Severe respiratory failure may be difficult to overcome by conventional mechanical ventilation. As an alternative to the very demanding lung support using various modalities of extracorporeal circulation (ECMO, ECLA, etc.) we evaluated an intravascular gas exchanger (IVOX) in a "reversible" bovine model. Several degrees of hypoventilation were studied with and without intravascular gas exchange in 5 endotracheal intubated, anaesthetized, and volume-controlled ventilated animals (body weight 73 +/- 4 kg). After systematical heparinization (300 IU/kg body weight) the animals were instrumented with EKG electrodes, thermodilution pulmonary artery catheter with continuous measurement of O2-saturation, central venous and femoral arterial catheter, etc. The intravascular gas exchanger made from siliconized microporous polypropylene hollow fibres was placed in the caval veins under radiofluoroscopic control. The following scenarios were studied without and with intravascular gas exchange (gas inlet 100% O2): Normoventilation (with 14-20 strokes/min) at F10(2) 0.50 and at F10(2) 0.21; Hypoventilation (ventilator frequency reduced to 50% and tidal volume reduced to 50% of normoventilation) at F10(2) 0.50 and at F10(2) 0.21. Hemodynamics, mixed venous O2-saturation, arterial and venous blood gases, and gas-exchanger exhaust were analyzed after stabilization over 15 minutes (mean +/- standard deviation). Blood gas analyses showed significant improvement with intravascular gas exchange during hypoventilation at F10(2) 0.21: pH moved from 7.10 +/- 0.17 to 7.19 +/- 0.15*, PaCO2 moved from 9.9 +/- 4.2 kPa to 8.7 +/- 2.8*, PaO2 moved from 6.5 +/- 1.2 kPa to 7.3 +/- 0.8* and mixed venous O2-saturation moved from 33.9 +/- 16.0% to 48.1 +/- 4.6* (* = p less than 0.05 for without versus with intravascular gas exchange).(ABSTRACT TRUNCATED AT 250 WORDS)