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) ↑