Titration and implementation of neurally adjusted ventilatory assist in critically ill patients.
BACKGROUND
Neurally adjusted ventilatory assist (NAVA) delivers assist in proportion to the patient's respiratory drive as reflected by the diaphragm electrical activity (EAdi). We examined to what extent NAVA can unload inspiratory muscles, and whether unloading is sustainable when implementing a NAVA level identified as adequate (NAVAal) during a titration procedure.


METHODS
Fifteen adult, critically ill patients with a Pao(2)/fraction of inspired oxygen (Fio(2)) ratio < 300 mm Hg were studied. NAVAal was identified based on the change from a steep increase to a less steep increase in airway pressure (Paw) and tidal volume (Vt) in response to systematically increasing the NAVA level from low (NAVAlow) to high (NAVAhigh). NAVAal was implemented for 3 h.


RESULTS
At NAVAal, the median esophageal pressure time product (PTPes) and EAdi values were reduced by 47% of NAVAlow (quartiles, 16 to 69% of NAVAlow) and 18% of NAVAlow (quartiles, 15 to 26% of NAVAlow), respectively. At NAVAhigh, PTPes and EAdi values were reduced by 74% of NAVAlow (quartiles, 56 to 86% of NAVAlow) and 36% of NAVAlow (quartiles, 21 to 51% of NAVAlow; p < or = 0.005 for all). Parameters during 3 h on NAVAal were not different from parameters during titration at NAVAal, and were as follows: Vt, 5.9 mL/kg predicted body weight (PBW) [quartiles, 5.4 to 7.2 mL/kg PBW]; respiratory rate (RR), 29 breaths/min (quartiles, 22 to 33 breaths/min); mean inspiratory Paw, 16 cm H(2)O (quartiles, 13 to 20 cm H(2)O); PTPes, 45% of NAVAlow (quartiles, 28 to 57% of NAVAlow); and EAdi, 76% of NAVAlow (quartiles, 63 to 89% of NAVAlow). Pao(2)/Fio(2) ratio, Paco(2), and cardiac performance during NAVAal were unchanged, while Paw and Vt were lower, and RR was higher when compared to conventional ventilation before implementing NAVAal.


CONCLUSIONS
Systematically increasing the NAVA level reduces respiratory drive, unloads respiratory muscles, and offers a method to determine an assist level that results in sustained unloading, low Vt, and stable cardiopulmonary function when implemented for 3 h.
Brander
Lukas
L
Department of Critical Care Medicine, University Hospital-Inselspital, Bern, Switzerland.
Leong-Poi
Howard
H
Division of Cardiology, St. Michael's Hospital, Toronto, ON, Canada.
Beck
Jennifer
J
St. Michael's Hospital, Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada.
Brunet
Fabrice
F
St. Michael's Hospital, Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada.
Hutchison
Stuart J
SJ
Division of Cardiology, St. Michael's Hospital, Toronto, ON, Canada.
Slutsky
Arthur S
AS
St. Michael's Hospital, Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada.
Sinderby
Christer
C
St. Michael's Hospital, Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada. Electronic address: sinderbyc@smh.toronto.on.ca.
D000328:Adult; D000368:Aged; D000403:Airway Resistance; D016638:Critical Illness / Q000628:therapy*; D003964:Diaphragm / Q000294:innervation*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D012121:Respiration, Artificial / Q000379:methods*; D015656:Respiratory Mechanics; D013990:Tidal Volume