Thermocycling: enhancing efficiency of anesthetic reflectors through cyclic heating and cooling—finding the optimal temperature in a bench study

BACKGROUND: Volatile anesthetics are widely used for sedation in intensive care. Being potent greenhouse gases, their efficient utilization is imperative. We investigated whether the efficiency of anesthetic reflection devices, such as Sedaconda ACD-S (ACD), can be improved by thermocycling, i.e., cooling the reflector during expiration and warming it during inspiration, and aimed to identify the optimal temperatures required. METHODS: A test lung connected to the ACD was ventilated under body temperature pressure saturated and normocapnic conditions. Isoflurane and sevoflurane were infused at rates of 0.5, 1, 2, and 5 mL/h, with sevoflurane additionally administered at 10 mL/h. For thermocycling, inspired air was heated to 37 °C by an active humidifier without water. Cooling in steps of 26, 21, 16, 11, 6, and 1 °C was achieved by passing air from the test lung through a freezer before reaching the ACD. RESULTS: Thermocycling significantly increased concentrations of isoflurane and sevoflurane in the test lung compared with control conditions. Cooling of the expired air led to substantial increases down to a cooling temperature of 16 °C; below 16 °C, further increases in concentrations were much smaller. Interpolation of our data shows that at clinically used concentrations (isoflurane: 0.4-0.6 Vol%; sevoflurane: 0.9-1.1 Vol%), consumption could be reduced by 70% (isoflurane from 2.46 to 0.74 mL/h) and 72% (sevoflurane from 5.73 to 1.60 mL/h). Reflection efficiencies-the ratio of re-inspired from exhaled anesthetic molecules in one breath-increased from around 70% to 90%. CONCLUSIONS: Thermocycling significantly enhances the efficiency of volatile anesthetic reflection, offering a promising strategy to reduce the impact of intensive care sedation on climate change.