Figure 1

Continuous recording of ventilatory parameters for 24 hours (case 1). Figure demonstrates in the first patient the 24-hour evolution of FiO2 (Panel A), expiratory tidal volume (Panel B), mean airway pressure (Panel C), peak inspiratory pressure (Panel D), respiratory rate (Panel E) and Edi max (Panel F). The upward vertical arrows indicate the time point where the ventilator mode was switched from SIMV over to NAVA. (A first brief NAVA period was tested at 14:00). Upper panels: After starting NAVA, (A) FiO₂ gradually decreased to 21% in 12 hours, and (B) tidal volume became much more variable from one cycle to another. Middle panels: One of the most remarkable changes observed with switching to the NAVA mode was the immediate reduction in the mean airway pressure (C) and in the peak airway pressure (D) which decreased from 30 to 10 cm H₂O. Bottom panels: After starting NAVA, the respiratory rate became very variable over time (E). From a mandatory frequency set at 30 breaths per minute, respiratory rate increased to 40 and 60 breaths per minute. Clinically, the breathing became easier with harmonious chest movements. (F) Edi max that it is the sum of inspiratory Edi and Edi min corresponds to the peak of electrical activity of the diaphragm. In SIMV, this activity is depressed, and in NAVA, the inspiratory Edi (Edi max - Edi min) drives ventilation. Abbreviations: FiO₂, fraction of inspired oxygen; Edi, electrical activity of the diaphragm; SIMV, synchronized intermittent mandatory ventilation.