To inflate the lung-ventilator unit pressure is required to both overcome the resistance in the tube that opposes gas flow and to distend the balloon where:
- Pressure required to overcome the resistance in the tube is determined by the flow down the tube and the resistance to flow
PRES = Flow x Resistance
- Pressure required to distend the balloon (alveolar inflation pressure) is determined by the volume of gas passing into the balloon and the compliance of the balloon
PELAST = Volume/Compliance
- Therefore, the total pressure required to inflate the balloon is:
PTOT = PRES + PELAST
= (Flow x Resistance) + (Volume/Compliance)
PAWis the pressure measured by the ventilator and is due to the sum of all pressures within the respiratory unit
Includes both the pressure required to inflate the alveoli and the baseline pressure in the balloon
Baseline pressure = PEEP
PAW = PRES + PELAST + PEEP
PAW = (Flow x Resistance) + (Volume/Compliance) + PEEP
