Which statement about permissive hypercapnia in ARDS management is true?

• A. Tromethamine (THAM) may be used to keep the pH above 7.2.
• B. Bicarbonate infusion is required to correct acidosis.
• C. Permissive hypercapnia requires PaCO2 below 40 mmHg.
• D. pH should be maintained above 7.4 with aggressive ventilation.

Answer: (A)

Permissive hypercapnia in ARDS management means letting PaCO2 rise and pH fall to protect the lungs from ventilator-induced injury, typically by using lower tidal volumes and careful pressures. When the acidity becomes a concern, buffering can be considered. Tromethamine (THAM) acts as a base that buffers acid without creating extra CO2, helping keep the pH above a threshold such as 7.2 even as CO2 remains elevated. That makes THAM a viable adjunct in situations where acidosis would be problematic. Bicarbonate infusion isn’t routinely required and can worsen hypercapnia by generating more CO2. The goal isn’t to force PaCO2 below normal or to keep pH above 7.4 with aggressive ventilation; that would counter the permissive approach and risk lung injury.