THE USE of respirators in the treatment of pulmonary insufficiency is well established.1,2 They are also increasingly used for patients with heart failure to relieve them of the work of respiration and so to reduce oxygen consumption.3-7 There is, however, little information on how the use of respirators affect specific cardiovascular complications such as left heart failure, pulmonary edema and pulmonary diffusion problems. In the treatment of these complications as they occasionally follow open-heart surgery, we have noted important changes in respiratory gas exchange with changes in mean expiratory airway pressure which were small enough not to affect cardiac output.
Thirteen patients who had undergone open-heart surgery were studied. Eight of these had mitral disease, three had mitral disease associated with aortic or tricuspid disease, and two had tetralogy of Fallot. Studies were carried out in the recovery room during the first ten hours after surgery. Endotracheal