AIRWAY-CLOSURE, ATELECTASIS AND GAS-EXCHANGE DURING GENERAL-ANESTHESIA

Airway closure and the formation of atelectasis have been proposed as important contributors to impairment of gas exchange during general an aesthesia. We have elucidated the relationships between each of these two mechanisms and gas exchange. We studied 35 adults with healthy lun gs, undergoing elective surgery. Airway closure was measured using the foreign gas bolus technique, atelectasis was estimated by analysis of computed x-ray tomography, and ventilation-perfusion distribution ((V ) over dot)/(Q) over dot) was assessed by the multiple inert gas elimi nation technique. The difference between closing volume and expiratory reserve volume (CV-ERV) increased from the awake to the anaesthetized state. Linear correlations were found between atelectasis and shunt ( r=0.68, P<0.001), and between CV-ERV and the amount of perfusion to po orly ventilated lung units (''low (V) over dot A/(Q) over dot'', r=0.5 7, P=0.001). Taken together, the amount of atelectasis and airway clos ure may explain 75% of the deterioration in Pa-O2. There was no signif icant correlation between CV-ERV and atelectasis. We conclude that in anaesthetized adults with healthy lungs, undergoing mechanical ventila tion, both airway closure and atelectasis contributed to impairment of gas exchange. Atelectasis and airway closure do not seem to be closel y related.