2002 OPEN FORUM Abstracts
LUNG INJURY TYPE DETERMINES THE LUNG VOLUME-OXYGENATION RELATIONSHIP.
Alexander Adams MPH, RRT, Dana Simonson BS, Sungchul Lim MD, John Hotchkiss MD, David Dries MD, John Marini MD. Regions Hospital/Univ of MN, St. Paul, MN.
Background: A direct, but not necessarily linear, relationship is assumed to exist between mean lung volume and oxygenation. This study investigated the relationship between lung volume and oxygenation in three porcine models of acute lung injury.
Methods: In deeply anesthetized pigs, acute lung injury was induced by either: 1) Oleic acid-induced injury (OAI) - OA was infused via pulmonary artery over 90 min (0.1-0.2ml/kg) 2) Ventilator-induced lung injury (VILI) ? pressure control ventilation was set to an inspiratory Ptp of 35 cmH2O over 6 hours on FIO2 = 0.60, 3) Pneumonia - Instillation of Streptococcus pneumoniae inoculum via bronchoscope to lower lobes of both lungs and pneumonia was allowed to develop over 6 hours. Injury was established when PaO2/FIO2 = 80-140 mmHg, After stabilization of each injury model, a pressure generated (PEEP increased in 3 cmH2O steps from PEEP of 3 to 27 cmH2O) volume -oxygenation curve was constructed. Lung volume was recorded by respiratory inductive plethysmography as oxygenation was monitored continuously by an indwelling ABG analysis catheter system. During the protocol, ventilation was set to minimize lung excursion (f=30, VT =150 mL).
Results: For the OAI and PNM models, PaO2 increased with increasing lung volume in a concave relationship. In PNM, PaO2 decreased after a certain threshold. The relationship was concave for the VILI model.
Conclusions: The three models displayed differences in their oxygenation response to increasing lung volume - as increased by incrementing PEEP. The results suggest that different pathophysiological factors determine the oxygenation-lung volume relationship and that ventilatory strategy must be customized to treat the prevalent lung injury. AHA SDG 9930184N;NIH SCOR 50152.