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Objectives: Mechanical ventilation is an essential life support technology, but it is associated with side effects in case of over or under-assistance. The monitoring of respiratory effort may facilitate titration of the support. The gold standard for respiratory effort measurement is based on esophageal pressure monitoring, a technology not commonly available at bedside. Diaphragmatic electrical activity can be routinely monitored in clinical practice and reflects the output of the respiratory centers. We hypothesized that diaphragmatic electrical activity changes accurately reflect changes in mechanical efforts. The objectives of this study were to characterize the relationship between diaphragmatic electrical activity and esophageal pressure., Design: Prospective crossover study., Setting: Esophageal pressure and diaphragmatic electrical activity were simultaneously recorded using a specific nasogastric tube in three conditions: in pressure support ventilation and in neurally adjusted ventilatory support in a random order, and then after extubation., Patients: Children in the weaning phase of mechanical ventilation., Interventions: The maximal swing in esophageal pressure and esophageal pressure-time product, maximum diaphragmatic electrical activity, and inspiratory diaphragmatic electrical activity integral were calculated from 100 consecutive breaths. Neuroventilatory efficiency was estimated using the ratio of tidal volume/maximum diaphragmatic electrical activity., Measurements and Main Results: Sixteen patients, with a median age of 4 months (interquartile range, 0.5-13 mo), and weight 5.8 kg (interquartile range, 4.1-8 kg) were included. A strong linear correlation between maximum diaphragmatic electrical activity and maximal swing in esophageal pressure (r > 0.95), and inspiratory diaphragmatic electrical activity integral and esophageal pressure-time product (r > 0.71) was observed in all ventilatory conditions. This correlation was not modified by the type of ventilatory support., Conclusions: On a short-term basis, diaphragmatic electrical activity changes are strongly correlated with esophageal pressure changes. In clinical practice, diaphragmatic electrical activity monitoring may help to inform on changes in respiratory efforts.

Background: The present study aimed to characterize the behavior of 3 components of respiratory muscle function during mechanical ventilation weaning in children to better understand the respective impact of a spontaneous breathing trial on ventilatory mechanical action (esophageal pressure [P es ], ventilatory demand (electrical activity of the diaphragm [EA di ]), and oxygen consumption., Methods: This was a prospective single-center study. All children > 1 months and <18 y old who were intubated and on mechanical ventilation, and who were hospitalized in the pediatric ICU were eligible. Subjects considered as ready to extubate were included. Simultaneous recordings of oxygen consumption, P es , and EA di were performed during 3 steps: before, during, and after the spontaneous breathing test., Results: Twenty subjects (median age, 5.5 mo) were included. Half of them were admitted for a respiratory cause. The increase in P es swings and esophageal pressure-time product during the spontaneous breathing trial was not significant ( P = .33 and P = .75, respectively), and a similar trend was observed with peak EA di ( P = .06). Oxygen consumption obtained by indirect calorimetry was stable in the 3 conditions ( P = .98)., Conclusions: In these children who were critically ill, a spontaneous breathing trial induced a moderate and nonsignificant increase in work of breathing, as reflected by the respiratory drive with EA di and respiratory mechanics with P es . However, indirect calorimetry did not seem to be a sensitive tool to assess respiratory muscle function during the weaning phase in children who were on mechanical ventilation, especially when work of breathing was slightly increased., (Copyright © 2019 by Daedalus Enterprises.)

Background: Diaphragm weakness occurs rapidly in adult animals treated with mechanical ventilation (MV), but the effects of MV on the neonatal diaphragm have not been determined. Furthermore, it is unknown whether co-existent lung disease exacerbates ventilator-induced diaphragmatic dysfunction (VIDD). We investigated the impact of MV (mean duration = 7.65 h), either with or without co-existent respiratory failure caused by surfactant deficiency, on the development of VIDD in newborn lambs., Methods: Newborn lambs (1-4 days) were assigned to control (CTL, non-ventilated), mechanically ventilated (MV), and MV + experimentally induced surfactant deficiency (MV+SD) groups. Immunoblotting and quantitative PCR assessed inflammatory signaling, the ubiquitin-proteasome system, autophagy, and oxidative stress. Immunostaining for myosin heavy chain (MyHC) isoforms and quantitative morphometry evaluated diaphragm atrophy. Contractile function of the diaphragm was determined in isolated myofibrils ex vivo., Results: Equal decreases (25-30%) in myofibrillar force generation were found in MV and MV+SD diaphragms compared to CTL. In comparison to CTL, both MV and MV+SD diaphragms also demonstrated increased STAT3 transcription factor phosphorylation. Ubiquitin-proteasome system (Atrogin1 and MuRF1) transcripts and autophagy indices (Gabarapl1 transcripts and the ratio of LC3B-II/LC3B-I protein) were greater in MV+SD relative to MV alone, but fiber type atrophy was not observed in any group. Protein carbonylation and 4-hydroxynonenal levels (indices of oxidative stress) also did not differ among groups., Conclusions: In newborn lambs undergoing controlled MV, there is a rapid onset of diaphragm dysfunction consistent with VIDD. Superimposed lung injury caused by surfactant deficiency did not influence the severity of early diaphragm weakness.

Background: Infants have to actively maintain their end expiratory lung volume (EELV). In mechanically ventilated infants, the diaphragm stays activated until the end of expiration (tonic activity), contributing to EELV maintenance. It is unclear whether tonic activity compensates for the lack of laryngeal braking due to intubation or if it is normally present., Objective: To determine if tonic diaphragm activity remains after extubation in infants, and if it can be observed in older children., Methods: Prospective observational study of pediatric patients ventilated for >24 hr. Diaphragm electrical activity (EAdi) was recorded using a specific nasogastric catheter during four periods: (i) the acute phase, (ii) pre-extubation, (iii) post-extubation, and (iv) at PICU discharge. Tonic EAdi was defined as the EAdi in the last quartile of expiration., Results: Fifty-five patients, median age 10 months (Interquartile range: 1-48) were studied. In infants (<1 year, n = 28), tonic EAdi was always present, and represented 33% (22-43) of inspiratory EAdi at PICU discharge. No significant change was observed between pre- and post-extubation periods. In older patients (n = 27), tonic activity was negligible as a whole, but 10 patients exhibited significant tonic EAdi at one time-point during PICU stay. Bronchiolitis was the only independent factor associated with tonic EAdi., Conclusions: In infants, tonic EAdi remains involved in ventilatory control after extubation and restoration of laryngeal braking. Tonic EAdi may play a pathophysiological role in bronchiolitis and it can be reactivated in older patients. The interest of tonic EAdi as a tool to titrate mechanical ventilation warrants further evaluation., (© 2015 Wiley Periodicals, Inc.)

Purpose: Diaphragm function should be monitored in critically ill patients, as full ventilatory support rapidly induces diaphragm atrophy. Monitoring the electrical activity of the diaphragm (EAdi) may help assess the level of diaphragm activity, but such monitoring results are difficult to interpret because reference values are lacking. The aim of this study was to describe EAdi values in critically ill children during a stay in the pediatric intensive care unit (PICU), from the acute to recovery phases, and to assess the impact of ventilatory support on EAdi., Methods: This was a prospective longitudinal observational study of children requiring mechanical ventilation for ≥24 h. EAdi was recorded using a validated method in the acute phase, before extubation, after extubation, and before PICU discharge., Results: Fifty-five critically ill children were enrolled in the study. Median maximum inspiratory EAdi (EAdimax) during mechanical ventilation was 3.6 [interquartile range (IQR) 1.2-7.6] μV in the acute phase and 4.8 (IQR 2.0-10.7) μV in the pre-extubation phase. Periods of diaphragm inactivity (with no detectable inspiratory EAdi) were frequent during conventional ventilation, even with a low level of support. EAdimax in spontaneous ventilation was 15.4 (IQR 7.4-20.7) μV shortly after extubation and 12.6 (IQR 8.1-21.3) μV before PICU discharge. The difference in EAdimax between mechanical ventilation and post-extubation periods was significant (p < 0.001). Patients intubated mainly because of a lung pathology exhibited higher EAdi (p < 0.01), with a similar temporal increase., Conclusions: This is the first systematic description of EAdi evolution in children during their stay in the PICU. In our patient cohort, diaphragm activity was frequently low in conventional ventilation, suggesting that overassistance or oversedation is common in clinical practice. EAdi monitoring appears to be a helpful tool to detect such situations.

Background: Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation controlled by the electrical activity of the diaphragm (Edi). The aim was to evaluate patient-ventilator interaction in infants during NAVA as compared with conventional ventilation., Methods: Infants were successively ventilated with NAVA, pressure control ventilation (PCV), and pressure support ventilation (PSV). Edi and ventilator pressure (Pvent) waveforms were compared and their variability was assessed by coefficients of variation., Results: Ten patients (mean age 4.3 ± 2.4 mo and weight 5.9 ± 2.2 kg) were studied. In PCV and PSV, 4 ± 4.6% and 6.5 ± 7.7% of the neural efforts failed to trigger the ventilator. This did not occur during NAVA. Trigger delays were shorter with NAVA as compared with PCV and PSV (93 ± 20 ms vs. 193 ± 87 ms and 135 ± 29 ms). During PCV and PSV, the ventilator cycled off before the end of neural inspiration in 12 ± 13% and 21 ± 19% of the breaths (0 ± 0% during NAVA). During PCV and PSV, 24 ± 11% and 25 ± 9% of the neural breath cycle was asynchronous with the ventilator as compared with 11 ± 3% with NAVA. A large variability was observed for Edi in all modes, which was transmitted into Pvent during NAVA (coefficient of variation: 24 ± 8%) and not in PCV (coefficient of variation 2 ± 1%) or PSV (2 ± 2%)., Conclusion: NAVA improves patient-ventilator interaction and delivers adequate ventilation with variable pressure in infants.

The presence of diaphragm electrical activity (EAdi) during expiration is believed to be involved in the maintenance of end-expiratory lung volume (EELV) and has never been studied in intubated and mechanically ventilated infants. The aim of this study was to quantify the amplitude of diaphragm electrical activity present during expiration in mechanically ventilated infants and to measure the impact of removing positive end-expiratory pressure (PEEP) on this activity. We studied the EAdi in 16 ready-to-be weaned intubated infants who were breathing on their prescribed ventilator and PEEP settings. In all 16 patients, 5 min of data were collected on the prescribed ventilator settings. In a subset of eight patients, the PEEP was briefly reduced to zero PEEP (ZEEP). EAdi was recorded with miniaturized sensors placed on a conventional nasogastric feeding tube. Airway pressure (Paw) was also measured. For each spontaneous breath, we identified the neural inspiration and neural expiration. Neural expiration was divided into quartiles (Q1, Q2, Q3, and Q4), and the amplitude of EAdi calculated for each Q1-Q4 represented 95 +/- 29%, 31 +/- 15%, 15 +/- 8%, and 12 +/- 7%, respectively, of the inspiratory EAdi amplitude. EAdi for Q3-Q4 significantly increased during ZEEP, and decreased after reapplication of PEEP. These findings confirm that the diaphragm remains partially active during expiration in intubated and mechanically ventilated infants and that removal of PEEP affects this tonic activity. This could have potential implications on the management of PEEP in intubated infants.