Permissive hypercapnia is a controlled increase in carbon dioxide (CO2) levels in the blood, often intentionally allowed during mechanical ventilation to reduce lung injury and improve oxygenation in patients with acute respiratory distress syndrome (ARDS). This approach is clinically relevant as it balances the need for adequate ventilation with the risks of barotrauma and volutrauma. A key association is its use in lung-protective ventilation strategies, which can enhance patient outcomes.