Hypercapnia usually makes clinicians uncomfortable.
That discomfort is understandable. Carbon dioxide affects pH, pulmonary vascular tone, mental status, and cardiovascular physiology.
But in ARDS, trying too aggressively to normalize PaCO2 can injure the lung.
The injured ARDS lung is small and heterogeneous. Some regions are collapsed, some are flooded, some are recruitable, and some are already overdistended.
When tidal volume or respiratory rate is increased to eliminate CO2, the cost may be higher airway pressure, higher driving pressure, greater mechanical power, and more ventilator-induced lung injury.