Determination of Auto-PEEP During Spontaneous and Controlled Ventilation by Monitoring Changes in End-Expiratory Thoracic Gas Volume

Auto-PEEP, or PEEPi, occurs when alveolar pressure fails to decrease to zero at the end of exhalation. While PEEPi can be measured in paralyzed or apneic patients by occlusion of the ventilator expiratory valve at end-exhalation (PEEPi-OC), this may not be possible in patients with spontaneous respiratory efforts. When adjusting the ventilator PEEP valve, FRC increases only after PEEP, has been exceeded. In both mechanically ventilated and spontaneously breathing patients, changes in FRC are mirrored by changes in end-expiratory TCV as measured with RIP set in the DC mode. We compared PEEPi as measured by RIP to PEEPi-OC in 20 patients receiving mechanical ventilator support. Noninvasive measurement of changes in end-expiratory TGV by RIP is a convenient alternative method to estimate PEEPi in both controlled, assisted, and spontaneously ventilating patients.