Reverse-thrust ventilation in hypercapnic patients with acute respiratory distress syndrome - Acute physiological effects

Techniques of tracheal gas insufflation (TGI) have been shown to enhance CO 2 clearance efficiency in mechanically ventilated patients with acute respi ratory distress syndrome (ARDS). Clinical studies have explored the effects of such techniques only at moderate intratracheal gas flow rates, with TGI superimposed to mechanical ventilation in a continuous fashion, or synchro nized to the expiratory phase of the duty cycle. We examined the effects of intratracheal pulmonary ventilation (ITPV), delivering the entire tidal vo lume (VT) in the proximity of the tracheal carina, with all the gas flow su pplied continuously through a reverse-thrust catheter (RTC). A potential li mitation in the application of TGI is dynamic hyperinflation. Therefore, in a subgroup of patients, we also evaluated the effects of ITPV on end-expir atory lung volume (EELV) by respiratory inductive plethysmography (RIP). El even patients with ARDS under volume-cycled mechanical ventilation were sub sequently switched to ITPV at the same baseline respiratory rate, I:E ratio , and VT. At the same minute volume, Pace, decreased from 70 +/- 12.3 to 59 +/- 9.5 mm Hg, with a percent reduction of 15 +/- 4% (range from 10 to 20% ). The CO, decrease was greater in patients with higher baseline Pa-CO2 lev els (Delta Pa-CO2 = 0.29 x Pa-CO2 - 9.48, r = 0.95). During transition from mechanical ventilation to ITPV, tracheal positive end-expiratory pressure (PEEP,,) decreased with a correspondent decrease in EELV. Both were restore d by increasing the PEEP at the ventilator by 3.6 +/- 2.0 cm H2O. These dat a suggest that in patients with ARDS ITPV effectively reduces dead space ve ntilation and the employment of the RTC may limit or avoid dynamic hyperinf lation.