaired and there was no new barotrauma or hemodynamic instability. The heterogeneous responses in lung volume changes underscore the need for monitoring tools during high-frequency oscillatory ventilation.

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.