title: Under open lung conditions inverse ratio ventilation causes intrinsic PEEP and hemodynamic impairment.
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, extrathermal 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.
authors.affiliation: Department of Anesthesiology, University Hospital, Uppsala, Sweden.
authors.forename: A M
authors.initials: AM
authors.lastname: Markström
authors.forename: M
authors.initials: M
authors.lastname: Lichtwarck-Aschoff
authors.forename: A J
authors.initials: AJ
authors.lastname: Hedlund
authors.forename: K A
authors.initials: KA
authors.lastname: Nordgren
authors.forename: U H
authors.initials: UH
authors.lastname: Sjöstrand
mesh_terms: D000818:Animals; D006439:Hemodynamics; D008168:Lung / Q000502:physiology*; D008170:Lung Compliance; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D011312:Pressure; D011652:Pulmonary Circulation; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D012121:Respiration, Artificial; D013552:Swine
chemical_list: D010100:Oxygen