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Peak Pressures vs Plateau Pressures

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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?

I think about the peak inspiratory pressure as the sum of the plateau pressure (pressure used to keep air in the lungs) and pressure used to overcome airway resistance to get the air into the lungs (elastic recoil of the lungs and chest wall, friction, etc.). In other words: Ppeak = Pplat + Presistance. Consequently, Pplat can never be more than Ppeak, because there’s always going to be intrinsic resistance which must be overcome by Presistance.

Pplat is determined by an inspiratory hold maneuver in which the patient is given a fixed volume of air. Ppeak is determined at the end of that inspiration. The drop-off that occurs between Ppeak and Pplat is airway resistance which was overcome during the inspiratory phase by Presistance. The pressure that remains during the hold maneuver is the Pplat and is a product of the lung tissue itself. Decreased pulmonary compliance, pulmonary edema, and interstitial lung disease can all affect this.

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). Let’s say I do an inspiratory hold maneuver, and Pplat is only 20 cm H2O. 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, the patient was biting his endotracheal tube and there’s a huge kink in the tubing coming off the ventilator.

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 alveoli or small airways. Did the patient develop a pneumothorax? Is his pneumonia evolving?

Also, it’s important to consider that once the underlying pulmonary issue begins to resolve, pressures will change. Compliance will change. Pressure/volume curves will change. Peak and plateau pressures are a crude way to assess clinical improvement (all other factors being equal).

Drop me a comment below with questions! 🙂

17 Comments

  1. Alexandra Yeates Reply

    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?

    • 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.

  2. 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?

  3. Pradhan Bhat Reply

    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?

    • 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.

      • Pradhan Bhat Reply

        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.

  4. DR.Rakesh Chintalapudi Reply

    wonderful attempt. very much useful. But approach is much useful

  5. Khalid zafar Reply

    Beautifully explained. looking forward to read more such articles. Keep up the good work.

  6. Thank you for this simple explanation.. never saw it in this way .. will pass it on to my juniors!

  7. Deniz Kızılaslan Reply

    Thanks for this. I am very happy if u will write mu email.

  8. This is awesome—I especially appreciate your ability to write in a way that’s conversational and framed in simple (read: clerkship student-friendly) terms. Thanks!

    • 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! 🙂

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