Driving pressure vs plateau pressure: which do you target in moderate ARDS?

55F with moderate ARDS (P/F ratio 142) secondary to aspiration pneumonitis. On volume-controlled ventilation: TV 320 mL (6 mL/kg PBW), PEEP 14, RR 24, FiO2 0.7. Plateau pressure 28 cmH2O, driving pressure 14 cmH2O.

She is obese (BMI 38), which complicates the mechanics. Compliance is low and I am struggling to keep TV at 6 mL/kg while maintaining adequate ventilation.

Questions:

In obese patients, should I tolerate higher plateau pressures (>30) if driving pressure remains < 15?
The Amato 2015 meta-analysis identified driving pressure as the strongest predictor of mortality. Has your practice shifted to targeting driving pressure over plateau pressure?
At what point do you escalate to prone positioning vs higher PEEP?
Role of esophageal balloon manometry in obese patients?

Excellent question. The interplay between obesity and ARDS ventilation mechanics is a nuanced topic.

1. Plateau pressure in obesity: Yes, I tolerate plateau pressures up to 33 to 35 cmH2O in obese patients if driving pressure is < 15. The reason: in obesity, a significant portion of the airway pressure is spent overcoming chest wall elastance (abdominal contents pushing up on the diaphragm). The transpulmonary pressure, which is what actually matters for lung injury, is lower than the airway pressure suggests. A patient with BMI 38 might have a chest wall elastance contributing 8 to 12 cmH2O of the measured plateau pressure.

2. Driving pressure targeting: My practice has absolutely shifted. Post-Amato 2015, driving pressure is my primary ventilator target. The data showed that each 1 cmH2O increase in driving pressure above 15 was associated with increased mortality, even when plateau pressure was "acceptable." I target driving pressure < 14 cmH2O as my primary goal, and use plateau pressure as a secondary safety check.

3. Prone positioning timing: The PROSEVA trial showed mortality benefit for P/F < 150 with PEEP ≥ 5. Your patient qualifies. I prone early (within 12 to 24 hours of meeting criteria), before escalating to heroic PEEP levels. Prone positioning in obese patients actually improves mechanics more than in non-obese patients because it offloads the abdomen from the dorsal lung.

4. Esophageal balloon: I use esophageal balloon manometry (transpulmonary pressure measurement) in every obese patient with ARDS if available. It transforms your ventilator management by separating lung from chest wall contributions. The EPVent-2 trial did not show overall mortality benefit, but the subgroup analysis suggested benefit in patients with high chest wall elastance, precisely this population.

One practical addition regarding prone positioning in obese patients: the logistics are more challenging but not impossible. We use a "swimming" prone position with gel rolls supporting the chest and pelvis, allowing the abdomen to hang freely. This improves respiratory mechanics more than standard prone because it further unloads the abdominal contents.

Key precautions in obese proning:

Ensure adequate staffing (minimum 5 people for a patient > 120 kg)
Pressure point mapping before and after each turn
ETT fixation must be impeccable, re-intubating a prone obese patient is an airway catastrophe
Consider paralytics for the first 12 to 24 hours of proning to prevent self-extubation

2 Answers