Respiratory changes during prolonged increased intra-abdominal pressure in pigs

Background: Increased intra-abdominal pressure (IAP) elevates thoracic pressure and airway pressures and reduces lung compliance in humans and laboratory animals. We studied respiratory alterations and arterial blood gas changes in pigs with IAP maintained at 20 mmHg or 30 mmHg for 3 h. Methods: Domestic pigs of both sexes weighing 30.0 +/- 5.1 kg (mean +/- SD) (n = 21) were divided into three groups. The animals were anesthetized and kept at 20 mmHg IAP (n = 7) or 30 mmHg IAP (n = 7) for 3 h. The third group (n = 7) served as control without an elevated IAP. We recorded respiratory alterations and changes in acid-based parameters at baseline and after 90 min and 180 min of increased IAP. Results: No significant hypoxia or hypercarbia was found in animals with an IAP of 20 mmHg IAP. At an IAP of 30 mmHg, pO(2) decreased to an average 19.6 kPa and pCO(2) increased to about 6 kPa, and the animals were slightly acidotic. Airway pressure increased significantly and lung compliance decreased in both groups of elevated IAP. Conclusion: In our porcine model, an IAP of 20 mmHg or higher for 3 h is harmful for the respiratory function of the animals due to deterioration of respiratory parameters, increased airway pressure and decreased lung compliance.