Guillaume Carteaux1, Ana Córdoba-Izquierdo, Aissam Lyazidi, Leo Heunks, Arnaud W Thille, Laurent Brochard. 1. 1Assistance Publique-Hôpitaux de Paris, CHU Henri Mondor, DHU A-TVB, Service de Réanimation Médicale, Créteil, France.2Université Paris Est Créteil, Faculté de Médecine de Créteil, Groupe de recherche clinique CARMAS, Créteil, France.3INSERM, Unité U955, IMRB, Créteil, France.4Servei de Pneumologia, Hospital Universitari de Bellvitge, L'Hospitalet de Llobregat, Barcelona, Spain.5Université Hassan 1er, Institut Supérieur des Sciences de la Santé, Laboratoire Rayonnement & Matière, Settat, Maroc.6Department of Critical Care Medicine, Radboud University Medical Center, Nijmegen, The Netherlands.7CHU de Poitiers, Réanimation Médicale, Poitiers, France.8INSERM CIC 1402, Université de Poitiers, Poitiers, France.9Keenan Research Centre, St. Michael's Hospital, Toronto, ON, Canada.10Interdepartmental Division of Critical Care, University of Toronto, Toronto, ON, Canada.
Abstract
OBJECTIVES: To understand the potential equivalence between neurally adjusted ventilatory assist and pressure support ventilation levels in terms of respiratory muscle unloading. To compare the respiratory pattern, variability, synchronization, and neuromuscular coupling within comparable ranges of assistance. DESIGN: Prospective single-center physiologic study. SETTING: A 13-bed university medical ICU. PATIENTS: Eleven patients recovering from respiratory failure. INTERVENTIONS: The following levels of assistance were consecutively applied in a random order: neurally adjusted ventilatory assist levels: 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, and 7 cm H2O/μvolt; pressure support levels: 7, 10, 15, 20, and 25 cm H2O. MEASUREMENTS AND MAIN RESULTS: Flow, airway pressure, esophageal pressures, and peak electrical activity of the diaphragm were continuously recorded. Breathing effort was calculated. To express the percentage of assist assumed by the ventilator, the total pressure including muscular and ventilator pressure was calculated. The median percentage of assist ranged from 33% (24-47%) to 82% (72-90%) between pressure support 7 and 25 cm H2O. Similar levels of unloading were observed for neurally adjusted ventilatory assist levels from 0.5 cm H2O/μvolt (46% [40-51%]) to 2.5 cm H2O/μvolt (80% [74-84%]). Tidal variability was higher during neurally adjusted ventilatory assist and ineffective efforts appeared only in pressure support. In neurally adjusted ventilatory assist, double triggering occurred sometimes when electrical activity of the diaphragm signal depicted a biphasic aspect, and an abnormal oscillatory pattern was frequently observed from 4 cm H2O/μvolt. For both modes, the relationship between peak electrical activity of the diaphragm and muscle pressure depicted a curvilinear profile. CONCLUSIONS: In patients recovering from acute respiratory failure, levels of neurally adjusted ventilatory assist between 0.5 and 2.5 cm H2O/μvolt are comparable to pressure support levels ranging from 7 to 25 cm H2O in terms of respiratory muscle unloading. Neurally adjusted ventilatory assist provides better patient-ventilator interactions but can be sometimes excessively sensitive to electrical activity of the diaphragm in terms of triggering.
OBJECTIVES: To understand the potential equivalence between neurally adjusted ventilatory assist and pressure support ventilation levels in terms of respiratory muscle unloading. To compare the respiratory pattern, variability, synchronization, and neuromuscular coupling within comparable ranges of assistance. DESIGN: Prospective single-center physiologic study. SETTING: A 13-bed university medical ICU. PATIENTS: Eleven patients recovering from respiratory failure. INTERVENTIONS: The following levels of assistance were consecutively applied in a random order: neurally adjusted ventilatory assist levels: 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, and 7 cm H2O/μvolt; pressure support levels: 7, 10, 15, 20, and 25 cm H2O. MEASUREMENTS AND MAIN RESULTS: Flow, airway pressure, esophageal pressures, and peak electrical activity of the diaphragm were continuously recorded. Breathing effort was calculated. To express the percentage of assist assumed by the ventilator, the total pressure including muscular and ventilator pressure was calculated. The median percentage of assist ranged from 33% (24-47%) to 82% (72-90%) between pressure support 7 and 25 cm H2O. Similar levels of unloading were observed for neurally adjusted ventilatory assist levels from 0.5 cm H2O/μvolt (46% [40-51%]) to 2.5 cm H2O/μvolt (80% [74-84%]). Tidal variability was higher during neurally adjusted ventilatory assist and ineffective efforts appeared only in pressure support. In neurally adjusted ventilatory assist, double triggering occurred sometimes when electrical activity of the diaphragm signal depicted a biphasic aspect, and an abnormal oscillatory pattern was frequently observed from 4 cm H2O/μvolt. For both modes, the relationship between peak electrical activity of the diaphragm and muscle pressure depicted a curvilinear profile. CONCLUSIONS: In patients recovering from acute respiratory failure, levels of neurally adjusted ventilatory assist between 0.5 and 2.5 cm H2O/μvolt are comparable to pressure support levels ranging from 7 to 25 cm H2O in terms of respiratory muscle unloading. Neurally adjusted ventilatory assist provides better patient-ventilator interactions but can be sometimes excessively sensitive to electrical activity of the diaphragm in terms of triggering.
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