title: Effect of inverse I:E ratio ventilation on pulmonary gas exchange in acute respiratory distress syndrome.
abstract: BACKGROUND
  It is not known whether inverse I:E ratio ventilation (IRV) offers any real benefit over conventional mechanical ventilation with positive end-expiratory pressure (CMV-PEEP) at similar levels of end-expiratory pressure.
  
  
  METHODS
  The effects of volume-controlled and pressure-controlled IRV (VC-IRV and PC-IRV, respectively) on VA/Q inequality were compared with those of CMV-PEEP at a similar level of end-expiratory pressure and with CMV without PEEP (CMV) in eight patients in the early stages of acute respiratory distress syndrome (ARDS). Respiratory blood gases, inert gases, lung mechanics, and hemodynamics were measured 30 min after the onset of each ventilatory mode.
  
  
  RESULTS
  Recruitment of nonventilated, poorly ventilated (or both) but well-perfused alveoli increased the partial pressure of oxygen (PaO2) during CMV-PEEP (+13 mmHg) and IRV-VC (+10 mmHg; P < 0.05) compared with CMV. In contrast, PC-IRV did not affect PaO2 but caused a decrease in PaCO2 (-7 mmHg; P < 0.05). The latter was due to a concomitant decrease in dead space (P < 0.01) and shift to the right of VA/Q distributions. During PC-IRV, the increase in the mean of blood flow distribution (mean Q; P < 0.01) without a change in the dispersion (log SD Q) did not result in an increase in PaO2, probably because it reflected redistribution of blood flow within well-ventilated areas.
  
  
  CONCLUSIONS
  Short-term PC-IRV improved carbon dioxide clearance, but the lung became less efficient as an oxygen exchanger. Furthermore, based on mean airway and plateau pressures, the risk of barotrauma was not reduced with this type of ventilation.
authors.affiliation: Departament de Medicina i Unitat de Cures Intensives de Cirurgia, Hospital Clinic, Universitat de Barcelona, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Zavala
authors.forename: M
authors.initials: M
authors.lastname: Ferrer
authors.forename: G
authors.initials: G
authors.lastname: Polese
authors.forename: J R
authors.initials: JR
authors.lastname: Masclans
authors.forename: M
authors.initials: M
authors.lastname: Planas
authors.forename: J
authors.initials: J
authors.lastname: Milic-Emili
authors.forename: R
authors.initials: R
authors.lastname: Rodriguez-Roisin
authors.forename: J
authors.initials: J
authors.lastname: Roca
authors.forename: A
authors.initials: A
authors.lastname: Rossi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*