Education

Peak Pressures vs Plateau Pressures

An important aspect of understanding mechanical ventilation is knowing how to interpret peak inspiratory pressures (Ppeak) and plateau pressures (Pplat). What’s the difference, and why does it even matter?

Think of the ventilator, inspiratory limb tubing, endotracheal tube, and your patient’s airway as a long, continuous pipe with a diameter much smaller than the overall length. Poiseuille’slaw shows that the resistance (‘R’) in this “airway pipe” is directly related to the length of the pipe and indirectly related to the radius raised to the 4th power. In other words: R ~ length / radius4. For example, if the radius of the pipe is cut in half, the resistance increases by a factor of 16.

What can cause this “pipe” to be narrowed? What if the tubing leaving the ventilator is kinked? What if the patient is biting the endotracheal tube? What if the airway lumen is reduced because of bronchospasm or mucous plugs? These are all going to effectively increase airway resistance to varying degrees… but how does this affect the peak and plateau pressures?

During an inspiratory hold maneuver, a fixed volume of air is delivered into the lungs. Ppeak is determined at the end of that inspiration. This breath is then held in (ie, the patient is not allowed to exhale). During this time, the airway pressure drops down to a new level – this is the plateau pressure (Pplat). The degree of drop-off is the amount of pressure that was required to overcome resistive forces (Presistance) such as chest wall/lung elastic recoil, friction, etc. during inspiration. In other words: Ppeak = Pplat + Presistance

Now how does this translate to a real world example? Let’s say you walk into the room and see a Ppeak of 60 cm H2O (normal is 25-30 cm H2O). Pplat is only 20 cm H2O during inspiratory hold. That means there’s a huge pressure overcoming airway resistance (ie, a very high Presistance)! Now I’m thinking more about things which are decreasing the radius of the airway pipe. For example, narrowing of the endotracheal tube, mucous plugs, and circuit kinks could be causes.

What if the Ppeak was 50 cm H2O and the Pplat was 45 cm H2O? The high Pplat points towards a lung issue affecting the lung itself such as decreased pulmonary compliance, edema, pneumothorax, or evolving parenchymal disease like pneumonia or ILD.

Drop me a comment below with questions! 🙂

Related Articles

26 Comments

  1. This was wonderfully explained. I was scared when you started with physics but you did it in a great way and i feel so much more comfortable!

      1. Dr. Rishi, thank you for this concise, clear explanation of things. PIP must always be greater than plateau pressure. If something affects airway resistance alone (narrowed airway lumen), then the difference between PIP and PEEP will increase. If something affects the compliance of the alveoli alone, raising plateau pressure, does that always raise the PIP? If so, does it raise it by the same amount, assuming that airway resistance stays the same?

        Ex: PIP 30 cm H2O with P-Plateau 20 cm H2O. If we increase the P-Plateau to 25 cm H2O, does PIP increase to 35 cm H2O with it, does PIP remain at 30, or is there a different relationship?

        1. Hey Stephen, please just call me Rishi! I wouldn’t assume that changes in Pplat or Presistance occur in isolation. For example, let’s say a patient has worsening pulmonary edema. Their lung compliance will worsen (increasing Pplat) but perhaps their airway secretions may worsen as well (for the same reason) causing an increase in the PIP higher than an increase in Pplat alone would explain.

          At the end of the day, we just check peak and plateau pressures.

  2. Excellent sr… I understood.. I do critical care technology lll yr . if I have doubts , I’ll ask you sr..

  3. what is the relation of peak and plateau once the patient position is changed, like putting in prone with the patient on PCV mode of ventilation? Do they still remain the same?

  4. Hi Rishi!
    I am an anesthesiologist assistant student and I wanted to know what kinds of interventions you could perform in a ventilated patient who has high peak airway pressures? What settings could you adjust to fix this?

    1. Hey Alexandra! So first thing you want to do is rule out any “easy fixes” like mainstem intubation, mucous plugging, and possibly bronchospasm (low dose epinephrine/ketamine, deepening the anesthetic, etc.). Next, you could optimize the actual ventilator parameters by adjusting the I:E ratio (sometimes patients need more expiratory time), decreasing tidal volume a bit (and going up on respiratory rate to maintain minute ventilation), increasing PEEP (which sounds like it’ll increase overall airway pressure, but sometimes you’ll actually see a decrease in the mean airway pressure since less inspiratory pressure is required to open the alveoli each time), or changing your overall mode to something like auto flow.

  5. Is there any relationship between the duration of pause period and plateau pressure? For example, will a longer inspiratory pause period result in lower plateau pressure?

  6. Does a high respiratory rate affect obtaining a plateau pressure? For example, if I have a patient on volume control with a RR: 34 and I change the inspiratory time to 50% to perform an inspiratory hold on an anesthesia machine will I get an accurate plateau pressure?

    1. I’ve not actually done this manually on an anesthesia ventilator (it usually calculates this periodically on its own). A true inspiratory hold maneuver is just that – a transient hold. There’s no adjusting I:E ratio or anything. Most ICU ventilators will have an option to perform this maneuver, and as long as the patient doesn’t have any spontaneous inspiratory effort and there’s no circuit leak, it should be fine.

      1. Thanks Rishi! We are using many of our anesthesia machines as vents for our COVID+ patients in our makeshift ICUs, so getting a plateau pressure has been an adventure.

    1. Thanks Amol! I aim to write in simple terms so everyone, regardless of trainee level, can understand more complex concepts. Hope you’ve been well bro! 🙂

Leave a Reply

Your email address will not be published. Required fields are marked *

Check Also
Close
Back to top button