Hypoxemia, atelectasis, and the elevation of arterial pressure and heart rate in paralyzed artificially ventilated rat.

Rats prepared while anesthetized with halothane, ether or pentobarbital, subsequently paralyzed with curare, and maintained with or without anesthetic, by artificial ventilation with room air are hypoxemic in association with elevated arterial pressures and heart rates. The hypoxemia can occur with normal Pa_CO2, is associated with a marked increase in the alveolar-arterial P_O2 difference, and is not reversed by hyperventilation or hyperinflation. The lungs, visualized directly through a thoracotomy during ing artificial ventilation, are segmentally collapsed and at postmortem demonstrate focal and diffuse signs of atelectasis. Hypoxemia and an elevation of the alveolar-arterial P_O2 difference occur within 20 minutes after the onset of anesthesia, prior to paralysis. We conclude that anesthetized rats develop atelectasis soon after the onset of anesthesia. The atelectasis, and resultant hypoxemia persist during subsequent paralysis despite an adequate minute volume and absence of anesthesia. Despite atelectasis, blood gases, arterial pressures and heart rates may be maintained near normal values by ventilation of paralyzed rats with 50% O₂ and 50% N₂.