Volatile anesthetics are increasingly used for sedation in intensive care units. The most common administration system is AnaConDa-100 mL (ACD-100; Sedana Medical, Uppsala, Sweden), which reflects volatile anesthetics in open ventilation circuits. AnaConDa-50 mL (ACD-50) is a new device with half the volumetric dead space. Carbon dioxide (CO2) can be retained with both devices. We therefore compared the CO2 elimination and isoflurane reflection efficiency of both devices.
A test lung constantly insufflated with CO2 was ventilated with a tidal volume of 500 mL at 10 breaths/min. End-tidal CO2 (Etco2) partial pressure was measured using 3 different devices: a heat-and-moisture exchanger (HME, 35 mL), ACD-100, and ACD-50 under 4 different experimental conditions: ambient temperature pressure (ATP), body temperature pressure saturated (BTPS) conditions, BTPS with 0.4 Vol% isoflurane (ISO-0.4), and BTPS with 1.2 Vol% isoflurane. Fifty breaths were recorded at 3 time points (n = 150) for each device and each condition. To determine device dead space, we adjusted the tidal volume to maintain normocapnia (n = 3), for each device. Thereafter, we determined reflection efficiency by measuring isoflurane concentrations at infusion rates varying from 0.5 to 20 mL/h (n = 3), for each device.
Etco2 was consistently greater with ACD-100 than with ACD-50 and HME (ISO-0.4, mean ± standard deviations: ACD-100, 52.4 ± 0.8; ACD-50, 44.4 ± 0.8; HME, 40.1 ± 0.4 mm Hg; differences of means of Etco2 [respective 95% confidence intervals]: ACD-100 − ACD-50, 8.0 [7.9–8.1] mm Hg, P < .001; ACD-100 − HME, 12.3 [12.2–12.4] mm Hg, P < .001; ACD-50 − HME, 4.3 [4.2–4.3] mm Hg, P < .001). It was greatest under ATP, less under BTPS, and least with ISO-0.4 and BTPS with 1.2 Vol% isoflurane. In addition to the 100 or 50 mL “volumetric dead space” of each AnaConDa, “reflective dead space” was 40 mL with ACD-100 and 25 mL with ACD-50 when using isoflurane. Isoflurane reflection was highest under ATP. Under BTPS with CO2 insufflation and isoflurane concentrations around 0.4 Vol%, reflection efficiency was 93% with ACD-100 and 80% with ACD-50.
Isoflurane reflection remained sufficient with the ACD-50 at clinical anesthetic concentrations, while CO2 elimination was improved. The ACD-50 should be practical for tidal volumes as low as 200 mL, allowing lung-protective ventilation even in small patients.
From the *Department of Anesthesiology, Intensive Care Medicine and Pain Medicine, Saarland University Medical Centre, University of Saarland, Homburg/Saar, Germany
†Department of Anesthesiology and Intensive Care Medicine, St Josef Hospital, Katholisches Klinikum Bochum, University Hospital, Ruhr-University of Bochum, Bochum, Germany
‡Department of Outcomes Research, Anesthesiology Institute, Cleveland Clinic, Cleveland, Ohio.
Published ahead of print 12 April 2018.
Accepted for publication April 12, 2018.
Funding: The AnaConDa-50 mL reflectors were kindly provided by the manufacturer Sedana Medical, Uppsala, Sweden.
Conflicts of Interest: See Disclosures at the end of the article.
H. Bomberg and F. Meiser contributed equally and share first authorship.
Reprints will not be available from the authors.
Address correspondence to Hagen Bomberg, MD, Department of Anaesthesiology, Intensive Care Medicine and Pain Medicine, Saarland University Medical Center, University of Saarland, Kirrbergerstrasse 1, 66421 Homburg/Saar, Germany. Address e-mail to email@example.com.