AN ALTERNATIVE METHOD OF NITROUS-OXIDE DELIVERY INTO A MINIMAL-FLOW CIRCLE BREATHING SYSTEM

We have sought to define a way in which nitrous oxide can be safely an d universally used at minimal to low flows by utilising a circle syste m with a controlled leak provided by a standard gas analyser sampling line and a fresh gas supply of 50% nitrous oxide in oxygen, entering f rom a trunk interposed between the ventilator and the circle system. A lthough preliminary calculations suggested that this arrangement was l ikely to work, it was found that 13 of 23 patients studied prospective ly developed an inspired oxygen fraction below 0.3. We conclude that, although this arrangement provides a new means of introducing nitrous oxide into the circle breathing system, it does not appear inherently safer or more convenient than the conventional route.