Reducing inadvertent PEEP by controlling end-tidal pressures in the trachea

Mechanical ventilation using exhalation times too brief for completion of exhalation results in inadvertent positive end-expiratory pressure (IPEEP) and increased functional residual capacity (FRC). The endotracheal (ET) tube with side lumen allows us to monitor tracheal airway pressures and to determine the contributions of the ET tube to IPEEP. We hypothesized that, during rapid rate ventilation, controlling the positive end-expiratory pressure (PEEP) level in the trachea rather than at the ET tube adaptor will counter effects of the ET tube on IPEEP and result in less increase of FRC. Thirteen anesthetized rabbits were ventilated at rates of 30, 60, 90, and 120 breaths per minute (BPM). Peak inspiratory pressure was held constant, and PEEP was adjusted to 2 cmH2O, measured conventionally at the proximal end of the ET tube. Pulmonary function tests were made and then repeated while PEEP was held constant in the trachea, measured at the distal end of the ET tube. Controlling PEEP conventionally resulted in mean (+/- SE) FRC values of 13.7 +/- 3.8, 14.8 +/- 3.9, 17.1 +/- 4.5, and 21.1 +/- 5.3 ml/kg at 30, 60, 90, and 120 BPM, respectively. Controlling PEEP at the trachea yielded FRC values of 13.7 +/- 3.8, 13.6 +/- 3.4, 15.3 +/- 4.4, and 16.3 +/- 5.4 ml/kg, respectively. Increasing the ventilator rate above 60 BPM did not affect minute ventilation or blood gases. These results suggest that controlling PEEP in the trachea reduces effects of IPEEP on FRC by countering the contribution of the ET tube to the resistance of gas flow during exhalation.