Eric Mortier

The mechanisms of carbon monoxide production by inhalational agents.

Carbon monoxide can be formed when volatile anaesthetic agents such as desflurane and sevoflurane are used with anaesthetic breathing systems containing carbon dioxide absorbents. This review describes the possible chemical processes involved and summarises the experimental and clinical evidence for the generation of carbon monoxide. We emphasise the different conditions that were used in the experimental work, and explain some of the features of the clinical reports. Finally, we provide guidelines for the prevention and detection of this complication.

Only Carbon Dioxide Absorbents Free of Both NaOH and KOH Do Not Generate Compound A during In Vitro Closed-system Sevoflurane Evaluation of Five Absorbents

BackgroundInsufficient data exist on the production of compound A during closed-system sevoflurane administration with newer carbon dioxide absorbents. MethodsA modified PhysioFlex apparatus (Dräger, Lübeck, Germany) was connected to an artificial test lung (inflow at the top of the bellow ≅ 160 ml/min CO2; outflow at the Y piece of the lung model ≅ 200 ml/min, simulating oxygen consumption). Ventilation was set to obtain an end-tidal carbon dioxide partial pressure of approximately 40 mmHg. Various fresh carbon dioxide absorbents were used: Sodasorb (n = 6), Sofnolime (n = 6), and potassium hydroxide (KOH)–free Sodasorb (n = 7), Amsorb (n = 7), and lithium hydroxide (n = 7). After baseline analysis, liquid sevoflurane was injected into the circuit by syringe pump to obtain 2.1% end-tidal concentration for 240 min. At baseline and at regular intervals thereafter, end-tidal carbon dioxide partial pressure, end-tidal sevoflurane concentration, and canister inflow (T°in) and canister outflow (T°out) temperatures were measured. To measure compound Ainsp concentration in the inspired gas of the breathing circuit, 2-ml gas samples were taken and analyzed by capillary gas chromatography plus mass spectrometry. ResultsThe median (minimum–maximum) highest compound Ainsp concentrations over the entire period were, in decreasing order: 38.3 (28.4–44.2)* (Sofnolime), 30.1 (23.9–43.7) (KOH-free Sodasorb), 23.3 (20.0–29.2) (Sodasorb), 1.6 (1.3–2.1)* (lithium hydroxide), and 1.3 (1.1–1.8)* (Amsorb) parts per million (*P < 0.01 vs. Sodasorb). After reaching their peak concentration, a decrease for Sofnolime, KOH-free Sodasorb, and Sodasorb until 240 min was found. The median (minimum–maximum) highest values for T°out were 39 (38–40), 40 (39–42), 41 (40–42), 46 (44–48)*, and 39 (38–41) °C (*P < 0.01 vs. Sodasorb), respectively. ConclusionsWith KOH-free (but sodium hydroxide [NaOH]–containing) soda limes even higher compound A concentrations are recorded than with standard Sodasorb. Only by eliminating KOH as well as NaOH from the absorbent (Amsorb and lithium hydroxide) is no compound A produced.

Production of compound A and carbon monoxide in circle systems: an in vitro comparison of two carbon dioxide absorbents*

Two new generation carbon dioxide absorbents, DrägerSorb® Free and Amsorb® Plus, were studied in vitro for formation of compound A or carbon monoxide, during minimal gas flow (500u2003ml.min−1) with sevoflurane or desflurane. Compound A was assessed by gas chromatography/mass spectrometry and carbon monoxide with continuous infrared spectrometry. Fresh and dehydrated absorbents were studied. Mean (SD) time till exhaustion (inspiratory carbon dioxide concentration ≥u200a1u2003kPa) with fresh absorbents was longer with DrägerSorb® Free (1233 (55) min) than with Amsorb® Plus (1025 (55) min; pu2003<u20030.01). For both absorbents, values of compound A were <u200a1u2003ppm and therefore below clinically significant levels, but were up to 0.25u2003ppm higher with DrägerSorb® Free than with Amsorb® Plus. Using dehydrated absorbents, values of compound A were about 50% lower than with fresh absorbents and were identical for DrägerSorb® Free and Amsorb® Plus. With dehydrated absorbents, no detectable carbon monoxide was found with desflurane.