Category: Critical Care
Keywords: PEEP, Driving Pressure, Ventilator Management, ARDS (PubMed Search)
As the debate regarding the pathophysiology and ventilator mechanics of COVID pneumonia rages on, it is important to have a method to evaluate the distensibility of patients' lungs so that we can minimize lung injury. It has been well shown that both under- and over-distention lead to acute lung injury and inducing or worsening ARDS.
One method to find the "best" level of PEEP is through the PEEP titration test (also called a Driving Pressure titration test). High Driving Pressure (DP), which is equal to Plateau Pressure - PEEP, has been shown to be associated with lung injury, and the minimal DP obtainable for a given patient while still meeting ventilatory goals is often an objective in the ICU (common DP goal is < 15 cm H2O). A PEEP titration is optimally done on paralyzed patients, although it can be used on sedated or very calm patients as a "best guess" approximation. It will not work well on agitated patients or those participating heavily in their ventilation. Be sure not to do this if you are not authorized to make vent changes, and always make sure to coordinate appropriately with your RT.
To perform a PEEP titration:
*Consider placing the patient on square waveform VC, as this will also allow evaluation of stress index (if patient is not participating). This can be skipped if not evaluating stress index
1) Make a table for yourself on a piece of paper where you can record PEEP, Plateau Pressure, Driving Pressure, Blood Pressure, and SpO2.
2) Write down the initial PEEP, BP, and SpO2. Clearly document for yourself that this is the initial PEEP, so you do not inadvertantly leave the vent on different settings at the end. Perform an inspiratory hold to measure a plateau pressure. Fill in DP by using the equation DP = Pplat - PEEP
3) Change the PEEP. You can either increase or decrease. If you have a suspicion that the patient is over or under distended, go towards optimal distention, but if unsure it is ok to guess. Usually we go by increments of 2 cm H2O. Wait about 20-30 seconds on the new PEEP.
4) Measure a new plateau pressure and calculate a new DP. At each step, write down the BP and SpO2 as well to ensure you are not generating decreased cardiac preload or derecruitment/hypoxia (keep in mind that due to pulse ox lag, you may not see hypoxia for up to a few minutes).
5) Repeat at a few different PEEP levels. Typically in more unstable patients who may not tolerate aggressive vent changes you may only want to check 2-3 levels of PEEP. In more stable patients or if concern for ongoing lung injury is high, you might check up to 5-6 different levels of PEEP. Please note that some COVID ARDS patients are so unstable that they will not tolerate any derecruitment, and this manuever should not be used in those patients as they could desaturate during the titration.
Once you have all of your data, consider changing to whichever PEEP level gives the lowest driving pressure. Keep in mind that while data from a PEEP titration can be very useful, it is only one data point and should be considered in combination with blood pressure, volume status, CXR findings, habitus, FiO2 weaning, and other factors. PEEP titrations should be reperformed periodically (usually daily in most semi-stable ICU patients, more often in unstable patients). it is also recommended to write a note in the chart with your initial vent settings, data from the titration, and settings upon termination of the titration -- and call your RT if you changed the vent settings.
Bottom Line: PEEP titration (aka Driving Pressure titration) aims to identify the PEEP level where (PPlat - PEEP) is minimal and may help reduce risk of ongoing lung injury in ventilated patients.