Reflection efficiencies of AnaConDa-S and AnaConDa-100 for isoflurane under dry laboratory and simulated clinical conditions: a bench study using a test lung.

Background: Adequate sedation is important for the treatment of ICU patients. AnaConDa (Anesthetic-Conserving-Device; ACD; Sedana Medical, Sweden), connected between ventilator and the patient, retains isoflurane during expiration, and releases it back during inspiration. The reflection efficiency (RefEff) corresponds to the percentage of expired anesthetic molecules that are re-inspired. We compared RefEff of AnaConDa-S (ACD-50) and AnaConDa-100 (ACD-100) under laboratory (DRY) and simulated clinical conditions (CLIN) using a test lung.Methods: Measurements were made under DRY and CLIN, with different tidal volumes (TV: 300 mL & 500 mL) and infusion rates (0.5-10 mL·h-1). RefEff was calculated from the isoflurane concentration in the test-lung (CISO) and plotted against the anesthetic vapor volume exhaled in one breath (V-exh = CISO·TV).Results: DRY: RefEff of both devices was ≈90% over a wide range of V-exh, but decreased when V-exh exceeded 5-7 mL (ACD-50) or 10-15 mL (ACD-100).CLIN: RefEff of ACD-50 was 70-80% (ACD-100: 80-90%), decreasing gradually with increasing V-exh. For 1 Vol.% isoflurane at TV500, the infusion rate with ACD-50 was twofold higher compared to ACD-100 (4 versus 2 mL·h-1).Conclusion: Under DRY and concentrations <1.5 Vol.%, RefEff of both devices is around 90%. Under CLIN, ACD-100 performs better with RefEff between 80% and 90% (ACD-50:70-80%), decreasing with increased vapor volume exhaled in one breath.