Figure 2. Esophageal and transpulmonary pressures measured in an 8-year-old morbidly obese patient with the Avea ventilator ^® from CareFusion.

(1) Transpulmonary pressure (TPP = plateau pressure – esophageal pressure: to calculate TPP, esophageal pressure is used as a surrogate of intrapleural pressure) is 14 cmH ₂O at the end of insufflation (red circle). This means that despite a positive plateau pressure of 34 cmH ₂O in this obese child, lung parenchyma does not experience much distension (14 cmH ₂O) at the end of insufflation. (2) Positive end expiration pressure (PEEP) set on the ventilator is 2 cmH ₂O above esophageal pressure (yellow circle). This means that there is minimal risk of lung collapse at the end of expiration. Figure adapted from RM DiBlasi database with permission.