Matching positive end-expiratory pressure to intra-abdominal pressure prevents end-expiratory lung volume decline in a pig model of intra-abdominal hypertension
Objective: Intra-abdominal hypertension is common in critically ill patients and is associated with increased morbidity and mortality. In a previous experimental study, positive end-expiratory pressures of up to 15 cm H2O did not prevent end-expiratory lung volume decline caused by intra-abdominal hypertension. Therefore, we examined the effect of matching positive end-expiratory pressure to the intra-abdominal pressure on cardio-respiratory parameters.
Design: Experimental pig model of intra-abdominal hypertension.
Setting: Large animal facility, University of Western Australia.
Subjects: Nine anesthetized, nonparalyzed, and ventilated pigs (48 ± 7 kg).
Interventions: Four levels of intra-abdominal pressure (baseline, 12, 18, and 22 mm Hg) were generated in a randomized order by inflating an intra-abdominal balloon. At each level of intra-abdominal pressure, three levels of positive end-expiratory pressure were randomly applied with varying degrees of matching the corresponding intra-abdominal pressure: baseline positive end-expiratory pressure (= 5 cm H2O), moderate positive end-expiratory pressure (= half intra-abdominal pressure in cm H2O + 5 cm H2O), and high positive end-expiratory pressure (= intra-abdominal pressure in cm H2O).
Measurements: We measured end-expiratory lung volume, arterial oxygen levels, respiratory mechanics, and cardiac output 5 mins after each new intra-abdominal pressure and positive end-expiratory pressure setting.
Main Results: Intra-abdominal hypertension decreased end-expiratory lung volume and PaO2 (−49% [p < .001] and −8% [p < .05], respectively, at 22 mm Hg intra-abdominal pressure compared with baseline intra-abdominal pressure) but did not change cardiac output (p = .5). At each level of intra-abdominal pressure, moderate positive end-expiratory pressure increased end-expiratory lung volume (+119% [p < .001] at 22 mm Hg intra-abdominal pressure compared with 5 cm H2O positive end-expiratory pressure) while minimally decreasing cardiac output (−8%, p < .05). High positive end-expiratory pressure further increased end-expiratory lung volume (+233% [p < .001] at 22 mm Hg intra-abdominal pressure compared with 5 cm H2O positive end-expiratory pressure) but led to a greater decrease in cardiac output (−26%, p < .05). Neither moderate nor high positive end-expiratory pressure improved PaO2 (p = .7).
Intra-abdominal hypertension decreased end-expiratory transpulmonary pressure but did not alter end-inspiratory transpulmonary pressure. Intra-abdominal hypertension decreased total respiratory compliance through a decrease in chest wall compliance. Positive end-expiratory pressure decreased the respiratory compliance by reducing lung compliance.
Conclusions: In a pig model of intra-abdominal hypertension, positive end-expiratory pressure matched to intra-abdominal pressure led to a preservation of end-expiratory lung volume, but did not improve arterial oxygen tension and caused a reduction in cardiac output. Therefore, we do not recommend routine application of positive end-expiratory pressure matched to intra-abdominal pressure to prevent intra-abdominal pressure–induced end-expiratory lung volume decline in healthy lungs.
Regli, A., Chakera, J., De Keulenaer, B. L., Roberts, B., Noffsinger, B., et al. (2012). Matching positive end-expiratory pressure to intra-abdominal pressure prevents end-expiratory lung volume decline in a pig model of intra-abdominal hypertension. Critical Care Medicine, 40(6), 1879–1886. doi:10.1097/CCM.0b013e31824e0e80