Gas concentrations and ventilation levels have been measured within a conventional Magill circuit when conscious volunteers breathed a non-narcotic gas mixture at varying fresh gas flows. When ...evidence of rebreathing of alveolar gas was detected, the fresh gas flow was kept constant until a steady state developed. All subjects showed evidence of rebreathing when the fresh gas flow approached the predicted alveolar ventilation levels. A variety of subject-circuit interactions was seen and shown to be precipitated by naturally occurring breath-to-breath variations in ventilation. A single large breath could perturb the system. This could have a temporary effect, when the fresh gas flow was sufficient to wash the increased aliquot of expired carbon dioxide from the circuit. At other times a progressive response occurred as ventilatory stimulation as a result of the increased inspired carbon dioxide concentrations caused alveolar gas to reach the reservoir bag and converted the system behaviour from that of a simple added deadspace to that of a total mixing device. Whilst marked changes occurred commonly in both ventilation and inspired gas concentrations, only slight changes in end-tidal gas concentrations occurred.
The acute haemodynamic effects of thiopentone, methohexitone and propanidid have been compared in anaesthetized dogs. All three drugs caused a reduction in arterial blood pressure and minor changes ...in cardiac output, but whereas thiopentone and methohexitone had similar effects propanidid was found to be three times as potent as thiopentone in its effect upon arterial systolic pressure. Thiopentone and methohexitone had slight effects upon right ventricular pressures, whilst propanidid markedly increased right ventricular systolic pressure.
The TM3 Gas differentiator, a simple device introduced to differentiate between nitrous oxide and oxygen, was found to be capable of positively distinguishing between these gases when only they were ...known to be present. The differentiator gave nearly equal responses to nitrous oxide and carbon dioxide. Cyclopropane, halothane, methoxyflurane, trichloroethylene and nitrogen all produced smaller responses on the differentiator's built-in meter. This apparatus has proved in use to be a practicable and simple method of checking the composition of gases emerging from pipelines.
The Lack anaesthetic system is a coaxial modification of the Magill circuit. The resistance of the system was found to be unacceptably high. When air was administered through the system to ...spontaneously breathing trained volunteers, marked evidence of rebreathing was present when fresh gas flow equalled minute volume. It is suggested that a fresh gas glow equal to one and a half-times minute volume would be required to prevent rebreathing of alveolar gas.
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