Mean Airway Pressure Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Dominika Śmiałek, MD, PhD candidate and Steven Wooding
Based on research by
Glenski JA, Marsh HM, Hall RT. Calculation of mean airway pressure during mechanical ventilation in neonates. Critical Care Medicine (August 1984)See 1 more source
Anesthesia UCSF, Zuckerberg San Francisco General Respiratory Therapy Pocket Reference (2020)
Last updated: Mar 01, 2023

The mean airway pressure calculator allows you to discover respiratory mechanics in the easiest way possible; follow the article below to learn about ventilator Paw, PIP normal range, and the mean airway pressure formula. 💨

We don't stop here – the Paw calculator belongs to a series of tools that facilitate the knowledge of the human respiratory system and its functions; let's enumerate a few of them! We may start with the Fev1/FVC ratio calculator (for the Tiffneau index), proceed with the PF ratio calculator (computes the PaO₂/FiO₂ ratio), and finish with the vital capacity calculator.

What is mean airway pressure?

We can describe mean airway pressure as the average pressure of inhalation and exhalation that acts on the lungs during mechanical ventilation.

Mean airway pressure is also called ventilator Paw – its values can be closely correlated to alveolar pressure, which allows the physicians to estimate potential lung trauma, and evaluate the cases' mortality and arterial oxygenation.

💡 Mean airway pressure can often be confused with MAPmean arterial pressure.

How to calculate inspiratory time?

Let's make it nice and simple:

  1. We know that the average exhalation is twice as long as the inhalation, which gives us a ratio of 2:1 (exhale:inhale). Out of every 3 seconds, exactly one is spent on inhalation.

  2. We also need to know the frequency the respiration per minute.

  3. Now, let's make good use of all this information:

    Inspiratory time (s) = (60 s / Frequency) / 3

    Inspiratory time (s) = 20 s / Frequency

How to calculate mean airway pressure?

The mechanical ventilation calculation formula for Paw (mean airway pressure) requires:

  • Inspiratory time given in seconds;
  • Total respiratory cycle time in seconds;
  • PIP in cmH₂O; and
  • PEEP in cmH₂O.

Paw = K × (Inspiratory time / Total cycle time) × (PIP - PEEP) + PEEP

K is the waveform constant that changes value according to the graphical representation of the breath delivered to the patient (the waveform).

  • Rectangular: K = 1
  • Triangular: K = 0.5
  • Sine-like K = 2/π (~0.64)

How to use the mean airway pressure calculator?

We'll make it easy in five simple steps:

  1. Choose what kind of data you'd like to base your calculation on:
    • Total respiratory cycle time; or
    • Frequency of breathing.
  2. Input the data chosen in the previous step.
  3. Enter the inspiration time.
  4. Choose PEEP.
    Positive end-expiratory pressure.
  5. Choose PIP.
    Peak inspiratory pressure
  6. And voilà – that's it! 🥂

The mean airway pressure calculation formula is presented in the paragraph above.

What is the normal mean airway pressure?

The typical, normal mean airway pressure in two-lungs ventilation usually oscillates between 10 and 15 mmHg (13.6-20.4 cmH₂O). Bear in mind that this value might be entirely different and might depend, e.g., on height and age.

High mean airway pressure may lower the cardiac index & cardiac output.


What is PEEP?

PEEP stands for the positive end-expiratory pressure. PEEP mimics the process that occurs during natural respiration. When we exhale, some air stays in our alveoli, keeping them open at all times. If we do not apply PEEP, the alveoli may collapse.

→ PEEP enables physicians to use lower oxygen concentrations and protects the lung against secondary trauma.

→ Typical range of PEEP oscillates between 4-8 cmH₂O

What is PIP normal range?

Normal range of peak inspiratory pressure (PIP) in ventilation is ~20 cmH₂O and ranges 15-25 cmH₂O in preterm neonates.

PIP measures the highest pressure working on the lungs in a respiratory cycle.

What is I time in ventilation?

I time in ventilation stands for the inspiratory time (Ti).

Its value is usually set as ~1.9s, with the respiration rate close to 12/min.

Łucja Zaborowska, MD, PhD candidate
Equation type:
Total cycle time
Total cycle time
Inspiratory time
Mean airway pressure
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