Atelectasis and Shunting During Spontaneous Ventilation in Anesthetized Patients

Abstract

The hypothesis is tested that progressive atelectasis, with shunting of venous blood into the arterial bloodstream, may occur with ventilation which is normal by the usual criteria, but lacking in periodic deep breaths capable of re inflating collapsed airspaces. A previous study found such shunting to occur in anesthetized patients, ventilated by mechanical respirators; in the present study 25 patients were anesthetized with ether and oxygen and breathed spontaneously for an average period of 130 minutes. At the end of this period of spontaneous ventilation the average arterial oxygen tension was 402 mm. of mercury. Following a period of three to five minutes of controlled ventilation, using large tidal volumes, the average arterial oxygen tension rose to 553 mm. of mercury. The greatest fall in arterial oxygen tension occurred in the patients whose spontaneous tidal volumes were the most shallow. It is concluded that spontaneous ventilation in anesthetized patients, even when adequate in terms of carbon dioxide elimination, should be supplemented with periodic passive hyperinflations.