Severity scale: SOFA, SAPSII, APACHE II In our study, there were 13 patients who failed at weaning the NAVA machine, at SOFA> 4 cutoff point 9 times higher risk of failure with p <0.05; SAPS II score> 33.5 had 6.19 times higher risk of failure with p <0.05; APACHE II cut-off score> 14.5 had 5.5 times higher risk of failure with p <0.05 4.3.2.