Which instrument measures both peak inspiratory pressure and plateau pressure in the breathing circuit?

• A. Flowmeter
• B. Oxygen analyzer
• C. Ventilator
• D. Circuit pressure gauge

Answer: (D)

The key idea is that measuring pressures in the breathing circuit requires an instrument that directly reads the pressure inside the circuit itself. The circuit pressure gauge sits in the airway path and records the pressure as gas is delivered, giving the peak inspiratory pressure when there is flow. If you pause flow at end-inspiration, the same gauge reflects the pressure when flow is zero—the plateau pressure, which corresponds to alveolar pressure and is used to assess lung compliance. This single instrument thus provides both values needed to assess airway resistance (through PIP) and lung compliance (through plateau pressure).

Flowmeters only track gas flow, oxygen analyzers measure FiO2, and while the ventilator can display both PIP and plateau pressures, the instrument described here—the circuit pressure gauge—directly measures the pressures within the circuit itself, including during the inspiratory hold.