Measuring Expiratory Diaphragm Activity: An Electrifying Tool to Guide Positive End-Expiratory Pressure Strategy in Critically Ill Children?*

While normal, quiet expiration is a passive process with relaxation of the inspiratory respiratory muscles, it appears that in De Causis Respirationis Galen (129–200 AD) already considered the possibility of sustained diaphragm activity during expiration under certain circumstances (1). Indeed, upon lung deflation, the Hering-Breuer reflex stimulates the respiratory center to control and slow down expiration, much like Galen’s analogy of gently lowering an uplifted arm instead of letting it drop suddenly. Infants are prone for lung collapse even during normal tidal breathing. They, therefore, exploit an active diaphragm during expiration, in addition to laryngeal braking of flow and a high respiratory rate, to maintain end-expiratory lung volume (EELV) (2). With landmark observations in 1968 of grunting neonates at risk for alveolar derecruitment due to classic hyaline membrane disease (3), pioneers in this field soon realized the clinical importance of maintaining EELV in respiratory disease states for patients of all ages, leading toward first applications of continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) during mechanical ventilation (4,5).

By detailed characterization of the electrical activity of the diaphragm (Edi) using electromyography techniques in the last decades, it is now recognized that indeed post-inspiratory sustained electric activity throughout expiration (tonic Edi [Editonic]) occurs in infants (6) but may also be observed during disease in older children (7). Moreover, animal experiments have shown increased Editonic upon endotracheal intubation, potentially due to loss for the possibility of laryngeal braking, and upon removal of PEEP during mechanical ventilation (8). Could measurement of Editonic thus be a valuable tool to estimate the patient’s effort to maintain or increase EELV and therefore help to titrate PEEP settings? With this relevant question in mind, Plante et al (9) make an important contribution to this field in the current issue of Pediatric Critical Care Medicine. They report a retrospective study involving a large cohort (overall n = 431) of critically ill children from a single-center PICU, at which the Edi signal was routinely measured by an indwelling esophageal catheter during either invasive mechanical ventilation (IMV) or noninvasive ventilation (NIV, defined here with including CPAP). Because any potential future application of Editonic monitoring in ventilator strategies demands an age-specific “normal” reference value, they first analyzed Editonic in a subcohort of 221 children during the recovery of their critical illness. It is important to note here that Editonic in this reference cohort was measured for 3 hours somewhere in the final 3 days of NIV, while patients had no evidence for remaining oxygenation failure (median Fio2 [interquartile range (IQR)] 0.23 [0.21–0.3]), but still received some level of PEEP (median [IQR], 6 cm H2O [5–7 cm H2O]) (9). Also, by far, the largest proportion of children in this reference cohort received NIV (83%). As expected from earlier work (2,7), the 97.5th percentile, which was used as the upper threshold reference value, of Editonic in infants (0–1 yr) was significantly higher as compared to older children (> 1 yr) (3.2 vs 1.9 µV) (9).

Next, using this threshold value obtained from patients receiving respiratory support in their recovery phase, which evidently should not be confused with a normal reference for spontaneously breathing healthy children, Plante et al (9) determined the prevalence of elevated Editonic in ventilated children during the first 48 hours of ventilation (acute phase cohort). Of note, the original reference cohort has substantial overlap with this acute phase cohort, which may have introduced some bias, thus diminishing external validity. The authors find that almost one-third of patients on IMV and two-thirds on NIV had at least one episode of elevated Editonic with a considerable and clinical relevant length of time (9). A central question is now: does this rather large group of ventilated critically ill children with high Editonic represent patients who signal their need for increased EELV and would thus benefit from increasing PEEP? Here, we are limited in our conclusions, as lung volumes including EELV, and importantly, any dynamic and temporal correlation between Editonic and changes in PEEP, could not be measured in the study by Plante et al (9). In stable preterm infants on nasal CPAP, sustained post-inspiratory diaphragm activity is correlated with varying CPAP levels, albeit with small absolute differences (10). In addition, elevated Editonic may not always indicate the need for more PEEP. For example, in pure obstructive respiratory diseases with risk for hyperinflation, the authors rightly point out that Editonic may be related to (expiratory) airway resistance and not so much with alveolar volumes. In this light, the finding that a diagnosis of viral bronchiolitis, which was very prevalent in the cohort under study, was highly associated with elevated Editonic is of particular interest, as it may temper the usefulness of Editonic to detect impaired EELV (9). On the other hand, to consider bronchiolitis as a pure and sole obstructive disease may certainly be an oversimplification, as evidence for widespread involvement of the alveolar compartment and restrictive lung function does often exist (11,12).

So, will the electrified signal of expiratory diaphragm activity be helpful to the PICU clinician in guiding ventilator strategies, in particular setting PEEP (13), in the future? The current study by Plante et al (9), building upon previous work by this experienced group, certainly is an important first step toward an answer for this question. However, much further work needs to be done. For example, we need prospective testing of Editonic changes in relation to dynamic PEEP settings, including external validation. Homogenous patient groups at specific risk for decreased EELV could be considered here, to filter out variability of Editonic levels introduced by high respiratory rates and increased airway resistance issues. In addition, specific attention is needed for deeply sedated and, of course, paralyzed, ventilated children, as Editonic monitoring is less likely to be useful in those patients. Ultimately challenging, Editonic-mediated PEEP setting should be tested for benefit on clinically relevant endpoints, such as ventilator-free days, but also including short-term surrogate outcomes such as patient-ventilator (a)synchrony, need for sedation, oxygenation, and so on. Here, Editonic will have to compete, or better, work together with many other variables that may help PEEP titration such as compliance/volume-pressure curves, hemodynamics, Fio2, esophageal pressure, dead space estimation, and volumetric capnography. Finally, esophageal Edi catheters with sizes across the entire pediatric age spectrum should be made more readily available and compatible with existing pediatric ventilators from different manufacturers. In this light, upcoming technologies that measure diaphragm activity in a noninvasive manner using skin electrodes may also be of great benefit in the future (14).

1. Derenne JP, Debru A, Grassino AE, et al.: History of diaphragm physiology: The achievements of Galen. Eur Respir J. 1995; 8:154–160 2. Colin AA, Wohl ME, Mead J, et al.: Transition from dynamically maintained to relaxed end-expiratory volume in human infants. J Appl Physiol (1985). 1989; 67:2107–2111 3. Harrison VC, Heese Hde V, Klein M: The significance of grunting in hyaline membrane disease. Pediatrics. 1968; 41:549–559 4. Gregory GA, Kitterman JA, Phibbs RH, et al.: Treatment of the idiopathic respiratory-distress syndrome with continuous positive airway pressure. N Engl J Med. 1971; 284:1333–1340 5. Inkster JS, Pearson DT: Infant ventilator systems. Br J Anaesth. 1968; 40:307 6. Hutten GJ, van Eykern LA, Latzin P, et al.: Relative impact of respiratory muscle activity on tidal flow and end expiratory volume in healthy neonates. Pediatr Pulmonol. 2008; 43:882–891 7. Larouche A, Massicotte E, Constantin G, et al.: Tonic diaphragmatic activity in critically ill children with and without ventilatory support. Pediatr Pulmonol. 2015; 50:1304–1312 8. Allo JC, Beck JC, Brander L, et al.: Influence of neurally adjusted ventilatory assist and positive end-expiratory pressure on breathing pattern in rabbits with acute lung injury. Crit Care Med. 2006; 34:2997–3004 9. Plante V, Poirier C, Guay H, et al.: Elevated Diaphragmatic Tonic Activity in PICU Patients: Age-Specific Definitions, Prevalence, and Associations. Pediatr Crit Care Med. 2023; 24:447–457 10. van Leuteren RW, de Waal CG, Hutten GJ, et al.: Transcutaneous monitoring of diaphragm activity as a measure of work of breathing in preterm infants. Pediatr Pulmonol. 2021; 56:1593–1600 11. Bem RA, Kneyber MC, van Woensel JB: Respiratory syncytial virus-induced paediatric ARDS: Why we should unpack the syndrome. Lancet Respir Med. 2017; 5:9–10 12. Cruces P, Gonzalez-Dambrauskas S, Quilodran J, et al.: Respiratory mechanics in infants with severe bronchiolitis on controlled mechanical ventilation. BMC Pulm Med. 2017; 17:129 13. Rochon ME, Lodygensky G, Tabone L, et al.: Continuous neurally adjusted ventilation: A feasibility study in preterm infants. Arch Dis Child Fetal Neonatal Ed. 2020; 105:640–645 14. van Leuteren RW, de Waal CG, de Jongh FH, et al.: Diaphragm activity pre and post extubation in ventilated critically ill infants and children measured with transcutaneous electromyography. Pediatr Crit Care Med. 2021; 22:950–959

留言 (0)

沒有登入
gif