[PEEP ventilation without hyperinflation of the lungs. A primary ventilatory pattern of controlled respiration based on expiratory volume curves]

When starting controlled ventilation with PEEP, a ventilation within the mid-third of the inspiratory capacity (IC) with a tidal volume (VT) of IC/3 ("primary VT") is recommended, to increase functional residual capacity (FRC) effectively and to avoid adverse haemodynamic effects related to hyperinflation of the lung. The quasi-static expiratory pressure-volume curves (VPE) of 28 patients with acute respiratory failure were graphically analyzed to evaluate the PEEP which could be expected to increase FRC by 1/3 of the IC ("primary PEEP"). the volume by which VT must be reduced, to keep the endinspiratory lung volume constant, if a higher PEEP would be desired. The "primary PEEP" was found to be 12,2 +/- 2,5 cmH2O, thus confirming the clinical practice to use preferentially 10 cmH2O. In 3 patients with progressive pulmonary failure and severely reduced IC as well as in 3 grossly obese patients the "primary PEEP" was markedly higher (15-18 cmH2O). The volume-pressure relation in the steep linear mid-third of the VPE correlated closely with the IC (r = 0.92). This means that the increase in FRC per 1 cmH2O PEEP in this range can be expressed as a nearly constant fraction of the IC (delta FRC/ delta PEEP = IC/32). Hence, to avoid endinspiratory hyperinflation of the lung, it is recommended to reduce the "primary VT" by IC/32 or, which means the same, by VT/10 per 1 cmH2O PEEP exceeding 10. If, however, a ventilatory pattern has to be chosen with respect to gas exchange, where hyperinflation cannot be excluded, this should be done under close haemodynamic control using a Swan-Ganz catheter.