Tonic diaphragmatic activity in critically ill children with and without ventilatory support.
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.
Pediatric Intensive Care Unit, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.
Alexandrine
A
Larouche
Pediatric Intensive Care Unit, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.
Erika
E
Massicotte
Pediatric Intensive Care Unit, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.
Gabrielle
G
Constantin
Pediatric Intensive Care Unit, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.
Laurence
L
Ducharme-Crevier
Pediatric Intensive Care Unit, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.|Pediatric Intensive Care Unit, CHU Kremlin Bicêtre, Université Paris Sud, Le Kremlin Bicêtre, France.
Sandrine
S
Essouri
Keenan Research Centre for Biomedical Science and Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, Canada.|Department of Medicine and Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Ontario, Canada.
Christer
C
Sinderby
Keenan Research Centre for Biomedical Science and Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, Canada.|Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada.
Jennifer
J
Beck
Pediatric Intensive Care Unit, CHU Sainte-Justine, Université de Montréal, Montreal, Quebec, Canada.
Guillaume
G
Emeriaud
D000367:Age Factors; D060666:Airway Extubation; D001988:Bronchiolitis / Q000503:physiopathology; D002675:Child, Preschool; D016638:Critical Illness; D003964:Diaphragm / Q000503:physiopathology*; D055724:Electrophysiological Phenomena; D045853:Exhalation / Q000502:physiology; D005260:Female; D006801:Humans; D007223:Infant; D015278:Intensive Care Units, Pediatric; D008297:Male; D011446:Prospective Studies; D012121:Respiration, Artificial
diaphragm function; end expiratory lung volume; expiration; mechanical ventilation; pediatric intensive care unit; positive end expiratory pressure