Dynamic measurement of intrinsic PEEP does not represent the lowest intrinsic PEEP

Objective:Dynamic intrinsic PEEP (PEEPi-dyn) is the airway pressure require d to overcome expiratory flow and is considered to represent the lowest reg ional PEEPi. However, there are few data to validate this assumption. We in vestigated if PEEPi-dyn represents the lowest PEEPi. Setting: The animal laboratory at the Osaka University Medical School. Measurements and results: We compared static PEEPi (PEEPi-stat) and PEEPi-d yn in healthy animals. Five adult white rabbits (2.77 +/- 0.05 kg) were ane sthetized, tracheostomized, and intubated with several different sizes of e ndotracheal tubes (ETT) (2.0, 2.5, 3.0, 3.5, or 4.0 mm i.d.). The animals w ere paralyzed and ventilated (Siemens Servo 900C). Baseline ventilator sett ings were at a rate of 50/min, inspiratory:expiratory (I:E) ratio of 2:1 or 4:1, and minute ventilation was manipulated to create 3 or 5 cm H2O PEEPi- stat. PEEPi-stat was measured using the expiratory bold button of the venti lator. PEEPi-dyn showed large variations. In all ventilator settings, PEEPi -dyn was higher than PEEPi-stat (p < 0.001). The larger the ETT, the higher the PEEPi-dyn at an I:E ratio of 2:1 (p < 0.05). The higher the minute ven tilation, the greater the difference between PEEPi-stat and PEEPi-dyn. The tidal volume and the difference showed a significant correlation (r(2) = 0. 514, p < 0.001). Conclusions: The value of PEEPi-dyn was dependent on ventilatory settings, and PEEPi-dyn does not necessarily represent the lowest regional PEEPi with in the lungs.