Use this respiratory calculation when pressures, gas fractions, flows, and volumes use the stated units and were measured under compatible conditions. It can reproduce a defined mechanics or gas-exchange quantity.

Tidal volume

A finite measured or assumed value greater than or equal to 0, expressed in mL.

Dead space volume

A finite measured or assumed value greater than or equal to 0, expressed in mL.

Respiratory rate

A finite measured or assumed value, expressed in breaths/min.

The implementation follows this calculation rule: Compute alveolar ventilation in litres per minute as (tidal volume - dead space) x respiratory rate / 1000.

Alveolar ventilation

The calculated alveolar ventilation in L/min.

These simplified equations do not replace pulmonary-function testing or clinical assessment. Barometric pressure, temperature, water-vapour pressure, respiratory quotient, leaks, ventilator timing, spontaneous effort, and measurement site can change the result. Preserve the input values and units so the result can be audited and recalculated.

Interpret the result with arterial or end-tidal gases, ventilator waveforms, oxygen saturation, and serial measurements as appropriate. Directly measured mechanics or gas exchange is preferable when the simplifying assumptions do not hold.

• Dynamic Compliance

  Compute dynamic respiratory compliance as tidal volume divided by peak inspiratory pressure minus PEEP.

• Static Compliance

  Compute static respiratory compliance as tidal volume divided by plateau pressure minus PEEP.

• Total Compliance

  Compute total respiratory system compliance as exhaled tidal volume divided by the driving pressure between plateau pressure and total PEEP.