Elevated Diaphragmatic Tonic Activity in PICU Patients: Age-Specific Definitions, Prevalence, and Associations*

Abstract

OBJECTIVES: Tonic diaphragmatic activity (tonic Edi, i.e., sustained diaphragm activation throughout expiration) reflects diaphragmatic effort to defend end-expiratory lung volumes. Detection of such elevated tonic Edi may be useful in identifying patients who need increased positive end-expiratory pressure. We aimed to: 1) identify age-specific definitions for elevated tonic Edi in ventilated PICU patients and 2) describe the prevalence and factors associated with sustained episodes of high tonic Edi. DESIGN: Retrospective study using a high-resolution database. SETTING: Single-center tertiary PICU. PATIENTS: Four hundred thirty-one children admitted between 2015 and 2020 with continuous Edi monitoring. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We characterized our definition of tonic Edi using data from the recovery phase of respiratory illness (i.e., final 3 hr of Edi monitoring, excluding patients with significant persistent disease or with diaphragm pathology). High tonic Edi was defined as population data exceeding the 97.5th percentile, which for infants younger than 1 year was greater than 3.2 μV and for older children as greater than 1.9 μV. These thresholds were then used to identify patients with episodes of sustained elevated tonic Edi in the first 48 hours of ventilation (acute phase). Overall, 62 of 200 (31%) of intubated patients and 138 of 222 (62%) of patients on noninvasive ventilation (NIV) had at least one episode of high tonic Edi. These episodes were independently associated with the diagnosis of bronchiolitis (intubated patients: adjusted odds [aOR], 2.79 [95% CI, 1.12–7.11]); NIV patients: aOR, 2.71 [1.24–6.0]). There was also an association with tachypnea and, in NIV patients, more severe hypoxemia. CONCLUSIONS: Our proposed definition of elevated tonic Edi quantifies abnormal diaphragmatic activity during expiration. Such a definition may help clinicians to identify those patients using abnormal effort to defend end-expiratory lung volume. In our experience, high tonic Edi episodes are frequent, especially during NIV and in patients with bronchiolitis.

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

“…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 Edi tonic in infants (0-1 yr) was significantly higher as compared to older children (> 1 yr) (3.2 vs 1.9 µV) (9).…”

“…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.…”

“…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 Edi tonic 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.…”

“…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 Edi tonic 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 Edi tonic represent patients who signal their need for increased EELV and would thus benefit from increasing PEEP?…”

Editor’s Choice Articles for June

“…Plante V, Poirier C, Guay H, et al: Elevated Diaphragmatic Tonic Activity in PICU Patients: Age-Specific Definitions, Prevalence, and Association (14).…”