title: Distribution of ventilation and perfusion with different modes of mechanical ventilation.
abstract: We compared pulmonary gas exchange during synchronized intermittent mandatory ventilation (SIMV), pressure support ventilation (PSV), and airway pressure release ventilation (APRV). Nine subjects aged 56 to 75 yr were studied from 4 to 19 h after cardiac operations. When subjects were ready to be weaned from mechanical ventilation their ventilation-perfusion distribution was estimated using the multiple inert gas elimination technique during SIMV. The subjects then received PSV and APRV during alternating periods on a randomized basis, and the gas-exchange measurements were repeated. Vasoactive infusions and inspired oxygen fraction were held constant throughout the investigation. The results indicated that the major characteristics of the main mode of the VA/Q distributions (mean, standard deviation, and skew) were similar during all three modes. Dead space was lower during APRV (30.1 +/- 1.7% [SEM]) than during SIMV (36.2 +/- 1.5%) and PSV (37.1 +/- 2.7%) (p less than 0.05). Right-to-left shunt was significantly greater during APRV (19.9 +/- 2.3%) than during SIMV (15.4 +/- 1.7%) (p less than 0.05). Peak airway pressure (Paw) was higher during SIMV (32.8 +/- 1.3 cm H2O) than both PSV (19.4 +/- 2.1 cm H2O) and APRV (14.3 +/- 1.0 cm H2O) (p less than 0.05). Minute ventilation was lower during APRV (7.5 +/- 0.07 L/min) than during SIMV (9.4 +/- 0.6 L/min) and PSV (9.0 +/- 0.5 L/min) (p less than 0.05). Hemodynamic variables were similar during all three modes. We conclude that all three modes provide acceptable oxygenation and ventilatory support.
authors.affiliation: Department of Anesthesiology, University of South Florida College of Medicine, Tampa 33612.
authors.forename: D D
authors.initials: DD
authors.lastname: Valentine
authors.forename: M D
authors.initials: MD
authors.lastname: Hammond
authors.forename: J B
authors.initials: JB
authors.lastname: Downs
authors.forename: N J
authors.initials: NJ
authors.lastname: Sears
authors.forename: W R
authors.initials: WR
authors.lastname: Sims
mesh_terms: D000368:Aged; D006348:Cardiac Surgical Procedures; D006439:Hemodynamics; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008875:Middle Aged; D011184:Postoperative Period; D011312:Pressure; D012119:Respiration; D012121:Respiration, Artificial; D014692:Ventilation-Perfusion Ratio