Abstract
Inverse ratio ventilation (IRV) is commonly used in clinical practice. Several studies have used IRV in order to recruit collapsed alveoli. In a randomised trial in twelve surfactant depleted piglets, the lungs were ventilated with sufficient positive end-expiratory pressure (PEEP) to prevent end-expiratory collapse, and the effects of increased inspiration-to-expiration (I:E ratio) were evaluated. Pressure regulated ventilation (with I:E of 1:1, constant tidal volume and decelerating inspiratory flow) was used at 30 breaths per minute (bpm). I:E ratios of 1.5:1,2.3:1 and 4:1 were applied sequentially. When the I:E ratio was increased, external PEEP had to be reduced in order to keep total PEEP constant. Functional residual capacity, airway pressures, gas exchange, extra-thermal volume and hemodynamics were measured. With I:E ratios above 2:1 intrinsic PEEP was generated and with concomitant decrease in cardiac index. PaO2 was not affected, but oxygen delivery was reduced. It is concluded that I:E ratios of 2:1, or above, generate increased intrinsic PEEP with compromised hemodynamics.