Background: Tension pneumothorax is a reported risk with pneumoperitoneum in the presence of diaphragmatic injuries. A goat model with and without diaphragmatic injury was used to determine if varying levels of intra-abdominal pressure (IAP) result in tension pneumothorax.
Methods: Twenty-four goats were divided equally into four groups: (1) 5 mm Hg IAP control, (2) 15 mm Hg IAP control, (3) 5 mm Hg IAP with diaphragmatic injury, (4) 15 mm Hg IAP with diaphragmatic injury. Chest x-ray films were made and heart rate (HR), mean arterial pressure, central venous pressure (CVP), arterial blood gases, and airway pressure (AP) were measured at 10-minute intervals up to 30 minutes. Significant changes were determined by using the one-way analysis of variance and Mann-Whitney test with alpha set at p < 0.05.
Results: In group 4, 100% (all six goats) developed radiographic evidence of tension pneumothorax by 10 minutes. Mean changes from baseline at 20 minutes for the following parameters were all significantly different from controls: HR (p < 0.05), CVP (p < 0.0001), PaO2 (p < 0.001), and AP (p < 0.004). Mortality was 67% (four of six) at 25 minutes. In group 3, 100% (all six goats) of the animals developed radiographic evidence of a simple pneumothorax without mediastinal shift. In this group, there were significant changes in PaO2 (p < 0.003), AP (p < 0.04), and HR (p < 0.05). Mortality was 16% (one of six) at 25 minutes.
Conclusion: In this goat model of diaphragmatic injury, tension pneumothorax is a significant threat when pneumoperitoneum is maintained at 15 mm Hg IAP. Pneumoperitoneum at 5 mm Hg IAP leads to simple pneumothorax with deleterious effects on oxygenation. Changes in AP, CVP, HR, and PaO2 provide early clues to the development of the problem.