Volume-controlled inverse ratio ventilation: effect on dynamic hyperinflation and auto-PEEP.

Abstract

The effects of inverse ratio ventilation (IRV) and PEEP on dynamic hyperinflation and auto-PEEP were studied in sedated, paralysed patients with adult respiratory distress syndrome (ARDS) (n = 9) and in 10 postoperative patients after coronary artery by-pass (CABG). During volume-controlled mechanical ventilation with constant tidal volume (V(T) 12 ml.kg-1) and respiratory rate (12.min-1), two consecutive experiments were carried out: (1) with constant I:E ratio PEEP was increased in steps of 2 cmH2O (0.2 kPa) from 0 to 12 cmH2O (0 to 1.2 kPa) and (2) with no PEEP I:E ratio was changed stepwise from 1:4 to 4:1. Flow, V(T), peak airway pressure (Pmax) and static end-expiratory pressure (PEEPtot) were registered. PEEPtot was measured while occluding the airway in the end-expiration. The changes in the end-expiratory lung volume (EELV) were measured with respiratory inductive plethysmograph. We found that: (1) increasing PEEP and IRV caused a similar increase in EELV and PEEPtot in ARDS, but in CABG the increase in EELV was greater with PEEP; (2) at the same PEEPtot the increase in EELV was similar with PEEP and IRV in both groups; and (3) the reduction in Pmax was marginal during IRV. We conclude that the effect of reduced expiratory time on end-expiratory lung volume and pressure during volume controlled IRV is similar to the use of PEEP.