Inspiratory Pressure (pInsp) in Ventilation

pInsp

Inspiratory pressure (pInsp) plays a pivotal role in ventilation by controlling ventilation of the lungs and thereby ensuring gas exchange. However, if the pInsp values are too high, peak pressures can occur that damage the lungs, which is why the precise setting of this parameter is particularly important. Find out everything you need to know about pInsp in ventilation – from its advantages and disadvantages along with guidelines for the specification of pInsp. 

Definition: What is pInsp in ventilation?

pInsp, also known as IPAP (inspiratory positive airway pressure) is the abbreviation for inspiratory pressure. It indicates the pressure that should be achieved during inspiration on mechanical ventilation. pInsp determines how much ventilation pressure is supplied to a patient with each mechanical breath.1

Inspiratory pressure is a key setting parameter in pressure-controlled ventilation and is always set higher than the positive end-expiratory pressure (PEEP). This is the pressure that is maintained during expiration. PEEP ensures that the airways remain open during exhalation. Depending on the ventilator, the pInsp is either added to the PEEP as a sum or set separately.

Using pInsp during pressure-controlled ventilation

During pressure-controlled ventilation, also known as PCV, the parameters PEEP, pInsp and pMax are set first. To initiate ventilation, the ventilator generates a positive pressure that does not exceed the preset pMax. This leads to an increase in transpulmonary pressure, which causes respiratory gas to flow into the lungs. The flow velocity of the air is high at the beginning, but then decreases – the flow is thus decelerating.2

The device supplies the patient with air until the preset pInsp is reached. The inspiratory pressure should always be set high enough to ensure adequate ventilation.3 In general, the air is delivered with a ramp of around 0.2 seconds such that the peak flow is reached with somewhat of a delay.4 Once the set pInsp for ventilation is reached, it is maintained throughout the entire inspiratory phase. 

Difference between pInsp, pAw and pMax

In ventilation technology, there are various pressure parameters that are interrelated to each other but have different meanings. The pInsp is the set ventilation pressure that should be reached during inspiration in pressure-controlled ventilation. 

By contrast, the parameter airway pressure (pAw) refers to the airway pressure measured by the ventilator.5 This provides information about the mechanics of the lungs (resistance and compliance) and can be determined during both pressure- and volume-controlled ventilation. As a ventilation parameter, the mean airway pressure (pMean) is also gaining importance given its role in influencing hemodynamics.6

pMax is the maximum set airway pressure that limits the pAw and reduces the risk of ventilator-associated lung damage such as barotrauma. This is particularly relevant as high ventilation pressures occur primarily during inspiration. If pMax is reached before pInsp has been fully applied during ventilation, the ventilator can react in 2 ways: 

  1. The patient’s inspiration is terminated prematurely.
  2. The air pressure is maintained at the limited level until the inspiration time has ended.3

In the following table, you will find an overview of the 3 parameters for comparison.

Definition

pInsp: Set inspiratory pressure

pAw: Measured airway pressure

pMax: Maximum set airway pressure

Description

pInsp: Determines the volume delivered per mechanical breath

pAw: Indicates the pressure in the airways measured by the ventilator during the ventilation cycle

pMax: Preset pressure limit that may not be exceeded in any phase of ventilation

Function

pInsp: Ensures adequate ventilation of the lungs

pAw: Provides information about the mechanics of the lungs

pMax: Avoids high air pressures and the resulting barotrauma

Standard values for pInsp

When setting the pInsp, attention must be paid to prevent lung tissue from being damaged by overdistension. At the same time, the set pInsp value must ensure that the tidal volume determined is administered reliably. The correct setting of the pInsp is therefore of great importance in ventilation. 

The pInsp value should be adapted to the patient’s age and severity of the lung disease and, as a rule, should not exceed 20–25 mbar.7 Since the pInsp is highly patient-dependent and needs to be adjusted individually, it should be checked regularly and adjusted as needed – for example during changes in positioning. Adjustment in increments of 2–3 mbar is recommended.8

Nevertheless, when setting pInsp, the tidal volume must be considered first and foremost. Based on the ideal body weight (BW), the tidal volume should be a maximum of 6 ml/kgBW. 

In addition, the pressure difference between the set PEEP and the pInsp, also known as the “driving pressure”, should not be more than 15 mbar. Maintaining this limit corresponds to the requirements of lung-preventive ventilation, in which all ventilation parameters are specifically set to protect lung tissue.9 The following guide values apply:

  • Tidal volume: 4–6 ml/kg IBW
  • FiO2: < 60 %
  • PEEP: According to PEEP table
  • Plateau pressure: < 30 mbar
  • Pressure difference between PEEP and upper pressure level: < 15 mbar

Deviation from the normal range

During ventilation, a higher pInsp setting leads to a rapid inspiratory flow such that the maximum inspiratory pressure is reached quickly. At a lower pInsp, the air is also pumped quickly, but the flow reaches a lower pMax. If the pInsp exceeds or drops below the stated standard values during ventilation, 2 consequences can result:

  1. Barotrauma: Ventilation pressures that are too high due to elevated pInsp can damage lung tissue by overdistension of alveoli and capillaries. This can lead to macrodamage such as alveolar rupture or pneumothorax.
  2. Hypoventilation: If the pInsp is too low, this can result in the patient receiving a tidal volume that is too low. Since the air exchange becomes insufficient, the paCO₂ value in the blood is elevated and CO₂ narcosis can be caused.10

Factors that are influenced by pInsp

pInsp is closely linked to various ventilation parameters and factors that are mutually interdependent. The following aspects are influenced by pInsp:

  • Minute volume: The minute volume is the volume of respiratory air exhaled in one minute.¹¹ It increases with increasing tidal volume. At a higher pInsp, more air can enter the lungs per breath, which increases the minute volume.
  • Oxygenation: A high pInsp improves oxygen uptake because a higher inspiratory pressure allows more air to flow into the lungs.
  • Ventilation: CO₂ elimination likewise depends on pInsp. If the inspiratory pressure is too low, the exchange of air is diminished and CO₂ exhalation impaired.
  • Potential lung damage: A pInsp that is too high can cause barotrauma and significantly increase the risk of ventilation-associated lung damage.

pInsp and tidal volume 

In particular, pInsp and tidal volume are closely interdependent. In pressure-controlled ventilation, pInsp controls tidal volume: A certain volume is delivered depending on resistance and respiratory system compliance. During volume-controlled ventilation, pInsp is determined in turn by the tidal volume administered and the compliance of the lungs. The higher the compliance and the greater the set tidal volume, the higher the pInsp.

The tidal volume is dependent on the pressure difference between PEEP and pInsp. At a constant pressure difference, a larger volume is delivered at lower pressure values. For example, a PEEP of 5 mbar and a pInsp of 15 mbar results in more volume than a PEEP of 20 mbar and a pInsp of 30 mbar.1

Importance of pInsp for ventilation in clinical practice

The pInsp is of great importance for ventilation in clinical practice as it ensures sufficient ventilation of the lungs. pInsp is particularly relevant in pressure-controlled ventilation because it is set directly on the ventilator – for example in the following ventilation modes: 

  • PCV ventilation: The ventilator specifies the pInsp and administers it according to the preset respiratory rate.
  • Ventilation in the aPCV mode: Assisted PCV ventilation enables the patient-controlled induction of spontaneous breaths within a specified time window. Breathing is synchronized with the patient’s own activity, which can influence the start of administration of pInsp.
  • BiLevel/BIPAP ventilation: In this mode, ventilation takes place at 2 pressure levels: pInsp and PEEP. The patient can breathe spontaneously at any time; each breath can be synchronized as required. That means that during BIPAP ventilation, the pInsp can also be induced in a patient-controlled manner.
  • CPAP ventilation: No respiratory rate is specified here, which is why this mode requires spontaneous breathing. Ventilation takes place at a continuous pressure level such that pInsp and PEEP are identical.

pInsp is therefore a key parameter for controlling respiratory support in various ventilation modes. That makes it relevant to all clinical pictures – including ARDS12 and COPD13.

Displaying pInsp during ventilation

On WEINMANN ventilators, the ventilation pressures (inspiratory pressure, pInsp, airway pressure, pAw) can be precisely monitored by displaying pressure and flow curves. The set pInsp is indicated on a real-time display and the pAw is visualized by a graphical representation of the ventilation curve. That way, the ventilator enables precise control of the airway pressure values while supporting safe use for patients.

1 Lang, H. (2017): Außerklinische Beatmung. Berlin Heidelberg: Springer Verlag, p. 123–125

2 Larsen R, Ziegenfuß T (2013). Beatmung. 5th Edition, Berlin-Heidelberg: Springer-Verlag, p. 205.

3 Lang, H. (2017): Außerklinische Beatmung, Berlin Heidelberg: Springer Verlag, p. 129.

4 https://www.thieme.de/statics/dokumente/thieme/final/de/dokumente/sonderseiten/covid_19_kurzinfo_beatmungsparameter.pdf

5 https://www.thieme-connect.de/products/ebooks/lookinside/10.1055/b-0040-178949

6 https://www.sciencedirect.com/science/article/pii/S2667100X21000116

3 Lang, H. (2017): Außerklinische Beatmung, Berlin Heidelberg: Springer Verlag, p. 129.

7 https://www.thieme-connect.de/products/ebooks/lookinside/10.1055/b-0034-22916#

8 Lang, H. (2017): Außerklinische Beatmung. Berlin Heidelberg: Springer Verlag, p. 123.

9 Lang, H. (2020): Beatmung für Einsteiger. Berlin Heidelberg: Springer Verlag, p. 100f.

10 Lang, H. (2017): Außerklinische Beatmung. Berlin Heidelberg: Springer Verlag, p. 226, 256, 301.

11 https://flexikon.doccheck.com/de/Atemzeitvolumen

1 Lang, H. (2017): Außerklinische Beatmung. Berlin Heidelberg: Springer Verlag, p. 123–125.

12 https://www.weinmann-emergency.com/de/themen/notfallbeatmung/bipap

13 https://link.springer.com/content/pdf/10.1007/s00740-013-0077-8.pdf