An Evaluation of Respiratory Depression by Alveolar Gas Changes During Pentothal Sodium Anesthesia.

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Abstract
The alveolar O2, CO2 and R.Q., as well as ventilation vol. and breathing rate, were recorded continuously before, during and after admn. of Na pentothal in man and dogs. By plotting these values on an O2/CO2 diagram, one can describe a typical anesthesia pathway (a closed loop), each point simultaneously describing the O2, CO2, R.Q. and relative alveolar ventilation. With a single dose of anesthetic the alveolar gas exchange is a continuously changing picture. At first the greatest ventilating depression is reached with the highest CO2, lowest O2 and R.Q. value. This is followed by a period of compensation with return of these values to the preinjection level, except for the CO2, which is still high. The last stage is a release of the respiratory depression with relative hyperventilation, very high R.Q.''s and O2, while the CO2 level assumes its original value. The appln. of alveolar gas concns. to a quantitative formulation of respiratory depression and stimulation after drug admn. is discussed.