[Deterioration of pulmonary gas exchange caused by PEEP in a pulmonary vascular shunt (Rendu-Osler-Weber syndrome)].

A 25-year-old patient with headache was admitted to the neurology department. Computerized tomography revealed an intracerebral abscess of unknown origin, which was removed by craniotomy. After an uneventful operation and anesthetic low arterial oxygen tensions were noted that did not respond to increased FiO2. Angiography revealed a pulmonary arteriovenous (a-v) fistula (angioma), which was responsible for the right-left shunt. A Swan-Ganz catheter was inserted and the effects of varying levels of PEEP on the magnitude of the shunt during spontaneous breathing of 100% oxygen were determined. At zero PEEP the arterial pO2 was 211 mm Hg (AaDO2 470 mm Hg). 5 mbar PEEP caused the arterial pO2 to fall to 118 mm Hg (AaDO2 563 mm Hg). Increasing PEEP to 15 mbar caused a further decrease in arterial pO2 to 72 mm Hg (AaDO2 603 mm Hg), which resulted in arterial desaturation. The arterial pCO2 remained constant. At a virtually constant cardiac output the shunt volume increased from 23% at zero PEEP to 30% at a PEEP of 15 mbar--a relative increase of 30%. Elevating the intrathoracic pressure presumably caused redistribution of the pulmonary perfusion toward the shunt vessels, probably because the vascular resistance increased more rapidly in the normal vasculature than in the angioma. The therapeutic consequences were to reduce the PEEP and avoid mechanical ventilation. Pulmonary a-v-fistulas are not uncommonly associated with brain abscesses, probably because the normal filter function of the pulmonary vascular bed is disrupted. Therapy consists either in resecting the afflicted lung segment or in transvenous occlusion of the fistula with a silicon ballon.