369

Abstract

Introduction: The respiratory system can be viewed as three interdependent components comprised by the left hemithorax, right hemithorax, and the infra-diaphragmatic chamber. Alterations in one or more compartments with relative sparing of others can lead to monitoring challenges distinct from those encountered with symmetric pathology. Our intent was to explore the impact of intra-abdominal hypertension (IAH) on isolated lung mechanics, functional residual capacity, and gas exchange in a porcine model of unilateral atelectasis and unilateral lung injury, comparing the results with those obtained in normal and symmetrically diseased lung. Methods: This protocol was approved by our institution’s Animal Care and Use Committee. 10 Yorkshire pigs (mean weight, 46.2 ± 6.2 kg) were anesthetized and instrumented according to our protocol. High intra-abdominal pressure was created by a laparostomy tube connected to a continuous positive airway pressure circuit at 20 cm H2O. Pigs were ventilated in volume control 10 mL/kg, frequency15 breaths per minute. Unilateral atelectasis was created experimentally by using an Arndt endobronchial blocker (Cook) to occlude the left main bronchus. Unilateral lung injury was created experimentally by occluding the left main bronchus as above, and using saline to lavage the right lung. Diffuse lung injury was created experimentally by bi-lateral saline lavage. Results: Transpulmonary Pressure In unilateral lavage, IAH increased the end inspiratory transpulmonary pressure significantly relative to values for unilateral lavage at normal intra-abdominal pressure (IAP). This relationship in bilateral lavage approached significance. Functional Residual Capacity FRC values in unilateral and bilateral lavage were significantly decreased compared to normal lungs, but were similar to each other. These relationships held in the setting of IAH. Oxygenation With and without IAH, atelectasis produced a higher p:f ratio than unilateral lavage. IAH decreased paO2:FiO2 ratio in unilateral lung injury compared to normal IAP values, but had no effect in the atelectasis model. Conclusions: 1) IAH significantly reduced FRC in both asymmetric pathologies. 2) In lungs injured by saline lavage, calculated lung elastance was increased by IAH; this was statistically significant for unilateral lavage and approached significance for bilateral lavage. 3) Atelectasis and unilateral lavage, though not differentiated by FRC, did experience different paO2:FiO2 ratios with and without IAH.