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A. Appleyard writes: > For trimix: is there such a thing as a ppN2 meter that could be put in an >AMRB? I do not know of any affordable ppN2 meters (or for that matter, any affordable ppCO2 meters) that are available. In clinical anesthesia, we do monitor end tidal and inhaled CO2 and N2, but these devices use fairly expensive technology. > Since when have ppO2 meters been available that would have been suitable >for use in AMRB's? ppO2 meters for use in rebreathers have been used since at least the late 1960 commercially - and are essential a galvanic fuel cell type that changes it's output in direct relation to the partial pressure of oxygen present. The oxygen analyzers that are currently in use in the technical diving community use these sensors, and the fact that they measure ppO2 and that reading is then converted to a FiO2 has led to some confusion and errors in analysis. (Analyzing under a constant flow situation can give falsely elevated readings, as the measuring system is at a pressure that is higher than ambient - must be higher than ambient or else there would be no pressure gradient to produce the flow. This erroneous reading probably is not a major concern, but if the meter is zero'd under one flow, and then the gas in question is introduced at a lower flow, the error could be to the high side.). John Submariner Research, Ltd. (johncrea@de*.co*)
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