Erroneous mass spectrometer readings caused by desflurane and sevoflurane

Medical mass spectrometers are configured to detect and measure specific respiratory and anesthetic gases. Unrecognized gases entering these systems may cause erroneous readings. We determined how the Advantage 1100 (Perkin-Elmer, now Marquette Gas Systems, Milwaukee, WI) and PPG-SARA (PPG Biomedical Systems, Lenexa, KS) systems that were not configured to measure desflurane or sevoflurane respond to increasing concentrations of these new potent volatile anesthetic agents.

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 agent, the displayed gas analysis readings and uncompensated collector plate voltages were recorded.

The Advantage 1100 system read both desflurane and sevoflurane mainly as enflurane and, to a lesser extent, 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 of the summation bus. PPG-SARA read desflurane mainly as isoflurane(I) and, to a lesser extent, as nitrous oxide. PPG-SARA read sevoflurane mainly as enflurane(E) and, to a lesser extent, as nitrous oxide and halothane. The approximate relationships are: %Desflurane = 1.11 (for I < 9%); %Sevoflurane = 2.1E.

Advantage 1100 and PPG-SARA systems not configured for desflurane or sevoflurane display erroneous anesthetic agent readings when these new agents are sampled. Advantage 1100 also displays falsely elevated carbon dioxide readings when desflurane is sampled.