[The PEEP wave: an automated technic for bedside determination of the volume/pressure ratio in the lungs of ventilated patients].

The volume/pressure (V/P) ratio in the lungs has been reported to be useful in the adjustment of mechanical ventilation equipment to suit individual pulmonary mechanics. Most of the techniques used so far (e.g. the super-syringe technique) need an apneic period of approximately 60-120 s, in which the pulmonary gas volume is reduced by the continuing oxygen uptake. Thus, a bias of 200-400 ml in volume is superimposed on the record. In contrast to the super-syringe technique, a new automatic procedure has been developed for which no apneic period is needed. This technique is called the PEEP wave technique: it is based on the imbalance between inspiratory and expiratory volumes after a sudden change in PEEP. The software of a Dräger Evita respirator was adapted to allow automatic application of a special sequence of respiratory cycles with stepwise increase and decreases in PEEP between two preselectable borderline levels. The equipment is switched to the next PEEP level when the difference between two consecutive expiratory tidal volumes is less than 15 ml. After the highest level of PEEP is reached the procedure is reversed until PEEP returns to its initial value. Constant inspiratory tidal volumes (Vti) are achieved by a high pressure servo valve (HPSV) under conditions of chocked flow, resulting in inspiratory tidal volumes which are independent of back-pressure. Thus, only the difference in expiratory tidal volumes (Vte) before and after a PEEP change is necessary to determine gain and loss in lung volume (delta FRC).(ABSTRACT TRUNCATED AT 250 WORDS)