ERROR IN MEASUREMENT OF OXYGEN AND CARBON-DIOXIDE CONCENTRATIONS BY THE DELTATRACII METABOLIC MONITOR IN THE PRESENCE OF DESFLURANE

In experiments in dogs on the metabolic effects of inhalation anaesthe tics, we noticed that in the presence of desflurane, oxygen uptake ((V ) over dot O-2) measured with the Deltatracll metabolic monitor seemin gly increased whereas it decreased when determined independently by th e Fick principle. This difference remained even after correction for c hanges in gas concentration on addition of an inhalation anaesthetic. Therefore, we suspected that desflurane interferes with the measuremen t of gas concentrations. Using different precision gases, we found tha t desflurane disturbed both the paramagnetic oxygen sensor and the inf rared carbon dioxide detector so that the measured oxygen (when Fi(O2) was >0.21) and carbon dioxide concentrations were greater than expect ed. These errors multiply in the computing process of oxygen uptake by the Deltatracll. When the Deltatracll is to be used during inhalation anaesthesia, its results should be corrected for the presence of an a naesthetic gas. More importantly, corrections must also be made for me asurement errors of the oxygen and carbon dioxide sensors, unless the device has been equipped with a modified (nickel membrane) oxygen sens or insensitive to the presence of volatile agents.