Mean airway pressure typically refers to the mean pressure applied during positive-pressure mechanical ventilation. Mean airway pressure correlates with alveolar ventilation, arterial oxygenation, hemodynamic performance, and barotrauma. It can also match the alveolar pressure if there is no difference between inspiratory and expiratory resistance.
Equations There are several equations aimed at determining the real mean airway pressure.
Volume control ventilation In ventilation with a square flow waveform this equation can be used:
P ¯ a w = 0.5 × ( P I P − P E E P ) × ( T I / T t o t ) + P E E P {\displaystyle {\bar {P}}_{aw}=0.5\times (PIP-PEEP)\times (T_{I}/T_{tot})+PEEP}
where:
P ¯ a w {\displaystyle {\bar {P}}_{aw}} = mean airway pressure
P I P {\displaystyle PIP} = peak inspiratory pressure
P E E P {\displaystyle PEEP} = peak end expiratory pressure
T I {\displaystyle T_{I}} = inspiratory time
T t o t {\displaystyle T_{tot}} = cycle time
Pressure control ventilation During pressure control ventilation this variant of the equation can be used:
P ¯ a w = ( P I P − P E E P ) × ( T I / T t o t ) + P E E P {\displaystyle {\bar {P}}_{aw}=(PIP-PEEP)\times (T_{I}/T_{tot})+PEEP}
where:
P ¯ a w {\displaystyle {\bar {P}}_{aw}} = mean airway pressure
P I P {\displaystyle PIP} = peak inspiratory pressure
P E E P {\displaystyle PEEP} = peak end expiratory pressure
T I {\displaystyle T_{I}} = inspiratory time
T t o t {\displaystyle T_{tot}} = cycle time
Airway pressure release ventilation
In airway pressure release ventilation (APRV) a variation of the previous equation must be used for the variables:
P ¯ a w = ( P h i g h × T h i g h ) + ( P l o w × T l o w ) T h i g h + T l o w {\displaystyle {\bar {P}}_{aw}={\frac {(P_{high}\times T_{high})\,+(P_{low}\times T_{low})}{T_{high}+T_{low}}}}
where:
P ¯ a w {\displaystyle {\bar {P}}_{aw}} = mean airway pressure
P h i g h {\displaystyle {P}_{high}} = peak inspiratory pressure (PIP)
P l o w {\displaystyle {P}_{low}} = peak end expiratory pressure
T h i g h {\displaystyle {T}_{high}} = time spent at P h i g h {\displaystyle {P}_{high}}
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