Predict Transpulmonary Pressure Through ZAM

Stable patient with ARF spontaneously breathing light sedation (not too awake but with stable breathing pattern) and EAdi >8 uV. Four modes of mechanical ventilation were performed under different support level for the measuring of EAdi, air way pressure and other parameters.

Mode NAVA spontaneous breathing select a NAVA level that gives peak pressure about 9-10 cm H2O assist keep NAVA level for 15 minutes, do ZAM breaths every 3 minutes (make sure not to disturb the patient). Insp Hold after every ZAM. Increase NAVA level by 50% and repeat the protocol when patient's breathing has stabilized (only one increase).Do ZAM breaths every 3 minutes (make sure not to disturb the patient). Insp Hold after every ZAMAt the end of protocol (minute 15) do one end-inspiratory hold-maneuver and one end-expiratory occlusion. Mode N- PSV spontaneous breathing :PS level of 8-10 cmH2O, keep PS level for 15 minutes, do ZAM every 3 minutes (make sure not to disturb patient). Inspiratory Hold after every ZAM。At the end of protocol (minute 15) do one end-inspiratory hold-maneuver and one end-expiratory occlusion.Increase PS by 50% and repeat protocol when patient's breathing has stabilized (only 1 increase). Do ZAM every 3 minutes (make sure not to disturb patient). Inspiratory Hold after every ZAM.At the end of protocol (minute 15) do one end-inspiratory hold-maneuver and one end-expiratory occlusion. Make record of RR, Vt, Flow, Ti during both periods. Mode VCV no spontaneous breathing：Set Vt, Ti and RR to match the breathing pattern observed during NAVA Mode PCV no spontaneous breathing-do ZAM after each PS level：Increase PSV level from 8 to 20 in steps of 1 cmH2O every 2 minutes.

st select a NAVA level that gives peak pressure about 9-10 cm H2O assist keep NAVA level for 15 minutes, do ZAM breaths every 3 minutes (make sure not to disturb the patient). Insp Hold after every ZAM nd increase NAVA level by 50% and repeat the protocol when patient's breathing has stabilized (only one increase) Do ZAM breaths every 3 minutes (make sure not to disturb the patient). Insp Hold after every ZAM

st PS level of 8-10 cmH2O, keep PS level for 15 minutes, do ZAM every 3 minutes (make sure not to disturb patient). Insp Hold after every ZAM At the end of protocol (minute 15) do one end-inspiratory hold-maneuver and one end-expiratory occlusion. nd increase PS by 50% and repeat protocol when patient's breathing has stabilized (only 1 increase). Do ZAM every 3 minutes (make sure not to disturb patient). Insp Hold after every ZAM

no spontaneous breathing Set Vt, Ti and RR to match the breathing pattern observed during NAVA. Make sure each change in "level" does not increase the pressure by more than 1 cmH2O. Mode PCV no spontaneous breathing-do ZAM after each PS level Increase PSV level from 8 to 20 in steps of 1 cmH2O every 2 minutes. Be careful at the higher pressures.

Increase PSV level from 8 to 20 in steps of 1 cmH2O every 2 minutes. Be careful at the higher pressures The idea is not to have pressures as high as 20 cmH2O, it is important to have high enough VCV & PCV flow rates so we can match the flow rates during spontaneous breathing. You might find that 15 or 16 cmH2O is enough to generate flow rates that match the "maximum" flow rate you saw during spontaneous breathing.

Inclusion Criteria: Stable patient with acute respiratory failure on invasive mechanical ventilation Can tolerate pressure support ventilation light sedation with RASS between -2 and 1 Exclusion Criteria: EAdi<8 uV contraindication for nasogastric tube insertion neuromuscular disease affecting spontaneous breathing lack of informed consent, and patients included in other intervention study