V Q DISTRIBUTION AND CORRELATION TO ATELECTASIS IN ANESTHETIZED PARALYZED HUMANS/

Regional ventilation and perfusion were studied in 10 anesthetized par alyzed supine patients by single-photon emission computerized tomograp hy. Atelec tasis was estimated from two transaxial computerized tomogr aphy scans. The ventilation-perfusion (over dotV/over dotQ) distributi on was also evaluated by multiple inert gas elimination. While the pat ients were awake, inert gas over dotV/over dotQ ratio was normal, and shunt did not exceed 1% in any patient. Computerized tomography showed no atelectasis. During anesthesia, shunt ranged from 0.4 to 12.2%. Ni ne patients displayed atelectasis (0.6-7.2% of the intrathoracic area) , and shunt correlated with the atelectasis (r = 0.91, P < 0.001). Shu nt was located in dependent lung regions corresponding to the atelecta tic area. There was considerable over dotV/over dotQ mismatch, with ve ntilation mainly of ventral lung regions and perfusion of dorsal regio ns. Little perfusion was seen in the most ventral parts (zone I) of ca udal (diaphragmatic) lung regions. In summary, shunt during anesthesia is due to atelectasis in dependent lung regions. The over dotV/over d otQ distributions differ from those shown earlier in awake subjects.