Lightning rounds 68: Setting PEEP in the obese with Olivia Serigano

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EM intensivist Olivia Serigano tells us about their recent publication in Anaesthesia Critical Care & Pain Medicine evaluating the use of two rules (BMI/3 or PEEP 10 in everyone) for setting PEEP in obese patients on the ventilator.

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Takeaway pearls

1. Many obese patient require high PEEP to oppose the extrinsic weight of their chest wall/abdomen compressing the lungs and predisposing to atelectasis. This is separate from PEEP needed to recruit areas of consolidation and shunt due to lung disease; it is their “baseline” needed to recruit their lungs in normal conditions.
2. The best way to determine this PEEP may be esophageal manometry, i.e. placing a balloon in the esophagus. Transducing here approximates the pleural pressure, allowing calculation of the transpulmonary or transpleural gradient. This should probably be about zero, i.e. the pleural pressure should be about the same as the PEEP. So an esophageal pressure of 20 cm H2O means you should set the baseline PEEP around 20.
3. Most places don’t have esophageal balloons, so it would be useful to have a practical rule for approximating this.
4. In their study (Lentz et al.), they reviewed OR cases across a range of normal and elevated BMIs, and asked whether two strategies (setting a PEEP of 10 across the board, or using the calculation of BMI/3) approximated the manometry-derived best PEEP within 5 cmH2o.
5. Setting a PEEP of 10 on all patients worked in just about a quarter of patients, especially tending to over-PEEP non-obese patients.
6. BMI/3 hit the right PEEP in about a third of cases, performing equally well across all BMI ranges, though variation existed in each group.
7. Treat these values as a floor and consider adding more PEEP to recruit disease. You might wean to this number as a floor and extubate, though it may be safest to wean at least a little lower to ensure they’ll tolerate the (potentially lower) retained volumes once they’re off positive pressures; their lung physiology may improve off the vent in some ways, but it may still take time to achieve their true baseline mechanics.
8. Pleural pressure will vary widely with positioning, which pertains to both measurement, but also clinical optimization—i.e. sitting or standing an obese patient will likely improve their recruitment on any given PEEP.