Table 2 Respiratory effects related to increased IAP

1. Effects on respiratory mechanics (Diaphragm elevation)

 Intra-thoracic pressure ↑

 • Pleural pressure ↑

 • Peak airway pressure ↑ (volume controlled)

 • Mean airway pressure ↑

 • Plateau airway pressure ↑

 Respiratory system compliance ↓

 • Chest wall compliance ↓

 • Lung compliance =

 • Lung volumes ↓ (pressure controlled)

 Functional residual capacity (FRC) ↓

 Compression atelectasis ↑

 Pulmonary vascular resistance ↑

 Lower inflection point on PV curve ↑

2. Effects on gas exchange (Reduced gas exchange)

 Hypercarbia ↑

 Oxygenation ↓

 • Dead-space ventilation ↑

 • Intra-pulmonary shunt ↑

 • Ventilation perfusion mismatch ↑

 • Alveolar oedema ↑

3. Clinical effects (Difficult weaning)

 Oxygen consumption ↑

 Metabolic cost and work of breathing ↑

4. Biological effects

 Activated lung neutrophils (experimental) ↑

 Pulmonary inflammatory infiltration (experimental) ↑