Inspiratory muscle unloading by neurally adjusted ventilatory assist during maximal inspiratory efforts in healthy subjects.
BACKGROUND
Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation in which the ventilator is controlled by the electrical activity of the diaphragm (EAdi). During maximal inspirations, the pressure delivered can theoretically reach extreme levels that may cause harm to the lungs. The aims of this study were to evaluate whether NAVA could efficiently unload the respiratory muscles during maximal inspiratory efforts, and if a high level of NAVA would suppress EAdi without increasing lung-distending pressures.


METHODS
In awake healthy subjects (n = 9), NAVA was applied at increasing levels in a stepwise fashion during quiet breathing and maximal inspirations. EAdi and airway pressure (Paw), esophageal pressure (Pes), and gastric pressure, flow, and volume were measured.


RESULTS
During maximal inspirations with a high NAVA level, peak Paw was 37.1 +/- 11.0 cm H(2)O (mean +/- SD). This reduced Pes deflections from - 14.2 +/- 2.7 to 2.3 +/- 2.3 cm H(2)O (p < 0.001) and EAdi to 43 +/- 7% (p < 0.001), compared to maximal inspirations with no assist. At high NAVA levels, inspiratory capacity showed a modest increase of 11 +/- 11% (p = 0.024).


CONCLUSIONS
In healthy subjects, NAVA can safely and efficiently unload the respiratory muscles during maximal inspiratory maneuvers, without failing to cycle-off ventilatory assist and without causing excessive lung distention. Despite maximal unloading of the diaphragm at high levels of NAVA, EAdi is still present and able to control the ventilator.
Sinderby
Christer
C
Department of Critical Care Medicine, St. Michael's Hospital, Department of Medicine, University of Toronto, Toronto, ON, Canada. Electronic address: sinderby@rogers.com.
Beck
Jennifer
J
Department of Newborn and Developmental Pediatrics, Sunnybrook Health Sciences Centre, Department of Pediatrics, University of Toronto, Toronto, ON, Canada.
Spahija
Jadranka
J
Sacré-Coeur Hospital Research Center, Department of Medicine, University of Montreal, Montreal, QC, Canada.
de Marchie
Michel
M
Sir Mortimer B. Davis Jewish General Hospital, McGill University, Montreal, QC, Canada.
Lacroix
Jacques
J
Pediatric Intensive Care Unit, Department of Pediatrics, Hôpital Sainte-Justine Research Center, Université de Montréal, Montreal, QC, Canada.
Navalesi
Paolo
P
Pulmonary Rehabilitation and Respiratory Intensive Care Unit, Fondazione S. Maugeri, Pavia, Italy.
Slutsky
Arthur S
AS
Department of Critical Care Medicine, St. Michael's Hospital, Department of Medicine, University of Toronto, Toronto, ON, Canada.
D000328:Adult; D003964:Diaphragm / Q000503:physiopathology*; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D008451:Maximal Voluntary Ventilation / Q000502:physiology*; D011175:Positive-Pressure Respiration / Q000295:instrumentation*; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000503:physiopathology*; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D012984:Software; D013813:Therapy, Computer-Assisted / Q000295:instrumentation*; D014939:Work of Breathing / Q000502:physiology*