Evaluating the efficiency of desflurane reflection in two commercially available reflectors.

With the AnaConDa™ and the MIRUS™ system, volatile anesthetics can be administered for inhalation sedation in intensive care units. Instead of a circle system, both devices use anesthetic reflectors to save on the anesthetic agent. We studied the efficiency of desflurane reflection with both devices using different tidal volumes (V _T ), respiratory rates (RR), and 'patient' concentrations (C _Pat ) in a bench study. A test lung was ventilated with four settings (volume control, RR × V _T : 10 × 300 mL, 10 × 500 mL, 20 × 500 mL, 10 × 1000 mL). Two different methods for determination of reflection efficiency were established: First (steady state), a bypass flow carried desflurane into the test lung (flow _in ), the input concentration (C _in ) was varied (1-17 vol%), and the same flow (flow _ex , C _ex ) was suctioned from the test lung. After equilibration, C _Pat was stored online and averaged; efficiency [%] was calculated [Formula: see text]. Second (washout), flow _in and flow _ex were stopped, the decline of C _Pat was measured; efficiency was calculated from the decay constant of the exponential regression equation. Both measurement methods yielded similar results (Bland-Altman: bias: -0.9 %, accuracy: ±5.55 %). Efficiencies higher than 80 % (>80 % of molecules exhaled are reflected) could be demonstrated in the clinical range of C _Pat and V _T . Efficiency inversely correlates with the product of C _Pat and V _T which can be imagined as the volume of anesthetic vapor exhaled by the patient in one breath, but not with the respiratory frequency. Efficiency of the AnaConDa™ was higher for each setting compared with the MIRUS™. Desflurane is reflected by both reflectors with efficiencies high enough for clinical use.