Mean airway pressure explained

Mean airway pressure typically refers to the mean pressure applied during positive-pressure mechanical ventilation. Mean airway pressure correlates with alveolar ventilation, arterial oxygenation,^[1] hemodynamic performance, and barotrauma.^[2] It can also match the alveolar pressure if there is no difference between inspiratory and expiratory resistance.^[3]

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:

\bar{P} _{aw} =0 . 5 x (PIP - PEEP) x (T _{I/T} _{tot} ) + PEEP

where:

\bar{P} _{aw} = mean airway pressurePIP = peak inspiratory pressurePEEP = peak end expiratory pressureT _{I} = inspiratory timeT _{tot} = cycle time

Pressure control ventilation

During pressure control ventilation this variant of the equation can be used:

\bar{P} _{aw} = (PIP - PEEP) x (T _{I/T} _{tot} ) + PEEP where:\bar{P} _{aw} = mean airway pressurePIP = peak inspiratory pressurePEEP = peak end expiratory pressureT _{I} = inspiratory timeT _{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:

\bar{P} _{aw} = ((P _{high} x T _{high} ) + (P _{low} x T _{low} ))/(T _{high} + T _{low})

where:

\bar{P} _{aw} = mean airway pressure{P} _{high} = peak inspiratory pressure (PIP){P} _{low} = peak end expiratory pressure{T} _{high} = time spent at {P} _{high} {T} _{low} = time spent at {P} _{low} ^[4]

Other equations

M _{PAW} = (f x T _{i})/(60) x (P _{IP} - PEEP) + PEEP M _{PAW} = (F _{1})/(F _{1+F} _{E}) x P _{IP} + \left( 1 - (F _{1})/(F _{1+F} _{E}) \right) x PEEP M _{PAW} = ((R)(T _{i)(P} _{I)+[60-(R)(T} _{i)](PEEP)})/(60) M _{PAW} = (f x T _{i})/(60) x (P _{IP} - PEEP) + PEEP ^[5] M _{PAW} = ((T _{i} x P _{IP} ) + (T _{e} x PEEP))/(T _{i+T} _{e})

Clinical significance

Mean airway pressure has been shown to have a similar correlation as plateau pressure to mortality.^[6]

MAP is closely associated with mean alveolar pressure and shows the stresses exerted on the lung parenchyma on mechanical ventilation.^[7]

In high frequency oscillatory ventilation, it has been suggested to set the mean airway pressure six above the lower inflection point on the lungs P-V curve.^[8]

See also

• Ventilators
• Mechanical ventilation
• Modes of ventilation
• Mean systemic pressure

References

1. Stewart AR, Finer NN, Peters KL . Effects of alterations of inspiratory and expiratory pressures and inspiratory/expiratory ratios on mean airway pressure, blood gases, and intracranial pressure. . Pediatrics . 1981 . 67 . 4 . 474–81 . 10.1542/peds.67.4.474 . 6789294 . 2214900 .
2. Marini JJ, Ravenscraft SA . Mean airway pressure: physiologic determinants and clinical importance--Part 2: Clinical implications. . Crit Care Med . 1992 . 20 . 11 . 1604–16 . 1424706 . 10.1097/00003246-199211000-00020. 42496727 .
3. Hess . Dean . October 21, 2014 . Respiratory Mechanics in Mechanically Ventilated Patients . Respiratory Care . 59 . 11 . 1773–1794 . 10.4187/respcare.03410. 25336536 . 5706765 .
4. Daoud . Ehab G. . 2007 . Airway pressure release ventilation . Annals of Thoracic Medicine . 2 . 4 . 176–179 . 10.4103/1817-1737.36556 . 1817-1737 . 2732103 . 19727373 . free .
5. Book: David W. Chang. Respiratory care calculations. 30 March 2012. 1999. Cengage Learning. 978-0-7668-0517-0. 251–.
6. Sahetya . Sarina . Wu . David . Brooks . Morgan . May 2020 . Mean Airway Pressure As a Predictor of 90-Day Mortality in Mechanically Ventilated Patients . Critical Care Medicine . 48 . 5 . 688–695 . 10.1097/CCM.0000000000004268. 32079893 . 8273919 .
7. Su . Longxiang . Pan . Pan . Liu . Dawei . Long . Yun . 2021-10-01 . Mean airway pressure has the potential to become the core pressure indicator of mechanical ventilation: Raising to the front from behind the clinical scenes . Journal of Intensive Medicine . en . 1 . 2 . 96–98 . 10.1016/j.jointm.2021.04.002 . 36788801 . 9923962 . 236575021 . 2667-100X. free .
8. Goddon . Sven . Fujino . Yuji . Hromi . Jonathan M. . Kacmarek . Robert M. . May 2001 . Optimal Mean Airway Pressure during High-frequency Oscillation: Predicted by the Pressure–Volume Curve . Anesthesiology . 94 . 5 . 862–869 . 10.1097/00000542-200105000-00026 . 11388539 . 9604584 . 0003-3022. free .