Anesthesiology
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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.
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Comparative Study
Racial differences in sacral structure important in caudal anesthesia.
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The hemodynamic and renal effects of mechanical ventilation with positive end-expiratory pressure (PEEP) were studied with and without continuous dopamine administration in ten patients who had acute pulmonary failure. The application of 20 cm H2O PEEP during mechanical ventilation resulted in improvements in arterial blood oxygen tension, from 63 +/- 6 to 81 +/- 12 torr (mean +/- SE), and intrapulmonary shunt fraction, from 29 +/- 3 to 21 +/- 3 per cent, whereas cardiac output, systemic oxygen transport and renal function were impaired by 20, 19 and 47 per cent, respectively. ⋯ The authors conclude that the depression of cardiovascular and renal functions that may occur in patients who need high levels of PEEP for the treatment of acute pulmonary failure can be treated successfully with dopamine infusion. This represents a valuable alternative to expansion of blood volume for the improvement of systemic oxygen transport and arterial blood oxygen tension in critically ill patients.