Effects of Secretion Removal in Ventilated Patients

Acute Respiratory Failure

In this study the investigators will assess the effects of secretion removal on noninvasive respiratory mechanics, in deeply sedated mechanically ventilated patients All the mechanically ventilated patients will be submitted to the recording of compliance and resistance at baseline (time0), immediately after the application of 10 cycles alternating 30 cmH20 during expiration and -30 cmH20 during exhalation (time1). Afterward the patients will undergo an additional trail using the so called percussion technique, to assess any synergic effect of this procedure (time2)

In this observational study, the investigators will assess the effects of two secretion removal techniques on passive respiratory mechanics, in patients undergoing invasive mechanical ventilation. Consecutive patients will undergo 3 sequential assessments at time0 (baseline), at time1 after the application of of 10 cycles alternating 30 cmH20 during expiration and -30 cmH20 during exhalation and finally after a 20 sec application of a percussion technique. Protocol: The patients will be ventilated without PEEP and sedated with a benzodiazepine infusion to produce complete relaxation and adaptation to the ventilator, as assessed by the complete absence of spontaneous efforts, so that there was no change in inspiratory flow rate, tidal volume, or respiratory rate during the three measurement periods. Airway pressure (Paw) and flow (V) will be measured continuously throughout the respiratory cycle with the transducer and expiratory tidal volume will obtained by electrical integration of the flow signal. Arterial blood gas specimens will be withdrawn from the radial artery and analyzed with a blood gas analyzer The patients will be studied in the semi recumbent position. After baseline measurements of respiratory mechanics will recorded under control conditions. Direct measurement of PEEPi will be obtained using the following method: After several breaths under controlled mechanical ventilation, and with the patient relaxed, the airway opening is occluded at the end of a tidal expiration, using the end-expiratory hold button incorporated in the ventilator. The occlusion will be then released for the mechanical lung inflation, and after a few breaths the airway opening will be again occluded at the end of the inflation, using the end-inspiratory hold button of the ventilator. The static compliance of the total respiratory system (Cst rs) will be corrected for the compliance of the ventilator tubing and the gas compression (0.8 ml/cm H20 2). The end-inspiratory occlusion technique also allows determination of the inspiratory resistive properties of the respiratory system, named R,rs min and R,rsmax, that means the minimal respiratory resistances (those due mainly to the airways) and maximal respiratory resistances (those mainly due to stress relaxation and Pendelluft)

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