Biphasic Positive Airway Pressure (BIPAP) can be described as pressure controlled ventilation in a system allowing unrestricted spontaneous breathing at any moment of the ventilatory cycle. It can also be described as a Continuous Positive Airway Pressure (CPAP) system with a time-cycled change of the applied CPAP level. As with a pressure controlled, time-cycled mode, the duration of each phase (T(high), T(low)) as well as the corresponding pressure levels (P(high), P(low)) can be adjusted independently. Depending on the spontaneous breathing activity, BIPAP can be subdivided into: no spontaneous breathing: CMV-BIPAP; spontaneous breathing at the lower pressure level: IMV-BIPAP; spontaneous breathing at the upper pressure level: APRV-BIPAP; spontaneous breathing at both CPAP levels: genuine BIPAP. Since it enables progressive transition from controlled to all levels of augmented mechanical ventilation, BIPAP appears to be a suitable mode for the entire period of mechanical ventilation of the patient. There are difficulties neither in choosing the correct moment for switching nor the further respiratory management of the ventilated patient under BIPAP. The necessary adaptation (ventilation, oxygenation) can be individualized on the basis of blood gas analyses. An increase or reduction of the invasivity of ventilation can be attained without any problems with BIPAP. Furthermore, spontaneous breathing of the patient does not necessitate any switching of the mode of ventilation. The transition from controlled to augmented ventilation is smooth. BIPAP enables the therapist to let the patient breathe freely even under the most invasive ventilation conditions.(ABSTRACT TRUNCATED AT 250 WORDS)