What PS is sufficient to overcome the endotracheal tube but not contribute to ventilatory support?

• A. 4
• B. 5
• C. 6
• D. 8

Answer: (B)

The idea is to use just enough pressure support to overcome the extra work created by the endotracheal tube and circuit, without actually providing meaningful ventilatory assistance. The endotracheal tube adds a pressure drop as air flows through it, so a small amount of PS can neutralize that drop and make spontaneous breaths easier for the patient. About five centimeters of water is typically sufficient to overcome the tube’s resistance while not delivering additional tidal volume or flow that would count as ventilatory support. If you use less, the patient still has to work harder to pull air through the tube; if you use more, you’re providing real ventilatory help, which can mask fatigue and alter readiness for weaning. So a level around five cm H2O is the right balance to just overcome the tube without contributing to ventilation.