Thread by @IM_Crit_

ICU (evolving) stories: A young patient was admitted with "aspiration pneumonia" a few days ago. On mechanical ventilation. Afebrile. Negative cultures. CXR when you first see him (ET tube a bit deep, by the way):

You take a look at the ventilator screen. Patient on assist/volume control, 25 breaths, Vt 300 cc, FiO2 80%, PEEP 5.

U are a strong believer of guideline-directed medical therapies (GDMT). U know that following the PEEP table - as used in the ARDSnet study (NEJM 2004; 351(4): 327-36.
doi: 10.1056/NEJMoa032193) - is a well-tested way to set PEEP. For FiO2 of 80%, the recommended PEEP is:

The ARDSnet/ALVEOLI study had a "low" and a "high" PEEP group (with similar outcomes; rates of death before hospital discharge were 24.9% and 27.5%, respectively; P=0.48):

So, now what PEEP would you choose?

It's a good idea to gather some information about the lung mechanics, especially in really sick ARDS patients. You don't have to be very fancy. A plateau pressure is important to be checked. Let's try at the set PEEP level of 5:

Plateau is 45 at PEEP of 5... Increasing PEEP to even 8 was bringing the Ppl > 50. What happens if the PEEP level is decreased to < 5? I know, you think it's crazy for a bad ARDS to be ventilated with a PEEP of 3, right?

A PEEP level decrease of 2 points was leading to decrease of Ppl of 8 points (from 45 to 37). Overdistention, maybe? Still terrible plateau & driving pressure (> 30... 🤦‍♂️). Did I mention that patient was already prone/paralyzed & had normal intra-abd pressure? Very tough case...

Take-home message:
Patients do not read textbooks and guidelines. And even if they read them, they do whatever they like... Blind application of guidelines and algorithms is ill-advised...

@msiuba has a nice discussion about setting PEEP.

Thanks for reading!

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