Anesthesiology
-
Following the observation that mice manifest a characteristic withdrawal syndrome after an hour of exposure to nitrous oxide, the authors reasoned that there might be a very rapidly developing tolerance to nitrous oxide. Thus, they determined the inspired concentrations that cause loss of the righting reflex in mice (i.e, the ED50), in the presence of 1 atm of oxygen, of: 1) nitrous oxide alone; 2) cyclopropane alone; 3) nitrous oxide plus 13.6 atm helium; 4) ethylene plus 13.6 atm helium. In each instance the ED50 was determined after averages of 6,34 and 64 min of exposure to the anesthetic agents. ⋯ For ethylene plus helium the ED50 increased from 1.21 +/- 0.033 atm at 6 min to 1.31 +/- 0.039 atm at 64 min, indicating the development of acute tolerance. Neither cyclopropane alone nor nitrous oxide plus helium caused acute tolerance. This absence of tolerance may have resulted from a slower development of an alveolar anesthetic concentration.
-
Comparative Study
Racial differences in sacral structure important in caudal anesthesia.