PULMONARY MECHANICS AND GAS EXCHANGE DURING NEUROSURGICAL ANAESTHESIA

We have made serial measurements of CT, CL, and A-aDo2 during anaesthesia with controlled ventilation in 27 patients undergoing surgical procedures not involving the thorax or abdomen. These patients were divided into three groups, according to the technique of controlled ventilation: group 1, Bird, no sighs; group 2, Bird with sighs; and group 3, Engstrõm, no sighs. We found generally low values for CT and CL and abnormally wide values for A-aDo2, and these were not reversed by hyperinflation. However, the patients who were sighed did maintain higher CL than did patients on the same ventilator who were not sighed. Values for A-aDo2, however, were not consistently lower in the sighed group. In addition, CL was higher in patients on the Engström, than in patients on the Bird, no sighs being given to either group. In spite of this, the Engström did not prove to be a more effective respirator, since A-aDo2 widened to the same degree with both ventilators. In other words, our data suggest that pulmonary mechanics decline less if sighs are given, and if the Engström ventilator rather than the Bird is employed, but that these advantages in terms of mechanical properties are not accompanied by better gas exchange. This study has not a ready explanation for the low compliance values and the high values for A-aDo2 found by us and by others1-3, 17 during anaesthesia. © 1969 Canadian Anesthesiologists.