ERRONEOUS MASS-SPECTROMETER READINGS CAUSED BY DESFLURANE AND SEVOFLURANE

Objective. Medical mass spectrometers are configured to detect and mea sure specific respiratory and anesthetic gases. Unrecognized gases ent ering these systems may cause erroneous readings. We determined how th e Advantage 1100 (Perkin-Elmer, now Marquette Gas Systems, Milwaukee, WI) and PPG-SARA (PPG Biomedical Systems, Lenexa, KS) systems that wer e not configured to measure desflurane or sevoflurane respond to incre asing concentrations of these new potent volatile anesthetic agents. M ethods. Desflurane 0% to 18% in 3% increments or sevoflurane 0% to 7% in 1% increments in 5-L/min oxygen was delivered to the Advantage and PPG-SARA mass spectrometry systems. For each concentration of each age nt, the displayed gas analysis readings and uncompensated collector pl ate voltages were recorded. Results. The Advantage 1100 system read bo th desflurane and sevoflurane mainly as enflurane and, to a lesser ext ent, as carbon dioxide and isoflurane. For enflurane(E) readings <9.9% , the approximate relationships are: %Desflurane = 1.6E; %Sevoflurane = 0.3E. These formulas do not apply if E >9.9% because of saturation o f the summation bus. PPG-SARA read desflurane mainly as isoflurane(I) and, to a lesser extent, as nitrous oxide. PPG-SARA read sevoflurane m ainly as enflurane(E) and, to a lesser extent, as nitrous oxide and ha lothane. The approximate relationships are: %Desflurane = 1.1I (for I <9%); %Sevoflurane = 2.1E. Conclusions. Advantage 1100 and PPG-SARA sy stems not configured for desflurane or sevoflurane display erroneous a nesthetic agent readings when these new agents are sampled. Advantage 1100 also displays falsely elevated carbon dioxide readings when desfl urane is sampled.